5814
Human T-cell leukemia virus type 1 ( HTLV-1 ) Tax is thought to play a pivotal role in immortalization of T cells .
 T cells, Tax
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:
 T cells, Tax