Strong CD4+ T-Cell Responses to Ancestral and Variant Spike Proteins Are Established by NVX-CoV2373 Severe Acute Respiratory Syndrome Coronavirus 2 Primary Vaccination

BACKGROUND: NVX-CoV2373 is an efficacious coronavirus disease 2019 (COVID-19) vaccine comprising full-length recombinant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (rS) glycoprotein and Matrix-M adjuvant. Phase 2 of a randomized, placebo-controlled, phase 1/2 trial in healthy adults (18-84 years of age) previously reported good safety/tolerability and robust humoral immunogenicity. METHODS: Participants were randomized to placebo or 1 or 2 doses of 5-µg or 25-µg rS with 50 µg Matrix-M adjuvant 21 days apart. CD4+ T-cell responses to SARS-CoV-2 intact S or pooled peptide stimulation (with ancestral or variant S sequences) were measured via enzyme-linked immunosorbent spot assay and intracellular cytokine staining. RESULTS: A clearly discernable spike antigen-specific CD4+ T-cell response was induced after 1 dose, but markedly enhanced after 2 doses. Counts and fold increases in cells producing Th1 cytokines exceeded those secreting Th2 cytokines, although both phenotypes were clearly present. Interferon-γ responses to rS were detected in 93.5% of 2-dose 5-µg recipients. A polyfunctional CD4+ T-cell response was cross-reactive and of equivalent magnitude to all tested variants, including Omicron BA.1/BA.5. CONCLUSIONS: NVX-CoV2373 elicits a moderately Th1-biased CD4+ T-cell response that is cross-reactive with ancestral and variant S proteins after 2 doses. CLINICAL TRIALS REGISTRATION: NCT04368988.