PBMCs from some T-LGL leukemia patients had higher response to exogenously added IL-15 compared with those of normal donors. (A) Six-day spontaneous proliferation of PBMCs from T-LGL leukemic patients and normal donors ex vivo without addition of antigens or mitogens. (B) The proliferation of PBMCs from select T-LGL leukemia patients (LGL1 and LGL4) in response to exogenously added IL-15. Two concentrations of IL-15 (200 pg/mL and 20 ng/mL) were used in the assay. The proliferation of normal donors represented data from 5 normal donors.