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In addition , immune responses can be further customized though optimization of delivery systems , tuning the size of particulate vaccines , targeting specific cells of the immune system ( e . g . dendritic cells ) , and adding components to aid vaccine efficacy in whole immunized populations ( e . g . promiscuous T - helper epitopes ) .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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