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Introduction: Checkpoint inhibitor (CI) therapy has revolutionized treatment for non-small cell lung cancer (NSCLC). However, a proportion of patients do not respond to CI therapy for unknown reasons. Although the current paradigm in anti-tumor immunity evolves around T cells, the presence of tertiary lymphoid structures and memory B cells has been positively correlated with response to CI therapy in NSCLC. In addition, double negative (DN) (CD27 - IgD - ) B cells have been shown to be abundant in NSCLC compared to healthy lung tissue and inversely correlate with the intratumoral presence of memory B cells. Nonetheless, no study has correlated DN B cells to survival in NSCLC., Methods: In this study, we evaluated the presence and phenotype of B cells in peripheral blood with flow cytometry of patients with NSCLC and mesothelioma before receiving CI therapy and correlated these with clinical outcome., Results: Non-responding patients showed decreased frequencies of B cells, yet increased frequencies of antigen-experienced CD21- DN (Atypical) B cells compared to responding patients and HC, which was confirmed in patients with mesothelioma treated with CI therapy., Conclusions: These data show that the frequency of CD21- DN B cells correlates with lack of response to CI therapy in thoracic malignancies. The mechanism by which CD21- DN B cells hamper CI therapy remains unknown. Our findings support the hypothesis that CD21- DN B cells resemble phenotypically identical exhausted B cells that are seen in chronic infection or function as antigen presenting cells that induce regulatory T cells., Competing Interests: Declaration of Competing Interest Daphne Dumoulin reports personal fees from Roche, BMS, MSD, Pfizer, Astra Zeneca and Novartis outside the submitted work. Joachim Aerts reports personal fees and nonfinancial support from MSD, personal fees from BMS, Boehringer Ingelheim, Amphera, Eli-Lilly, Takeda, Bayer, Roche, Astra Zeneca outside the submitted work; in addition, Joachim Aerts has a patent allogenic tumor cell lysate licensed to Amphera, a patent combination immunotherapy in cancer pending, and a patent biomarker for immunotherapy pending; Joachim Aerts served as an unpaid editorial board member of Translational Lung Cancer Research from September 2019 to September 2021. The other authors do not have a conflict of interest to disclose., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Introduction: Malignant mesothelioma (MM) is an aggressive cancer that primarily arises from the pleura (MPM) or peritoneum (MPeM), mostly due to asbestos exposure. This study reviewed the Dutch population-based incidence, treatment and survival since the national ban on asbestos in 1993., Materials and Methods: Patients with MPM or MPeM diagnosed from 1993 to 2018 were selected from the Dutch cancer registry. Annual percentage change (APC) was calculated for (age-specific and sex-specific) revised European standardised incidence rates (RESR). Treatment pattern and Kaplan-Meier overall survival analyses were performed., Results: In total, 12 168 patients were included in the study. For male patients younger than 80 years, the MM incidence significantly decreased in the last decade (APC ranging between -9.4% and -1.8%, p<0.01). Among both male and female patients aged over 80 years, the incidence significantly increased during the entire study period (APC 3.3% and 4.6%, respectively, p<0.01). From 2003 onwards, the use of systemic chemotherapy increased especially for MPM (from 9.3% to 39.4%). Overall, 62.2% of patients received no antitumour treatment. The most common reasons for not undergoing antitumour treatment were patient preference (42%) and performance status (25.6%). The median overall survival improved from 7.3 (1993-2003) to 8.9 (2004-2011) and 9.3 months from 2012 to 2018 (p<0.001)., Conclusion: The peak of MM incidence was reached around 2010 in the Netherlands, and currently the incidence is declining in most age groups. The use of systemic chemotherapy increased from 2003, which likely resulted in improved overall survival over time. The majority of patients do not receive treatment though and prognosis is still poor., Competing Interests: Competing interests: JAB reports reimbursements for his institution (Netherlands Cancer Institute) outside the submitted work from Roche, AstraZeneca and Boehringer Ingelheim. JA reports grants from Amphera, grants from Roche, ownership interest (including patents) from Amphera, and advisory roles for Amphera, Boehringer Ingelheim, Bristol Myers Squibb, Eli Lilly, MSD and Roche, outside the submitted work. PB reports financial support to his institution (Netherlands Cancer Institute) for studies by Bristol Myers Squibb and Merck, and advisory roles for Bristol Myers Squibb, Merck and BeiGene. RC reports personal speakers fees from Roche, Pfizer and Bristol Myers Squibb, and personal advisory fees from MSD and Roche, outside the submitted work., (© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Background: Malignant pleural mesothelioma (MPM) is a highly lethal malignancy in need for new treatment options. Although immunotherapies have been shown to boost a tumor-specific immune response, not all patients respond and prognostic biomarkers are scarce. In this study, we determined the peripheral blood T cell receptor β (TCRβ) chain repertoire of nine MPM patients before and 5 weeks after the start of dendritic cell (DC)-based immunotherapy., Materials and Methods: We separately profiled PD1 + and PD1 - CD4 + and CD8 + T cells, as well as Tregs and analyzed 70 000 TCRβ sequences per patient., Results: Strikingly, limited TCRβ repertoire diversity and high average clone sizes in total CD3 + T cells before the start of immunotherapy were associated with a better clinical response. To explore the differences in TCRβ repertoire prior-DC-therapy and post-DC-therapy, for each patient the TCRβ clones present in the total CD3 + T cell fractions were classified into five categories, based on therapy-associated frequency changes: expanding, decreasing, stable, newly appearing and disappearing clones. Subsequently, the presence of these five groups of clones was analyzed in the individual sorted T cell fractions. DC-therapy primarily induced TCRβ repertoire changes in the PD1 + CD4 + and PD1 + CD8 + T cell fractions. In particular, in the PD1 + CD8 + T cell subpopulation we found high frequencies of expanding, decreasing and newly appearing clones. Conversion from a PD1 - to a PD1 + phenotype was significantly more frequent in CD8 + T cells than in CD4 + T cells. Hereby, the number of expanding PD1 + CD8 + T cell clones-and not expanding PD1 + CD4 + T cell clones following immunotherapy positively correlated with overall survival, progression-free survival and reduction of tumor volume., Conclusion: We conclude that the clinical response to DC-mediated immunotherapy is dependent on both the pre-existing TCRβ repertoire of total CD3 + T cells and on therapy-induced changes, in particular expanding PD1 + CD8 + T cell clones. Therefore, TCRβ repertoire profiling in sorted T cell subsets could serve as predictive biomarker for the selection of MPM patients that benefit from immunotherapy., Trial Registration Number: NCT02395679., Competing Interests: Competing interests: JGJVA reports receiving commercial grants from Amphera, holds ownership interests (including patents) in Amphera BV, and is a consultant/advisory board member for Amphera., (© Author(s) (or their employer(s)) 2020. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)