To elucidate cellular immune protective mechanism of EIAV.Four horses were immunized with (DLV) by subcutaneous injection and 2 horses with 0.85% sodium chloride as the negative control. Rectal temperatures and clinical features were recorded daily. Whole blood samples were collected, from which PBMC were separated and used for CTL assay and lymphocyte proliferation assay.The target cells were activated by PWM and treated with DLV or recombinant vaccinia vectors expressing DLV and LN Gag or Env separately. The percentage of EIAV-specific CTL lysis was under 5% in the negative control group, however, that was 20% to 30% in the group of immunized horses. The stimulation index (SI) from proliferation assay was 3 in the group immunized with attenuated DLV vaccine.The results indicated that EIAV-specific cellular immune-response induced by DLV immunization may contribute to the immune protective effect against EIAV virus infection.