Abstract
Objective The objective of this study was to estimate the humoral immune response evaluated by immunoglobulin G (IgG) against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike receptor-binding domain (RBD-IgG) following the third mRNA coronavirus disease 2019 (COVID-19) vaccination in patients with kidney disease who received immunosuppressive treatment. Methods The primary outcome was RBD-IgG levels after the third SARS-CoV-2 vaccination. The primary comparison was the RBD-IgG levels between patients with kidney disease who received immunosuppressive treatment (n=124) and those who did not (n=33). Results The RBD-IgG levels were significantly lower in the patients with kidney disease who received immunosuppressive treatment than in those who did not receive immunosuppressive treatment. The RBD-IgG levels were lower in patients treated with glucocorticoid monotherapy than in those who did not receive immunosuppressive treatment. Even in patients who received ≤5 mg prednisolone, the RBD-IgG levels were significantly lower. Nine of the 10 patients who received rituximab within one year before the first vaccination did not experience seroconversion after the third vaccination. Meanwhile, all nine patients who received rituximab only after the second vaccination experienced seroconversion, even if B cell recovery was insufficient. Patients treated with mycophenolate mofetil plus glucocorticoid plus belimumab had significantly lower RBD-IgG levels than those treated with mycophenolate mofetil plus glucocorticoid. Conclusion The RBD-IgG levels were lower in patients with kidney disease who received immunosuppressive treatment than in those who did not receive immunosuppressive treatment. Low-dose glucocorticoid monotherapy affected the humoral immune response following the third mRNA COVID-19 vaccination.