Immunogenic Properties of a Novel Hepatitis A Vaccine Candidate Based on a Fast-Growing Viral Strain

Background/Objectives: Hepatitis A virus (HAV) yearly causes over 150 million new infections and around 40,000 deaths. Current vaccines are based on strains that grow poorly in cell culture, leading to high production costs and limited availability. This study aimed to compare the immunogenic properties of a novel HAV vaccine candidate based on the fast-growing HM175-HP strain with those of the parental slow-growing HM175-L0 strain, which derives from the cytopathic HM175 strain, like the prototype strain used in certain existing vaccines. Methods: The humoral and cellular immune response elicited by either HM175-HP or HM175-L0 vaccines was assessed in female BALB/c mice. Results: Both HM175-HP and HM175-L0 vaccines induced comparable levels of anti-HAV IgG, as well as similar numbers of antibody-secreting cells and cellular proliferation rates in immunized mice. Importantly, anti-HAV antibodies developed by HM175-HP-immunized mice were able to neutralize the HM175-L0 strain. In addition, both vaccines induced anti-HAV IgG1 antibodies, which are associated with Th2 immune response, but the HM175-HP vaccine showed a tendency to produce a greater IgG2a response, suggesting that it might elicit a higher Th1 response, which is of utmost importance for host defense against viruses. Conclusions: Our findings indicated that the fast-growing HM175-HP strain has similar immunogenic properties to the vaccine prototype-like HM175-L0, making it a promising candidate to reduce the elevated costs and time-consuming procedures of producing the current HAV vaccines. The novel HM175-HP-based vaccine would therefore facilitate mass vaccination programs and prevent vaccine shortages.