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Flow Cytometry and Fluorescence-Activated Cell Sorting (FACS): Isolation of Splenic B Lymphocytes

Source: Perchet Thibaut1,2,3, Meunier Sylvain1,2,3, Sophie Novault4, Rachel Golub1,2,3 
1 Unit for Lymphopoiesis, Department of Immunology, Pasteur Institute, Paris, France 
2 INSERM U1223, Paris, France 
3 Universit&#233; Paris Diderot, Sorbonne Paris Cit&#233;, Cellule Pasteur, Paris, France 
4 Flow Cytometry Platfrom, Cytometry and Biomarkers UtechS, Center for Translational Science, Pasteur Institute, Paris, France
The overall function of the immune system is to defend the body against infectious organisms and other invaders. White blood cells, or leukocytes, are the key players of the immune system. Upon infection, they are activated and initiate an immune response. Leukocytes can be divided into various sub-populations (e.g., myeloid cells, lymphocytes, dendritic cells) based on different parameters that can be biological, physical, and/or functional (e.g., size, granularity, and secretion). One way to characterize leukocytes is through their surface proteins, which are mainly receptors. Each leukocyte population expresses a specific combination of receptors (e.g., cytotoxic, activating, migration receptors) that can define subsets among populations. As the immune system encompasses a wide range of cell populations, it is essential to characterize them to decipher their participation in the immune response.
Flow cytometry (FC or FCM) is a widely used method for analyzing the expression of cell surface and intracellular molecules, characterizing and defining different cell types in a heterogenous cell mixture. Flow cytometers are composed of three main sub-systems: fluidics, optics, and electronics. The fluidics system transports the cells in a stream such that they pass in front of a laser one by one. The optics system consists of light sources (lasers) to illuminate the particles, optical filters to direct the resulting light, and fluorescent signals to appropriate detectors. Finally, the electronics system converts the detected light signals into electronic signals that can be processed by the computer. As an individual cell passes in front of the laser beam, it scatters light. A detector in front of the beam measures forward scatter (FS) and several detectors to the side measure side scatter (SC). The FS correlates with cell size and SC is proportional to the granularity of the cells. In this manner, cell populations can often be distinguished based on differences in their size and granularity alone.
In addition to analyzing a cell&#39;s size, shape, and complexity, flow cytometry is widely used for detecting the expression of cell surface receptors (1). This is accomplished by using fluorochrome-labelled monoclonal antibodies which bind to known cell-specific receptors. Upon excitation, these bound fluorochromes emit a light of specific wavelength, called emission wavelength, which can be detected and scored. Fluorescence measurements provide quantitative and qualitative data about fluorochrome-labeled cell surface receptors. Hematologists were first to use FC for the therapeutic follow up of immune cell populations (2). Now, it is used for a wide range of applications such as immunophenotyping, cell viability, gene expression, cell counting, and GFP analysis.
FACS (Fluorescent Activated Cell Sorter) is a specialized type of flow cytometry, which sorts a population of cells into subpopulation using fluorescent labelling. Just like conventional flow cytometry, first FS, SC, and fluorescent data are collected. Then, the machine applies a charge (negative or positive) and an electrostatic deflection system (electromagnets) facilitates the collection of charged droplets containing cells into appropriate tubes.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/10494/10494fig1.jpg" /> 
Figure 1: Schematic representation of FACS. Sample (1) is aspirated in the FACS (2) and passed in front of the laser (3). Cell fluorescence is sensed by fluorescence detectors (4). Finally, cells are incorporated in droplets and the cells of interest are deflected by deflection plates (5) and collected in a collection tube (6). The remaining cells go into the trash (7). <a href="https://www.jove.com/files/ftp_upload/10494/10494fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The sorting aspect of the FACS presents many advantages. Many tests can help understand the role of specific cells in immune system, such as analyses of gene expression like RT-qPCR, cell cycle, or cytokine secretion. However, cells should be purified upstream to obtain clear and specific results. Here, FACS comes in useful and the desired cells can be sorted with great purity, yielding highly reliable and reproducible results. FACS can also be used to sort cells based on nuclear or other intracellular staining and according to the presence, absence, and density of surface receptors. FACS is now a standard technique for the purification of subpopulations of cells and has the ability sort up to four populations simultaneously.
This lab exercise demonstrates how to isolate splenic leukocytes and then how to specifically sort B lymphoid cells from the splenic leukocyte cell mixture using FACS.

Flow Cytometry and FACS: Isolation of Splenic B Lymphocytes

Source: Perchet Thibaut1,2,3, Meunier Sylvain1,2,3, Sophie Novault4, Rachel Golub1,2,3
1 Unit for Lymphopoiesis, Department of Immunology, Pasteur ...

Magnetic Activated Cell Sorting (MACS): Isolation of Thymic T Lymphocytes

Source: Meunier Sylvain1,2,3, Perchet Thibaut1,2,3, Sophie Novault4, Rachel Golub1,2,3 
1 Unit for Lymphopoiesis, Department of Immunology, Pasteur Institute, Paris, France 
2 INSERM U1223, Paris, France 
3 Universit&#233; Paris Diderot, Sorbonne Paris Cit&#233;, Cellule Pasteur, Paris, France 
4 Flow Cytometry Platfrom, Cytometry and Biomarkers UtechS, Center for Translational Science, Pasteur Institute, Paris, France
Defence against pathogens depends on surveillance by the immune system. This system is complex and comprises many cell types, each one with specific functions. This complex composition enables immune responses to a large diversity of pathogens and injuries. Adaptive immunity allows specific responses against specific pathogens. The majority of cells responsible for this type of immunity are the lymphocytes (B cells and T cells). Usually, B cells respond to extracellular infections (such as bacterial infections), and T cells respond to intracellular infections (such as viral infections). The different types of cells in lymphocyte populations can be characterized by the combination of cell surface proteins they express and/or by a panel of secreted cytokines.
Magnetic sorting allows enrichment of targeted cell populations using magnetic properties and expression of one or several cell surface proteins (1, 2). This technique consists of three steps. First, the cells are incubated with magnetic beads that are coupled with one or several monoclonal-specific antibodies. Cells that express surface proteins that bind to these antibodies attach to the magnetic beads. Then, the targeted cell populations are captured with a magnet. To finish, the targeted cells are eluted from the magnet. At the end, two sorting products are obtained, one containing unlabeled cells and the second containing the target cells coupled with the magnetic beads. Columns can be used to improve the efficiency of magnetic sorting. In the column, a non-magnetic element lengthens the path of cell through the column. Hence, cell flow is slowed down, facilitating cell capture by the magnet.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/10495/10495fig1.jpg" /> 
Figure 1: Schematic representation of magnetic separation. Thymic leukocytes are stained with anti-CD3 biotinylated antibodies. After washing, streptavidin (SAV) coupled beads specifically fix the biotin on anti-CD3 antibodies. (1) Cells are transferred in a column. (2) The magnet does not retain unlabeled cells, while CD3-positive cells remain in the column. Finally, the column is separated from the magnet and (3) CD3-positive cells are eluted in medium. <a href="https://www.jove.com/files/ftp_upload/10495/10495fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
There are two types of magnetic sorting (3). In positive sorting, cells of interest are captured with the magnetic beads. In negative sorting, unwanted cells are removed by capturing with the magnetic beads carrying the appropriate antibodies. This MACS technique permits good enrichment of targeted cells and improves the percentage of recovered cells from 1-20% to 60-98% in an organ. After sorting, it is necessary to verify cell purity and sorting by different methods (e.g. flow cytometry). The MACS technique is ideal to enrich a target population for other experiments such as cell culture or cell cycle analysis.
In this lab exercise, we demonstrate how to isolate thymic leukocytes and thereafter enrich thymic CD3-positive cells from the mix using magnetic cell sorting technique.

