FC002: Humoral and Cellular Immune Responses After a Three-Dose Course of Mrna-1273 Covid-19 Vaccine in Kidney Transplant Recipients: A Prospective Cohort Study

Abstract BACKGROUND AND AIMS Seroconversion after a two-dose course of mRNA COVID-19 vaccination in kidney transplant recipients ranges between 30% and 50% in different series. We previously demonstrated that a substantial proportion of patients (35%) without a humoral response, develop a cellular response after the second dose assessed by the ELISpot technique. We aim to study the evolution of both humoral and cellular responses in the same cohort before and 1 month after the administration of the third dose of 100 mcg of mRNA-1273 COVID-19 vaccine. METHOD Final population included 129 KTRs studied at four time-points: at baseline before the first dose, after the second dose (median 42 days) and before (203 days) and after (232 days) the third dose. At all the time-points, IgG and IgM were assessed as well as N- and S-protein specific ELISpot. The main outcome was seroconversion after the third dose. RESULTS After the second dose, 26.7% of naïve cases experienced seroconversion. Before the third dose and in the absence of clinically evident COVID-19, this percentage increased to 61.9%. After the third dose, seroconversion was observed in 80.0% of patients. S-ELISpot positivity after the second dose was significantly associated with final seroconversion [OR (95% CI) 3.14 (1.10–8.96); P = .032], while transplantation < 1 year and previous kidney transplant were negatively associated with [OR (95% CI) 0.23 (0.07–0.80); P = .021 and OR (95% CI) 0.22 (0.06–0.78); P = .020, respectively). IgG after third dose were significantly higher (P < .001) in patients who maintained S-ELISpot positivity throughout the study (34.3%) and were correlated with S-spots after the second dose (r = 0.344, P < .001). CONCLUSION A substantial proportion of KTRs vaccinated with mRNA-1273 develops a late seroconversion after two doses and only a fifth remained seronegative after a third. Cellular immunity seems to play a major role in the development of a final strong humoral response.