ABSTRACT
OBJECTIVES: B-cell depletion time after rituximab (RTX) treatment is prolonged in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) compared with other autoimmune diseases. We investigated central and peripheral B-cell development to identify the causes for the defect in B-cell reconstitution after RTX therapy. METHODS: We recruited 91 patients with AAV and performed deep phenotyping of the peripheral and bone marrow B-cell compartment by spectral flow and mass cytometry. B-cell development was studied by in vitro modelling and the role of BAFF receptor by quantitative PCR, western blot analysis and in vitro assays. RESULTS: Treatment-naïve patients with AAV showed low transitional B-cell numbers, suggesting impaired B-lymphopoiesis. We analysed bone marrow of treatment-naïve and RTX-treated patients with AAV and found reduced B-lymphoid precursors. In vitro modelling of B-lymphopoiesis from AAV haematopoietic stem cells showed intact, but slower and reduced immature B-cell development. In a subgroup of patients, after RTX treatment, the presence of transitional B cells did not translate in replenishment of naïve B cells, suggesting an impairment in peripheral B-cell maturation. We found low BAFF-receptor expression on B cells of RTX-treated patients with AAV, resulting in reduced survival in response to BAFF in vitro. CONCLUSIONS: Prolonged depletion of B cells in patients with AAV after RTX therapy indicates a B-cell defect that is unmasked by RTX treatment. Our data indicate that impaired bone marrow B-lymphopoiesis results in a delayed recovery of peripheral B cells that may be further aggravated by a survival defect of B cells. Our findings contribute to the understanding of AAV pathogenesis and may have clinical implications regarding RTX retreatment schedules and immunomonitoring after RTX therapy.
ABSTRACT
While in patients with rheumatoid arthritis B-cell repopulation starts within 9 months after rituximab (RTX) therapy, a delayed B-cell repopulation was reported in some RTX-treated patients with ANCA-associated vasculitides (AAV). To date, the frequency of AAV patients with impaired peripheral B-cell regeneration and the mechanisms leading to the constricted regenerative capacity are unknown. We analyzed the B-cell repopulation kinetic in 37 AAV patients treated with RTX followed by maintenance immunosuppressants. We report on serum concentrations of the B-cell-activating factor BAFF, immunoglobulins and B-cell subpopulations in patients that relapsed after RTX. B-cells were re-detectable in only one patient within 9 months after RTX. In 14 patients (41%), B-cell repopulation started later, after a mean observation time of 21 months. Only seven of these patients had detectable B-cells within the first year after RTX. Twenty patients (59%) had no B-cell reconstitution within the observation period. BAFF was increased in RTX-treated AAV patients compared to healthy controls and correlated inversely with peripheral B-cell numbers, IgG- and IgA concentrations. Immunoglobulin concentrations declined significantly after RTX and the IgG concentration correlated with B-cell numbers. Thirteen patients relapsed after RTX. Relapses occurred exclusively either after B-cell reconstitution had started or were accompanied by rising ANCA titres. In relapsed patients, the B-lymphocyte compartment consisted mainly of switched memory B-cells. Our data indicate that RTX treatment can induce secondary immunodeficiency in AAV, with hypogammaglobulinemia and long-lasting B-lymphopenia. Further studies are needed to define the pathophysiology of the impaired B-cell development in RTX-treated AAV patients.
