In vivo survival of lethally irradiated (DBA/2 × B10.D2)F1 mice grafted with B10.D2 cells from adult TCD BM (– –) or from NBB (––) collected on the day of birth. 10⁶B10.D2 donor splenocytes (Spl) were injected or not 7 and 14 days after the graft of NBB (–·–) or of TCD BM (···) cells. Mortality was recorded daily and mice were examined for the presence of clinical GVHD (number of live mice/total number of mice).