Table 3.

 Flow cytometric analysis of cell surface markers on CX+ and CX− tumor cells after long-term treatment with +13-RA and +ATRA and 4 weeks after removal of 13-RA (−13-RA). Exponen tially growing tumor cells were maintained either untreated or treated with freshly prepared 13-RA (10 μM) for 6 weeks and ATRA (1 μM) for 5 weeks at each cell passage. Percentage positively stained cells minus the number of cells stained with an isotype-matched control antibody are indicated. Data represent mean values of at least 3 independent experiments^a