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Among natural killer ( NK ) cells , highly active NK cells ( CD 16 + CD 57 - ) markedly increased shortly after BMT , and gradually returned to normal .
 natural killer ( NK ) cells, NK cells
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Anatomy 
Text: {0} 
Answer:
 natural killer ( NK ) cells, NK cells