Effects of adjuvants in a rabies-vectored Ebola virus vaccine on protection from surrogate challenge.

Ebola virus is the primary contributor to the global threat of filovirus severe hemorrhagic fever, and Ebola virus disease has a case fatality rate of 50-90%. An inactivated, bivalent filovirus/rabies virus vaccine, FILORAB1, consists of recombinant rabies virus virions expressing the Ebola virus glycoprotein. FILORAB1 is immunogenic and protective from Ebola virus challenge in mice and non-human primates, and protection is enhanced when formulated with toll-like receptor 4 agonist Glucopyranosyl lipid adjuvant (GLA) in a squalene oil-in-water emulsion (SE). Through an adjuvant comparison in mice, we demonstrate that GLA-SE improves FILORAB1 efficacy by activating the innate immune system and shaping a Th1-biased adaptive immune response. GLA-SE adjuvanted mice and those adjuvanted with the SE component are better protected from surrogate challenge, while Th2 alum adjuvanted mice are not. Additionally, the immune response to FILORAB1 is long-lasting, as exhibited by highly-maintained serum antibody titers and long-lived cells in the spleen and bone marrow.

Inactivated rabies-vectored SARS-CoV-2 vaccine provides long-term immune response unaffected by vector immunity.

The objective of this study is to further analyze recombinant rabies virus-vectored SARS-CoV-2 vaccine, CORAVAX, as an effective COVID-19 vaccine strategy. CORAVAX has proven immunogenic and protective against SARS-CoV-2 in animal models. Here, we have screened adjuvants for the highest quality antibody titers, negated the concern of pre-existing rabies-vector immunity, and established its potential as a long-term COVID-19 vaccine. We have tested toll-like receptor 4 (TLR4) agonists, inflammasome activators, and alum adjuvants in CORAVAX and found TLR4-activating MPLA-AddaVax to have the greatest potential. We followed the humoral immune response to CORAVAX in mice with pre-existing rabies virus immunity and saw no significant differences compared to naive mice. We then followed the immune response to CORAVAX over several months and 1-year post-immunization. Mice maintained high antigen-specific serum antibody titers as well as long-lived antibody-secreting cells in the spleen and bone marrow. We believe this rabies-vector strategy combats the problem of waning immunity of other COVID-19 vaccines. These results together support CORAVAX's potential during the ongoing COVID-19 pandemic.

Tetravalent Rabies-Vectored Filovirus and Lassa Fever Vaccine Induces Long-term Immunity in Nonhuman Primates.

BACKGROUND: The objective of this study is to evaluate the immunogenicity of adjuvanted monovalent rabies virus (RABV)-based vaccine candidates against Ebola virus (FILORAB1), Sudan virus (FILORAB2), Marburg virus (FILORAB3), Lassa virus (LASSARAB1), and combined trivalent vaccine candidate (FILORAB1-3) and tetravalent vaccine candidate (FILORAB1-3 and LASSARAB) in nonhuman primates. METHODS: Twenty-four Macaca fascicularis were randomly assigned into 6 groups of 4 animals. Each group was vaccinated with either a single adjuvanted vaccine, the trivalent vaccine, or the tetravalent vaccine at days 0 and 28. We followed the humoral immune responses for 1 year by antigen-specific enzyme-linked immunosorbent assays and RABV neutralization assays. RESULTS: High titers of filovirus and/or Lassa virus glycoprotein-specific immunoglobulin G were induced in the vaccinated animals. There were no significant differences between immune responses in animals vaccinated with single vaccines vs trivalent or tetravalent vaccines. In addition, all vaccine groups elicited strong rabies neutralizing antibody titers. The antigen-specific immune responses were detectable for 1 year in all groups. CONCLUSIONS: In summary, this study shows the longevity of the immune responses up to 365 days for a pentavalent vaccine-against Ebola virus, Sudan virus, Marburg virus, Lassa virus, and RABV-using a safe and effective vaccine platform.