Abstract A11: Preclinical assessment of CD3 bispecific antibody efficacy: A comparison of humanized mouse models bearing xenografts and syngeneic mouse models using surrogate antibodies

CD3bispecific antibodies target both CD3on T cells, and a tumor-specific antigenon cancer cells to harness the ability of cytotoxic T cellsto eradicate solid tumors. Preclinical modeling of potential clinical leads in animal models can be challenging due to the need to have both a human immune system and a tumor model to study. Here we describe using various humanized mousemodels in immune-compromised NSG mice as well as the use of surrogate antibodies in syngeneicmodels in mice with a competent immune system. To reconstitute the human immune system, female NSG mice were inoculated either intravenously with PBMCs or intraperitoneally with T cellsthat were expanded and activated in vitro. Engraftment of human T cellswas evaluated in PBMC and T-cellhumanized NSG mice in peripheral blood. In the absence of treatment, PBMC humanized mice had a greater reconstitution of T cellsin the peripheral blood (~10-40%) compared to T-cellhumanized mice (~3-10%). An antibody-specific expansion of T cellswas observed in the T-cell humanized modelin response to CD3bispecific treatment. The slower engraftment of effector T cellsin the T-cell humanized modelcorrelated with slower onset to GVHD (graft versus host disease), allowing for extended evaluation of antitumor responses. Bispecific CD3redirection antibodies elicited antitumor efficacy and T-cellinfiltration in various human xenografts in both T-celland PBMC- humanized mousemodels. Additionally, mouse surrogate bispecific antibodies were generated that bind CD3on mouse T cells. CT26 murine mouse colon carcinoma syngeneictumors were transfected with a human cancer antigen for use in immune-competent Balb/c mice. Treatment with a surrogate bispecific molecule resulted in significant tumor growth inhibition (greater than 60%) and significant increase in life span. To confirm the mechanism of action, histologic analyses of T-cellinfiltration into tumors was performed as well as T-cellcytokine analysis. These data showed that the level of T-cellinfiltration and cytokine production correlated well with in vivo efficacy, demonstrating a T cell-mediated elimination of antigen-presenting tumor cells. In summary, both humanized mousemodels and syngeneicmouse models using surrogate antibodies were successfully employed to study antitumor effects of CD3bispecific antibodies. Citation Format: Bethany Mattson, Krista Menard, Damon Hamon, Darlene Pizutti, Emily Chen, Margarita Romero, Kristen Chevalier, Karla Wiehagen, Mark Richter, Gerald Chu, Brenda Hertzog, Anna Hughes, John Alvarez, Raluca Verona, Colleen Kane, Sheri Moores, Sylvie Laquerre, Joseph Erhardt, Kathryn Packman. Preclinical assessment of CD3bispecific antibody efficacy: A comparison of humanized mousemodels bearing xenografts and syngeneicmouse models using surrogate antibodies [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr A11.