Abstract 612: Control of the Basal Molecular Subtype of Murine Bladder Cancer by Adaptive Immunity

Abstract

Abstract Introduction: Developing optimized bladder cancer mouse models that can be used in the evaluation of immune based therapeutics remains a high priority in ongoing research.Experimental Procedures: In previous work by our collaborators, murine cell lines were generated that recapitulate the basal (BBN964, BBN966, and BBN975) molecular subtype of human bladder cancer (Saito et al. Cancer Res. 2018;78(14):3954-3968). Here we compared their tumorigenicity and growth rates in immunocompetent C57BL/6 mice and in immunodeficient Rag1-KO mice lacking B and T cells. Changes in the tumor and stromal compartments were correlated with the differences in growth rates observed. Observations and New Data: Tumors derived from all three BBN basal cell lines grew robustly in Rag1-KO mice (10/10 BBN964 tumors, 19/19 BBN966 tumors and 19/19 BBN975 tumors >100 mm3 by 10 weeks post-injection). Conversely, very few tumors grew in immunocompetent (C57BL/6, e.g. B6) mice (0/9 BBN964 at 8 weeks, 0/17 BBN966 at 16 weeks, 4/15 BBN975 at 9 weeks). BBN966 tumors conditioned to grow in Rag1-KO mice were also highly tumorigenic when they were subsequently transferred into immunocompetent mice (Rag1-KO ◊ B6, 16/20 mice with tumors >100 mm3 at 4 weeks), and they displayed increased tumorigenicity when they were reintroduced into immunodeficient mice (Rag1-KO ◊ Rag1-KO, 20/20 mice with tumors >100 mm3 at 3 weeks). BBN966 tumors harvested from B6 mice and passaged in vitro for 5 weeks maintained tumorigenicity when reimplanted into immunocompetent mice, and BBN966 tumors grown in female B6 mice grew robustly when transferred into male B6 mice. Bulk RNA sequencing of tumors comparing the BBN966 Rag1-KO (1st passage) to BBN966 Rag1-KO (2nd passage) demonstrated decreased expression of genes associated with tumor infiltrating macrophages in the 2nd passage tumors. Conclusions: Our results demonstrate that basal BBN syngeneic bladder tumors display markedly different growth rates in wild-type and T- and B-cell-deficient mice. The results suggest that adaptive immunity controls basal bladder cancer tumorigenicity, which is consistent with the immune infiltrated landscape observed in basal human bladder cancers. Further results described in this poster will include deeper molecular characterizations of the immune microenvironments of these tumors. Citation Format: Burles Avner Johnson, Mingxiao Feng, Woonyoung Choi, Gabriela Colocho, Alyssa Arbuiso, Samuel Jin, Adam K. Aragaki, Charles Ruland, Stanley Rapiey, Noah M. Hahn, David J. McConkey. Control of the Basal Molecular Subtype of Murine Bladder Cancer by Adaptive Immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 612.