Circadian variations of bone marrow engraftability.

Circadian rhythms exist for hematopoiesis, but little is known about circadian variation of bone marrow engraftability and host "acceptability". Using a B6.SJL to C57BL/6J congenic transplant model, we chose 3-times with light on: Hours After Light Onset (HALO) 4, 8, and 12 and 3-times with light off: HALO 16, 20, and 24. The mice were conditioned on a 12-h light/dark cycles. Recipient mice (100 cGy) received 40 million cells. We demonstrated a significant variation of bone marrow engraftability into bone marrow, spleen, and thymus when donor animals were subjected to changes in their light/dark cycles. Two statistically significant nadirs in all three organs were observed at HALO 8 and 24 in experiments carried out in July, while an identical set of experiments in February analyzing engraftment in marrow and spleen showed nadirs at HALO 8, but not at HALO 24. Marrow progenitors from the July experiments showed nadirs at HALO 12 and 24. The percentage of progenitors in S phase peaked at HALO 8 and 24. Interestingly, there were no changes in the ability of host to accept grafts with changes in the light/dark cycles of host animals. Circadian variations of bone marrow engraftability are important and should be considered in bone marrow transplant strategies.

Engraftment of post 5-fluorouracil murine marrow into minimally myeloablated (100 cGy) murine hosts.

Minimal myeloablative approaches are now being widely applied in the treatment of different hematological malignancies. One hundred cGy whole-body irradiation is a stem-cell-toxic, relatively non-myelotoxic treatment that allows for relatively high levels of donor chimerism. 5-Fluorouracil (5-FU) treatment leads to a relative concentration of high proliferative potential-colony-forming cell (HPP-CFC) and is an approach that has been used to induce in vivo progenitor/stem cell cycling to facilitate retroviral integration in gene therapy approaches. We have now evaluated the capacity of marrow harvested 1, 2, 6, or 12 days after 5-FU treatment (150 mg/kg) to engraft in 100 cGy-treated female BALB/c mice. Engraftment was assessed at 3, 10, and 24 weeks. A rapid induction of an engraftment defect occurred 1 day post 5-FU and persisted through day 6 with a recovery by day 12. To evaluate cell cycle status of normal and 5-FU-treated marrow cells, male donors received hydroxyurea (900 mg/kg i.v.) or phosphate-buffered saline (PBS), 2 h prior to marrow harvest and transplantation into submyeloablated female recipients. Engraftment levels were similar for hydroxyurea-treated mice and controls. Thus, these studies show transiently defective engraftment of 5-FU-treated marrow into submyeloablated hosts, which may be related to the cell cycle status of the stem cells.