MACS: Isolation of Thymic T Lymphocytes

Source: Meunier Sylvain1,2,3, Perchet Thibaut1,2,3, Sophie Novault4, Rachel Golub1,2,3
1 Unit for Lymphopoiesis, Department of Immunology, Pasteur ...

ELISA Assays: Indirect, Sandwich, and Competitive

Source: Whitney Swanson1,2, Frances V. Sjaastad2,3, and Thomas S. Griffith1,2,3,4 
1 Department of Urology, University of Minnesota, Minneapolis, MN 55455 
2 Center for Immunology, University of Minnesota, Minneapolis, MN 55455 
3 Microbiology, Immunology, and Cancer Biology Graduate Program, University of Minnesota, Minneapolis, MN 55455 
4 Masonic Cancer Center, University of Minnesota, Minneapolis, MN 55455
Enzyme-linked immunosorbent assay (ELISA) is frequently used to measure the presence and/or concentration of an antigen, antibody, peptide, protein, hormone, or other biomolecule in a biological sample. It is extremely sensitive, capable of detecting low antigen concentrations. The sensitivity of ELISA is attributed to its ability to detect the interactions between a single antigen-antibody complex (1). Moreover, the inclusion of an enzyme-conjugated antigen-specific antibody permits the conversion of a colorless substrate into a chromogenic or fluorescent product that can be detected and easily quantitated by a plate reader. When compared to the values generated by titrated amounts of a known antigen of interest, the concentration of the same antigen in the experimental samples can be determined. Different ELISA protocols have been adapted to measure antigen concentrations in a variety of experimental samples, but they all have the same basic concept (2). Choosing the type of ELISA to perform, indirect, sandwich, or competitive, depends on a number of factors, including the complexity of the samples to be tested and the antigen-specific antibodies available to use. The indirect ELISA is frequently used to determine the outcome of an immunological response, such as measuring the concentration of an antibody in a sample. The sandwich ELISA is best suited for analyzing complex samples, such as tissue culture supernatants or tissue lysates, where the analyte, or antigen of interest, is part of a mixed sample. Finally, the competitive ELISA is most often used when there is only one antibody available to detect the antigen of interest. Competitive ELISAs are also useful for detecting a small antigen with only a single antibody epitope that cannot accommodate two different antibodies due to steric hinderance. The protocol will describe the basic procedures for the indirect, sandwich, and competitive ELISA assays.
The indirect ELISA assay is commonly used to measure the amount of antibodies in serum or in the supernatant of a hybridoma culture. The general procedure for the indirect ELISA assay is:
<ol>
	<li>Coat wells with antigens</li>
	<li>Add serum or hybridoma culture supernatant containing antibody (primary or 1&#176; antibody)</li>
	<li>Incubate and wash</li>
	<li>Add secondary (or 2&#176;) enzyme-conjugated antibody</li>
	<li>Incubate and wash</li>
	<li>Add substrate</li>
</ol>
The sandwich ELISA assay differs from the indirect ELISA assay in that the method does not involve coating the plates with a purified antigen. Instead, a &#34;capture&#34; antibody is used to coat the wells of the plate. The antigen is &#34;sandwiched&#34; between the capture antibody and a second &#34;detection&#34; enzyme-conjugated antibody - where both antibodies are specific for the same antigen, but at different epitopes (3). By binding to the capture antibody/antigen complex, the detection antibody remains in the plate. Either monoclonal antibodies or polyclonal antisera can be used as the capture and detection antibodies. The main advantage of the sandwich ELISA is that the sample does not have to be purified before analysis. Moreover, the assay can be quite sensitive (4). Many commercially available ELISA kits are of the sandwich variety and use tested, matched pairs of antibodies. The general procedure for the sandwich ELISA assay is:
<ol>
	<li>Coat wells with capture antibody</li>
	<li>Add test samples containing antigen</li>
	<li>Incubate and wash</li>
	<li>Add enzyme-conjugated detection antibody.</li>
	<li>Incubate and wash</li>
	<li>Add substrate</li>
</ol>
Most commercially available sandwich ELISA kits come with enzyme-conjugated detection antibodies. In cases where an enzyme-conjugated detection antibody is not available, a secondary enzyme-conjugated antibody specific for the detection antibody can be used. The enzyme on the secondary antibody performs the same role, which is to convert the colorless substrate to a chromogenic or fluorescent product. The above-mentioned secondary enzyme-conjugated antibody would more like to be used in a &#34;homemade&#34; sandwich ELISA developed by an investigator who has generated their own monoclonal antibodies, for example. One drawback to using a secondary enzyme-conjugated antibody is to be sure it only binds to the detection antibody, and not the capture antibody bound to the plate. This would result in a measurable product in all wells, regardless of the presence or absence of antigen or detection antibody.
Finally, the competitive ELISA assay is used to detect soluble antigens. It is simple to perform, but it is only suitable when the purified antigen is available in a relatively large amount. The general procedure for the competitive ELISA assay is:
<ol>
	<li>Coat wells with antigen</li>
	<li>Incubate and wash</li>
	<li>Preincubate test sample with enzyme-conjugated primary antibodies</li>
	<li>Add mixture to well</li>
	<li>Incubate and wash away any unbound enzyme-conjugated primary antibody</li>
	<li>Add substrate</li>
</ol>
The &#34;competition&#34; in this assay comes from the fact that more antigen in the test sample used in step 3 will result in less antibody available to bind to the antigen coating the well. Thus, the intensity of the chromogenic/fluorogenic product in the well at the end of the assay is inversely related to the amount of antigen present in the test sample.
A key component in any type of ELISA is the titrated standards of known concentrations that will allow the user to determine the antigen concentration present in the test samples. Typically, a series of wells are designated for creating a standard curve, where known amounts of a purified recombinant protein are added to the wells in decreasing amounts. When these wells are processed at the same time as the test samples, the user can then have a reference set of absorbance values obtained from a microplate reader for known protein concentrations to go along with the absorbance values for the test samples. The user can then calculate a standard curve to which the test samples can be compared for determining the amount of protein of interest present. The standard curve can also determine the degree of precision of the user&#39;s dilution making.
Finally, the last step in each of the ELISA types listed above calls for the addition of a substrate. The degree of conversion of the substrate to product is directly related to the amount of enzyme present in the well. Horseradish peroxidase (HRP) and alkaline phosphatase (AP) are the most common enzymes found conjugated to antibodies. As expected, there are a number of substrates available specific for either enzyme that produce a chromogenic or fluorescent product. Moreover, substrates are available in a range of sensitivities that can increase the overall sensitivity of the assay. The user must also take into consideration the type of instrumentation available for reading the plate at the end of the experiment when picking the type of substrate to use, along with its corresponding enzyme-conjugated antibody.
Commonly used chromogenic substrates for HRP include 2,2&#39;-Azinobis [3-ethylbenzothiazoline-6-sulfonic acid]-diammonium salt (ABTS) and 3,3&#39;,5,5&#39;-tetramethylbenzidine (TMB), whereas p-Nitrophenyl Phosphate (PNPP) is used for AP. ABTS and TMB produce water-soluble green and blue colored reaction products, respectively. The green ABTS product has two major absorbance peaks, 410 and 650 nm, while the blue TMB product is best detected at 370 and 652 nm. The colors of ABTS and TMB change to yellow upon the addition of an acidic stop solution, which is best read at 450 nm. Color development for ABTS is slow, while it is fast for TMB. TMB is more sensitive than ABTS, and may produce a higher background signal if the enzymatic reaction proceeds too long. PNPP produces a yellow water-soluble product after AP conversion that absorbs light at 405 nm.

