In vitro studies demonstrated that the retinoid X receptor (RXR) retinoid, << bexarotene >>, at biologically relevant concentrations of 10(-6) M to 10(-8) M, upregulated both the [[ p55 ]] and p75 subunits of the IL-2R and enhanced 5- to 10-fold the susceptibility of T-cell leukemia cells to denileukin diftitox.