MACROPHAGE-COLONY-STIMULATING FACTOR COMPLEMENTARY-DNA - A CANDIDATE FOR GENE-THERAPY IN METASTATIC MELANOMA

Background: At present, there is no highly effective treatment for met astatic melanoma. Innovative approaches aimed at inducing a more effec tive immune response against tumors have shown promising results in an imal models. One approach involves the genetic modification of tumor c ells so that they produce cytokines that stimulate an immune response. Purpose: The aim of this study was to determine the effectiveness of cytokine gene therapy for metastatic melanoma in a murine melanoma mod el. Methods: B16F10 murine melanoma cells, which readily metastasize t o the lungs, were transduced with a retroviral vector containing genes encoding neomycin resistance and human macrophage colony-stimulating factor (M-CSF). The presence of M-CSF messenger RNA in transduced cell s was examined by coupled reverse transcription and polymerase chain r eaction, Concentrations of soluble M-CSF in cell culture supernatants were determined by enzyme-linked immunosorbent assays (ELISAs). A clon al cell line, designated N+/CSF+, that expressed and secreted M-CSF wa s identified, Another clonal cell line, designated N+/CSF-, did not se crete M-CSF at levels detectable by ELISA, B16F10, N+/CSF-, and N+/CSF + cells, individually or in combination, were injected intravenously o r subcutaneously into C57BL/6 mice; we then evaluated the tumorigenici ty and metastatic behavior of the cells, as well as the immune respons es and survival of the mice, The immune responses assayed were the cyt otoxic T lymphocyte (CTL) and peritoneal exudate cell (PEG) tumoricida l activities. Results: Injection of B16F10 cells into the tail vein of C57BL/6 mice led to the establishment of lung metastases by week 2 an d death by week 8. Injection of the N+/CSF+ or N+/CSF- cells led to th e establishment of lung metastases that were detected at 2 and 3 weeks , respectively; however, these metastatic lesions were eliminated, and the animals had survival rates similar to those of the noninjected co ntrol mice. Injection of mice with a mixture of B16F10 and N+/CSF- cel ls resulted in the development of metastatic disease and 0% survival a t 8 weeks, whereas mice that had been given an injection of a mixture of B16F10 and N+/CSF+ cells had an 80% survival rate at 8 weeks and su rvived at least two times longer (P =.007), The CTL and PEC tumoricida l activities in animals given an injection of N+/CSF+ cells suggested that monocytes and lymphocytes were responsible for the observed antit umor response. Conclusion: These findings suggest that the expression of M-CSF by genetically modified melanoma cells caused an effective an titumor immune response in host C57BL/6 mice and, thus, prolonged surv ival over that observed in the control mice.