Source: Whitney Swanson1,2, Frances V. Sjaastad2,3, and Thomas S. Griffith1,2,3,4
1 Department of Urology, University of Minnesota, Minneapolis, MN 55455
...

ELISPOT Assay: Detection of IFN-&#947; Secreting Splenocytes

Source: Tonya J. Webb1 
1 Department of Microbiology and Immunology, University of Maryland School of Medicine and the Marlene and Stewart Greenebaum Comprehensive Cancer Center, Baltimore, Maryland 21201
ELISPOT is a standardized, reproducible assay used to detect cellular immune responses. The assay utilizes an enzyme-linked immunosorbent assay (ELISA)- based method to detect single-cell immune responses which can be visualized by spots, hence the name ELISPOT. ELISPOT was first described in 1983, by Czerkinsky, as a method of enumerating the number of B cell hybridomas producing antigen-specific immunoglobulins (1). The same group further developed the assay to measure the frequency of cytokine producing T lymphocytes. Now ELISPOT has become a gold standard for measuring antigen-specific T cell immunity in clinical trials and vaccine candidates. For example, after vaccination or during an infection, plasma cells and memory B cells secrete antibodies that provide protection. Typically, these B cell responses are assessed by measuring serum titers of antigen-specific antibodies. However, this type of analysis, typically measured by ELISA, may not include memory B cells, which can be present even in the absence of detectable serum antibody levels. Furthermore, it has been well-established that circulating memory B cells are important for the rapid and protective antibody response observed following pathogen re-exposure, thus it is critical to be able to detect these cells. Therefore, to clearly assess antigen-specific memory B-cell responses, both ELISA and ELISPOT should be used (2).
ELISPOT assay uses a plate containing membrane-lined wells that are coated with antibodies in order to capture secreted proteins of interest. Then, the plate is loaded with cells and stimuli to induce protein production. The secreted proteins are captured by the antibodies coated on the surface. After appropriate incubation time, cells are removed and the secreted molecule is detected by using a biotinylated antibody that is specific for a different epitope, as compared to the capture antibody. Next, streptavidin peroxidase is added, followed by the addition of a substrate that allows the detection of the spots (Figure 1). The strength of this assay is that it allows one to quantitate the number of cells producing the protein of interest. Importantly, one can assess if there are changes in the total number of cells producing a specific protein or if individual cells within a population are producing more protein. Moreover, it can provide information regarding kinetics and can be used to assess overall immune activation (mitogen stimulation) relative to antigen-specific responses (antigen simulation). The ELISPOT assay will permit the detection one activated cell amongst 300,000 cells following mitogenic or antigen-specific activation.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/10497/10497fig1.jpg" /> 
Figure 1: ELISPOT protocol overview.
The major advantages of this assay are its- a. Simplicity- the protocol is relatively simple and straightforward. It does not require technical expertise, b. Sensitivity- it permits the detection of immune cells at the single cell level and requires very few cells compared to other methods such as flow cytometry, c. Functionality- it provides quantitative data regarding immune function.
This lab exercise demonstrates the ELISPOT protocol for detection of IFN-&#947; secreting-splenocytes, but as mentioned above this assay can also be used to assess antibody secretion by B cells (3).

ELISPOT Assay: Detection of IFN-&amp;#947; Secreting Splenocytes

Source: Tonya J. Webb1
1 Department of Microbiology and Immunology, University of Maryland School of Medicine and the Marlene and Stewart Greenebaum ...

Immunohistochemistry and Immunocytochemistry: Tissue Imaging via Light Microscopy

