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

Abstract

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^hiICOS^hiCD4^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.