CHARACTERIZATION OF MONOCLONAL-ANTIBODIES THAT RECOGNIZE CANINE CD34

Using a polyclonal antiserum against canine CD34, we previously found that CD34 is expressed on canine bone marrow progenitor cells in a man ner analogous to that found in humans, To further characterize CD34(+) cells and to facilitate preclinical canine stem cell transplant studi es, monoclonal antibodies (MoAbs) were raised to CD34. A panel of 10 M oAbs was generated that reacted with recombinant CD34 and with CD34(+) cell lines and failed to react with CD34(-) cell lines, Binding prope rties of five purified MoAbs were determined by BIAcore analysis and f low cytometric staining, and several MoAbs showed high affinity for CD 34, Two antibodies, 1H6 and 2E9, were further characterized, and in fl ow cytometry studies typically 1% to 3% of stained bone marrow cells w ere CD34(+), Purified CD34(+) bone marrow cells were 1.8- to 55-fold e nriched for colony-forming unit-granulocyte-macrophage and for long-te rm culture initiating cells as compared with bone marrow mononuclear c ells, whereas CD34(-) cells were depleted of progenitors. Three autolo gous transplants were performed with CD34(+) cell fractions enriched b y immunomagnetic separation. After marrow ablative total body irradiat ion (920 cGy), prompt hematopoietic recovery was seen with transplante d cell doses of less than or equal to 1.1 x 10(7) /kg that were 29% to 70% CD34(+). Engraftment kinetics were similar to those of dogs previ ously transplanted with approximately 10- to 100-fold more unmodified autologous marrow cells. This suggests that CD34(+) is a marker not on ly of canine bone marrow progenitors but also for cells with radioprot ective or marrow repopulating function in vivo. MoAbs to CD34 will be valuable for future studies of canine hematopoiesis and preclinical st udies concerning stem cell transplantation, gene therapy, and ex vivo progenitor cell expansion. (C) 1998 by The American Society of Hematol ogy.