Analysis of human haemopoietic cells isolated with the novel AC 133 monoclonal antibody

The AC133 antibody recognises a cell surface antigen present on haemopoietic stem and progenitor cells. The antigen is selectively expressed on a subset of CD34cells thought to contain all of the primitive stem cell activity (Yin et al 1997). We used the antibody to assess the distribution of the antigen on CD34' cells from normal bone marrow, cord blood and apheresis samples. Using two populations, CD34 AC133 and CD34'ACI33- isolated from cord blood we assessed the function of these cells in in vitro clonogenic assays, twostage long-term bone marrow cultures, and in NOD/SCID mice. ACI33 stained 28% (S.E.+/- 9.1) of the CD34cells in normal bone marrow, 43% (S.E.+/-3.5) in cord blood. This figure increased to 87% (S.E.+/- 2.1) of CD34' cells in apheresis samples About 60% of alt the colony-forming cells were contained in the double positive, CD34 AC133 population Long-term culture on irradiated bone marrow stroma for eight weeks indicated that the CD34 AC133' population was highly enriched in LTC-IC There was a 70 - 200 fold increase in the number of GM-CFC generated, compared with CD34 AC133-cells. As few as 5 x 103 CD34 AC133' engrafted and proliferated in the NOD/SCID mice and human cells could be detected eight weeks post transplant. No engraftment was observed in animals transplanted with CD34 AC 133" cells AC133 binds to a-subset of CD34+ cells which is enriched in cells with primitive characteristics In combination with other markers, the antibody should prove useful in distinguishing haemopoietic stem cells.