There are three types of blood cells: red, white, and platelets. They provide oxygen supply, facilitate the healing of wounds, and protect the body from pathogens.

Whatever their type, the majority of mature blood cells are derived from hematopoietic stem cells or HSCs. HSCs are capable of self-generation. That's why they're used to treat cancers affecting the blood or immune system, such as leukemia.

These blood stem cells migrate from one location to another, where they amplify and reside until they are needed, at their organ of origin. This process is called "homing", and it's key to the success of transplants. But the how and why of homing has been unclear, until now. Shanghai-based Professor Pan Weijun and his colleagues have unlocked the secrets.

Pan said it took their lab six years and they used a new research method. Through advanced live imaging and a cell-labeling system, they directly observed the complete process of HSC homing. With more analysis and experiments, they systematically revealed the architectural basis for the micro-environment, as well as some features of the molecular cells.

For the first time, Pan and his colleagues identified "usher cells," the doormen for hematopoietic cells that are "homing." Once the door is open, the stem cells can easily return to the bone marrow.

The findings have been published in leading science journal Nature. Senior Editor Nathalie Le Bot recognizes the importance of Professor Pan's high-resolution analyses of the HSC homing. She said this study uncovered unprecedented insights into how hematopoietic cells homing occurred in live animals. This finding could also be key to the success of bone marrow transplantation in the future.