Development of a Subunit Vaccine against Duck Hepatitis A Virus Serotype 3.

In this study, we sought to develop a subunit vaccine against the increasingly prevalent Duck hepatitis A virus serotype 3 (DHAV-3). The VP1 protein of DHAV-3 and a truncated version containing the C-terminal region of VP1, termed VP1-C, were expressed recombinantly in Escherichia coli as vaccine antigens. For enhanced immune response, a truncated version of flagellin, n FliC, was included as vaccine adjuvant. Ducklings were vaccinated once for immune response analysis and challenge test. Results showed that VP1-C elicited a higher level of virus-specific antibody response and neutralization titer than VP1. The addition of n FliC further enhanced the antibody response. In terms of cellular immune response, the VP1-C + n FliC vaccine elicited the highest level of T cell proliferation among the vaccine formulations tested. Examination of the cytokine expression profile showed that peripheral blood mononuclear cells from the VP1-C + n FliC vaccine group expressed the highest levels of pro-inflammatory (IL-6) and TH-1 type (IL-12 and IFN-γ) cytokines. Finally, in a DHAV-3 challenge test, the VP1-C + n FliC vaccine provided a 75% protection rate ( n = 8), in contrast to 25% for the VP1 vaccine. In conclusion, E. coli -expressed VP1-C has been shown to be a promising antigen when combined with n FliC and may be further developed as a single-dose subunit vaccine against DHAV-3.