Immunotherapy based on two checkpoint inhibitors (ICI), programmed cell death 1 (PD-1, Nivolumab) and cytotoxic T-lymphocyte 4 (CTLA-4, Ipilimumab), has provided a significant improvement in overall survival for malignant mesothelioma (MM). Despite this major breakthrough, the median overall survival of patients treated with the two ICIs only reached 18.1 months vs. 14 months in standard chemotherapy. With an objective response rate of 40%, only a subset of patients benefits from immunotherapy. A critical step in the success of immunotherapy is the presentation of tumor-derived peptides by the major histocompatibility complex I (MHC-I) of tumor cells. These neoantigens are potentially immunogenic and trigger immune responses orchestrated by cytotoxic cells. In MM, tumor development is nevertheless characterized by a low mutation rate despite major structural chromosomal rearrangements driving oncogenesis (BAP1, NF2, CDKN2AB). In this opinion, we propose to investigate an approach based on the mechanisms of the DNA damage tolerance (DDT) pathways to increase the frequency of non-synonymous mutations. The idea is to transiently activate the error-prone DDT in order to generate neoantigens while preserving a fully competent antitumor immune response.

The composition of the tumor microenvironment (TME) mediates the outcome of chemo- and immunotherapies in malignant pleural mesothelioma (MPM). Tumor-associated macrophages (TAMs) and monocyte myeloid-derived immunosuppressive cells (M-MDSCs) constitute a major fraction of the TME. As central cells of the innate immune system, monocytes exert well-characterized functions of phagocytosis, cytokine production, and antibody-dependent cell-mediated cytotoxicity (ADCC). The objective of this study was to evaluate the ability of monocytes to exert a direct cytotoxicity by cell-to-cell contact with MPM cells. The experimental model is based on cocultures between human blood-derived monocytes sorted by negative selection and mesothelioma cell lines. Data show (i) that blood-derived human monocytes induce tumor cell death by direct cell-to-cell contact, (ii) that VPA is a pharmacological enhancer of this cytotoxic activity, (iii) that VPA increases monocyte migration and their aggregation with MPM cells, and (iv) that the molecular mechanisms behind VPA modulation of monocytes involve a downregulation of the membrane receptors associated with the M2 phenotype, i.e., CD163, CD206, and CD209. These conclusions, thus, broaden our understanding about the molecular mechanisms involved in immunosurveillance of the tumor microenvironment and open new prospects for further improvement of still unsatisfactory MPM therapies

Tumor-associated macrophages (TAM) are particularly abundant (i.e. 27% ± 9%) in the microenvironment of malignant pleural mesothelioma (MPM). These macrophages do not correspond to classical (M1) and alternatively-activated (M2) phenotypes but, instead, are shaped by local inflammatory mediators released in the pleura. We previously showed that, besides classical functions exerted by macrophages (i.e. phagocytosis, cytokine expression and antigen presentation), murine RAW264.7 cells are directly cytotoxic to MPM tumors (Hamaidia et al, JCI Insight 4:e128474). Upon direct cell-to-cell contact, RAW264.7 macrophages kill mesothelioma cells by a mechanism of oxeiptosis involving the enhancer of zeste homolog 2 (EZH2) methyltransferase. We have now investigated this immune-editing activity in human mesothelioma. We show that M1-activated primary macrophages are more cytotoxic for M14K cells than M2. The killing activity of M1 macrophages is dependent on NADPH oxidase activity and peroxynitrite levels. Mesothelioma cells and M2 macrophages interact through an inhibitory synapse characterized by engagement of the PD-1 receptor. Consistently, the immune-editing activity of M2 macrophages is partially restored in presence of neutralizing anti-PD1 antibody. Primary human macrophages cultured in presence of pleural effusions of MPM patients are less cytotoxic than M1 and are unable to inhibit tumor growth in mice. Macrophages differentiated in pleural effusions display a broad spectrum of cytotoxic activities (i.e. from complete inactivity to rates similar to those of M2). Luminex profiling of pleural fluids has identified a series of key mediators associated with the cytotoxic phenotype. The best correlation is obtained with resistin (RETN, FIZZ3, ADSF). Recombinant human resistin improves the killing activity of pleural effusion macrophages in cell culture. Gene transduction of RETN in RAW264.7 impairs growth of AB12 tumors in BALB/c mice. In conclusion, we have shown that resistin is the main factor that mediates immunoediting activity exerted by primary human macrophages towards mesothelioma cells, opening new prospects for therapeutic intervention. Citation Format: Malik Hamaidia, Majeed Jamakhani, Jean-Rock Jacques, Alexis Fontaine, Arnaud Scherpereel, Eric Wasielewski, Louis Renaud, Vincent Heinen, Bernard Duysinx, Luc Willems. Resistin mediates the immunoediting activity exerted by primary human macrophages towards mesothelioma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 663.

BackgroundOnly a fraction of patients with malignant pleural mesothelioma (MPM) will respond to chemo- or immunotherapy. For the majority, the condition will irremediably relapse after 13 to 18 months. In this study, we hypothesized that patients’ outcome could be correlated to their immune cell profile. Focus was given to peripheral blood eosinophils that, paradoxically, can both promote or inhibit tumor growth depending on the cancer type.MethodsThe characteristics of 242 patients with histologically proven MPM were retrospectively collected in three centers. Characteristics included overall survival (OS), progression-free survival (PFS), overall response rate (ORR) and disease control rate (DCR). The mean absolute eosinophil counts (AEC) were determined by averaging AEC data sets of the last month preceding the administration of chemo- or immunotherapy.ResultsAn optimal cutoff of 220 eosinophils/µL of blood segregated the cohort into two groups with significantly different median OS after chemotherapy (14 and 29 months above and below the threshold, p = 0.0001). The corresponding two-year OS rates were 28% and 55% in the AEC ≥ 220/µL and AEC < 220/µL groups, respectively. Based on shorter median PFS (8 vs 17 months, p < 0.0001) and reduced DCR (55.9% vs 35.2% at 6 months), the response to standard chemotherapy was significantly affected in the AEC ≥ 220/µL subset. Similar conclusions were also drawn from data sets of patients receiving immune checkpoint-based immunotherapy.ConclusionIn conclusion, baseline AEC ≥ 220/µL preceding therapy is associated with worse outcome and quicker relapse in MPM.