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

PROSPECTUS SUPPLEMENT

(To prospectus dated JULY 7, 2022)

Up to $60,000,000

American Depositary Shares Representing Ordinary Shares

We have entered into a sales agreement, dated as of March 29, 2021 (the “Original Sales Agreement”), as amended by Amendment No. 1, dated as of January 4, 2023 (the “Amendment” and the Original Sales Agreement, as amended by the Amendment, the “Sales Agreement”) with Jefferies LLC, or Jefferies, relating to the sale of American Depositary Shares, or ADSs, each ADS representing one ordinary share, €0.05 nominal value per share, offered by this prospectus supplement and the accompanying prospectus. In accordance with the terms of the Sales Agreement, we may offer and sell ADSs having an aggregate offering price of up to $60.0 million from time to time from the date of the Amendment through Jefferies, acting as sales agent.

Our ADSs are listed on the Nasdaq Global Market, or Nasdaq, under the symbol “CLLS.” On January 3, 2023, the last reported sale price of our ADSs on Nasdaq was $2.27 per ADS. Our ordinary shares are traded on Euronext Growth market of Euronext Paris, or Euronext Growth, under the symbol “ALCLS.” On January 3, 2023, the last reported sale price of our ordinary shares on Euronext Growth was €2.20 per share.

Sales of our ADSs, if any, under this prospectus supplement may be made in sales deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended, or the Securities Act, from time to time. Jefferies is not required to sell any specific number or dollar amount of securities, but will act as sales agent and use commercially reasonable efforts to arrange on our behalf for the sale of all ADSs requested to be sold by us, consistent with its normal sales practices, on mutually agreed terms between us and Jefferies. There is no arrangement for funds to be received in any escrow, trust or similar arrangement.

Jefferies will be entitled to compensation at a commission rate of 3.0% of the gross sales price per ADS sold under the Sales Agreement. See “Plan of Distribution” beginning on page S-15 of this prospectus supplement for additional information regarding the compensation to be paid to Jefferies. In connection with the sale of the ADSs on our behalf, Jefferies will be deemed to be an “underwriter” within the meaning of the Securities Act, and the compensation of Jefferies will be deemed to be underwriting commissions. We have also agreed to provide indemnification and contribution to Jefferies with respect to certain liabilities, including liabilities under the Securities Act or the Securities Exchange Act of 1934, as amended, or the Exchange Act.

Only eligible investors as authorized by the relevant shareholders general meeting resolutions will be allowed to subscribe.

Investing in our ADSs involves a high degree of risk. See “Risk Factors” beginning on page S-6 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.

Jefferies

The date of this prospectus supplement is January 4, 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.

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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. Under this prospectus supplement, we may from time to time from the date of the Amendment sell ADSs representing our ordinary shares having an aggregate offering price of up to $60.0 million in sales deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act. 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 Certain 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 Certain 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 Jefferies 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 Jefferies 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

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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.

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.

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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.

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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:

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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 those 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 Certain 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.

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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 Certain 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 January 3, 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.

In the future, the offering price per ADS may be higher than our net tangible book value per ADS prior to this offering, in which case new investors would suffer immediate dilution to the extent the public offering price per ADS in the offering exceeds our net tangible book value per ADS after this offering. For a further description of the dilution or accretion that you will experience immediately after this offering, see the section of this prospectus supplement titled “Dilution.”

Because the sales of ADSs offered hereby will be made at other than a fixed price, the prices at which we sell these ADSs may vary significantly. Purchasers of the ADSs we sell, as well as our existing shareholders and holders of ADSs, will experience significant dilution if we sell additional ADSs at prices significantly below the price at which they invested.

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

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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 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 anticipate that we will use the net proceeds from this offering to fund the continued clinical development of UCART 123, UCART22, UCART20x22, and UCARTCS1, and the remainder for working capital and other general corporate purposes. 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. We expect to use the net proceeds from the offering as described under the heading “Use of Proceeds”.

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.

The ADSs offered hereby will be sold at other than fixed prices, and investors who buy ADSs at different times will likely pay different prices.

Because the sales of ADSs offered hereby will be made at other than fixed prices from time to time, the prices at which we sell these ADSs will vary and these variations may be significant. Investors who participate in this offering at different times will likely pay different prices. We will have discretion, subject to investor demand, to vary the timing, prices, and numbers of ADSs sold, and there is no minimum or maximum sale price. Investors may experience a decline in the value of their investment as a result of sales made at prices lower than the prices they paid.

The actual number of ADSs we will issue under the Sales Agreement at any one time or in total is uncertain.

We have not committed to sell, and Jefferies has not committed to purchase or underwrite, any specific number of ADSs under the Sales Agreement. The number of ADSs that are sold in this offering will be determined by us during the pendency of the Sales Agreement based on, among other things, market conditions and the market price of our ADSs and ordinary shares. Accordingly, it is not possible to predict the number of ADSs that will ultimately be issued under the Sales Agreement, if any ADSs are issued thereunder.

