The co-immunization of CD4-IL-10ko mice, where no Env-mediated suppression was observed, as well as the anti-IL-10 treatment in the context of both the suppression of tumor control by Env SU+TM and the suppression of CD8+ T-cell responses by Env SU, clearly shows that mechanistically, an increased IL-10 production by CD4+ T cells underlies the Env SU+TM as well as Env SU-mediated suppression. The gene discussed is ERVW-1; the disease is neoplasm.