JBIO · Jade Biosciences, Inc.

1/36th of the total number of shares of common stock subject to the option vest monthly following the date of grant, subject to the Reporting Person's continued service to the Issuer through each vesting date.

This option represents a right to purchase shares of the Issuer's common stock, which vests in full on the earlier of (i) June 9, 2027 or (ii) the date of the next annual meeting of the Issuer's stockholders, in each case, subject to the Reporting Person's continued service to the Issuer.

This option represents a right to purchase shares of the Issuer's common stock, which vests in full on the earlier of (i) June 9, 2027 or (ii) the date of the next annual meeting of the Issuer's stockholders, in each case, subject to the Reporting Person's continued service to the Issuer.

This option represents a right to purchase shares of the Issuer's common stock, which vests in full on the earlier of (i) June 9, 2027 or (ii) the date of the next annual meeting of the Issuer's stockholders, in each case, subject to the Reporting Person's continued service to the Issuer.

Under the Reporting Person's arrangement with Fairmount Funds Management LLC ("Fairmount"), the Reporting Person holds the option for one or more investment vehicles managed by Fairmount (each, a "Fairmount Fund"). The Reporting Person is obligated to turn over to Fairmount any net cash or stock received from the option for the benefit of such Fairmount Fund. The Reporting Person therefore disclaims beneficial ownership of the option and underlying common stock. Fairmount disclaims beneficial ownership of any of the reported securities, except to the extent of its pecuniary interest therein.

This option represents a right to purchase shares of the Issuer's common stock, which vests in full on the earlier of (i) June 9, 2027 or (ii) the date of the next annual meeting of the Issuer's stockholders, in each case, subject to the Reporting Person's continued service to the Issuer.

This option represents a right to purchase shares of the Issuer's common stock, which vests in full on the earlier of (i) June 9, 2027 or (ii) the date of the next annual meeting of the Issuer's stockholders, in each case, subject to Tomas Kiselak's continued service to the Issuer.

Fairmount Funds Management LLC ("Fairmount") is the investment manager for Fairmount Healthcare Fund II LP ("Fund II") and Fairmount Healthcare Co-Invest IV L.P. ("Co-Invest"). Peter Harwin and Tomas Kiselak are the managers of Fairmount. Under Mr. Kiselak's arrangement with Fairmount, Mr. Kiselak holds the option for one or more investment vehicles managed by Fairmount (each, a "Fairmount Fund"). Mr. Kiselak is obligated to turn over to Fairmount any net cash or stock received from the option for the benefit of such Fairmount Fund. Fairmount, Mr. Harwin, and Mr. Kiselak disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

Represents restricted stock units ("RSUs"). 1/4 of the total number of RSUs granted shall vest on each of the first four anniversaries of February 15, 2026, the vesting commencement date, subject to the Reporting Person's continued service through each vesting date. Each RSU represents a contingent right to receive one share of common stock of the Issuer.

Includes 1,581 shares acquired under the Issuer's employee stock purchase plan in December 2025.

Represents restricted stock units ("RSUs"). 1/4 of the total number of RSUs granted shall vest on each of the first four anniversaries of February 15, 2026, the vesting commencement date, subject to the Reporting Person's continued service through each vesting date. Each RSU represents a contingent right to receive one share of common stock of the Issuer.

This option represents a right to purchase shares of the Issuer's common stock, one quarter of which will vest on February 15, 2027, with the remaining three quarters vesting in equal monthly installments over the following three years, subject to the Reporting Person's continued service to the Issuer on each such vesting date.

Represents restricted stock units ("RSUs"). 1/4 of the total number of RSUs granted shall vest on each of the first four anniversaries of February 15, 2026, the vesting commencement date, subject to the Reporting Person's continued service through each vesting date. Each RSU represents a contingent right to receive one share of common stock of the Issuer.

This option represents a right to purchase shares of the Issuer's common stock, one quarter of which will vest on February 15, 2027, with the remaining three quarters vesting in equal monthly installments over the following three years, subject to the Reporting Person's continued service to the Issuer on each such vesting date.

This option represents a right to purchase shares of the Issuer's common stock, one quarter of which will vest on February 15, 2027, with the remaining three quarters vesting in equal monthly installments over the following three years, subject to the Reporting Person's continued service to the Issuer on each such vesting date.

Represents restricted stock units ("RSUs"). 1/4 of the total number of RSUs granted shall vest on each of the first four anniversaries of February 15, 2026, the vesting commencement date, subject to the Reporting Person's continued service through each vesting date. Each RSU represents a contingent right to receive one share of common stock of the Issuer.

This option represents a right to purchase shares of the Issuer's common stock, one quarter of which will vest on February 15, 2027, with the remaining three quarters vesting in equal monthly installments over the following three years, subject to the Reporting Person's continued service to the Issuer on each such vesting date.

