| Objective: Acute myeloid leukemia (AML) is a heterogeneous leukemia characterized by excessive proliferation of leukemic blast cells that results in blockage of myeloid differentiation at different stages, which define distinct AML subtypes. Therefore, elimination of proliferating leukemic cells is essential to effectively cure AML patients. Because of chemoresistance, however, chemotherapy rarely eradicates leukemic clone thoroughly. Sachs put forward the concept of differentiation therapy for the first time in 1970's. Chinese researchers succeeded in acute promyelocytic leukemia therapy through induced differentiation with all-trans-retinoic acid (ATRA) for the first time in the middle of 1980's, and improved survival quality of patients significantly. Unfortunately, the existing differentiating agents such as ATRA and As2O3 are only effective in APL, and have little effect on most other AML. So, differentiation mechanism research and new differentiating agents development are always challenges for haematologist. CD44 adhesion molecule is class I transmembrane glycoprotein widely present on the surface of most vertebrate cells, which mediates the adhesive action between cells or cell and extracellular matrix. It takes part in many physiological and pathological processes such as signaling transduction and activation of cellular function, cell growth and differentiation, tumor development and metastasis, immune response, blood clotting, etc. CD44 molecule is expressed on most CD34+ cells and on all types of lineage-restricted hematopoietic progenitors present in normal human bone marrow, and it is involved in normal myeloid differentiation. Function-blocking monoclonal antibodies against CD44 inhibit in vitro myelopoiesis. It has reported recently that CD44 cell surface adhesion molecule is strongly expressed on leukemic blasts in all AML subtypes, and itcan induce differentiation of fresh leukemic blasts from all kinds of AML patients after ligation of CD44 on cell surface with its activating mAb or its natural ligand hyaluronan (HA) (1999). It has been found through in vitro study that CD44 monoclonal antibodies can inhibit proliferation of all acute myeloid leukemia cell lines and induce terminal differentiate or apoptosis of some cell lines to diverse extent (2002). Because CD44 adhesion molecule is expressed on cell surface, thus it is easily accessible to extracelluler stimulation, and it is also involved in hematopoiesis and in normal myeloid differentiation. Moreover, CD44 mediates the cascade reaction of transmembrane signals, and influences the biological functions of cells through regulating the expression of some oncogenes, transcription factors, cell growth factors and its receptor genes, and enzyme and cell structural protein genes. So, CD44 may become a new possible therapeutic target for inducing differentiation of AML blasts. However, there are still many problems concerning about the detailed molecular mechanism of CD44 on inducing differentiation of leukemic blast cells. In present study, we investigated the effects of A3D8, an anti-CD44 monoclonal antibody on proliferation and differentiation of HL-60 cells, and discussed the molecular mechanism of CD44 to put forward a new way for inducing differentiation therapy of leukemia.Methods: 1 Cell culture and CD44 ligation with A3D8 anti-CD44 mAb HL-60 cells derived from human AML-M2, were cultured in RPMI1640 medium supplemented with 15% (V/V) heat-inactivated fetal bovine serum (Hyclone), lOOU/ml penicillin G and lOOjig/ml streptomycin sulfate at 37癈 with 5% CO2 enrichment. The cells were seeded at a density of 2X103 cells/ml and passaged every 2 to 3 days. Logarithmically growing cells with viability ^95% as assayed by trypan blue exclusion staining were used for the studies described below. Cells were placed triplicate in 96-well flat-bottomed tissue culture plates (200jj.l/well) at a density of 105cells/ml suspension. They were independently treated with specific concentration of anti-CD44 monoclonal antibodies (Clone A3D8, Mouse IgGl, Sigm... |
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