Acknowledgments
This work was supported by grants from the National Natural Science Foundation of China (Grant NO 81290342 and 81501757); the development grants of State Key Laboratory of Infectious Disease Prevention and Control (Grant NO 2014SKLID103 and 2015SKLID505); the Special National Project on Research and Development of Key Biosafety Technologies (2016YFC1201900); and the National Key Plan for Scientific Research and Development of China (2016YFD0500300).