The quality of data received from clinical specialty testing labs is largely dependent on the integrity of the samples tested. One critical aspect of this is the proper isolation of PBMCs - peripheral blood mononuclear cells - often used in high-complexity flow cytometry research. To get the best quality results, researchers must use the most optimal tubes to isolate these cells. Three main types of tubes are commonly used: SepMate tubes, CPT tubes, and Manual Ficoll Gradient tubes. Each of these tubes has advantages and disadvantages that researchers must consider carefully. In this blog post, we will look at the pros and cons of each tube type and what you should consider before selecting one for your clinical trial.

SepMate Tubes:

SepMate tubes come in different sizes that enable researchers to isolate PBMCs from different numbers of tubes at once. These tubes work by using an inserted plastic separation technology that helps remove unwanted clumps of cells. One of the most significant advantages of these tubes is that they can be used for small to medium-sized samples with ease. The technology also separates cells significantly, making it easy to measure the concentration of cells after the separation procedure accurately. Furthermore, the tube also allows for rapid and consistent layering and easy collection of PBMCs, making it ideal for research. However, obtaining a high percentage of neutrophils is not possible, as they would be trapped below the barrier inside the tube. SepMate tubes are disposable, which makes them less financially sensible in the long run.

CPT Tubes:

CPT tubes are anticoagulant-based layered tubes that allow for the collection directly to cell separation without any additional processing. CPT tubes simplify the separation process and reduce the risk of contamination. They offer a more robust PBMC isolation process, and specific manufacturers produce four types to suit different research needs regarding testing human cells. The tubes generate high PBMC yields with high cell viability, making them an optimal option where quality is paramount. The primary disadvantage of CPT tubes is that they are quite expensive when compared to other tube types for PBMC isolation.

Manual Ficoll Gradient Tubes:

Manual Ficoll Gradient tubes require manual handling and processing, so they aren't automated. Due to this, the individual processing of Ficoll gradient tubes can cause variability in the manual layering steps, leading to variation in the final cell yield. The biggest issue with this type of isolation tube is that it takes longer to obtain the actual PBMCs than using SepMate or CPT tubes, which may create more significant delays in your research. Additionally, due to the manual nature of this type of PBMC isolation, final PBMC recovery rates are usually dependent on the experience of the researcher.

In conclusion, the right tube type will depend on your primary requirements for your research. Regardless of your choice, there is still a need to make sure you select a tube type that meets the technical requirements of your studies and delivers high-quality results. Champions Oncology has expertise in GCLP-compliant PBMC isolation using SepMate, CPT, and manual Ficoll Gradient tube types and can advise the best choice for your upcoming clinical trial.

The development of new oncology treatments has focused on strategies that alter immune responses. Many of these novel therapies use antibodies that bind to receptors on different immune cell subsets and either activate or suppress their functions depending on the immune response being targeted. Antibody-drug conjugates are also becoming more widely used for improved targeting of drugs to specific cell subsets. Flow cytometry-based receptor occupancy (RO) assays are a valuable tool for quantifying cell surface expression of target molecules and are used to generate pharmacodynamic (PD) data, which can be used with pharmacokinetic (PK) data to guide dosing strategies. Consider these different types of receptor occupancy assays as you develop the most useful tools for screening therapeutic molecules.

1. Total receptor assay: The evaluation of a potential therapeutic target usually begins with an assessment of how many receptors are expressed by a given cell subset. If a receptor is abundantly expressed, it may be a difficult target to use due to potential off-target effects or the requirement of high doses of a therapeutic antibody. Measurement of total receptor involves using a fluorescently labeled antibody that binds to a receptor at a site that is different from the binding site of the therapeutic antibody of interest.
2. Free receptor assay: In this assay, cells are first stained with an unlabeled therapeutic antibody and then stained with a labeled version of the same antibody, which will only bind to the remaining free receptors. Measurement of free receptor levels at different doses is required for generating PK/PD datasets.
3. Drug-occupied receptor assay: This assay labels cells with your antibody of interest (“drug”), and then a labeled secondary antibody binds to a different site on your antibody of interest. This measurement can be used in place of free receptor assays when they are not technically feasible.

Combining data from free and total receptor assays over time is a useful method for measuring the kinetics of antibody binding and calculating potential half-lives of these molecules for therapeutic applications. Consider the type of assay you need for your phase of development. Engage with RO experts who can help you develop validated assays that can be used in preclinical and clinical settings. Flow cytometry-based RO assays will continue to be an essential tool in the development of novel oncology therapeutics.

Clinical flow cytometry is now a standard tool used by clinical researchers in numerous fields, especially immuno-oncology. Consider these “Do’s & Don’ts” of clinical flow cytometry as you decide to use this tool for clinical research.

Do Perfect Your Panel - A staining panel includes the set of antibodies used to identify different cell subsets within a sample and depends on the use of multiple antibodies conjugated with different fluorochromes. These fluorochromes are excited by specific light wavelengths from the cytometer’s lasers, and the emitted light is analyzed and interpreted as different cell types. Researchers take time to develop staining panels that can reasonably distinguish between cell types and avoid aberrations such as spectral overlap.