Source: Michael S. Lee1 and Tonya J. Webb1 
1 Department of Microbiology and Immunology, University of Maryland School of Medicine and the Marlene and Stewart Greenebaum Comprehensive Cancer Center, Baltimore, Maryland 21201
Immunohistochemistry (IHC) and immunocytochemistry (ICC) are techniques used to visualize the expression and localization of specific antigens using antibodies. The first published use of IHC was in 1941 when Albert Coons used the technique to visualize the presence of pneumococcal antigen in tissue sections from mice infected with Pneumococcus (1). The name, immunohistochemistry, is derived from the roots &#34;immuno-,&#34; in reference to antibodies, and &#34;histo-,&#34; in reference to the tissue sections used in IHC. The root &#34;cyto-&#34; in immunocytochemistry highlights the key difference between ICC and IHC. Whereas IHC uses sections of whole tissue, ICC uses cells that have been isolated from tissue or grown in culture. The difference in samples used means sample preparation technically differs between IHC and ICC, but otherwise the protocols for ICC and IHC are identical and one will find the terms are frequently used interchangeably.
In both IHC and ICC, antibodies with either chemical or fluorescent tags, such as peroxidase or rhodamine, respectively, are used to visualize the distribution of any antigen of interest through specific binding of the tagged antibody to the antigen. In the case of IHC, thin slices of tissue are immobilized on a slide to maintain the structure of the tissue before being stained, allowing the visualization of antigens in the context of whole tissues (Figure 1). In the case of ICC, cells are distributed evenly on a slide before being stained, allowing the visualization of antigen distribution within individual cells but not within the structure of any specific tissue. Due to the similarities between the two protocols, this protocol will focus on IHC to address the additional complexities of sample preparation involved in IHC.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/10498/10498fig1.jpg" /> 
Figure 1: Outline of IHC Protocol. Visual outline of an IHC protocol for paraffin-embedded tissue dissected from a mouse. This protocol uses a biotinylated secondary antibody and strepavidin-HRP to visualize the location of antibody binding. Other options, such as fluorescently tagged antibodies, are also possible. <a href="https://www.jove.com/files/ftp_upload/10498/10498fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The first major decision when performing IHC is how to prepare the tissue sections in order to maintain the structure of the tissue throughout the staining process. The two main choices are formalin-fixed sections of paraffin-embedded tissue or fresh sections of frozen tissue. There is no simple answer as to which method to use as it depends on what downstream analysis will be conducted. Formalin-fixation of paraffin embedded tissues is generally thought to better preserve tissue morphology for optimal imaging while freezing fresh tissue can preserve protein function for subsequent assays outside of IHC. In addition, fresh frozen tissue sections have been shown to be more suitable for gene expression analysis (2). A third consideration is whether or not the antibodies for your antigen of interest are suitable for either fixed or frozen tissue sections, as some antibodies have only been optimized for a specific type of section and may not work for others. Finally, one also needs to determine how long they need to store the tissue sections, as fresh frozen samples must be kept at -80&#176;C and may not last beyond one year while fixed sections can be stored for much longer at room temperature. These are a few of the major considerations for determining whether to use formalin-fixed sections of paraffin-embedded tissue or fresh sections of frozen tissue. Ultimately, if one has enough tissue, it may be best just to have some of both.
In this experiment, we set out to determine if cyclin D1 expression was increased in enlarged spleens from a spontaneous mouse model of lymphoma development. Splenic tissue samples were first isolated from either wild-type mice, transgenic mice that do not have lymphoma, or transgenic mice that have spontaneously developed lymphoma. The spleen tissue samples were fixed in paraformaldehyde, embedded in paraffin, sectioned, stained using a mouse anti-cyclin D1 primary antibody followed by a horse anti-mouse secondary antibody, and developed using 3,3-diaminobenzidine (DAB). The sections were then counterstained in Harris Hematoxylin Solution and then the sections were imaged at 20X magnification.
Reagents
Paraffin-Embedded Sections
<ol type="a">
	<li>4% Paraformaldehyde (PFA)</li>
	<li>Ethanol (anhydrous denatured, histological grade 100%, 95%, 80%, 75%, and 50%). Can be diluted from 100% stock using double distilled water (ddH2O)</li>
	<li>Xylene</li>
	<li>IHC compatible glass slide to ensure tissue section remains attached throughout the entire procedure. IHC compatible glass slides have a specialized coating and are readily available from multiple retailers. If performing ICC, use a chambered slide. Chambered slides allow for cells to be seeded in the chambers and placed in the incubator until cells attach to the slide and reach proper confluency, at which point the chambers can be removed and staining can proceed in the same manner as IHC.</li>
	<li>Paraffin</li>
	<li>0.3% Hydrogen peroxide (H2O2)/methanol: To prepare, add 1 mL 30% H2O2 to 99 mL methanol. Store at -20&#176;C</li>
	<li>Antigen retrieval buffer: IHC citrate buffer pH 6.0</li>
</ol>
Fresh Frozen Sections
<ol type="a">
	<li>Optimal cutting temperature (OCT) embedding compound</li>
	<li>Optimal fixative: 4% PFA or acetone that has been cooled to -20&#176;C</li>
</ol>
Staining
<ol type="a">
	<li>Blocking buffer: Should be determined by user. One example is horse serum diluted in 1X PBS</li>
	<li>Diluted primary antibody: see manufacturer specifications</li>
	<li>Diluted biotinylated secondary antibody: see manufacturer specifications</li>
	<li>Diluted avidin-Horseradish Peroxidase (HRP): Only for peroxidase visualization. See manufacturer specifications.</li>
	<li>DAB or another compatible substrate</li>
	<li>Counterstain (optional)</li>
	<li>Ethanol (anhydrous denatured, histological grade 100% and 95%)</li>
	<li>Xylene</li>
	<li>Organo/Limonene Mount</li>
</ol>

Immunohistochemistry &amp; Immunocytochemistry: Tissue Imaging

Source: Michael S. Lee1 and Tonya J. Webb1
1 Department of Microbiology and Immunology, University of Maryland School of Medicine and the Marlene and ...

Antibody Generation: Producing Monoclonal Antibodies Using Hybridomas

Source: Frances V. Sjaastad1,2, Whitney Swanson2,3, and Thomas S. Griffith1,2,3,4 
1 Microbiology, Immunology, and Cancer Biology Graduate Program, University of Minnesota, Minneapolis, MN 55455 
2 Center for Immunology, University of Minnesota, Minneapolis, MN 55455 
3 Department of Urology, University of Minnesota, Minneapolis, MN 55455 
4 Masonic Cancer Center, University of Minnesota, Minneapolis, MN 55455
Polyclonal antibodies are defined as a collection of antibodies directed against different antigenic determinants of an antigen or several antigens (1). While polyclonal antibodies are powerful tools for identifying biological molecules, there is one important limitation - they are unable to distinguish between antigens that share antigenic determinants. For example, when bovine serum albumin is used to immunize an animal, B cells with different surface Ig will respond to different antigenic determinants on bovine serum albumin. The result is a mixture of antibodies in the antiserum. Because bovine serum albumin shares some epitopes with human serum albumin in evolutionarily conserved regions of the protein, this anti-bovine serum albumin antiserum will also react with human serum albumin. Therefore, this antiserum will not be useful for distinguishing between bovine and human serum albumins.
Several approaches have been taken to overcome the specificity issue of polyclonal antisera. One is by absorbing the unwanted antibodies by passing the antiserum through a chromatography column of immobilized antigens (2). This method is tedious and frequently unable to completely remove the unwanted antibodies. Another approach is to isolate individual antibody-producing B cells and expand them in culture. However, like most normal untransformed cells, B cells do not survive in long-term culture.
To overcome the inability of B cells to survive in culture, one approach is to prepare a myeloma-B cell hybridoma. In 1847, Henry Bence-Jones discovered that patients with multiple myeloma, a lymphoid tumor, produced a large quantity of antibodies (3). B cells in these patients have become malignant and grow uncontrollably. Since the malignant B cells are derived from a single clone, they are identical and produce only a single type of antibody (i.e., a monoclonal antibody, or mAb). However, most of these myeloma cells produce antibodies of unknown specificities. In 1975, by fusing a myeloma cell to a B cell, Cesar Milstein and Georges Kohler succeeded in producing a hybridoma that can be cultured indefinitely in vitro and produces an unlimited number of monoclonal antibodies of known antigenic specificity (4). The rationale behind their approach is to combine the immortal properties of the myeloma cell and the antibody producing properties of the B cell. Their technique revolutionized antibody production and provides a powerful means for identification and purification of biological molecules using monoclonal antibodies.
Generally, preparing a monoclonal antibody requires several months. The general procedure includes the following steps:
<ol>
	<li>Immunization and screening of antibody titer</li>
	<li>Fusion of antibody-producing B cells and myeloma cells</li>
	<li>Selective growth of the hybridoma</li>
	<li>Screening the hybridomas for producing the desired monoclonal antibody</li>
	<li>Cloning by limiting dilution - a process whereby cells are diluted to a concentration to statistically allow for less than 1 cell to be added to the wells of a 96-well plate. Some wells will end up with 0 cells and some will have 1 cell. The wells with seeded with 1 cell will eventually grow into a monoclonal population of cells.</li>
	<li>Growth of the hybridoma and preparation of monoclonal antibody</li>
</ol>
This protocol focuses on the last step - growth of the hybridoma and preparation of the monoclonal antibody. The antibody is purified from the culture supernatant by ammonium sulfate precipitation (often referred to as salting out) - a commonly used method of removing proteins from a solution. Proteins in solution form hydrogen bonds, along with other hydrophilic interactions, with water through their exposed polar and ionic groups. When concentrations of small, highly charged ions (such as ammonium or sulfate) are added, these groups compete with the proteins for binding to water. This removes the water molecules from the protein and decreases its solubility, resulting in precipitation of the protein.

