TRANSENDOTHELIAL MIGRATION OF CD34(-CELLS - AN IN-VITRO STUDY USING AHUMAN BONE-MARROW ENDOTHELIAL-CELL LINE() AND MATURE HEMATOPOIETIC)

To study the role of bone marrow endothelial cells (BMEC) in the regul ation of hematopoietic cell trafficking, we have designed an in vitro model of transendothelial migration of hematopoietic progenitor cells and their progeny. For these studies, we have taken advantage of a hum an BMEC-derived cell line (BMEC-1), which proliferates independent of growth factors, is contact inhibited, and expresses adhesion molecules similar to BMEC in vivo. BMEC-1 monolayers were grown to confluency o n 3 mu m microporous membrane inserts and placed in 6-well tissue cult ure plates. Granulocyte-colony stimulating factor (G-CSF)-mobilized pe ripheral blood CD34(+) cells were added to the BMEC-1 monolayer in the upper chamber of the 6-well plate. After 24 hours of coincubation, th e majority of CD34(+) cells remained nonadherent in the upper chamber, while 1.6 +/- 0.3% of the progenitor cells had transmigrated. Transmi grated CD34 cells expressed a higher level of CD38 compared with nonmi grating CD34(+) cells and may therefore represent predominantly commit ted progenitor cells. Accordingly, the total prating efficiency of the transmigrated CD34(+) cells for lineage-committed progenitors was hig her (14.0 +/- 0.1 v 7.8% +/- 1.5%). In particular, the prating efficie ncy of transmigrated cells for erythroid progenitors was 27-fold great er compared with nonmigrating cells (8.0% +/- 0.8% v 0.3% +/- 0.7%) an d 5.5-fold compared with unprocessed CD34(+) cells (22% +/- 0.4%). Whi le no difference in the expression of the beta 1-integrin very late ac tivation antigen (VLA)-4 and beta 2-integrin lymphocyte function-assoc iated antigen (LFA)-1 was found, L-selectin expression on transmigrate d CD34(+) cells was test, suggesting that shedding had occurred during migration. The number of transmigrated cells was reduced by blocking antibodies to LFA-1, while L-selectin and VLA-4 antibodies had no inhi bitory effect. Continuous coculture of the remaining CD34(+) cells in the upper chamber of the transwell inserts resulted in proliferation a nd differentiation into myeloid and megakaryocytic cells. While the ma jority of calls in the upper chamber comprised proliferating myeloid p recursors such as promyelocytes and myelocytes, only mature monocytes and granulocytes were detected in the lower chamber. In conclusion, BM EC-1 cells support transmigration of hematopoietic progenitors and mat ure hematopoietic cells. Therefore, this model may be used to study me chanisms involved in mobilization and homing of CD34(+) cells during p eripheral blood progenitor cell transplantation and trafficking of mat ure hematopoietic cells. (C) 1997 by The American Society of Hematolog y.