Frequency of regulatory T cells in peripheral blood and in tumour-infiltrating lymphocytes correlates with poor prognosis in renal cell carcinoma

OBJECTIVE To compare the frequency of T regulatory cells (Tregs) in peripheral blood of patients (pPB) affected by renal cell carcinoma (RCC) both with the frequency of Tregs found in PB of healthy donors (hPB) and that of Tregs present in tumour infiltrating lymphocytes (TILs). To verify in vitro the inhibitory activity of tumour isolated Tregs on the effector T cells and, finally, to assess the prognostic role of Treg frequency determination. PATIENTS AND METHODS Treg frequency in hPB, pPB and TILs was evaluated in 30 patients and 20 healthy controls by measuring both membrane-CD25 and intracytoplasmic-Foxp3 expression by flow cytometry. Treg inhibitory activity was evaluated by an in vitro proliferation assay performed on total, CD25-depleted mononuclear cells (MNC) and CD25-depleted MNC cultured in the presence of purified CD25(+) Tregs. Finally, Treg frequency in pPB and TIL were correlated with conventional prognostic factors and scores of University of California Los Angeles and Kattan predictive models. RESULTS Treg frequency was higher in TILs than in pPB (P = 0.002), whereas there were no important differences between hPB and pPB. CD25(+) cells isolated either from PB and tumours showed the ability to significantly suppress in vitro both proliferation and interferon-gamma production by CD25-depleted MNC, thus demonstrating that they are active Tregs. Treg frequency was found to significantly correlate both with pathological stage (pPB, P = 0.03; TIL, P = 0.04) and nuclear grade (TIL, P = 0.005), both for UCLA and Kattan models (all: P < 0.05 for both pPB and TIL). CONCLUSION Treg frequency is significantly higher in TIL than in pPB of patients with RCC. Tregs showed in vitro an inhibitory activity on effector T cells isolated from kidney tumours. The increase in both peripheral and intratumoral Tregs in subjects affected with RCC were associated with worse prognosis.