Evaluation of T-Cell Responses to Sars-Cov-2 Spike Antigens in Pfizer/Biotech and Janssen Booster Vaccinations in Fully Vaccinated Individuals: A Retrospective Longitudinal Study

Abstract

With the recent emergence of the deadly COVID-19 and its worldwide spread, vaccines of different formulations; the viral-vector, m-RNA and subunit vaccines among others were developed to curb the spread of the virus and reduce its disease burden. Very little is known about the durability of these vaccines and immune protection mechanisms from homologous and heterologous booster vaccines and their effectiveness remains largely understudied. Therefore, this study aimed to assess the longevity of cellular immune responses (interferon-gamma release) following the administration of Janssen or Pfizer booster doses. Archived PBMCs obtained across four time points; Pre-booster, Month 3, Month 6 and Month 9, isolated from subjects from the Legon community, Ghana, were used in this study. In-silico HLA restriction epitope prediction of SARS-CoV-2 spike protein was done to determine immunogenic peptides after which the Interferon-gamma release response ELISpot Assay was conducted. Briefly, 60% of all samples registered positive responses to at least one of the spike peptides with 55.5% from the Janssen booster vaccination and 44.4% Pfizer booster vaccination. Against all the peptides a comparison of responses between the two vaccine boosters was done across the four time points. Both Pfizer and Janssen boosters elicited durable spike-specific T-cell responses, with persistence observed for up to 6 months. The study found that homologous prime-boosting with a viral-vectored vaccine (Janssen) produced stronger T-cell responses compared to heterologous boosting. Heterologous m-RNA prime-boosting using Pfizer led to stronger T-cell responses than homologous m-RNA prime-boosting.