The shares of Common Stock and Pre-Funded Warrants were purchased from the Issuer in a private placement, which transaction is exempt from Section 16(b) in accordance with Rule 16b-3(d)(1) promulgated under the Securities Exchange Act of 1934, as amended.

Fairmount Funds Management LLC ("Fairmount") is the investment manager for Fairmount Healthcare Fund II L.P. and Fairmount Healthcare Co-Invest IV L.P. The managers of Fairmount are Peter Harwin and Tomas Kiselak. Fairmount, Mr. Harwin, and Mr. Kiselak disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

The shares of Common Stock and Pre-Funded Warrants were purchased from the Issuer in a private placement, which transaction is exempt from Section 16(b) in accordance with Rule 16b-3(d)(1) promulgated under the Securities Exchange Act of 1934, as amended.

The Pre-Funded Warrants have no expiration date and are exercisable at any time after the date of issuance. A holder of Pre-Funded Warrants may not exercise the Pre-Funded Warrant if the holder, together with its affiliates, would beneficially own more than 9.99% of the number of outstanding shares of common stock of the Issuer immediately after giving effect to such exercise.

Fairmount Funds Management LLC ("Fairmount") is the investment manager for Fairmount Healthcare Fund II L.P. and Fairmount Healthcare Co-Invest IV L.P. The managers of Fairmount are Peter Harwin and Tomas Kiselak. Fairmount, Mr. Harwin, and Mr. Kiselak disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

This option represents a right to purchase 526,000 shares of the Issuer's common stock, one quarter of which will vest on July 14, 2026, with the remaining three quarters vesting in equal monthly installments over the following three years, subject to the Reporting Person's continued service to the Issuer on each such vesting date.

This option represents a right to purchase 23,017 shares of the Issuer's common stock, which vests in full on the earlier of (i) April 29, 2026 or (ii) the date of the next annual meeting of the Issuer's stockholders, in each case, subject to the recipient's continued service to the Issuer.

Under the Reporting Person's arrangement with Fairmount Funds Management LLC ("Fairmount"), the Reporting Person holds the option for one or more investment vehicles managed by Fairmount (each, a "Fairmount Fund"). The Reporting Person is obligated to turn over to Fairmount any net cash or stock received from the option for the benefit of such Fairmount Fund. The Reporting Person therefore disclaims beneficial ownership of the option and underlying common stock. Fairmount disclaims beneficial ownership of any of the reported securities, except to the extent of its pecuniary interest therein.

This option represents a right to purchase 23,017 shares of the Issuer's common stock, which vests in full on the earlier of (i) April 29, 2026 or (ii) the date of the next annual meeting of the Issuer's stockholders, in each case, subject to the recipient's continued service to the Issuer.

This option represents a right to purchase 23,017 shares of the Issuer's common stock, which vests in full on the earlier of (i) April 29, 2026 or (ii) the date of the next annual meeting of the Issuer's stockholders, in each case, subject to the recipient's continued service to the Issuer.

Under Mr. Kiselak's arrangement with Fairmount Funds Management LLC ("Fairmount"), Mr. Kiselak holds the option for one or more investment vehicles managed by Fairmount (each, a "Fairmount Fund"). Mr. Kiselak is obligated to turn over to Fairmount any net cash or stock received from the option for the benefit of such Fairmount Fund. Mr. Kiselak therefore disclaims beneficial ownership of the option and underlying common stock. Fairmount disclaims beneficial ownership of any of the reported securities, except to the extent of its pecuniary interest therein.

This option represents a right to purchase 23,017 shares of the Issuer's common stock, which vests in full on the earlier of (i) April 29, 2026 or (ii) the date of the next annual meeting of the Issuer's stockholders, in each case, subject to the recipient's continued service to the Issuer.

This option represents a right to purchase 23,017 shares of the Issuer's common stock, which vests in full on the earlier of (i) April 29, 2026 or (ii) the date of the next annual meeting of the Issuer's stockholders, in each case, subject to the recipient's continued service to the Issuer.

On April 28, 2025, the Issuer completed the transactions contemplated by the Agreement and Plan of Merger, dated October 30, 2024, by and among the Issuer, Caribbean Merger Sub I, Inc. ("Merger Sub I"), Caribbean Merger Sub II, LLC ("Merger Sub II") and Jade Biosciences, Inc. (" Old Jade"), pursuant to which, Merger Sub I merged with and into Old Jade, with Old Jade surviving the merger as the surviving corporation (the "First Merger"), and as part of the same overall transaction, Old Jade merged with and into Merger Sub II, with Merger Sub II continuing as a wholly owned subsidiary of the Issuer and the surviving corporation of the merger (the "Second Merger"). At the effective time of the First Merger, each share of Old Jade common stock was converted based on an exchange ratio (after giving effect to the Reverse Stock Split, as defined below) of 0.6311 shares of the Issuer's common stock for each share of Old Jade common stock.

