Abstract 1655: Human immune cell infiltration of tumors in a PBMC-humanized NSG mouse xenograft model changes with treatment of an anti-tissue factor antibody

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Immunocompromised mice engrafted with human hematopoietic stem cells (HSC) or peripheral blood mononuclear cells (PBMC) can be promising models of human immune system compartments, useful for studying diseases such as diabetes, lupus, GVHD, and cancer. We have utilized the PBMC-humanized mouse as a platform for xenograft models. To investigate the effect of human antibody (Ab) treatment on immune cells and xenografts using this platform, we examined the infiltrate of human immune cells in A431 xenografts with treatment of an effector function-enhanced anti-tissue factor VIIA (TFVIIA) Ab. Female NSG mice were intravenously engrafted with human PBMC, and subcutaneously implanted two weeks later with A431 human SCC cells. One week post tumor cell implant and thereafter twice weekly, mice received treatment with anti-TFVIIA Ab. Peripheral blood, bone marrow and spleen were analyzed by FACS and terminal tumor samples were analyzed by FACS and immunohistochemistry (IHC). FACS analysis of blood from Ab treated and untreated tumor-bearing mice collected from baseline to termination, showed an overall increase in the frequency of human CD45+, CD3+, CD8+, and CD4+ cells, while the frequency of CD56+ cells remained stable. In comparison, non-tumor bearing mice had increased CD56+ cells and decreased CD3+ cells. FACS analysis of tumors showed a robust increase in the frequency of CD56+ cells and a decrease in the frequency of CD3+ cells with treatment of anti-TF Ab. With treatment, the frequency of CD8+ cells was markedly lower and the frequency of CD4+ cells unchanged. Histological analysis was performed on A431 FFPE xenografts from both the treated and non-treated groups. Hematoxylin and eosin (H&E) staining of the xenografts confirmed the presence of inflammatory cells in the tumors and also showed greater PBMC infiltration of the tumors in the presence of the anti-TFVIIA Ab. Xenografts treated with anti-TFVIIA Ab exhibited greater infiltration of human CD3+, CD8+, and CD57+ cells. There was an increase in cleaved caspase-3 (CC3)+ cells in Ab-treated xenografts, indicating an increase in apoptosis with anti-TFVIIA Ab treatment. In conclusion, anti-TFVIIA Ab treatment causes changes in immune cell populations in xenografts. While the mechanism is unknown, one possibility is that NK migration into the tumor coupled with increased apoptosis with treatment indicates ADCC activity by the NK cells. This would signify some preservation of immune cell function in the PBMC engraftment model, and would enhance studying the effects of experimental antibodies in a more humanized setting. Citation Format: Hillary Millar-Quinn, Brenda Hertzog, Rebecca Hanson, Jeffrey Nemeth, John Alvarez. Human immune cell infiltration of tumors in a PBMC-humanized NSG mouse xenograft model changes with treatment of an anti-tissue factor antibody. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1655. doi:10.1158/1538-7445.AM2014-1655