Studies of the SARS-CoV-2 Spike Protein

Division Of Basic Sciences - Nci

Investigators

Linked publications, trials & patents

Abstract

In vitro studies in macaque bronchioalveolar lavage cells: We found some effects in vitro on these cells of stimulating them with recombinant spike protein to affect expression of ACE2 and of interferons, that may play a role in infection. Little effect was seen on other cytokine or chemokine production. We recently published that S1 protein acts on macaque lung bronchoalveolar lavage cells to downregulate expression of the ACE2 receptor and also inhibit type I interferon production. Type I interferons have been shown to be essential for protection against SARS-CoV-2, and ACE2, besides being a receptor for spike protein, also protects the lung against respiratory viruses by cleaving angiotensin II, so downregulating these could worsen COVID-19. In vivo vaccine studies in macaques: Rhesus macaques have been primed IM with spike in different adjuvants and boosted systemically with spike in alum or mucosally intranasally with spike in nanoparticles with IL-15 and TLR ligand adjuvants. We have found and published that nanoparticles 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 nanoparticle 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. The beta variant mucosal nanoparticle 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 nanoparticle 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 new delta and omicron variants This second NHP study was also published. In addition, two more studies were 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. In vivo studies in mice: ACE2-transgenic mice have been purchased despite delays, and are being bred. In wild type B6 mice, we have 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. Studies are in progress to determine which components contribute the most to protection. 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.