Producing Monoclonal Antibodies Using Hybridomas

Source: Frances V. Sjaastad1,2, Whitney Swanson2,3, and Thomas S. Griffith1,2,3,4
1 Microbiology, Immunology, and Cancer Biology Graduate Program, ...

Immunofluorescence Microscopy: Immunofluorescence Staining of Paraffin-Embedded Tissue Sections

Source: Thomas Chaffee1, Thomas S. Griffith2,3,4, and Kathryn L. Schwertfeger1,3,4 
1 Department of Lab Medicine and Pathology, University of Minnesota, Minneapolis, MN 55455 
2 Department of Urology, University of Minnesota, Minneapolis, MN 55455 
3 Masonic Cancer Center, University of Minnesota, Minneapolis, MN 55455 
4 Center for Immunology, University of Minnesota, Minneapolis, MN 55455
Pathologic analyses of tissue sections can be used to obtain a better understanding of normal tissue structure and contribute to our understanding of mechanisms of disease. Tissue biopsies, either from patients or from experimental in vivo models, are often preserved by fixing in formalin or paraformaldehyde and embedding in paraffin wax. This allows for long-term storage and for the tissues to be sectioned. Tissues are cut into thin (5 &#181;m) sections using a microtome and the sections are adhered to glass slides. The tissues sections can be stained with antibodies, which allow for the detection of specific proteins within the tissue sections. Staining with antibodies conjugated to fluorophores (also known as fluorochromes) - compounds that emit light at specific wavelengths when excited by a laser - is known as immunofluorescence. The ability to detect proteins within a section can provide information such as cell type heterogeneity within the tissue, activation of specific signaling pathways, and expression of biomarkers. Depending on the fluorophores used and type of microscope available for analysis, multiple colors can be used, which allows for multiplexed analysis of targets.
The following protocol outlines the basic steps involved in immunofluorescence staining of paraffin embedded tissue sections. It is important to note that this protocol will not include any details on the fixation of tissue, process of paraffin embedding, or sectioning of the tissues. Once tissues have been sectioned and placed on glass slides, they are rehydrated through a series of graded ethanol (EtOH) incubations. The sections are incubated with a blocking reagent to reduce non-specific binding of antibody to the tissue section. The sections are then incubated with a primary antibody that may or may not be directly labeled with a fluorophore. If the primary antibody is not directly labeled, the sections are then incubated with a secondary antibody labeled with a fluorophore. Different antibodies may require different staining conditions, thus suggestions for optimization of antibodies are included. Following washing to remove all unbound antibody, the slides are mounted with media containing DAPI to fluorescently label the nucleus. Once the mounting media has dried, the slides can be imaged using a microscope with lasers that can detect the different fluorophores.

Immunofluorescence Staining and Microscopy

Source: Thomas Chaffee1, Thomas S. Griffith2,3,4, and Kathryn L. Schwertfeger1,3,4
1 Department of Lab Medicine and Pathology, University of Minnesota, ...

Confocal Fluorescence Microscopy: A Technique to Determine the Localization of Proteins in Mouse Fibroblasts

