Malignant pleural mesothelioma (MPM) is a rare and incurable cancer. Most patients are diagnosed with unresectable disease for which treatment options are limited. The lack of prognostic biomarkers further complicates the decision-making. Recently, the introduction of immune checkpoint inhibitors (ICIs) has marked a shift but has failed to produce significant benefits for a large proportion of patients. Maximizing the efficiency of ICIs and developing new protocols to improve drug efficacy is the best possible strategy for improving the life expectancy and quality of life of patients with MPM. This study aims to characterize the organization of the immune system infiltrating mesothelioma and the dynamics of its interaction with the tumor. The rationale is that deciphering this complexity will help improve our understanding of the mechanisms underlying this disease and provide a new tool to optimize the use of ICIs in these patients.