Abstract 1629: An innovative approach to improve bispecific T-cell engagers for solid tumor therapy

Abstract T cell engagers (TCEs), mainly in the format of Bispecific T-cell Engagers (BiTE), are promising anti-cancer immunotherapies for hematological malignancies. However, solid tumors create immunosuppressive microenvironments and physical structures that hinder the effectiveness of T- cell engagers and preclude tumor infiltration by CD8+ T cells. Our hypothesis for overcoming these barriers is to add components to the BiTE format that alleviate immunosuppression and promote activation and tumor infiltration of CD8+ T cells. To test this hypothesis, we used our novel TRBC platform to construct HCW11-018b, a tetravalent heterodimeric TCE. The BiTE portion of HCW11-018b contains an antibody that targets human tissue factor (TF), which is overexpressed in a wide spectrum of solid tumors; an anti-CD3 single-chain antibody; and an IL-15Rα domain. The other chain of HCW11-018b comprises a dimeric soluble TGFβRII domain (i.e., TGFβ trap), TRβC1 and a soluble IL-15. The plasmids carrying the coding regions of the two fusion proteins were co-transfected into CHO cells and the fully functional TCE was purified from culture supernatant. In vitro, we found HCW11-018b induced robust, antigen-specific tumor cell killing, which was sustained up to five rounds. Increased phosphorylation of STAT5, expression of activation markers (CD69, CD25), chemokine receptor (CCR5), and anti-apoptosis marker (BCL2) were observed on T cells by HCW11-018b treatments. RNAseq analysis revealed that increased expression of BCL2 and other genes associated with T-cell effector function were specifically attributable to the IL-15 component of HCW11-018b. In SCID mice subcutaneously (s.c.) implanted human AsPC-1 pancreatic cancer cells with human PBMCs, we demonstrated that s.c. administered HCW11-018b could infiltrate into implants and activate bystander CD8+ T cells for potent anti-tumor activities. In AsPC-1 tumors (NSG mice models) and adoptively transferred human T cells, HCW11-018b stimulated expression of CCR5 and promoted tumor infiltration of human T cells, upregulated T cell expression of CD25, NKG2D, DNAM1, Granzyme B, and IFNγ, and enhanced their cytotoxicity against cancer cells. Treatment also reduced tumor cell metastasis from the primary site. We further demonstrated that the upregulation of NKG2D and DNAM1 on HCW11-018b-activated CD8+ T cells played a role in the cytotoxicity against AsPC-1 tumor cells. In a PDX model, we further demonstrated the potency of HCW11-018b which directed hPBMCs against TF+ patient-derived pancreatic cancer tissues. HCW11-018b was well tolerated in mice and non-human primates with s.c. administration. HCW11-018b is currently in IND-enabling studies for clinical development against solid tumors. In summary, we demonstrate that the addition of TGFβ-trap and IL-15 components onto BiTE using our novel TRBC platform can overcome the deficiencies of BiTE for solid tumor therapy. Citation Format: Hing C. Wong, Xiaoyun Zhu, Varghese George, Hamidreza Farzaneh, Crystal Gilkes, Natalia Valderrama, Alyssa Thompson, Lijing You, Lucas Gomez, Christian Echeverri, Niraj Shrestha, Peter R. Rhode, Jack Egan, . An innovative approach to improve bispecific T-cell engagers for solid tumor therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1629.