1. Division of Gastroenterology, First Affiliated Hospital; Sun Yat-Sen University; Guangzhou Guangdong 510080 People's Republic of China
2. VA Palo Alto Health Care System; Stanford University Medical School; Palo Alto CA 94304 USA
3. Stem Cell and Cancer Center, First Affiliated Hospital; Jilin University; Changchun Jilin 130061 People's Republic of China