Ligation of the CD44 adhesion molecule inhibits drug-induced apoptosis in human myeloid leukemia cells.

Adhesion molecules can improve hematopoietic cell survival; however, their role in leukemic cell resistance to drug-induced apoptosis is poorly documented. The CD44 adhesion molecule is strongly expressed on acute myeloid leukemia (AML) blasts. Using 2 myeloid cell lines, HL60 and NB4, evidence is presented that prior incubation with the CD44-specific monoclonal antibody (mAb) A3D8, reported to induce differentiation of AML blasts, significantly decreases apoptosis induced by 3 drugs used in AML chemotherapy: daunorubicin (DNR), mitoxantrone, and etoposide. In addition, in HL60 cells, CD44 ligation with A3D8 mAb fully abrogates the DNR-triggered generation of ceramide, a lipid second messenger involved in the DNR apoptotic signaling pathway. Moreover, results show that the A3D8 mAb and Bcl-2 additively inhibit DNR-induced apoptosis in HL60 cells overexpressing Bcl-2. These results suggest that, to eradicate AML blasts, the differentiation-inducing anti-CD44 mAb A3D8 should not be administered prior to apoptosis-inducing drugs.

Ligation of the CD44 adhesion molecule reverses blockage of differentiation in human acute myeloid leukemia.

Blockage in myeloid differentiation characterizes acute myeloid leukemia (AML); the stage of the blockage defines distinct AML subtypes (AML1/2 to AML5). Differentiation therapy in AML has recently raised interest because the survival of AML3 patients has been greatly improved using the differentiating agent retinoic acid. However, this molecule is ineffective in other AML subtypes. The CD44 surface antigen, on leukemic blasts from most AML patients, is involved in myeloid differentiation. Here, we report that ligation of CD44 with specific anti-CD44 monoclonal antibodies or with hyaluronan, its natural ligand, can reverse myeloid differentiation blockage in AML1/2 to AML5 subtypes. The differentiation of AML blasts was evidenced by the ability to produce oxidative bursts, the expression of lineage antigens and cytological modifications, all specific to normal differentiated myeloid cells. These results indicate new possibilities for the development of CD44-targeted differentiation therapy in the AML1/2 to AML5 subtypes.

CD44-mediated adhesiveness of human hematopoietic progenitors to hyaluronan is modulated by cytokines.

Adhesive interactions between CD34+ hematopoietic progenitor cells (HPC) and bone marrow stroma are crucial for normal hematopoiesis, yet their molecular bases are still poorly elucidated. We have investigated whether cell surface proteoglycan CD44 can mediate adhesion of human CD34+ HPC to immobilized hyaluronan (HA), an abundant glycosaminoglycan of the bone marrow extracellular matrix. Our data show that, although CD34+ cells strongly express CD44, only 13.3% +/- 1.1% spontaneously adheres to HA. Short-term methylcellulose assay showed that HA-adherent CD34+ cells comprised granulo-monocytic and erythroid committed progenitors (19.6% +/- 2.5% and 7.3% +/- 1.0% of the input, respectively). More primitive progenitors, such as pre-colony-forming units, also adhered to HA. Moreover, we found that CD44-mediated adhesion of CD34+ cells to HA could be enhanced by phorbol 12-myristate 13-acetate (PMA), the function-activating anti-CD44 monoclonal antibody H90, and cytokines such as granulocyte-monocyte colony-stimulating factor, interleukin-3 (IL-3), and stem cell factor. Enhancement through PMA required several hours, was protein-synthesis-dependent, and was associated with an increase of CD44 cell surface expression, whereas stimulation of adhesion by H90 monoclonal antibody and cytokines was very rapid and without alteration of CD44 expression. H90-induced activation occurred at 4 degrees C and lasted for at least 2 hours, whereas activation by cytokines required incubation at 37 degrees C and was transient. These data, which show for the first time that CD34+ HPC can directly adhere to HA via CD44, point out that this adhesive interaction to HA is a process that may also be physiologically regulated by cytokines.

[Tetralogy of Fallot and mitral valve stenosis]. / Tétralogie de Fallot et rétrécissement mitral.

The association of tetralogy of Fallot and mitral stenosis is extremely rare. This is probably the first description of this association. The clinical and haemodynamic presentation is similar to that of cyanotic heart disease with pulmonary stenosis and post-capillary pulmonary hypertension. The mitral stenosis was probably congenital as it was diagnosed at 14 months of age.