11006
The key challenges in transplanted islets are the generation of reactive oxygen species ( ROS ) and associated oxidative stress , pro - inflammatory cytokine - ( TNF alpha ) mediated apoptotic induction , attack by immune cells , and achieving revascularization with minimal hypoxic microenvironment .
 Chemical: oxygen
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: oxygen