An approach to a selection system for adenosine-deaminase-positive (ADA+) cells and detection of rat ADA+ “revertants”

We have substituted deoxyadenosine or adenosine for hypoxanthine in the standard HAT selection system in an attempt to select for ADA-normal (ADA+) cells. ADA− human lymphoid line cells could not utilize deoxyadenosine as an alternative to hypoxanthine as a purine source (DAT) and failed to grow but were only somewhat inhibited in growth when adenosine was substituted for hypoxanthine (AAT). In contrast, ADA+ cells utilized adenosine or deoxy-adenosine as efficiently as hypoxanthine as a purine source. Growth in DAT, but not in HAT, of an artificial mixture of one ADA+ human lymphoid cells in 1,000 ADA− cells resulted in enrichment of ADA+ cells to 25–86% of total cells. When we grew a rat ADA− cell line in two variations of the DAT system, we detected at least three electrophoretically different ADA+ patterns, one of which corresponded to normal rat ADA. These could represent “revertants.”