Alloantigen presentation by malignant T cells to nonmalignant T cells stimulates growth of malignant T cells. (A) HLA-DPB*0401–positive malignant T cells (MyLa 2039) were grown with and without SEA (100 ng/mL) and/or HLA-DP*0401–, HLA-DP*0501–, and HLA-DP*0601–specific nonmalignant T cells (irradiated to avoid proliferation) for 48 hours in microtiter plates. The data are representative of 3 independent experiments. (B) HLA-DPB*0401–positive malignant T cells (MyLa 2039) were grown with or without HLA-DPB*0401–specific T cells (irradiated) with or without HLA-DP, HLA-DQ, HLA-DR, CD8, LFA-3, or CD29 mAb (10 μg/mL) for 48 hours in microtiter plates. The percentage inhibition of growth stimulation by coculture was calculated as described in “Materials and methods.” The data are representative of 3 independent experiments. Error bars indicate SD.