A cautionary tale: how to delete mouse haemopoietic stem cells with busulphan.

In this study treating mice with the 'correct' dose of busulphan did not necessarily destroy all haematopoietic stem cells. In certain circumstances host stem cells survived undetected and subsequently resumed haemopoiesis. This may apply to the use of busulphan clinically. We found that the following conditions determined the deletion of mouse stem cells using busulphan: (1) graft size--grafting more than 106 marrow cells ( approximately 0.3% of the animal's stem cells) concealed the survival of stem cells; (2) dose of busulphan--insufficient busulphan did not kill all host stem cells; (3) old or improperly stored busulphan failed to delete all host stem cells; furthermore (4) the survival of host stem cells should be assessed by typing many kinds of circulating cells; and (5) tests should be carried out to determine if busulphan has killed all host stem cells by typing circulating blood cells at appropriate intervals.