Gating strategy for detection of circulating hematopoietic progenitor cells (cHPCs) on the basis of the ISHAGE guidelines.¹⁷ We used CD34 and CD45 expression as well as the morphologic qualities of cHPCs for their detection. The upper panels (A-D) represent a patient sample stained with anti-CD45–fluorescein isothiocyanate (FITC) and anti-CD34–phycoerythrin (PE). The lower panels (E-H) show the same sample using an isotype control for anti-CD34. We first counted 200 000 CD45⁺ cells (panels A and E). From this primary gate, cHPCs were identified by means of the additional expression of CD34 (panels B and F). The CD45 antigen expression (panels C and G) and the characteristic light-scatter properties (panels D and H) are shown.