As filed with the Securities and Exchange Commission on June 26, 2024. Registration No. 333-280226 UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 AMENDMENT NO.1 TO FORM S-1 Delaware 2834 81-1567056 (I.R.S. Employer Identification Number) 2401 4th Avenue, Suite 1050 Seattle, Washington, 98121 (206) 838-0500 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 APTEVO THERAPEUTICS INC. (Exact Name of Registrant as Specified in Its Charter) (State or Other Jurisdiction of Incorporati ...