Serum Unconjugated Bilirubin as a Predictor of Specific Cellular Immunity Response in Kidney Transplant Recipients after Administration of SARS-CoV-2 Inactivated Vaccine

Abstract Purpose The immunogenicity of SARS-CoV-2 vaccines is poor in kidney transplant recipients (KTRs). The factors related to poor immunogenicity to vaccination in KTRs are not well defined. Methods An observational study was conducted in KTRs and healthy individuals who had received two doses of SARS-CoV-2 inactivated vaccine. IgG antibodies against the receptor-binding domain found in the S1 subunit of the spike protein, and against nucleocapsid protein were measured using enzyme-linked immunosorbent assay. Receptor-binding domain (RBD)-angiotensin-converting enzyme 2 interaction-blocking antibodies were measured using commercial kits. T cell responses against the spike and nucleocapsid proteins were detected using enzyme-linked immunosorbent spot assay. Results No severe adverse effects were observed in KTRs after first or second dose of SARS-CoV-2 inactivated vaccine. IgG antibodies against the receptor- binding domain, and nucleocapsid protein were not effectively induced in a majority of KTRs after second dose of inactivated vaccine. Specific T cell immunity response was detectable in 32%-40% KTRs after second doses of inactivated vaccine. KTRs who developed specific T cell immunity were more likely to be female, and have lower levels of total bilirubin, unconjugated bilirubin, and blood tacrolimus concentration. Multivariate logistic regression analysis found that blood unconjugated bilirubin was significantly negatively associated with SARS-CoV-2 specific T cell immunity response in k KTRs. Conclusions Specific T cell immunity response could be induced in 32%-40% KTRs after two doses of inactivated vaccine. Blood unconjugated bilirubin was negatively associated with specific cellular immunity response in KTRs following vaccination.