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The replicative form of Epstein-Barr virus ( EBV ) DNA was studied using two lymphoblastoid cell lines , X50-7 and 6F11, which are latently infected by Epstein-Barr virus .
 lymphoblastoid cell lines
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:
 lymphoblastoid cell lines