5661
In contrast, APC pulsed with Ala -substituted peptides 430-444 , 442A or 433-442A at neutral pH failed to stimulate the T cell clone , while APC pulsed at acidic pH and subsequently washed led to successful T cell activation .
 APC, APC, T cell clone
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:
 APC, APC, T cell clone