Promissory Note by and between the Registrant and Hudson Bay Master Fund Agreement, dated February 9, 2018

Exhibit 10.78

CONVERTIBLE PROMISSORY NOTE

For value received SELLAS Life Sciences Group, Inc., a Delaware corporation (the “Company”), promises to pay to HUDSON BAY MASTER FUND LTD or its assigns (“Holder”) the principal sum of $343,200.00 (the “Principal”) together with accrued and unpaid interest thereon (the “Interest”), each due and payable on the date and in the manner set forth below.

This convertible promissory note (the “Note”) was issued in reliance on the exemption provided in Rule 3(a)(9) of the Securities Act of 1933, as amended, pursuant to the terms of that certain Exchange Agreement, dated February 9, 2018 (the “Exchange Agreement”), by and between the Company and the Holder in exchange for that certain Warrant (as defined in the Exchange Agreement) originally issued on February 13, 2017 and shall be subject to the following terms (capitalized terms not defined herein shall have the meaning as set forth in the Exchange Agreement):

1. Repayment. All payments of Interest and Principal shall be in lawful money of the United States of America. All payments shall be applied first to accrued Interest, and thereafter to Principal. The outstanding Principal amount of the Note shall be due and payable on August 9, 2018 (the “Maturity Date”).

2. Interest. The Company promises to pay simple Interest on the outstanding Principal amount hereof from the date hereof until payment in full, which Interest shall be payable at the rate of 5% per annum (the “Interest Rate”) or the maximum rate permissible by law, whichever is less. Interest shall be due and payable by way of inclusion of the Interest in the Conversion Amount on any Conversion Date in accordance with Section 3 below or in cash on the Maturity Date and shall be calculated on the basis of a 365-day year for the actual number of days elapsed. From and after the occurrence and during the continuance of any Event of Default (as defined below), the Interest Rate shall automatically be increased to eighteen percent (18.0%) per annum (the “Default Rate”). In the event that such Event of Default is subsequently cured (and no other Event of Default then exists (including, without limitation, for the Company’s failure to pay such Interest at the Default Rate on the Maturity Date)), the adjustment referred to in the preceding sentence shall cease to be effective as of the calendar day immediately following the date of such cure; provided that the Interest as calculated and unpaid at such increased rate during the continuance of such Event of Default shall continue to apply to the extent relating to the days after the occurrence of such Event of Default through and including the date of such cure of such Event of Default.

3. Conversion.

At the election of the Holder made at any time after April 30, 2018, this Note shall be convertible into validly issued, fully paid and non-assessable shares of Common Stock (as defined below), on the terms and conditions set forth in this Section 3.

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(a) Conversion Right. Subject to the provisions of Section 3(d), at any time or times on or after April 30, 2018, the Holder shall be entitled to convert any portion of the outstanding and unpaid Conversion Amount (as defined below) into validly issued, fully paid and non-assessable shares of Common Stock in accordance with Section 3(c), at the Conversion Rate (as defined below). The Company shall not issue any fraction of a share of Common Stock upon any conversion. If the issuance would result in the issuance of a fraction of a share of Common Stock, the Company shall round such fraction of a share of Common Stock up to the nearest whole share. The Company shall pay any and all transfer, stamp, issuance and similar taxes, costs and expenses (including, without limitation, fees and expenses of the Company’s transfer agent (the “Transfer Agent”)) that may be payable with respect to the issuance and delivery of Common Stock upon conversion of any Conversion Amount.

(b) Conversion Rate. The number of shares of Common Stock issuable upon conversion of any Conversion Amount pursuant to Section 3(a) shall be determined by dividing (x) such Conversion Amount by (y) the Conversion Price (the “Conversion Rate”).

(i) “Conversion Amount” means the sum of (x) portion of the Principal to be converted, redeemed or otherwise with respect to which this determination is being made and (y) all accrued and unpaid Interest with respect to such portion of the Principal amount.

(ii) “Conversion Price” means, as of any Conversion Date or other date of determination, $7.00, subject to adjustment as provided herein.

(c) Mechanics of Conversion.

(i) Optional Conversion. To convert any Conversion Amount into shares of Common Stock on any date (a “Conversion Date”), the Holder shall deliver (whether via facsimile, electronic mail or otherwise), for receipt on or prior to 11:59 p.m., New York time, on such date, a copy of an executed notice of conversion (the “Conversion Notice”) to the Company. If required by Section 3(c)(iii), within two (2) Trading Days following a conversion of this Note as aforesaid, the Holder shall surrender this Note to a nationally recognized overnight delivery service for delivery to the Company (or an indemnification undertaking with respect to this Note in the case of its loss, theft or destruction). On or before the first (1st) Trading Day following the date of receipt of a Conversion Notice, the Company shall transmit by facsimile or electronic mail an acknowledgment of confirmation and representation as to whether such shares of Common Stock may then be resold pursuant to Rule 144 or an effective and available registration statement, of receipt of such Conversion Notice to the Holder and the Transfer Agent which confirmation shall constitute an instruction to the Transfer Agent to process such Conversion Notice in accordance with the terms herein. On or before the second (2nd) Trading Day following the date on which the Company has received a Conversion Notice (or such earlier date as required pursuant to the Exchange Act or other applicable law, rule or regulation for the settlement of a trade initiated on the applicable Conversion Date of such shares of Common Stock issuable pursuant to such Conversion Notice) (the “Share Delivery Deadline”), the Company shall (1) provided that the Transfer Agent is participating in the DTC Fast Automated Securities Transfer Program, credit such aggregate number of shares of Common Stock to which the Holder shall be entitled pursuant to such conversion to the Holder’s or its designee’s balance account with DTC through its Deposit/Withdrawal at Custodian system or (2) if the Transfer Agent is not

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participating in the DTC Fast Automated Securities Transfer Program, upon the request of the Holder, issue and deliver (via reputable overnight courier) to the address as specified in the Conversion Notice, a certificate, registered in the name of the Holder or its designee, for the number of shares of Common Stock to which the Holder shall be entitled pursuant to such conversion. If this Note is physically surrendered for conversion pursuant to Section 3(c)(iii) and the outstanding Principal of this Note is greater than the Principal portion of the Conversion Amount being converted, then the Company shall as soon as practicable and in no event later than two (2) Business Days after receipt of this Note and at its own expense, issue and deliver to the Holder (or its designee) a new Note representing the outstanding Principal not converted.

