Characterization of Monoclonal Antibodies That Recognize Canine CD 34

Using a polyclonal antiserum against canine CD34, we previously found that CD34 is expressed on canine bone marrow progenitor cells in a manner analogous to that found in humans. To further characterize CD341 cells and to facilitate preclinical canine stem cell transplant studies, monoclonal antibodies (MoAbs) were raised to CD34. A panel of 10 MoAbs was generated that reacted with recombinant CD34 and with CD341 cell lines and failed to react with CD342 cell lines. Binding properties of five purified MoAbs were determined by BIAcore analysis and flow cytometric staining, and several MoAbs showed high affinity for CD34. Two antibodies, 1H6 and 2E9, were further characterized, and in flow cytometry studies typically 1% to 3% of stained bone marrow cells were CD341. Purified CD341 bone marrow cells were 1.8to 55-fold enriched for colony-forming unit–granulocyte-macrophage and for long-term culture initiating cells as compared with bone marrow mononuclear cells, whereas CD342 cells were depleted of progenitors. Three autologous transplants were performed with CD341 cell fractions enriched by immunomagnetic separation. After marrow ablative total body irradiation (920 cGy), prompt hematopoietic recovery was seen with transplanted cell doses of I1.1 3 107 /kg that were 29% to 70% CD341. Engraftment kinetics were similar to those of dogs previously transplanted with approximately 10to 100-fold more unmodified autologous marrow cells. This suggests that CD341 is a marker not only of canine bone marrow progenitors but also for cells with radioprotective or marrow repopulating function in vivo. MoAbs to CD34 will be valuable for future studies of canine hematopoiesis and preclinical studies concerning stem cell transplantation, gene therapy, and ex vivo progenitor cell expansion. r 1998 by The American Society of Hematology.