Exploring TREC and KREC Levels in Nursing Home Residents and Staff and Their Association with SARS-CoV-2 Antibody Response After Vaccination.

Background: T-cell receptor excision circles (TRECs) and kappa-deleting recombination excision circles (KRECs) are markers of recent thymic and bone marrow output, respectively. As they have previously been associated with immunosenescence, we aimed to investigate their association with anti-spike SARS-CoV-2 (S1RBD) IgG antibody response after COVID-19 vaccination in nursing home residents (NHRs) and staff (NHS).

Methods: We measured TREC and KREC levels and S1RBD IgG antibody levels from dried blood spots (DBSs) using in-house qPCRs and a commercial ELISA kit, respectively, in 200 participants (50 NHRs and 150 NHS). DBSs were collected in April 2021, approximately two months after primary course COVID-19 vaccination (BNT162b2). We assessed the association between TREC and KREC as dependent variables and age, sex, infection-priming status, and post-vaccination S1RBD-specific IgG concentrations as independent variables by simple and multiple linear regression.

Results: TREC and KREC levels were significantly lower in NHRs compared with NHS and were negatively correlated with age ( < 0.001). Neither TREC nor KREC levels were significantly associated with SARS-CoV-2 antibody concentrations ( > 0.05).

Conclusions: In our study population, TREC and KREC levels decreased with age and were statistically significantly lower in NHRs than NHS. They were, however, not associated with the antibody response after COVID-19 vaccination. Yet, additional research is warranted to explore their potential relevance in cellular immune responses or in combination with other biomarkers of immune function.