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Low-Dose Covid-19 Vaccine Generates Strong Immune Response

Exosome illustration

Exosome illustration (NIH)

27 Apr. 2023. Ultra-low quantities of an experimental Covid-19 protein vaccine delivered in synthetic cell components are shown in lab animals to generate strong immune responses. Results of the preclinical study by a team from Capricor Therapeutics Inc. in San Diego appear in the 24 Apr. 2023 issue of the journal Microbiology Spectrum.

Capricor Therapeutics is a biotechnology company developing treatments with engineered cells or cellular components for Duchenne muscular dystrophy, a rare genetic disorder in boys resulting in progressive muscle degeneration, and infectious diseases. For infectious diseases, Capricor harnesses exosomes, tiny bubble-like components secreted by cells with DNA, RNA, or proteins from the producing cells that travel to other nearby cells in the body. Exosomes are only about 100 nanometers in size and believed to carry out many housekeeping functions for cells, but more recent research suggests they may play more active roles in promoting or limiting disease.

Capricor is designing exosomes to deliver therapeutic payloads in the interior, as well as load proteins such as antigens on the exosome surface. The first products from the company’s StealthX exosome technology are vaccines against infectious diseases that deliver multiple protective proteins, beginning with a Covid-19 vaccine. As reported by Science & Enterprise in Sept. 2016, the U.S. Department of Defense recognized the public health potential of Capricor’s exosome technology by underwriting commercial-scale expansion of the company’s exosome manufacturing process.

Two SARS-CoV-2 target proteins

Capricor says exosome vaccines have several advantages over the messenger RNA or mRNA and other engineered protein vaccines for Covid-19 developed so far. Unlike mRNA vaccines delivered with lipid nanoparticles that are toxic to some people, exosomes are self-contained and non-toxic, and do not need refrigeration or freezing for storage and transport. In addition, says the company, mRNA vaccines need periodic boosters to remain active against mutating viruses. And, says Capricor, exosome vaccines can be produced faster than conventional vaccines delivering protective proteins.

In the peer-reviewed Microbiology Spectrum paper, researchers led by Capricor’s vice-president for research Minghao Sun, tested a vaccine with engineered exosomes expressing the protein found on the SARS-CoV-2 viral spike, a target of most Covid-19 vaccines so far. But the vaccine also contains exosomes designed with the SARS-CoV-2 nucleocapsid protein, a more basic protein to the viral genome. The team tested the exosome vaccines first with only the spike or nucleocapsid protein, then combined, in lab mice and rabbits, and in tiny nanoscale doses ranging from 3 to 25 nanograms in mice, and 10 to 125 nanograms in rabbits.

The researchers tested the combined spike and nucleocapsid protein vaccine in a primary injection and two booster shots for mice and one booster shot for rabbits. In neither case, did the the team add an adjuvant to promote an immune response. The authors report no adverse effects seen in the animals’ weight, blood cells, or tissue reactions. The researchers also report strong antibody responses from the spike protein in both animal species, as well as a strong T-cell response from the nucleocapsid proteins. The nucleocapsid T-cell response, say the authors, is particularly important for added protection against a continually mutating virus.

“Exosomes offer a new approach to drug delivery with this study showing the potential to rapidly generate multivalent protein-based vaccines,” says Capricor’s CEO Linda Marbán in a company statement. Marbán adds, “The data from this study suggests that StealthX could potentially deliver a more potent vaccine with broader immunity by combining the advantages of both mRNA and recombinant protein vaccines into a potentially superior, rapidly generated, low-dose vaccine.”

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