Filed Pursuant to Rule 424(b)(5)
Registration Statement File No. 333-265826

The information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and accompanying prospectus are not an offer to sell these securities and are not soliciting an offer to buy these securities in any jurisdiction where the offer or the sale is not permitted.

Subject to Completion, Dated February 2, 2023

PRELIMINARY PROSPECTUS SUPPLEMENT

(TO PROSPECTUS DATED JULY 7, 2022)

$22,000,000 of American Depositary Shares

Representing                  Ordinary Shares

We are offering $22,000,000 of our ordinary shares, €0.05 nominal value per share, in the form of American Depositary Shares, or ADSs. Each ADS represents one ordinary share.

Our ADSs are listed on the Nasdaq Global Market under the symbol “CLLS”. On February 1, 2023, the last reported sale price of our ADSs was $3.10 per ADS. Our ordinary shares are traded on Euronext Growth market of Euronext Paris under the symbol “ALCLS”. On February 1, 2023, the last reported sale price of our ordinary shares was €2.79 per share.

Investing in our ADSs involves a high degree of risk. See “Risk Factors” beginning on page S-7 of this prospectus supplement and on page 2 of the accompanying prospectus, as well as the risk factors incorporated by reference into this prospectus supplement for risks you should consider before you make your investment decision.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

Delivery of the ADSs against payment in U.S. dollars in New York, New York, is expected to be made on or about February                 , 2023. We have granted the underwriters an option for a period of 30 days to purchase up to                  additional ADSs. If the underwriters exercise the option in full, the total underwriting commissions payable by us will be $            , and the total proceeds to us, before expenses, will be $            .

Joint Book-Running Managers

Prospectus supplement dated February                 , 2023.

TABLE OF CONTENTS

Prospectus Supplement

Prospectus

We have not authorized anyone to provide any information other than that contained in this prospectus supplement, the accompanying prospectus or in any free writing prospectus prepared by or on behalf of us or to which we have referred you. We take no responsibility for, and provide no assurances as to the reliability of, any other information that others may give you.

S-i

ABOUT THIS PROSPECTUS SUPPLEMENT

This document is part of the registration statement that we filed with the Securities and Exchange Commission, or the SEC, using a “shelf” registration process and consists of two parts. The first part is this prospectus supplement, including the documents incorporated by reference, which describes the specific terms of this offering and also adds to and updates information contained in the accompanying prospectus. The second part, the accompanying prospectus, including the documents incorporated by reference, gives more general information, some of which may not be applicable to this offering. Generally, when we refer to the “prospectus” we are referring to both parts combined. The information contained in this prospectus supplement and in the accompanying prospectus may be supplemented from time-to-time with applicable free writing prospectuses prepared by us or on our behalf or to which we may have referred you in connection with this offering.

If information in this prospectus supplement is inconsistent with the accompanying prospectus or with any document incorporated by reference that was filed with the SEC before the date of this prospectus supplement, you should rely on this prospectus supplement. If any statement in this prospectus supplement or the accompanying prospectus is inconsistent with a statement in another document that is incorporated by reference into this prospectus and having a later date, the statement in the document having the later date modifies or supersedes the earlier statement.

This prospectus supplement, the accompanying prospectus and the documents incorporated by reference into each include important information about us, the ADSs being offered and other information that you should know before investing in our ADSs. You should also read and consider information in the documents we have referred you to in the sections of this prospectus supplement and the accompanying prospectus entitled “Incorporation of Information by Reference” and “Where You Can Find More Information.”

You should assume that the information in this prospectus supplement and the accompanying prospectus is accurate only as of the date on the front of the respective document and that any information that we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus supplement or the accompanying prospectus or the time of any sale of an ADS. Our business, financial condition, liquidity, results of operations and prospects may have changed since those dates.

This prospectus supplement and the accompanying prospectus contain summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated herein by reference as exhibits to the registration statement, and you may obtain copies of those documents as described below under the sections entitled “Incorporation of Information by Reference” and “Where You Can Find More Information.”

We further note that the representations, warranties and covenants made by us in any agreement that is filed as an exhibit to any document that is incorporated by reference herein were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating risk among the parties to such agreements, and should not be deemed to be a representation, warranty or covenant to you. Moreover, such representations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties and covenants should not be relied on as accurately representing the current state of our affairs.

Neither we nor the underwriters are making offers to sell or solicitations of offers to buy our ADSs in any jurisdiction in which an offer or solicitation is not permitted or in which the person making that offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make an offer or solicitation.

For investors outside the United States: Neither we nor the underwriters have done anything that would permit this offering or possession or distribution of this prospectus supplement in any jurisdiction where action for that purpose is required, other than in the United States. Persons outside the United States who come into possession of this prospectus supplement must inform themselves about, and observe any restrictions relating to, the offering of the securities described herein and the distribution of this prospectus supplement outside the United States.

S-ii

Unless otherwise indicated or the context otherwise requires, references in this prospectus supplement to “Cellectis,” “the Company,” “we,” “us,” and “our” refer to Cellectis S.A. and its consolidated subsidiaries. References to “Calyxt” refer to Calyxt, Inc. and its subsidiaries, which we consolidate in our financial results. In light of the Merger Agreement discussed under “Recent Developments” in this prospectus supplement, in connection with the filing of our annual report on Form 20-F for the year ended December 31, 2022, we will begin reporting Calyxt as “held for sale” and therefore as a discontinued operation.

S-iii

PRESENTATION OF FINANCIAL AND OTHER INFORMATION

We prepare our consolidated financial statements in accordance with International Financial Reporting Standards (“IFRS”) as issued by the International Accounting Standards Board (“IASB”). Our consolidated financial statements are presented in U.S. dollars.

All references in this prospectus supplement to “$” and “U.S. dollars” mean U.S. dollars and all references to “€” and “euros” mean euros, unless otherwise noted. Throughout this prospectus supplement, references to ADSs mean ADSs or ordinary shares represented by such ADSs, as the case may be.

S-iv

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement and the accompanying prospectus contain and incorporate by reference “forward-looking statements” within the meaning of applicable federal securities laws, including the Private Securities Litigation Reform Act of 1995, as amended. All statements other than present and historical facts and conditions contained in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference, including statements regarding our future results of operations and financial position, business strategy, plans and our objectives for future operations, are forward-looking statements. These forward-looking statements are subject to numerous risks and uncertainties and are made in light of information currently available to us. Many important factors, in addition to the factors described in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference, may adversely affect such forward-looking statements. When used in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference, the words “anticipate,” “believe,” “can,” “could,” “estimate,” “expect,” “intend,” “is designed to,” “may,” “might,” “plan,” “potential,” “predict,” “objective,” “should,” or the negative of these and similar expressions identify forward-looking statements. Forward-looking statements include, but are not limited to, statements about:

S-v

Particular caution should be exercised when interpreting preliminary results and results relating to a small number of patients or individually presented case studies—such results should not be viewed as predictive of future results.

You should refer to the section titled “Risk Factors” in this prospectus supplement, the accompanying prospectus, in our Annual Report on Form 20-F for the year ended December 31, 2021 (the “Annual Report”), which is incorporated by reference into this prospectus supplement, and in the reports on Form 6-K that we file with the SEC and incorporate by reference into this prospectus supplement, for a discussion of important factors that may cause our actual results to differ materially from those expressed or implied by our forward-looking statements. See “Incorporation of Information by Reference.” As a result of these factors, we cannot assure you that the forward-looking statements contained or incorporated by reference in this prospectus supplement or the accompanying prospectus will prove to be accurate.

Furthermore, if our forward-looking statements prove to be inaccurate, the inaccuracy may be material. In light of the significant uncertainties in these forward-looking statements, you should not regard these statements as a representation or warranty by us or any other person that we will achieve our objectives and plans in any specified time frame or at all. We undertake no obligation to publicly update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law. We qualify all of our forward-looking statements by these cautionary statements.

The information incorporated by reference in this prospectus supplement contains market data and industry forecasts that were obtained from industry publications. These data and forecasts involve a number of assumptions and limitations, and you are cautioned not to give undue weight to such estimates. While we believe the market and industry data included in the information incorporated by reference in this prospectus supplement is generally reliable, such information is inherently imprecise.

S-vi

S-1

S-2

S-3

S-4

S-5

S-6

RISK FACTORS

An investment in our ADSs involves a high degree of risk. Prior to making a decision about investing in our ADSs, you should carefully consider the specific factors discussed below, together with all of the other information contained or incorporated by reference into this prospectus supplement and the accompanying prospectus, as well as the risks, uncertainties and assumptions discussed under Item 3, “Risk Factors,” in our Annual Report on Form 20-F for the year ended December 31, 2021, under Item 1.A. “Risk Factors” in our report on Form 6-K filed with the SEC on August 4, 2022 relating to our financial results for the three- and six-months periods ended June 30, 2022, and under Item 1.A. “Risk Factors,” in our report on Form 6-K filed with the SEC on November 3, 2022 relating to our financial results for the three- and nine-months periods ended September 30, 2022, which are incorporated herein by reference. See “Incorporation of Information by Reference.” The risks and uncertainties we have described are not the only ones we face. Additional risks and uncertainties not presently known to us or that we currently deem immaterial may also affect our operations.

Risks Related to the Ordinary Shares, the ADSs and this Offering

The market price for our ADSs may be volatile or may decline regardless of our operating performance.

The trading price of the ADSs has fluctuated, and is likely to continue to fluctuate, substantially. Since the ADSs were sold in our initial public offering in March 2015 at a price of $41.50 per ADS, the price per ADS has ranged as low as $1.85 and as high as $47.66 through February 1, 2023. The market price of the ADSs may fluctuate significantly in response to numerous factors, including those described in this “Risk Factors” section and the “Risk Factors” sections of the documents incorporated by reference herein identified above, many of which are beyond our control. The market price and demand for our ADSs may also fluctuate substantially, regardless of our actual operating performance, which may limit or prevent holders from readily selling their ADSs and may otherwise negatively affect the liquidity of our capital shares.

Any downward pressure on the price of ADSs caused by the sale of ADSs, including in this offering, could also encourage short sales by third parties. In a short sale, a prospective seller borrows ADSs from a shareholder or broker and sells the borrowed ADSs. The prospective seller hopes that the per ADS price will decline, at which time the seller can purchase ADSs at a lower price for delivery back to the lender. The seller profits when the per ADS price declines because it is purchasing ADSs at a price lower than the sale price of the borrowed ADSs. Such sales could place downward pressure on the price of our ADSs by increasing the number of ADSs being sold, which could further contribute to any decline in the market price of our ADSs.

You should consider an investment in our ADSs as risky and invest only if you can withstand a significant loss and wide fluctuations in the market value of your investment. If you invest in our ADSs, you could lose some or all of your investment. You may be unable to sell your ADSs at or above the public offering price due to fluctuations in the market price.

If you purchase ADSs in this offering, you may experience substantial and immediate dilution.

You may experience future dilution as a result of future equity offerings or other transactions.

