SCHEDULE 13D 0001232621 XXXXXXXX LIVE Common Stock, par value $0.0001 per share 05/02/2025 false 0001888012 43157M102 HilleVax, Inc.

321 Harrison Avenue Suite 500 Boston MA 02118

Kevin Tang 858-200-3830 4747 Executive Drive Suite 210 San Diego CA 92121 0001232621 N TANG CAPITAL MANAGEMENT, LLC WC N DE 0.00 4920000.00 0.00 4920000.00 4920000.00 N 9.8 OO Tang Capital Management, LLC ("TCM") shares voting and dispositive power over such shares with Tang Capital Partners, LP ("TCP"), Tang Capital Partners International, LP ("TCPI") and Kevin Tang. The percentages used herein are based on 50,141,064 shares of Common Stock outstanding as of March 10, 2025, as set forth in the Issuer's Annual Report filed on Form 10-K that was filed with the Securities and Exchange Commission on March 28, 2025. 0001178579 N KEVIN TANG WC N X1 0.00 4920000.00 0.00 4920000.00 4920000.00 N 9.8 IN Kevin Tang shares voting and dispositive power over such shares with TCP, TCPI and TCM. 0001191935 N TANG CAPITAL PARTNERS, LP WC N DE 0.00 2767008.00 0.00 2767008.00 2767008.00 N 5.5 PN TCP shares voting and dispositive power over such shares with TCM and Kevin Tang. 0002064011 N TANG CAPITAL PARTNERS INTERNATIONAL, LP WC N DE 0.00 2152992.00 0.00 2152992.00 2152992.00 N 4.3 PN TCPI shares voting and dispositive power over such shares with TCM and Kevin Tang. Y TANG CAPITAL PARTNERS III, INC WC N NV 0.00 0.00 0.00 0.00 0.00 N 0 CO Y TANG CAPITAL PARTNERS IV, INC WC N NV 0.00 0.00 0.00 0.00 0.00 N 0 CO 0001970065 N CONCENTRA BIOSCIENCES, LLC WC N DE 0.00 0.00 0.00 0.00 0.00 N 0 OO Common Stock, par value $0.0001 per share HilleVax, Inc. 321 Harrison Avenue Suite 500 Boston MA 02118 This Statement is filed by TCM, a Delaware limited liability company that is the general partner of TCP and TCPI; Kevin Tang, a United States citizen; TCP, a Delaware limited partnership engaged in capital management; TCPI, a Delaware limited partnership engaged in capital management; Tang Capital Partners III, Inc., a Nevada corporation that is indirectly wholly owned by TCP ("TCP III"); Tang Capital Partners IV, Inc., a Nevada corporation that is indirectly wholly owned by TCP ("TCP IV"); and Concentra Biosciences, LLC, a Delaware limited liability company controlled by TCP ("Concentra" and, collectively with TCM, Kevin Tang, TCP, TCPI, TCP III and TCP IV, the "Reporting Persons"). The address of TCM, Kevin Tang, TCP, TCPI and Concentra is 4747 Executive Drive, Suite 210, San Diego, CA 92121. The address of TCP III and TCP IV is 400 S. 4th Street, 3rd Floor, Las Vegas, NV 89101. Kevin Tang is the manager of TCM. Kevin Tang is the sole director and Chief Executive Officer of TCP III and TCP IV. Kevin Tang is the Chief Executive Officer of Concentra. During the past five years, none of the Reporting Persons have been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors). During the past five years, none of the Reporting Persons have been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws. See Item 2(a) above. The Common Stock was acquired with approximately $8.9 million of working capital set aside by TCP and TCPI for the general purpose of investing. TCP and TCPI maintain commingled margin accounts with various financial institutions, which may extend margin credit to TCP and TCPI as and when required, to open or carry positions in the margin accounts, subject to applicable federal margin regulations, stock exchange rules and credit policies. In such instances, the positions held in the margin accounts are pledged as collateral security for the repayment of debit balances in the accounts. The margin accounts may from time to time have debit balances. Since multiple different securities are held in the margin accounts, it is not possible to determine the amounts, if any, of margin used to purchase the Common Stock reported herein. The Reporting Persons are filing this Statement as an amendment to their Schedule 13G previously filed on July 22, 2024. The Reporting Persons purchased the Common Stock reported hereunder for investment purposes, and such purchases were made in the Reporting Persons' ordinary course of business. As with their other investments, the Reporting Persons continuously evaluate the Issuer, including, but not limited to, its businesses, operations and prospects. The Reporting Persons may engage in discussions with the Issuer and its representatives and/or other stockholders, seek to enter into a confidentiality agreement with the Issuer and/or discuss with the Issuer different strategic alternatives or changes to the Issuer's operations. There can be no certainty as to whether discussions with the Issuer will occur, the outcome of any such discussions or whether the Reporting Persons will take any actions relating to the Issuer. Subject to applicable law and regulation, the Reporting Persons may modify their ownership of the Common Stock, including acquiring additional Common Stock or disposing of some or all of the Common Stock beneficially owned by them. Such actions may be based on the Reporting Persons' assessment of the Issuer's operations and prospects, prevailing market conditions or other investment considerations. The information set forth in the cover pages of this Schedule 13D is hereby incorporated by reference into this Item 5. As of the date hereof the Reporting Persons beneficially own an aggregate of 4,920,000 shares of the Issuer's Common Stock, representing 9.8% of the outstanding shares. See item 5(a) above. There have been no transactions in the Issuer's Common Stock during the past 60 days by the Reporting Persons. No person other than a Reporting Person has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, Common Stock beneficially owned by the Reporting Persons. Not applicable To the best of the knowledge of the Reporting Persons, there are no contracts, arrangements, understandings or relationships (legal or otherwise) among the Reporting Persons or between the Reporting Persons and any person with respect to any securities of the Issuer, including but not limited to transfer or voting of any of the securities, finder's fees, joint ventures, loan or option arrangements, puts or calls, guarantees of profits, division of profits or loss, or the giving or withholding of proxies. Exhibit 1: Joint Filing Agreement by and among the Reporting Persons. TANG CAPITAL MANAGEMENT, LLC /s/ Kevin Tang 05/02/2025 KEVIN TANG /s/ Kevin Tang 05/02/2025 TANG CAPITAL PARTNERS, LP /s/ Kevin Tang 05/02/2025 TANG CAPITAL PARTNERS INTERNATIONAL, LP /s/ Kevin Tang 05/02/2025 TANG CAPITAL PARTNERS III, INC /s/ Kevin Tang 05/02/2025 TANG CAPITAL PARTNERS IV, INC /s/ Kevin Tang 05/02/2025 CONCENTRA BIOSCIENCES, LLC /s/ Kevin Tang 05/02/2025