Development and characterization of a novel CD34 monoclonal antibody that identifies sheep hematopoietic stem/progenitor cells

Objective We and many others have long used sheep as a predictive model system in which to explore stem cell transplantation. Unfortunately, while numerous markers are available to identify and isolate human hematopoietic stem cells (HSC), no reagents exist that allow HSC/progenitors from sheep to be identified or purified, greatly impeding the application of this well-established large animal model to the study of autologous or allogeneic HSC transplantation. The current studies were undertaken to create a monoclonal antibody to sheep CD34 that would enable isolation and study of sheep HSC/progenitors. Materials and Methods A partial cDNA to the extracellular domain of the sheep CD34 antigen was polymerase chain reaction cloned, characterized, and used to genetically immunize mice and create hybridomas. Results The resultant monoclonal antibody to sheep CD34 allows flow cytometric detection of sheep HSC/progenitors present within bone marrow, cord blood, and mobilized peripheral blood. Moreover, this antibody can be used to enrich for HSC/progenitors with enhanced in vitro colony-forming potential, and also identifies endothelial cells in situ within paraffin-embedded tissue sections, similarly to antibodies to human CD34. Conclusions The availability of this monoclonal antibody recognizing the stem cell antigen CD34 in sheep will greatly facilitate the study of autologous and allogeneic HSC transplantation using this clinically relevant large animal model.