Suppression of lymphocyte proliferation by human tumor cells grown in short term cultures

We studied the effect of human tumor cells grown in short term cultures on the proliferative response of normal human peripheral blood mononuclear cells (PBMC) to mitogens and alloantigens. In 6 of 7 short term cancer cell lines studied, the addition of 10³ cells to mitogen- or alloantigen-stimulated cultures of 10⁵ PBMC caused from 20 to 60% suppression of ³H thymidine incorporation. Cells from short term cultures established from biopsies of normal skin did not suppress at these concentrations. The suppression was not due to a change in kinetics, or to a decrease in viability or recovery of either the tumor cells or PBMC in the cultures. Prior treatment of tumor cells with mitomycin C abrogated the suppression, while prior X-irradiation with 1,000, 2,000 or 3,000 rads had no effect. One of the tumor cells caused suppression when separated from the PBMC by a cell-impermeable membrane while another line required cell-to-cell contact for suppression.