Systemic immune profiling of heterologous versus homologous boosting of COVID-19 vaccination

BACKGROUND: Compared with homologous boosting, heterologous boosting with a different COVID-19 vaccine following priming generates stronger antibody responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as well as variants, particularly for inactivated COVID-19 vaccine(CoronaVac). However, it is still unclear about the potential immune enhancement mechanism underlying heterologous boosting. METHODS: In this study, we isolated spike protein binding-specific monoclonal antibodies at day 180 post a homologous booster with CoronaVac or a heterologous booster with Ad5-nCoV based on two-dose of CoronaVac using the single B cell sorting platform. Subsequently, we verified their neutralization activity to SARS-CoV-2 variants, germline gene sequences and affinity kinetics targeting SARS-CoV-2 NTD/RBD/S1. Additionally, we conducted an in-depth analysis of the immunological response characteristics, by integrating single-cell RNA/V(D)J sequencing(scRNA/ V(D)J-seq). RESULTS: Our study demonstrated that heterologous boosting with Ad5-nCoV elicited more mature B cells with higher affinity and activated more abundant immune-related pathways compared to the homologous boosting with CoronaVac. In addition, Ad5-nCoV boosting expanded unique clonal types of B and T cells, whereas CoronaVac boosting led to a small-sized clonal expansion. Furthermore, the utilization of germlines associated with neutralizing antibody were preferentially enriched in recipients with Ad5-nCoV boosting. CONCLUSIONS: Above all, our study gives insights for elaborating the systemic immune landscape of heterologous-boosting COVID-19 immunization by the novel single B cell sorting platform and scRNA/V(D)J-seq technology. TRIAL REGISTRATION NUMBER: NCT04892459.