The Role of Interleukin-21 in COVID-19 Vaccine-Induced B Cell-Mediated Immune Responses in Kidney Disease Patients and Kidney Transplant Recipients

T cell mediated help to B cells is required for the development of humoral responses, in which the cytokine interleukin (IL)-21 is key. Here, we studied the mRNA-1273 vaccine-induced SARS-CoV-2-specific memory T cell IL-21 response, memory B cell response and IgG antibody levels in peripheral blood at 28 days after the 2nd vaccination by ELISpot and the fluorescent bead-based multiplex-immunoassay, respectively. We included 40 chronic kidney disease (CKD) patients, 34 patients on dialysis, 63 kidney transplant recipients (KTR) and 47 controls. We found that KTR, but not CKD and dialysis patients, had a significantly lower number of SARS-CoV-2-specific IL-21 producing T cells than controls (p