(ii) Company’s Failure to Timely Convert. If the Company shall fail, for any reason or for no reason, on or prior to the applicable Share Delivery Deadline, if the Transfer Agent is not participating in the DTC Fast Automated Securities Transfer Program, to issue and deliver to the Holder (or its designee) a certificate for the number of shares of Common Stock to which the Holder is entitled and register such shares of Common Stock on the Company’s share register or, if the Transfer Agent is participating in the DTC Fast Automated Securities Transfer Program, to credit the balance account of the Holder or the Holder’s designee with DTC for such number of shares of Common Stock to which the Holder is entitled upon the Holder’s conversion of this Note (as the case may be) (a “Conversion Failure”), and if on or after such Share Delivery Deadline the Holder purchases (in an open market transaction or otherwise) shares of Common Stock corresponding to all or any portion of the number of shares of Common Stock issuable upon such conversion that the Holder is entitled to receive from the Company and has not received from the Company in connection with such Conversion Failure (a “Buy-In”), then, in addition to all other remedies available to the Holder, the Company shall, within two (2) Business Days after receipt of the Holder’s request and in the Holder’s discretion, either: (I) pay cash to the Holder in an amount equal to the Holder’s total purchase price (including brokerage commissions and other out-of-pocket expenses, if any) for the shares of Common Stock so purchased (including, without limitation, by any other Person in respect, or on behalf, of the Holder) (the “Buy-In Price”), at which point the Company’s obligation to so issue and deliver such certificate (and to issue such shares of Common Stock) or credit the balance account of such Holder or such Holder’s designee, as applicable, with DTC for the number of shares of Common Stock to which the Holder is entitled upon the Holder’s conversion hereunder (as the case may be) (and to issue such shares of Common Stock) shall terminate, or (II) promptly honor its obligation to so issue and deliver to the Holder a certificate or certificates representing such shares of Common Stock or credit the balance account of such Holder or such Holder’s designee, as applicable, with DTC for the number of shares of Common Stock to which the Holder is entitled upon the Holder’s conversion hereunder (as the case may be) and pay cash to the Holder in an amount equal to the excess (if any) of the Buy-In Price over the product of (x) such number of shares of Common Stock multiplied by (y) the lowest Closing Sale Price of the Common Stock on any Trading Day during the period commencing on the date of the applicable Conversion Notice and ending on the date of such issuance and payment under this clause (II) (the “Buy-In Payment Amount”). Nothing shall limit the Holder’s right to pursue any other remedies available to it hereunder, at law or in equity, including, without limitation, a decree of specific performance and/or injunctive relief with respect to the Company’s failure to timely deliver certificates representing shares of Common Stock (or to electronically deliver such shares of Common Stock) upon the conversion of this Note as required pursuant to the terms hereof.

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(iii) Registration; Book-Entry. The Holder and the Company shall maintain records showing the Principal and Interest converted and/or paid (as the case may be) and the dates of such conversions, and/or payments (as the case may be) or shall use such other method, reasonably satisfactory to the Holder and the Company, so as not to require physical surrender of this Note upon conversion. Notwithstanding anything to the contrary set forth in this Section 3, following conversion of any portion of this Note in accordance with the terms hereof, the Holder shall not be required to physically surrender this Note to the Company unless (A) the full Conversion Amount represented by this Note is being converted (in which event this Note shall be delivered to the Company following conversion thereof as contemplated by Section 3(c)(i)) or (B) the Holder has provided the Company with prior written notice (which notice may be included in a Conversion Notice) requesting reissuance of this Note upon physical surrender of this Note.

(d) Limitations on Conversions. The Company shall not effect the conversion of any portion of this Note, and the Holder shall not have the right to convert any portion of this Note pursuant to the terms and conditions of this Note and any such conversion shall be null and void and treated as if never made, to the extent that after giving effect to such conversion, the Holder together with the other Attribution Parties collectively would beneficially own in excess of 9.99% (the “Maximum Percentage”) of the shares of Common Stock outstanding immediately after giving effect to such conversion. For purposes of the foregoing sentence, the aggregate number of shares of Common Stock beneficially owned by the Holder and the other Attribution Parties shall include the number of shares of Common Stock held by the Holder and all other Attribution Parties plus the number of shares of Common Stock issuable upon conversion of this Note with respect to which the determination of such sentence is being made, but shall exclude shares of Common Stock which would be issuable upon (A) conversion of the remaining, nonconverted portion of this Note beneficially owned by the Holder or any of the other Attribution Parties and (B) exercise or conversion of the unexercised or nonconverted portion of any other securities of the Company (including, without limitation, any convertible notes or convertible preferred stock or warrants, including, without limitation, the Warrants) beneficially owned by the Holder or any other Attribution Party subject to a limitation on conversion or exercise analogous to the limitation contained in this Section 3(d). For purposes of this Section 3(d), beneficial ownership shall be calculated in accordance with Section 13(d) of the Exchange Act. For purposes of determining the number of outstanding shares of Common Stock the Holder may acquire upon the conversion of this Note without exceeding the Maximum Percentage, the Holder may rely on the number of outstanding shares of Common Stock as reflected in (x) the Company’s most recent Annual Report on Form 10-K, Quarterly Report on Form 10-Q, Current Report on Form 8-K or other public filing with the SEC, as the case may be, (y) a more recent public announcement by the Company or (z) any other written notice by the Company or the Transfer Agent, if any, setting forth the number of shares of Common Stock outstanding (the “Reported Outstanding Share Number”). If the Company receives a Conversion Notice from the Holder at a time when the actual number of outstanding shares of Common Stock is less than the Reported Outstanding Share Number, the Company shall notify the Holder in writing of the number of shares of Common Stock then outstanding and, to the extent that such Conversion Notice would otherwise cause the Holder’s beneficial ownership, as determined pursuant to this Section 3(d), to exceed the Maximum Percentage, the Holder must notify the Company of a reduced number of shares of Common Stock to be purchased pursuant to such Conversion Notice. For any reason at any time, upon the written or oral request of the Holder, the Company shall within one (1) Business Day

