Vaccinia virus and Cowpox virus are not susceptible to the interferon-induced antiviral protein MxA.

MxA protein is expressed in response to type I and type III Interferon and constitute an important antiviral factor with broad antiviral activity to diverse RNA viruses. In addition, some studies expand the range of MxA antiviral activity to include particular DNA viruses like Monkeypox virus (MPXV) and African Swine Fever virus (ASFV). However, a broad profile of activity of MxA to large DNA viruses has not been established to date. Here, we investigated if some well characterized DNA viruses belonging to the Poxviridae family are sensitive to human MxA. A cell line inducibly expressing MxA to inhibitory levels showed no anti-Vaccinia virus (VACV) virus activity, indicating either lack of susceptibility of the virus, or the existence of viral factors capable of counteracting MxA inhibition. To determine if VACV resistance to MxA was due to a virus-encoded anti-MxA activity, we performed coinfections of VACV and the MxA-sensitive Vesicular Stomatitis virus (VSV), and show that VACV does not protect VSV from MxA inhibition in trans. Those results were extended to several VACV strains and two CPXV strains, thus confirming that those Orthopoxviruses do not block MxA action. Overall, these results point to a lack of susceptibility of the Poxviridae to MxA antiviral activity.