Internalization of rituximab and the efficiency of B Cell depletion in rheumatoid arthritis and systemic lupus erythematosus.
OBJECTIVE
Rituximab, a type I anti-CD20 monoclonal antibody (mAb), induces incomplete B cell depletion in some patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), thus contributing to a poor clinical response. The mechanisms of this resistance remain elusive. The purpose of this study was to determine whether type II mAb are more efficient than type I mAb at depleting B cells from RA and SLE patients, whether internalization influences the efficiency of depletion, and whether Fcγ receptor type IIb (FcγRIIb) and the B cell receptor regulate this internalization process.


METHODS
We used an in vitro whole blood B cell-depletion assay to assess the efficiency of depletion, flow cytometry to study cell surface protein expression, and surface fluorescence-quenching assays to assess rituximab internalization, in samples from patients with RA and patients with SLE. Paired t-test or Mann-Whitney U test was used to compare groups, and Spearman's rank correlation test was used to assess correlation.


RESULTS
We found that type II mAb internalized significantly less rituximab than type I mAb and depleted B cells from patients with RA and SLE at least 2-fold more efficiently than type I mAb. Internalization of rituximab was highly variable between patients, was regulated by FcγRIIb, and inversely correlated with cytotoxicity in whole blood B cell-depletion assays. The lowest levels of internalization were seen in IgD- B cells, including postswitched (IgD-CD27+) memory cells. Internalization of type I anti-CD20 mAb was also partially inhibited by anti-IgM stimulation.


CONCLUSIONS
Variability in internalization of rituximab was observed and was correlated with impaired B cell depletion. Therefore, slower-internalizing type II mAb should be considered as alternative B cell-depleting agents for the treatment of RA and SLE.
University College London, London, UK.
Venkat
V
Reddy
University College London, London, UK.
Geraldine
G
Cambridge
University College London, London, UK.
David A
DA
Isenberg
Southampton University, Southampton, UK.
Martin J
MJ
Glennie
Southampton University, Southampton, UK.
Mark S
MS
Cragg
University College London, London, UK.
Maria
M
Leandro
D000328:Adult; D000368:Aged; D000911:Antibodies, Monoclonal / Q000378:metabolism / Q000494:pharmacology; D061067:Antibodies, Monoclonal, Humanized / Q000378:metabolism / Q000494:pharmacology; D058846:Antibodies, Monoclonal, Murine-Derived / Q000378:metabolism / Q000494:pharmacology*; D018501:Antirheumatic Agents / Q000378:metabolism / Q000494:pharmacology*; D001172:Arthritis, Rheumatoid / Q000276:immunology*; D001402:B-Lymphocytes / Q000187:drug effects* / Q000378:metabolism; D004351:Drug Resistance; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D017452:Receptors, IgG / Q000378:metabolism; D000069283:Rituximab; D055815:Young Adult
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D058846:Antibodies, Monoclonal, Murine-Derived; D018501:Antirheumatic Agents; C080571:Fc gamma receptor IIB; D017452:Receptors, IgG; D000069283:Rituximab; C543332:obinutuzumab