DOWN-REGULATION OF MURINE FIBROSARCOMA TRANSFORMING GROWTH-FACTOR-BETA-1 EXPRESSION BY INTERLEUKIN-7

Background: Cytokine genes encode proteins that modulate immune system responses, Modification of tumor cells by the introduction of cytokin e genes has been used as a strategy to augment host immunity. Interleu kin 7 (IL-7) gene transfer enhances the immune response to tumor cells and can result in tumor regression. Transforming growth factor-beta 1 (TGF-beta 1) is a potent immunosuppressive cytokine produced by many tumors. We have previously reported that recombinant IL-7 decreases th e expression of TGF-beta 1 by murine macrophages. Purpose: This study investigates the inhibition of tumor-derived TGF-beta 1 production as a possible mechanism for the enhanced antitumor immunity that accompan ies IL-7 gene transfer. Methods: A fibrosarcoma cell line (FSA-JmIL-7) genetically modified to produce IL-7 was used to evaluate the effects of IL-7 on tumor production of TGF-beta 1. The control cell line (FSA -Jneo) originated from the same parental fibrosarcoma cell line (FSA) and was produced by transduction with the same retroviral vector witho ut the IL-7 gene. FSA-Jneo and FSA-JmIL-7 tumor cells were evaluated f or the expression of TGF-beta 1 messenger RNA (mRNA). To determine if the observed change in TGF-beta 1 mRNA was associated with an alterati on in protein secretion, we compared supernatants from tumor cell cult ures for TGF-beta 1 production. Specific anti-TGF-beta 1 monoclonal an tibody (MAb) was used to confirm the role of TGF-beta 1 in these assay s. Results: Compared with FSA parental and FSA-Jneo cells, FSA-JmIL-7 cells expressed TGF-beta 1 mRNA at a lower level. Compared with supern atants from FSA-Jneo cells, FSA-JmIL-7 supernatants contained consiste ntly lower levels of TGF-beta 1 activity (P<.05). In addition, FSA-Jne o supernatants suppressed lymphocyte proliferation to a significantly greater degree than supernatants from FSA-JmIL-7 cells (P<.05). Studie s with anti-TGF-beta 1 MAb added to the supernatants confirmed the rol e of TGF-beta 1 in inhibition of lymphocyte proliferation. Conclusion: These findings suggest that IL-7 gene transfer inhibits the productio n of TGF-beta 1 by tumor cells and thus may enhance the efficacy of th e host's antitumor immune response. Implication: The regulation of end ogenous tumor-derived cytokines in response to cytokine gene transfer may contribute to altered immune responses in the tumor microenvironme nt and thus may be an important additional parameter to assess in gene therapy.