Source: Dominique R. Bollino1, Eric A. Legenzov2, Tonya J. Webb1 
1 Department of Microbiology and Immunology, University of Maryland School of Medicine and the Marlene and Stewart Greenebaum Comprehensive Cancer Center, Baltimore, Maryland 21201 
2 Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland 21201
Confocal fluorescence microscopy is an imaging technique that enables increased optical resolution as compared to conventional &#34;wide-field&#34; epifluorescence microscopy. Confocal microscopes are able to achieve improved x-y optical resolution through &#34;laser scanning&#34;- typically a set of voltage-controlled mirrors (galvanometer or &#34;galvo&#34; mirrors) that direct laser-illumination to each pixel of the specimen at a time. More importantly, confocal microscopes achieve superior z-axial resolution by using a pinhole to remove out of focus light originating from locations that are not in the z-plane being scanned, thus enabling the detector to collect data from a specified z-plane. Because of the high z-resolution achievable in confocal microscopy, it is possible to collect images from a series of z-planes (also-called z-stack) and construct a 3D image through software.
Before discussing the mechanism of a confocal microscope, it is important to consider how a sample interacts with light. Light is composed of photons, packets of electromagnetic energy. A photon impinging on a biological sample can interact with the molecules comprising the sample in one of four ways: 1) the photon does not interact and passes through the sample; 2) the photon is reflected/scattered; 3) the photon is absorbed by a molecule and the absorbed energy is released as heat through processes collectively known as nonradiative decay; and 4) the photon is absorbed and the energy is then rapidly reemitted as a secondary photon through the process known as fluorescence. A molecule whose structure permits fluorescence emission is called a fluorophore. Most biological samples contain negligible endogenous fluorophores; therefore exogenous fluorophores must be used to highlight features of interest in the sample. During fluorescence microscopy, the sample is illuminated with light of the appropriate wavelength for absorption by the fluorophore. Upon absorbing a photon, a fluorophore is said to be &#34;excited&#34; and the process of absorption is referred to as &#34;excitation&#34;. When a fluorophore gives up energy in the form of a photon, the process is known as &#34;emission&#34;, and the emitted photon is called fluorescence.
The light beam used to excite a fluorophore is focused by the objective lens of a microscope and converges at a &#34;focal point&#34; where it is maximally focused. Beyond the focal point the light again diverges. The entering and exiting beams may be visualized as a pair of cones touching at the focal point (see Figure 1, left panel). The phenomenon of diffraction imposes a limit on how tightly a beam of light can be focused - the beam actually focuses to a spot of finite size. Two factors determine the size of the focal spot: 1) the wavelength of the light, and 2) the light-gathering ability of the objective lens, which is characterized by its numerical aperture (NA). The focal &#34;spot&#34; extends not only in the x-y plane, but also in the z direction, and is in reality a focal volume. The dimensions of this focal volume define the maximum resolution achievable by optical imaging. Although the number of photons is greatest within the focal volume, the conical light paths above and below the focus also contain a lower density of photons. Any fluorophore in the light path can thus be excited. In conventional (wide-field) epifluorescence microscopy, emission from fluorophores above and below the focal plane contribute out-of-focus fluorescence (a &#34;hazy background&#34;), which reduces image resolution and contrast, as demonstrated in Figure 1, with the red cube representing fluorophore emission above the focal plane (red star) that results in out-of-focus fluorescence (top right). This problem is ameliorated in confocal microscopy, due to the utilization of a pinhole. (Figure 2, bottom right). As depicted in Figure 3, the pinhole allows emissions originating from the focal place to reach the detector (left), while blocking the out-of-focus fluorescence (right) from reaching the detector, thus improving both resolution and contrast.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/10501/10501fig1.jpg" /> 
Figure 1. Optical resolution of epifluorescence versus confocal microscopy. <a href="https://www.jove.com/files/ftp_upload/10501/10501fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The light beam used to excite a fluorophore is focused by the objective lens of a microscope and converges at a focal volume and then diverges (left). The red star represents the focal plane of a sample that is being imaged while the red square represents fluorophore emission above the focal plane. When capturing an image of this sample using an epifluorescent microscope, the emission from the out-of-focus red square will visible and contribute to a &#34;hazy background&#34; (top right). Confocal microscopes have a pinhole which prevents the detection of light emitted outside of the focal plane, eliminating the &#34;hazy background&#34; (bottom right).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/10501/10501fig2.jpg" /> 
Figure 2. Pinhole effect in confocal microscopy. <a href="https://www.jove.com/files/ftp_upload/10501/10501fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Although the highest intensity of the excitation light is at the focal point of the lens (left, red oval), other parts of the sample not in the focal point (right, red star) will get light and fluoresce. To prevent light emitted from these out-of-focus regions to reach the detector, a screen with a pinhole is present in front of the detector. Only the in-focus light (left) emitting from the focal plane is able to travel through the pinhole and reach the detector. The out-of-focus light (right) is blocked with the pinhole and fails to reach the detector.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/10501/10501fig3.jpg" /> 
Figure 3. Principal components of a confocal laser scanning microscope. <a href="https://www.jove.com/files/ftp_upload/10501/10501fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
For the sake of simplicity, the mechanistic description of a confocal microscope will be limited to that of the Nikon Eclipse Ti A1R. Although there may be minor technical differences between different confocal microscopes, the A1R serves well as a good model for describing confocal microscope function. The excitation light beam, produced by an array of diode lasers, is reflected by the primary dichroic mirror into the objective, which focuses the light onto the specimen being imaged. The primary dichroic mirror selectively reflects the excitation light while allowing light at other wavelengths to pass through. The light then encounters the scanning mirrors that sweep the light beam across the specimen in an x-y manner, illuminating a single (x,y) pixel at a time. Fluorescence emitted by fluorophores at the illuminated pixel is collected by the objective lens and passes through the primary dichroic mirror to reach an array of photomultiplier tubes (PMTs). Secondary dichroic mirrors direct the emission light to the appropriate PMT. Excitation light scattered by the sample back into the objective is reflected by the primary dichroic mirror back towards the specimen, and thus prevented from entering the detection light path and reaching the PMTs (see Figure 3). This allows the relatively feeble fluorescence to be quantified without contamination by light scattered from the excitation light beam, which is typically orders of magnitude more intense than the fluorescence. Because the pinhole blocks light from outside of the focal volume, the light arriving at the detector comes from a narrow, selected z-plane. Therefore, images can be collected from a series of adjacent z-planes; this series of images is often referred to as a &#39;z-stack&#39;. By using the appropriate software, a z-stack can be processed to generate a 3D image of the specimen. A particular advantage of confocal microscopy is the ability to distinguish the subcellular localization of staining. For example, the differentiation between membrane staining from intracellular staining, which is very challenging with conventional epifluorescence microscopy (1, 2, 3).
Sample preparation is an important facet of confocal imaging. A strength of optical microscopy techniques is the flexibility to image live or fixed cells. When attempting to produce 3D images, because of the number of images that must be acquired for a z-stack, the difficulty of maintaining cell health, and the movement of live cells and their organelles, the use of fixed cells is typical. The procedure for fixing and staining cells for confocal fluorescence is similar to that conventionally used in immunofluorescence. After culture in chamber slides or on coverslips, cells are fixed using paraformaldehyde to preserve cellular morphology. Non-specific antibody binding is blocked using bovine serum albumin, milk, or normal serum. In order to maintain the specificity of the secondary antibodies, the solution used should not originate from the same species in which the primary antibodies were generated. The cells are incubated with primary antibodies that bind the antigen of interest. When labeling several cellular targets, the primary antibodies must each be derived from a different species. Antibodies tagging an antigen are then bound by fluorophore-conjugated secondary antibodies. Fluorophore-conjugated secondary antibodies should be selected so that they are compatible with the wavelengths of laser excitation available in the confocal microscope. When visualizing multiple antigens, the excitation/emission spectra of the fluorophores should differ enough so that their signals can be discriminated by microscopic analysis. The stained specimen is then mounted on a slide for imaging. A mounting medium is used to prevent photobleaching and specimen dehydration. If desired, a mounting medium containing a nuclear counterstain (e.g. DAPI or Hoechst) can be used (4).
In the following protocol, mouse fibroblasts transfected to express CD1d (LCD1) were stained with antibodies recognizing CD1d and CD107a (LAMP-1). CD1d is a major histocompatibility complex 1 (MHC 1)-like receptor present on the surface of antigen presenting cells that presents lipid antigens. LAMP-1 (lysosomal associated membrane protein-1) is a transmembrane protein primarily present in lysosomal membranes. For proper antigen presentation, CD1d is trafficked through the low pH lysosomal compartment, so LAMP-1 is being used as a marker of the lysosomal compartment for this protocol. By probing the LCD1 cells with anti-CD1d and anti- LAMP-1 that were produced in different species, secondary antibodies with unique fluorophores can be used to determine the localization of each protein in the cell and whether CD1d is present in the LAMP-1 positive lysosomal compartments.

Confocal Fluorescence Microscopy and Localization of Proteins

Source: Dominique R. Bollino1, Eric A. Legenzov2, Tonya J. Webb1
1 Department of Microbiology and Immunology, University of Maryland School of Medicine ...

