Given the concern for on-target, off-tumor systemic toxicity of HER2-directed CAR T cells [25] and the propensity for medulloblastoma to metastasize along the leptomeninges of the brain and spinal cord, intraventricular delivery of HER2-BBz-CAR T cells may be preferred over IV administration. Here, ERBB2 is linked to medulloblastoma.