High grade gliomas such as glioblastoma (GBM) and diffuse midline gliomas (DMG) are the most fatal and aggressive forms of brain cancer, and existing treatments have limited efficacy. Chimeric Antigen Receptor (CAR) T cell therapies are a promising approach to treat brain cancer due to their targeted nature and ability to cross the blood brain barrier. A major challenge for translating this therapy into the clinic is the limited number of antigens that are actively being explored. Our group have employed cell surface proteomics to map the surface proteome of adult and paediatric high grade glioma patient samples to identify novel CAR T cell targets. Ephrin tyrosine kinase A3 (EphA3) protein belongs to a family of Ephrin proteins that are highly expressed in brain cancer. EphA3 was a predominant protein identified in our primary patient datasets, further confirming existing evidence of EphA3 overexpression in GBM patient samples and cell lines. We therefore pursued EphA3 as a promising immunotherapy target.
This study aims to investigate an EphA3 CAR T cell targeted therapy for adult and paediatric high grade gliomas. A second generation EphA3-targeted CAR was designed and transduced into primary human T cells. EphA3-targeted CD8+ CAR T cells were effective in killing GBM and DIPG cell lines in an antigen specific manner in vitro. These findings were subsequently translated into an intracranial orthotopic preclinical model of luciferase-labelled GBM and DIPG tumour bearing NSG mice. We generated human EphA3-targeted CAR T cells from three independent human donors and treated GBM and DIPG-tumour bearing mice. Mice were imaged weekly to monitor tumour burden. Excitingly, EphA3-targeted CAR T cells demonstrated potent anti-tumour efficacy, completely reducing the tumour burden within 4 weeks post treatment. We then performed rechallenge experiments in tumour-cleared mice to test for remaining functional CAR T cells. Mice exhibited full clearance of the second intracranially implanted tumours and sustained complete response up to 6 months post treatment.
Future work will incorporate this EphA3-targeted CAR T cell therapy into other brain cancer models and combination approaches for translation into promising novel immunotherapies, to help brain cancer patients and their families.