Intranasal immunization of recombinant vaccinia virus bearing FeLV SU elicits systemic and mucosal immunity.

Feline leukemia virus (FeLV) is a major cause of mortality in domestic and wild felids, primarily spread through mucosal routes. Current FeLV vaccines offer moderate systemic protection but limited mucosal immunity. Previously, we showed that intranasal vaccination with a recombinant vaccinia virus (VV) can induce strong mucosal immune responses against multiple pathogens. Here, we constructed a recombinant VV expressing the surface unit (SU) of the FeLV envelope (VV) and assessed its immunogenicity in a murine model following intranasal delivery. VV was validated for FeLV SU expression and assessed replication kinetics in vitro. Intranasal immunization of BALB/c mice with VV (1 ×10 PFU) induced humoral and cellular immune responses, including antibodies capable of neutralizing FeLV pseudovirus and FeLV SU-specific T cells producing IFN-γ, TNFα, and IL-4. Notably, mucosal secretory IgA specific to FeLV SU was also detectable after vaccination. Together, these results demonstrate that VV has a favorable safety profile and moderate immunogenicity in mice, supporting further evaluation as a mucosal vaccine candidate against FeLV.