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Adenovirus (Ad) infection and E1A transfection were used to model changes in susceptibility to NK cell killing caused by transient vs stable E1A expression in human cells .
 E1A, human cells, E1A
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:
 E1A, human cells, E1A