Transdominant repressors of viral gene phenotypic expression derived from the rev gene product of HIV-1 or the rex gene product of HTLV-1 and corresponding mutated genes, having the capability of repressing the Rev function in HIV-1 and/or the Rex function in HTLV-I and HTLV-II. And in some cases both the Rev and the Rex function and are, active in more than one viral species. Such transdominant viral mutants are useful as anti-viral agents to, for example of these transdominant inhibitors may be used in such therapeutic approaches as intracellular immunization in order to protect cells against the deleterious effects of viral, e.g. HIV-1, infection.