Abstract 1662: Development and validation of humanized mice models implanted with patient derived colorectal cancer xenografts
Authors: Anna Capasso, Julie Lang, Todd M. Pitts, Sarah Lindsey Davis, Christopher Lieu, Scott Kopetz, Stacey Bagby, Paul Francoeur, John J. Tentler, Jill Slansky, Roberta Pelanda, Gail Eckhardt
Journal: Cancer Research (2017)

Abstract Introduction: Agents that reverse T cell inhibitory signals have reinvigorated the strategy of cancer immunotherapy and are leading to robust clinical responses. In colorectal cancer (CRC), objective responses to single-agent therapy with anti-PD-1/PD-L1 antibodies have largely been restricted to the small proportion of CRC patients with microsatellite unstable (MSI-high) disease. Although there are additional subsets of advanced CRC patients that are responsive to immune checkpoint inhibition in combination with tumor-targeted agents, preclinical models have been hampered by their immune-compromised status. In order to gain a better biological understanding of the context of immune responses and facilitate preclinical evaluation of combination strategies incorporating cancer immunotherapy, we developed a “hematopoietic” humanized mouse model utilizing patient-derived CRC xenografts with the intent of leveraging this model for the development of rational combinations. Methods: BRG.NODSirpalfa newborn pups were humanized through transplantation of 1x105 CD34+ cells purified from umbilical cord blood. Mice were evaluated for chimerism at 8 and 12 weeks. At 16 weeks, tumor tissue from established PDX models was implanted on the right and left flanks of humanized mice. When the average tumor size reached a volume of ~150-300 mm3, the mice were randomized into vehicle or nivolumab (30 mg/kg twice weekly i.p.) treatment groups according to %chimerism. Mice were monitored for signs of toxicity and tumor size was evaluated twice weekly by caliper measurements (tumor volume= (length × width2) × 0.52). At the end of the treatment, mice were euthanized while sera, lymph nodes, spleen, bone marrow and tumors were collected for immunological assessment. Results: As preliminary proof-of-concept, we successfully established 3 humanized CRC PDX models and one breast cancer cell line (MDA-MB-231). In one of the CRC (MSI-high) and in the breast model we observed tumor growth inhibition in the treated groups vs control. We detected differences in PD-1 expression among treated versus control mice, with lower expression in the nivolumab-treated groups. We also observed an increased number of TILs, CD8+ T cells and greater numbers of T cells in the lymph nodes of treated mice, suggesting T cell expansion. Mice were highly chimeric with high TILs whereas responder tumors exhibited an increase of CD44 high IFN+ T cells, high CD8% and a higher effector memory% (HLADR+, CD45RO+). Conclusions: Humanized PDX models were successfully established and tumor engraftment occurred in all humanized mice with nivolumab-treated mice demonstrating the development of lymph nodes that were populated by activated T cells. These preliminary results demonstrate that human immunity and PD-1 expressing T cells exist in these models and provide the basis for planned immunotherapy combination studies. Citation Format: Anna Capasso, Julie Lang, Todd M. Pitts, Sarah Lindsey Davis, Christopher Lieu, Scott Kopetz, Stacey Bagby, Paul Francoeur, John J. Tentler, Jill Slansky, Roberta Pelanda, Gail Eckhardt. Development and validation of humanized mice models implanted with patient derived colorectal cancer xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1662. doi:10.1158/1538-7445.AM2017-1662