1. Jiangsu Center for Drug Screening, China Pharmaceutical University, Nanjing 210038, PR China
2. Animal Infectious Disease Laboratory, College of Veterinary Medicine, Yangzhou University, Yangzhou 225009, PR China
3. Laboratory of Nucleic Acid Vaccines, Department of Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
4. China–US Vaccine Research Center, the First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, PR China