T follicular helper cell-mediated IL-21 production suppresses FOXP3 expression of T follicular regulatory-like cells in diffuse large B cell lymphoma patients.

Based on CD25 expression, T follicular helper cells (Tfh) could be divided into T follicular regulatory (Tfr)-like subset (CD25CD4CXCR5) and CD25 Tfh subset (CD25CD4CXCR5). Patients with diffuse large B cell lymphoma (DLBCL) display high level of Tfr-like cells in blood and tumor. This Tfr-like subset could suppress CD8 T cell response while promote tumor cell proliferation. In this study, we investigated the transcription factors and regulatory elements associated with Tfr-like cells in DLBCL patients. Both circulating and tumor-infiltrating Tfr-like cells presented slightly higher Blimp-1 expression and significantly higher Foxp3 expression than the CD25 Tfh subset. As the IL-2 receptor, CD25 could be moderately upregulated in stimulated CD25 Tfh cells. However, stimulated CD25 Tfh cells could not upregulate Foxp3, indicating that the distinction between Foxp3-low CD25CXCR5CD4 T cells and Foxp3-high CD25CXCR5CD4 T cells was not due to differences in stimulation status. Regarding cytokine production, while both Tfr-like and CD25 Tfh cells upregulated IL-21 and IL-10 during stimulation, the CD25 Tfh cells presented significantly higher IL-21 and lower IL-10 expression than the Tfr-like cells, and the TGF-β expression was only increased in Tfr-like cells. Interestingly, IL-21 secreted from CD25 Tfh cells negatively regulated the expression of Foxp3 and IL-10 of autologous Tfr-like cells. Together, these results demonstrated that the Tfr-like and CD25 Tfh subsets of circulating Tfh cells presented different functions and should be investigated separately.