T cell and antibody responses induced by a single dose of ChAdOx1 nCoV-19 (AZD1222) vaccine in a phase 1/2 clinical trial

A single dose of the ChAdOx1 nCoV-19 vaccine elicits antibodies and cytokine-producing T cells that might help control or prevent SARS-CoV-2 infection. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of Coronavirus Disease 2019 (COVID-19), has caused a global pandemic, and safe, effective vaccines are urgently needed(1). Strong, Th1-skewed T cell responses can drive protective humoral and cell-mediated immune responses(2) and might reduce the potential for disease enhancement(3). Cytotoxic T cells clear virus-infected host cells and contribute to control of infection(4). Studies of patients infected with SARS-CoV-2 have suggested a protective role for both humoral and cell-mediated immune responses in recovery from COVID-19 (refs. (5,6)). ChAdOx1 nCoV-19 (AZD1222) is a candidate SARS-CoV-2 vaccine comprising a replication-deficient simian adenovirus expressing full-length SARS-CoV-2 spike protein. We recently reported preliminary safety and immunogenicity data from a phase 1/2 trial of the ChAdOx1 nCoV-19 vaccine (NCT04400838)(7) given as either a one- or two-dose regimen. The vaccine was tolerated, with induction of neutralizing antibodies and antigen-specific T cells against the SARS-CoV-2 spike protein. Here we describe, in detail, exploratory analyses of the immune responses in adults, aged 18-55 years, up to 8 weeks after vaccination with a single dose of ChAdOx1 nCoV-19 in this trial, demonstrating an induction of a Th1-biased response characterized by interferon-gamma and tumor necrosis factor-alpha cytokine secretion by CD4(+) T cells and antibody production predominantly of IgG1 and IgG3 subclasses. CD8(+) T cells, of monofunctional, polyfunctional and cytotoxic phenotypes, were also induced. Taken together, these results suggest a favorable immune profile induced by ChAdOx1 nCoV-19 vaccine, supporting the progression of this vaccine candidate to ongoing phase 2/3 trials to assess vaccine efficacy.

Automated summary

A single dose of the ChAdOx1 nCoV-19 vaccine can induce favorable immune responses that may help control or prevent SARS-CoV-2 infection.