Samples were analyzed after expansion in vitro after sorting to eliminate preexisting mutants. Pseudo-density dot plots are shown for analyses using FITC-conjugated antibodies specific for transmembrane proteins (left panels) or the FLAER Alexa-488 reagent, which binds to the GPI structure directly (right panels). In all 3 examples, there are distinct populations of spontaneously arising cells that neither express GPI-linked proteins nor take up the FLAER reagent, but which do express transmembrane proteins. (A) A subclone of PR1-C (transformed lymphoma); (B) Jurkat, a T cell ALL cell line; (C) HBL2-A, derived from a Mantle Cell Lymphoma.