Abstract 2583: Utilization of a novel double knock-in humanized mouse model to evaluate the efficacy of ipilimumab and pembrolizumab against EMT-6 mammary carcinoma tumors

The cancer immunotherapy field has seen an increasing demand for identifying and characterizing pre-clinical models to evaluate the efficacy of the checkpoint inhibitors such as, ipilimumab and pembrolizumab. PBMC- or CD34-humanized mouse models are invaluable tools to assess effector functions of human T-cells to immune check point inhibitors (ICI). However, these models offer limited understanding of the overall potential therapeutic activity as they lack a complete repertoire of human immune cells required to elicit a full immune response. Thus, the development of multigenic humanized knock-in models provide a unique approach to evaluate the efficacy of ICI specific for human cancer targets in a fully immunocompetent organism. Here we describe the response of the EMT-6 murine breast cancer tumor model to ipilimumab and pembrolizumab in a novel hPDCD1/hCTLA4-KI double knock-in humanized BALB/c mouse model. EMT-6 tumors were implanted subcutaneously in the flank of hPDCD1/hCTLA4-KI mice. Three days post-implant we initiated treatment with ipilimumab or pembrolizumab alone and in combination. We observed significant ipilimumab anti-tumor activity, whereas pembrolizumab did not show efficacy despite effective T-cell PD-1 blockade. Unexpectedly, sudden respiratory distress occurred in animals receiving the 4th dose of combination therapy and the treatment was discontinued. To assess the immune phenotypic profiles in response to ipilimumab and/or pembrolizumab therapies, we performed multi-parameter flow cytometry analysis of peripheral blood, spleens and tumors. Additionally, we performed histopathological evaluation of lung tissues to assess potential neutrophil infiltration-mediated anaphylaxis in the mice treated with the combination treatment. The preliminary results highlight the value of the hPDCD1/hCTLA4-KI double knock-in humanized Balb/c model as a tool to evaluate human-specific immune-checkpoint based modalities. These models represent some of the difficulties faced in treating refractory tumors as well as reproducing some of the adverse effects seen in the clinic. Citation Format: Murray Stackhouse, Mariah Kuta, Joseph Kolb, Sydney Scatigno, Amber Blackwell, Chassidy Hall, Christopher Dowdy, Payel Sil, Diana Gietl, Steve Festin, Paula L. Miliani De Marval. Utilization of a novel double knock-in humanized mouse model to evaluate the efficacy of ipilimumab and pembrolizumab against EMT-6 mammary carcinoma tumors [abstract]. In: Proceedings of the A