Candidate: HDT-301 (also called repRNA-CoV2S)
Type: Alphavirus-derived replicon RNA vaccine encoding the SARS-CoV-2 spike (S) protein. The RNA replicons are formulated with Lipid InOrganic Nanoparticles (LIONs), which are designed to enhance vaccine stability, delivery, and immunogenicity.
Status: Researchers from UW Medicine, HDT Bio, and partners on July 20 published a study in Science Translational Medicine reporting that its replicating RNA vaccine HDT-301 (also called repRNA-CoV2S) produced anti-SARS-CoV-2 S protein IgG antibody isotypes indicating a Type 1 T helper cell response against SARS-CoV-2, potentially neutralizing the virus, in mice and primates with a single immunization. Effects occurred within two weeks after administration through intramuscular injection. The level of antibodies generated was comparable to those in people who are recovering from COVID-19, the researchers reported.
A prime/boost regimen induced potent T-cell responses in mice including antigen-specific responses in lung and spleen, while prime-only immunization of aged (17-month old) mice induced smaller immune responses compared to young mice—a difference that was abrogated by booster immunization, the researchers added. In nonhuman primates, prime-only immunization in one intramuscular injection site or prime/boost immunizations in five intramuscular injection sites elicited modest T cell responses and robust antibody responses. The antibody responses persisted for at least 70 days and neutralized SARS-CoV-2 at titers comparable to those in human serum samples collected from individuals convalescing from COVID-19.
“These data support further development of LION/repRNA-CoV2S as a vaccine candidate for prophylactic protection against SARS-CoV-2 infection,” the researchers concluded.
They also said they plan to advance the vaccine into Phase I human studies.
By creating a replicating RNA vaccine, investigators aim to address limitations of conventional nucleic acid vaccines, such as the need for at least two immunizations, and traditional messenger RNA vaccines formulated with lipid nanoparticles, which face obstacles of mass-production and shelf life, stated Deborah Heydenberg Fuller, PhD, professor of microbiology at UW School of Medicine and division chief of Infectious Diseases and Translational Medicine at the Washington National Primate Research Center.
The vaccine uses LIONs, next-generation nanoparticle formulations designed to protect the RNA molecule and enables in vivo delivery of the vaccine after a simple mixing step, thus enhancing its ability to provoke the desired immune reaction, and its stability, sinced the vaccine is stable at room temperature for at least one week.
The vaccine research received funding from the Washington National Primate Research Center (P51OD010425); the National Institutes of Health (75N93019C00037, 75N93019C00008, R01GM120553, HHSN272201700059C, HHSN 27220140006C, and 199 1F32AI136371); HDT Bio Corp.; a Pew Biomedical Scholars Award, and the Burroughs Wellcome Fund.
COVID-19: 200 Candidates and Counting
To navigate through the >200 potential therapeutic and vaccine options for COVID-19, GEN has grouped the candidates into four broad categories based on their developmental and (where applicable) clinical progress:
● FRONT RUNNER – the most promising therapeutics/vaccines based on clinical progress, favorable data or both.
● DEFINITELY MAYBE – earlier phases with promising partners, or more advanced candidates in development that have generated uneven data.
● KEEPING AN EYE ON… – interesting technology, attracting notable partners, or both, but preliminary data.
● TOO SOON TO TELL – longshots pending additional experimental and/or clinical data.
GEN has also tagged the most common treatment types: