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Human T-cell leukemia virus type I ( HTLV-I ) is the etiologic agent of the adult T-cell leukemia , an aggressive and often fatal malignancy of activated human CD4 T cells .
 activated human CD4 T cells
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:
 activated human CD4 T cells