Early transcriptional responses following Ad26.COV2.S vaccination in individuals with prior SARS-CoV-2 infection

<h4>Background</h4>Ad26.COV2.S is a recombinant, replication-incompetent human adenovirus serotype 26 (Ad26) vectored vaccine encoding a full-length SARS-CoV-2 spike protein in a prefusion-stabilised conformation. The genes and pathways which are differentially regulated following vaccination with Ad26.COV2.S, how these differ over time, and under different regimens, have not been investigated.<h4>Methods</h4>Gene expression changes were profiled via RNAseq following the first and second dose of Ad26.COV2.S in a subset of individuals with pre-existing SARS-CoV-2 immunity due to prior SARS-CoV-2 infection, included in a randomised, double-blind, Phase 3 study (NCT#04908722). Transcriptional responses induced by a 1- and 2-dose regimen were assessed, each at two different dose levels: the marketed 5 × 10¹⁰vp dose level and a lower 1.25 × 10¹⁰vp dose level.<h4>Findings</h4>Consistent with other vaccine studies, antiviral, interferon, cytokine, and monocyte blood transcriptional modules were differentially regulated one day post-Ad26.COV2.S vaccination. At three days post-vaccination, innate immunity was still transcriptionally active at lower levels than one day post-vaccination. By seven days post-Ad26.COV2.S, increased immunoglobulin gene expression dominated the transcriptome response, indicating a shift towards humoural and B cell responses and activation of adaptive immunity. Transcriptional responses post-Ad26.COV2.S were generally stronger after the first dose versus the second dose.<h4>Interpretation</h4>In this study in whole blood, innate and adaptive immune transcripts were upregulated as early as one and seven days post-Ad26.COV2.S, respectively. These findings add to the limited data on innate immune responses to adenovirus-based vaccines in a clinical setting and contribute to understanding the mechanisms behind the adaptive immune responses that may contribute to protective immunity.<h4>Funding</h4>This study was funded by Johnson & Johnson Innovative Medicine.