Fetal bovine bone marrow is a rich source of CD34+ hematopoietic progenitors with myelo-monocytic colony-forming activity.

The CD34 glycoprotein is an important marker of hematopoietic stem cells. We used a polyclonal rabbit anti-bovine CD34 antibody to stain fetal and adult bovine bone marrow cells. Flow cytometry revealed a low side scatter (SSC(low)) population of cells that were CD34(+) but negative for leukocyte lineage markers CD11b, CD14 or CD2. Hematopoietic colony assays with CD34(+) and CD34(-) bone marrow cells suggested that the colony-forming potential in SSC(low) bone marrow cells was confined to the CD34(+) fraction. In contrast, this population was not enriched for cells expressing high aldehyde dehydrogenase activity, a metabolic marker that has been used to characterize hematopoietic stem cells. Thus, the CD34 antigen can be used to identify and isolate bovine bone marrow cells exhibiting clonogenic potential in vitro. Moreover, the proportion of CD34(+) cells is very high in fetal bovine bone marrow, indicating it as a rich source of hematopoietic progenitors.