Vaccine-induced protection against SARS-CoV-2 requires IFN-γ-driven cellular immune response.

The overall success of worldwide mass vaccination in limiting the negative effect of the COVID-19 pandemics is inevitable, however, recent SARS-CoV-2 variants of concern, especially Omicron and its sub-lineages, efficiently evade humoral immunity mounted upon vaccination or previous infection. Thus, it is an important question whether these variants, or vaccines against them, induce anti-viral cellular immunity. Here we show that the mRNA vaccine BNT162b2 induces robust protective immunity in K18-hACE2 transgenic B-cell deficient (µMT) mice. We further demonstrate that the protection is attributed to cellular immunity depending on robust IFN-γ production. Viral challenge with SARS-CoV-2 Omicron BA.1 and BA.5.2 sub-variants induce boosted cellular responses in vaccinated µMT mice, which highlights the significance of cellular immunity against the ever-emerging SARS-CoV-2 variants evading antibody-mediated immunity. Our work, by providing evidence that BNT162b2 can induce significant protective immunity in mice that are unable to produce antibodies, thus highlights the importance of cellular immunity in the protection against SARS-CoV-2.

Bacillus Calmette-Guérin-induced trained immunity protects against SARS-CoV-2 challenge in K18-hACE2 mice.

SARS-CoV-2 has been confirmed in over 450 million confirmed cases since 2019. Although several vaccines have been certified by the WHO and people are being vaccinated on a global scale, it has been reported that multiple SARS-CoV-2 variants can escape neutralization by antibodies, resulting in vaccine breakthrough infections. Bacillus Calmette-Guérin (BCG) is known to induce heterologous protection based on trained immune responses. Here, we investigated whether BCG-induced trained immunity protected against SARS-CoV-2 in the K18-hACE2 mouse model. Our data demonstrate that i.v. BCG (BCG-i.v.) vaccination induces robust trained innate immune responses and provides protection against WT SARS-CoV-2, as well as the B.1.617.1 and B.1.617.2 variants. Further studies suggest that myeloid cell differentiation and activation of the glycolysis pathway are associated with BCG-induced training immunity in K18-hACE2 mice. Overall, our study provides the experimental evidence that establishes a causal relationship between BCG-i.v. vaccination and protection against SARS-CoV-2 challenge.

Intradermal delivery of mRNA using cryomicroneedles.

Microneedles can realize the intradermal and transdermal delivery of drugs. However, most conventional microneedles made of metal, polymer and ceramics are unsuitable for the delivery of mRNA drugs that are fragile and temperature-sensitive. This study explores the usage of cryomicroneedles (CryoMNs) for the intradermal delivery of mRNA molecules. Taking luciferase mRNA as an example, we first optimize the formulation of CryoMNs to maximize mRNA stability. Later, in the mouse model, we compare the delivery efficiency with the conventional subcutaneous injection for both the luciferase mRNA and COVID-19 Comirnaty mRNA vaccines, where CryoMNs delivered mRNA vaccines successfully induce specific B-cell antibody, neutralizing activity and T-cell responses. STATEMENT OF SIGNIFICANCE: mRNA vaccines are fragile and temperature-sensitive, so they are mainly delivered by intramuscular injection that often causes pain and requires clinical expertise to immunize patients. Microneedles permit convenient, fast and safe vaccination. However, existing microneedle platforms are ineffective to protect the integrity of mRNA vaccines in fabrication, storage, and administration. This work utilizes cryomicroneedles (CryoMNs) technology to intradermally deliver mRNA. In the mouse model, CryoMNs are compared with the subcutaneous injection for the delivery efficiency of both the luciferase mRNA and COVID-19 Comirnaty mRNA vaccines, where CryoMNs delivered mRNA vaccines successfully produce specific B-cell antibodies, T-cell responses, and neutralizing activity. This work is expected to provide a new delivery strategy for the emerging mRNA therapeutics.

A novel linker-immunodominant site (LIS) vaccine targeting the SARS-CoV-2 spike protein protects against severe COVID-19 in Syrian hamsters.

The Coronavirus Disease 2019 (COVID-19) pandemic is unlikely to abate until sufficient herd immunity is built up by either natural infection or vaccination. We previously identified ten linear immunodominant sites on the SARS-CoV-2 spike protein of which four are located within the RBD. Therefore, we designed two linkerimmunodominant site (LIS) vaccine candidates which are composed of four immunodominant sites within the RBD (RBD-ID) or all the 10 immunodominant sites within the whole spike (S-ID). They were administered by subcutaneous injection and were tested for immunogenicity and in vivo protective efficacy in a hamster model for COVID-19. We showed that the S-ID vaccine induced significantly better neutralizing antibody response than RBD-ID and alum control. As expected, hamsters vaccinated by S-ID had significantly less body weight loss, lung viral load, and histopathological changes of pneumonia. The S-ID has the potential to be an effective vaccine for protection against COVID-19.