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SARS-CoV-2-specific adaptive immune response after mRNA vaccination in liver transplanted patients

Background and aim Liver transplant recipients have an increased risk to develop severe or prolonged COVID-19. Therefore, these individuals particularly benefit from prophylactic vaccination. Recent studies demonstrated reduced antibody response rates upon COVID-19 mRNA vaccination in immunosuppressed individuals, however, little is known about the role of cellular immunity in this setting. Methods We analyzed T cell responses after bnt162b2 vaccination using overlapping peptides spanning the SARS-CoV-2 spike protein and a set of pre-described epitopes located in different SARS-CoV-2 proteins, as well as the humoral response (serology and neutralizing antibodies) in 10 patients following liver transplantation. Results Importantly, all patients showed T cell and/or antibody responses after vaccination. In line with previous studies, detectable levels of S1-specific IgG and titers of neutralizing antibodies were lower compared to the general vaccinated population. Similarly, the CD4 + and CD8 + T cell epitope repertoire was narrow and cytokine production was reduced. Hypothesizing that the phenotype of T cells is different under immunosuppression with imminent implications for the long-time immunity, we currently perform in-depth phenotypical profiling of the detectable CD8 + T cells using tetramer-based enrichment and multi-parameter FACS analysis. Conclusions Our data suggest an impaired immune response after SARSCoV- 2 vaccination in the vulnerable cohort of individuals after liver transplantation. Cellular immune responses may however compensate for lacking antibody responses. Our data support the notion that immunocompromised patients may benefit from an early third vaccination.