Adhesion of Human Hematopoietic Progenitor Cells to Bone-Marrow-Derived Stromal Cells Is Enhanced by Antibodies to CD44

Abstract

It has been suggested that CD44 mediates adhesive interactions between hematopoietic progenitor cells and the stromal microenvironment. Ligands of CD44 include several extracellular matrix components, such as hyaluronic acid and fibronectin. Antibodies against CD44 have been shown to induce homotypic T cell aggregation, and to stimulate T and natural killer cell activity. We hypothesized that CD44 could similarly amplify interactions between blast-colony-forming cells and bone marrow stromal cells (BMSCs). Indeed, we have previously found that the anti-CD44 antibody NKI-P2 enhanced VLA-4-dependent interactions. Here, we studied an additional panel of nineteen anti-CD44 antibodies from the 5th Workshop on Leukocyte Differentiation antigens, to find out whether amplification was associated with a particular CD44 epitope. None of these antibodies showed inhibitory activity, whereas nine significantly increased the number of blast colonies more than 2-fold. Seven of these recognized epitope 1, and two epitope 2. More than 4-fold enhancement was only observed with epitope 1 antibodies: 4.C3 (4.4-fold), 212.3 (6.3-fold), L178 (9.1-fold), and NIH44-1 (9.2-fold). Our data suggest that primarily epitope 1 is associated with enhancement of colony formation. Furthermore, the findings support a role for CD44 as an amplifier in progenitor-BMSC interactions.

Adhesion of Human Hematopoietic Progenitor Cells to Mesenchymal Stromal Cells Involves CD44

“…Antibodies in group 1 and 2 recognize epitopes that reside on the N-terminal disulphide-bonded domain of CD44 involved in hyaluronic acid binding, whereas epitope 3 includes a cell-binding domain. Oostendorp et al [1996] have demonstrated that antibodies to epitope 1 enhance colony formation of HPC and Bendall et al [1997] have shown that such antibodies enhance adhesion of HPC to bone marrow stroma. In line with these studies, we observed increased adhesion of KG1a cells to MSC upon treatment with the monoclonal CD44 antibody BU52, directed against the same epitope 1 [Cao et al, 1995].…”

Diverse effects of anti‐CD44 antibodies on the stromal cell‐mediated support of normal but not leukaemic (CML) haemopoiesis in vitro

“…Studies by others have identified anti-CD44 mAbs that are able to exert either inhibitory or activating effects by modulating CD44 conformation, distribution, ligand-binding and signalling in a variety of cell types (Zheng et al, 1995;Lesley et al, 1993;Oostendorp et al, 1995). Parameters affected include cell adhesion properties, lymphocyte activation, growth factor production, GTP-ase activity and haemopoiesis in LTC (Lesley et al, 1993;Rossbach et al, 1996;Oostendorp et al, 1995Oostendorp et al, , 1996. Given these diversity of effects and the ubiquitous expression of CD44, it will be of interest to investigate potentially distinct contributions of the haemopoietic progenitors and the stromal cells to the inhibitory and/or enhancing effects observed here.…”

Evidence for differences in the mechanisms by which antibodies against CD44 promote adhesion of erythroid and granulopoietic progenitors to marrow stromal cells

“…We previously reported that many mAb against CD44 which recognize epitopes on the globular ‘head’ of the extracellular portion of the CD44 molecule as described in the Workshops on HLDA ( Spring et al , 1995 ) may increase the number of stroma‐adherent blast colonies ( Oostendorp et al , 1995 , 1996). However, by the nature of their design, these experiments did not emable effects on adhesion and growth to be distinguished.…”

“…The present studies also reinforce previous findings that most of the anti-CD44 mAb that are able to enhance progenitor adhesion to stroma react with epitope group 1, a common region of CD44 that, according to a model proposed by Lesley et al (1993), is located on its globular head (Spring et al, 1995;Dittel & LeBien, 1995;Oostendorp et al, 1996Oostendorp et al, , 1997; Fig 1). One possible explanation for this finding might be that these anti-CD44 mAb are all mimicking the effect of some unidentified physiological ligand for CD44 which also binds to this region.…”

“…The first four of these mAb had all been previously determined to react with epitopes on the globular head of CD44 (Spring et al, 1995). Interestingly, although in our previous study we did not find any mAb that inhibited CFC adhesion to stroma (Oostendorp et al, 1996), in the present experiments, CD44-6B6, which binds to a different part of CD44, which is involved in HA-binding, and 156-3C11, which binds to a third region of CD44 close to the cell membrane, reduced slightly, but significantly, the proportion of both BFU-E and CFU-GM (Figs 1A and 1B) and CFU-GM ( Fig 1A) respectively, that adhered to stromal cells in 2 h of culture.…”