Vaccinia virus (VACV) is the current vaccine for the highly infectious smallpox disease. Since the eradication of smallpox, VACV has been developed extensively as a heterologous vaccine vector for several pathogens. However, due to the complications associated with this replication competent virus, the safety and efficacy of VACV vaccine vector has been reevaluated. To evaluate the safety and efficacy of VACV, we study the interactions between VACV and the host innate immune system, especially the type I interferon (IFN) signaling pathways. In this work, we evaluated the role of protein kinase R (PKR) and Adenosine Deaminase Acting on RNA 1(ADAR1), which are induced by IFN, in VACV infection. We found that PKR is necessary but is not sufficient to activate interferon regulatory factor 3 (IRF3) in the induction of type I IFN; and the activation of the stress-activated protein kinase/ c-Jun NH2-terminal kinase is required for the PKR-dependent activation of IRF3 during VACV infection. Even though PKR was found to have an antiviral effect in VACV, ADAR1 was found to have a pro-viral effect by destabilizing double stranded RNA (dsRNA), rescuing VACVΔE3L, VACV deleted of the virulence factor E3L, when provided in trans. With the lessons we learned from VACV and host cells interaction, we have developed and evaluated a safe replication-competent VACV vaccine vector for HIV. Our preliminary results indicate that our VACV vaccine vector can still induce the IFN pathway while maintaining the ability to replicate and to express the HIV antigen efficiently. This suggests that this VACV vector can be used as a safe and efficient vaccine vector for HIV.