Different kinetics of IL-15/IL-15Rα heterodimers after CTX administration or whole-body irradiation. Six- to 8-week-old C57BL/6 mice were treated with CTX (□) or exposed to 6 Gy of whole-body irradiation (▴). Arrows indicate day 7 after treatment. (A). Mice were bled at the indicated time points after treatment, and the circulating IL-15/IL-15Rα heterodimers were measured by ELISA (eBioscience) and reported as mean ± SEM of 2 to 33 mice per time point. represents the average level of circulating mouse IL-15/IL-15Rα from 10 normal mice. **P = .007. (B-C) Mice were killed at the indicated time points after treatment, and spleens were collected for analysis. Total number of NK cells (B) and CD8⁺ T cells (C) per spleen over time was determined by flow cytometry. (D) Absolute count of lymphocytes in blood at day 7 after cytoreductive treatments. Three mice per group were analyzed. Hematologic profile on 10 untreated mice was also performed as control. **P < .01. ns indicates not significant.