TfR expression and antiproliferative effect of A24 on tumor cells. (A) TfR expression was examined on different cell subtypes: resting T cells (i), PHA/IL-2–activated T cells (ii), lymphoma cell line (Jurkat) (iii), HTLV-1⁺ cell lines (HUT-102 and MT-2, respectively; iv-v), ex vivo lymphocytes of acute ATL patients (vi-vii), ex vivo lymphocytes of patients with a chronic ATL form (viii). The expression level of TfR was expressed on histograms plotting the fluorescence intensity of anti-CD71 (gray) as compared to that of the isotype control (open). Numbers in the upper right corners represent the median fluorescence intensity of the gray histograms. (B) Coexpression of TfR and CD25 on healthy and tumor cells. Resting T cells (i), PHA/IL-2–activated T cells (ii), HTLV-1⁺ cells line (MT-2 and HUT-102, respectively; iii-iv), ex vivo lymphocytes of patients with an ATL acute form (v-vi), ex vivo lymphocytes of patients with an ATL chronic form (vii). (C) PBMCs from healthy individuals (i) and HTLV-1–infected patients with an acute ATL (ii) or a chronic ATL (iii) were plated in culture wells with A24 or a control antibody (30.9) in the presence of PHA/IL-2, for 72 hours before [³H]-thymidine incorporation. (D) PBMCs from HTLV-1–infected patients with a chronic ATL form were plated in culture wells with the 30.9, A24, or Ars for 2 weeks. Emergence of HTLV-1 clones was evaluated by [³H]-thymidine incorporation. Data are means ± SD of one of at least 3 separate experiments with 4 acute and 3 chronic ATL patients.