Although the matter is not free from doubt, we do not believe that we were a “passive foreign investment company,” or PFIC, for U.S. federal income tax purposes for the taxable year ended December 31, 2021. However, it is possible that we will be a PFIC for the taxable year ending December 31, 2022 or for 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,

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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 will be a PFIC for the taxable year ending December 31, 2022 or for subsequent taxable years. 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”.

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USE OF PROCEEDS

We may issue and sell from time to time following the Amendment ADSs, each ADS representing one of our ordinary shares, having aggregate gross sales proceeds of up to $60.0 million before payment of sales agent commissions and offering expenses payable by us. Because there is no minimum offering amount required as a condition to close any transaction as a part of this offering, the actual total public offering amount, commissions and proceeds to us, if any, are not determinable at this time. There can be no assurance that we will sell any ADSs under or fully utilize the Sales Agreement as a source of financing.

We currently intend to use the net proceeds from this offering, if any, primarily (i) to fund the continued clinical development of UCART 123, UCART22, UCART20x22, and UCARTCS1, and (ii) for working capital and general corporate purposes. The expected use of net proceeds from this offering represents our intentions based upon our current plans and business conditions, which could change in the future as our plans and business conditions evolve. The amounts and timing of our actual revenue and expenditures may vary significantly depending on numerous factors, including the actual net proceeds from this offering, the progress of our clinical development programs, feedback and decisions from regulatory authorities, the status of and results from clinical trials, the timing of regulatory submissions and the outcome of regulatory review, as well as any collaborations that we may enter into with third parties for our product candidates or technology, and any unforeseen cash needs. As a result, our management will have broad discretion to allocate the net proceeds, if any, we receive in connection with ADSs offered pursuant to this prospectus supplement for any purpose. 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, investment-grade and interest-bearing securities.

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DILUTION

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 in the aggregate amount of $30,974,815 million at an assumed offering price of $2.27 per ADS (equivalent to the maximum of 13,645,293 ADSs that we are permitted to issue under the applicable shareholder authorizations), the last reported sale price of our ADSs on Nasdaq on January 3, 2023, and after deducting estimated commissions and estimated offering expenses payable by us, our as adjusted net tangible book value as of September 30, 2022 would have been approximately $173.6 million, or $2.93 per ADS and per ordinary share. This represents an immediate decrease in net tangible book value of $0.23 per ADS and per ordinary share to our existing holders and an immediate accretion of $0.66 per ADS issued to the new investors purchasing ADSs in this offering.

The following table illustrates such per ADS accretion. The information is illustrative only and will adjust based on the actual prices at which ADSs are sold, the actual number of ADSs sold and other terms of the offering determined at the time our ADSs are sold pursuant to this prospectus supplement.

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.

The above discussion is based on 45,567,810 ordinary shares outstanding as of September 30, 2022 and does not include:

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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 listed above.

Sales of our ADSs, if any, under this prospectus supplement may be made in sales deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act from time to time and, therefore, the price of any such securities sold may vary. If the price at which the ADSs are sold increased to an assumed offering price of $4.39 per ADS, which represents the price at which the full aggregate amount of $60.0 million could be raised through the sale of the maximum number of ADSs that we are permitted to offer under the applicable shareholder authorizations (i.e., 13,645,293), and assuming all such ADSs in the aggregate amount of $60.0 million are sold during the term of the Sales Agreement at that price of $4.39 per ADS, this would increase our as adjusted net tangible book value per ADS after the offering to $3.41 per ADS, which would represent an increase in net tangible book value per ADS attributable to new investors in this offering of $0.24 per ADS, after deducting commissions and estimated offering expenses payable by us, and dilution of $0.98 per ADS to new investors purchasing ADSs in the offering. A decrease of $1.00 per ADS in the price at which the ADSs are sold from the assumed offering price of $2.27 per ADS shown in the table above, assuming all of our ADSs in the aggregate amount of $17,329,522 (equivalent to the maximum of 13,645,293 ADSs that we are permitted to issue under the applicable shareholder authorizations) are sold during the term of the Sales Agreement at that price of $1.27 per ADS, would decrease our as adjusted net tangible book value per ADS after the offering to $2.71 per ADS, which would represent a decrease in net tangible book value per ADS attributable to new investors in this offering of $0.45 per ADS, after deducting commissions and estimated offering expenses payable by us. This information is supplied for illustrative purposes only.

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DIVIDEND POLICY

We have never declared or paid any cash dividends on our ordinary shares. 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.

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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.

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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.

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PLAN OF DISTRIBUTION

We have entered into the Sales Agreement with Jefferies, under which we may offer and sell ADSs, each ADS representing one ordinary share, having an aggregate offering price of up to $60.0 million from time to time through Jefferies acting as agent. Sales of our ADSs, if any, under this prospectus supplement and the accompanying prospectus may be made in sales deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act.

Under the authority granted by our shareholders to conduct the offering, the ADSs that we are offering may only be purchased initially by (i) any person or legal entity, whether French or foreign (i.e., non-French), that invests on a regular basis or has invested at least €5.0 million over the preceding 36 months in the health or biotechnology sector or (ii) any industrial company, institution or entity, whether French or foreign (i.e., non-French), active in the health or biotechnology sectors or any affiliate thereof. In order to purchase ADSs in the offering, you will be required to execute and provide to Jefferies an investor letter representing that you satisfy the foregoing investor criteria.

