As filed with the Securities and Exchange Commission on January 28, 2026 Registration No. 333- UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM S-1 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 Incorporation or Organization) (Primary Standard Industrial Classification Code Number) Delaware 2834 81-1567056 (I.R.S. Employer Identification Number) 2401 4th Avenue ...

Core Insights - Aptevo Therapeutics has entered into a $60 million equity line of credit (ELOC) agreement with Yorkville Advisors Global, LP, enhancing its financial flexibility and extending its funding runway into 2029 [1][2][3] Financial Flexibility - The ELOC allows Aptevo to raise funds incrementally at its discretion under market-based conditions, providing affordable capital financing with minimal fees and no warrants [2][3] - The combination of the ELOC and cash on hand is projected to fund the company for three years, allowing for the achievement of key clinical and preclinical milestones [1][3] Clinical Development - Aptevo's portfolio includes five CD3-engaging assets, with mipletamig being a first-in-class CD123 x CD3 bispecific currently evaluated in a Phase 1b/2 trial for frontline acute myeloid leukemia (AML) [5][7] - Mipletamig has shown high remission rates and a favorable safety profile in over 100 patients across three trials, with no observed cytokine release syndrome events [5][6] Pipeline and Innovation - The company is advancing a portfolio of tumor-directed CD3 programs, including bispecific candidates for prostate cancer and solid tumors, utilizing proprietary CRIS-7-derived CD3 binding domains [6][7] - Aptevo has two clinical candidates and six preclinical candidates targeting various solid tumors, all developed from its ADAPTIR and ADAPTIR-FLEX platforms [7]

Core Insights - Aptevo Therapeutics has presented preclinical data for its trispecific antibody candidate, APVO451, at the Society for Immunotherapy of Cancer Annual Meeting, highlighting its potential in treating hard-to-treat solid tumors [1][2]. Company Update - APVO451 is designed to address the challenge of immune suppression in solid tumors, such as urothelial, breast, and pancreatic cancers, by utilizing a proprietary CRIS-7-derived CD3 binding domain [2][3]. - The molecule aims to activate the intratumoral immune system, enhancing the ability to target and kill tumor cells effectively [3]. Key Findings from the Presentation - APVO451 demonstrated local activation of T-cells and antigen-presenting cells (APCs) only when bound to the target protein, nectin-4, indicating a favorable safety profile [4]. - The candidate showed dual immune re-activation by stimulating T-cell effector functions and restoring APC function, addressing a common failure point in solid tumor treatments [4]. - In tumor models simulating suppression, APVO451 was more effective in eliminating nectin-4-positive tumor cells compared to standard CD3 T-cell engagers, suggesting its potential to overcome suppressive tumor environments [4]. Next Steps - Aptevo is advancing APVO451 through ongoing preclinical studies to support IND-enabling work and future clinical development targeting nectin-4-expressing solid tumors [5]. About APVO451 - APVO451 is a trispecific ADAPTIR-FLEX therapeutic candidate designed to engage CD3 and CD40, aiming to restore immune engagement in suppressive solid tumors while minimizing off-tumor activation [6]. About Aptevo Therapeutics - Aptevo Therapeutics is a clinical-stage biotechnology company focused on developing novel bispecific and trispecific immunotherapies for cancer treatment, with two clinical candidates currently in trials [7].

Core Insights - Aptevo Therapeutics reported that 89% of evaluable frontline AML patients achieved remission in combination therapy across two trials, with a notable 100% remission rate in Cohort 3 of the ongoing RAINIER trial [1][1][1] - The company introduced its first trispecific molecules, APVO451 and APVO452, aimed at overcoming immune suppression in certain solid tumors, utilizing a unique CRIS-7-derived CD3 binding domain [1][1][1] - Aptevo's CD3 T-cell engager portfolio has been expanded to five molecules, indicating growth in its therapeutic offerings [1][1][1] - The company raised $18.7 million in the third quarter and an additional $4.1 million since the quarter ended, extending its cash runway into the fourth quarter of 2026 [1][1][1] Financial Performance - The financial results for the quarter ended September 30, 2025, were reported alongside a business update, highlighting the company's ongoing development in immune-oncology therapeutics [1][1][1]

As filed with the Securities and Exchange Commission on October 1, 2025 Registration No. 333- UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM S-1 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 APTEVO THERAPEUTICS INC. (Exact Name of Registrant as Specified in Its Charter) Delaware 2834 81-1567056 (State or Other Jurisdiction of Incorporation or Organization) (Primary Standard Industrial Classification Code Number) (I.R.S. Employer Identification Number) 2401 4th Avenue, ...