T(H)9, T(H)17, and T(H)22 Cell Subsets and Their Main Cytokine Products in the Pathogenesis of Colorectal Cancer

In recent years, several newly identified T helper (T(H)) cell subsets, such as T(H)9, T(H)17, and T(H)22 cells, and their respective cytokine products, IL-9, IL-17, and IL-22, have been reported to play critical roles in the development of chronic inflammation in the colorectum. Since chronic inflammation is a potent driving force for the development of human colorectal cancer (CRC), the contributions of T(H)9/IL-9, T(H)17/IL-17, and T(H)22/IL-22 in the pathogenesis of CRC have recently become an increasingly popular area of scientific investigation. Extensive laboratory and clinical evidence suggests a positive relationship between these new T(H) subsets and the growth and formation of CRC, whereas, administration of IL-9, IL-17, and IL-22 signaling inhibitors can significantly alter the formation of colorectal chronic inflammation or CRC lesions in animal models, suggesting that blocking these cytokine signals might represent promising immunotherapeutic strategies. This review summarizes recent findings and currently available data for understanding the vital role and therapeutic significance of T(H)9/IL-9, T(H)17/IL-17, and T(H)22/IL-22 in the development of colorectal tumorigenesis.