Importance of CD44v7 isoforms for homing and seeding of hematopoietic progenitor cells

The adhesion molecule CD44 consists of many isoforms of which particularly CD44v7 is of major importance in hematopoietic progenitor cell homing, An i ncrease of progenitor cells in the periphery was observed after treating mi ce with a CD44v7-specific antibody, concomitant with a substantially augmen ted marrow-repopulating ability (MRA). Because CD44v7 is expressed on a fra ction of bone marrow cells (BMC) as well as on long-term bone marrow cultur e-derived stromal cells, we aimed to differentiate between the functional r elevance of CD44v7 on either cell type by transferring CD44v7(+/+) BMC into CD44v7(-/-) mice and vice verse, CD44v7(+/+) BMC homed poorly in the bone marrow of CD44v7(-/-) mice and their MRA was severely impaired. CD44v7(-/-) BMC, instead, exhibited an improved MRA when transferred into the CD44v7(/+) host, although their MRA remained below that of CD44v7(+/+) BMC. Thus, it is predominantly, but not exclusively, expression of CD44v7 on stromal c ells which supports progenitor cell homing.