Each time we wish to issue and sell our ADSs under the Sales Agreement, we will notify Jefferies of the number of ADSs to be issued, any time period over which such sales may be made, any limitation on the number of ADSs to be sold, and any limitation on the price at which such sales may be made. Once we have so instructed Jefferies, unless Jefferies declines to accept the terms of such notice, Jefferies has agreed to use its commercially reasonable efforts, consistent with its normal trading and sales practices, to arrange on our behalf for the sale of all such ADSs requested to be sold by us on the specified terms.

The obligations of Jefferies under the Sales Agreement to sell our ADSs are subject to a number of conditions that we must meet including the determination of our CEO or board of directors to issue the shares underlying the ADSs to be sold under the Sales Agreement.

Jefferies or we may suspend the offering of our ADSs being made through Jefferies under the Sales Agreement upon proper notice to the other party.

We expect to deliver ordinary shares to Jefferies for settlement on the second trading day following the date on which the sale of the ADSs was made. However, in certain circumstances, the purchaser of any ADSs in the offering may agree for settlement to occur on an alternative settlement cycle, as permitted under Rule 15c6-1 promulgated under the Exchange Act.

Sales of our ADSs as contemplated in this prospectus supplement will be settled through the facilities of The Depository Trust Company or by such other means as we and Jefferies may agree upon. There is no arrangement for funds to be received in an escrow, trust or similar arrangement.

We will pay Jefferies a commission equal to 3.0% of the aggregate gross proceeds we receive from each sale of our ADSs. Because there is no minimum offering amount required as a condition to close this offering, the actual total public offering amount, commissions and proceeds to us, if any, are not determinable at this time. In addition, we have agreed to reimburse Jefferies for the incurred fees and disbursements of its outside counsel, payable upon execution of the Original Sales Agreement, in an amount not to exceed $200,000 and payable upon execution of the Amendment, in an amount not to exceed $100,000, in addition to certain ongoing disbursements of its legal counsel, unless we and Jefferies otherwise agree. We estimate that the total expenses for the offering, excluding any commissions or expense reimbursement payable to Jefferies under the terms of the Sales Agreement, will be approximately $500,000. The remaining sale proceeds, after deducting any other transaction fees, will equal our net proceeds from the sale of such ADSs. We will report at least quarterly the number of ADSs sold through Jefferies under the Sales Agreement, the net proceeds to us and the compensation paid by us to Jefferies in connection with the sale of ADSs. In connection with any proposed sale, Jefferies will provide copies of such documents as required by French law.

In connection with the sale of our ADSs on our behalf, Jefferies will be deemed to be an “underwriter” within the meaning of the Securities Act, and the compensation of Jefferies will be deemed to be underwriting commissions. We have agreed to indemnify Jefferies against certain civil liabilities, including liabilities under the Securities Act. We have also agreed to contribute to payments Jefferies may be required to make in respect of such liabilities.

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The offering of our ADSs pursuant to the Sales Agreement will terminate upon the earlier of (i) the sale of all ADSs subject to the Sales Agreement and (ii) the termination of the Sales Agreement as permitted therein. We and Jefferies may each terminate the Sales Agreement at any time upon ten trading days’ prior notice.

This summary of the material provisions of the Sales Agreement does not purport to be a complete statement of its terms and conditions. A copy of the Sales Agreement will be filed as an exhibit to a report on Form 6-K filed under the Exchange Act, and incorporated by reference in this prospectus supplement.

Jefferies and its affiliates have provided and may in the future provide various investment banking, commercial banking, financial advisory and other financial services for us and our affiliates, for which services they have received, and may in the future receive, customary fees. In the course of its business, Jefferies may actively trade our securities for its own account or for the accounts of customers, and, accordingly, Jefferies may at any time hold long or short positions in such securities.

This prospectus supplement and the accompanying prospectus in electronic format may be made available on a website maintained by Jefferies, and Jefferies may distribute this prospectus supplement and the accompanying prospectus electronically.

The address of Jefferies LLC is 520 Madison Avenue New York, New York 10022.

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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 (“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:

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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 will be a PFIC for the taxable year ending December 31, 2022 or for subsequent taxable years. 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 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

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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 are a PFIC, for the taxable year ending December 31, 2022 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 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

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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

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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

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Considerations,” it is possible that we will be a PFIC for the taxable year ending December 31, 2022 or for 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.

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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.

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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-000467-29/12/2021 issued on December 29, 2021, 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).

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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 26.5%, 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.

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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.

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EXPENSES

Set forth below is an itemization of the estimated total expenses (excluding commissions or expense reimbursement payable to Jefferies, as Sales Agent), 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.

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INCORPORATION OF CERTAIN 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.

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

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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.

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Up to $60,000,000

American Depositary Shares Representing Ordinary Shares

PROSPECTUS SUPPLEMENT

Jefferies

January 4, 2023

Exhibit 107

The prospectus supplement to which this exhibit is attached is a final prospectus for the related offering. The maximum aggregate offering price of that offering is $60,000,000.