6404
It was shown by transient expression assay that HS - 40 behaved as an authentic enhancer for high - level zeta 2 globin promoter activity in K562 cells , an erythroid cell line of embryonic and / or fetal origin .
 HS - 40, zeta 2 globin promoter
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 HS - 40, zeta 2 globin promoter