Belimumab is an anti-BAFF monoclonal antibody that has reached Phase II trials in SLE and RA, while atacicept (previously known as TACI-Ig), a recombinant fusion protein that neutralizes both BAFF and APRIL (a related B cell survival factor), has undergone Phase I evaluation in SLE [90]. Here, TNFRSF13B is linked to systemic lupus erythematosus.