A self-amplifying RNA vaccine against COVID-19 with long-term room-temperature stability

Abstract

mRNA vaccines were the first to be authorized for use against SARS-CoV-2 and have since demonstrated high efficacy against serious illness and death. However, limitations in these vaccines have been recognized due to their requirement for cold storage, short durability of protection, and lack of access in low-resource regions. We have developed an easily-manufactured, potent self-amplifying RNA (saRNA) vaccine against SARS-CoV-2 that is stable at room temperature. This saRNA vaccine is formulated with a nanostructured lipid carrier (NLC), providing enhanced stability, improved manufacturability, and protection against degradation. In preclinical studies, this saRNA/NLC vaccine induced strong humoral immunity, as demonstrated by high pseudovirus neutralization titers to the Alpha, Beta, and Delta variants of concern and induction of long-lived bone marrow-resident antibody secreting cells. Robust Th1-biased T-cell responses were also observed after prime or homologous prime-boost in mice. Notably, the saRNA/NLC platform demonstrated thermostability at room temperature for at least 6 months when lyophilized. Taken together, this saRNA delivered by NLC represents a potential improvement in RNA technology that could allow wider access to RNA vaccines for the current COVID-19 and future pandemics.

Heterologous saRNA Prime, DNA Dual-Antigen Boost SARS-CoV-2 Vaccination Elicits Robust Cellular Immunogenicity and Cross-Variant Neutralizing Antibodies

“…The heterologous vaccine regimens resulted in lower capability of neutralizing Omicron BA.1 variant, reported to be more resistant to neutralization than the BA.2 variant (41) now displacing BA.1. This neutralization capability reflects the strength of humoral responses to the AAHI-SC2 vaccine and is consistent with reported findings for this vaccine (13). The validity of such pseudovirus-based assay results and their correlation to live virus assays has been reported elsewhere (42,43).…”

“…The RNA is generated by T7 promoter-mediated in vitro transcription using a linearized DNA template. In vitro transcription is performed using an in house-optimized protocol (13,36,37) using T7 polymerase, RNase inhibitor, and pyrophosphatase enzymes. The DNA plasmid is digested with DNase I, and the RNA is capped by vaccinia capping enzyme, guanosine triphosphate, and S-adenosyl-methionine.…”

“…Despite the promising findings with the AdS+N vaccine candidate, we wish to continue to investigate vaccine regimens with the potential to maximize immune responsesboth humoral and cellular. One such approach is by heterologous vaccination utilizing multiple nucleic acid-based vaccine platforms, such as ImmunityBio's hAd5-vectored DNA vaccine and the Access to Advanced Health Institute's (AAHI) RNA-based vaccine (13). Heterologous vaccination using vaccine constructs expressing the same or different antigens vectored by different platforms has previously been reported to significantly increase immune responses (14)(15)(16), and specifically for COVID-19 vaccines, heterologous prime-boost regimens including the available mRNA and adenovirus-based vaccines elicit humoral and cellular responses in human subjects that are at least as good as or better than homologous vaccination (17)(18)(19)(20).…”

“…To assess the potential for enhanced immune responses by heterologous vaccination, we tested prime > boost combinations of the AdS+N vaccine with a self-amplifying and self-adjuvanted S(wt) RNA-based vaccine (AAHI-SC2) delivered in a nanostructured lipid carrier (NLC) (21,22) that has recently been reported to elicit robust, virus-neutralizing humoral responses, establishment of long-lived antibody-secreting plasma cell populations, and polyfunctional CD4+ and CD8+ T-cell responses after both prime and prime-boost regimens in C57BL/6 mice (13). The NLC stabilizes the self-amplifying RNA (23)(24)(25) and delivers it to cells, where the vaccine RNA is then amplified and S protein is expressed.…”