5644
Gene therapy has proven to be effective in experimental stroke , but it suffers from disadvantages that limit its clinical application , such as difficulty in intracranial delivering of therapeutic genes , low efficacy in transfecting host cells and long - term expression of exogenous genes .
 None
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None