Quantification of cells with specific phenotypes I: Determination of CD4+ cell count per microliter in reconstituted lyophilized human PBMC prelabeled with anti‐CD4 FITC antibody

Abstract

A surface-labeled lyophilized lymphocyte (sLL) preparation has been developed using human peripheral blood mononuclear cells prelabeled with a fluorescein isothiocyanate conjugated anti-CD4 monoclonal antibody. The sLL preparation is intended to be used as a reference material for CD4+ cell counting including the development of higher order reference measurement procedures and has been evaluated in the pilot study CCQM-P102. This study was conducted across 16 laboratories from eight countries to assess the ability of participants to quantify the CD4+ cell count of this reference material and to document cross-laboratory variability plus associated measurement uncertainties. Twelve different flow cytometer platforms were evaluated using a standard protocol that included calibration beads used to obtain quantitative measurements of CD4+ T cell counts. There was good overall cross-platform and counting method agreement with a grand mean of the laboratory calculated means of (301.7 ± 4.9) μL−1 CD4+ cells. Excluding outliers, greater than 90% of participant data agreed within ±15%. A major contribution to variation of sLL CD4+ cell counts was tube to tube variation of the calibration beads, amounting to an uncertainty of 3.6%. Variation due to preparative steps equated to an uncertainty of 2.6%. There was no reduction in variability when data files were centrally reanalyzed. Remaining variation was attributed to instrument specific differences. CD4+ cell counts obtained in CCQM-P102 are in excellent agreement and show the robustness of both the measurements and the data analysis and hence the suitability of sLL as a reference material for interlaboratory comparisons and external quality assessment. © 2015 The Authors. Published by Wiley Periodicals, Inc.

Consistent, multi‐instrument single tube quantification of CD20 in antibody bound per cell based on CD4 reference

“…Currently, there are no internationally recognized or validated biological cell reference standards with well characterized biomarker expression levels due to the complexity of producing such reference materials, that is, larger quantity, tight biomarker expression levels measured by two different techniques, resemblance of clinical samples, long term stability, and low cost storage conditions. While the development of biological cell reference materials are emerging (10,16,17,27), it is feasible to advance quantification schemes that take advantage of the known expression level of CD4 on normal human T lymphocytes (10,12,13). To extend this approach to other cell types, autofluorescence of the reference cell type and the measured cell type should be taken into account.…”

“…Another way to accomplish the goal of cell surface marker quantification is to use a biological reference cell, which is known to possess a fixed number of well characterized protein biomarkers such as CD4 (12)(13)(14)(15)(16)(17). An international cell reference material of lyophilized peripheral blood mononuclear cells (PBMC) prelabeled with anti-CD4 fluorescein isothiocyanate (FITC) antibody has recently come out for calibration and standardization of CD41 cell enumeration for quality assurance of HIV/AIDS monitoring as well as quantitative expression analysis in the FITC channel (16,17). This cell reference material only enables quantitative expression analysis in the unit of equivalent fluorescein fluorophore (EFF) because the link between EFF and ABC has not yet been established.…”

Cell therapy products: focus on issues with manufacturing and quality control of chimeric antigen receptor T‐cell therapies

“…Making available suitable antibodies and standardised preparations representing defined cellular phenotypes is now a priority to improve measurement standardisation across cytometers and analytical laboratories . The Biotherapeutics Division at the National Institute for Biological Standards and Control (NIBSC) has produced CE‐marked fluorochrome labelled T‐cell subsets and is working up similar materials to support cytometer based measurement across life‐sciences …”

Standardization, Calibration, and Control in Flow Cytometry

“…The ratio, r, of sample particle events (e.g., CD4 T cells) to reference particle events is measured in the flow cytometer. Then, the number of sample particles is computed from the product r × N (Stewart and Steinkamp, 2005;Stebbings et al, 2015).…”