PiP-plex: A Particle-in-Particle System for Multiplexed Quantification of Secreted Proteins by Single Cells

Abstract

Cell signaling is modulated by the secretion of various proteins, which can be used to infer a cells phenotype. However, these proteins cannot be readily detected in multiplex by commonly used methods at the single cell level. Here, we present PiP-plex, a particles-in-particle (PiPs) system comprising (i) fluorescence intensity barcoded microparticles (BMPs) co-entrapped with (ii) a single cell inside an alginate hydrogel particle for multiplex protein secretion analysis by confocal microscopy. We show that developed PiPs maintained >90 % cellular viability and allowed live cells retrieval. A seven-plex fluorescent barcoding and concomitant sandwich immunoassay in PiPs were implemented with limits of detection ranging from 0.8 pg mL-1 to 2 ng mL-1 depending on the protein. PiP-plex assays were benchmarked with bulk immunoassays and found to rival or outperform them. We applied PiP-plex to analyze protein secreted by THP-1 cells upon exposure to lipopolysaccharide and detected varying cell responses, with a significant increase in MIP-1, TNF- and IL-17A. Multivariate analysis revealed that the majority of stimulated cells secreted either MIP-1 or IL-17A, while other cytokines were typically co-secreted. Using PiP-plex, we analyzed [~]750 THP-1 cells, showcasing its potential for characterizing cells and cell-based therapeutics for cancer immunotherapies.