3305
In these cells, the expression of MHC-class I antigens is repressed and might allow them to escape from recognition by cytotoxic T lymphocytes ( CTL ) and to develop in tumor .
 ( cell type: cytotoxic T lymphocytes, None) , ( cell type: CTL, None) , ( protein: MHC-class I antigens, 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: cytotoxic T lymphocytes, None) , ( cell type: CTL, None) , ( protein: MHC-class I antigens, None) 