T follicular helper cells in germinal center B cell selection and lymphomagenesis

Germinal centers (GCs) are confined anatomic regions where rapidly proliferating B cells undergo somatic mutation and selection and eventual differentiation into memory B cells or long‐lived plasma cells. GCs are also the origin of malignancy, namely follicular lymphoma (FL), GC B cell‐diffuse large B cell lymphoma (GCB‐DLBCL), and Burkitt lymphoma (BL). GC B cell lymphomas maintain their GC transcriptional signatures and sustain many features of the GC microenvironment, including CD4+ T follicular helper (Tfh) cells. Tfh cells are essential for the formation and maintenance of GCs, providing critical helper signals such as CD40L. Large‐scale sequencing efforts have led to new insights about the tightly regulated selection mechanisms that are commonly targeted during GC B cell lymphomagenesis. For instance, HVEM, a frequently mutated surface molecule in GC‐derived lymphomas, engages the inhibitory receptor BTLA on Tfh cells and loss of HVEM leads to exaggerated T cell help. Here, we review current understanding of how Tfh cells contribute to the selection of GC B cells, with a particular emphasis on how Tfh cell signals may contribute to lymphomagenesis. The possibility of targeting Tfh cells for the treatment of GC‐derived lymphomas is discussed.