In order to raise additional capital, we expect in the future to offer additional ADSs, ordinary shares, or other securities convertible into or exchangeable for our ADSs or ordinary shares. We cannot assure you that we will be able to sell shares or other securities in any other offering in the future at a price per share that is equal to or greater than the price per share paid by investors in this offering, and investors purchasing shares or other securities in the future could have rights superior to existing holders of ADSs or ordinary shares. The price per share at which we sell additional ADSs, ordinary shares, or other securities convertible into or exchangeable for its ordinary shares in future transactions may be higher or lower than the price per ADS in this offering. In addition, you may experience dilution upon exercise of any outstanding options or warrants to purchase ordinary shares under our equity incentive plans, if we issue free shares (actions gratuites) to our employees under our equity incentive plans.

We have broad discretion in the use of the net proceeds from this offering and may not use them effectively.

Our management will have broad discretion in the application of the net proceeds that we receive from this offering, including applications for working capital and other general corporate purposes, and we may spend or invest these proceeds in a way with which our shareholders disagree. We currently intend to use the net proceeds from this offering to fund the continued clinical development of UCART123, UCART22, UCART20x22, and UCARTCS1, and

S-7

the remainder for working capital and other general corporate purposes. See “Use of Proceeds” for additional information. Because of the number and variability of factors that will determine our use of the net proceeds from this offering, their ultimate use may vary substantially from their currently intended use. As a result, we may spend or invest these proceeds in a way with which our shareholders disagree. Moreover, the failure by our management to apply these funds effectively could harm our business and financial condition. Pending their use, we may invest the net proceeds from this offering in a manner that does not produce income or that loses value. These investments may not yield a favorable return to our investors.

If securities or industry analysts do not publish research or publish inaccurate or unfavorable research about our business, the price of our ADSs and trading volume could decline.

The trading market for our ADSs depends in part on the research and reports that securities or industry analysts publish about us or our business. If few or no securities or industry analysts cover us, the trading price for our ADSs would be negatively impacted. If one or more of the analysts who covers us downgrades our ADSs or publishes incorrect or unfavorable research about our business, the price of our ADSs would likely decline. If one or more of these analysts ceases coverage of our company or fails to publish reports on us regularly, or downgrades our ADSs, or if we fail to meet the expectations of analysts, that could also cause the price of our ADSs or trading volume to decline.

Although the matter is not free from doubt, we do not believe that we were a PFIC for U.S. federal income tax purposes for the taxable year ended December 31, 2021. However, it is possible that we were a PFIC for the taxable year ended December 31, 2022 and/or will be a PFIC for the current or subsequent taxable years. If we are determined to be a PFIC for any taxable year, there may be adverse U.S. federal income tax consequences to U.S. holders (as defined in the section titled “Certain Income Tax Considerations—Material U.S. Federal Income Tax Considerations”).

A non-U.S. corporation will be considered a PFIC for any taxable year if either (1) at least 75% of its gross income for such year is passive income or (2) at least 50% of the value of its assets (based on an average of the quarterly values of the assets during such year) is attributable to assets that produce or are held for the production of passive income. Passive income for this purpose generally includes, among other things, dividends, interest, rents, royalties, gains from commodities and securities transactions, and gains from assets that produce passive income. In determining whether a foreign corporation is a PFIC, a pro rata portion of the income and assets of each corporation in which it owns, directly or indirectly, at least a 25% interest (by value) is taken into account. Although not free from doubt, we do not believe that we were a PFIC for the taxable year ended December 31, 2021. However, it is possible that we were a PFIC for the taxable year ended December 31, 2022 and/or will be a PFIC for the current or subsequent taxable years. In particular, the decline in the market value of the ADSs and our ordinary shares during the taxable year ended December 31, 2022 has increased the likelihood that we will be considered a PFIC for such taxable year. The determination of PFIC status is fact-specific, and a separate determination must be made each taxable year as to whether we are a PFIC (after the close of each such taxable year). Our status as a PFIC depends on the composition of our income (including whether reimbursements of certain refundable research tax credits will constitute gross income for purposes of the PFIC income test) and the composition and value of our assets. The value of our assets may be determined in large part by reference to the market value of the ADSs and our ordinary shares, which may fluctuate substantially. Our status as a PFIC may also depend in part upon how quickly we utilize the cash proceeds from the offering (and the cash proceeds from other fund-raising activities) in our business.

If we are a PFIC for any taxable year during which a U.S. holder holds ADSs, the U.S. holder may be subject to adverse tax consequences, including (1) the treatment of all or a portion of any gain on disposition as ordinary income, (2) the application of an interest charge with respect to such gain and certain dividends and (3) compliance with certain reporting requirements. Each U.S. holder is strongly urged to consult its tax advisor regarding these issues and any available elections to mitigate such tax consequences. See “Certain Income Tax Considerations—Material U.S. Federal Income Tax Considerations”.

S-8

USE OF PROCEEDS

We expect to receive net proceeds of approximately $            million from the sale of                  ADSs in this offering, or $             million if the underwriters exercise in full their option to purchase additional ADSs, based on a public offering price of $             per ordinary share, after deducting the estimated expenses related to this offering and the underwriting commissions payable by us.

We currently intend to use the net proceeds we receive from this offering for the following purposes:

Cellectis intends to deploy the net proceeds from the Global Offering at a rate consistent with its cash spending in 2022 through September 30 and, accordingly, such net proceeds would proportionately extend Cellectis’ ability to fund its therapeutic operations beyond early 2024 based on such run rate. We cannot specify with certainty all of the particular uses for the net proceeds to be received upon the closing of this offering. Due to uncertainties inherent in the product development, manufacturing and commercialization processes, it is difficult to estimate the exact amounts of the net proceeds that will be used for any particular purpose. We may use our existing cash and future revenue, if any, generated from our existing, and any future, collaboration agreements to fund our operations, either of which may alter the amount of net proceeds used for a particular purpose. In addition, the amount, allocation and timing of our actual expenditures will depend upon numerous factors. Accordingly, we will have broad discretion in using these proceeds.

Pending application of the net proceeds as described above, we may initially invest the net proceeds, in accordance with our investment policy, in short-term capital preservation investments.

S-9

DIVIDEND POLICY

We have never declared or paid any cash dividends on our ordinary shares. In addition, the EIB Finance Contract restricts our ability to distribute any dividends on our equity securities without the consent of EIB. We do not anticipate paying cash dividends on our equity securities in the foreseeable future and intend to retain all available funds and any future earnings for use in the operation and expansion of our business, given our state of development.

Pursuant to French law, our board of directors may propose a dividend and/or reserve distribution for approval by the shareholders at the annual general meeting related to the statutory financial statements of Cellectis. Upon recommendation of our board of directors, our shareholders may decide to allocate all or part of any distributable profits to special or general reserves, to carry them forward to the next fiscal year as retained earnings or to allocate them to the shareholders as dividends. However, dividends may not be distributed when as a result of such distribution, our net assets are or would become lower than the amount of the share capital plus the amount of the legal reserves which, under French law, may not be distributed to shareholders

Our board of directors may distribute interim dividends after the end of the fiscal year but before the approval of the financial statements for the relevant fiscal year when the interim balance sheet, established during such year and certified by an auditor, reflects that we have earned distributable profits since the close of the last financial year, after recognizing the necessary depreciation and provisions and after deducting prior losses, if any, and the sums to be allocated to reserves, as required by law or the By-laws, and including any retained earnings. The amount of such interim dividends may not exceed the amount of the profit so defined.

Dividends are distributed to shareholders proportionally to their shareholding interests. In the case of interim dividends, distributions are made to shareholders on the date set by our board of directors during the meeting in which the distribution of interim dividends is approved. The actual dividend payment date is decided by the shareholders at an ordinary general shareholders’ meeting or by our board of directors in the absence of such a decision by the shareholders. Shareholders that own shares on the actual payment date are entitled to the dividend.

Dividends may be paid in cash or, if the shareholders’ meeting so decides, in kind, provided that all the shareholders receive a whole number of assets of the same nature paid in lieu of cash. Our By-laws provide that, subject to a decision of the shareholders’ meeting taken by ordinary resolution, each shareholder may be given the choice to receive his dividend in cash or in shares.

Dividend distributions, if any in the future, will be made in respect of ADSs, as provided deposit agreement for the ADSs.

S-10

CAPITALIZATION

The following table sets forth our current financial assets and cash and cash equivalents and capitalization as of September 30, 2022:

You should read this table together with our financial statements and the related notes thereto incorporated by reference herein and the other financial information incorporated by reference into this prospectus supplement and the accompanying prospectus.

Cash and cash equivalents as of September 30, 2022 includes approximately $7.0 million of cash and cash equivalents of Calyxt, Inc., of which we own 49.1% (as of November 3, 2022) of the outstanding shares of common stock and consolidated in our financial results and, immediately upon completion of the proposed merger between Calyxt and Cibus, subject to customary closing conditions, Cellectis is expected to own approximately 2.5% of the equity interests of the combined company.

Except as otherwise noted, in this prospectus supplement, the number of shares that will be outstanding after this offering is based on 45,567,810 ordinary shares outstanding as of September 30, 2022, and does not include:

S-11

Except as otherwise noted, the information in this prospectus supplement assumes no exercise of the options and non-employee warrants listed above, no expiry of the vesting period of the free shares (actions gratuites) listed above and no exercise by the underwriters of their option to purchase additional ADSs in this offering.

S-12

DILUTION

If you invest in our ADSs, dilution (accretion) will be represented by the difference between the public offering price per ADS and our net tangible book value per ordinary share immediately after this offering. For purposes of this “Dilution” section, we assume all outstanding ordinary shares are held in the form of ADSs for the purposes of per ADS calculations.

Our net tangible book value as of September 30, 2022 was $144.1 million or $3.16 per ordinary share and per ADS. Net tangible book value per ordinary share is determined by dividing total tangible assets less total liabilities by the aggregate number of ordinary shares outstanding as of September 30, 2022.

After giving effect to the sale by us of                 ADSs at the public offering price of $            per ADS and after deducting the underwriting commissions and estimated offering expenses, our net tangible book value as of September 30, 2022 would have been approximately $             million, or $             per ADS and per ordinary share. This represents an immediate decrease in net tangible book value of $             per ADS and per ordinary share to our existing holders and immediate dilution (accretion) of $             per ADS issued to the new investors purchasing ADSs in this offering.

The following table illustrates such per share accretion:

If the underwriters exercise their option in full to purchase                  additional ADSs in this offering at the public offering price of $             per ADS, the net tangible book value per ADS and per ordinary share after the offering would be $             per ADS and per ordinary share, the increase (decrease) in the net tangible book value per ADS and per ordinary share to existing stockholders would be $             per ADS and per ordinary share and the dilution (accretion) to new investors purchasing ADSs in this offering would be $             per ADS.

To the extent that options or warrants are exercised, new options are issued under our existing or future equity incentive plans, free shares are issued, or we issue additional ADSs or ordinary shares in the future, there may be dilution to investors participating in this offering. In addition, we may choose to raise additional capital because of market conditions or strategic considerations, even if we believe that we have sufficient funds for our current or future operating plans. If we raise additional capital through the sale of additional equity, the issuance of these securities could result in dilution.

