Response of fresh ATL cells to IL-15. ATL cells from seven patients were examined for their response to IL-15 (×) or IL-2 (○). The results were expressed as relative values against control cultured without these cytokines. The results of a representative four cases were shown. ATL cells of all patients (A, B, and C) but one (D) responded to IL-15 to the same degree as to IL-2.