13863
We examined signaling by erythropoietin in highly purified human colony forming unit-erythroid cells , generated in vitro from CD34(+) cells .
 ( cell type: highly purified human colony forming unit-erythroid cells, None) , ( cell type: CD34(+) cells, None) , ( protein: erythropoietin, None) 
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: RNA,cell type,protein,cell line,DNA, Arguments type: . 
Text: {0} 
Answer:
 ( cell type: highly purified human colony forming unit-erythroid cells, None) , ( cell type: CD34(+) cells, None) , ( protein: erythropoietin, None) 