Except as otherwise noted, in this prospectus supplement, the above discussion is based on 45,567,810 ordinary shares outstanding as of September 30, 2022 and does not include:

S-13

Except as otherwise noted, the information in this prospectus supplement assumes no exercise of the options and non-employee warrants listed above and no expiry of the vesting period of the free shares (actions gratuites) listed above and no exercise by the underwriters of their option to purchase additional ADSs in this offering.

S-14

LIMITATIONS AFFECTING SHAREHOLDERS OF A FRENCH COMPANY

Ownership of ADSs or Shares by Non-French Persons

Neither French law nor our By-laws presently impose any restrictions on the right of non-French residents or non-French shareholders to own and vote shares.

However, (a) any non-French citizen, (b) any French citizen not residing in France, (c) any non-French entity or (d) any French entity controlled by one of the aforementioned persons or entities may have to file a declaration for statistical purposes with the Bank of France (Banque de France) within twenty working days following the date of certain direct foreign investments in us, including any purchase of our ADSs. In particular, such filings are required in connection with investments exceeding €15,000,000 that lead to the acquisition of at least 10% of our share capital or voting rights or cross such 10% threshold. Violation of this filing requirement may be sanctioned by five years of imprisonment and a fine of up to twice the amount of the relevant investment. This amount may be increased fivefold if the violation is made by a legal entity.

Further, any investment:

For the purposes of (i) in the second bullet above, ownership of at least 40% of our share capital or voting rights is regarded as a controlling interest, but a lower percentage might be held to be a controlling interest in certain circumstances depending upon factors such as the acquiring party’s intention, the acquiring party’s ability to elect directors, and financial reliance by the company on the acquiring party.

If an investment requiring the prior authorization of the French Minister of Economy is completed without such authorization having been granted, the French Minister of Economy might direct the relevant investor to nonetheless (i) submit a request for authorization, (ii) have the previous situation restored at its own expense or (iii) amend the investment. The relevant investor might also be found criminally liable and might be sanctioned with a fine which cannot exceed the greater of: (i) twice the amount of the relevant investment, (ii) 10% of the annual turnover before tax of the target company and (iii) €5 million (for a legal entity) or €1 million (for an individual).

Foreign Exchange Controls

Under current French foreign exchange control regulations there are no limitations on the amount of cash payments that we may remit to residents of foreign countries. Laws and regulations concerning foreign exchange controls do, however, require that all payments or transfers of funds made by a French resident to a non-resident such as dividend payments be handled by an accredited intermediary. All registered banks and substantially all credit institutions in France are accredited intermediaries.

S-15

Availability of Preferential Subscription Rights

In accordance with French law, our existing shareholders have preferential subscription rights to subscribe for new shares or other securities giving rights to acquire additional shares on a pro rata basis, as described under the section of the accompanying prospectus titled “Description of Share Capital—Key Provisions of Our By-laws and French Law—Changes in Share Capital—Preferential Subscription Right.”

Holders of our securities in the U.S. (which may be in the form of shares or ADSs) may not be able to exercise preferential subscription rights for their securities unless a registration statement under the Securities Act is effective with respect to such rights or an exemption from the registration requirements imposed by the Securities Act is available. We may, from time to time, issue new shares or other securities giving rights to acquire additional shares (such as warrants) at a time when no registration statement is in effect and no Securities Act exemption is available. If so, holders of our securities in the U.S. will be unable to exercise any preferential subscription rights and their interests will be diluted. We are under no obligation to, and cannot provide any assurance that we will, file any registration statement in connection with any issuance of new shares or other securities.

For holders of our ordinary shares in the form of ADSs, the depositary may make these rights or other distributions available to ADS holders. If the depositary does not make the rights available to ADS holders and determines that it is impractical to sell the rights, it may allow these rights to lapse. In that case the holders will receive no value for them. The section of the accompanying prospectus titled “Description of American Depositary Shares—Dividends and Distributions” explains in detail the depositary’s responsibility in connection with a rights offering.

S-16

UNDERWRITING

Subject to the terms and conditions set forth in the underwriting agreement, dated                , 2023, between us and Jefferies LLC and Barclays Capital Inc., as the representatives of the underwriters named below and the joint book-running managers of this offering, we have agreed to sell to the underwriters, and each of the underwriters has agreed, severally and not jointly, to purchase from us, the respective number of ADSs shown opposite its name below:

The underwriting agreement provides that the obligations of the several underwriters are subject to certain conditions precedent such as the receipt by the underwriters of officers’ certificates and legal opinions and approval of certain legal matters by their counsel. The underwriting agreement provides that the underwriters will purchase all of the ADSs if any of them are purchased. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of the nondefaulting underwriters may be increased or the underwriting agreement may be terminated. We have agreed to indemnify the underwriters and certain of their controlling persons against certain liabilities, including liabilities under the Securities Act, and to contribute to payments that the underwriters may be required to make in respect of those liabilities.

The underwriters have advised us that, following the completion of this offering, they currently intend to make a market in the ADSs as permitted by applicable laws and regulations. However, the underwriters are not obligated to do so, and the underwriters may discontinue any market-making activities at any time without notice in their sole discretion. Accordingly, no assurance can be given as to the liquidity of the trading market for the ADSs, that you will be able to sell any of the ADSs held by you at a particular time or that the prices that you receive when you sell will be favorable.

The underwriters are offering the ADSs subject to their acceptance of the ADSs from us and subject to prior sale. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part.

Commission and Expenses

The underwriters have advised us that they propose to offer the ADSs to the public at the public offering price set forth on the cover page of this prospectus supplement and to certain dealers, which may include the underwriters, at that price less a concession not in excess of $            per ADS. The underwriters may allow, and certain dealers may reallow, a discount from the concession not in excess of $            per ADS to certain brokers and dealers. After the offering, the public offering price, concession and reallowance to dealers may be reduced by the representatives. No such reduction will change the amount of gross proceeds to be received by us for the ordinary shares underlying the ADSs as set forth on the cover page of this prospectus supplement.

S-17

The following table shows the public offering price, the underwriting commissions that we are to pay the underwriters and the proceeds, before expenses, to us in connection with this offering. Such amounts are shown assuming both no exercise and full exercise of the underwriters’ option to purchase additional ADSs.

We estimate expenses payable by us in connection with this offering, other than the underwriting commissions referred to above, will be approximately $            .

Listing

Our ADSs are listed on The Nasdaq Global Market under the symbol “CLLS”. Our ordinary shares are listed on the Euronext Growth market of Euronext in Paris under the symbol “ALCLS”.

Stamp Taxes

If you purchase ADSs offered in this prospectus supplement, you may be required to pay stamp taxes and other charges under the laws and practices of the country of purchase, in addition to the offering price listed on the cover page of this prospectus supplement.

Option to Purchase Additional ADSs

We have granted to the underwriters an option, exercisable for 30 days from the date of this prospectus supplement, to purchase, at any time, in whole or in part, up to an aggregate of                ADSs from us at the public offering price set forth on the cover page of this prospectus supplement, less underwriting commissions. If the underwriters exercise this option, each underwriter will be obligated, subject to specified conditions, to purchase a number of additional ADSs proportionate to that underwriter’s initial purchase commitment as indicated in the table above.

No Sales of Similar Securities

We and our officers and directors have agreed, subject to specified exceptions, not to directly or indirectly:

This lock-up provision applies to ordinary shares, ADSs and to securities convertible into or exchangeable or exercisable for or repayable with ordinary shares or ADSs. It also applies to ordinary shares or ADSs owned now or acquired later by the person executing the agreement or for which the person executing the agreement later acquires the power of disposition.

S-18

In case of the lock-up agreements executed by our directors and executive officers, the foregoing lock-up restrictions do not apply to transfers:

provided that in the case of any transfer or distribution pursuant to any of the clauses above (except in the case of transfers pursuant to a 10b5-1 plan), any such transfer shall not involve a disposition for value and each donee, distributee, transferee, nominee, custodian or trustee shall execute a lock-up agreement. The lock-up restrictions shall also not apply to sales of ordinary shares or ADSs purchased on the open market or in the public offering, provided that such sales are not required to be publicly reported and no voluntary public filing is made.

In addition, nothing in the lock-up agreements shall prohibit the establishment of a new Rule 10b5-1 plan under the Exchange Act, so long as the securities subject to such plan may not be sold and no public disclosure of the establishment of such plan shall be required or voluntarily made during the 90-day restricted period.

Jefferies LLC and Barclays Capital Inc. may, in their discretion and at any time or from time to time before the termination of the 90-day period release all or any portion of the securities subject to lock-up agreements. There are no existing agreements between the underwriters and any of our shareholders who will execute a lock-up agreement, providing consent to the sale of ADSs or ordinary shares prior to the expiration of the lock-up period.

Stabilization

The underwriters have advised us that, pursuant to Regulation M under the Exchange Act, certain persons participating in the offering may engage in short sale transactions, stabilizing transactions, syndicate covering transactions or the imposition of penalty bids in connection with this offering. Furthermore, stabilization transactions will also need to comply with EU laws and notably the Regulation (EU) No 596/2014 of the European Parliament and of the Council of 16 April 2014 on market abuse, as amended. These activities may have the effect of stabilizing or maintaining the market price of the ADSs at a level above that which might otherwise prevail in the open market. Establishing short sales positions may involve either “covered” short sales or “naked” short sales.

“Covered” short sales are sales made in an amount not greater than the underwriters’ option to purchase additional ADSs in this offering. The underwriters may close out any covered short position by either exercising their option to purchase additional ADSs or purchasing our ADSs in the open market. In determining the source of ADSs to close out the covered short position, the underwriters will consider, among other things, the price of ADSs available for purchase in the open market as compared to the price at which they may purchase ADSs through the option to purchase additional ADSs.

“Naked” short sales are sales in excess of the option to purchase additional ADSs. The underwriters must close out any naked short position by purchasing ADSs in the open market. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of our ADSs in the open market after pricing that could adversely affect investors who purchase in this offering.

S-19

A stabilizing bid is a bid for the purchase of ADSs on behalf of the underwriters for the purpose of fixing or maintaining the price of the ADSs. A syndicate covering transaction is the bid for or the purchase of ADSs on behalf of the underwriters to reduce a short position incurred by the underwriters in connection with the offering. Similar to other purchase transactions, the underwriter’s purchases to cover the syndicate short sales may have the effect of raising or maintaining the market price of our ADSs or preventing or retarding a decline in the market price of our ADSs. As a result, the price of our ADSs may be higher than the price that might otherwise exist in the open market. A penalty bid is an arrangement permitting the underwriters to reclaim the selling concession otherwise accruing to a syndicate member in connection with the offering if the ADSs originally sold by such syndicate member are purchased in a syndicate covering transaction and therefore have not been effectively placed by such syndicate member.

Neither we nor any of the underwriters make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of ADSs. The underwriters are not obligated to engage in these activities and, if commenced, any of the activities may be discontinued at any time.

