Minimal myeloablation of the host increases THB competitive dominance of donor stem cells: implications for human gene therapy

F. M. Stewart, S. Zhong, S. Nilsson, P. J. Quesenberry

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Successful long-term engtaftment of normal male donor bone marrow transfused into nonablated female mice challenged the assumption that niches need to ha created for marrow to engraft. To evaluate whether minimal myeloablation could further enhance marrow engraftment, Balb/c female hosts received low doses of whole animal irradiation followed by a single infusion of 40 million bone marrow cells from male donors. To evaluate repopulation patterns we used Southern blot analysis using the murinc Y-chromosome specific pY2 probe. Thtt percentage of male DNA was calculated on the basis of phosphorimage analysis of post-transplant DNA samples and male marine DNA. Doses of 0. 50 and 100 cGy yielded engraftment rates of 9%+. 2, 33 %± 3 and 91 % t 20, respectively, in marrow at five months and 21 %. ±. 4, 45% Ji5, and 82% ±. 5 at eight months, The number of cells infused at various doses of irradiation appeared to influença cell readout. Groups of animals receiving 0, 100, and 700 cGy were transfused with 2, 10 of 40 x 10 cells. At 100 cGy there was a clear dose response with 4(i x 10 giving full engraftment and 10 x 10 showing approximately 409) engraftment. Removal of potential long-lived lymphocytes and/or potential accessory cells through lineage depletion showed engraftment (23. 3%±2. 67 at lOOcGy) but at diminished levels with an overall trend confirming the do dependent effect of low levels of irradiation. Highly purified progenitor/stem cells (HoechstlowRhodamine10) were capable of engrafting and proliferating but at lower levels (27. 4SSj+7. 55 at lOOcGy). In order to determine the cycling status of the engrafting stem cell, male marrow cells were harvested from animals treated with hydroxyurea (900mg/kg) two hours prior to transplant into female hosts. Analysis of percent engraftment showed a relative failure of early engraftment at 3 weeks in animals treated with hydroxyurea compared with untreated controls (27%. +4 versus 16%±2, p=<0. 01). but equivalent engraftment at 2 months. Thus, the long-term engrafting stem cell in this model is non-cycling. In experiments to calculate the effects of irradiation on stem cells (Do) and peripheral blood counts/marrow cellularity, low levels of irradiation were found to be highly stem cell toxic but minimally myelotoxic. Thus minima) myeloablation allowed for a significant competitive advantage for engrafting donor male marrow cells. These data indicate that minimal ablation with irradiation may be an attractive approach for human gene therapy in nonmalienant marrow disorders or the establishment of allochimeras.

Original languageEnglish
Number of pages1
JournalExperimental Hematology
Issue number8
Publication statusPublished - 1997
Externally publishedYes

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