CX3CL1 and glioblastoma: However, the recruitment of microglia to a GBM tumor does not depend on the CX3CL1-CX3CR1 axis [212,213], although one study on the polymorphism of the CX3CR1 gene showed that the CX3CL1-CX3CR1 axis is important for the recruitment of tumor tissue by microglia [214].