Immunoprecipitation-Based Techniques: Purification of Endogenous Proteins Using Agarose Beads

Source: Susannah C. Shissler1, Tonya J. Webb1 
1 Department of Microbiology and Immunology, University of Maryland, Baltimore, MD 21201
Immunoprecipitation (IP, also known as a &#39;pull-down&#39; assay) is a widely used technique that has applications in a variety of fields. First conceived in 1984, it was refined in 1988 (1, 2). The fundamental goal of IP is purification and isolation of a specific protein using an antibody against that protein. The word &#34;immuno&#34; refers to the use of an antibody while the word &#34;precipitation&#34; refers to pulling down a specific substance from a solution. The target protein might be endogenous or recombinant. Most recombinant proteins have an epitope tag (i.e. myc or flag) attached to them to simplify subsequent purification. Typically, it is easier to optimize recombinant protein IP because the antibodies against recombinant epitope tags are very strong and effective. Antibodies against endogenous proteins have extremely variable efficacy - making it much more difficult to optimize these IPs. A necessary step after immunoprecipitation is verification of purification. The isolated protein is resolved using SDS-PAGE and subsequently probed for purity by western blots (Figure 1). An important control is the use of a different antibody during the Western blot to verify pull down of the correct protein. The combination of IP with subsequent techniques is a powerful analysis tool. The goal after purification may be characterization of the protein itself by NMR, mass spectrometry, and in vitro assays, or analysis of the protein&#39;s interacting partners (i.e. protein, DNA, RNA) (3, 4, 5).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/10502/10502fig1.jpg" /> 
Figure 1: Overview of Immunoprecipitation Procedure. Immunoprecipitation is the isolation of a specific protein using an antibody. After production of lysate from cells, there are two major steps- pre-clearing and pull down. During pre-clearing step, the cell-lysates are pre-cleared of proteins that bind to antibodies non-specifically using an isotype control antibody. In pull down step, the target protein is pulled down using a protein-specific antibody. The isolated protein is then analyzed by Western blot. Isotype antibodies and protein specific antibodies have the same constant domain, but different antigen binding domains. A key component of this protocol is Protein A/G agarose beads that bind the constant domain of antibodies- allowing immunoprecipitation of the target protein. <a href="https://www.jove.com/files/ftp_upload/10502/10502fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Antibodies are the key component of an immunoprecipitation that differentiate it from other forms of protein purification (i.e. nickel affinity column purification). Antibodies are molecules made by B cells that can recognize specific protein epitopes. Antibodies have two domains: constant (Fc) and antigen binding (Fab) (Figure 1). The constant domain identifies the type of antibody and dictates function in vivo. Usually, the constant domains of antibodies used for IP are mouse, rat, or rabbit IgG. The antigen binding portion of the antibody recognizes a specific epitope of a specific protein. Antibodies can recognize epitopes on folded proteins that may not exist when the protein is denatured and vice versa. Therefore, the availability of the epitope depends on protein folding - identifying an important factor to consider when choosing antibodies and conditions for IP.
Both prokaryotic and eukaryotic systems have antibody-binding proteins. In eukaryotic systems, the purpose is immune protection from bacteria while in prokaryotic systems, the purpose is protection from the immune system. Antibody-binding proteins affect IP methodology in two ways. First, there is a necessary pre-clearing step (Figure 1) to rid the lysate of proteins that bind antibodies - thereby reducing non-specific binding in the final product. This step uses an isotype antibody that has the same constant domain as but a different antibody binding domain than your protein-specific antibody. Bacterial antibody-binding proteins are the second key component of this method. After the protein-specific antibody binds the target protein, the antibody: protein complex must be pulled down (Figure 1). Proteins A, G, and L are bacterial proteins that bind the constant domain of antibodies. While bacteria use this to subvert the immune system, researchers have co-opted this system for easy antibody purification, and it is used during both the pre-clearing and pull-down steps. These proteins have different binding affinities for different species and different constant domain subtypes - another factor to consider when choosing conditions for IP. Many companies sell Protein A/G labeled agarose beads (Figure 1), pre-made spin columns, or resins to make columns. In general, beads and spin columns are used for smaller sample sizes while resins are used for bulk purification.
In this lab exercise, we demonstrate how to purify the endogenous protein c-myc, from primary murine thymocytes, using Protein A/G Plus agarose beads based basic immunoprecipitation technique. The protocol starts from cell lysate preparation and ends with the with verification of successful protein pull down using Western blot analysis.

Immunoprecipitation Techniques: Purification of Proteins

Source: Susannah C. Shissler1, Tonya J. Webb1
1 Department of Microbiology and Immunology, University of Maryland, Baltimore, MD 21201
Immunoprecipitation ...

Cell Cycle Analysis: Assessing CD4 and CD8 T Cell Proliferation After Stimulation Using CFSE Staining and Flow Cytometry

Source: Perchet Thibaut1,2,3, Meunier Sylvain1,2,3, Sophie Novault4, Rachel Golub1,2,3 
1 Unit for Lymphpoiesis, Department of Immunology, Pasteur Institute, Paris, France 
2 INSERM U1223, Paris, France 
3 Universit&#233; Paris Diderot, Sorbonne Paris Cit&#233;, Cellule Pasteur, Paris, France 
4 Flow Cytometry Platfrom, Cytometry and Biomarkers UtechS, Center for Translational Science, Pasteur Institute, Paris, France
The cell cycle is a universal process of life. During the cell cycle, a cell undergoes several modifications to divide into two daughter cells. This mechanism occurs throughout an organism&#39;s life in response to its needs. Cell divisions and embryonic development produce a full organism from a single-celled zygote. During adulthood, the cell cycle is central to many critical biological processes, such as tissue repairs.
Mechanisms of cell division are tightly controlled events where the cell undergoes stepwise modifications before final division. Cells that are not yet in the cycle are described as being in the Gap 0 (G0) phase. During this stage the cell is considered quiescent. When the cell starts to cycle, four distinct phases are recognized: Gap 1 (G1), Synthesis (S), Gap 2 (G2) and Mitosis (M). G1 phase is a checkpoint for resources needed by the cell for DNA synthesis. Then, S phase occurs, and DNA replication starts, followed by the G2 interphase, another checkpoint that controls all elements necessary to for the cell to divide. Finally, the cell enters mitosis and divides into two daughter cells.
Cell division is a highly informative parameter in many different biological systems. In the field of immunology, analysis of leukocyte proliferation can indicate the mechanism of the immune response. Other domains of investigation also rely on cell cycle analysis. For instance, analysis of the cell cycle during tumor development has improved our understanding of cancer.
Many fluorescent dyes are now available for tracking cell proliferation. These dyes differ in their chemical and spectral properties. Two different classes of dyes exist: protein dyes permanently combine with protein by forming a covalent bond, and membrane dyes stably intercalate within cell membranes via strong hydrophobic associations. In vitro and in vivo studies of immune cell proliferation by flow cytometry are among the most common applications of both classes of cell tracking dyes (1, 2).
CFSE (Carboxyfluorescein succinimidyl ester) is a fluorescent dye that marks dividing cells. Initially, all the cells receive the same amount of dye; dividing cells evenly split the dye they received between their two daughter cells. Consequently, the cell cycle can be followed by the progressive decrease of dye intensity in the cells. CFSE staining is followed by conventional multi-parametric flow cytometry, a high-throughput, fluorescence-based technology that allows phenotypic and functional characterization of cells based on their degree of CFSE staining (3).
In the following experiment, we assess the proliferation of CD4+ and CD8+ T cells in-vitro, following CD3 stimulation, using CFSE staining and flow cytometry.

Cell Cycle Analysis: Assessing CD4 and CD8 T Cell Proliferation

Source: Perchet Thibaut1,2,3, Meunier Sylvain1,2,3, Sophie Novault4, Rachel Golub1,2,3
1 Unit for Lymphpoiesis, Department of Immunology, Pasteur ...

