BAFF and CD4+ T cells are major survival factors for long-lived splenic plasma cells in a B-cell–depletion context

Previous data have suggested that B-cell–depletion therapy may induce the settlement of autoreactive long-lived plasma cells(LLPCs) in the spleen of patients with autoimmune cytopenia. To investigate this process, we used the AID-CreERT2-EYFP mouse model to follow plasma cells(PCs) engaged in an immune response. Multiplex polymerase chain reactionat the single-cell level revealed that only a small fraction of splenic PCs had a long-lived signature, whereas PCs present after anti- CD20antibody treatment appeared more mature, similar to bone marrow PCs. This observation suggested that, in addition to a process of selection, a maturation induced on B-cell depletion drove PCs toward a long-lived program. We showed that B-cell activating factor(BAFF) and CD4 + T cells play a major role in the PC survival niche, because combining anti- CD20with anti-BAFF or anti-CD4 antibody greatly reduce the number of splenic PCs. Similar results were obtained in the lupus-prone NZB/W model. These different contributions of soluble and cellular componentsof the PC niche in the spleen demonstrate that the LLPC expression profile is not cell intrinsic but largely depends on signals provided by the splenic microenvironment, implying that interfering with these components at the time of B-cell depletion might improve the response rate in autoimmune cytopenia.