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To gain a better understanding of the impact of long terminal repeat ( LTR ) sequence diversity on LTR -directed gene expression in cells of the central nervous system ( CNS ) and immune system , we amplified and cloned LTRs from proviral DNA in HIV-1 -infected peripheral blood .
 LTR, proviral DNA, LTRs, LTR, HIV-1 -infected peripheral blood, LTR -directed gene, long terminal repeat
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 LTR, proviral DNA, LTRs, LTR, HIV-1 -infected peripheral blood, LTR -directed gene, long terminal repeat