Approximately 80% of patients with advanced
bladder cancer do not respond to
immune checkpoint inhibitor (ICI)
immunotherapy. Therefore, there is an urgent unmet need to develop clinically relevant preclinical models so that factors governing
immunotherapy responses can be studied in immunocompetent mice. We developed a line of mouse triple knockout (TKO: Trp53, Pten, Rb1) urothelial
carcinoma organoids transplanted into immunocompetent mice. These
bladder tumors recapitulate the molecular phenotypes and heterogeneous
immunotherapy responses observed in human
bladder cancers. The TKO organoids were characterized in vivo and in vitro and compared to the widely used MB49 murine
bladder cancer model. RNAseq analysis of the TKO
tumors demonstrated a basal subtype. The TKO xenografts demonstrated the expression of urothelial markers (CK5, CK7, GATA3, and p63), whereas MB49 subcutaneous xenografts did not express urothelial markers. Anti-PD-1
immunotherapy resulted in a mixed pattern of treatment responses for individual
tumors. Eight immune cell types were identified (basophils, B cells, dendritic cells, macrophages, monocytes, neutrophils, NK cells, and T cells) in ICI-treated xenografts. Responder xenografts displayed significantly increased immune cell infiltration (15.3%, 742 immune cells/4861 total cells) compared to the non-responder
tumors (10.1%, 452 immune cells/4459 total cells, Fisher Exact Test p < 0.0001). Specifically, there were more T cells (1.0% vs. 0.4%, p = 0.002) and macrophages (8.6% vs. 6.4%, p = 0.0002) in responder xenografts than in non-responder xenografts. In conclusion, we have developed a novel preclinical model that exhibits a mixed pattern of response to anti-PD-1
immunotherapy. The higher percentage of macrophage
tumor infiltration in responders suggests a potential role for the innate immune microenvironment in regulating ICI treatment responses.