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confirm orally and in writing or by electronic mail to the Holder the number of shares of Common Stock then outstanding. In any case, the number of outstanding shares of Common Stock shall be determined after giving effect to the conversion or exercise of securities of the Company, including this Note, by the Holder and any other Attribution Party since the date as of which the Reported Outstanding Share Number was reported. In the event that the issuance of shares of Common Stock to the Holder upon conversion of this Note results in the Holder and the other Attribution Parties being deemed to beneficially own, in the aggregate, more than the Maximum Percentage of the number of outstanding shares of Common Stock (as determined under Section 13(d) of the Exchange Act), the number of shares so issued by which the Holder’s and the other Attribution Parties’ aggregate beneficial ownership exceeds the Maximum Percentage (the “Excess Shares”) shall be deemed null and void and shall be cancelled ab initio, and the Holder shall not have the power to vote or to transfer the Excess Shares. Upon delivery of a written notice to the Company, the Holder may from time to time increase (with such increase not effective until the sixty-first (61^st) day after delivery of such notice) or decrease the Maximum Percentage to any other percentage not in excess of 9.99% as specified in such notice; provided that (i) any such increase in the Maximum Percentage will not be effective until the sixty-first (61^st) day after such notice is delivered to the Company and (ii) any such increase or decrease will apply only to the Holder and the other Attribution Parties and not to any other holder of Notes that is not an Attribution Party of the Holder. For purposes of clarity, the shares of Common Stock issuable pursuant to the terms of this Note in excess of the Maximum Percentage shall not be deemed to be beneficially owned by the Holder for any purpose including for purposes of Section 13(d) or Rule 16a-1(a)(1) of the Exchange Act. No prior inability to convert this Note pursuant to this paragraph shall have any effect on the applicability of the provisions of this paragraph with respect to any subsequent determination of convertibility. The provisions of this paragraph shall be construed and implemented in a manner otherwise than in strict conformity with the terms of this Section 3(d) to the extent necessary to correct this paragraph (or any portion of this paragraph) which may be defective or inconsistent with the intended beneficial ownership limitation contained in this Section 3(d) or to make changes or supplements necessary or desirable to properly give effect to such limitation. The limitation contained in this paragraph may not be waived and shall apply to a successor holder of this Note. Further, notwithstanding anything in this Note to the contrary, under no circumstances shall the Company be obligated to issue or the Holder entitled to receive, an aggregate number of shares of Common Stock that would exceed 19.9% of the total number of shares of Common Stock issued and outstanding as of the date of this Note (the “Maximum Issuance”); provided, that to the extent the aggregate number of shares of Common Stock would exceed the Maximum Issuance, the Company shall issue and deliver to Holder a number of shares of Common Stock up to the Maximum Issuance and the unconverted Principal of this Note shall remain outstanding.

(e) Right of Alternate Conversion.

(i) General. At any time at any time after the occurrence of an Event of Default (regardless of whether such Event of Default has been cured), the Holder may, at the Holder’s option, convert (each, an “Alternate Conversion”, and the date of such Alternate Conversion, each, an “Alternate Conversion Date”) all, or any part of, the Conversion Amount (such portion of the Conversion Amount subject to such Alternate Conversion, the “Alternate Conversion Amount”) into shares of Common Stock at the Alternate Conversion Price.

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(ii) Mechanics of Alternate Conversion. On any Alternate Conversion Date, the Holder may voluntarily convert any Alternate Conversion Amount pursuant to Section 3(c) (with “Alternate Conversion Price” replacing “Conversion Price” for all purposes hereunder with respect to such Alternate Conversion) by designating in the Conversion Notice delivered pursuant to this Section 3(e) of this Note that the Holder is electing to use the Alternate Conversion Price for such conversion. Notwithstanding anything to the contrary in this Section 3(e), but subject to Section 3(d), until the Company delivers shares of Common Stock representing the applicable Alternate Conversion Amount to the Holder, such Alternate Conversion Amount may be converted by the Holder into shares of Common Stock pursuant to Section 3(c) without regard to this Section 3(e).

(f) Voluntary Adjustment by Company. The Company may at any time during the term of this Note, with the prior written consent of the Holder, reduce the then current Conversion Price of each of the Notes to any amount and for any period of time deemed appropriate by the board of directors of the Company.

4. Maturity. Unless this Note has been previously converted or prepaid in accordance with the terms of Section 3(a) above, the entire outstanding Conversion Amount shall become fully due and payable in cash on the Maturity Date; provided, that if the Conversion Amount is not paid in full in cash on the Maturity Date, subject to Section 3(d) above, the Holder shall retain the right to convert all, or any part, at such Holder’s sole discretion, of the Conversion Amount into shares of Common Stock in accordance with Section 3 above.

5. Expenses. In the event of any default hereunder, the Company shall pay all reasonable attorneys’ fees and court costs incurred by Holder in enforcing and collecting this Note.

6. Prepayment. The Company may prepay this Note and accrued but unpaid Interest prior to the Maturity Date at any time without the consent of the Holder; provided, that the Company may not prepay any Conversion Amount submitted for conversion pursuant to Section 3 above from and after the applicable Conversion Date unless such corresponding Conversion Notice is withdrawn by the Holder.

