Relevance of myeloablative conditioning in the engraftment of limiting numbers of normal and genetically marked lympho-hematopoietic stem cells.
We have studied the relevance of using myeloablative conditioning in the engraftment of limiting numbers of normal and retrovirally transduced bone marrow (BM) cells. The administration of high doses (10-12 Gy) of split-dose irradiation (4 h or 24 h intervals) to mice transplanted with small grafts (10(4)-10(6) cells) of normal BM not only minimized the endogenous reconstitution of recipients but also increased, with respect to single irradiation protocols, the survival rate of the animals in the long-term. The efficiency of these myeloablative regimens in BM transplantation protocols involving the use of transduced grafts was tested in mice transfused with 5 x 10(4)-2 x 10(6) genetically marked BM cells. Ninety percent of recipients survived in the long-term and, in most cases, predominant engraftment of the transduced population was apparent for up to 11 months post-transplantation. This was confirmed in hematopoietic samples corresponding to the CFU-S, the preCFU-S and the long-term repopulating cells of primary recipients. It was of significance, however, that reductions in the engraftment of the genetically marked cells were not associated with the engraftment of exogenous untransduced cells, but rather with rises in the extent of endogenous repopulation, revealing the difficulties of preventing the repopulation of residual endogenous stem cells when limiting numbers of transduced cells are transplanted. Our results emphasize the relevance of using efficient myeloablative conditioning regimens in those cases in which predominant and sustained engraftment of limiting numbers of transduced repopulating cells is required.
Varas
F
F
Unidad de Biología Molecular y Celular CIEMAT, CSIC-UAM, Madrid, Spain.
Bernad
A
A
Almendral
J M
JM
Bueren
J A
JA
D000818:Animals; D001772:Blood Cell Count; D006085:Graft Survival; D018380:Hematopoietic Stem Cell Transplantation / Q000379:methods*; D006412:Hematopoietic Stem Cells / Q000473:pathology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D011827:Radiation; D019172:Transplantation Conditioning