Enhanced Humoral and Cellular Immune Responses Elicited by a Liposomal Subunit Vaccine Based on Gyrovirus homsa1 VP1 Protein in Chickens

Gyrovirus homsa1 (GyH1) causes immunosuppression and multi-organ damage in young poultry. The VP1 capsid protein (VP1) is a key target for subunit vaccine development; however, recombinant VP1 alone elicits limited immunogenicity and requires an efficient delivery system. Here, we developed a liposomal formulation associated with the GyH1 VP1 protein (LNP-VP1) and evaluated its immunogenicity and preliminary safety in specific-pathogen-free chickens. The prepared LNP-VP1 had a mean particle size of 230.11 ± 5.95 nm, a polydispersity index of 0.204 ± 0.023, a zeta potential of −36.55 ± 0.99 mV, and an apparent encapsulation efficiency of 84.03% ± 2.10%. In addition, immunization of chicks with LNP-VP1 induced robust antigen-specific IgG responses and significantly enhanced the infiltration of CD4+ and CD8+ T cells in the spleen. Furthermore, cytokine analysis revealed upregulation of IFN-γ, IL-4, and IL-17 levels following vaccination. Importantly, no vaccine-associated histopathological changes were observed in major immune or metabolic organs after immunization. Overall, LNP-VP1 effectively elicited both humoral and cellular immune responses with a favorable safety profile, indicating its potential as a candidate vaccine against GyH1 and providing experimental evidence supporting lipid nanoparticles as a delivery platform for avian subunit vaccines.