To determine if YKL-40-expressing tumors are associated with PD-L1-positive vessel development and decreased immune toxicity in vivo, we transplanted mouse glioma GL261 cells over-expressing the control vector or YKL-40 orthotopically into the brains of C57BL/6 mice (Figure 2A and Figure S2A). Here, CHI3L1 is linked to central nervous system cancer.