The underwriters may also engage in passive market making transactions in our ADSs on The Nasdaq Global Market in accordance with Rule 103 of Regulation M during a period before the commencement of offers or sales of our ADSs in this offering and extending through the completion of distribution. A passive market maker must display its bid at a price not in excess of the highest independent bid of that security. However, if all independent bids are lowered below the passive market maker’s bid, that bid must then be lowered when specified purchase limits are exceeded.

Electronic Distribution

A prospectus supplement in electronic format may be made available by e-mail or on the web sites or through online services maintained by one or more of the underwriters or their affiliates. In those cases, prospective investors may view offering terms online and may be allowed to place orders online. The underwriters may agree with us to allocate a specific number of ADSs for sale to online brokerage account holders. Any such allocation for online distributions will be made by the underwriters on the same basis as other allocations. Other than the prospectus supplement in electronic format, the information on the underwriters’ web sites and any information contained in any other web site maintained by any of the underwriters is not part of this prospectus supplement, has not been approved and/or endorsed by us or the underwriters and should not be relied upon by investors.

Other Activities and Relationships

The underwriters and certain of their affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment research, principal investment, hedging, financing and brokerage activities. The underwriters and certain of their affiliates have, from time to time, performed, and may in the future perform, various commercial and investment banking and financial advisory services for us and our affiliates, for which they received or will receive customary fees and expenses. For example, we entered into the Sales Agreement with Jefferies LLC as the sales agent and pursuant to which we were able offer and sell ADSs through Jefferies LLC in an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act.

In the ordinary course of their various business activities, the underwriters and certain of their affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers, and such investment and securities activities may involve securities and/or instruments issued by us and our affiliates. If the underwriters or their respective affiliates have a lending relationship with us, they routinely hedge their credit exposure to us consistent with their customary risk management policies. The underwriters and their respective affiliates may hedge such exposure by entering into transactions which consist of either the purchase of credit default swaps or the creation of short positions in our securities or the securities of our affiliates, including potentially the ADSs offered hereby. Any such short positions could adversely affect future trading prices of the ADSs offered hereby. The underwriters and certain of their respective affiliates may also communicate independent investment recommendations, market color or trading ideas and/or publish or express independent research views in

S-20

respect of such securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

Disclaimers About Non-U.S. Jurisdictions

Canada

The distribution of ADSs in Canada is being made only in the provinces of Ontario, Quebec, Alberta, British Columbia, Manitoba, New Brunswick and Nova Scotia on a private placement basis exempt from the requirement that we prepare and file a prospectus supplement with the securities regulatory authorities in each province where trades of these securities are made. Any resale of the ADSs in Canada must be made under applicable securities laws which may vary depending on the relevant jurisdiction, and which may require resales to be made under available statutory exemptions or under a discretionary exemption granted by the applicable Canadian securities regulatory authority. Purchasers are advised to seek legal advice prior to any resale of the securities.

By purchasing ADSs in Canada and accepting delivery of a purchase confirmation, a purchaser is representing to us and the dealer from whom the purchase confirmation is received that:

Canadian purchasers are hereby notified that certain of the underwriters are relying on the exemption set out in section 3A.3 or 3A.4, if applicable, of National Instrument 33-105—Underwriting Conflicts from having to provide certain conflict of interest disclosure in this document.

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if the prospectus supplement (including any amendment thereto) such as this document contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser of these securities in Canada should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

All of our directors and officers as well as the experts named herein may be located outside of Canada and, as a result, it may not be possible for Canadian purchasers to effect service of process within Canada upon us or those persons. All or a substantial portion of our assets and the assets of those persons may be located outside of Canada and, as a result, it may not be possible to satisfy a judgment against us or those persons in Canada or to enforce a judgment obtained in Canadian courts against us or those persons outside of Canada.

Canadian purchasers of ADSs should consult their own legal and tax advisors with respect to the tax consequences of an investment in the ADSs in their particular circumstances and about the eligibility of the ADSs for investment by the purchaser under relevant Canadian legislation.

S-21

Australia

This prospectus is not a disclosure document for the purposes of Australia’s Corporations Act 2001 (Cth) of Australia (the “Corporations Act”), has not been lodged with the Australian Securities & Investments Commission and is only directed to the categories of exempt persons set out below. Accordingly, if you receive this prospectus supplement in Australia:

You confirm and warrant that you are either:

To the extent that you are unable to confirm or warrant that you are an exempt sophisticated investor, associated person or professional investor under the Corporations Act any offer made to you under this prospectus supplement is void and incapable of acceptance.

You warrant and agree that you will not offer any of the securities issued to you pursuant to this prospectus supplement for resale in Australia within 12 months of those securities being issued unless any such resale offer is exempt from the requirement to issue a disclosure document under section 708 of the Corporations Act.

France

The securities have not been and will not be offered or sold to the public in the Republic of France, and no offering of this prospectus or any marketing materials relating to securities may be made available or distributed in any way that would constitute, directly or indirectly, an offer to the public in the Republic of France (except for public offerings defined in Article L.411-2 1° of the French Code monétaire et financier to qualified investors (investisseurs qualifiés)).

The securities may only be offered or sold in France pursuant to Article L. 411-2 1° of the French Code monétaire et financier to qualified investors (investisseurs qualifiés) (as such term is defined in Article 2(e) of the Prospectus Regulation), and in accordance with Articles L. 411-1, L. 411-2 and D. 411-2 to D.411-4, D.744-1 and D. 754-1 and D. 764-1 of the French Code monétaire et financier.

Prospective investors are informed that:

S-22

European Economic Area

In relation to each Member State of the European Economic Area (each, a “Relevant State”), no ADSs have been offered or will be offered pursuant to the offering to the public in that Relevant State prior to the publication of a prospectus in relation to the ADSs which has been approved by the competent authority in that Relevant State or, where appropriate, approved in another Relevant State and notified to the competent authority in that Relevant State, all in accordance with the Prospectus Regulation, except that the ADSs may be offered to the public in that Relevant State at any time:

provided that no such offer of the ADSs shall require us or any of the underwriters to publish a prospectus pursuant to Article 3 of the Prospectus Regulation or supplement a prospectus pursuant to Article 23 of the Prospectus Regulation. Each person who initially acquires any ADSs or to whom any offer is made will be deemed to have represented, warranted, acknowledged and agreed to and with us and each of the underwriters that it is a “qualified investor” within the meaning of Article 2(e) of the Prospectus Regulation.

In the case of any ADSs being offered to a financial intermediary as that term is used in the Prospectus Regulation, each such financial intermediary will be deemed to have represented, warranted, acknowledged and agreed that the ADSs acquired by it in the offering have not been acquired on a non-discretionary basis on behalf of, nor have they been acquired with a view to their offer or resale to, persons in circumstances which may give rise to an offer of any ADSs to the public other than their offer or resale in a Relevant State to qualified investors as so defined or in circumstances in which the prior consent of the underwriters has been obtained to each such proposed offer or resale.

For the purposes of this provision, the expression “offer to the public” in relation to the ADSs in any Relevant State means the communication in any form and by any means of sufficient information on the terms of the offer and any ADSs to be offered so as to enable an investor to decide to purchase or subscribe for any ADSs, and the expression “Prospectus Regulation” means Regulation (EU) 2017/1129, as amended.

According to the product governance requirements contained within: (a) EU Directive 2014/65/EU on markets in financial instruments, as amended (“MiFID II”); (b) Articles 9 and 10 of Commission Delegated Directive (EU) 2017/593 supplementing MiFID II; and (c) local implementing measures (together the “MiFID II Product Governance Requirements”), and disclaiming all and any liability, which any “manufacturer” (for the purposes of the MiFID II Product Governance Requirements) may otherwise have with respect thereto, the target market assessment in respect of the ADSs offered in the offering has led to the conclusion that the ADSs are: (i) compatible with an end target market of retail investors and investors who meet the criteria of eligible counterparties and professional clients, each as defined in MiFID II; and (ii) eligible for distribution through all distribution channels as are permitted by MiFID II (the “Target Market Assessment”). The Target Market Assessment is conducted solely for the purposes of the manufacturer’s product approval process and neither constitutes an assessment for any particular client of suitability or appropriateness for the purposes of MiFID II nor a recommendation to invest in, or purchase, or take any other action whatsoever with respect to the ordinary shares.

Hong Kong

No securities have been offered or sold, and no securities may be offered or sold, in Hong Kong, by means of any document, other than to persons whose ordinary business is to buy or sell shares or debentures, whether as principal or agent; or to “professional investors” as defined in the Securities and Futures Ordinance (Cap. 571) of Hong Kong (“SFO”) and any rules made under that Ordinance; or in other circumstances which do not result in the document being a “prospectus” as defined in the Companies Ordinance (Cap. 32) of Hong Kong (“CO”) or which do not constitute an offer or invitation to the public for the purpose of the CO or the SFO. No document, invitation or advertisement relating to the securities has been issued or may be issued or may be in the possession of any person for the purpose of issue (in each case whether in Hong Kong or elsewhere), which is directed at, or the contents of which are likely to be accessed or read by, the public of Hong Kong (except if permitted under the securities laws of

S-23

Hong Kong) other than with respect to securities which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” as defined in the SFO and any rules made under that Ordinance.

This prospectus supplement has not been registered with the Registrar of Companies in Hong Kong. Accordingly, this prospectus supplement may not be issued, circulated or distributed in Hong Kong, and the securities may not be offered for subscription to members of the public in Hong Kong. Each person acquiring the securities will be required, and is deemed by the acquisition of the securities, to confirm that he is aware of the restriction on offers of the securities described in this prospectus supplement and the relevant offering documents and that he is not acquiring, and has not been offered any securities in circumstances that contravene any such restrictions.

Israel

This document does not constitute a prospectus under the Israeli Securities Law, 5728-1968 (the “Securities Law”), and has not been filed with or approved by the Israel Securities Authority. In Israel, this prospectus supplement is being distributed only to, and is directed only at, and any offer of the ADSs is directed only at, (i) a limited number of persons in accordance with the Israeli Securities Law and (ii) investors listed in the first addendum (the “Addendum”) to the Israeli Securities Law, consisting primarily of joint investment in trust funds, provident funds, insurance companies, banks, portfolio managers, investment advisors, members of the Tel Aviv Stock Exchange, underwriters, venture capital funds, entities with equity in excess of NIS 50 million and “qualified individuals,” each as defined in the Addendum (as it may be amended from time to time), collectively referred to as qualified investors (in each case, purchasing for their own account or, where permitted under the Addendum, for the accounts of their clients who are investors listed in the Addendum). Qualified investors are required to submit written confirmation that they fall within the scope of the Addendum, are aware of the meaning of same and agree to it.

Japan

The offering has not been and will not be registered under the Financial Instruments and Exchange Law of Japan (Law No. 25 of 1948 of Japan, as amended) (“FIEL”), and the underwriters will not offer or sell any securities, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan (which term as used herein means any person resident in Japan, including any corporation or other entity organized under the laws of Japan), or to others for re-offering or resale, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan, except pursuant to an exemption from the registration requirements of, and otherwise in compliance with, the FIEL and any other applicable laws, regulations and ministerial guidelines of Japan.

