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Although erythropoietin ( Epo ) is essential for the production of mature red blood cells , the cooperation with other factors is required for a proper balance between progenitor proliferation and differentiation .
 erythropoietin, mature red blood cells, Epo
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:
 erythropoietin, mature red blood cells, Epo