title: Antitumor effect of interleukin (IL)-12 in the absence of endogenous IFN-gamma: a role for intrinsic tumor immunogenicity and IL-15.
abstract: IFN-gamma knockout mice (GKO) rejected C26 colon carcinoma cells transduced to secrete interleukin(IL)-12 but do not reject similarly transduced TSA mammary adenocarcinoma (C26/12 and TSA/12 cells, respectively). To determine whether such difference could be because of a different tumor response to IFN-gamma, we injected BALB/c mice with TSA, C26, and their IL-12-transduced counterparts rendered unresponsive to IFN-gamma by stable transduction of a dominant negative (DN), truncated IFN-gamma receptor alpha chain. TSA/DN and C26/DN showed the same in vivo growth kinetics as parental cells, whereas coexpression of IL-12 induced rejection independent of tumor-cell responsiveness to IFN-gamma. This suggests that the role of IFN-gamma is primarily in activating the host immune response, which appears to depend on the intrinsic immunogenicity of the target tumor. C26 and TSA share a common tumor-associated antigen, yet C26 cells are more immunogenic than TSA. C26/12 expressed 10-fold higher levels of class I MHC molecules and induced higher CTL activity compared with TSA/12 cells in GKO mice. Moreover, whereas in GKO mice the TSA/12 tumor was associated with a greater number of infiltrating T cells, only those infiltrating C26/12 tumor expressed the activation marker OX40. The search for cytokine(s) that might contribute in determining the different T-cell response to these IL-12-transduced tumors in GKO mice revealed a role of IL-15. In situ hybridization showed IL-15 expression in C26/12 but not in TSA/12 tumors. In addition, injection of GKO mice with soluble IL-15 receptor-alpha to block IL-15 expression prevented rejection of C26/12 cells. Together, the results suggest that in the absence of IFN-gamma, IL-12 can exert antitumor activity through alternative mechanisms, depending on the tumor cell type and the availability of cytokines that can replace IFN-gamma in sustaining T-cell functions.
authors.affiliation: Immunotherapy and Gene Therapy Unit, Department of Experimental Oncology, Istituto Nazionale per lo Studio e la Cura dei Tumori, 20133 Milan, Italy.
authors.forename: Giorgia
authors.initials: G
authors.lastname: Gri
authors.forename: Claudia
authors.initials: C
authors.lastname: Chiodoni
authors.forename: Elena
authors.initials: E
authors.lastname: Gallo
authors.forename: Antonella
authors.initials: A
authors.lastname: Stoppacciaro
authors.forename: Foo Y
authors.initials: FY
authors.lastname: Liew
authors.forename: Mario P
authors.initials: MP
authors.lastname: Colombo
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics / Q000276:immunology* / Q000473:pathology / Q000628:therapy; D000818:Animals; D002455:Cell Division / Q000276:immunology / Q000502:physiology; D003110:Colonic Neoplasms / Q000235:genetics / Q000276:immunology* / Q000473:pathology / Q000628:therapy; D016219:Immunotherapy, Adoptive; D007371:Interferon-gamma / Q000172:deficiency / Q000235:genetics / Q000276:immunology*; D018664:Interleukin-12 / Q000235:genetics / Q000276:immunology*; D019409:Interleukin-15 / Q000096:biosynthesis / Q000276:immunology*; D007694:Killer Cells, Natural / Q000276:immunology; D016246:Lymphocytes, Tumor-Infiltrating / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D013601:T-Lymphocytes / Q000276:immunology; D014161:Transduction, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D019409:Interleukin-15; D018664:Interleukin-12; D007371:Interferon-gamma