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Nipocalimab is a neonatal Fc receptor (FcRn)-blocking monoclonal antibody approved for the treatment of generalized myasthenia gravis (gMG) and is being evaluated for other immunoglobulin G (IgG) autoantibody- or alloantibody-mediated diseases. Nipocalimab binds to FcRn with high specificity and affinity, eliciting increased clearance of IgG antibodies without affecting IgG production or other immune functions. However, nipocalimab's impact on vaccine responses in patients has not been previously reported. The effect of nipocalimab on pre-existing antibodies against tetanus toxoid (TT) and herpes zoster virus (HZV) vaccines as well as humoral responses to TT vaccines, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines, and SARS-CoV-2 infections was examined in post hoc analyses of data from three randomized, placebo-controlled trials in participants with gMG, rheumatoid arthritis, and Sjögren's disease. The levels of pre-existing anti-TT and anti-HZV IgG followed the kinetics of total IgG during nipocalimab treatment (60%-65% and 53%-68% IgG reduction, respectively) and returned to baseline after discontinuation. Nevertheless, the majority of nipocalimab-treated participants maintained pre-existing anti-HZV (66/90, 73.3% above ≥100 IU/L reference threshold) and anti-TT IgG levels (62/81, 76.5% ≥0.16 IU/mL protective threshold) throughout the study period. Participants treated with nipocalimab elicited positive IgG responses to TT and SARS-CoV-2 vaccination, similar to placebo-treated participants. SARS-CoV-2 infections during the studies were mild to moderate in severity with no complications. These results suggest that nipocalimab does not impair the development of humoral responses to vaccines or viral infections in patients with IgG autoantibody-mediated diseases.Trial registration number: NCT04951622, NCT04991753, NCT04968912.