FROM VEIN TO BRAIN: ENHANCING TRAffiCKING OF CAR T-CELLS IN DIFFUSE MIDLINE GLIOMA

Abstract AIMS H3K27M-altered diffuse midline glioma (DMG) is the deadliest childhood brain tumour, with treatment limited by anatomical location and chemoresistance; palliative radiotherapy remains the mainstay of treatment. Chimeric antigen receptor (CAR) T-cell therapy produces promising pre-clinical results in treating these tumours whilst leaving interspersed normal brain cells intact. Early clinical outcomes of GD2-CAR T-cell therapy for H3K27M-altered DMG demonstrate short-lived neurological and radiological improvement. Enhancing trafficking to and infiltration into the tumour core may enhance CAR T-cell efficacy. Here, advanced T-cell engineering modules are tested for their ability to improve CAR T-cell trafficking. METHOD A library of T-cell engineering modules was created each with a unique DNA barcode to allow identification of CAR T-cells expressing a given module. The library includes chemokine receptors (CCR) to improve tumour homing by chemotaxis towards tumour-secreted chemokines, adhesion molecules to increase extravasation across the blood-brain-barrier, and molecules to degrade upregulated tumour extracellular matrix (ECM) components to improve CAR T-cell motility through the tumour. Murine T-cells were co-transduced with a CAR and barcoded advanced T-cell engineering modules and administrated intravenously in syngeneic models of high-grade glioma (HGG)/DMG. Tumour, normal brain, bone marrow, spleen and liver tissue were collected at several time points post CAR T-cell administration to assess presence of CAR T-cells using genetic barcodes. RESULTS Co-expression of advanced T-cell engineering modules did not impair CAR T-cell function in vitro. CARs co-expressing selected CCRs were preferentially detected in tumour tissue in mice with GL261-EGFRvIII or H3.3K27Mp53LOFPDGFRAWT-engrafted tumours. Findings were further validated by flow cytometry detection of selected CCR-expressing CAR T-cells as compared to CAR T-cells without additional engineering components. Similar experiments for adhesion molecules and ECM modifiers are planned. CONCLUSION Results to date indicate that CAR T-cells co-expressing selected CCRs enhance their homing to HGG/DMG tumours, encouraging further in vivo research to assess impact on CAR T-cell efficacy.