1. ¹Stem Cell and Leukamia Biology Group, and Paterson Institute for Cancer Research, Manchester, UK
2. ²Department of Medical Oncology, University of Manchester School of Cancer Studies, Manchester, UK

Correspondence: Dr R Chopra, Astra Zeneca, Experimental Medicine, Mereside, Alderley Park, Macclesfield, Cheshire SK10 4TG, UK. E-mail: rchopra@picr.man.ac.uk

Received 16 February 2004; Accepted 19 August 2004; Published online 20 December 2004.

Abstract

Murine side population (SP) cells may have an increased ability to engraft lethally irradiated mice and lack CD34 expression. Strategies using CD34 as a primary marker of haemopoietic stem cells may therefore result in the exclusion of a primitive stem cell population. The molecular basis for the murine SP phenotype has been attributed to the multidrug-resistance transporter ABCG2. This study aimed to investigate ABCG2 expression from a variety of human sources and investigate the relationship between ABCG2 expression, the SP phenotype, and expression of markers such as CD34 and CD133. SP cells were observed in different haemopoietic sources, but a significant increase in the number of SP cells was observed in PB following granulocyte colony-stimulating factor mobilisation. No direct correlation between the frequency of SP cells and the expression of ABCG2 was observed. SP cells were identified in both lineage-positive and lineage-negative population and ABCG2 expression was enriched in lineage-negative SP cells. Lineage-negative SP cells were devoid of CD34 expression but enriched for CD133. Subsequent analysis revealed that ABCG2 and CD133 are coexpressed. Together, these data suggest that the ABCG2 transporter is neither required nor responsible for the SP phenotpye in many human blood cells.