Cutting Edge: Nucleocapsid Vaccine Elicits Spike-Independent SARS-CoV-2 Protective Immunity

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the COVID-19 pandemic. Neutralizing Abs target the receptor binding domain of the spike (S) protein, a focus of successful vaccine efforts. Concerns have arisen that S-specific vaccine immunity may fail to neutralize emerging variants. We show that vaccination with a human adenovirus type 5 vector expressing the SARS-CoV-2 nucleocapsid (N) protein can establish protective immunity, defined by reduced weight loss and viral load, in both Syrian hamsters and K18-hACE2 mice. Challenge of vaccinated mice was associated with rapid N-specific T cell recall responses in the respiratory mucosa. This study supports the rationale for including additional viral Ags in SARS-CoV-2 vaccines, even if they are not a target of neutralizing Abs, to broaden epitope coverage and immune effector mechanisms.

Figure 1.. Ad5-N vaccine confers protection against SARS-CoV-2 infection in Syrian hamsters and K18 mice.

A) Median and B) peak weight change after vaccinated hamsters were challenged 7–8 weeks later with WA SARS-CoV-2. C) Lung viral titers three days post-challenge with WA (left) or B.1.1.7 (right) SARS-CoV-2. D) Median and E) peak weight change (dashed lines represent humane endpoint), and F) survival of vaccinated K18 mice following IN WA SARS-CoV-2 challenge. Bars denote median and interquartile range *, P < 0.05; **, P < 0.01; ***, P < 0.001. Individual comparisons were analyzed using two-sided Mann–Whitney tests (A-E) using Bonferroni-Dunn correction for multiple comparisons (A, D) and survival by the log-rank test (F).

Figure 2.. Memory T cells respond to SARS-CoV-2 challenge.

A) Number of N_219–227-specific CD8 T cells 40 to 86 days after Ad5-N vaccination. B) Percent CD4 and CD8 T cells among IVneg lung or total splenocytes in isotype or T cell depleted Ad5-N vaccinated mice. C) Total N_219–227-specific CD8 T cells in IVneg lung or MedLN of Ad5-N vaccinated mice following T cell depletion. D) Four days after WA SARS-CoV-2 challenge, viral titers in lungs of naive and Ad5-N vaccinated K18 mice ± T cell depletion (left) and viral titers plotted against N_219–227-specific CD8 T cells within IVneg lung (right). E) Abundance of granzyme B+ N_219–227-specific CD8 T cells in IVneg lung or mediastinal LN and F) of total N_219–227-specific CD8 T cells within indicated compartments immediately prior (baseline) and four days after challenge. Bars denote median and interquartile range. Flow plots were gated on lymphocytes, single cells, live, CD8a IVneg cells followed by the gates indicated in each panel, except in (D) where IVpos cells were also independently evaluated*, P < 0.05; **, P < 0.01; ***, P < 0.001 as determined by a two-sided Mann–Whitney test (A-F).