Hybridoma-derived human suppressor factors: Inhibition of growth of tumor cell lines and effect on cytotoxic cells

Abstract

With the objective of developing human T-T cell hybrids producing B-cell growth factor, we fused concavalin A–activated T lymphocytes with cells of the lurkat T cell line. The hybrids were selected on the basis of their ability to form colonies in soft agar, whereas the parent Jurkat T cell line did not. T-T cell hybrids were HLA-typed, screened by functional tests, and recloned by limiting dilution. In addition to obtaining B-cell growth factor-producing hybrids, we also obtained certain other T-T cell hybrids (as determined by HLA-typing) producing suppressor factors inhibiting proliferative responses and antibody production by human lymphocytes. Subsequently, a suppressor factor with similar inhibitory properties was identified in supernatants of the Jurkat T cell line. However, the Jurkat factor exhibited different biochemical and functional properties than the hybridoma-derived suppressor factors. Using two-parameter cell cycle analysis and the metachromatic fluorochrome acridine orange, we found that the hybridoma-derived 160 and 169 suppressor factors arrested phytohemagglutinin-induced proliferation of peripheral blood mononuclear cells in the G₀/G₁ phase of the cell cycle, whereas the Jurkat suppressor factor arrested proliferation in the S phase. Incubation of peripheral blood mononuclear cells with the 160, 169, or Jurkat suppressor factors for 24 hr at 37° C, followed by washing, did not alter their cell cycle progression (or RNA content) in response to stimulation with phytohemagglutinin. The hybridoma-derived 160 and 169 suppressor factors and the Jurkat factor inhibited the growth but not the viability of cells from the following human tumor cell lines: A673 sarcoma cell line, SK-LC-6 and SK-LC-14 lung cell lines, SB, Raji, and Daudi lymphoblastoid cell lines, and FARR malignant melanoma cell line. In contrast, it did not affect the growth of murine L1210 cells and FS-4 normal human diploid fibroblasts. The hybridoma-derived 160 suppressor factor was selected to investigate its effect on cell-mediated cytotoxicity: The 160 suppressor factor did not inhibit natural killer cytotoxicity or its augmentation by interferon alpha or interleukin 2 or the generation of lymphokine-activated killer cells. However, this factor partially inhibited the generation of specific T cell-mediated cytotoxicity.