Adoptive Cell Transfer: Introducing Donor Mouse Splenocytes to a Host Mouse and Assessing Success via FACS

Source: Meunier Sylvain1,2,3, Perchet Thibaut1,2,3, Sophie Novault4, Rachel Golub1,2,3 
1 Unit for Lymphopoiesis, Department of Immunology, Pasteur Institute, Paris, France 
2 INSERM U1223, Paris, France 
3 Universit&#233; Paris Diderot, Sorbonne Paris Cit&#233;, Cellule Pasteur, Paris, France 
4 Flow Cytometry Platfrom, Cytometry and Biomarkers UtechS, Center for Translational Science, Pasteur Institute, Paris, France
Adoptive cell transfer is a method for introducing cells into a patient or study organism in order to treat a disease or study a biological process, such as haematopoiesis. Aims of adoptive transfer are various; it can be used in fundamental biology as well as in medical sciences (1, 2). In mouse models, migration and distribution of transferred cells can be studied and followed by a tracking system (cell surface marker, staining by CFSE, etc.). In cancer studies on mouse models, transfer of specific cell populations can be used as experimental treatment against tumors. Another example for this technique is creation of chimeric mice by transfer of bone marrow cells to irradiated mice or mice with a severe immunodeficiency phenotype. This mouse model can be used to assess the impact of gene deletion on a specific cell population for instance. Transfer of bone borrow cells is also used in human medical treatment. When patients are irradiated in case of cancer therapy, adoptive transfer of bone marrow allows immune system reconstitution.
The first step in this technique is to obtain the cell population of interest. The technique chosen to isolate this population depends on the level of specificity of the targeted population. The largest level of selection is the whole organ, in which all cell populations present in the organ are taken. A more precise method is selection of a target cell population, often selected by one cell surface marker. The ideal method to sort cells in this case is by magnetic sorting. Finally, the most stringent level is the selection of cells by several cell surface markers to sort very specific cell populations. Flow cytometry sorting is the most popular method for this level of selection. Once population of interest is obtained, it can be transferred to the host. Before adoptive transfer it is essential to ensure compatibility between host and donor. Indeed, regardless of transfer goal, compatibility is crucial to assure cells adoption by the host without cells rejection.
In this lab exercise, we demonstrate the adoptive cell transfer technique by transferring splenocytes from a CD45.2 mouse into a CD45.1 Rag&#947;c mouse (lacking lymphocytes) and four days later confirm the splenocytes transfer using flow cytometry (see Figure 1).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/10504/10504fig1.jpg" /> 
Figure 1: Schematic representation of adoptive transfer. (1) Splenocytes are isolated from CD45.2 mice and (2) transferred in CD45.1 Rag&#947;c mouse, control mouse is injected with PBS only. (3) 4 days after adoptive transfer, splenocytes are recovered from mice and (4) analyzed by flow cytometry. <a href="https://www.jove.com/files/ftp_upload/10504/10504fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Adoptive Cell Transfer Technique

Assay for Cell Death: Chromium Release Assay of Cytotoxic Ability

Source: Frances V. Sjaastad1,2, Whitney Swanson2,3, and Thomas S. Griffith1,2,3,4 
1 Microbiology, Immunology, and Cancer Biology Graduate Program, University of Minnesota, Minneapolis, MN 55455 
2 Center for Immunology, University of Minnesota, Minneapolis, MN 55455 
3 Department of Urology, University of Minnesota, Minneapolis, MN 55455 
4 Masonic Cancer Center, University of Minnesota, Minneapolis, MN 55455
One of the main functions of the cells of the immune system is to remove target cells that have been infected with viruses or have undergone transformation into a tumor cell. In vitro assays for measuring the cytotoxic capacity of immune cells have been a staple in laboratories for many years. These assays have been used to determine the ability of T cells, NK cells, or any other immune cell to kill target cells in an antigen-specific or -nonspecific manner. Death ligands (e.g., Fas ligand or TRAIL), cytokines (e.g., IFNg or TNF), or cytotoxic granules (i.e., perforin/granzyme B) expressed by effector cells are some ways in which target cell death can be induced. With the explosion in tumor immunotherapy research in recent years, there is growing interest in finding agents to increase the cytotoxic activity of immune cells to improve patient outcomes. Conversely, some diseases are hallmarked by the overexuberant activity of immune cell cytotoxic activity, resulting in efforts to identify agents to temper these responses. Thus, having an assay in which the user can easily integrate any number of different effector cells, target cells, and/or response modifiers into the experimental design can serve as a valuable means of quickly assessing the cytotoxic capacity of effector cells and/or the responsiveness of the target cell.
These in vitro assays involve the mixing of different cell populations, as well as using a relatively low number of both effector and target cells. Thus, one necessity of the assay is to label the target cells in a manner that can easily be detected and quantitated, allowing the user to then determine the &#39;percent specific lysis&#39; mediated by the effector cells. Radioactivity - especially, chromium 51 (51Cr) in the form of Na251CrO4- is an inexpensive way to rapidly and nonspecifically label cellular proteins within the target cells (1). The short labeling and total assay times reduces the potential for significant changes in the number and/or phenotype of the target cells, which could influence the outcome of the assay. Upon the loss of membrane integrity of the target cells as a result of the cytotoxic activity of the effector cells, the 51Cr-labelled cellular proteins within the target cells are released into the culture supernatant, becoming available for quantitation. As with any assay examining the function of immune cells in vitro, there are a number of important considerations to consider improving the performance of the experiment. One of the most critical features is to use healthy effector (for maximal cytotoxic activity) and target (for maximal responsiveness and minimal spontaneous death/51Cr release) cells. Effector and target cell contact is required (leading to the common use of round-bottom 96-well plates to encourage cell-cell contact) (2). Finally, data analysis is dependent on the inclusion of positive and negative control target cell populations.
The following protocol will outline the steps for performing a standard 51Cr release assay to measure the cytotoxic ability of a population of effector cells, though a nonradioactive version using Europium has recently been developed. 51Cr is a powerful &#947;-radiation emitter. Consequently, the use of this assay requires proper radiation safety training, dedicated laboratory space, a gamma counter, and disposal of radioactive samples.
The general sequence of events in this assay are: 1) prepare 51Cr-labeled targets; 2) prepare effector cells and add to plate while target cells are labeling; 3) add labeled targets to plate; 4) incubate plate; 5) harvest supernatants; and 6) analyze data after running samples on counter. Samples are commonly prepared in triplicate, and then averaged to account for any subtle pipetting differences.
Proper PPE is important for this assay. Specifically, the user should wear a lab coat and gloves. Safety glasses may be required based on the laboratory or institution. There should be ample lead shielding for safe storage and use of the 51Cr during all steps. Finally, there should be dedicated lab space and equipment set aside for using 51Cr, including all the proper signage to indicate where samples with 51Cr are being kept and a Geiger counter equipped with gamma probe to survey the space for possible contamination.
In this lab exercise, we will determine the ability human peripheral blood mononuclear cells (PBMCs), (CpG stimulated vs. unstimulated) to kill melanoma cells, using human melanoma cell line WM793 as model and the chromium release assay.

Chromium Release Assay for Testing Cytotoxicity

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