Characterization and clinical significance of T follicular helper cells in follicular lymphoma

Abstract

Abstract T follicular helper (T FH) cells are a subset of CD4 +T cells that reside within the follicles of secondary lymphoid organs and play an essential role in the germinal center (GC) reaction. To examine the role T FHcells in follicular lymphoma (FL), we first characterized T FHcells using single cell analysis with the high-throughput technologies of mass cytometry (CyTOF) and the Indexing of Transcriptomes and Epitopes by Sequencing (CITE-seq). Clustering analysis revealed that T FHcells form subsets with unique phenotypes, and the expression of many common markers including CXCR5, ICOS, IL-21, TOX2, CD57, GZMK, XCL1, XCL2, CXCL13 and CD40L varies on T FHsubsets. We found that T FHcells are phenotypically more heterogenous in FL than benign tonsil tissues by both proteomic (n=82) and transcriptomic (n=8) profiling. Each FL patient showed different dominant T FHsubsets, in contrast to tonsil donors which were highly homogenous. Some T FHsubsets were only present in FL and absent in tonsil tissues, suggesting the existence of FL-specific T FHcells. Cytokines (IL-2, IL12, IL-17 and IL-21) and activated B cells upregulated T FHmarkers including PD-1, CXCR5 and IL-21 to induce the development of T FHsubsets such as IL-21 +or IL-21 +IFN-g +T FHcells, which was inhibited by rapamycin, an immunosuppressor. We observed that the T FHcell frequency significantly correlated with the number of lymphoma B cells. Futhermore, while T FHcells as a whole showed no correlation with prognosis, T FHsubsets such as CD57 +T FHcells were significantly associated with an inferior patient outcome. Taken together, our results indicate that T FHcells are highly heterogenous with different tumor-specific T FHsubsets present in FL and associated with patient outcomes in FL.