13785
Indeed, USA-derived PC2 was found to act synergistically with PC4 in reproducing the function of intact USA in the assay system .
 USA-derived PC2, PC4
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:
 USA-derived PC2, PC4