Differential contribution of single BM CRU to hematopoietic engraftment. Recipient mice that were repopulated with a single, fresh (□) or homed (▨) CRU were identified as described in the Figure 4 legend and in “Materials and methods.” The differential contribution of individual CRUs to engraftment was defined as the proportion of all circulating B (CD45R/B220⁺) or T (CD90/Thy-1.2⁺) lymphocytes or myeloid (Gr-1/Ly6G⁺ and Mac-1/CD11b⁺) cells that were Ly-5.2⁺. Values shown for the 3 combinations of variably aged donors and recipients represent the mean ± SEM of 2 pooled experiments with 3 to 6 mice per group. Note that data for the young-to-young group were collected contemporaneously with those for other groups but were, in part, reported in Szilvassy et al.²³