AQP1 and acute myeloid leukemia: Immunofluorescence staining of seven sporadic human AML tumours revealed that all tumours contained cells that express proteins that are expressed in proximal tubular epithelial cells in the kidney, namely NAPI2A, pan-CD133 and AQP1, but did not contain cells expressing THP, a marker of epithelial cells of the thick ascending limb of the loop of Henle (Fig. 6a).