The flow cytometry protocol used was similar to the immunofluorescence protocol described earlier, in terms of the cell preparation and treatment. However, the selected polyclonal antibodies used were as follows: Anti-vimentin, anti-CD44 and anti-CD71 antibodies (all rabbit anti-chicken antibodies; dilution, 1:100; cat. nos. bs-0756R, bs-2507R and bs-1782R, respectively; Beijing Biosynthesis Biotechnology Co. Ltd.). Flow cytometric analysis was performed on the mononuclear cell suspension, and 5×104 cells were incubated with 10 µl FITC-conjugated antibodies (18 (link)). Cells were acquired using a FACSCalibur flow cytometer and CytExpert Cell Quest software, and then analyzed with Paint-A-Gate software (BD Biosciences, San Jose, CA, USA).