Abstract A11: Preclinical assessment of CD3 bispecific antibody efficacy: A comparison of humanized mouse models bearing xenografts and syngeneic mouse models using surrogate antibodies
Authors: Mattson Bethany , Menard Krista , Hamon Damon , Pizutti Darlene , Chen Emily , Romero Margarita , Chevalier Kristen , Wiehagen Karla , Richter Mark , Chu Gerald , Hertzog Brenda , Hughes Anna , Alvarez John , Verona Raluca , Kane Colleen , Moores Sheri , Laquerre Sylvie , Erhardt Joseph , Packman Kathryn 
Published: May 2018

Abstract
CD3 bispecific antibodies target both CD3 on T cells, and a tumor-specific antigen on cancer cells to harness the ability of cytotoxic T cells to 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 mouse models in immune-compromised NSG mice as well as the use of surrogate antibodies in syngeneic models 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 cells that were expanded and activated in vitro. Engraftment of human T cells was evaluated in PBMC and T-cell humanized NSG mice in peripheral blood. In the absence of treatment, PBMC humanized mice had a greater reconstitution of T cells in the peripheral blood (~10-40%) compared to T-cell humanized mice (~3-10%). An antibody-specific expansion of T cells was observed in the T-cell humanized model in response to CD3 bispecific treatment. The slower engraftment of effector T cells in the T-cell humanized model correlated with slower onset to GVHD (graft versus host disease), allowing for extended evaluation of antitumor responses. Bispecific CD3 redirection antibodies elicited antitumor efficacy and T-cell infiltration in various human xenografts in both T-cell and PBMC-humanized mouse models.
Additionally, mouse surrogate bispecific antibodies were generated that bind CD3 on mouse T cells. CT26 murine mouse colon carcinoma syngeneic tumors 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-cell infiltration into tumors was performed as well as T-cell cytokine analysis. These data showed that the level of T-cell infiltration and cytokine production correlated well with in vivo efficacy, demonstrating a T cell-mediated elimination of antigen-presenting tumor cells.
In summary, both humanized mouse models and syngeneic mouse models using surrogate antibodies were successfully employed to study antitumor effects of CD3 bispecific 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 CD3 bispecific antibody efficacy: A comparison of humanized mouse models bearing xenografts and syngeneic mouse 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.