Dynamics of SARS‐CoV‐2 Spike Receptor‐Binding Domain‐Targeted Specific Peripheral Memory B Cells in Patients With End‐Stage Chronic Kidney Disease Undergoing Replacement Therapy Following COVID‐19 Vaccination

Memory B cells (MBCs) are responsible for maintaining long-lasting functional B-cell immune responses. Little is known about the kinetics of peripheral blood (PB) SARS-CoV-2 vaccine-induced MBCs in end-stage chronic kidney disease (CKD) patients undergoing replacement therapies. We investigated this issue in this prospective, observational cohort study including 27 patients (9 females and 18 males; median age, 68.4 years, range 48-82) comprising 20 hemodialysis patients and 7 Kidney transplant recipients. SARS-CoV-2-Receptor-Binding Domain (RBD)-targeted PB-MBCs were enumerated by flow cytometry using a tetramer-binding assay after the second COVID-19 mRNA vaccine dose (Post-2D), before (Pre-3D), and after the first mRNA vaccine booster dose (Post-3D). Commercially available electrochemiluminescent immunoassays were used to measure total anti-RBD antibodies targeting an IgG against the S trimeric protein. Overall, 18/27 patients (66.6%) exhibited detectable RBD-MBC responses at Post-2D, 12/27 (44.4%) at Pre-3D, and 16/27 (59.2%) at Post-3D. RBD-MBC levels dropped non-significantly between post-2D and Pre-3D (p = 0.38). A nonsignificant increase in RBD-MBCs was noticed post-3D (p = 0.65). Overall, both antibody specificities displayed the same dynamics but the drop in anti-trimeric spike antibody levels between Post-2D and Pre-3D and increases post-3D were statistically significant (p < 0.001). No correlation (rho = 0.05; p = 0.64) was observed between total antibodies against RBD and RBD-MBC counts. The correlation between IgG antibodies against the trimeric S protein and SARS-CoV-2 RBD-MBC counts was very weak (rho, 0.18; p = 0.11). In summary, waning RBD-MBC counts Pre-3D and increases post-3D are less marked than that of anti-RBD and anti-S trimeric antibodies.