X0306 4 2021-10-11 0 0001661460 Poseida Therapeutics, Inc. PSTX 0001765987 Ostertag Eric C/O POSEIDA THERAPEUTICS, INC. 9390 TOWNE CENTRE DRIVE, STE 200 SAN DIEGO CA 92121 1 1 1 0 Chief Executive Officer Common Stock 2021-10-11 4 M 0 18525 9.15 A 696422 D Common Stock 3669376 I See footnote Common Stock 3367506 I See footnote Common Stock 629194 I See footnote Common Stock 961445 I See footnote Common Stock 160696 I See footnote Employee Stock Option (Right to Buy) 9.15 2021-10-11 4 M 0 18525 0.00 D 2031-02-03 Common Stock 18525 740995 D Includes 2,482 shares acquired by the Reporting Person under the Issuer's 2020 Employee Stock Purchase Plan on September 20, 2021. The shares are held in the name of the Eric Ostertag Living Trust dated March 30, 2016, of which the reporting person is the sole trustee. The shares are held in the name of Titan, LLC, which is owned by the Ostertag Descendents' Trust, of which the reporting person's minor daughter is the sole beneficiary. The reporting person disclaims beneficial ownership of these securities, and this report shall not be deemed an admission that the reporting person is the beneficial owner of the securities for purposes of Section 16 or for any other purpose. The shares are held in the name of Twin Prime Investments, an entity wholly owned by the reporting person. The shares are held in the name of the Ostertag Family Trust dated March 30, 2016, of which the reporting person is a trustee. The shares are held in the name of Transposagen Biopharmaceuticals, Inc., of which Dr. Ostertag is a majority stockholder. 12.5% of the shares originally subject to the stock option vested and became exercisable on August 4, 2021, and the remaining shares vest in 42 equal monthly installments thereafter. /s/ Harry J. Leonhardt, Attorney-in-Fact 2021-10-13