Mesothelioma location influences the tumour microenvironment and immune checkpoint therapy response in preclinical models.

Mesothelioma is a cancer derived from mesothelial cells, most commonly arising from the pleura or the peritoneum. Immune checkpoint therapy (ICT) has shown survival benefit for pleural mesothelioma, but little is known about the response in peritoneal mesothelioma. Most preclinical mesothelioma models involve subcutaneous cancer cell implantation, which lacks the relevant tumour microenvironment of peritoneal mesothelioma and does not resemble the clinical presentation. We therefore set out to explore the influence of location on the mesothelioma tumour microenvironment, comparing pleural, peritoneal, and subcutaneous models using identical cell line-derived syngeneic mesotheliomas. We found that the peritoneal location conferred an anti-inflammatory tumour microenvironment, characterised by low IFN, TNFα, and STAT signalling activity, low immune cell infiltration and a gene signature associated with non-response to ICT. ICT was effective in subcutaneous models, but the same cell line-derived tumours were irresponsive when inoculated intraperitoneally. Together, these findings show that peritoneal location is associated with an immune suppressive tumour microenvironment.