Expression of thymidine kinase activity in hybrids between human leukemic cells and a TK-mouse cell line.

A series of actively proliferating clones have been isolated after PEG-induced fusion of a thymidine kinase deficient murine line and white blood cells from two leukemic patients. Their hybrid nature was proved both cytologically and biochemically. All the hybrids tested showed levels of TK activity significantly higher than the TK- mouse parental cell line and comparable to those exhibited by replicating TK+ cells.