Availability of haematopoietic niches for transplanted stem cells

Following transplantation, donor haematopoietic stem cells (HSCs) must reach specific parts of haematopoietic stroma tissue known as stem cell niches to become engrafted and to start blood cell production. Regularly, they have to compete with the host's HSCs for a limited number of niches. The exact mechanisms of HSC engraftment as well as of niche "opening" to incoming HSCs by conditioning treatments are not well-known yet. Significant and stable engraftment of syngeneic donor HSCs can be achieved in untreated mice only after transplantation of very large numbers of marrow cells. Engraftment can be largely facilitated by the stem cell mutations reducing numbers of the host HSCs. Pre-transplantation manipulations of the host haematopoietic tissue enhance engraftment depending on how much they damage HSCs. Ionizing radiation appears to be the most effective in this respect despite proliferative quiescence of a majority of HSCs. The review summarizes major achievements in deciphering biological principles of the HSCs and their engraftment after transplantation obtained in experimental research studying murine haematopoiesis.