Background: Multiple vaccinations have potential inimical effects on the immune system aging process. We examined whether response to SARS-CoV-2 vaccination with Tozinameran is associated with immunosenescence and immunoexhaustion in kidney transplant recipients (KTRs). Methods: In this prospective observational study, we observed 39 adult kidney transplant recipients (KTRs) who had no pre-existing anti-SARS-CoV-2 antibodies and were on stable immunosuppression. CD4+ and CD8+ T-cell subpopulations [comprising CD45RA+CCR7+ (naïve), CD45RA−CCR7+ (T-central memory, TCM), CD45RA−CCR7− (T-effector memory, TEM) and CD45RA+CCR7− (T-effector memory re-expressing CD45RA, TEMRA, senescent), CD28− (senescent) and PD1+ (exhausted)] were evaluated at 2 time points: T1 (48 h prior to the 3rd), and T2 (3 weeks following the 3rd Tozinameran dose administration). At each time point, patients were separated into Humoral and/or Cellular Responders and Non-Responders. Results: From T1 to T2, CD4+TCM and CD8+TEM were increased, while naïve CD4+ and CD8+ proportions were reduced in the whole cohort of patients, more prominently among responders. At T2, responders compared to non-responders had higher CD8+CD28+ [227.15 (166) vs. 131.44 (121) cells/µL, p: 0.036], lower CD4+CD28− T-lymphocyte numbers [59.65 (66) cells/µL vs. 161.19 (92) cells/µL, p: 0.026] and percentages [6.1 (5.5)% vs. 20.7 (25)%, p: 0.04]. Conclusion: In KTRs, response to vaccination is not associated with an expansion of senescent and exhausted T-cell concentrations, but rather with a switch from naïve to differentiated-activated T-cell forms.