Singapore

This prospectus supplement has not been and will not be lodged or registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus supplement and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the ADSs may not be circulated or distributed, nor may the ADSs be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore (the “SFA”), (ii) to a relevant person pursuant to Section 275(1), or any person pursuant to Section 275(1A), and in accordance with the conditions specified in Section 275, of the SFA, or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the ADSs are subscribed or purchased under Section 275 of the SFA by a relevant person which is:

S-24

Switzerland

The securities may not be publicly offered in Switzerland and will not be listed on the SIX Swiss Exchange (“SIX”) or on any other stock exchange or regulated trading facility in Switzerland. This prospectus supplement has been prepared without regard to the disclosure standards for issuance prospectuses under art. 652a or art. 1156 of the Swiss Code of Obligations or the disclosure standards for listing prospectuses under art. 27 ff. of the SIX Listing Rules or the listing rules of any other stock exchange or regulated trading facility in Switzerland. Neither this prospectus supplement nor any other offering or marketing material relating to the securities or the offering may be publicly distributed or otherwise made publicly available in Switzerland.

Neither this prospectus supplement nor any other offering or marketing material relating to the offering, the Company or the securities have been or will be filed with or approved by any Swiss regulatory authority. In particular, this prospectus supplement will not be filed with, and the offer of securities will not be supervised by, the Swiss Financial Market Supervisory Authority FINMA, and the offer of securities has not been and will not be authorized under the Swiss Federal Act on Collective Investment Schemes (“CISA”). The investor protection afforded to acquirers of interests in collective investment schemes under the CISA does not extend to acquirers of securities.

United Kingdom

No ADSs have been offered or will be offered pursuant to the offering to the public in the United Kingdom prior to the publication of a prospectus in relation to the ADSs which has been approved by the Financial Conduct Authority in the United Kingdom, except that the ADSs may be offered to the public in the United Kingdom at any time:

provided that no such offer of the ADSs shall require us or any of the underwriters to publish a prospectus pursuant to Section 85 of the FSMA or Article 3 of the UK Prospectus Regulation or supplement a prospectus pursuant to Article 23 of the UK Prospectus Regulation. Each person in the United Kingdom who initially acquires any ADSs or to whom any offer is made will be deemed to have represented, warranted, acknowledged and agreed to and with us and each of the underwriters that it is a “qualified investor” within the meaning of the UK Prospectus Regulation.

In the case of any ADSs being offered to a financial intermediary as that term is used in Article 5(1) of the UK Prospectus Regulation, each such financial intermediary will be deemed to have represented, warranted, acknowledged and agreed that the ADSs acquired by it in the offer have not been acquired on a non-discretionary basis on behalf of, nor have they been acquired with a view to their offer or resale to, persons in circumstances which may give rise to an offer to the public other than their offer or resale in the United Kingdom to qualified investors, in circumstances in which the prior consent of the underwriters has been obtained to each such proposed offer or resale.

For the purposes of this provision, the expression an “offer to the public” in relation to the ADSs in the United Kingdom means the communication in any form and by any means of sufficient information on the terms of the offer and any ADSs to be offered so as to enable an investor to decide to purchase or subscribe for any ADSs, the expression “UK Prospectus Regulation” means Regulation (EU) 2017/1129 as it forms part of domestic law in the United Kingdom by virtue of the European Union (Withdrawal) Act 2018, and the expression “FSMA” means the Financial Services and Markets Act 2000.

In the United Kingdom, this prospectus is being distributed only to, and is directed only at, and any offer subsequently made may only be directed at persons who are “qualified investors” (as defined in the UK Prospectus Regulation) (i) who have professional experience in the matters relating to investments falling within Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005, as amended, or the Order and/or

S-25

(ii) who are high net worth companies falling within Article 49(2)(a) to (d) of the Order and other persons to whom it may lawfully be communicated or caused to be communicated (all such persons together being referred to as “relevant persons”). In the United Kingdom, this document is directed only at relevant persons and must not be acted on or relied on by persons who are not relevant persons. Any investment or investment activity to which this document relates is available in the United Kingdom to relevant persons and will be engaged in only with relevant persons.

S-26

CERTAIN INCOME TAX CONSIDERATIONS

Material U.S. Federal Income Tax Considerations

The following is a discussion of the material U.S. federal income tax consequences of purchasing, owning and disposing of ADSs acquired pursuant to this offering. This summary does not address any aspect of U.S. federal non-income tax laws, such as U.S. federal estate and gift tax laws, or state, local or non-U.S. tax laws, and does not purport to be a comprehensive description of all of the U.S. tax considerations that may be relevant to a particular person’s decision to acquire ADSs (such as the effects of section 451(b) of the Code).

The discussion applies to you only if you acquire the ADSs in this offering and you hold the ADSs as capital assets for U.S. federal income tax purposes (generally, for investment). This section does not apply to you if you are a member of a special class of holders subject to special tax rules, including:

This section is based on the Internal Revenue Code of 1986, as amended (the “Code”), existing and proposed income tax regulations issued under the Code, legislative history, and judicial and administrative interpretations thereof, all as of the date of this offering. All of the foregoing are subject to change at any time, and any change could be retroactive and could affect the accuracy of this discussion. In addition, the application and interpretation of certain aspects of the PFIC rules, referred to below, require the issuance of regulations which in many instances have not been promulgated and which may have retroactive effect. There can be no assurance that any of these regulations will be enacted or promulgated, and if so, the form they will take or the effect that they may have on this discussion. This discussion is not binding on the U.S. Internal Revenue Service, or IRS, or the courts. No ruling has been or will be sought from the IRS with respect to the positions and issues discussed herein, and there can be no assurance that the IRS or a court will not take a different position concerning the U.S. federal income tax consequences of an investment in the ADSs or that any such position would not be sustained.

PROSPECTIVE INVESTORS SHOULD CONSULT THEIR OWN TAX ADVISORS CONCERNING THE U.S. FEDERAL, STATE, LOCAL AND NON-U.S. TAX CONSEQUENCES OF PURCHASING, OWNING AND DISPOSING OF THE ADSs IN THEIR PARTICULAR SITUATIONS.

You are a “U.S. holder” if you are a beneficial owner of ADSs that acquired the ADSs pursuant to this offering and you are:

S-27

In addition, this discussion is limited to holders who are not resident in France for purposes of the income tax treaty between the United States and France.

If a partnership (including for this purpose any entity treated as a partnership for U.S. federal income tax purposes) is a beneficial owner of the ADSs, the U.S. tax treatment of a partner in the partnership generally will depend on the status of the partner and the activities of the partnership. A holder of the ADSs that is a partnership and partners in such a partnership should consult their own tax advisors concerning the U.S. federal income tax consequences of purchasing, owning and disposing of ADSs.

A “non-U.S. holder” is a beneficial owner of ADSs that acquired the ADSs pursuant to this offering and that is neither a U.S. holder nor a partnership for U.S. federal income tax purposes.

Generally, holders of ADSs should be treated for U.S. federal income tax purposes as holding the ordinary shares represented by the ADSs. Accordingly, no gain or loss will be recognized upon an exchange of ordinary shares for ADSs or an exchange of ADSs for ordinary shares. Nevertheless, U.S. holders should consult their tax advisers regarding their beneficial ownership of ordinary shares for U.S. federal income tax purposes, including with respect to the credibility of foreign taxes, if any.

PFIC Considerations

The Code provides special rules regarding certain distributions received by U.S. persons with respect to, and sales, exchanges and other dispositions, including pledges, of, shares of stock (including ordinary shares represented by ADSs) in a PFIC. A non-U.S. corporation will be treated as a PFIC for any taxable year in which either: (1) at least 75% of its gross income is “passive income” or (2) at least 50% of its gross assets during the taxable year (based on the average of the fair market values of the assets determined at the end of each quarterly period) are “passive assets,” which generally means that they produce passive income or are held for the production of passive income. Passive income for this purpose generally includes, among other things, dividends, interest, rents, royalties, gains from commodities and securities transactions, and gains from assets that produce passive income. In determining whether a foreign corporation is a PFIC, a pro rata portion of the income and assets of each corporation in which it owns, directly or indirectly, at least a 25% interest (by value) is taken into account.

Although the matter is not free from doubt, we do not believe that we were a PFIC for the taxable year ended December 31, 2021. However, it is possible that we were a PFIC for the taxable year ended December 31, 2022 and/or will be a PFIC for the current or subsequent taxable years. In particular, the decline in the market value of the ADSs and our ordinary shares during the taxable year ended December 31, 2022 has increased the likelihood that we will be considered a PFIC for such taxable year. PFIC status must be determined annually and therefore is subject to change. Because this determination is made annually at the end of each taxable year and is dependent upon a number of factors, some of which are beyond our control, including the amount and nature of our income, as well as on the market valuation of our assets (which may be determined in large part by reference to the market value of the ADSs and our ordinary shares, which may fluctuate substantially) and our spending schedule for our cash balances and the proceeds of this offering, and because certain aspects of the PFIC rules are not entirely certain, there can be no assurance that we are or are not a PFIC or that the IRS will agree with any position we take regarding our PFIC status. If we are not a PFIC during any taxable year in which you hold ADSs, then the remainder of the discussion under “—Material U.S. Federal Income Tax Considerations,” outside of this “—PFIC Considerations” portion may be relevant to you.

A U.S. holder that holds ADSs during any taxable year in which we qualify as a PFIC is subject to special tax rules with respect to (a) any gain realized on the sale, exchange or other disposition of the ADSs and (b) any “excess

S-28

distribution” by the corporation to the holder, unless the holder elects to treat the PFIC as a “qualified electing fund,” or QEF, or makes a “mark-to-market” election, each as discussed below. An “excess distribution” is that portion of a distribution with respect to ADSs that exceeds 125% of the annual average of such distributions over the preceding three-year period or, if shorter, the U.S. holder’s holding period for its ADSs. Excess distributions and gains on the sale, exchange or other disposition of ADSs of a corporation which was a PFIC at any time during the U.S. holder’s holding period are allocated ratably to each day of the U.S. holder’s holding period. Amounts allocated to the taxable year in which the disposition occurs and amounts allocated to any period in the shareholder’s holding period before the first day of the first taxable year that the corporation was a PFIC will be taxed as ordinary income (rather than capital gain) earned in the taxable year of the disposition. Amounts allocated to each of the other taxable years in the U.S. holder’s holding period are not included in gross income for the year of the disposition, but are subject to the highest ordinary income tax rates in effect for individuals or corporations, as applicable, for each such year and the interest charge generally applicable to income tax deficiencies will be imposed on the resulting tax attributable to each year. The tax liability for amounts allocated to years before the year of disposition or “excess distribution” cannot be offset by any net operating losses for such years, and gains (but not losses) realized on the sale of the ADSs cannot be treated as capital, even if a U.S. holder held such ADSs as capital assets.

