# Intermethod Characterization of Commercially Available Extracellular Vesicles as Reference Materials

## TL;DR

This paper evaluates different methods to measure extracellular vesicles, showing significant variability and the need for standardized reference materials.

## Contribution

The study compares multiple orthogonal techniques for EV characterization, revealing discrepancies and emphasizing the need for standardized methods.

## Key findings

- PSDs measured by all methods were larger than Cryo-EM, with MRPS being the closest and AF4 the most divergent.
- Quantitative PNC discrepancies across methods and cell sources reached up to two orders of magnitude.
- Proteomic analysis identified syntenin-1 and tetraspanins CD9, CD63, and CD81 as EV-specific proteins.

## Abstract

The National Institute of Standards and Technology (NIST) is developing analytical methods to characterize extracellular vesicles (EVs) to support the urgent need for standardized EV reference materials (RMs). This study used orthogonal techniques, cryogenic electron microscopy (Cryo-EM), particle tracking analysis (PTA), asymmetrical flow field-flow fractionation (AF4), and microfluidic resistive pulse sensing (MRPS), to evaluate particle size distributions (PSDs) and particle number concentrations (PNCs) of human mesenchymal stem cells (MSCs) and LNCaP prostate cancer cell EVs. Proteomic profiles were assessed by mass spectrometry (MS), and microRNA (miRNA) content of LNCaP EVs was evaluated by small RNA-seq at two independent laboratories. A commercial green fluorescent protein exosome served as a control, except in Cryo-EM, proteomic, and miRNA analyses. Cryo-EM, regarded as the gold standard for morphological resolution, served as PSD reference. PSDs from all methods skewed larger than Cryo-EM, with MRPS closest, AF4 most divergent, and PTA intermediate with broader distributions. All techniques reported broad PSDs (30 nm to >350 nm) with PNCs decreasing with increasing particle size, except for AF4. Quantitative discrepancies in PNCs reached up to two orders of magnitude across methods and cell sources. MS identified global and EV-specific proteins, including syntenin-1 and tetraspanins CD9, CD63, and CD81. RNA-seq revealed notable inter-laboratory variation. These findings highlight the variability across measurement platforms and emphasize the need for reproducible methods to support NIST’s mission of developing reliable EV reference materials.