Dr N Kang, Department of Immunology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, National Key Laboratory of Medical Molecular Biology, 5 Dong Dan San Tiao, Beijing 100005, China. E-maih n.kang@ibms.pumc.edu.cn Correspondence: Dr W He Department of Immunology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, National Key Laboratory of Medical Molecular Biology, 5 Dong Dan San Tiao, Beijing 100005, China. E-mail: hewei@ngd.org.cn