Lung cancer is the most common cause of cancer related death worldwide. Circulating tumour cells (CTCs) allows the assessment of tumor changes over time. Tumor cells may escape from the immune system through, among others, the PD-1/PD-L1 interaction between tumor cells and immune system which results to immunosuppression. The expression of PD-1/PD-L1 on CTCs isolated from NSCLC patients was investigated.
CTCs were isolated, based on their size, using the ISET platform from 30 chemo-naïve patients with stage IV NSCLC before chemotherapy and after the 3rd cycle. CTCs were detected after staining with Giemsa, as well as after immunofluorescence double staining with Cytokeratin (A45-B/B3)/PD-1 and Cytokeratin (CK)//PD-L1 antibodies and analysis with the ARIOL system. Spiking experiments using the NSCLC H460, H1299, HCC827 and SKMES cell lines in normal blood were used to evaluate the detection method.
Twenty five and 12 out of 30 patients' samples were evaluable for analysis at baseline and after the 3rd cycle, respectively. CTCs could be detected in 56% (14/25) and 85.7% (10/12) patients at baseline and after the 3rd cycle of chemotherapy, respectively. Giemsa staining revealed tumor cells in 60% (15/25) at baseline and in 67% (8/12) after 3rd cycle. PD-1 expression was observed in 71.4% (10/14) and 10% (1/10) (p = 0.044) of the CTC-positive patients at baseline and after the 3rd, respectively. Conversely, PD-L1 was observed in 42,9% (6/14) and 50% (5/10) (p = 0.311) of the CTC-positive patients at baseline and after the 3rd cycle. Among the total number of detected CTCs, 47.8% were PD-1-positive at baseline and 30% after the 3rd cycle whereas, 35.7% and 50% at baseline and after the 3rd cycle, respectively, were PD-L1-positive.
PD-1- and PD-L1 positive CTCs can be observed during the treatment of metastatic NSCLC, suggesting that they can be used as a potential biomarker to monitor the expression of PD-L1 on tumor cells during the clinical phases of the disease and understand the mechanisms of tumor immune escape.
Clinical trial identification
Legal entity responsible for the study
Laboratory of Translational Oncology, School of Medicine, University of Crete
All authors have declared no conflicts of interest.