X0306 4 2021-07-28 0 0001739410 Rallybio Corp RLYB 0001414815 MACKAY MARTIN C/O RALLYBIO CORPORATION 234 CHURCH STREET, SUITE 1020 NEW HAVEN CT 06510 1 1 0 0 Chief Executive Officer Common Stock 2021-07-28 4 J 0 272609 A 272609 D Common Stock 2021-07-28 4 J 0 436517 A 436517 I See Footnote Common Stock 2022-01-10 4 P 0 5504 10.10 A 278113 D Common Stock 2022-01-11 4 P 0 4496 10.65 A 282609 D Common Units 2021-07-28 4 J 0 2255001 D Common Stock 272609 0 D Common Units 2021-07-28 4 J 0 2564999 D Common Stock 380312 0 I See Footnote Series A-1 Preferred Units 2021-07-28 4 J 0 150000 D Common Stock 23557 0 I See Footnote Series A-2 Preferred Units 2021-07-28 4 J 0 100000 D Common Stock 15704 0 I See Footnote Series B Preferred Units 2021-07-28 4 J 0 107891 D Common Stock 16944 0 I See Footnote Option (Right to Buy) 13.00 2021-07-28 4 A 0 160000 0.00 A 2031-07-28 Common Stock 160000 160000 D The Common Units, Series A-1 Preferred Units, Series A-2 Preferred Units and Series B Preferred Units (collectively with the Series A-1 Preferred Units and Series A-2 Preferred Units, the "Preferred Units") reported herein were units of Rallybio Holdings, LLC. The shares of common stock of the Issuer were received on July 28, 2021 pursuant to the Plan of Liquidation and Dissolution, dated July 28, 2021, among Rallybio Holdings, LLC and its members (the "Plan of Liquidation"). Pursuant to the Plan of Liquidation, the holders of Common Units, on an aggregate basis, received approximately 7.38 shares of common stock of the Issuer for each Common Unit and approximately 6.37 shares of common stock of the Issuer for each Preferred Unit. Rallybio Holdings, LLC was subsequently dissolved. The Common Units and Preferred Units had no expiration date prior to the liquidation. Shares of common stock are held directly by a limited liability company, of which Martin Mackay is the managing member. As a result, Dr. Mackay may be deemed to share beneficial ownership of the shares held by the limited liability company. The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $9.66 to $10.65, inclusive. The reporting person undertakes to provide to Rallybio Corporation, any security holder of Rallybio Corporation, 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 ranges set forth in footnotes (3) and (4) to this Form 4. The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $10.01 to $11.00, inclusive. The option vests as to 25% of the underlying shares of Common Stock on July 28, 2022 and as to the remaining 75% of the underlying shares of Common Stock in 36 equal monthly installments thereafter. /s/ Michael Greco, Attorney-in-Fact 2022-01-12