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In preliminary studies, we have analyzed the hematopoietic growth factor ( HGF ) requirement of hematopoietic progenitor cells ( HPCs ) purified from embryonic-fetal liver ( FL ) and grown in fetal calf serum-supplemented (FCS+) clonogenic culture .
 HPCs, hematopoietic progenitor cells, HGF, hematopoietic growth factor
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 HPCs, hematopoietic progenitor cells, HGF, hematopoietic growth factor