Humanized Rag2 Mice As Patient-Derived Orthotopic Mouse Models For Immune Checkpoint Blockade And Conventional Chemotherapeutic Drug Treatment For Human Solid Tumors

Abstract To evaluate therapeutic efficacy of immune checkpoint blockade (ICB) and conventional chemotherapy in pre-clinical models, we developed humanized patient-derived orthotopic xenograft (PDOX) models for colorectal cancer (CRC) and renal cell carcinoma (RCC). Rag2 mice were humanized by donor peripheral blood mononuclear cells (PBMC) transfer. Luciferase-tagged CRC and RCC tumor cells were injected intra-rectally and intra renal subcapsular, respectively. Groups of mice (n=5–10) received ICB, anti-PD-1 and anti-PD-L1 antibodies (Nivolumab and Atezolizumab, 200 μg each/mouse) for 4 weeks, and conventional therapy of 5FU (200 mg/kg, for CRC) alone or in combination. Tumor growth was measured by weekly bioluminescent image (BLI) and tumor weight at necropsy. The presence of human immune cells and tumor infiltrating lymphocytes were confirmed by flow cytometry and immunohistochemistry staining. Humanization was evidenced by >45% HLA-ABC+CD45+ circulating human cells in both CRC and RCC models. CRC tumor weight showed significant reduction in group treated with combination of ICB and 5FU compared with untreated controls or 5FU monotherapy group (p<0.05) using patient tumor cell CoCa302. The lung/liver metastasis detected by ex vivo BLI were reduced from 50% of mice in control group to 33% and 11%, respectively. For RCC, tumor size was reduced by >30% from controls in ICB treated group using patient tumor cell KiCa118 and cell line SN12K1. The later had 20% reduction of liver metastasis. The combination of ICB and conventional chemotherapies for CRC and RCC can be tested in our humanized PDOX mouse models. The effect of the combination therapy using MHC matched donors or patient autologous PBMC will be further investigated.