Secondary transplantation does not promote further declines in hematopoietic repopulating potential. To determine whether engraftment would decrease upon transplantation into secondary recipients, the chimeric mice that received BM cells 16 weeks earlier were killed, and the BM cells were collected and then injected into lethally irradiated CD45.1 secondary hosts. (A) The mice were bled 8 weeks, 12 weeks, and 16 weeks following secondary transplantation. Peripheral blood leukocytes were analyzed by flow cytometry for the expression of CD45.2. The results are represented as the average plus or minus a SD from the combination of 2 independent transplantation experiments with 10 recipient mice in each group. *P > .001 relative to wild-type BM. (B) Donor contribution to myeloid, lymphoid, and erythroid lineages in long-term reconstituted mice is shown. Average multilineage analysis at 16 weeks showed that the defects affected multiple hematopoietic lineages. *P > .001 relative to wild-type BM. Error bars represent the average plus or minus a standard deviation.