Abstract

A Feasibility Study to Detect PD-L1 and PD-L2 on the Surface of Circulating Tumor Cells Using Microfluic-Based Chipcytometry

Jinkai Teo, Scientist, Merck

Antibodies that block the programmed death-1 pathway (PD-1/ PD-L1) have shown unprecedented clinical benefits against various cancers. However the high rate of resistance to this immunotherapy approach has highlighted the need for biomarkers able to predict response. The expression of PD-L1 in the tumor has been associated with more favorable response rates and is used as a companion diagnostic anti-PD-1 therapy in non-small cell lung cancer (NSCLC). However, obtaining tumor biopsies for PD-L1 interrogation is an invasive procedure not suited for frequent longitudinal monitoring during cancer therapy. An alternative, minimally invasive, approach is the analysis of blood samples for circulating tumor cells which have broken away from the tumor and entered the periphery. In this work, we describe the development of an assay workflow to isolate circulating tumor cells in peripheral blood samples and detect PD-L1 and PD-L2 expression on their surface. Our approach uses the ClearCell® FX System, sized-based microfluidic enrichment system, and subsequent characterization with microfluidic based cytometry (Chipcytometry). We used flow cytometry and chipcytometry to establish the detection of PD-L1 and PD-L2 on single tumor cells. Spiking experiments revealed that our workflow can detect tumor cells in whole blood samples with a mean detection rate of 22.8 % (+/- 5.4 %). Feasibility of circulating tumor cell detection and PD-L1 and PD-L2 expression assessment on blood samples from patients with breast cancer was also demonstrated. This is the first report using chipcytometry for the characterization of circulating tumor cells.