7. Default. If there shall be any Event of Default hereunder, at the option and upon the declaration of the Holder and upon written notice to the Company (which election and notice shall not be required in the case of an Event of Default under Section 7(v), 7(vi) or 7(vii)), this Note shall accelerate and all Principal and unpaid accrued Interest shall become immediately due and payable. The occurrence of any one or more of the following shall constitute an “Event of Default”:

(i) the suspension (or threatened suspension) from trading or the failure (or threatened failure) of the Common Stock to be trading or listed (as applicable) on the Nasdaq Capital Market for a period of five (5) consecutive Trading Days;

(ii) the Company’s (A) failure to cure a Conversion Failure by delivery of the required number of shares of Common Stock within five (5) Trading Days after the applicable Conversion Date or exercise date (as the case may be) or (B) notice, written or oral, to any holder of the Notes, including, without limitation, by way of public announcement or through any of its agents, at any time, of its intention not to comply, as required, with a request for conversion of any Notes into shares of Common Stock that is requested in accordance with the provisions of the Notes, other than pursuant to Section 3(d);

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(iii) the Company’s or any Subsidiary’s failure to pay to the Holder any amount of Principal, Interest or other amounts when and as due under this Note (including, without limitation, the Company’s failure to pay any redemption payments or amounts hereunder) or any other Exchange Document or any other agreement, document, certificate or other instrument delivered in connection with the transactions contemplated hereby and thereby, except, in the case of a failure to pay Interest when and as due, in which case only if such failure remains uncured for a period of at least two (2) Trading Days;

(iv) [INTENTIONALLY OMITTED];

(v) bankruptcy, insolvency, reorganization or liquidation proceedings or other proceedings for the relief of debtors shall be instituted by or against the Company or any Subsidiary and, if instituted against the Company or any Subsidiary by a third party, shall not be dismissed within thirty (30) days of their initiation;

(vi) the commencement by the Company or any Subsidiary of a voluntary case or proceeding under any applicable federal, state or foreign bankruptcy, insolvency, reorganization or other similar law or of any other case or proceeding to be adjudicated a bankrupt or insolvent, or the consent by it to the entry of a decree, order, judgment or other similar document in respect of the Company or any Subsidiary in an involuntary case or proceeding under any applicable federal, state or foreign bankruptcy, insolvency, reorganization or other similar law or to the commencement of any bankruptcy or insolvency case or proceeding against it, or the filing by it of a petition or answer or consent seeking reorganization or relief under any applicable federal, state or foreign law, or the consent by it to the filing of such petition or to the appointment of or taking possession by a custodian, receiver, liquidator, assignee, trustee, sequestrator or other similar official of the Company or any Subsidiary or of any substantial part of its property, or the making by it of an assignment for the benefit of creditors, or the execution of a composition of debts, or the occurrence of any other similar federal, state or foreign proceeding, or the admission by it in writing of its inability to pay its debts generally as they become due, the taking of corporate action by the Company or any Subsidiary in furtherance of any such action or the taking of any action by any Person to commence a Uniform Commercial Code foreclosure sale or any other similar action under federal, state or foreign law;

(vii) the entry by a court of (i) a decree, order, judgment or other similar document in respect of the Company or any Subsidiary of a voluntary or involuntary case or proceeding under any applicable federal, state or foreign bankruptcy, insolvency, reorganization or other similar law or (ii) a decree, order, judgment or other similar document adjudging the Company or any Subsidiary as bankrupt or insolvent, or approving as properly filed a petition seeking liquidation, reorganization, arrangement, adjustment or composition of or in respect of the Company or any Subsidiary under any applicable federal, state or foreign law or (iii) a decree, order, judgment or other similar document appointing a custodian, receiver, liquidator, assignee, trustee, sequestrator or other similar official of the Company or any Subsidiary or of any substantial part of its property, or ordering the winding up or liquidation of its affairs, and the continuance of any such decree, order, judgment or other similar document or any such other decree, order, judgment or other similar document unstayed and in effect for a period of thirty (30) consecutive days; or

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(viii) other than as specifically set forth in another clause of this Section 7, the Company or any Subsidiary breaches any representation, warranty, covenant or other term or condition of any Exchange Document, except, in the case of a breach of a covenant or other term or condition that is curable, only if such breach remains uncured for a period of three (3) consecutive Trading Days.

8. Adjustment of Conversion Price upon Subdivision or Combination of Common Stock. If the Company at any time on or after the date hereof subdivides (by any stock split, stock dividend, stock combination, recapitalization or other similar transaction) one or more classes of its outstanding shares of Common Stock into a greater number of shares, the Conversion Price in effect immediately prior to such subdivision will be proportionately reduced. If the Company at any time on or after the date hereof combines (by any stock split, stock dividend, stock combination, recapitalization or other similar transaction) one or more classes of its outstanding shares of Common Stock into a smaller number of shares, the Conversion Price in effect immediately prior to such combination will be proportionately increased. Any adjustment pursuant to this Section 8 shall become effective immediately after the effective date of such subdivision or combination. If any event requiring an adjustment under this Section 8 occurs during the period that a Conversion Price is calculated hereunder, then the calculation of such Conversion Price shall be adjusted appropriately to reflect such event.

9. Rights upon Fundamental Transaction. The Company shall not enter into or be party to a Fundamental Transaction unless (i) the Successor Entity assumes in writing all of the obligations of the Company under this Note and the other Exchange Documents in accordance with the provisions of this Section 9 pursuant to written agreements in form and substance satisfactory to the Holder and approved by the Holder prior to such Fundamental Transaction, including agreements to deliver to each holder of Notes in exchange for such Notes a security of the Successor Entity evidenced by a written instrument substantially similar in form and substance to the Notes, including, without limitation, having a principal amount and interest rate equal to the principal amounts then outstanding and the interest rates of the Notes held by such holder, having similar conversion rights as the Notes and having similar ranking and security to the Notes, and satisfactory to the Holder and (ii) the Successor Entity (including its Parent Entity) is a publicly traded corporation whose common stock is quoted on or listed for trading on an Eligible Market. Upon the occurrence of any Fundamental Transaction, the Successor Entity shall succeed to, and be substituted for (so that from and after the date of such Fundamental Transaction, the provisions of this Note and the other Exchange Documents referring to the “Company” shall refer instead to the Successor Entity), and may exercise every right and power of the Company and shall assume all of the obligations of the Company under this Note and the other Exchange Documents with the same effect as if such Successor Entity had been named as the Company herein. Upon consummation of a Fundamental Transaction, the Successor Entity shall deliver to the Holder confirmation that there shall be issued upon conversion or redemption of this Note at any time after the consummation of such Fundamental Transaction, in lieu of the shares of Common Stock (or other securities, cash, assets or other property (except such items still issuable under Sections 10(a) and 11, which shall continue to be receivable thereafter) issuable upon the conversion or

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redemption of the Notes prior to such Fundamental Transaction, such shares of the publicly traded common stock (or their equivalent) of the Successor Entity (including its Parent Entity) which the Holder would have been entitled to receive upon the happening of such Fundamental Transaction had this Note been converted immediately prior to such Fundamental Transaction (without regard to any limitations on the conversion of this Note), as adjusted in accordance with the provisions of this Note. Notwithstanding the foregoing, the Holder may elect, at its sole option, by delivery of written notice to the Company to waive this Section 9 to permit the Fundamental Transaction without the assumption of this Note. The provisions of this Section 9 shall apply similarly and equally to successive Fundamental Transactions and shall be applied without regard to any limitations on the conversion of this Note.

