RANTES Secretion by Gene-Modified Tumor Cells Results in Loss of TumorigenicityIn Vivo:Role of Immune Cell Subpopulations

Abstract

An immunogenic murine fibrosarcoma cell line was genetically modified to express and produce the human RANTES chemokine stably. In in vitro chemotaxis assays purified recombinant human RANTES as well as human RANTES secreted by the modified murine tumor cells were strongly chemoattractant for mouse CD8⁺/Thy-1⁺ tumor-infiltrating lymphocytes (TIL). RANTES production did not alter the growth of these cytokine gene-modified tumor cells in vitro, but injection of RANTES-secreting cells resulted in the abolition of the ability of those cells to form solid tumors in vivo. The growth of tumors could be restored by co-administration of monoclonal antibodies that inhibit the function of various subsets of immune cells. For example, depletion of CD8⁺ T cells by antibody administration resulted in complete restoration of solid tumor formation by RANTES-secreting cells, whereas depletion of the CD4⁺ T cell population resulted in a partial restoration of tumor formation. Additionally, administration of an anti-CR3 monoclonal antibody known to inhibit the in vivo migration of macrophages also completely restored the tumorigenicity of RANTES-secreting fibrosarcoma cells. Thus, the human RANTES chemokine can abolish tumorigenicity of an immunogenic fibrosarcoma in an in vivo murine model, and this process is mediated by various subpopulations of immune effector cells. Members of the chemokine superfamily mediate potent and selective chemoattraction of a variety of immune cell subsets, which is concentration dependent. This important and novel biologic activity raises the possibility of using chemokines as adjuvants in cancer vaccine strategies. We describe here the in vitro chemotactic capacity of RANTES for murine CD8⁺ tumor-infiltrating lymphocytes (TIL). Moreover, murine fibrosarcoma cells transfected with the cDNA encoding RANTES and secreting high levels of this chemokine become nontumorigenic in immunocompetent mice. The antitumor effect of RANTES is dependent on inherent tumor immunogenicity and is mediated through the participation of host-derived T cells and macrophages. Thus, the general chemoattractant properties exhibited by RANTES in vitro appear to be relevant in an in vivo model. These data warrant further investigation of other distinct members of the chemokine superfamily for their potential use, either alone or in combination, in gene therapy approaches that employ tumor cells as immunogens.