Survival of mice transplanted with marrow cells from previously transplanted Tpo^+/+ or Tpo^–/– mice. The curves shown are survival as a function of time for: normal recipient mice transplanted with 3 × 10⁵ marrow cells from normal recipient mice transplanted 7.5 weeks earlier with 2 × 10⁵ normal marrow cells (solid line); 1 × 10⁶ marrow cells from Tpo^–/– mice transplanted 7.5 weeks earlier with 2 × 10⁵ normal marrow cells (dashed line); and 2.5 × 10⁶ marrow cells from Tpo^–/– mice transplanted 7.5 weeks earlier with 2 × 10⁵ normal marrow cells (dotted line).