Retroviral vector-mediated transfer of the tumor necrosis factor alpha gene into human cancer cells restores an apoptotic cell death program and induces a bystander-killing effect

Tumor necrosis factor alpha (TNF alpha) may induce tumor cell death by apoptosis, the physiologic program of cell death usually lost during neoplastic progression. However, many tumor cells are resistant to its effect unless high doses are administered, By retroviral vector-mediated gene transfer, we have transduced the TNF alpha gene into the DNA of human tumor cells to investigate whether the indefinite neoplastic cell proliferation could be blocked and the lost physiologic program of cell death restored. Evidence is provided that high-TNF alpha-producing clones generated from a human lymphoma T-cell line (ST4) can undergo apoptosis following transduction of the TNF alpha gene, Internucleosomal DNA cleavage was documented by May-Grunwald-Giemsa and by propidium iodide staining, as well as by gel electrophoresis. The induced apoptotic phenomenon is TNF alpha-mediated, since it can be reverted following incubation with anti-TNF alpha monoclonal antibodies (MoAbs), and it occurs with cytokine levels released in the supernatant by the engineered cells much lower (>100 times) than those required to promote the same effect on parental ST4 cells following administration of exogenous recombinant TNF alpha. The process is associated with a downregulation of the apoptosis-preventing gene, bcl-2, while the expression of bar and p53, genes usually involved in promoting apoptosis, persists. Mixed-culture experiments performed coincubating TNF alpha-transduced and untransduced ST4 cells allowed documentation of a bystander-killing effect on the parental cells. This phenomenon still occurred at transduced to parental cell ratios as low as 1:20 and was blocked in the presence of an anti-TNF alpha MoAb. These findings indicate that TNF alpha may play a regulatory role in the proliferation of human tumor cells, and suggest potential new antitumor therapeutic strategies based on the direct delivery of the TNF alpha gene into cancer cells. (C) 1996 by The American Society of Hematology.