ABSTRACT
Purpose: Seroconversion after a 2 doses of mRNA COVID-19 vaccine in kidney transplant recipients (KTR) ranges between 30 and 50% in different series. We previously demonstrated that a substantial proportion of KTRs (35%) without a humoral response, develops a cellular response after the second dose assessed by the ELISpot technique. We aim to study the evolution of both humoral and cellular response in the same cohort before and 1 month after the administration of the third dose of mRNA-1273 COVID-19 vaccine. Method(s): We included in the final analysis KTRs without evidence of previous exposure to COVID-19 and who were not infected during the course of the study and with complete data in all the time-points (n=105). The four time-points studied were at baseline before the first dose (T1), after the second dose (T2, 2 months) and before (T3, 6 months) and after (T4, 7 months) the administration of the third dose of 100mcg mRNA-1273 COVID-19 vaccine. In all the time points, IgG and IgM titre against protein S assessed by Luminex technique and cellular immunity assessed by N- and S-protein specific ELISpot were studied. Result(s): The percentage of patients with a positive humoral or cellular immunity against the S-protein were 24.8% and 51.4% after the second dose (T2). This percentages changed to 54.3% and 48.6% at 6 months (T3), respectively for IgG and S-ELISpot, in the absence of proven COVID-19. After the administration of the 3rd dose (T4) these percentages increased to 75.2% for IgG and 61.0% of S-ELISpot respectively. At multivariate analysis, the only factor that was positively associated with IgG development at T4 was S-ELIspot positivity after the 2nd dose (T2) [OR(CI) 3.14[1.10-8.96], p=0.032). Factors negatively associated with seroconversion were being transplanted during the last year [OR(CI) 0.23[0.07-0.80], P=0.021] and previous transplantation [OR(CI) 0.22[0.06-0.78], P=0.020). Conclusion(s): After a 3 doses-course of mRNA-1273 COVID-19 vaccine, three quarters of kidney transplant recipients developed finally IgG against protein S. Developing a cellular response after the second dose was positively associated with the final seroconversion, while being transplanted previously or being vaccinated during the first year after KT impacted negatively on the vaccine outcome.