Abstract Pathogenic B lymphocytes removal through therapy with depleting monoclonal antibodies results in clinical benefit in both oncology and immunological indications. Incomplete rates of clinical response and the realization that B cell depletion following immunotherapy is incomplete fuels the need for better therapies. BAFF/BLyS signaling through its BAFFR/BR3 receptor have a critical role on B cell proliferation and survival in the mouse and to some extent in non-human primates and humans. In order to combine B cell depletion with the blockade of BAFF mediated B cell survival, we generated depleting, BAFF-blocking, non-agonistic anti-BR3 monoclonal antibodies. The results from this study indicate that in mice anti-BR3 monoclonal antibody reduces B cells to a higher degree when compared to anti-CD20 or BAFF-blockade through BR3-Fc. Anti-BR3 depletes B cells with a slower kinetics than anti-CD20 but showed high B cell depletion and a decrease in bone marrow plasma cells which was not seen with anti-CD20. Anti-BR3 treatment of NZB/W lupus mouse model results in significant survival benefit and reduction of established nephritic clinical symptoms indicating potential therapeutically value for human disease. In conclusion, in vivo comparison in mice of anti-BR3 antibodies with other B cell immunotherapies (anti-CD20 and BR3-Fc) shows characteristics in B cell subset reduction that can guide translation to treatment of human disease. This work was supported by Genentech Inc.