10. Rights Upon Issuance of Purchase Rights and Other Corporate Events.

(a) Purchase Rights. If at any time the Company grants, issues or sells any Options, Convertible Securities or rights to purchase stock, warrants, securities or other property pro rata to all or substantially all of the record holders of any class of Common Stock (the “Purchase Rights”), then the Holder will be entitled to acquire, upon the terms applicable to such Purchase Rights, the aggregate Purchase Rights which the Holder could have acquired if the Holder had held the number of shares of Common Stock acquirable upon complete conversion of this Note (without taking into account any limitations or restrictions on the convertibility of this Note and assuming for such purpose that the Note was converted at the Alternate Conversion Price as of the applicable record date) immediately prior to the date on which a record is taken for the grant, issuance or sale of such Purchase Rights, or, if no such record is taken, the date as of which the record holders of shares of Common Stock are to be determined for the grant, issue or sale of such Purchase Rights (provided, however, that to the extent that the Holder’s right to participate in any such Purchase Right would result in the Holder and the other Attribution Parties exceeding the Maximum Percentage, then the Holder shall not be entitled to participate in such Purchase Right to the extent of the Maximum Percentage (and shall not be entitled to beneficial ownership of such shares of Common Stock as a result of such Purchase Right (and beneficial ownership) to the extent of any such excess) and such Purchase Right to such extent shall be held in abeyance (and, if such Purchase Right has an expiration date, maturity date or other similar provision, such term shall be extended by such number of days held in abeyance, if applicable) for the benefit of the Holder until such time or times, if ever, as its right thereto would not result in the Holder and the other Attribution Parties exceeding the Maximum Percentage, at which time or times the Holder shall be granted such right (and any Purchase Right granted, issued or sold on such initial Purchase Right or on any subsequent Purchase Right held similarly in abeyance (and, if such Purchase Right has an expiration date, maturity date or other similar provision, such term shall be extended by such number of days held in abeyance, if applicable)) to the same extent as if there had been no such limitation).

(b) Other Corporate Events. In addition to and not in substitution for any other rights hereunder, prior to the consummation of any Fundamental Transaction pursuant to which holders of shares of Common Stock are entitled to receive securities or other assets with respect to or in exchange for shares of Common Stock (a “Corporate Event”), the Company shall make appropriate provision to ensure that the Holder will thereafter have the right to receive upon a conversion of this Note, at the Holder’s option (i) in addition to the shares of Common Stock receivable upon such conversion, such securities or other assets to which the Holder would have

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been entitled with respect to such shares of Common Stock had such shares of Common Stock been held by the Holder upon the consummation of such Corporate Event (without taking into account any limitations or restrictions on the convertibility of this Note) or (ii) in lieu of the shares of Common Stock otherwise receivable upon such conversion, such securities or other assets received by the holders of shares of Common Stock in connection with the consummation of such Corporate Event in such amounts as the Holder would have been entitled to receive had this Note initially been issued with conversion rights for the form of such consideration (as opposed to shares of Common Stock) at a conversion rate for such consideration commensurate with the Conversion Rate. Provision made pursuant to the preceding sentence shall be in a form and substance satisfactory to the Holder. The provisions of this Section 10(b) shall apply similarly and equally to successive Corporate Events and shall be applied without regard to any limitations on the conversion or redemption of this Note.

11. Remedies, Characterizations, Other Obligations, Breaches and Injunctive Relief. The remedies provided in this Note shall be cumulative and in addition to all other remedies available under this Note and any of the other Exchange Documents at law or in equity (including a decree of specific performance and/or other injunctive relief), and nothing herein shall limit the Holder’s right to pursue actual and consequential damages for any failure by the Company to comply with the terms of this Note. The Company covenants to the Holder that there shall be no characterization concerning this instrument other than as expressly provided herein. Amounts set forth or provided for herein with respect to payments, conversion and the like (and the computation thereof) shall be the amounts to be received by the Holder and shall not, except as expressly provided herein, be subject to any other obligation of the Company (or the performance thereof). The Company acknowledges that a breach by it of its obligations hereunder will cause irreparable harm to the Holder and that the remedy at law for any such breach may be inadequate. The Company therefore agrees that, in the event of any such breach or threatened breach, the Holder shall be entitled, in addition to all other available remedies, to specific performance and/or temporary, preliminary and permanent injunctive or other equitable relief from any court of competent jurisdiction in any such case without the necessity of proving actual damages and without posting a bond or other security. The Company shall provide all information and documentation to the Holder that is requested by the Holder to enable the Holder to confirm the Company’s compliance with the terms and conditions of this Note.

12. Severability. If any provision of this Note is prohibited by law or otherwise determined to be invalid or unenforceable by a court of competent jurisdiction, the provision that would otherwise be prohibited, invalid or unenforceable shall be deemed amended to apply to the broadest extent that it would be valid and enforceable, and the invalidity or unenforceability of such provision shall not affect the validity of the remaining provisions of this Note so long as this Note as so modified continues to express, without material change, the original intentions of the parties as to the subject matter hereof and the prohibited nature, invalidity or unenforceability of the provision(s) in question does not substantially impair the respective expectations or reciprocal obligations of the parties or the practical realization of the benefits that would otherwise be conferred upon the parties. The parties will endeavor in good faith negotiations to replace the prohibited, invalid or unenforceable provision(s) with a valid provision(s), the effect of which comes as close as possible to that of the prohibited, invalid or unenforceable provision(s).

