In this study, we demonstrated that: (i) infection with MDV resulted in early induction of IL-17A and IFN-γ expression in chicken splenocytes; (ii) based on FACS analysis, IL-17A+ T cells could be detected in splenocytes from vvMDV-RB1B infected chickens with the highest proportion of IL-17A+ T cells peaking at 21 dpi; and (iii) in vivo inoculation with a recombinant chIL-17A post-HVT vaccination significantly reduced tumor incidence compared to infected-only chickens compared to HVT+IL-17A or HVT+vector control. The gene discussed is IL17A; the disease is neoplasm.