Use of enzyme-deficient cell lines as feeder layers.

Enzyme-deficient cell lines, lacking TK or HPRT and therefore unable to grow in HAT medium, may be used as feeder layers to enhance clonal growth of wild-type cells. Low numbers of wild-type test cells may be plated in HAT medium with 5 X 10(5) HAT-sensitive feeder cells per Petri dish. The feeder cells remain attached and metabolizing for 1 to 2 weeks, but ultimately die and detach, leaving colonies of test cells. This feeder layer technique is very simple and flexible and could have wide applicability.