Abstract 2380: Preclinical safety and efficacy of a tumor-directed T cell activating 4-1BB x 5T4 ADAPTIR™ bispecific antibody
Authors: Dahlman Anna , Nelson Michelle , Bannink Jeannette , Johnson Starrla , Werchau Doreen , Nilsson Anneli , Ljung Lill , Blahnik-Fagan Gabriele , Bader Robert , Deronic Adnan , Ellmark Peter , Askmyr Maria , Hernandez-Hoyos Gabriela , McMahan Cathy , Fritzell Sara 
Published: August 2019

Abstract
The ability to induce potent anti-tumor activity by stimulating 4-1BB (CD137), a key co-stimulatory receptor, makes 4-1BB an attractive immunotherapeutic target. However, a clinically tested, 4-1BB targeting monospecific antibody has been hampered by dose-limiting hepatic toxicities. To improve safety of 4-1BB targeting therapies we have developed a 4-1BB x 5T4 bispecific antibody designed to direct tumor-specific T cell responses to the tumor by stimulating 4-1BB only when co-engaged with 5T4, a tumor-associated antigen. The preclinical dataset presented here provides an overview of the mechanism of action and the efficacy and safety profile of ALG.APV-527, supporting its advancement into the clinic. ALG.APV-527 was built using the ADAPTIR™ platform with binding domains from the ALLIGATOR-GOLD® human scFv library. Its 5T4-dependent agonistic function was assessed using primary CD8+ T cells or NK cells in the presence of 5T4-expressing cells. Secretion of IFN-γ or granzyme B was measured at 72 hrs using ELISA. To measure proliferation, PBMCs were labelled with Cell Trace™ and gated CD8+ T cells were analyzed using flow cytometry. For tumor inhibition studies, the human 5T4-expressing colon carcinoma HCT116 xenograft model was used. 5T4 expression was evaluated in normal human tissues and different human tumors by immunohistochemistry. The preclinical safety profile of ALG.APV-527 was evaluated in a single and repeated dose, dose-range finding toxicology study in non-human primates (NHP). The study design included all the standard repeated dose toxicity parameters and in addition, pharmacokinetics, immunogenicity, and pharmacodynamic end-points. ALG.APV-527 induces a 5T4-dependent increase in IFN-γ and granzyme B production and enhances proliferation of T cells and NK cells. Furthermore, ALG.APV-527 inhibits tumor growth in a human 5T4-expressing colon carcinoma xenograft model. 5T4 is overexpressed in multiple solid tumors, potentially directing the activity of 4-1BB induced by ALG.APV-527 to 5T4-expressing tumors, improving the risk/benefit profile. Four doses (administered once weekly) did not cause any adverse events in the NHP toxicity study. In conclusion, ALG.APV-527 induces potent CD8+ T cell and NK co-stimulation but only in the presence of 5T4. Based on its efficacy and preclinical safety profile, ALG.APV-527 is a promising anti-cancer therapeutic for the treatment of multiple 5T4-expressing solid tumors.
Citation Format: Anna Dahlman, Michelle Nelson, Jeannette Bannink, Starrla Johnson, Doreen Werchau, Anneli Nilsson, Lill Ljung, Gabriele Blahnik-Fagan, Robert Bader, Adnan Deronic, Peter Ellmark, Maria Askmyr, Gabriela Hernandez-Hoyos, Cathy McMahan, Sara Fritzell. Preclinical safety and efficacy of a tumor-directed T cell activating 4-1BB x 5T4 ADAPTIR™ bispecific antibody [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2380.