Genetic immune response and antibody repertoire of heterologous ChAdOx1-BNT162b2 vaccination in a Korean cohort

Heterologous ChAdOx1-BNT162b2 vaccination induces a stronger immune response than two doses of BNT162b2 or ChAdOx1. Yet, the molecular transcriptome, the germline allelic variants of immunoglobulin loci and anti-Omicron antibody levels induced by the heterologous vaccination have not been formally investigated. Moreover, there is a paucity of COVID vaccine studies including diverse genetic populations. Here, we show a robust molecular immune transcriptome and antibody repertoire in 51 office workers from the Republic of Korea after a heterologous ChAdOx1-BNT162b2 vaccination or a homologous ChAdOx1-ChAdOx1 vaccination. Anti-spike-specific IgG antibody levels in the heterologous group increased from 14,000 U/ml to 142,000 AU/ml within eight days after the BNT162b2 vaccination. In contrast, antibody levels in the homologous group increased two-fold after the second ChAdOx1 dose. Antibody titers against the Omicron spike protein as compared to the ancestral strain were reduced to a lesser extent in the heterologous group. RNA-seq conducted on immune cells demonstrated a stronger activation of interferon-induced genetic programs in the heterologous cohort. An increase of specific IGHV clonal transcripts encoding neutralizing antibodies was preferentially detected in the heterologous cohort. Enrichment of B cell and CD4+ T cell responses were observed following both heterologous and homologous vaccination using scRNA-seq, but clonally expanded memory B cells were relatively stronger in the ChAdOx1-BNT162b2 cohort. In summary, a heterologous vaccination with ChAdOx1 followed by BNT162b2 provides an innate and adaptive immune response exceeding that seen in homologous ChAdOx1 vaccinations but equivalent to that seen in homologous BNT162b2 vaccination.