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Thymic dendritic cells ( DC ) mediate negative selection at a relatively late stage of the T-cell developmental pathway .
 Thymic dendritic cells, DC
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:
 Thymic dendritic cells, DC