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Abstract
Metastatic non-small cell lung cancer (NSCLC) is a highly fatal and immunogenic malignancy. Although the immune system is known to recognize these tumor cells, one mechanism by which NSCLC can evade the immune system is via overexpression of programmed cell death ligand 1 (PD-L1). Recent clinical trials of PD-1 and PD-L1 inhibitors have returned promising clinical responses. Important for personalizing therapy, patients with higher intensity staining for PD-L1 on tumor biopsies responded better. Thus, there has been interest in using PD-L1 tumor expression as a criterion for patient selection. Currently available methods of screening involve invasive tumor biopsy, followed by histological grading of PD-L1 levels. Biopsies have a high risk of complications, and only allow sampling from limited tumor sections, which may not reflect overall tumor heterogeneity. Circulating tumor cell (CTC) PD-L1 levels could aid in screening patients, and could supplement tissue PD-L1 biopsy results by testing PD-L1 expression from disseminated tumor sites. Towards establishing CTCs as a screening tool, we developed a protocol to isolate CTCs at high purity and immunostain for PD-L1. Monitoring of PD-L1 expression on CTCs could be an additional biomarker for precision medicine that may help in determining response to immunotherapies.
Highlights
The immune response to cancer involves a complex network of cellular interactions
We first confirmed that Circulating tumor cell (CTC) could be enriched from metastatic non-small cell lung cancer (NSCLC) patients with Vortex technology
Using the same enumeration criteria described for the patients, 0 to 1.25 cells per mL were isolated from healthy controls and characterized as CTCs
Summary
The immune response to cancer involves a complex network of cellular interactions. Antigen presenting cells (APCs) can recognize neoantigens from some immunogenic tumors[1,2]. Past studies of renal cancer show tumors with high PD-L1 levels respond, while those with low levels do not respond[10] Based on these findings, a clinical trial for anti-PD1 (pembrolizumab) was conducted where NSCLC patients were screened based on expression levels of PD-L1 on the primary tumor[7,14]. Biopsy of multiple sites or serial biopsies during treatment could address some of these issues, it may not be feasible due to the invasiveness of the procedure and the potential risks to the patient In this regard, PD-L1 expression on circulating tumor cells (CTCs) could aid in screening and monitoring patients[16]. Only one recent study from Nicolazzo et al evaluated PD-L1 expression in NSCLC CTCs and examined PD-L1 expression in the context of active immunotherapy treatment, PD-1/PD-L1 inhibition (nivolumab in their study)[22]. Tumors of patients receiving pembrolizumab were originally graded as positive for PD-L1 as this was one of the initial inclusion criteria for receiving this therapy
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