Adenosine deaminase augments SARS-CoV-2 specific cellular and humoral responses in aged mouse models of immunization and challenge.

Despite numerous clinically available vaccines and therapeutics, aged patients remain at increased risk for COVID-19 morbidity. Furthermore, various patient populations, including the aged can have suboptimal responses to SARS-CoV-2 vaccine antigens. Here, we characterized vaccine-induced responses to SARS-CoV-2 synthetic DNA vaccine antigens in aged mice. Aged mice exhibited altered cellular responses, including decreased IFNγ secretion and increased TNFα and IL-4 secretion suggestive of TH2-skewed responses. Aged mice exhibited decreased total binding and neutralizing antibodies in their serum but significantly increased TH2-type antigen-specific IgG1 antibody compared to their young counterparts. Strategies to enhance vaccine-induced immune responses are important, especially in aged patient populations. We observed that co-immunization with plasmid-encoded adenosine deaminase (pADA)enhanced immune responses in young animals. Ageing is associated with decreases in ADA function and expression. Here, we report that co-immunization with pADA enhanced IFNγ secretion while decreasing TNFα and IL-4 secretion. pADA expanded the breadth and affinity SARS-CoV-2 spike-specific antibodies while supporting TH1-type humoral responses in aged mice. scRNAseq analysis of aged lymph nodes revealed that pADA co-immunization supported a TH1 gene profile and decreased FoxP3 gene expression. Upon challenge, pADA co-immunization decreased viral loads in aged mice. These data support the use of mice as a model for age-associated decreased vaccine immunogenicity and infection-mediated morbidity and mortality in the context of SARS-CoV-2 vaccines and provide support for the use of adenosine deaminase as a molecular adjuvant in immune-challenged populations.

Anti‐S2 Protection in COVID‐19 Infection and SARS‐CoV‐2 Spike Vaccination

The overall goal of this project is to define the magnitude, quality, and duration of the primary immune response elicited against SARS‐CoV‐2 Spike by measuring domain‐specific antibody abundance and binding characteristics in plasmas after infection and vaccination. This investigation has enabled initiation of the screening of convalescent plasma polyclonal antibody (pAb) abundance and specificity through the IMPACC (Immunophenotyping Assessment in a COVID‐19 Cohort) at Drexel U College of Medicine (DUCOM) in collaboration with Tower Health Hospitals. We measured the active concentration of pAbs specific for RBD, S1 and S2 domains using SPR (surface plasmon resonance) molecular interaction analysis. By adopting a kinetic format, a complementary SPR analysis step was optimized to determine the binding rates and affinities of elicited antibodies targeting each domain of the Spike using the same plasma dilution aliquot. Most importantly, we found that the abundance of S2 reactive antibodies was comparable to that of anti‐S1 and RBD in convalescent plasmas. Plasmas obtained up to 6 months post‐vaccination are also becoming available through the TTC (Vaccination TetraCore cohort) assessment at DUCOM, and screening for these has demonstrated that anti‐S2 pAbs are also elicited, though intriguingly in lower abundance than after infection. To assess the importance anti‐S2 antibodies from convalescent plasmas, we purified anti‐S2 fractions by an SPR‐based microaffinity method and used the recovered antibodies in pseudovirus infection inhibition assays of ACE2 expressing cells to measure neutralization activity. Evidence for sustained generation of S2 antibodies up to 6 months post‐infection and occurrence of neutralizing anti‐S2 pAbs has begun to emerge with the possibility that antibodies targeting the S2 domain of the SARS‐CoV‐2 spike protein complex could provide pan‐coronavirus protection against COVID‐19, emerging variants, and other coronaviruses with conserved spike structures. Targeting the more conserved fusion machinery in the virus spike ultimately can lead to therapeutic antibodies or small molecule inhibitors effective on escape variants that occur mainly in S1 as well as other coronaviruses.

The Case for S2: The Potential Benefits of the S2 Subunit of the SARS-CoV-2 Spike Protein as an Immunogen in Fighting the COVID-19 Pandemic.

As COVID-19 cases continue to rise, it is imperative to learn more about antibodies and T-cells produced against the causative virus, SARS-CoV-2, in order to guide the rapid development of therapies and vaccines. While much of the current antibody and vaccine research focuses on the receptor-binding domain of S1, a less-recognized opportunity is to harness the potential benefits of the more conserved S2 subunit. Similarities between the spike proteins of both SARS-CoV-2 and HIV-1 warrant exploring S2. Possible benefits of employing S2 in therapies and vaccines include the structural conservation of S2, extant cross-reactive neutralizing antibodies in populations (due to prior exposure to common cold coronaviruses), the steric neutralization potential of antibodies against S2, and the stronger memory B-cell and T-cell responses. More research is necessary on the effect of glycans on the accessibility and stability of S2, SARS-CoV-2 mutants that may affect infectivity, the neutralization potential of antibodies produced by memory B-cells, cross-reactive T-cell responses, antibody-dependent enhancement, and antigen competition. This perspective aims to highlight the evidence for the potential advantages of using S2 as a target of therapy or vaccine design.