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This differential effect of E1A expression on the cytolytic phenotypes of infected and stably transfected human cells suggests that human NK cells provide an effective immunologic barrier against the in vivo survival and neoplastic progression of E1A-immortalized cells that may emerge from the reservoir of persistently infected cells in the human host .
 ( cell type: human NK cells, None) , ( cell line: E1A-immortalized cells, None) , ( cell type: human cells, None) , ( protein: E1A, None) , ( cell type: NK cells, None) , ( cell type: persistently infected cells, 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: human NK cells, None) , ( cell line: E1A-immortalized cells, None) , ( cell type: human cells, None) , ( protein: E1A, None) , ( cell type: NK cells, None) , ( cell type: persistently infected cells, None) 