CHI3L1 and cancer: Moreover, recent studies showed that YKL-40 negatively regulates Th1 cells and cytotoxic T lymphocyte (CTL) activity and so its reduction by siRNA could increase the anti-cancer T cell population in lung metastasis [13], and somehow IL-13Rα2, a putative receptor of YKL-40, might play a role in their interplay with T cells [17,48].