A bone marrow stem cell is thought to reside in a haemopoietic "niche", or a microenvironment containing specific slroma! and extracellular matrix elements. Successful long-term bone marrow transplants rely on stem cells homing to these niches. Traditionally, marrow transplants have been given to ablated hosts, as conventional dogma has suggested that ablation is required to free niches from host cells. However, we have demonstrated the successful homing of low numbers (2000) of primitive, Rhodamine 123/Hocchst 33342 dull (Rh/HO dull), stem cells into the marrow of nonablated murine hosts. We used multiple detection techniques to show the presence of donor cells six weeks post transplantation. Southern blot analysis of whole marrow to detect Y-specifk sequences in female hosts, clearly showed the presence of donor cells at a level of 1.3±O.I%. This low level engraftment was confirmed by fluorescent is situ hybridization (FISH) on bone marrow cell suspensions. FISH analysis of 7 factor responsive HPP-CFC from post transplant marrow, with the same Rh/Hö dull characteristics of the cells initially seeded, snowed a similar donor proportion to that found in whole marrow (-2%). The application of a new FISH technique on sections of paraffin embedded whole femurs allowed identification of individual engrafted ceils ex vivo, which had a strong spatial association with aie interface of marrow and femoral bone. The proportion of donor cells in the marrow reflects that previously seen following transplants with equivalent numbers of whole bone marrow cells, demonstrating that accessory cell interaction is not essential for stem cell engraftment. The data highlights a significant population of donor cells which have maintained a primitive, quiescent state, as well as demonstrating that the analysis of whole bone marrow truly reflects the proportion of donor cells in the stem cell compartment. We have shown engraftment of highly purified cells in normal hosts, which undergo maturation and differentiation to give equivalent proportions in both the mature, as well as the primitive progenitor cell compartments. In addition, these cells appear to selectively home to the interface of marrow and femoral bone.
|Number of pages||1|
|Publication status||Published - 1996|