A Self-amplifying mRNA vaccine for infectious laryngotracheitis virus (ILTV) induces efficient protective immunity

Infectious laryngotracheitis (ILT) continues to pose a significant threat to intensive poultry farming regions worldwide. Current control strategies primarily rely on live attenuated and recombinant live ILT virus (ILTV) vaccines. However, concerns persist regarding the potential reversion to virulence, recombination of vaccine viruses, and interference from maternal antibodies. mRNA vaccine platforms offer a novel and promising approach for developing next-generation ILTV vaccines. In this study, we designed a self-amplifying RNA (saRNA) vaccine incorporating the ILTV gD gene and evaluated its immunogenicity and protective efficacy in chickens. The saRNA-gD vaccine elicited robust humoral immunity, with serum neutralizing antibody titers reaching up to 1:415. All vaccinated chickens achieved seropositivity within 7 days post-vaccination (dpv). Significantly elevated levels of IL-2 cytokine were observed at 28 and 42 dpv compared to the LNP control group, suggesting the potential activation of cellular immune responses following vaccination. Animal challenge experiment revealed that the saRNA-gD vaccine effectively mitigated clinical symptoms induced by ILTV infection, conferring a protection rate of approximately 66.7%, which is comparable to that of the commercial recombinant fowl pox virus (rFPV-LT) vaccine. Quantification of viral loads in tracheal swabs and histopathological examination demonstrated that the saRNA-gD vaccine significantly reduced viral DNA copies in swabs and induced markedly milder histopathological changes. These findings indicate that the saRNA-gD vaccine induces potent immune responses and provides substantial protection against ILTV challenge, potentiating it as a highly promising vaccine candidate for the control of ILT in poultry.