REGULATION OF HUMAN LYMPHOCYTE-PROLIFERATION BY A TUMOR CELL-DERIVED DNA FRACTION

A suppressor activity was isolated and partially purified from culture supernatant of human myeloid leukaemic cell line HL-60 by ion-exchange chromatography, HPLC and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). This activity was capable of suppressing proliferation of mitogen-stimulated normal human lymphocytes in a dose-dependent manner. The suppressor activity was identified as DNA by its typical absorbance at 260 nm, and by its susceptibility to DNase digestion. The DNA with suppressive activity was found to be double-stranded with the molecular weight range between 0.6 and 1.5 kb. This DNA material did not have cytotoxic activity and did not alter interleukin-2 receptor expression. Cell cycle analysis has suggested that DNA molecules could interact with lymphocytes to arrest the stimulated lymphocytes in the G1 phase. apparently preventing the cells from entering into the proliferating S phase.