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Figure 3. pSTAT3+ reactive astrocytes block CD8+ cytotoxic T cells from cancer cells and upregulate programmed cell death 1 (PDL-1) and vascular endothelial growth factor A (VEGF-A)^[42]. Brain cancer cells also produce matrix metalloproteinases (MMPs) that degrade type IV collagen, the main vascular component of the basement membrane, thus enhancing the access points through the BBB^[46]. The BBB is not disrupted in patients who have the HER2+ subtype. (Image created in BioRender.com)