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In recent years , studies used stem cells that over - express different neurotrophic factors , such as BDNF , GDNT , or NT3 , and found that the delivery of these genetically - modified stem cells to animal models of ischemic stroke is safe and effective , thus suggesting that stem cell - based gene therapy may be a promising treatment for stroke .
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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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