Each Db‐Fc was assessed by flow cytometry for binding to TF‐1 cells, which are derived from a human erythroleukemia, display endogenous EPOR, and only grow in the presence of either EPO, granulocyte‐macrophage colony‐stimulating factor (GMCSF), or interleukin 3 (IL‐3) (Kitamura et al., 1989). Here, CSF2 is linked to erythroleukemia.