Abstract :
Bone marrow from neonatally and adult thymectomized (A.Tx) mice, had an impaired radioprotective effect upon inoculation into lethally irradiated recipients, due to decrease of HSC proliferative potential. The purpose of this study was to examine the competition for engraftment of HSC from A.Tx mice when these cells are infused into marrow-ablated mice together with normal cells. Four weeks old female mice were thymectomized and 8 months later they were used as donors of bone marrow HSC for reconstitution of lethally irradiated recipients. Normal males (NM) were the same age as females A.Tx. Female recipients were infused with equal number of female and male cells (FC and MC, respectively) or in a 30:1 ratio of FC to MC. Bone marrow of transplanted mice was collected repeatedly at 2, 6, and 10 months from femur and injected into secondary irradiated recipients for analysis of CFU-S-10. The resulting progenitors from individual colonies were analysed by PCR for Y chromosome sequences to determine the percent of male donor origin. A significant unfavourable competition for engraftment of A.Tx mice HSC versus NM was observed. 2-6 months post-transplantation, when mice were given equal numbers of MC and FC, average engraftment ranged from 71% to 100% male origin (83 from 103 colonies were Y-chromosome-positive) and from 72% to 89% (172 Y-positive colonies from 228) when mice given 30 times more FC then MC. 10 mo post-transplantation the engraftment of cells from A.Tx mice was clearly increased—only 40% of colonies were male origin. The reasons for unfavourable competition between A.Tx and normal mice HSC are unclear at present.
