Association of circulating regulatory T cell number with the incidence and prognosis of diffuse large B-cell lymphoma.

Regulatory T (Treg) cells are essential for maintaining immune tolerance. High Treg frequencies have been reported in peripheral blood and tissue samples of patients with solid tumors while their role in lymphomas, including diffuse large B-cell lymphoma (DLBCL) has not been clearly established. In this study, we analyzed the circulating Treg numbers in 27 patients with newly diagnosed DLBCL and 17 healthy individuals. Tregs were detected by flow cytometry based on CD4(+) CD25(high) FoxP3(+) phenotype. In addition, the expression of CD45RA, HLA-DR, CD62L, CD39, and CTLA4 was analyzed. The number of circulating Treg cells was lower in patients with DLBCL than in healthy controls: median 23 (range, 4-107)/μL vs. 41 (19-104)/μL (P = 0.04). In particular, the number of Tregs expressing CD45RA (naïve Tregs), HLA-DR (marker of activation), and CD62L (L-selectin) was decreased in the DLBCL group. Lower (below median) number of circulating Tregs was associated with reduced chance of achieving complete remission (29% vs. 69%, P = 0.05) and reduced probability of even-free survival (24% vs. 84% at 1 yr, P = 0.0004), independently on the International Prognostic Index. We conclude that low number of circulating Tregs may be associated with poor prognosis in patients with DLBCL. However, our observations require confirmation in larger patient population.