55 Influence of gender on immunosurveillance in a novel mouse model of clear cell renal cell carcinoma

Abstract Background Renal Cell Carcinoma (RCC) is a cancer that exhibits sex dimorphism. Males have twice the incidence rate of their female counterparts and more than twice the mortality rate. They frequently present with larger, higher-grade tumors, greater metastatic spread, and earlier diagnosis of disease. Many hormonal, genetic, and environmental reasons have been explored, however a considerable amount of uncertainty remains. Methods Here, we explored the immunologic differences using a novel syngeneic mouse model of ccRCC. Tumors were orthotopically implanted by sub-renal capsular injection in immunocompetent WT C57Bl/6 and immunodeficient mice NOD/Scid/Gamma (NSG) mice, and tumor growth was longitudinally monitored using ultrasound imaging. At necropsy, liver and lung metastases were quantified and immune populations in the tumor and peripheral blood were analyzed by flow cytometry. Results In the immune-competent model, female mice had lower tumor penetrance as well as delayed tumor growth compared to male mice. In contrast, in the immune-deficient model female mice had similar tumor penetrance and growth rates as males suggesting that the female immune system may be protective against tumor development. No metastases were seen in either sex in the immune-competent model, whereas both lung and liver masses were found in the immune-deficient model suggesting the immune system is critical for restricting metastatic development. Interestingly, increased lung metastases were observed in females compared with male counterparts in NSG mice, suggesting that perhaps hormonal or other non-adaptive immunity-mediated mechanisms can promote metastatic seeding into the lungs. Flow cytometry characterization revealed higher peripheral B- and T-cells in females, with a higher CD8/CD4 T-cell ratio. Tumors from females had more activated and cytotoxic CD8 T cells and were more frequently metastatic to the lung compared to male mice. Conclusions Our findings suggest sex-related immunologic differences in immunosurveillance and metastatic tropism that warrants further interrogation. DOD CDMRP Funding: yes