The prevalence and function of CD4⁺CXCR5⁺Foxp3⁺ follicular regulatory T cells in diffuse large B cell lymphoma

CD4⁺CXCR5⁺Foxp3⁺ follicular regulatory T (Tfr) cells possess critical roles in suppressing the germinal center reaction, B cell activation, and follicular helper T cell (Tfh) cytokine secretion. Since diffuse large B cell lymphoma (DLBCL) can arise from B cells undergoing germinal center reaction and/or differentiation, we hypothesized that Tfr cells might be involved in DLBCL. In the present study, we recruited thirty-five DLBCL patients and twenty-five healthy controls. Data showed that DLBCL patients presented an enrichment of circulating CD4⁺CXCR5⁺Foxp3⁺ Tfr cells compared to controls. In the primary tumor isolated from enlarged lymph nodes, Tfr cells made up of roughly 3% to 16% of infiltrating T cells. Higher levels of tumor-infiltrating Tfr cells were observed in patients with less advanced DLBCL stages, and in patients that stayed in remission 24 months after the initial R-CHOP treatment. High BCL6 and high FOXP3 expression was observed in Tfr cells ex vivo. After anti-CD3/CD28 and IL-2 stimulation, the Tfr cells more closely resembled Treg cells and presented high IL10 and TGFB1 expression. CD4⁺CD25⁺CXCR5⁺ Tfr cells and CD4⁺CD25⁺CXCR5^- non-Tfr Treg cells could suppress CD4⁺CD25^- Tconv cell and CD8⁺ T cell proliferation with similar capacity. However, Tfr cells were less capable of suppressing IFNG expression than Treg cells, and although both cell types supported CD19⁺ tumor cell proliferation, Tfr cells were less supportive than the non-Tfr Treg cells. Overall, this study suggested that Tfr cells were involved in intratumoral immunity, were likely beneficial to DLBCL patients, and were functionally distinctive from non-Tfr Treg cells. The distribution pattern and the prognostic value of Tfr cells in DLBCL should be examined in further studies.