Sunitinib's effect on tumor infiltration of CD8 T cells in renal cell carcinoma (RCC) and modulation of their function by altering VEGF-induced upregulation of PD1 expression.
591 Background: The effect of VEGF inhibitors such as sunitinib to modulate RCC tumor microenvironment and the effect on immunotherapy using checkpoint inhibitors is unknown and of clinical interest. Methods: Immune infiltrate in tissue sections from clear cell renal cell carcinomas (ccRCC) (n = 13) treated with sunitinib in the neoadjuvant setting were compared to that of untreated RCC patients with localized disease (n = 15). Immune infiltrate was scored in H&E stained tissue sections. Infiltrates were further characterized by IHC using antibodies against CD4 (Novocastra NCL-CD4-1F6 clone 1F6), CD8 (BiogeneX MU422-UC clone 1A5) or PD1 (Abcam ab52587 clone EPR4877). Intensity of staining was quantified using a Leica microscope equipped with a Retiga SRV camera. Scanned images of multiple tumor fields were analyzed using ImagePro Plus software. For pre-clinical studies, Balb/c mice bearing Renca tumors (RCC) were treated with sunitinib (40mg/kg) daily for 14 days, and tumors were dissociated and analyzed for CD8 and CD4 infiltrate by FACS analysis. Results: Qualitative analysis showed a more prominent accumulation of lymphocytes in tumor sections of patients receiving sunitinib. Quantitative analysis of these infiltrates revealed higher levels of CD8+ T cells in sunitinib treated patients (p = 0.04). By contrast, sunitinib treatment was associated with a reduction of intratumoral expression of PD1. Preclinical studies in the Renca model also showed an increase in the frequency of tumor infiltrating CD8+ T cells following sunitinib treatment. Remarkably, a higher fraction of these tumor infiltrating CD8 T cells were found to co-express the activation marker of cytotoxic effector cells (CD107a) when compared to untreated mice. Conclusions: These findings suggest that sunitinib not only promotes the accumulation of CD8+ T cells within the tumors, but also affects their activity by modulating PD1 expression and enhancing cytotoxic function.