The difference in BAFF and APRIL with regard to the induction of a regulatory profile in B cells might contribute to explain why atacicept, a TACI-Fc fusion protein inhibiting both BAFF and APRIL signaling, did not reach the primary end point in a phase II trial in RA (59), whereas belimumab, which specifically antagonizes BAFF, is approved for the treatment of SLE and obtained significant efficacy on ACR20 criteria in RA (24, 25, 60). Here, TNFSF13 is linked to systemic lupus erythematosus.