1. State Key Laboratory of Oncology in Southern China, Cancer Center, Sun Yat-sen University, Guangzhou 510060, China.
2. Present address: Department of Infectious Diseases, Thomas Jefferson University, Philadelphia, PA 19107.
3. Institute of Microbiology, Chinese Academy of Sciences, Beijing 100080, China.
4. Guangzhou Doublle Bio-products Company, Guangzhou 510961, China.