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Updated: May 10, 2026
Orthotopic Implantation and Peripheral Immune Cell Monitoring in the II-45 Syngeneic Rat Mesothelioma Model
Published on: October 2, 2015
Mesothelin antigen density influences anti-mesothelin chimeric antigen receptor T cell cytotoxicity
Gerard J Chu1, Charles G Bailey2, Rajini Nagarajah3
1Gene and Stem Cell Therapy Program Centenary Institute, Camperdown, NSW, Australia; Department of Clinical Immunology and Allergy, Royal Prince Alfred Hospital, Camperdown, NSW, Australia; Faculty of Medicine and Health, The University of Sydney, Sydney, NSW, Australia.
Background Aims:
Several anti-mesothelin (MSLN) chimeric antigen receptor (CAR) T cells are in phase 1/2 clinical trials to treat solid-organ malignancies. The effect of MSLN antigen density on MSLN CAR cytotoxicity against tumor cells has not been examined previously, nor are there data regarding the effect of agents that increase MSLN antigen density on anti-MSLN CAR T cell efficacy.
Methods:
MSLN antigen density was measured on a panel of pancreatic cancer and mesothelioma cell lines by flow cytometry. In parallel, the cytotoxicity and specificity of two anti-MSLN CAR T cells (m912 and SS1) were compared against these cell lines using a real-time impedance-based assay. The effect of two MSLN 'sheddase' inhibitors (lanabecestat and TMI-1) that increase MSLN surface expression was also tested in combination with CAR T cells.
Results:
SS1 CAR T cells were more cytotoxic compared with m912 CAR T cells against cell lines that expressed fewer than ∼170 000 MSLN molecules/cell. A comparison of the m912 and amatuximab (humanized SS1) antibodies identified that amatuximab could detect and bind to lower levels of MSLN on pancreatic cancer and mesothelioma cell lines, suggesting that superior antibody/scFv affinity was the reason for the SS1 CAR's superior cytotoxicity. The cytotoxicity of m912 CAR T cells was improved in the presence of sheddase inhibitors, which increased MSLN antigen density.
Conclusions:
These data highlight the value of assessing CAR constructs against a panel of cells expressing varying degrees of target tumor antigen as occurs in human tumors. Furthermore, the problem of low antigen density may be overcome by concomitant administration of drugs that inhibit enzymatic shedding of MSLN.
Insights
Chimeric antigen receptor (CAR) T cells targeting mesothelin (MSLN) show varying efficacy based on MSLN density. Combining CAR T cells with MSLN-sheddase inhibitors enhances anti-tumor activity, offering a strategy to overcome low antigen expression.
Area of Science:
- Immunotherapy
- Oncology
- Cellular Therapy
Background:
- Anti-mesothelin (MSLN) chimeric antigen receptor (CAR) T cells are under investigation for solid tumors.
- The impact of MSLN antigen density on CAR T cell efficacy and the role of MSLN-sheddase inhibitors remain unexplored.
Purpose of the Study:
- To investigate the relationship between MSLN antigen density and the cytotoxicity of anti-MSLN CAR T cells.
- To evaluate the effect of MSLN-sheddase inhibitors on anti-MSLN CAR T cell efficacy.
Main Methods:
- Quantified MSLN antigen density on pancreatic cancer and mesothelioma cell lines using flow cytometry.
- Assessed cytotoxicity of two anti-MSLN CAR T cells (m912 and SS1) against these cell lines.
- Tested the combination of CAR T cells with MSLN-sheddase inhibitors (lanabecestat and TMI-1).
Main Results:
- SS1 CAR T cells demonstrated superior cytotoxicity compared to m912 CAR T cells, particularly on cells with lower MSLN expression.
- Higher antibody/scFv affinity of the SS1 CAR construct correlated with enhanced cytotoxicity.
- MSLN-sheddase inhibitors increased MSLN surface expression and improved the efficacy of m912 CAR T cells.
Conclusions:
- CAR T cell efficacy is influenced by target antigen density, necessitating evaluation across varying antigen expression levels.
- Inhibiting MSLN enzymatic shedding represents a potential strategy to enhance anti-MSLN CAR T cell therapy for solid tumors.
