Three pieces of information led us to address whether NG2 is involved in CNS infiltration by MLLr blasts: (i) MLLr blasts upregulate NG2 expression in extramedullary hematopoietic sites, (ii) CNS infiltration is common in iMLLr-B-ALL and up to 75% of relapses occur within the CNS,43 and (iii) NG2 antigen has an important role in the developing brain and is associated with melanoma cell migration and metastasis.21, 22 As previously reported, leukemia infiltrates were consistently found in meninges/leptomeningeal space but were rarely found within brain parenchyma13 (Figure 5a). Here, CSPG4 is linked to acute lymphoblastic leukemia.