Even though renal cell carcinomas (RCC) are thought to be immunogenic, many tumors express variations in surface molecules and intracellular proteins that hinder induction of optimal antitumor responses. Interferon gamma (IFNgamma) stimulation can correct some of these deficiencies. Therefore, we introduced the complementary DNA (cDNA) encoding human IFNgamma into a well-characterized RCC line that has been selected for development of an allogeneic tumor cell vaccine for treatment of patients with metastatic disease. Studies were performed to determine how endogenous IFNgamma expression influences tumor cell immunogenicity. IFNgamma transductants showed minimal increases in surface expression of MHC class I and adhesion molecules but expression of class II molecules was induced. Proteins of the transporter associated with antigen processing (TAP) and low molecular weight polypeptide (LMP) were constitutively expressed at high levels. The transductants stimulated allospecific cytotoxic T lymphocytes (CTL); however, they were not better than unmodified tumor cells in this capacity. Endogenous IFNgamma expression enhanced tumor cell recognition by MHC-restricted, tumor antigen-specific CTL but suppressed recognition by non-MHC-restricted cytotoxic cells. Thus, the functional consequences of IFNgamma expression varied with respect to the type of effector cell and were not always beneficial for tumor cell recognition.