Abstract 1726: Evaluation of PD-L1/PD-1 on circulating tumor cells (CTCs) and on primary tumor in advanced non-small cell lung cancer (NSCLC)
Authors: Kallergi Galaktea , Vetsika Eleni Kyriaki , Aggouraki Despoina , Lagoudaki Eleni , Koutsopoulos Anastasios , Koinis Filippos , Katsarlinos Panagiotis , Trypaki Maria , Stournaras Christos , Georgoulias Vassilis , Kotsakis Athanasios 
Published: July 2017

Abstract
Introduction: Circulating tumour cells (CTCs) are responsible for the metastatic dissemination of the tumor. They have been shown to express Programmed Death-Ligand1 (PD-L1) to escape from the immune system surveillance through its ligation with the PD-1receptor on the surface of effector immune cells. We investigated the expression of PD-1/PD-L1 on CTCs isolated from NSCLC patients treated with chemotherapy.
Methods: CTCs were isolated based on their size using the ISET platform from 30 stage IV chemo-naïve NSCLC patients (before and after chemotherapy). CTCs were detected after staining with Giemsa and immunofluorescence (IF). Double and triple staining experiments with different combination of antibodies: [Cytokeratins(CK)/PD-1/CD45 and CK/PD-L1/CD45] were performed and the samples were analyzed with the ARIOL system.
Results Giemsa staining showed that twenty-three (77%) out of 30 and six (54.5%) out of 11 patients had detectable CTCs at baseline and after the 3rd cycle of front-line chemotherapy. IF staining revealed seventeen out of 30 (56.7%) patients positive for CTCs at baseline level and 8 out of 11 (72.7%) samples after the 3rd cycle of treatment. PD-1 and PD-L1 expression was observed in 53% (9/17) and in 47% of the CTC-positive patients at baseline; in addition, 13% (1/8) and 63% (5/8) patients had PD-1 and PD-L1, respectively after the 3rd cycle. Among the total number of detected CTCs, 67% were PD-1(+) at baseline and 25% after the 3rd cycle (p=0.069). In addition, 26% and 80% were PD-L1(+) at baseline and after the 3rd cycle, respectively. Patients with more than 3 PD-1 positive CTCs showed shorter PFS (p=0.022). Primary tissue from ten of the examined patients was also available. More than 5% of PD-L1 (+) tumor infiltrating lymphocytes (TILs) were observed in 20% (2/10) of the patients. More than 5% PD-L1 positive cells in the primary tumor were observed in 20%. However the two group of the patients were different. In addition both patients with PD-L1 (+) TILs harvested CTCs with PD-1 expression and one of them had also PD-L1 positive CTCs.
Conclusion: PD-1- and PD-L1-positive CTCs could be detected before and during 1st line treatment in metastatic NSCLC. This expression was related to patients’ prognosis, implying that these molecules can be served as targets for metastasis restoration. Furthermore the expression of PD-1 on CTCs suggests a bilateral cross-talk between tumor and immune cells.
Citation Format: Galaktea Kallergi, Eleni Kyriaki Vetsika, Despoina Aggouraki, Eleni Lagoudaki, Anastasios Koutsopoulos, Filippos Koinis, Panagiotis Katsarlinos, Maria Trypaki, Christos Stournaras, Vassilis Georgoulias, Athanasios Kotsakis. Evaluation of PD-L1/PD-1 on circulating tumor cells (CTCs) and on primary tumor in advanced non-small cell lung cancer (NSCLC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1726. doi:10.1158/1538-7445.AM2017-1726