If we are a PFIC for any taxable year during which a U.S. holder holds ADSs, then we generally will continue to be treated as a PFIC with respect to the holder for all succeeding years during which such holder holds ADSs, even if we no longer satisfy either the passive income or passive asset tests described above, unless the U.S. holder terminates this deemed PFIC status by making a “deemed sale” election. If such election is made, a U.S. holder will be deemed to have sold the ADSs at their fair market value on the last day of the last taxable year for which we were a PFIC, and any gain from such deemed sale would be subject to the excess distribution rules as described above. After the deemed sale election, the ADSs with respect to which the deemed sale election was made will not be treated as shares in a PFIC unless we subsequently become a PFIC.

If we are or become a PFIC, the excess distribution rules may be avoided if a U.S. holder makes a QEF election effective beginning with the first taxable year in the holder’s holding period in which we are treated as a PFIC with respect to such holder. A U.S. holder that makes a QEF election with respect to a PFIC is required to include in income its pro rata share of the PFIC’s ordinary earnings and net capital gain as ordinary income and capital gain, respectively, subject to a separate election to defer payment of taxes, which deferral is subject to an interest charge. If a foreign corporation ceases to be a PFIC, the U.S. holder’s QEF election would no longer require an annual income inclusion.

In general, a U.S. holder makes a QEF election by attaching a completed IRS Form 8621 to a timely filed (taking into account any extensions) U.S. federal income tax return for the year beginning with which the QEF election is to be effective. In certain circumstances, a U.S. holder may be able to make a retroactive QEF election. A QEF election can be revoked only with the consent of the IRS. In order for a U.S. holder to make a valid QEF election, the non-U.S. corporation must annually provide or make available to the holder certain information. If we were a PFIC for the taxable year ended December 31, 2022 or if we are or become a PFIC in the current or a subsequent taxable year, we intend to provide to U.S. holders the information required to make valid QEF elections. However, there can be no assurance that we will have timely knowledge of our status as a PFIC or of the required information to be provided.

As an alternative to making a QEF election, a U.S. holder may make a “mark-to-market” election with respect to its ADSs if the ADSs meet certain minimum trading requirements, as described below. If a U.S. holder makes a valid mark-to-market election for the first taxable year in which such holder holds (or is deemed to hold) ADSs in a corporation and for which such corporation is determined to be a PFIC, such holder generally will not be subject to the PFIC rules described above in respect of its ADSs. Instead, a U.S. holder that makes a mark-to-market election will be required to include in income each year an amount equal to the excess, if any, of the fair market value of the ADSs that the holder owns as of the close of the taxable year over the holder’s adjusted tax basis in the ADSs. The U.S. holder will be entitled to a deduction for the excess, if any, of the holder’s adjusted tax basis in the ADSs over the fair market value of the ADSs as of the close of the taxable year; provided, however, that the deduction will be limited to the extent of any net mark-to-market gains with respect to the ADSs included by the U.S. holder under the election for prior taxable years. The U.S. holder’s basis in the ADSs will be adjusted to reflect the amounts included or deducted pursuant to the election. Amounts included in income pursuant to a mark-to-market election, as well as

S-29

gain on the sale, exchange or other disposition of the ADSs, will be treated as ordinary income. The deductible portion of any mark-to-market loss, as well as loss on a sale, exchange or other disposition of ADSs to the extent that the amount of such loss does not exceed net mark-to-market gains previously included in income, will be treated as ordinary loss. If a U.S. holder makes a valid mark-to-market election, any distributions made by us in a year in which we are a PFIC would generally be subject to the rules discussed below under “—Taxation of Dividends,” except the lower rate applicable to qualified dividend income would not apply. If we are not a PFIC when a U.S. holder has a mark-to-market election in effect, gain or loss realized by a U.S. holder on the sale of our ADSs will be a capital gain or loss and taxed in the manner described below under “—Taxation of Sale, Exchange or other Disposition of ADSs.”

The mark-to-market election applies to the taxable year for which the election is made and all subsequent taxable years, unless the ADSs cease to meet applicable trading requirements (described below) or the IRS consents to its revocation. The excess distribution rules generally do not apply to a U.S. holder for taxable years for which a mark-to-market election is in effect. If we are a PFIC for any year in which the U.S. holder owns ADSs but before a mark-to-market election is made, the interest charge rules described above will apply to any mark-to-market gain recognized in the year the election is made.

A mark-to-mark election is available only if the ADSs are considered “marketable” for these purposes. ADSs will be marketable if they are regularly traded on a national securities exchange that is registered with the SEC (such as the Nasdaq Global Market) or on a non-U.S. exchange or market that the IRS determines has rules sufficient to ensure that the market price represents a legitimate and sound fair market value. For these purposes, ADSs will be considered regularly traded during any calendar year during which more than a de minimis quantity of the ADSs is traded on at least 15 days during each calendar quarter. Any trades that have as their principal purpose meeting this requirement will be disregarded. Each U.S. holder should ask its own tax advisor whether a mark-to-market election is available or desirable.

If we are a PFIC for any year in which a U.S. holder holds ADSs, such U.S. holder must generally file an IRS Form 8621 annually. A U.S. holder must also provide such other information as may be required by the U.S. Treasury Department if the U.S. holder (1) receives certain direct or indirect distributions from a PFIC, (2) recognizes gain on a direct or indirect disposition of ADSs, or (3) makes certain elections (including a QEF election or a mark-to-market election) reportable on IRS Form 8621.

Under attribution rules, if we are a PFIC, U.S. holders of our ADSs will be deemed to own their proportionate shares of our subsidiaries that are PFICs, if any. Like the determination of whether we are a PFIC, the determination of whether any of our subsidiaries is a PFIC is made annually at the end of each taxable year. Assuming a U.S. holder does not receive from a PFIC subsidiary the information that the U.S. holder needs to make a QEF election with respect to such a subsidiary, a U.S. holder generally will be deemed to own a portion of the shares of such lower-tier PFIC and may incur liability for a deferred tax and interest charge if we receive a distribution from, or dispose of all or part of our interest in, or the U.S. holder otherwise is deemed to have disposed of an interest in, the lower-tier PFIC, even though the U.S. holder has not received the proceeds of those distributions or dispositions directly. We currently do not have any non-U.S. subsidiaries that could be PFIC subsidiaries.

U.S. holders are urged to consult their tax advisors as to our status as a PFIC, and, if we are treated as a PFIC, as to the effect on them of, and the reporting requirements with respect to, the PFIC rules and the desirability of making, and the availability of, either a QEF election or a mark-to-market election with respect to our ADSs.

Taxation of Dividends

U.S. Holders. Subject to the PFIC rules described above under “—PFIC Considerations,” if you are a U.S. holder, you must include in your gross income the gross amount of any distributions of cash or property (other than certain pro rata distributions of ADSs) with respect to ADSs, to the extent the distribution is paid out of our current or accumulated earnings and profits, as determined for U.S. federal income tax purposes. A U.S. holder must include the dividend as ordinary income at the time of actual or constructive receipt. The amount of any dividend income paid in Euro will be the U.S. dollar amount calculated by reference to the exchange rate in effect on the date of receipt, regardless of whether the payment is in fact converted into U.S. dollars. If the dividend is converted into U.S. dollars on the date of receipt, a U.S. holder should not be required to recognize foreign currency gain or loss in respect of the dividend income. A U.S. holder may have foreign currency gain or loss if the dividend is converted into

S-30

U.S. dollars after the date of receipt. Distributions in excess of current and accumulated earnings and profits, as determined for U.S. federal income tax purposes, will be treated as a non-taxable return of capital to the extent of your basis in the ADSs and thereafter as capital gain from the sale or exchange of such ADSs. Notwithstanding the foregoing, we do not intend to maintain calculations of our earnings and profits as determined for U.S. federal income tax purposes. Consequently, distributions generally will be reported as dividend income for U.S. information reporting purposes. The dividend will not be eligible for the dividends-received deduction generally allowed to U.S. corporations in respect of dividends received from other U.S. corporations.

Subject to the PFIC rules described above under “—PFIC Considerations,” dividends paid by a non-U.S. corporation generally will be taxed at the preferential tax rates applicable to long-term capital gain of non-corporate taxpayers if (a) such non-U.S. corporation is eligible for the benefits of certain U.S. treaties or the dividend is paid by such non-U.S. corporation with respect to stock that is readily tradable on an established securities market in the United States, (b) the U.S. holder receiving such dividend is an individual, estate, or trust, (c) such dividend is paid on shares that have been held by such U.S. holder for at least 61 days during the 121-day period beginning 60 days before the “ex-dividend date,” and (d) we are not a PFIC in the year of the dividend or the immediately preceding year. If the requirements of the immediately preceding sentence are not satisfied, a dividend paid by a non-U.S. corporation to a U.S. holder, including a U.S. holder that is an individual, estate, or trust, generally will be taxed at ordinary income tax rates (and not at the preferential tax rates applicable to long-term capital gains). As discussed above under “—PFIC Considerations,” it is possible that we will be a PFIC for the taxable year ending December 31, 2022 or for subsequent taxable years. The dividend rules are complex, and each U.S. holder should consult its own tax advisor regarding the dividend rules.

The amount of dividend will include any amounts withheld by the Company in respect of French taxes. Subject to applicable limitations, some of which vary depending upon the U.S. holder’s circumstances and subject to the discussion above regarding concerns expressed by the U.S. Treasury, French income taxes withheld from dividends on ADSs at a rate not exceeding the rate provided by the Treaty will be creditable against the U.S. holder’s U.S. federal income tax liability.

Dividends received generally will be income from non-U.S. sources, which may be relevant in calculating your U.S. foreign tax credit limitation. Such non-U.S. source income generally will be “passive category income,” or in certain cases “general category income” or “foreign branch” income, which is treated separately from other types of income for purposes of computing the foreign tax credit allowable to you. The rules with respect to the foreign tax credit are complex and involve the application of rules that depend upon a U.S. holder’s particular circumstances. You should consult your own tax advisor to determine the foreign tax credit implications of owning the ADSs.

Non-U.S. Holders. If you are a non-U.S. holder, dividends paid to you generally will not be subject to U.S. income tax unless the dividends are “effectively connected” with your conduct of a trade or business within the United States, and the dividends are attributable to a permanent establishment (or in the case of an individual, a fixed place of business) that you maintain in the United States if that is required by an applicable income tax treaty as a condition for subjecting you to U.S. taxation on a net income basis. In such cases you generally will be taxed in the same manner as a U.S. holder (other than with respect to the Medicare Tax described below). If you are a corporate non-U.S. holder, “effectively connected” dividends may, under certain circumstances, be subject to an additional “branch profits tax” at a 30% rate or a lower rate if you are eligible for the benefits of an income tax treaty that provides for a lower rate.

Taxation of Sale, Exchange or other Disposition of ADSs

U.S. Holders. Subject to the PFIC rules described above under “—PFIC Considerations,” if you are a U.S. holder and you sell, exchange or otherwise dispose of your ADSs, you generally will recognize capital gain or loss for U.S. federal income tax purposes equal to the difference between the value of the amount realized and your tax basis in your ADSs. Gain or loss recognized on such a sale, exchange or other disposition of ADSs generally will be long-term capital gain if you have held the ADSs for more than one year. Long-term capital gains of U.S. holders who are individuals (as well as certain trusts and estates) are generally taxed at preferential rates. The gain or loss will generally be income or loss from sources within the United States for foreign tax credit limitation purposes, unless it is attributable to an office or other fixed place of business outside the United States and certain other conditions are met. Your ability to deduct capital losses is subject to limitations. As discussed above under “—PFIC

S-31

Considerations,” it is possible that we were a PFIC for the taxable year ended December 31, 2022 and/or will be a PFIC for the current or subsequent taxable years.

