How do we assess batch‐to‐batch consistency between extracellular vesicle products?

Abstract Background Extracellular vesicles (EVs) have gained interest in the field of regenerative and transfusion medicine. Specifically, current Good Manufacturing Practice (cGMP)‐grade EVs produced by mesenchymal stromal cells (MSCs) are an intriguing option for cell‐free therapeutics. With the development of cGMP‐grade EV products, a simple and reliable method for batch‐to‐batch consistency is needed. Study Design and Methods The objective of this study was to validate a method to semiquantitatively assess the batch‐to‐batch consistency of isolated EVs. A multiplex bead‐based flow cytometric assay containing 37 surface markers and 2 assay control antibody‐coated capture beads was validated. Detection limits ( n = 10 buffer samples), repeatability ( n = 9 EV samples), and intra‐observer reproducibility over 2 days ( n = 10 EV batches) were assessed. A Spearman correlation matrix was used to evaluate the batch‐to‐batch consistency of independently isolated EV products ( n = 37 surface markers). Batches with a Spearman correlation coefficient ≥0.9 and p < 0.05 were considered statistically indistinguishable from previous batches. Results This assay demonstrated robust repeatability as well as intra‐ and inter‐assay reproducibility. In‐house batches of EVs were significantly correlated (r ≥ 0.90; p ≤ 1×10 −14 ). Compared with buffer, EV batches had correlation coefficients near zero (r ≤ −0.10; p ≥ 0.12). Commercially sourced EVs significantly correlated with in‐house EV batches, but fell below the 90% correlation cutoff (r ≤ 0.71; p ≤ 0.0004). Discussion This time‐efficient and technically simple assay offers a robust method of quality control for assessing the batch‐to‐batch reproducibility of cGMP‐grade EV products.