Do Vigilant Validation - Clinical flow cytometry assay development must satisfy certain criteria, including accuracy, specificity, limit of detection, reproducibility, precision, linearity, and stability. By satisfying these criteria, researchers are able to have confidence in their clinical data, even if experiments were done at different times or in different locations.

Do Maintenance - Reliable flow cytometry data requires a well-designed and validated protocol as well as a properly maintained cytometer. Routine maintenance is carried out by cytometer users to assure that fluidic systems flow properly, lasers are firing correctly, and the emitted light is detected at the expected wavelength. Infrequent, but more involved, maintenance is carried out by technicians and is essential to the long-term functionality of a cytometer.

Don’t Pick the Wrong Test Tube - The very first step of a clinical flow cytometry protocol is collecting a sample, which is typically peripheral blood, cord blood, or tissue biopsy. These samples can be collected in tubes with preservatives or anti-clotting agents, but some of these additives can alter cell viability. It is worthwhile to evaluate different sample tube types to assure that your cells of interest are not being lost or damaged due to test tube effects.

Don’t Lose your Cells - Clinical flow cytometry protocols rely on the acquisition of thousands to millions of cells per sample in order to have a reasonable number of events to analyze. One essential step to acquiring usable data is the inclusion of a viability dye that discriminates between live and dead cells. Viability dyes come in different formats that work with specific flow cytometer configurations, so it is critical to determine which dye will work with your cytometer.

Don’t Screw Up Your Analysis - After you have completed the laborious process of sample staining and data acquisition on a cytometer, it is essential to execute the appropriate data analysis. Be sure you understand how to use the software needed for analysis, and this may mean including certain controls in your staining and acquisition protocols. Errors in analysis may result in your data being inaccurate or undetected.

Flow cytometry is a semi-quantitative method that is widely used for preclinical and clinical studies. Preclinical flow cytometry experiments rely on users who understand the fundamentals of setting up appropriate standards and controls, but these protocols do not need to typically meet specific clinical standards. In contrast, clinical flow cytometry protocols require adherence to good clinical laboratory practice (GCLP) standards. Here we provide an overview of GCLP standards with respect to clinical flow cytometry.

GCLP guidelines were developed in the early 2000s to provide a regulatory framework for labs performing assays for HIV-1 clinical trials. A large portion of these assays were flow cytometry-based^[1] and were being conducted on flow cytometers at multiple global sites, thus necessitating standardization. GCLP guidelines are a type of regulatory standard, with similarities to good laboratory practice (GLP) and clinical laboratory improvement amendments (CLIA) and have become essential to harmonizing clinical laboratory work taking place at different sites and times for clinical trials. GCLP standards can be applied to labs carrying out safety, diagnostic, or endpoint assays, and have been critical to the evaluation of immuno-oncology drugs and biologics being evaluated in clinical trials.

GCLP guidelines include personnel organization and training, equipment maintenance and validation, the development and validation of standard operating procedures (SOPs), assay development and validation, and audits to identify discrepancies in any of these areas^[2]. GCLP procedures for clinical flow cytometry assure that flow cytometers at different sites are performing consistently and within standards. Flow cytometry reagents are parallel tested with previous lot to assure their eligibility for use in an assay. Throughout the implementation of GCLP guidelines, a laboratory must maintain a document control plan that includes all SOPs currently in use and an archive system for SOPs that are no longer in use.

A quality control (QC) program is essential to a GCLP framework as it allows for the monitoring, documentation, and recognition of QC problems. QC programs track test standards, positive and negative controls, reagent performance, QC data analysis and logs, and parallel testing. QC is especially important for clinical flow cytometry to assure that the appropriate cell populations are being analyzed in a consistent and reproducible manner.

A proficiency testing program is another critical component of GCLP program because it involves analysis of a common set of samples by multiple laboratory sites to assure that performance can meet specific criteria^[3]. Clinical flow cytometry assays typically lack “gold standard” samples for evaluation because cells that are being analyzed in this manner are subject to intra- and inter-sample variability. Nonetheless, samples can be expected to fall within a specific predetermined range, thus assuring that the GCLP-compliant protocol, users, and equipment are performing proficiently.

GCLP standards for clinical flow cytometry are now being applied in different ways, including complex immunophenotyping of multiple immune cell subsets, comprehensive measurement of immune checkpoint molecule expression on T cells, and receptor occupancy assessment of therapeutic antibodies. The development of GCLP guidelines is often carried out with GCLP professionals who can advise on all aspects of this complex undertaking. Alternatively, individual assays, such as clinical flow cytometry experiments can be carried out by contract research organizations who are already GCLP compliant and experienced with running these assays.

[1] Todd CA, Sanchez AM, Garcia A, Denny TN, Sarzotti-Kelsoe M. Implementation of Good Clinical Laboratory Practice (GCLP) guidelines within the External Quality Assurance Program Oversight Laboratory (EQAPOL). J. Immunol. Methods. 2014;409:91-98.

[2] Sarzotti-Kelsoe M, Cox J, Cleland N, et al. Evaluation and recommendations on good clinical laboratory practice guidelines for phase I-III clinical trials. PLoS Med. 2009;6(5):e1000067.

[3] O'Hara, Denise M., et al. Recommendations for the validation of flow cytometric testing during drug development: II assays. J. Immunol. Methods. 363.2 (2011): 120-134.