Non-U.S. Holders. If you are a non-U.S. holder, you will not be subject to U.S. federal income tax on gain recognized on the sale, exchange or other disposition of your ADSs unless:

In the first case, the non-U.S. holder will be taxed in the same manner as a U.S. holder (other than with respect to the Medicare Tax described below). In the second case, the non-U.S. holder will be subject to U.S. federal income tax at a rate of 30% on the amount by which such non-U.S. holder’s U.S.-source capital gains exceed such non-U.S. holder’s U.S.-source capital losses.

If you are a corporate non-U.S. holder, “effectively connected” gains that you recognize may also, under certain circumstances, be subject to an additional “branch profits tax” at a 30% rate or at a lower rate if you are eligible for the benefits of an income tax treaty that provides for a lower rate.

Medicare Tax

Certain U.S. holders who are individuals, estates or trusts are required to pay a 3.8% Medicare surtax on all or part of that holder’s “net investment income”, which includes, among other items, dividends on, and capital gains from the sale or other taxable disposition of, the ADSs, subject to certain limitations and exceptions. Prospective investors should consult their own tax advisors regarding the effect, if any, of this surtax on their ownership and disposition of the ADSs.

Information with Respect to Foreign Financial Assets

U.S. holders that are individuals (and, to the extent provided in regulations, certain entities) that own “specified foreign financial assets,” including possibly the ADSs, with an aggregate value in excess of $50,000 are generally required to file IRS Form 8938 with information regarding such assets. Depending on the circumstances, higher threshold amounts may apply. Specified foreign financial assets include any financial accounts maintained by foreign financial institutions, as well as any of the following, but only if they are not held in accounts maintained by financial institutions: (i) stocks and securities issued by non-U.S. persons, (ii) financial instruments and contracts held for investment that have non-U.S. issuers or counterparties and (iii) interests in non-U.S. entities. If a U.S. holder is subject to this information reporting regime, the failure to timely file IRS Form 8938 may subject the U.S. holder to penalties. In addition to these requirements, U.S. holders may be required to annually file FinCEN Report 114 (Report of Foreign Bank and Financial Accounts) with the U.S. Department of Treasury. Prospective investors are encouraged to consult their own tax advisors with respect to these and other reporting requirements that may apply to their acquisition of the ADSs.

Backup Withholding and Information Reporting

In general, information reporting requirements will apply to distributions made on our ADSs within the United States to a non-corporate U.S. holder and to the proceeds from the sale, exchange, redemption or other disposition of ADSs by a non-corporate U.S. holder to or through a U.S. office of a broker. Payments made (and sales or other dispositions effected at an office) outside the U.S. will be subject to information reporting in limited circumstances.

In addition, U.S. holders may be subject to backup withholding with respect to dividends on and proceeds from the sale, exchange or other disposition of the ADSs. A paying agent within the United States will be required to withhold at the applicable statutory rate, currently 24%, in respect of any payments of dividends on, and the proceeds from the disposition of, ADSs within the United States to a U.S. holder (other than U.S. holders that are exempt from backup withholding and properly certify their exemption) if the holder fails to furnish its correct taxpayer identification number or otherwise fails to comply with applicable backup withholding requirements. U.S. holders who are required to establish their exempt status generally must provide a properly completed IRS Form W-9.

S-32

Backup withholding is not an additional tax. Amounts withheld as backup withholding may be credited against a U.S. holder’s U.S. federal income tax liability. A U.S. holder generally may obtain a refund of any amounts withheld under the backup withholding rules by filing the appropriate claim for refund with the IRS in a timely manner and furnishing any required information. U.S. holders are advised to consult with their own tax advisors regarding the application of the United States information reporting rules to their particular circumstances.

A non-U.S. holder generally may eliminate the requirement for information reporting and backup withholding by providing a properly completed and duly executed certification of its non-U.S. status to the payor, under penalties of perjury, on IRS Form W-8BEN, W-8BEN-E or other appropriate W-8, as applicable. You should consult your own tax advisor as to the qualifications for exemption from backup withholding and the procedures for obtaining the exemption.

The foregoing does not purport to be a complete analysis of the potential tax considerations relating to the offering. Prospective investors should consult their own tax advisors as to the particular tax considerations applicable to them relating to the purchase, ownership and disposition of the ADSs, including the applicability of U.S. federal, state and local tax laws or non-tax laws, non-U.S. tax laws and any changes in applicable tax laws, and any pending or proposed legislation or regulations.

Material French Income Tax Considerations

The following describes the material French income tax consequences to U.S. Holders (as defined below) of purchasing, owning and disposing of the ADSs and, unless otherwise noted, this discussion is the opinion of Jones Day, our French tax counsel, insofar as it relates to matters of French tax law and legal conclusions with respect to those matters.

This discussion does not purport to be a complete analysis or listing of all potential tax effects of the acquisition, ownership or disposition of our securities to any particular investor, and does not discuss tax considerations that arise from rules of general application or that are generally assumed to be known by investors. All of the following is subject to change. Such changes could apply retroactively and could affect the consequences described below.

In 2011, France introduced a comprehensive set of new tax rules applicable to French assets that are held by or in foreign trusts. Official guidelines issued by the French tax authorities were recently published on such rules (on March 30, 2022). These rules and guidelines, among other things, provide for the inclusion of trust assets in the settlor’s net assets for purpose of applying the French wealth tax, for the application of French gift and death duties to French assets held in trust, for a specific tax on capital on the French assets of foreign trusts not already subject to the French wealth tax and for a number of French tax reporting and disclosure obligations. The following discussion does not address the French tax consequences applicable to securities (including ADSs) held in trusts. If securities are held in trust, the grantor, trustee and beneficiary are urged to consult their own tax advisor regarding the specific tax consequences of acquiring, owning and disposing of securities.

The description of the French income tax and wealth tax consequences set forth below is based on the Convention between the Government of the United States of America and the Government of the French Republic for the Avoidance of Double Taxation and the Prevention of Fiscal Evasion with Respect to Taxes on Income and Capital of August 31, 1994 which came into force on December 30, 1995 (as amended by any subsequent protocols, including the protocol of January 13, 2009), and the tax guidelines issued by the French tax authorities in force as of the date of this prospectus supplement, or the Treaty.

For the purposes of this discussion, the term “U.S. Holder” means a beneficial owner of securities that is (1) an individual who is a U.S. citizen or resident for U.S. federal income tax purposes, (2) a U.S. domestic corporation or certain other entities created or organized in or under the laws of the United States or any state thereof, including the District of Columbia, or (3) otherwise subject to U.S. federal income taxation on a net income basis in respect of securities.

If a partnership holds securities, the tax treatment of a partner generally will depend upon the status of the partner and the activities of the partnership. If a U.S. Holder is a partner in a partnership that holds securities, such holder is urged to consult its own tax advisor regarding the specific tax consequences of acquiring, owning and disposing of securities.

S-33

This discussion applies only to investors that hold our securities as capital assets that have the U.S. dollar as their functional currency, that are entitled to Treaty benefits under the “Limitation on Benefits” provision contained in the Treaty, and whose ownership of the securities is not effectively connected to a permanent establishment or a fixed base in France. Certain U.S. Holders (including, but not limited to, U.S. expatriates, partnerships or other entities classified as partnerships for U.S. federal income tax purposes, banks, insurance companies, regulated investment companies, tax-exempt organizations, financial institutions, persons subject to the alternative minimum tax, persons who acquired the securities pursuant to the exercise of employee share options or otherwise as compensation, persons that own (directly, indirectly or by attribution) 5% or more of our voting stock or 5% or more of our outstanding share capital, dealers in securities or currencies, brokers, mutual funds, individual retirement or other tax-deferred accounts persons that elect to mark their securities to market for U.S. federal income tax purposes and persons holding securities as a position in a synthetic security, straddle or conversion transaction) may be subject to special rules not discussed below.

U.S. Holders are urged to consult their own tax advisors regarding the tax consequences of the purchase, ownership and disposition of securities in light of their particular circumstances, especially with regard to the “Limitations on Benefits” provision.

Estate and Gift Taxes and Transfer Taxes

In general, a transfer of securities by gift or by reason of death of a U.S. Holder that would otherwise be subject to French gift or inheritance tax, respectively, will not be subject to such French tax by reason of the Convention between the Government of the United States of America and the Government of the French Republic for the Avoidance of Double Taxation and the Prevention of Fiscal Evasion with Respect to Taxes on Estates, Inheritances and Gifts, dated November 24, 1978, unless the donor or the transferor is domiciled in France at the time of making the gift or at the time of his or her death, or the securities were used in, or held for use in, the conduct of a business through a permanent establishment or a fixed base in France.

Financial Transactions Tax

Pursuant to Article 235 ter ZD of the French Tax Code (Code général des impôts), or the FTC, purchases of certain securities issued by a French company, including ordinary shares and ADSs, which are listed on a regulated market of the EU or an exchange market formally acknowledged by the AMF (in each case within the meaning of the French Monetary and Financial Code, or the FMFC) are subject in France to a 0.3% tax on financial transactions, or the TFT, provided inter alia that the issuer’s market capitalization exceeds €1.0 billion at December 1 of the year preceding the taxation year. The Nasdaq Global Market is not currently acknowledged by the AMF but this may change in the future.

At December 1, 2022, our market capitalization did not exceed €1.0 billion.

A list of relevant French companies whose market capitalization exceeds €1.0 billion as of December 1 of the year preceding the taxation year within the meaning of Article 235 ter ZD of the FTC used to be published annually by the French Ministry of Economy. It is now published by the French tax authorities, and could be amended at any time. Pursuant to Regulations BOI-ANNX-000467- 21/12/2022 issued on December 21, 2022, we are currently not included in such list. Please note that such list may be updated from time to time, or may not be published anymore in the future.

As a result, neither the ADSs nor the ordinary shares are currently within the scope of the TFT.

Purchases of our securities may however become subject to the TFT at January 1, 2024, if our market capitalization exceeds €1.0 billion at December 1, 2023.

Registration Duties

In the case where the TFT is not applicable, (1) transfers of shares issued by a French company which are listed on a regulated or organized market within the meaning of the FMFC are subject to uncapped registration duties at the rate of 0.1% if the transfer is evidenced by a written statement (acte) executed either in France or outside France, whereas (2) transfers of shares issued by a French company which are not listed on a regulated or organized market within the meaning of the FMFC are subject to uncapped registration duties at the rate of 0.1% notwithstanding the existence of a written statement (acte).

S-34

As ordinary shares of Cellectis are listed on Euronext Growth, which is an organized market within the meaning of the FMFC, their transfer should be subject to uncapped registration duties at the rate of 0.1% subject to the existence of a written agreement (acte).

