Though the literature suggests that (i) HTLV-1-infected cells have an impaired ability to activate innate immunity and that (ii) a number of HTLV-1 encoded proteins blunt IFN-I signaling, a series of clinical trials using IFN-I were performed in Japan [77–83] and in the United States [84] to treat HAM/TSP patients with IFN-α or -β. Here, IFNA1 is linked to tropical spastic paraparesis.