The pandemic emergency has brought to light the need for a new generation of rapidly developed vaccines that induce longer-lasting, potent, and broader immune responses. While the mRNA vaccines played a critical role during the emergency in reducing SARS-CoV-2 hospitalization rates and deaths, more efficient approaches are needed.

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 StealthX^TM 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 StealthX^TM 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 necessary for mRNA vaccines. 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.

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 StealthX™ 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 StealthX™ 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.

Background: Endemic viruses are becoming increasingly the norm, and the development of a rapid and effective vaccine is necessary. Methods: Here, we used our StealthX^TM exosome platform to express either Influenza H3 (StealthX^TM-Hemagglutinin, STX-H3), SARS-CoV-2 Delta spike (StealthX^TM-Spike, STX-S) or respiratory syncytial virus proteins (StealthX^TM-RSV fusion protein, STX-RSV) protein on the membrane surface and facilitate their trafficking to the exosomes. Results: The administration of exosomes carrying one of the antigens by themselves resulted in a strong immune response with the production of a potent humoral and cellular immune response in mice. Interestingly, these effects were obtained with the administration of nanograms of protein and without adjuvant. We tested the possibility of manufacturing a multivalent vaccine by combining exosomes expressing either STX-H3, STX-RSV or STX-S exosomes in the same formulation, in a “mix and match” approach. Mice immunized with the cocktail vaccine showed an increased immune response against all three antigens received. Conclusions: The results further demonstrated that our STX trivalent cocktail vaccine elicited a strong immune response, and the magnitude of the responses was comparable to the single antigen administered individually. Our data show that our exosome platform has enormous potential to revolutionize vaccinology by rapidly facilitating antigen presentation, to tackle the fast-evolving viral infections.

Exosome-based vaccines represent a transformative platform in modern vaccinology, combining nanoscale delivery, biocompatibility, and potent immunogenicity. Among these, the StealthX platform developed by Capricor, Inc. has demonstrated exceptional versatility, enabling antigen presentation at nanogram level doses without the need for adjuvants. Preclinical studies using StealthX have shown strong humoral and cellular immune responses against SARS-CoV-2 variants, including Delta and Omicron, as well as broader applications against influenza and RSV antigens. The platform’s ability to accommodate multiple antigens within a single formulation addresses the challenges of viral variation and facilitates multivalent “mix-and-match” immunization strategies. This review offers an in-depth evaluation of the StealthX vaccine platform, covering the biological mechanisms underlying exosome function, the engineering approaches used to load antigens, and preclinical results demonstrated across three pivotal studies. By synthesizing current evidence, this review underscores the platform’s applicability for emerging infectious diseases and explores the strategic value of multivalent exosome-based vaccines in global immunization efforts as an emerging next-generation vaccine technology.

Arginase 1 (ARG1) deficiency (ARG1-D) is a rare genetic disorder due to loss of ARG1, the final enzyme in the urea cycle. ARG1-D hepatocytes are impaired in converting arginine into urea, resulting in elevated peripheral arginine and ammonia, which leads to progressive neurological symptoms. Current therapeutic strategies mainly focus on managing plasma arginine and ammonia level, but long-term outcomes remain poor. While no approved treatment specific for ARG1-D is available in the United States, a recombinant protein-based enzyme replacement therapy is available in Europe. Recently, extracellular vesicles (EVs) are emerging as a powerful therapeutic vehicle. By using Capricor’s StealthX^TM platform, EVs were engineered to express human ARG1 on their surface or encapsulated within. Regardless of their localization on the EV membrane, nanograms of ARG1 carried by EVs were biologically active and able to convert arginine into urea as potent as micrograms of human recombinant ARG1 (rHuArg1). Furthermore, ARG1-encapsulating EVs (STX-Arg1-in) were able to deliver ARG1 intracellularly but not EVs carrying ARG1 on their surface or rHuArg1. STX-Arg1-in EVs were further evaluated in a series of in vivo studies, and the results showed that STX-Arg1-in EVs were non-toxic and able to restore arginase activities in the liver of Arg1^−/− mice, which led to a lowered plasma arginine concentration similar to that in wild-type mice. Most importantly, Arg1-in EVs expanded the lifespan of the lethal neonatal Arg1 deficiency mouse model. Taken together, our data suggested StealthX^TM-engineered STX-Arg1-in EVs have a better safety profile due to the extremely low dosage and have great potential as a novel enzyme replacement strategy for patients suffering from ARG1-D. Significance statement: Intracellular delivery of recombinant protein and improved llifespanare endpoints of successful enzyme replacement therapy for the treatment of ARG1-D. Using the StealthX platform, a fully functional ARG1 enzyme was engineered to be carried inside of the extracellular vesicles, which allowed for the intracellular delivery of ARG1 protein in vitro and in vivo, with an improvement of lifespan in a lethal neonatal mouse model of Arg1 deficiency. More importantly, no toxicity was observed, and efficacy was achieved with a low dose, setting the base for an improved therapeutic approach.