On April 28, 2025, the Issuer effected a 1-for-35 reverse stock split of its common stock stock (the "Reverse Stock Split"). The share counts herein reflect the reverse stock split.

Held directly by RA Capital Healthcare Fund, L.P. (the "Fund").

RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund") and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, the Nexus Fund, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

A total of 72,325 shares subject to an employee stock option were granted on September 4, 2020, with 25% of the shares vested on August 1, 2021, and the remainder vesting in 36 substantially equal monthly installments thereafter.

A total of 72,325 shares subject to an employee stock option were granted on September 4, 2020, with 25% of the shares vested on August 1, 2021, and the remainder vesting in 36 substantially equal monthly installments thereafter.

A total of 48,293 shares subject to an employee stock option were granted on September 4, 2020, with 10% of the shares vested on January 1, 2020, an additional 22.5% of the shares vested on January 1, 2021, and the remainder vesting in 36 substantially equal monthly installments thereafter.

The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $1.51 to $1.75 inclusive. The Reporting Persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth in this footnote.

Held directly by RA Capital Healthcare Fund, L.P. (the "Fund").

RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund") and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, the Nexus Fund, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

This transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on November 17, 2023.

This transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on November 17, 2023.

25% of this option vested and became exercisable on March 21, 2023, with the remainder vesting in 36 substantially equal monthly installments thereafter.

This transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on March 17, 2023.

This transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on November 17, 2023.

This transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on March 17, 2023.

Includes 3,062 shares purchased under the Issuer's 2021 Employee Stock Purchase Plan on April 30, 2024 in a transaction that is exempt under Rule 16b-3(c) and 16b3(d).

This transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on March 17, 2023.

A total of 98,676 shares subject to an employee stock option were granted on April 2, 2021, with 25% of this option vested on June 4, 2022, and the remainder vesting in 36 substantially equal monthly installments thereafter.

This transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on January 19, 2023.

A total of 109,640 shares subject to an employee stock option were granted on April 2, 2021, with the first installment vested on July 4, 2021, with shares vesting in 48 substantially equal monthly installments.

This transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on January 19, 2023.

This transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on January 19, 2023.

The shares subject to this option will vest and become exercisable in full on the earlier of (i) June 5, 2025 or (ii) the next annual meeting of the Issuer's stockholders, subject to Mr. Resnick's continued service through the applicable vesting date.

RA Capital Management, L.P. (the "Adviser") is the investment manager for RA Capital Healthcare Fund, L.P. (the "Fund"), RA Capital Nexus Fund, L.P. (the "Nexus Fund"), and a separately managed account (the "Account"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, the Fund, the Nexus Fund, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

Joshua Resnick is a Senior Managing Director of the Adviser who serves on the Issuer's board of directors. Under Mr. Resnick's arrangement with the Adviser, Mr. Resnick holds the option for the benefit of the Fund. Mr. Resnick is obligated to turn over to the Adviser any net cash or stock received upon exercise of the option, which will offset advisory fees owed by the Fund to the Adviser. The Reporting Persons therefore disclaim beneficial ownership of the option and underlying common stock.

The shares subject to this option will vest and become exercisable in full on the earlier of (i) June 5, 2025 or (ii) the next annual meeting of the Issuer's stockholders, subject to the Reporting Person's continued service through the applicable vesting date.

This option was granted to the Reporting Person, a director of the Issuer. The proceeds of any sale of shares of common stock issued to the Reporting Person upon exercise of this option will be transferred to Atlas Venture Life Science Advisors, LLC and as such, the Reporting Person disclaims ownership of such securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, except to the extent of his pecuniary interest therein, if any.

The shares subject to this option will vest and become exercisable in full on the earlier of (i) June 5, 2025 or (ii) the next annual meeting of the Issuer's stockholders, subject to the Reporting Person's continued service through the applicable vesting date.

The shares subject to this option will vest and become exercisable in full on the earlier of (i) June 5, 2025 or (ii) the next annual meeting of the Issuer's stockholders, subject to the Reporting Person's continued service through the applicable vesting date.

The shares subject to this option will vest and become exercisable in full on the earlier of (i) June 5, 2025 or (ii) the next annual meeting of the Issuer's stockholders, subject to the Reporting Person's continued service through the applicable vesting date.

The shares subject to this option will vest and become exercisable in full on the earlier of (i) June 5, 2025 or (ii) the next annual meeting of the Issuer's stockholders, subject to the Reporting Person's continued service through the applicable vesting date.

The shares subject to this option will vest and become exercisable in full on the earlier of (i) June 5, 2025 or (ii) the next annual meeting of the Issuer's stockholders, subject to the Reporting Person's continued service through the applicable vesting date.

The shares subject to this option will vest and become exercisable in full on the earlier of (i) June 5, 2025 or (ii) the next annual meeting of the Issuer's stockholders, subject to the Reporting Person's continued service through the applicable vesting date.