IL27 encodes a heterodimeric cytokine that exhibits complex immunoregulatory functions with both pro- and anti-inflammatory properties. IL-27 plays a critical role in T cell differentiation, promoting Th1 responses while suppressing Th2 and Th17 development through STAT1/STAT3 signaling pathways 1. The cytokine demonstrates potent anti-tumor activity by directly enhancing CD8+ T cell persistence and effector function in tumor microenvironments, with high IL27 expression correlating with favorable responses to anti-PD-1/PD-L1 therapy in cancer patients 2. IL-27 also regulates metabolic processes by promoting adipocyte thermogenesis through p38 MAPK-PGC-1α signaling, with decreased serum IL-27 levels observed in obesity 3. In infectious diseases, IL-27 is essential for immunity against Epstein-Barr virus, as IL27RA deficiency leads to severe primary EBV infections due to impaired CD8+ T cell expansion 4. Additionally, IL-27 facilitates CD8+ T cell rescue in chr16 hepatitis B infection through Kupffer cell licensing and cytokine production 5. However, IL-27 signaling can also serve as an immunologic checkpoint in hepatocellular carcinoma, restraining innate cytotoxic lymphocyte function and promoting tumor development 6. These diverse functions make IL-27 a promising therapeutic target across multiple disease contexts.