Rift Valley fever virus vaccination induces long-lived, antigen-specific human T cell responses

Rift Valley fever virus (RVFV) is a zoonotic arbovirus of clinical significance in both livestock and humans. A formalin-inactivated virus preparation was initially developed for human use and tested in laboratory workers in the 1960s. Vaccination resulted in generation of neutralizing antibody titers in most recipients, but neutralization titers waned over time, necessitating frequent booster doses. In this study, T cell-based immune responses to the formalin-inactivated vaccine were examined in a cohort of seven individuals who received between 1 and 6 doses of the vaccine. RVFV-specific T cell responses were detectable up to 24 years post vaccination. Peripheral blood mononuclear cells from this cohort of individuals were used to map out the viral epitopes targeted by T cells in humans. These data provide tools for assessing human RVFV-specific T cell responses and are thus a valuable resource for future human RVFV vaccine efforts.