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13. Maximum Payments. Nothing contained herein shall be deemed to establish or require the payment of a rate of interest or other charges in excess of the maximum permitted by applicable law. In the event that the rate of interest required to be paid or other charges hereunder exceed the maximum permitted by such law, any payments in excess of such maximum shall be credited against amounts owed by the Company to the Holder and thus refunded to the Company.

14. Waiver. The Company hereby waives demand, notice, presentment, protest and notice of dishonor.

15. Governing Law. This Note shall be construed and enforced in accordance with, and all questions concerning the construction, validity, interpretation and performance of this Note shall be governed by, the internal laws of the State of New York, without giving effect to any choice of law or conflict of law provision or rule (whether of the State of New York or any other jurisdictions) that would cause the application of the laws of any jurisdictions other than the State of New York. The Company hereby irrevocably submits to the exclusive jurisdiction of the state and federal courts sitting in The City of New York, Borough of Manhattan, for the adjudication of any dispute hereunder or in connection herewith or with any transaction contemplated hereby or discussed herein, and hereby irrevocably waives, and agrees not to assert in any suit, action or proceeding, any claim that it is not personally subject to the jurisdiction of any such court, that such suit, action or proceeding is brought in an inconvenient forum or that the venue of such suit, action or proceeding is improper. Nothing contained herein shall be deemed to limit in any way any right to serve process in any manner permitted by law. Nothing contained herein shall be deemed to limit in any way any right to serve process in any manner permitted by law. Nothing contained herein shall be deemed or operate to preclude the Holder from bringing suit or taking other legal action against the Company in any other jurisdiction to collect on the Company’s obligations to the Holder, to realize on any collateral or any other security for such obligations, or to enforce a judgment or other court ruling in favor of the Holder. THE COMPANY HEREBY IRREVOCABLY WAIVES ANY RIGHT IT MAY HAVE TO, AND AGREES NOT TO REQUEST, A JURY TRIAL FOR THE ADJUDICATION OF ANY DISPUTE HEREUNDER OR IN CONNECTION WITH OR ARISING OUT OF THIS NOTE OR ANY TRANSACTION CONTEMPLATED HEREBY.

16. Failure Or Indulgence Not Waiver. No failure or delay on the part of the Holder in the exercise of any power, right or privilege hereunder shall operate as a waiver thereof, nor shall any single or partial exercise of any such power, right or privilege preclude other or further exercise thereof or of any other right, power or privilege. No waiver shall be effective unless it is in writing and signed by an authorized representative of the waiving party. Notwithstanding the foregoing, nothing contained in this Section 16 shall permit any waiver of any provision of Section 3(d).

17. Amending the Terms of this Note. The prior written consent of the Holder shall be required for any change, waiver or amendment to this Note.

Note: Page 12.

18. Notices; Currency; Payments.

(a) Notices. Whenever notice is required to be given under this Note, unless otherwise provided herein, such notice shall be given in accordance with the terms of the Exchange Agreement. The Company shall provide the Holder with prompt written notice of all actions taken pursuant to this Note, including in reasonable detail a description of such action and the reason therefore. Without limiting the generality of the foregoing, the Company will give written notice to the Holder (i) immediately upon any adjustment of the Conversion Price, setting forth in reasonable detail, and certifying, the calculation of such adjustment and (ii) at least fifteen (15) days prior to the date on which the Company closes its books or takes a record (A) with respect to any dividend or distribution upon the Common Stock, and (B) for determining rights to vote with respect to any Fundamental Transaction, dissolution or liquidation, provided in each case that such information shall be made known to the public prior to or in conjunction with such notice being provided to the Holder.

(b) Currency. All dollar amounts referred to in this Note are in United States Dollars (“U.S. Dollars”), and all amounts owing under this Note shall be paid in U.S. Dollars. All amounts denominated in other currencies (if any) shall be converted into the U.S. Dollar equivalent amount in accordance with the Exchange Rate on the date of calculation. “Exchange Rate” means, in relation to any amount of currency to be converted into U.S. Dollars pursuant to this Note, the U.S. Dollar exchange rate as published in the Wall Street Journal on the relevant date of calculation (it being understood and agreed that where an amount is calculated with reference to, or over, a period of time, the date of calculation shall be the final date of such period of time).

(c) Payments. Whenever any payment of cash is to be made by the Company to any Person pursuant to this Note, unless otherwise expressly set forth herein, such payment shall be made in lawful money of the United States of America by a certified check drawn on the account of the Company and sent via overnight courier service to such Person at such address as previously provided to the Company in writing, provided that the Holder may elect to receive a payment of cash via wire transfer of immediately available funds by providing the Company with prior written notice setting out such request and the Holder’s wire transfer instructions. Whenever any amount expressed to be due by the terms of this Note is due on any day which is not a Business Day, the same shall instead be due on the next succeeding day which is a Business Day.

19. Waiver of Notice. To the extent permitted by law, the Company hereby irrevocably waives demand, notice, presentment, protest and all other demands and notices in connection with the delivery, acceptance, performance, default or enforcement of this Note and the Exchange Agreement.

20. Assignment. This Note may be transferred only upon its surrender to the Company for registration of transfer, duly endorsed, or accompanied by a duly executed written instrument of transfer in form satisfactory to the Company. Thereupon, this Note shall be reissued to, and registered in the name of, the transferee, or a new Note for like Principal amount and Interest shall be issued to, and registered in the name of, the transferee. Interest and Principal shall be paid solely to the registered holder of this Note. Such payment shall constitute full discharge of the Company’s obligation to pay such Interest and Principal.

Note: Page 13.

21. CERTAIN DEFINITIONS. For purposes of this Note, the following terms shall have the following meanings:

(a) “Adjustment Right” means any right granted with respect to any securities issued in connection with, or with respect to, any issuance or sale (or deemed issuance or sale) of shares of Common Stock that could result in a decrease in the net consideration received by the Company in connection with, or with respect to, such securities (including, without limitation, any cash settlement rights, cash adjustment or other similar rights).

