Dynamics of Humoral and Cellular Responses in Renal Transplant Recipients Receiving 3 Doses of SARS-CoV-2 mRNA Vaccine

Background. The original SARS-CoV-2 vaccination regimen (2 doses) induces insufficient short-term response in kidney transplant (KT) recipients. This study assessed the response to a third dose and the long-term immunogenicity after 2 doses in KT. Methods. We analyzed the dynamics of the humoral and cellular response by monitoring SARS-CoV-2 IgG antibodies against the Spike-protein (IgG-Spike) and QuantiFERON SARS-CoV-2 IFN-gamma release assay 6 mo after the second dose (T2) and 28 d after the third dose of mRNA vaccines (T3) to KT and controls (dialysis patients and healthy individuals). Results. At T2, the percentage of IgG-Spike+ KT and dialysis patients decreased (KT 65.8%-52.6%, hemodialysis 92.6-81.5%, and peritoneal dialysis 100%-90%), whereas 100% of healthy controls remained positive. About the cellular response, the percentage of responders decreased in all groups, especially in KT (22.4%-9.2%, P= 0.081). At T3, 92% of KT, 94%-98% of dialysis patients, and 100% of healthy controls were IgG-Spike+. In terms of antibody titers, patients and controls showed a reduction between T2 and T3 and about 80% of dialysis patients and 100% of controls achieved high titers after the third dose (> 1479.5 Binding Antibody Units/mL), whereas this percentage was only 50% in KT. With respect to the cellular response, only KT displayed a significant rise after the third dose. Conclusions. The third dose of mRNA vaccine improves both humoral and cellular responses, but less effectively in KT compared with dialysis patients and healthy controls.