SPECIFICITY OF HEMATOPOIETIC STEM-CELL HOMING

Homing of hematopoietic stem cells (HSC) may be defined as the cells' ability to seek marrow stroma selectively, to interact with it and sub sequently to lodge within it to initiate hematopoiesis. This complex p rocess is no doubt mediated through multiple recognition/adhesion even ts. Homing may proceed through one of several alternative mechanisms, however, such as through physical trapping of stem cells by marrow ult rastructural elements or through the providing of a selective survival and/or proliferative advantage by marrow. A third alternative that pr ovides for the central element of stem cell homing-its high degree of specificity-is through the action of a specific homing protein in HSC. There are data to support this latter mechanism of stem cell homing a s the correct one, and the nature of this protein may be similar to th at of the lymphocyte homing receptors that are lectin-like molecules. Lectin-carbohydrate interactions are known to provide enormous specifi city to cell recognition processes and to participate in cellular targ eting. Leukemic cells have recently been demonstrated to home to marro w stroma and proliferate in the same way as normal stem cells. Thus, i dentification of proteins or other adhesion molecules that participate in normal and malignant cell homing could lead to more specific recru itment regimens for tumour-free collections.