According to the study, this showing the development of a DNA vaccine for Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV); which completely protects against lethal infection in ferrets. The team confirmed that ferrets immunized with DNA vaccines encoding all SFTSV proteins; showing 100% survival rate without detectable viremia and did not develop any clinical symptoms. Severe Fever with Thrombocytopenia Syndrome (SFTS) is a newly emerging tick-borne infectious disease.
The disease causes fever, severe thrombocytopenia, leukocytopenia as well as vomiting and diarrhea. Severe cases end up with organ system failure often accompanied by hemorrhages; and its mortality rate stands at 10-20%. But DNA vaccine for tick-borne disease ‘SFTS’ confers protection against lethal infection in ferrets. Although the incidence of severe fever with thrombocytopenia syndrome virus (SFTSV) infection has increased from its discovery with a mortality rate of 10–20%, no effective vaccines are currently available.
Thrombocytopenia syndrome virus
Vaccinated ferrets were completely protected from lethal SFTSV challenge without SFTSV detection in their blood, whereas all control ferrets died within 10 days’ post-infection. The team finding that anti-envelope antibodies play an important role in protective immunity, suggesting that envelope glycoproteins of SFTSV may be the most effective antigens for inducing protective immunity. Moreover, the study revealed that T cell responses specific to non-envelope proteins of SFTSV also can contribute to protection against SFTSV infection.
Vaccine candidates induce both a neutralizing antibody response and multifunctional SFTSV-specific T cell response in mice and ferrets. When the vaccine efficacy is investigated in aged-ferrets that recapitulate fatal clinical symptoms, vaccinated ferrets are completely protected from lethal SFTSV challenge without developing any clinical signs. However, the study demonstrating complete protection against lethal SFTSV challenge using an immunocompetent, middle-sized animal model with clinical manifestations of SFTSV infection.
We believe this study provides valuable insights into designing preventive vaccines for SFTSV. They constructed DNA vaccines that encode full-length Gn, Gc, N, NS; and RNA polymerase genes based on common sequences of 31 SFTSV strains isolated from patients. Their vaccine candidates induced both neutralizing antibody response and multifunctional SFTSV-specific T cell response in mice and ferrets. To investigate the vaccine’s efficacy in vivo; the research team applied a recently developed ferret model that recapitulates fatal clinical symptoms in SFTSV infection in humans.