The functional aspects of programmed death 1 ( PD-1 ) and PD ligand 1 ( PD-L1 ) immune checkpoints in malignant mesothelioma have not been studied.
Tumor samples from 65 patients with mesothelioma were evaluated for PD-L1 expression by immunohistochemistry and its prognostic significance.
Malignant effusions from patients with pleural and peritoneal mesothelioma were evaluated for PD-1+ and PD-L1+ infiltrating lymphocytes and their role in inducing tumor cell PD-L1 expression.
Antibody dependent cellular cytotoxicity ( ADCC ) of Avelumab, a fully humanized IgG1 anti PD-L1 antibody towards primary mesothelioma cell lines was evaluated in presence of autologous and allogeneic NK cells.
Of 65 pleural and peritoneal mesothelioma tumors examined, 41 ( 63% ) were PD-L1 positive, which was associated with slightly inferior overall survival compared to patients with PD-L1 negative tumors ( median 23.0 vs 33.3 months; p=0.35 ).
The frequency of PD-L1 expression was similar in pleural and peritoneal mesothelioma patients with 62% and 64% of samples positive, respectively.
Of nine mesothelioma effusion samples evaluated, the fraction of cells expressing PD-L1 ranged from 12 to 83%.
Of 7 patients with paired malignant effusion and peripheral blood mononuclear cells ( PBMC ) samples, PD-L1 expression was significantly higher on CD3+ T cells present in malignant effusions as compared with PBMC ( p=0.016 ).
In addition, CD14+PD-1+ cells were elevated in malignant effusions compared with PBMC ( p=0.031 ).
The lymphocytes present in malignant effusions recognized autologous tumor cells and induced IFN-gamma-mediated PD-L1 expression on the tumor cell surface.
Of the three primary mesothelioma cell lines tested, two were susceptible to Avelumab mediated ADCC in presence of autologous NK cells.
In conclusion, the majority of pleural as well as peritoneal mesothelioma express PD-L1. Malignant effusions in this disease are characterized by presence of tumor cells and CD3+ T cells that highly express PD-L1.
In addition, mesothelioma tumor cells are susceptible to ADCC by anti-PD-L1 antibody Avelumab. ( Xagena )
Khanna S et al, J Thorac Oncol 2016; Epub ahead of print