Flow cytometry is a widely used technique for single cell and particle analysis. In order for flow cytometry to be used in a clinical, industrial, or research setting, measurements must be made precisely and with certainty. Our objective is to develop reference materials, methodology, and procedures to enable quantitative measurements of biological substances such as cells, proteins, and nucleic acids. By providing quantitative flow cytometry measurement solutions, we ensure that researchers can produce reliable data, better drugs are developed, and patients get better treatment in the clinical setting.
Flow cytometry is an essential tool for basic immunological research, clinical discovery of potential therapeutics, development and approval of drugs and devices, disease diagnosis, and therapeutic treatment and monitoring. For example, flow cytometry is commonly used in pre-clinical and clinical trials for evaluating the safety/effectiveness of drugs including engineered T-cell. In HIV/AIDS monitoring, accurate measurement of CD4+ cell counts using flow cytometry is the key to ensuring that patients receive the appropriate antiretroviral treatment (ART). However, the measurements made on different instrument platforms at different times and places often cannot be compared. Discrepancies between and among measurements introduce uncertainty in diagnostic and therapeutic decisions, and impede advances in basic science. We collaborate with other government agencies, industry, academia, professional societies, standards organizations, and field experts to accelerate the standardization of flow cytometry measurements with the use of reference controls and standards, and measurement procedures.
1. Flow Cytometry Quantitation Consortium – The objective of the consortium is to collaboratively develop reference materials including biological reference materials, reference data, reference methods and service for assigning the equivalent number of reference fluorophores (ERF) to calibration microspheres and assessing the associated uncertainties and utilities. This is the first step towards reliable quantitative measurements in flow cytometry.
To learn more about the Flow Cytometry Quantitation Consortium, click here.
2. Quantification of Cells with Specific Phenotypic Characteristics – Accurate enumeration of cells with specific phenotypic characteristics is of critical importance in patient care. There are pertinent needs for cell reference materials for external measurement quality assessments in areas, such as HIV/AIDS monitoring (CD4+ cell count) and blood transfusion (CD45+CD34+ stem cell count) in clinics. Our scientists have produced and evaluated the first international reference standard for CD4+ cell counting for HIV/AIDS monitoring (WHO BS/10.2153). Accurate measurement of CD4+ cells is the key to ensuring that patients receive the appropriate anti-retroviral treatment (ART) once their CD4+ cell count falls below 350 cells per microliter.
3. Characterization of Commercially Available Human Peripheral Blood Mononuclear Cell (PBMC) Preparations for Quantitative Flow Cytometry – Multiplexed flow cytometry assays are routinely used in clinics for disease diagnosis, vaccine trials, and immunotherapies. Biological cell reference materials have been recognized as phenotypic benchmarks for quantitative and reproducible measure of patient characteristics in longitudinal studies and/or across locations. The objective of this project is to evaluate the expression levels of multiple biomarkers on different human blood cell subtypes from three commercially available candidate PBMC preparations and their utilities as cell reference controls for quantitative flow cytometry.
4. Fluorescently Labeled Monoclonal Antibody Metrology for Quantitative Flow Cytometry – A significant effort is underway to express flow cytometer measurements on a cell in terms of the number of antibodies bound to the cell. A critical part of this effort is the identification of a reference cell with a known number of bound antibodies (e.g., CD4+ T lymphocytes). A properly calibrated fluorescence intensity(FI) scale allows the comparison of the FIs from the test cell and the reference cell, and the assignment of the number of antibodies bound to the test cell. This procedure requires careful characterization of antibody binding affinities as well as any changes in fluorescence upon binding. The development of an antibody qualification matrix including binding affinity, staining index, and fluorescence yield (also called effective fluorophore(s) per antibody molecule) is hugely important for estimating the sensitivity and reproducibility of any flow cytometer assay.
5. Quantitative Measurements of Cell Functional Markers and Disease Biomarkers – For quantifying expression levels of cell functional markers, e.g. cytokines and chemokines, and disease biomarkers, e.g., CD20, ZAP-70, and CD38, multiplexed cytometric assays are being developed to take advantage of the known CD4 expression on healthy human T lymphocytes as a reference biomarker control. The CD4 expression levels on T helper cells from healthy individuals and a commercially available lyophilized PBMC product have been quantitatively measured using flow and mass cytometry, and mass spectrometry in our cell characterization project and are expressed in the unit of antibodies bound per cell (ABC). These biomarker expression results in the unit of ABC are quantitative and comparable across different instrument platforms and locations, and essentially are instrument independent.
6. Genomic Material Measurements Using Flow Cytometry – Researchers studying genetic profiles of different cell subsets currently have two different technology options available to them: affinity bead-based separation and cell sorting. Both affinity bead-based separation and cell sorting methods suffer from major limitations that have thus far limited clinical, therapeutic, and diagnostic advancements. With the advent of more quantitative technologies to measure isolated genomic material, improved microscopy functionality, and more powerful flow cytometry instrumentation, we are just beginning to break the barriers that previously limited us in quantitative genomic measurements. While our group is currently leveraging all of these different quantitative methodologies to measure genomic material, the cornerstone of our technology lies in our flow cytometry capabilities. This technology will allow us to decisively measure genomic material within intact cells while simultaneously cross referencing these measurements to specific cellular subsets.
NIST-NRC and NIH/NIST NRC Postdoctoral Fellowship Opportunities: