It seems that TYST cells were more sensitive to ATRA which had significantly inhibitory effects on cell proliferation in the concentrations of 10-7 M at 48 hours and 10-6 M at 24 hours, as compared with other cells, e.g. peripheral blood mononuclear cells and CD4+ T cells (>10-4 M [39]), human A375 melanoma cells (>10-5 M [40]), breast cancer cells (> > 10-5 M [41]), or small intestinal epithelium (>10-5 M [42]). Here, CD4 is linked to breast cancer.