CCL2 and graft versus host disease: Interestingly, several chemokines that we and others have shown to be critical to effector cell migration in GVHD — including CXCL10 via CXCR3 (33, 34), CCL3 via CCR1 (35, 36), and CCL2 via CCR2 (37, 38) — were found to be significantly elevated in the serum of KO recipients on day +7 (Figure 4C).