DIPG-36. ANTI-GD2 CHIMERIC ANTIGEN RECEPTOR T CELLS AS A POTENT IMMUNOTHERAPY REGIMEN IN XENOGRAFT MODELS OF HISTONE 3 K27M MUTANT DIFFUSE MIDLINE GLIOMA

Abstract

Histone 3 K27M mutated diffuse midline glioma (H3K27M DMG) is a universally fatal pediatric brain tumor. Despite improved understanding of the molecular origins of this disease, translations to improvement in clinical outcomes have yet to materialize. To date, there has been little target exploration for immunotherapy applications in H3K27M DMG. Here we report substantial preclinical efficacy of chimeric antigen receptor (CAR)-bearing T cells targeting the disialoganglioside GD2 in patient-derived orthotopic xenograft models of H3K27M DMG. GD2 is highly and uniformly expressed in patient-derived H3K27M DMG cultures, and in vitro assays demonstrate substantial targetdependent cytokine generation and target cell killing. Two H3 WT pediatric high-grade gliomas (HGG) cultures do not express significant levels of GD2, and the H3K27M mutation is associated with increased synthesis of ganglioside pathway synthesis enzymes, suggesting expression of the GD2 antigen is driven by H3K27M-induced transcriptional dysregulation. Single-dose systemic administration of GD2-4-1BBz-CAR T cells in multiple orthotopic xenograft models of H3K27M DMG achieves potent and lasting antitumor efficacy within a 4-week period of administration compared to a CD19-4-1BBz-CAR T cell control cohort. In brainstem xenografts, GD2-CAR T cell therapy cleared established tumor as measured by in vivo bioluminescence imaging and follow-up histology, and significantly prolonged survival. Using a fluorescently-labeled GD2- CAR, we demonstrate tumoricidal GD2-CAR T cells infiltrating the brain parenchyma and sparing of local neurons during tumor clearing. Treatment-associated neuroinflammation in brainstem xenografts is accompanied by transient ventriculomegaly due to swelling of the targeted tumors, which is accompanied by transient weight loss followed by full recovery. Similar swelling in thalamic xenograft models is lethal in a significant fraction of animals, presumably due to uncal herniation. These results demonstrate potent antitumor effects of GD2-directed CAR T cells in H3K27M DMG, and suggest an important role for neuroanatomic site in neurotoxicity associated with CAR T cell therapy. If these results are predictive of human response, GD2-directed CAR T cell therapy in the setting of careful clinical management could have a transformative impact upon H3K27M DMG outcomes.