Identification of T-Cell Epitopes Using a Combined In-Silico and Experimental Approach in a Mouse Model for SARS-CoV-2

Induction of Superior Systemic and Mucosal Protective Immunity to SARS-CoV-2 by Nasal Administration of a VSV-ΔG-Spike Vaccine

The emergence of rapidly spreading variants of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) poses a major challenge to vaccines' protective efficacy. Intramuscular (IM) vaccine administration induces short-lived immunity but does not prevent infection and transmission. New vaccination strategies are needed to extend the longevity of vaccine protection, induce mucosal and systemic immunity and prevent viral transmission. The intranasal (IN) administration of the VSV-ΔG-spike vaccine candidate directly to mucosal surfaces yielded superior mucosal and systemic immunity at lower vaccine doses. Compared to IM vaccination in the K18-hACE2 model, IN vaccination preferentially induced mucosal IgA and T-cells, reduced the viral load at the site of infection, and ameliorated disease-associated brain gene expression. IN vaccination was protective even one year after administration. As most of the world population has been vaccinated by IM injection, we demonstrate the potential of a heterologous IM + IN vaccination regimen to induce mucosal immunity while maintaining systemic immunity. Furthermore, the IM + IN regimen prevented virus transmission in a golden Syrian hamster co-caging model. Taken together, we show that IN vaccination with VSV-ΔG-spike, either as a homologous IN + IN regimen or as a boost following IM vaccination, has a favorable potential over IM vaccination in inducing efficient mucosal immunity, long-term protection and preventing virus transmission.

mRNA-LNP vaccine-induced CD8+ T cells protect mice from lethal SARS-CoV-2 infection in the absence of specific antibodies

The role of CD8+ T cells in SARS-CoV-2 pathogenesis or mRNA-LNP vaccine-induced protection from lethal COVID-19 is unclear. Using mouse-adapted SARS-CoV-2 virus (MA30) in C57BL/6 mice, we show that CD8+ T cells are unnecessary for the intrinsic resistance of female or the susceptibility of male mice to lethal SARS-CoV-2 infection. Also, mice immunized with a di-proline prefusion-stabilized full-length SARS-CoV-2 Spike (S-2P) mRNA-LNP vaccine, which induces Spike-specific antibodies and CD8+ T cells specific for the Spike-derived VNFNFNGL peptide, are protected from SARS-CoV-2 infection-induced lethality and weight loss, while mice vaccinated with mRNA-LNPs encoding only VNFNFNGL are protected from lethality but not weight loss. CD8+ T cell depletion ablates protection in VNFNFNGL but not in S-2P mRNA-LNP-vaccinated mice. Therefore, mRNA-LNP vaccine-induced CD8+ T cells are dispensable when protective antibodies are present but essential for survival in their absence. Hence, vaccine-induced CD8+ T cells may be critical to protect against SARS-CoV-2 variants that mutate epitopes targeted by protective antibodies.

Essential role for Batf3-dependent dendritic cells in regulating CD8 T-cell response during SARS-CoV-2 infection

SARS-CoV-2 infection elicits robust CD8 T-cell responses, yet the identity of the mechanisms playing dominant roles in initiating the virus-specific CD8 T-cell responses are largely unknown. In the present study, we interrogate the contribution of the cDC1 subset to SARS-CoV-2-specific CD8 T-cell immunity. For this purpose, we used a novel murine line which combines the SARS-CoV-2 susceptible K18-hACE2 transgenic and the Batf3 deficient mice which lack the cDC1 subset. We demonstrate that in the absence of cDC1, viral-specific CD8 T-cell responses were severely impaired both in the draining lymph node as well as in the lungs, during the effector phase of SARS-CoV-2 infection. Furthermore, SARS-CoV-2 specific memory CD8 T-cells in the lungs and spleens were also significantly impacted, whereas humoral responses, as well as CD4 T-cells were not affected. Additionally, we demonstrate that the absence of cDC1 subset, and the consequent impaired CD8 T-cell responses, resulted in significant increase in SARS-CoV-2 viral load in the lungs. The conclusions of the study were further independently corroborated in an additional COVID-19 murine model consisting infection with a mouse-adapted SARS-CoV-2 virus. These results underscore a specific role for Batf3-dependent DC in regulating SARS-CoV-2 specific CD8 T-cell responses and may contribute to future vaccine design and immunization strategies.