A study conducted on 44 healthy individuals (HDs) and 54 liver transplant recipients (LTRs) evaluated the antibody and cellular immune responses induced by COVID-19 mRNA vaccines. The researchers investigated the Pfizer BNT162b2 and Moderna mRNA-1273 vaccines and collected blood samples at various time points. The results showed that LTRs had significantly lower anti-RBD antibody titers compared to HDs at all time points. However, after the third vaccination, 92.2% of LTRs achieved antibody titers that exceeded the World Health Organization (WHO) standard, indicating the effectiveness of immune responses in immunosuppressed LTRs. The study also found that the number of medications taken by LTRs had a significant impact on antibody levels, with a decrease observed in individuals taking multiple drugs.
In terms of cellular immune responses, CD4+ T-cell responses were found to correlate with anti-RBD antibody titers in both HDs and LTRs. The study revealed that CD4+ T-cell responses in LTRs were lower than those in HDs, but still reactive to Omicron sublineages. There were no significant differences in CD8+ T-cell responses between HDs and LTRs, indicating that mRNA vaccines induce CD8+ T-cell responses that can recognize the Omicron variant. However, the frequency of spike-specific CD8+ T-cells was lower in LTRs compared to HDs at all time points.
Regarding the effectiveness of mRNA vaccines against Omicron sublineages, the study found that antibody titers against these variants were significantly reduced compared to the Wuhan-1 strain. Neutralizing activity against Omicron sublineages was also observed to be lower. Notably, the third vaccination did not improve the trend of lower antibody titers against variants. In contrast, CD4+ T-cell responses to mutant strains were maintained, while CD8+ T-cell responses showed no significant decrease.
Overall, the study suggests that mRNA vaccines can induce effective immune responses in both HDs and LTRs, although antibody levels and cellular immune responses may be lower in LTRs. These findings have implications for the management of immunocompromised individuals and highlight the need for additional vaccination strategies to enhance immune responses against emerging variants.
