In vitro stimulation by tumour cell media of [3H]-thymidine incorporation by mouse spleen lymphocytes.

Mouse spleen lymphocyte (SL) cells show a three to four-fold increase in [3H]-thymidine incorporation when incubated in tumour cell media, or in media containing tumour cell cytosol. Agarose gel chromatography of both [3H]-thymidine-labelled tumour cell media and cytosol shows a sharp peak of DNA-associated material eluting at about 60 kDa. This DNA-associated material is imported rapidly and efficiently by SL cells and is recoverable from their cytosol. The stimulating effect on SL cell thymidine incorporation resides primarily, if not exclusively, in this extruded/cytosolic 60 kDa DNA material. Tumour cells incubated in media containing normal or liver, but not tumour, cytosol show a reduced rate of [3H]-thymidine incorporation, indicating competition between normal and tumour associated DNA complexes. The results indicate that such cell-extruded DNA complexes may transmit 'genetic messages' to other cells, and are discussed in terms of interactions in the tumour-bearing host.