Transplantation of lethal T-cell leukemia requires irradiation. (A) Kaplan-Meier survival curves following transplantation of leukemic T cells into recipient animals receiving either no irradiation or 20 Gy of TBI. Performing transplantation into irradiated animals led to a dose-dependent decrease in survival over 30 days, whereas unirradiated controls remained healthy. (B) GFP⁺ donor cells colonize recipient thymi only after irradiation. (C) Examination of moribund animals 25 days after irradiation and transplantation showed the kidney to be almost completely replaced by leukemic lymphoblasts by FACS (middle) and WKM cytospins (right).