Targeting tumour associated antigens expressed in osteosarcoma and ewing's sarcoma with CAR-T cells

Abstract

Background & Aim The establishment of Chimeric Antigen Receptor (CAR) T cell immunotherapy as a treatment for refractory and relapsed B cell malignancies demonstrates that genetic modification of immune cells to circumvent tumour cell immune escape is a powerful strategy to pursue in the context of other paediatric cancers. However, efforts to develop effective CAR T cell therapies for solid tumours face a number of challenges; establishing an effective dose, route of administration, tumour cell mediated dampening of immune cell function, and overcoming heterogeneous antigen expression across the tumour cell population. The focus of our work is to translate the therapeutic potential of CAR-T cell therapy into an effective treatment for children with recurrent or refractory bone tumours. In addition, we are seeking to ensure effective targeting of metastatic spread of these tumours, since metastasis at the time of diagnosis is a significant problem in this patient population. Methods, Results & Conclusion We have developed reagents and methodology to generate CAR T cells specific for the protein Erythropoietin-producing Hepatocellular receptor tyrosine kinase class A2 (EphA2), which is expressed on a range of paediatric solid tumours. We can show that EphA2 CAR T cells specifically target and kill EphA2+ osteosarcoma and Ewing's sarcoma cell lines in vitro, alongside secretion of cytokines indicative of effector T cell activation. In in vivo sub-cutaneous osteosarcoma and Ewing's sarcoma xenograft models, EphA2 CAR T cells effectively mediate complete tumour regression in a dose and route dependent manner, with direct injection into established tumours resulting in extended survival. Systemic delivery of CAR T cells was also effective at mediating tumour regression and extending survival, but required a higher cell dose. Studies testing EphA2 CAR T cell efficacy against metastatic osteosarcoma deposits are currently ongoing. Further work focussing on safety and possible off-target effects, design of alternative gene therapy vectors and combinatorial testing of EphA2 CAR T cells with CAR T cells targeting alternative antigens, or immune checkpoint blockade, will elucidate a way forward in designing an effective CAR T cell therapy for osteosarcoma and Ewing's sarcoma.