Bexarotene-induced apoptosis of HTLV-1–infected cells before therapy and after relapse of disease. Patient PBMCs were cultured in vitro with medium only, bexarotene (10 μM), IFN-α2b (1000 U/mL), or a combination of bexarotene (10 μM) and IFN-α2b (1000 U/mL) and subjected to flow cytometry. (A) Cells isolated at day 0, before therapy. The percentage of apoptotic cells more than doubled with bexarotene, increasing from 17.9% to 37.8%. Combination treatment with both bexarotene and IFN-α2b yielded a higher level of apoptosis than either individual treatment, but no synergistic effect was seen. (B) PBMCs isolated at day 180 after initiating therapy. The percentage of apoptotic cells increased from 8.0% to just 10.3% with bexarotene. Of note, combination treatment with both bexarotene and IFN-α2b did not increase the percentage of apoptotic cells compared with treatment with bexarotene alone.