Studies of the SARS-CoV-2 Spike Protein

Division Of Basic Sciences - Nci

Investigators

Linked publications & trials

Abstract

In vivo vaccine studies in macaques and hamsters: Rhesus macaques have been primed IM with S1 spike protein in different adjuvants and boosted systemically with spike in alum or mucosally intranasally with spike in nanoparticles (NPs) with IL-15 and TLR ligand adjuvants. We have found and published that NPs containing S1 spike protein delivered intranasally can boost macaques primed IM with S1 in alum and result in better protection against respiratory challenge with SARS-CoV-2 than can the IM vaccine alone even though the S1-binding and neutralizing antibody levels are lower. Other mechanisms must play a role and we have found correlations with mucosal IgA, dimeric IgA, and type I interferon production in the lung, and certain types of myeloid cells. We then tested a mucosal NP boost with the B1.351 (South African) variant S1 protein to protect against this SARS-CoV-2 variant in macaques. The beta variant was the most difficult to neutralize before the appearance of the omicron variant, which had not been identified at the time we started this second study. The beta variant mucosal NP vaccine, given 1 full year after the animals had last been boosted systemically or mucosally with the original Wuhan strain, induced a 3-log increase in both IgG binding antibody in both the serum and bronchoalveolar lavage fluid (BAL, representing response in the lung). Further, it boosted the titer to the original Wuhan strain as much as to the beta variant. Neutralizing antibody titers were also similar against both virus variants. IgA and dimeric IgA to both strains were also increased. This suggests a role for original antigenic sin in determining the fine specificity of antibodies at the time of first primary vaccination. When challenged, the animals were well protected against intranasal challenge with the beta variant SARS-CoV-2. Thus, a variant intranasal vaccine can induce strong protective immunity in the lungs and nasal cavity and eliminate virus from these sites. These studies suggest that a human intranasal NP COVID-19 vaccine given to people who had been previously immunized systemically with one of the approved vaccines, could improve protection against infection and reduce the risk of forward transmission to others by reducing intranasal virus, which is especially a problem with the delta and omicron variants This second NHP study was also published. In addition, three more studies have been carried out in a hamster model, as hamsters get COVID disease more like humans. The intranasal vaccine was able to markedly reduce weight loss in the immunized animals compared to controls, implying the prevention of disease, and reduce virus particles in the lungs. It could also more effectively reduce virus in the oropharynx of hamsters than the S1 protein in alum, an important accomplishment that would be expected to reduce forward transmission. To test this hypothesis, we have now done a forward transmission study in hamsters (now published). In this study, we also examined priming with one of the licensed mRNA vaccines to compare. Groups of hamsters were vaccinated first IM with the Moderna mRNA spike protein vaccine. Then half of them were boosted with the same mRNA vaccine IM, but the other half were boosted with the nasal NP S1 vaccine incorporating the CpG/PolyI:C and IL15 adjuvants. All the animals were challenged with SARS-CoV-2, including a group that was not immunized at all. Then, they were cohoused with naive hamsters separated only by a screen that allowed air flow between them but did not allow touching or sharing of secretions. The naive hamsters were then monitored for infection. The intranasal nanoparticle vaccine boost was substantially superior to a second IM dose of the mRNA vaccine in preventing forward transmission to the co-housed naive hamsters! This finding is critical as it demonstrates that an intranasal boost with an effective vaccine such as the one we have developed is needed to prevent COVID-19 infections from spreading, the key public health goal. Gender effects: In the hamsters, we observed that female hamsters were better protected against SARS-CoV-2 infection and disease than males, but reagents are not available to study the hamster immune response in detail. To determine the mechanism, we carried out similar studies in mice and confirmed the gender difference in mice as well. The vaccine elicited strong systemic, nasal and BAL IgA responses and local lung T cell responses in two mouse strains, all in a sex-biased manner, and correlating with some myeloid cells. Suppressive myeloid cells higher in males may contribute to the difference. In wild type B6 mice, we have also immunized with recombinant spike protein S1, S1+S2, or RBD in several different adjuvants to determine the best formulation. The best combination so far is S1 antigen with IL-15 + ligands for TLR3 and 9, for both antibody and T cell responses, but the runner up was S1 with GM-CSF and IL-12. Studies are in progress to determine which components contribute the most to protection and whether they induce qualitatively different types of immune responses. The DNA vaccine with spike protein coupled to a chemokine has been constructed and initial results show that it can induce a strong CD8 T cell response. Human cell lines: We have received the immortalized human lung epithelial cell lines, which express ACE2, from John Minna at UTSW, as well as some of his non-small-cell lung cancer cell lines that also express ACE2. We have obtained an antibody to ACE2 to verify expression. Initial results show that omega-3 fatty acids and cholesterol differentially affect ACE2 expression on lung cancer cells as well as TMPRSS2 expression and may help explain how diet and obesity as well as lung cancer can affect susceptibility to SARS-CoV-2.