(b) “Alternate Conversion Price” means, with respect to any Alternate Conversion that price which shall be the lowest of (i) the applicable Conversion Price as in effect on the applicable Conversion Date of the applicable Alternate Conversion, (ii) 70% of the lowest VWAP of the Common Stock as of the Trading Day during the ten (10) consecutive Trading Day period ending and including the applicable Alternate Conversion Date (such period, the “Alternate Conversion Measuring Period”). All such determinations to be appropriately adjusted for any stock dividend, stock split, stock combination, reclassification or similar transaction that proportionately decreases or increases the Common Stock during such Alternate Conversion Measuring Period.

(c) “Attribution Parties” means, collectively, the following Persons and entities: (i) any investment vehicle, including, any funds, feeder funds or managed accounts, currently, or from time to time after the date hereof, directly or indirectly managed or advised by the Holder’s investment manager or any of its Affiliates or principals, (ii) any direct or indirect Affiliates of the Holder or any of the foregoing, (iii) any Person acting or who could be deemed to be acting as a Group together with the Holder or any of the foregoing and (iv) any other Persons whose beneficial ownership of the Company’s Common Stock would or could be aggregated with the Holder’s and the other Attribution Parties for purposes of Section 13(d) of the Exchange Act. For clarity, the purpose of the foregoing is to subject collectively the Holder and all other Attribution Parties to the Maximum Percentage.

(d) “Bloomberg” means Bloomberg, L.P.

(e) “Business Day” means any day other than Saturday, Sunday or other day on which commercial banks in The City of New York are authorized or required by law to remain closed.

(f) “Closing Bid Price” and “Closing Sale Price” means, for any security as of any date, the last closing bid price and last closing trade price, respectively, for such security on the Principal Market, as reported by Bloomberg, or, if the Principal Market begins to operate on an extended hours basis and does not designate the closing bid price or the closing trade price (as the case may be) then the last bid price or last trade price, respectively, of such security prior to 4:00:00 p.m., New York time, as reported by Bloomberg, or, if the Principal Market is not the principal securities exchange or trading market for such security, the last closing bid price or last trade price, respectively, of such security on the principal securities exchange or trading market where such security is listed or traded as reported by Bloomberg, or if the foregoing do not apply, the last closing bid price or last trade price, respectively, of such security in the over-the-counter market on the electronic bulletin board for such security as reported by Bloomberg, or, if no closing bid price or last trade price, respectively, is reported for such security by Bloomberg, the average of the bid prices, or the ask prices, respectively, of any market makers for such security as reported in the “pink sheets” by OTC Markets Group Inc. (formerly Pink Sheets LLC). If the Closing Bid Price or the Closing Sale Price cannot be calculated for a security on a particular date on any of

Note: Page 14.

the foregoing bases, the Closing Bid Price or the Closing Sale Price (as the case may be) of such security on such date shall be the fair market value as mutually determined by the Company and the Holder. If the Company and the Holder are unable to agree upon the fair market value of such security, then such dispute shall be resolved in accordance with the procedures in Section 22. All such determinations shall be appropriately adjusted for any stock splits, stock dividends, stock combinations, recapitalizations or other similar transactions during such period.

(g) “Common Stock” means (i) the Company’s shares of common stock, $0.0001 par value per share, and (ii) any capital stock into which such common stock shall have been changed or any share capital resulting from a reclassification of such common stock.

(h) “Convertible Securities” means any stock or other security (other than Options) that is at any time and under any circumstances, directly or indirectly, convertible into, exercisable or exchangeable for, or which otherwise entitles the holder thereof to acquire, any shares of Common Stock.

(i) “Eligible Market” means The New York Stock Exchange, the NYSE American, the Nasdaq Global Select Market, the Nasdaq Global Market or the Principal Market.

(j) “Fundamental Transaction” means (A) that the Company shall, directly or indirectly, including through subsidiaries, Affiliates or otherwise, in one or more related transactions, (i) consolidate or merge with or into (whether or not the Company is the surviving corporation) another Subject Entity, or (ii) sell, assign, transfer, convey or otherwise dispose of all or substantially all of the properties or assets of the Company or any of its “significant subsidiaries” (as defined in Rule 1-02 of Regulation S-X) to one or more Subject Entities, or (iii) make, or allow one or more Subject Entities to make, or allow the Company to be subject to or have its Common Stock be subject to or party to one or more Subject Entities making, a purchase, tender or exchange offer that is accepted by the holders of at least either (x) 50% of the outstanding shares of Common Stock, (y) 50% of the outstanding shares of Common Stock calculated as if any shares of Common Stock held by all Subject Entities making or party to, or Affiliated with any Subject Entities making or party to, such purchase, tender or exchange offer were not outstanding; or (z) such number of shares of Common Stock such that all Subject Entities making or party to, or Affiliated with any Subject Entity making or party to, such purchase, tender or exchange offer, become collectively the beneficial owners (as defined in Rule 13d-3 under the Exchange Act) of at least 50% of the outstanding shares of Common Stock, or (iv) consummate a stock or share purchase agreement or other business combination (including, without limitation, a reorganization, recapitalization, spin-off or scheme of arrangement) with one or more Subject Entities whereby all such Subject Entities, individually or in the aggregate, acquire, either (x) at least 50% of the outstanding shares of Common Stock, (y) at least 50% of the outstanding shares of Common Stock calculated as if any shares of Common Stock held by all the Subject Entities making or party to, or Affiliated with any Subject Entity making or party to, such stock purchase agreement or other business combination were not outstanding; or (z) such number of shares of Common Stock such that the Subject Entities become collectively the beneficial owners (as defined in Rule 13d-3 under the Exchange Act) of at least 50% of the outstanding shares of Common Stock, or (v) reorganize, recapitalize or reclassify its Common Stock, (B) that the Company shall, directly or indirectly, including through subsidiaries, Affiliates or otherwise, in one or more related transactions, allow any Subject Entity individually or the Subject Entities in the aggregate to be or become the “beneficial owner” (as

Note: Page 15.

