Brain cancer kills more children in Australia than any other disease. Childhood high-grade gliomas (HGG) are particularly deadly, with 5-year survival rates below 20%. Cancer immunotherapy has proven very successful for adult cancers, but the benefits are yet to be realised for paediatric brain cancer. Anti-CD47 is an immune modulating therapeutic antibody that blocks CD47, a “do not eat me” immune-suppressive signal on brain tumour cells. Blocking CD47 has been proven to render HGG vulnerable to attack by phagocytic immunocytes and extends survival in immune-deficient murine models of HGG. To assess anti-CD47 therapy in the context of a fully functioning immune system, we developed a mouse allograft model of paediatric HGG by deletion of Pten and Cdkn2a, and expression of myristoylated AKT2 in neural stem cells (TK-HGG/Akt2). Flow cytometry revealed that TK-HGG/Akt2 cells highly express CD47, and immune cell profiling showed that microglia (brain-resident phagocytes) were the most abundant immune cell within orthotopic tumours (61%). In vitro assays were performed to determine if anti-CD47 could stimulate phagocytosis using co-cultures of bone marrow-derived macrophages and TK-HGG/Akt2 cells. Phagocytotis was significantly increased anti-CD47 compared to IgG controls (p=0.002). In vivo, administration of anti-CD47 tripled microglial abundance within TK-HGG/Akt2 tumours (p=0.002) and significantly extended survival (34 days anti-CD47 vs 21 days IgG control, p=0.0008). To identify clinically relevant treatment regimens, we assessed the impact of conventional HGG therapies on microglia abundance within murine brain tumours. Tumour-bearing mice were treated with gemcitibine or fractionated radiotherapy (RT) and the effects on microglia were examined. Gemcitibine, currently being tested in ependymoma clinical trials, significantly depleted the proportion of microglia in the brain (20.23% GEM vs 49.5% vehicle), whereas no significant alterations were observed following RT, suggesting anti-CD47 would be best combined with RT. Future studies will investigate this novel combination to determine if combining anti-CD47 treatment with RT can extend survival in mice with HGG and other aggressive forms of paediatric brain cancer.