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After stimulation by PMA , RXR alpha expression increased in H9 and U937 cells but not in CEM cells .
 RXR alpha, U937 cells, H9, CEM cells
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:
 RXR alpha, U937 cells, H9, CEM cells