Objectives  To evaluate the tumor-infiltrating PD-1 positive lymphocytes and regulatory T cells (Treg) as prognosis predictors of metastatic renal cell carcinoma (mRCC), and investigate the expression of PD-1 and Treg cells in mRCC and elucidate their correlation with clinicopathological parameters and prognosis.

  Methods  A total of 269 mRCC patients from June 2007 to June 2017 in Zhongshan Hospital, Fudan University, were included in the study. The expression of PD-1 and Tregs in mRCC samples were detected by immunohistochemistry. The relationship between the expression of PD-1 and Tregs was analyzed.

  Results  PD-1 positive expression in mRCC was 31.60% (85/269) and it was positively correlated with the tumor Fuhrman grade and negatively correlated with prognosis. Tumor infiltration of Tregs in mRCC was 36.80% (99/269), and it was also positively correlated with the tumor Fuhrman grade and negatively correlated with prognosis. Univariate analysis showed that PD-1 positive lymphocytes and high Treg infiltration numbers were negatively correlated with overall survival (OS) and progression free survival (PFS) rates. Thus, PD-1 positive lymphocytes and high Treg infiltration numbers are independent prognostic indicators of OS and PFS and when combined, they can render a better prediction for prognosis.

  Conclusions  Intra-tumoral infiltration of PD-1 positive lymphocytes and Tregs can be used as significant prognostic indicators of mRCC, and the combined predictive effect is better than the individual predictive effect. Therefore, evaluating the number of PD-1 positive lymphocytes or infiltrating Tregs in mRCC is helpful in clinically estimating mRCC prognosis in patients.