4153
Using this system, we observed that CD28 stimulation by B7-transfected CHO cells induced a proliferative response in T cells that was not accompanied by measurable IL-2 production .
 ( protein: IL-2, None) , ( cell line: B7-transfected CHO cells, None) , ( protein: CD28, None) , ( cell type: T 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:
 ( protein: IL-2, None) , ( cell line: B7-transfected CHO cells, None) , ( protein: CD28, None) , ( cell type: T cells, None) 