ISOLATION AND CHARACTERIZATION OF 2 MONOCLONAL-ANTIBODIES THAT RECOGNIZE DIFFERENT EPITOPES OF THE HUMAN C-KIT RECEPTOR

After immunizing mice with a human megakaryoblastic leukemia cell line , M-MOK, we obtained two monoclonal antibodies which recognize the hum an c-kit receptor. The monoclonal antibodies, designated MTK1 and MTK2 , were found to specifically recognize Balb/3T3 cells transfected with human c-kit cDNA and not parent Balb/3T3 cells while showing differen t immunological, biochemical and biological behaviors. Both allowed vi sualization of the 140 kDa c-kit protein by Western blot analysis, but MTK1 detected only positive band with non-reducing conditions for sod ium dodecyl sulfate-polyacrylamide gel electrophoresis. MTK1 partially inhibited the stem cell factor (SCP) induced proliferation of M-MOK c ells, whereas, MTK2 was without effect. MTK1 also inhibited the bone m arrow derived colony forming unit granulocyte/macrophage (CFU-GM) form ed by granulocyte-macrophage colony stimulating factor (GM-CSP) and SC F. Not only anti-CD34 antibodies (HPCA-1) but also MTL1 could be shown to concentrate bone marrow CFU-GM and burst forming unit erythroid (B FU-E) effectively. The presently described monoclonal antibodies may t herefore be useful for functional analysis of the ligand binding domai n of the human c-kit receptor, as well as for further classification o f hematopoietic stem cells in addition to the CD34 positive cells.