Optimising the Efficacy and Safety of Anti-Mesothelin Chimeric Antigen Receptor T-cell Therapy in Cancer

Abstract

Chimeric Antigen Receptor (CAR) T-cells are genetically modified T-cells that express an antibody single-chain variable fragment (scFv) on the cell surface linked to intracellular T-cell signalling domains. This reprograms the T-cell to lyse tumours that express targeted antigens. CAR T-cells targeting CD19 on B-cells have revolutionised the therapy for CD19+ haematological malignancies; a major goal is to translate this technology into therapies against solid organ malignancies. One target protein in solid organ malignancies is mesothelin (MSLN), which is overexpressed in mesothelioma and pancreatic cancer. This study identified several ways to improve the efficacy and safety of anti-MSLN CAR T-cell therapy. First, immunohistochemistry of MSLN in mesothelioma specimens identified heterogeneity of MSLN expression between patients and within the same tumour specimen, emphasising the necessity for a companion diagnostic test to assess patient eligibility for anti-MSLN therapy. Second, in vitro assessment of the cytotoxicity of two current CAR T-cell scFvs revealed that the CARs based on the m912 scFv were not cytotoxic in the setting of low and medium MSLN antigen density, whereas CARs based on the SS1 scFv were cytotoxic against all MSLN-expressing cell lines. The cytotoxic activity of m912 CARs could be enhanced when administered with drugs that increased tumour cell MSLN antigen density. Finally, stimulation of CAR T-cells via their T Cell Receptor (TCR) revealed increased function in CD8+ CAR T-cells which have the CAR 4-1BB costimulatory domain. This novel biology is now a pertinent consideration when selecting costimulatory domains in CAR T-cell design. Therefore, this study contributes new insights to enhance the efficacy and safety of anti-MSLN CAR T-cells in future clinical trials.