Nanograms of SARS-CoV-2 Spike Protein Delivered by Exosomes Induce Potent Neutralization of Both Delta and Omicron Variants

Abstract

Exosomes are emerging as potent and safe delivery carriers for use in vaccinology and therapeutics. A better vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is needed to provide improved, broader, longer lasting neutralization of SARS-CoV-2, a more robust T cell response, enable widespread global usage, and further enhance the safety profile of vaccines given the likelihood of repeated booster vaccinations. Here, we use Capricor's StealthXTM platform to engineer exosomes to express native SARS-CoV-2 spike Delta variant (STX-S) protein on the surface for the delivery of a protein-based vaccine for immunization against SARS-CoV-2 infection. The STX-S vaccine induced a strong immunization with the production of a potent humoral immune response as demonstrated by high levels of neutralizing antibody not only against the delta SARS-CoV-2 virus but also two Omicron variants (BA.1 and BA.5), providing broader protection than current mRNA vaccines. Additionally, both CD4+ and CD8+ T cell responses were increased significantly after treatment. Quantification of spike protein by ELISA showed that only nanograms of protein were needed to induce a potent immune response. This is a significantly lower dose than traditional recombinant protein vaccines with no adjuvant required, which makes the StealthXTM exosome platform ideal for the development of multivalent vaccines with a better safety profile. Importantly, our exosome platform allows novel proteins, or variants in the case of SARS-CoV-2, to be engineered onto the surface of exosomes in a matter of weeks, comparable with mRNA vaccine technology, but without the cold storage requirements. The ability to utilize exosomes for cellular delivery of proteins, as demonstrated by STX-S, has enormous potential to revolutionize vaccinology by rapidly facilitating antigen presentation at an extremely low dose resulting in a potent, broad antibody response.

Multivalent Exosome based protein vaccine: a “mix and match” approach to epidemic viruses’ challenges

“…Here we apply the STX technology to produce a multivalent protein-based exosome delivered vaccine, against both Influenza and SARS-CoV-2. Previously, we demonstrated that STX-S and STX-N can elicit robust humoral and cellular immune responses against different variants of SARS-CoV-2 viruses [5,6]. Similarly in the present study, monovalent STX-H3 vaccination induced both IgG and T-cell responses against H3.…”

“…Response was comparable to previous studies using single injection of either STX-H3 (Fig. 2) or STX-S [5,6] To characterize the T-cell response to the STX-H3-S cocktail vaccine, antigen-specific T-cell responses were measured by ELISpot (Fig. 3).…”

“…We have previously showed that our Stealth-X TM platform can easily and rapidly provide a multiprotein-based vaccine delivered by exosomes because of its easy scale-up manufacturing process, and can produce a strong antibody response, demonstrated by neutralizing antibodies and a strong T-cell response with a minimum number of injections [5,6]. The platform allows multiplexing: because of the small amount of protein needed to induce an immune response, exosomes carrying different antigens can be individually prepared and subsequently combined according to the desired dose.…”

“…1A and 1B, >90% of the STX-H3 cells expressed H3. STX-H3 exosomes were purified according to the Capricor's protocol [5,6] and further validated. Purified STX-H3 exosomes showed an average concentration of 1.63E12 particles/mL with an expected, average diameter of 141 nm and an expected polydispersity index (PDI) of 0.164.…”

“…We have previously showed that our exosome platform StealthX TM can be used to generate a novel protein-based vaccine able to elicit a potent cellular and humoral immune response against SARS-CoV-2 spike and nucleocapsid [5,6]: both antigens were combined together with no effect on the immune response to each other, suggesting no immune competition between antigens from the same virus.…”