Although there is neither case law nor official guidelines published by the French tax authorities on this point, transfers of ADSs should remain outside of the scope of the aforementioned 0.1% registration duties.

Wealth Tax

The French wealth tax (impôt de solidarité sur la fortune) has been repealed by the finance bill for 2018 dated December 30, 2017. It has been replaced by a new real estate wealth tax (impôt sur la fortune immobilière) as from January 1, 2018. The scope of such new tax is narrowed to real estate assets (and certain assets deemed to be real estate assets) or rights, directly or indirectly through one or more legal entities and whose net taxable assets amount to at least €1.3 million. Cellectis’ securities owned by a U.S. Holder should not fall within the scope of the new real estate wealth tax provided that such U.S. Holder does not own directly or indirectly a shareholding exceeding 10% of the financial rights and voting rights of Cellectis.

Taxation of Dividends

Dividends paid by a French corporation to non-residents of France are generally subject to French withholding tax at a rate of 25%. Such withholding tax may be reduced to 12.8% for dividends paid to non-resident individuals. Dividends paid by a French corporation in a non-cooperative State or territory, as defined in Article 238-0 A of the FTC other than those mentioned in 2° of 2 bis of the same Article 238-0 A of the FTC, will generally be subject to French withholding tax at a rate of 75%. However, eligible U.S. Holders entitled to Treaty benefits under the “Limitation on Benefits” provision contained in the Treaty who are U.S. residents, as defined pursuant to the provisions of the Treaty, will not be subject to this 12.8%, 25% or 75% withholding tax rate, but may be subject to the withholding tax at a reduced rate (as described below).

Under the Treaty, the rate of French withholding tax on dividends paid to an eligible U.S. Holder who is a U.S. resident as defined pursuant to the provisions of the Treaty and whose ownership of the ordinary shares or ADSs is not effectively connected with a permanent establishment or fixed base that such U.S. Holder has in France, is generally reduced to 15%, or to 5% if such U.S. Holder is a corporation and owns directly or indirectly at least 10% of the share capital of the issuer; such U.S. Holder may claim a refund from the French tax authorities of the amount withheld in excess of the Treaty rates of 15% or 5%, if any.

For U.S. Holders that are not individuals but are U.S. residents, as defined pursuant to the provisions of the Treaty, the requirements for eligibility for Treaty benefits, including the reduced 5% or 15% withholding tax rates contained in the “Limitation on Benefits” provision of the Treaty, are complicated, and certain technical changes were made to these requirements by the protocol of January 13, 2009. U.S. Holders are advised to consult their own tax advisors regarding their eligibility for Treaty benefits in light of their own particular circumstances.

In the event that dividends are paid by Cellectis, dividends paid to an eligible U.S. Holder may immediately be subject to the reduced rates of 5% or 15% provided that such holder establishes before the date of payment that it is a U.S. resident under the Treaty by completing and providing the depositary with a treaty form (Form 5000). Otherwise, dividends paid to a U.S. Holder that is a legal person or another legal entity and has not filed the Form 5000 before the dividend payment date will be subject to French withholding tax at the rate of 25%, or 75% for any U.S. Holder if paid in a non-cooperative State or territory as defined in Article 238-0 A of the FTC other than those mentioned in 2° of 2 bis of the same Article 238-0 A of the FTC (unless the Company proves that neither the purpose nor the effect of paying the dividend in that State or territory are that of allowing, with the intent of tax evasion or avoidance, their location in such a State or territory), and then reduced at a later date to 5% or 15%, provided that such holder duly completes and provides the French tax authorities with the treaty forms Form 5000 and Form 5001 before December 31 of the second calendar year following the year during which the dividend is paid.

Certain qualifying pension funds and certain other tax-exempt entities are subject to the same general filing requirements as other U.S. Holders except that they may have to supply additional documentation evidencing their entitlement to these benefits.

S-35

Form 5000 and Form 5001, together with appropriate instructions, will be provided by the depositary to all U.S. Holders registered with the depositary. The depositary will arrange for the filing with the French tax authorities of all such forms properly completed and executed by U.S. Holders of ordinary shares or ADSs and returned to the depositary in sufficient time so that they may be filed with the French tax authorities before the distribution in order to obtain immediately a reduced withholding tax rate.

In addition, pursuant to Article 235 quater of the FTC and under certain conditions (in particular reporting obligations), a corporate U.S. Holder which is in a tax loss position for the fiscal year during which the dividend is received may be entitled to a deferral regime, and obtain a withholding tax refund. The tax deferral ends in respect of the first financial year during which this U.S. Holder is in a profit making position, as well as in the cases set out in Article 235 quater of the FTC.

Tax on Sale or Other Disposition

As a matter of principle, under French tax law, a U.S. Holder should not be subject to any French tax on any capital gain from the sale, exchange, repurchase or redemption by us of ordinary shares or ADSs, provided that all of the following apply to such holder:

In general, under the Treaty, a U.S. Holder who is a U.S. resident for purposes of the Treaty will not be subject to French tax on any capital gain from the redemption (other than redemption proceeds characterized as dividends under French domestic tax law or administrative guidelines), sale or exchange of ordinary shares or ADSs unless the ordinary shares or ADSs form part of the business property of a permanent establishment or fixed base that the U.S. Holder has in France.

A U.S. Holder that is not a U.S. resident for Treaty purposes or is not entitled to Treaty benefit (and in both cases is not resident, established or incorporated in a non-cooperative State or territory as defined in Article 238-0 A of the FTC other than those mentioned in 2° of 2 bis of the same Article 238-0 A of the FTC) and has held more than 25% of our dividend rights, known as “droits aux bénéfices sociaux” at any time during the preceding five years, either directly or indirectly, and, as relates to individuals, alone or with relatives, will be subject to a levy in France at the rate of 25%, if such U.S. Holder is a legal person, or 12.8% if such U.S. Holder is an individual.

Special rules apply to U.S. Holders who are residents of more than one country.

The discussion above is a summary of the material French tax consequences of an investment in our ADSs or ordinary shares and is based upon laws and relevant interpretations thereof in effect as of the date of this prospectus supplement, all of which are subject to change, possibly with retroactive effect. It does not cover all tax matters that may be of importance to a prospective investor. Each prospective investor is urged to consult its own tax advisor about the tax consequences to it of an investment in ADSs in light of the investor’s own circumstances.

S-36

EXPENSES

Set forth below is an itemization of the estimated total expenses, excluding underwriting commissions, which are payable by us in connection with the offer and sale of ADSs using this prospectus supplement.

MATERIAL CHANGES

Except as described in this prospectus supplement or otherwise described in our Annual Report on Form 20-F for the fiscal year ended December 31, 2021 and in our reports on Form 6-K incorporated by reference into this prospectus supplement, no reportable material changes have occurred since December 31, 2021.

WHERE YOU CAN FIND MORE INFORMATION

We have filed with the SEC a registration statement on Form F-3 under the Securities Act with respect to the securities described in this prospectus supplement. A related registration statement on Form F-6 has been filed with the SEC to register the ADSs. This prospectus supplement and the accompanying prospectus, which form a part of the registration statement on Form F-3, do not contain all of the information included in the registration statement on Form F-3.

We are subject to certain of the informational and periodic reporting requirements of the Exchange Act applicable to foreign private issuers and fulfill the obligations with respect to those requirements by filing reports with the SEC. However, as a foreign private issuer, we and our shareholders are exempt from some SEC reporting requirements, including proxy solicitation rules, short-swing insider profit disclosure rules of Section 16 of the Exchange Act with respect to our ordinary shares and the rules regarding the furnishing of quarterly reports to the SEC, which are required to be furnished only if required or otherwise provided in our home country domicile. The SEC maintains a website that contains reports and information statements and other information about issuers, such as ourselves, who file electronically with the SEC. The address of that website is www.sec.gov.

Our ordinary shares are listed on the Euronext Growth market of Euronext in Paris and on the Nasdaq Global Market, the latter in the form of ADSs. You can consult reports and other information about us that are filed pursuant to the rules of the Euronext Growth market of Euronext in Paris and of the Nasdaq Global Market at these exchanges.

You may request a copy of this prospectus supplement, the accompanying prospectus and any of the information that is incorporated by reference in this prospectus supplement and any document summarized in this prospectus supplement, without charge, upon written or oral request. If you would like to obtain this information from us, please direct your request, either in writing or by telephone, to Investor Relations, Cellectis S.A., 8, rue de la Croix Jarry, 75013 Paris, France, or Tel. +33 1 81 69 16 00.

We also maintain a website at www.cellectis.com through which you can access our SEC filings. The information set forth on our website is not part of this prospectus supplement or the accompanying prospectus. We have included our website address in this prospectus supplement solely as an inactive textual reference.

INCORPORATION OF INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” into this prospectus supplement the information in the documents that we file with the SEC. This means that we can disclose important information by referring you to another document filed separately with the SEC. The information incorporated by reference is considered to be a part of this prospectus supplement, and information that we file later with the SEC will also be deemed to be incorporated by reference into this prospectus supplement and to be a part hereof from the date of filing of such documents and will automatically update and supersede previously filed information, including information contained in this document.

S-37

We incorporate by reference into this prospectus supplement the following documents that we have filed with the SEC:

We are also incorporating by reference any additional documents we may file with the SEC under the Exchange Act, including all subsequent annual reports on Form 20-F that we file with the SEC and those of our reports on Form 6-K that we furnish to the SEC that we specifically identify in such form as being incorporated by reference into this prospectus supplement after the date hereof and prior to the completion of an offering of securities under this prospectus supplement.

Since information in this prospectus supplement and the accompanying prospectus may be modified by information included in subsequent Exchange Act filings that we incorporate by reference, only the information as modified will be a part of this prospectus supplement and the accompanying prospectus. Other information in this prospectus supplement and the accompanying prospectus will not be affected by the replacement of this superseded information, nor will an investor’s ability to rely on such superseded information be affected, to the extent such reliance occurs prior to the delivery of the superseding information.

LEGAL MATTERS

Jones Day, New York, New York, is representing the company in connection with this offering. Jones Day, Paris, France, will pass upon the validity of the ordinary shares represented by the ADSs offered hereby and other legal matters concerning this offering relating to French law, including matters of French income tax law. Cooley LLP, New York, New York, and Gide Loyrette Nouel A.A.R.P.I, Paris, France are representing the underwriters in connection with this offering.

EXPERTS

The consolidated financial statements of Cellectis appearing in Cellectis’ Annual Report on Form 20-F for the year ended December 31, 2021 and the effectiveness of Cellectis’ internal control over financial reporting as of December 31, 2021 have been audited by Ernst & Young et Autres, independent registered public accounting firm, as set forth in their reports thereon, included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such reports given on the authority of such firm as experts in accounting and auditing.

The offices of Ernst & Young et Autres are located at Tour First, 1 place des Saisons, 92037 Paris—La Défense Cedex, France.

S-38

$22,000,000 of American Depositary Shares

Representing                  Ordinary Shares

PROSPECTUS SUPPLEMENT

Joint Book-Running Managers

Jefferies

Barclays

February                 , 2023