Adjuvant combination for SARS-CoV-2 vaccine for the elderly

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PROJECT SUMMARY Severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2) is currently causing the coronavirus disease (COVID-19) in pandemic proportion. According to John Hopkins university data tracker, there were 120,217,175 global cases and 2,660,456 deaths worldwide on March 15, 2021. The disease ranges from asymptomatic to lethal, with the elderly patients most severely affected. Finding a successful strategy to protect most vulnerable aged population is vital. However, it is possible that protein-based vaccines will not be as effective in individuals over 65 years of age as in healthy younger adults. There are also indications that RNA vaccines that are currently used under emergency authorization elicit vaccine responses appear weaker in elderly . Protein-based vaccines are considered safe but they lack the ability to elicit Th1 type of responses especially needed for protection in aged populations. Recently we developed a novel combination adjuvant for use with a licensed influenza subunit vaccine in high-risk aged population and tested it in an aged mouse model. The formulation combines an agonist of the stimulator of interferon gene (STING) pathway 2,3’-cGAMP and saponin Quil-A. Activation of the STING pathway leads to production of interferons and cytokines in target cells, and enhances development of the immune response to vaccine antigens, while saponins stimulate both the Th1 immune response and cytotoxic T lymphocyte production against protein antigens. By co-delivering these two compounds, cGAMP and Quil-A, with the vaccine we combined their adjuvant potential and improved the protective immunity of influenza vaccine in the aged mice more effectively than either a 4x antigen dose or MF-59-like adjuvant, which are two current vaccination options for persons over 65 years of age. We propose that this combination will also potentiate the protective responses to a candidate SARS-CoV-2 vaccine and will test this in aged mice. We will test this hypothesis using both sexes of aged mice. As saponins have been previously shown to increase the duration of immune response we will also determine the persistence of neutralizing antibodies in vaccinated animals. Although we do not anticipate reactogenicity of this formulation based on our experience, we will also test if a novel and safer saponin Titerquil 1-0-5-5 can be used instead of Quil-A. The results will be directly relevant for development of SARS-CoV-2 protein vaccines for high-risk aged populations. The combination adjuvant can be directly added to existing vaccines.