defined in Rule 13d-3 under the Exchange Act), directly or indirectly, whether through acquisition, purchase, assignment, conveyance, tender, tender offer, exchange, reduction in outstanding shares of Common Stock, merger, consolidation, business combination, reorganization, recapitalization, spin-off, scheme of arrangement, reorganization, recapitalization or reclassification or otherwise in any manner whatsoever, of either (x) at least 50% of the aggregate ordinary voting power represented by issued and outstanding Common Stock, (y) at least 50% of the aggregate ordinary voting power represented by issued and outstanding Common Stock not held by all such Subject Entities as of the date of this Note calculated as if any shares of Common Stock held by all such Subject Entities were not outstanding, or (z) a percentage of the aggregate ordinary voting power represented by issued and outstanding shares of Common Stock or other equity securities of the Company sufficient to allow such Subject Entities to effect a statutory short form merger or other transaction requiring other shareholders of the Company to surrender their shares of Common Stock without approval of the shareholders of the Company or (C) directly or indirectly, including through subsidiaries, Affiliates or otherwise, in one or more related transactions, the issuance of or the entering into any other instrument or transaction structured in a manner to circumvent, or that circumvents, the intent of this definition in which case this definition shall be construed and implemented in a manner otherwise than in strict conformity with the terms of this definition to the extent necessary to correct this definition or any portion of this definition which may be defective or inconsistent with the intended treatment of such instrument or transaction.

(k) “Group” means a “group” as that term is used in Section 13(d) of the Exchange Act and as defined in Rule 13d-5 thereunder.

(l) “Options” means any rights, warrants or options to subscribe for or purchase shares of Common Stock or Convertible Securities issued to Persons other than the Company.

(m) “Parent Entity” of a Person means an entity that, directly or indirectly, controls the applicable Person and whose common stock or equivalent equity security is quoted or listed on an Eligible Market, or, if there is more than one such Person or Parent Entity, the Person or Parent Entity with the largest public market capitalization as of the date of consummation of the Fundamental Transaction.

(n) “Principal Market” means the Nasdaq Capital Market.

(o) “Subject Entity” means any Person, Persons or Group or any Affiliate or associate of any such Person, Persons or Group.

(p) “Successor Entity” means the Person (or, if so elected by the Holder, the Parent Entity) formed by, resulting from or surviving any Fundamental Transaction or the Person (or, if so elected by the Holder, the Parent Entity) with which such Fundamental Transaction shall have been entered into.

(q) “Trading Day” means, as applicable, (x) with respect to all price or trading volume determinations relating to the Common Stock, any day on which the Common Stock is traded on the Principal Market, or, if the Principal Market is not the principal trading market for the Common Stock, then on the principal securities exchange or securities market on which the

Note: Page 16.

Common Stock is then traded, provided that “Trading Day” shall not include any day on which the Common Stock is scheduled to trade on such exchange or market for less than 4.5 hours or any day that the Common Stock is suspended from trading during the final hour of trading on such exchange or market (or if such exchange or market does not designate in advance the closing time of trading on such exchange or market, then during the hour ending at 4:00:00 p.m., New York time) unless such day is otherwise designated as a Trading Day in writing by the Holder or (y) with respect to all determinations other than price determinations relating to the Common Stock, any day on which The New York Stock Exchange (or any successor thereto) is open for trading of securities.

(r) “VWAP” means, for any security as of any date, the dollar volume-weighted average price for such security on the Principal Market (or, if the Principal Market is not the principal trading market for such security, then on the principal securities exchange or securities market on which such security is then traded) during the period beginning at 9:30:01 a.m., New York time, and ending at 4:00:00 p.m., New York time, as reported by Bloomberg through its “HP” function (set to weighted average) or, if the foregoing does not apply, the dollar volume-weighted average price of such security in the over-the-counter market on the electronic bulletin board for such security during the period beginning at 9:30:01 a.m., New York time, and ending at 4:00:00 p.m., New York time, as reported by Bloomberg, or, if no dollar volume-weighted average price is reported for such security by Bloomberg for such hours, the average of the highest closing bid price and the lowest closing ask price of any of the market makers for such security as reported in the “pink sheets” by OTC Markets Group Inc. (formerly Pink Sheets LLC). If the VWAP cannot be calculated for such security on such date on any of the foregoing bases, the VWAP of such security on such date shall be the fair market value as mutually determined by the Company and the Holder. If the Company and the Holder are unable to agree upon the fair market value of such security, then such dispute shall be resolved in accordance with the procedures in Section 22. All such determinations shall be appropriately adjusted for any stock dividend, stock split, stock combination, recapitalization or other similar transaction during such period.

22. Disclosure. Upon receipt or delivery by the Company of any notice in accordance with the terms of this Note, unless the Company has in good faith determined that the matters relating to such notice do not constitute material, non-public information relating to the Company or any of its Subsidiaries, the Company shall within the later of (a) the Cleansing Deadline and (b) one (1) Business Day after any such receipt or delivery, publicly disclose such material, non-public information on a Current Report on Form 8-K or otherwise. In the event that the Company believes that a notice contains material, non-public information relating to the Company or any of its Subsidiaries, the Company so shall indicate to the Holder contemporaneously with delivery of such notice, and in the absence of any such indication, the Holder shall be allowed to presume that all matters relating to such notice do not constitute material, non-public information relating to the Company or any of its Subsidiaries. If the Company or any of its Subsidiaries provides material non-public information to the Holder after the Cleansing Deadline that is not simultaneously filed in a Current Report on Form 8-K and the Holder has not agreed to receive such material non-public information, the Company hereby covenants and agrees that the Holder shall not have any duty of confidentiality to the Company, any of its Subsidiaries or any of their respective officers, directors, employees, affiliates or agents with respect to, or a duty to any of the foregoing not to trade on the basis of, such material non-public information. Nothing contained in this Section 22 shall limit any obligations of the Company, or any rights of the Holder, under the Exchange Agreement.

[signature page follows]

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[SIGNATURE PAGE TO CONVERTIBLE PROMISSORY NOTE OF SELLAS LIFE SCIENCES GROUP, INC.]