MHC multimer

MHC multimers are oligomeric forms of , designed to identify and isolate T-cells with high affinity to specific antigens amid a large group of unrelated T-cells. Multimers generally range in size from dimers to octamers; however, some companies use even higher quantities of MHC per multimer. Multimers may be used to display class 1 MHC, class 2 MHC, or nonclassical molecules (e.g. CD1d) from species such as monkeys, mice, and humans.

Since T-cell receptors have a low affinity for their MHC counterparts, it was historically problematic to label T cells effectively using single MHC-T-cell interactions. However, in 1996 it was proposed by John Altman to use a complex of multiple MHC molecules to form a more stable bond between corresponding T-cells.

The most commonly used MHC multimers are tetramers. These are typically produced by biotinylating soluble MHC monomers, which are typically produced recombinantly in eukaryotic or bacterial cells. These monomers then bind to a backbone, such as streptavidin or avidin, creating a tetravalent structure. These backbones are conjugated with fluorochromes to subsequently isolate bound T-cells via flow cytometry.

MHC multimers allow for a previously unattainable level of specificity in antigen-specific T-cell detection and isolation. This ability gives rise to several clinical applications. MHC multimers allow for ex vivo selection and proliferation of T-cells specific to viral or tumor-related antigens, which can then be reintroduced to augment the immune system. MHC multimers can also be used to eliminate graft-originating T-cells on transplant organs, ex vivo. MHC multimers may also be used to eliminate harmful or unwanted T-cells in vivo, such as those that target self cells and lead to autoimmune disease. Cancer immunotherapy and vaccine development can also be largely influenced by this technology.

MHC tetramers consist of four MHC molecules, a tetramerization agent and a fluorescently labeled protein (usually streptavidin). Streptavidins have also been generated with 6 or 12 binding sites for MHC. MHC tetramers are used to identify and label specific T-cells by epitope specific binding, allowing the antigen specific immune response to be analyzed in both animal model and in man. MHC tetramers were originally developed using MHC class I molecules for the recognition of cytotoxic T cells, but over the last decade they have allowed for the recognition of CD4 T cells by a wide variety of antigens. Tetramer assays are used for single-cell phenotyping and cell counting, and offer an important advantage over other methods, such as ELISPOT and single-cell PCR because they enable the recovery and further study of sorted cells. As a flow-cytometry-based application, tetramers are also easy to use and have a short assay time, similar to Antibody-based flow cytometry studies.

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