Studies assessing tumor-infiltrating lymphocytes (TILs) in clear cell renal cell carcinoma (ccRCC) and clinical outcomes have mixed results. Given fundamental interaction of MHC class I with CD8+ T-cells, we hypothesized that expression of MHC class I associated protein, beta-2-microglobulin (B2M), may be an important immunologic marker in RCC. We sought to understand potential implications of CD8 + TILs and tumor B2M expression on overall survival and response to high-dose interleukin-2 (IL-2) therapy, in a cohort of patients with high-stage (clinical stage III and IV) ccRCC. Four tumor regions from 56 patients with ccRCC were retrospectively assessed immunohistochemically. At a median follow-up time of 33 months, 22 (39%) patients had died of disease, 23 (41%) were alive disease, and 11 (20%) had no evidence of disease. Tumors with high CD8 + TILs had a significantly lower death rate [hazard ratio (HR): 0.33, p = 0.02]. CD8 + TILs correlated with B2M expression (p = 0.007). On multivariable analyses, patients with both high B2M and CD8 + TILs had lower death rate (HR: 0.27, p = 0.03). Within the subgroup treated with IL-2 (n = 27, 48%), tumors with high CD8 + TILs were more likely to respond to IL-2 therapy [coefficient (coef): 1.6, p = 0.05]. On multivariable analyses, tumors with a combination of both high B2M expression and high CD8 + TILs also showed trend to responding to IL-2 therapy (coef: 2.5, p = 0.06). In conclusion, abundant CD8+ TILs and high tumor expression of beta-2-microglobulin were good prognostic indicators associated with longer survival in patients with high-stage ccRCC. Abundant CD8+ TILs may predict response to IL-2 therapy.
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