Abstract 6380: Ultrasensitive detection of circulating human PD-1 and PD-L1 using Single Molecule Counting (SMC) technology

Abstract

Abstract Immune checkpoint proteins are key regulators of the immune system and potential drug targets for cancer immunotherapy. Cancer immunotherapy targeting immune checkpoint, like programmed cell death protein-1 (PD-1) and programmed cell death ligand 1 (PD-L1) inhibitors has shown treatment efficacy for a broad spectrum of human cancers. Immune checkpoint molecules PD-1 and PD-L1 are expressed on the cell surface of immune cells and tumor cells. Recent studies have also reported these immune checkpoint proteins may undergo alternative splicing or proteolytic cleavage to produce soluble checkpoint proteins. Multiple molecular forms of soluble PD-1 (sPD-1) and PD-L1 (sPD-L1) are detectable in patient sera of multiple types of cancer, and these soluble checkpoint proteins have been reported as putative liquid biopsy biomarkers in the diagnosis and prognosis of oncological disease. Though the clinical significance of circulating soluble immune checkpoint protein profiles as predictive biomarkers has yet to be fully explored and validated, we have committed to develop better and more reliable bioassays to further this research. With that, we have developed 2 Luminex-based multiplex immunoassays for simultaneous quantitation of 48 immune checkpoint proteins, including PD-1 and PD-L1, for patient sera and tumor lysate samples. Here we report the development of 2 novel Single Molecule Counting (SMC) technology-based ultrasensitive single-plex immune checkpoint immunoassays for the detection of sPD-L1 and sPD-1 in human serum and plasma samples. Comparative studies demonstrate these SMC ultrasensitive assays possesses at least 10-100-fold higher sensitivity as compared with the Luminex-based immunoassays. Using these novel ultrasensitive assays, we have validated the detection of significant increases in sPD-L1 and sPD-1 in cancer serum samples as compared with the levels in healthy controls. We have also applied these high sensitivity assays to measure human PD-L1 and PD-1 biomarkers in other sample types including urine, tumor lysates and exosomes. In conclusion, we envision that these PD-1 and PD-L1 SMC assays may overcome a major limitation in biomarker utility and enable the ultrasensitive detection of sPD-1 and sPD-L1 in liquid biopsy and blood biomarker research. Citation Format: Laila Faramarzi, Wen-Rong Lie, Rick Wiese, Jared Fiske. Ultrasensitive detection of circulating human PD-1 and PD-L1 using Single Molecule Counting (SMC) technology [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6380.