The human cytomegalovirus immediate early promoter (CMV), the herpes simplex virus thymidine kinase promoter (TK), and the viral LTR promoter were tested as transcriptional control elements for the expression of the human tumor necrosis factor alpha (TNF) gene in a Moloney murine leukemia virus-based vector. Virus vector particles generated in the amphotropic packaging cell line PA317 were used to infect human colon adenocarcinoma cells LS174T. The strength of the different promoters was compared based on the amount of biologically active TNF produced by LS174T cells. Furthermore, the influence of the amount of secreted cytokine on growth characteristics of LS174T cells in vitro and on tumor growth in nude mice was analysed. Among different cell clones tested, the CMV-promoter was considerably stronger than the TK- and the viral LTR-promoter. However, despite of the amount of TNF produced by the tumor cells, individual LS174T cell clones were characterized by a similar growth inhibition of 65 to 80% in comparison to parental tumor cells or cells infected with the non-recombinat viral vector. When TNF-producing tumor cells were injected into nude mice, tumors were completely rejected only in case of CMV-promoted TNF-expression while only partial growth inhibition was obtained in case of TK- and LTR-promoted TNF-expression.

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