4 – Experimental Design

Flow cytometers are traditionally designed for measuring particles, like beads and cells. These tend to fall in the small micron size range. Looking at the relative size of different targets of biological interest, it is clear the most common targets for flow cytometry (cells) are comparatively large (figure 1). Figure 1:  Relative size of different biological targets of interest. Image modified from Bioninja.    In the visible spectrum, where most of the excitation light sources reside, it is clear the cells are larger than the light. This is important as one of the characteristics that we typically measure is the amount…

As the labeled cell passes through the interrogation point, it is illuminated by the excitation lasers. The fluorochromes, fluoresce; emitting photons of a higher wavelength than the excitation source. This is typically modeled using spectral viewers such as in the figure below, which shows the excitation (dashed lines) and emission (filled curves) for Brilliant Violet 421TM (purple) and Alexa Fluor 488Ⓡ (green).  Figure 1: Excitation and emission profiles of BV421TM and AF488Ⓡ  In traditional fluorescent flow cytometry (TFF), the instrument measures each fluorochrome off an individual detector. Since the detectors we use — photomultiplier tubes (PMT) and avalanche photodiodes (APD)…

Extracting specific cells still remains an important aspect of several emerging genomic techniques. Prior knowledge about the input cells helps to put the downstream results in context. The most common isolation technique is cell sorting, but it requires a single cell suspension and eliminates any spatial information about the microenvironment. Spatial transcriptomics is an emerging technique that can address some of these issues, but that is a topic for another blog.  So what does a researcher who needs to isolate a specific type of cell do? The answer lies in the technique of laser capture microdissection (LCM). Developed at the National…

Incorporating quality control as a part of the optimization process in  your flow cytometry protocol is important. Take a step back and consider how to build quality control tracking into the experimental protocol.  When researchers hear about quality control, they immediately shift their attention to those operating and maintaining the instrument, as if the whole weight of QC should fall on their shoulders.   It is true that core facilities work hard to provide high-quality instruments and monitor performance over time so that the researchers can enjoy uniformity in their experiments. That, however, is just one level of QC.  As the experimental…

Clinical trials are studies designed to test the novel methods of diagnosing and treating health conditions – by observing the outcomes of human subjects under experimental conditions.  These are interventional studies that are performed under stringent clinical laboratory settings. Contrariwise, non-interventional studies are performed outside the clinical trial settings that provide researchers an opportunity to monitor the effect of drugs in real-life situations. Non-interventional trials are also termed observational studies as they include post-marketing surveillance studies (PMS) and post-authorization safety studies (PASS). Clinical trials are preferred for testing newly developed drugs since interventional studies are conducted in a highly monitored…

As we continue to explore the steps involved in optimizing a flow cytometry experiment, we turn our attention to the detectors and optimizing sensitivity: instrument voltage optimization.  This is important as we want to ensure that we can make as sensitive a measurement as possible.  This requires us to know the optimal sensitivity of our instrument, and how our stained cells are resolved based on that voltage.  Let’s start by asking the question what makes a good voltage?  Joe Trotter, from the BD Biosciences Advanced Technology Group, once suggested the following:  Electronic noise effects resolution sensitivity   A good minimal PMT…

In the first blog of this series, we explored the power of sequencing the genome at various levels. We also dealt with how the characterization of the RNA expression levels helps us to understand the changes at the genome level. These changes impact the downstream expression of the target genes. In this blog, we will explore how NGS sequencing can help us comprehend DNA modification that affect the expression pattern of the given genes (epigenetic profiling) as well as characterizing the DNA-protein interactions that allow for the identification of genes that may be regulated by a given protein.  DNA Methylation Profiling…

Why is Next Generation Sequencing so powerful to explore and answer both clinical and research questions. With the ability to sequence whole genomes, identifying novel changes between individuals, to exploring what RNA sequences are being expressed, or to examine DNA modifications and protein-DNA interactions occurring that can help researchers better understand the complex regulation of transcription. This, in turn, allows them to characterize changes during different disease states, which can suggest a way to treat said disease.  Over the next two blogs, I will highlight these different methods along with illustrating how these can help clinical diagnostics as well as…

In my previous blog on  experimental optimization, we discussed the idea of identifying the best antibody concentration for staining the cells. We did this through a process called titration, which  focuses on finding the best signal-to-noise ratio at the lowest antibody concentration. In this blog we will deal with sample blocking As a reminder, there are two other major binding concerns with antibodies. The first is the specific binding of the Fc fragment of the antibody to the Fc Receptor expressed on some cells. This protein is critical for the process of destroying microbes or other cells that have been…

NGS methodologies have been used to produce high-throughput sequence data. These data with appropriate computational analyses facilitate variant identification and prove to be extremely valuable in pharmaceutical industries and clinical practice for developing drug molecules inhibiting disease progression. Thus, by providing a comprehensive profile of an individual’s variome — particularly that of clinical relevance consisting of pathogenic variants — NGS helps in determining new disease genes. The information thus obtained on genetic variations and the target disease genes can be used by the Pharma companies to develop drugs impeding these variants and their disease-causing effect. However simple this may allude…

Over the next series of blog posts, we will explore the different aspects of optimizing a polychromatic flow cytometry panel. These steps range from figuring out the best voltage to use, which controls are critical for data interpretation, what quality control tools can be integrated into the assay; how to block cells, and more. This blog will focus on determining the optimal antibody concentration.  As a reminder about the antibody structure, a schematic of an antibody is shown below.  Figure 1: Schematic of an antibody. Figure from Wikipedia. The antibody is composed of two heavy chains and two light chains that…

The heart and soul of the flow cytometry experiment is the ‘panel.’ The unique combinations of antibodies, antigens, fluorochromes, and other reagents are central to identifying the cells of interest and extracting the data necessary to answer the question at hand. Designing the right panel for flow cytometry is essential for detecting different modalities. The more parameters that can be interrogated will yield more information about the target cells. Current instruments can measure as many as 40 different parameters simultaneously. This is exciting, as it allows for more complex questions to be studied. Panel design is also valuable for precious samples,…