Single-EV Analyses Require Rigorous Antibody Qualification: PD-L1 Profiling in Cell Models and Patient Plasma
Tobias Tertel1, Fabiola Nardi Bauer1,2, Oumaima Stambouli1
1Institute for Transfusion Medicine University Hospital Essen University of Duisburg-Essen Essen Germany.
Insights
Antibody performance is crucial for imaging flow cytometry (IFCM) of extracellular vesicles (EVs). This study developed a validated IFCM workflow for detecting PD-L1 positive EVs in patient plasma, highlighting the need for application-specific antibody validation.
Area of Science:
- Extracellular vesicle (EV) research
- Immunophenotyping
- Biomarker discovery
Background:
- Imaging flow cytometry (IFCM) offers high-throughput, single-vesicle analysis of extracellular vesicles (sEVs).
- Antibody performance is critical for IFCM reliability and sensitivity in sEV detection.
- Existing antibody validation for cellular targets may not translate to sEV analysis.
Purpose of the Study:
- To systematically compare commercial anti-PD-L1 antibodies for sEV detection using IFCM.
- To develop and validate a standardized IFCM workflow for sEV profiling.
- To assess the potential of IFCM for semi-quantitative analysis of PD-L1 positive sEVs in patient plasma.
Main Methods:
- Systematic comparison of anti-PD-L1 antibodies for labeling PD-L1 positive sEVs.
- Development of a robust IFCM workflow adhering to MIFlowCyt-EV standards.
- Application of the validated workflow to analyze PD-L1 positive sEVs in unprocessed plasma from cancer patients and healthy donors.
- Comparison of IFCM with bead-based methods and dilution experiments for quantitative assessment.
Main Results:
- Significant differences in labeling efficiency were observed among anti-PD-L1 antibodies from different manufacturers.
- A validated IFCM workflow enabled reproducible detection of PD-L1 positive sEVs in patient plasma.
- IFCM demonstrated semi-quantitative capability by revealing distinct PD-L1 positive sEV levels, unlike bead-based methods.
- Elevated PD-L1 positive sEV levels were detected in plasma subsets from head and neck, lung, and breast cancer patients.
Conclusions:
- Antibody suitability for sEV analysis requires rigorous, application-specific validation beyond standard cellular assays.
- A standardized IFCM workflow provides a reliable method for single-EV profiling.
- Elevated PD-L1 positive sEVs in cancer patient plasma suggest potential clinical relevance.
- The quality of antibodies is paramount for accurate analytical results in single-EV studies.
Abstract:
Imaging flow cytometry (IFCM) has emerged as a powerful method for high-throughput phenotyping of small extracellular vesicles (sEVs) at single-vesicle resolution. However, the reliability and sensitivity of IFCM critically depend on the performance of the antibodies used. In this study, we systematically compared several commercially available anti-PD-L1 antibodies for their ability to detect PD-L1-positive sEVs. Despite being derived from the same clone, antibodies from different manufacturers showed striking differences in labelling efficiency. These findings demonstrate that antibody validation for cellular targets does not ensure suitability for single-EV analysis and underscore the need for rigorous, application-specific qualification. To address this, we developed a robust IFCM workflow in full alignment with MIFlowCyt-EV reporting standards. Using a qualified anti-PD-L1 antibody, we achieved reproducible detection of PD-L1+ sEVs directly in unprocessed plasma samples from tumour patients. To assess the quantitative potential of single-EV analysis, we compared this approach with bead-based capture and performed dilution experiments. While bead-based methods yielded a relatively narrow range of mean fluorescence intensities across samples, IFCM revealed distinct PD-L1+ sEV levels, supporting its semi-quantitative capability. Finally, we applied this workflow to plasma samples from patients with head and neck, lung, and breast cancer, as well as healthy donors. In subsets of all three cancer cohorts, elevated PD-L1+ sEV levels were observed, suggesting potential clinical relevance. While in-depth clinical correlations lie beyond the scope of this study, our findings establish a validated, standardized protocol for IFCM-based single-EV profiling and highlight the central role of antibody quality in ensuring analytical accuracy.
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