9951
CXCR4 is a chemokine receptor and a coreceptor for T - cell - line - tropic ( X4 ) and dual - tropic ( R5X4 ) human immunodeficiency virus type 1 ( HIV - 1 ) isolates .
 CXCR4
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 CXCR4