Xbeads: A Platform for Flow Cytometry Sample QC and Harmonization

SummaryFlow cytometry assays continue to expand in basic research and development, diagnostics, and clinical studies, particularly in the fields of immuno-oncology, CAR-T cells, and antibody therapeutics for various oncology and autoimmune diseases. The success of this platform is largely due to its unmatched ability to measure 30 or more proteins per cell in complex primary blood cell populations at a rate of thousands of cells per second. However, the complexity of these assay systems makes them challenging to standardize and perform reproducibly over time and across instruments, severely hampering the types of flow cytometry assays that can be applied in diagnostic and clinical settings. The variability associated with flow cytometry assays arises from the difficulty in standardizing across the many instrument, reagent, and experimental variables that multiply rapidly in more complex, high-parameter flow cytometry experiments. While external quality control reagents and platforms such as instrument setup and compensation beads and stabilized PBMC and whole blood controls exist, their utility is limited because they are run in parallel to the test sample and therefore cannot capture and correct for any errors that occur during processing or acquisition of individual test samples. Assay data can therefore vary significantly from sample to sample or day to day, and the data acquired on different instruments is difficult to compare. Here, we propose a novel solution to these limitations by creating an internal assay quality control system, termed Xbeads, that can be added to each sample prior to staining and processing for flow cytometry. The beads are engineered to assess the performance of the sample processing and data acquisition, and quantitatively measure the activity of each antibody reagent. Importantly, any fluctuations in instrument or assay performance are directly reflected by the fluorescent signals of the Xbeads. In this manner, samples can be normalized to the internal Xbead signals and quantitatively compared over time, across instruments, or testing sites. Preliminary data showed that Xbeads could be mixed, stained, and analyzed with PBMC samples, then separated during data analysis, and each Xbead population could be clearly resolved. In this Phase I SBIR, we will build upon these initial results by optimizing the Xbead system for reproducibility, specificity, and long-term stability. The system will be tested by acquiring samples that have known errors in processing, antibody performance, or instrument setup. The successful completion of the Phase I experiments will form the foundation of a complete internal assay QC system for flow cytometry that will enable site to site, day to day, and instrument to instrument normalization for highly complex antibody panels.