Abstract
B cells present in human cutaneous melanoma have been associated with protective or detrimental effects on disease progression according to their phenotype. By using the RET model of spontaneous melanoma and adoptive transfer of B16 melanoma cells, we show that immature and follicular B2 (B2-FO) cells exert a protective effect on melanoma progression by promoting the generation of effector memory T cells and limiting the recruitment of polymorphonuclear myeloid-derived suppressor cells. Unfortunately, this beneficial effect progressively wanes as a consequence of enhanced expression of the IL4-induced gene 1 (IL4I1) enzyme by immature B cells and B2-FO cells. Endogenous IL4I1 selectively decreases CXCR5 expression in splenic immature B cells, subverting their trafficking to primary tumors and enhancing the production of IL-10 by B2 cells, thereby promoting an immunosuppressive microenvironment. Accordingly, B2 cells from RET IL4I1KO mice more efficiently controlled B16 melanoma growth than B2 cells from IL4I1-competent RET mice. Collectively, immature B cells and B2-FO cells are key actors in the control of melanoma growth, but their mobility and functions are differently impaired by IL4I1 overexpression during melanoma progression. Thus, our present data strongly urge us to associate an IL4I1 antagonist with current immunotherapy to improve the treatment of metastatic melanoma.