Characterization of intratumoral follicular helper T cells in follicular lymphoma: role in the survival of malignant B cells

Accumulating evidences indicate that the cellular and molecular microenvironment of follicular lymphoma (FL) has a key role in both lymphomagenesis and patient outcome. Malignant FL B cells are found admixed to specific stromal and immune cell subsets, in particular CD4 pos T cells displaying phenotypic features of follicular helper T cells (T FH ). The goal of our study was to functionally characterize intratumoral CD4 pos T cells. We showed that CXCR5 hi ICOS hi CD4 pos T cells sorted from FL biopsies comprise at least two separate cell populations with distinct genetic and functional features: (i) CD25 pos follicular regulatory T cells (T FR ), and (ii) CD25 neg T FH displaying a FL-B cell supportive activity without regulatory functions. Furthermore, despite their strong similarities with tonsil-derived T FH , purified FL-derived T FH displayed a specific gene expression profile including an overexpression of several genes potentially involved directly or indirectly in lymphomagenesis, in particular TNF , LTA , IL4 or CD40LG . Interestingly, we further demonstrated that these two last signals efficiently rescued malignant B cells from spontaneous and rituximab-induced apoptosis. Altogether, our study demonstrates that tumor-infiltrating CD4 pos T cells are more heterogeneous than previously presumed, and underlines for the first time the crucial role of T FH in the complex set of cellular interactions within FL microenvironment.