Objectives
To investigate key factors that may contribute to the variability of rituximab-mediated peripheral and renal B cell depletion (BCD) in Systemic Lupus Erythematosus (SLE).
Methods
We analysed: 1) CD19+ B cell counts in patients with SLE before and one, two, three and six months after treatment with rituximab, comparing them with Rheumatoid Arthritis (RA) patients; 2) the presence of B cells in renal biopsies after rituximab therapy; 3) whether the duration of BCD correlated with patient demographics and B cell expression of CD20 and FcγRIIb; and 4) the effect of BAFF on the efficiency of rituximab and obinutuzumab at inducing BCD in whole blood assays, in vitro.
Results
In SLE (n = 71), the duration of BCD was shorter compared with RA (n = 27). B cells were detectable in renal biopsy samples (n = 6) after treatment with rituximab in all patients with poor response whilst peripheral blood B cells remained low or undetectable in the same patients. There were no significant relationships between peripheral BCD and patient age, disease duration, serum C3 levels or the level of expression of B cell surface proteins CD20 and FcγRIIb. Obinutuzumab was more efficient than rituximab at inducing BCD in whole blood assays, regardless of excess BAFF.
Conclusions
BCD in SLE is less efficient than in RA. Renal B cell presence following rituximab treatment was associated with poor outcomes. No significant relationships between any measured B cell related, clinical or laboratory parameters and the efficiency of BCD by rituximab was found. Obinutuzumab was superior to rituximab at inducing BCD.
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