770
However, this efficient propagation of the LTR-modified tat mutants was restricted to some lymphoid cell lines that have been transformed with other viruses .
 ( protein: tat mutants, None) , ( cell line: lymphoid cell lines, None) , ( protein: LTR-modified tat mutants, 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:
 ( protein: tat mutants, None) , ( cell line: lymphoid cell lines, None) , ( protein: LTR-modified tat mutants, None) 