Mass cytometry (MC), imaging mass cytometry (IMC), and multiplexed ion beam imaging (MIBI) represent a new generation of tools to understand increasingly complex systems. Although these technologies differ in their intended applications, with MC being most similar to flow cytometry, and IMC/MIBI being similar to immunohistochemistry, they all share a time of flight mass spectrometry (TOF MS) platform. These TOF MS platforms use metal conjugated antibodies as opposed to fluorophores, increasing the measurable parameters up to approximately 50 with a theoretic limit approximately 100 parameters. These tools are being adapted to understand highly complex systems in basic and clinical research.
Mass-tag–based antibody detection enables high-parameter analysis of cellular antigens by avoiding the spectral overlap that limits fluorescent-based antibody detection methods. Currently, this enables 40 to 60 parameter detection, but the theoretic limit is 100+ simultaneous measurement channels.
Mass cytometry is used for measurement of cells in solution, whereas imaging mass cytometry and multiplexed ion beam imaging create high-parameter images of tissue sections.
Each system can generate very high-dimensional data that are best analyzed with clustering or dimensionality reduction methods.
These systems are ideal for characterizing complex cellular mixtures, or for monitoring functional processes at high resolution.
Flow cytometry (FC) is a widely used tool in basic and clinical research with its ability to study malignancies, infectious diseases, and immune system function. Its utility is due to its ability, at a single-cell level, to detect any component recognized by an antibody. This utility, however, is constrained by the number of parameters that can be analyzed simultaneously. Most clinical flow cytometers can analyze between 4 and 15 parameters, this limitation is primarily due to fluorescent reporters and their spectral emission overlap. Recent advancements are overcoming this limitation such as multispectral flow cytometers that can recognize approximately 32 different parameters ; however, one of the most significant developments is mass cytometry (MC), and MC-based imaging.
In principle, MC is similar to FC, as both use antibody-based detection at a single-cell level and generate similar data. The difference is that MC uses metal-tagged antibodies instead of fluorescently labeled antibodies. The cells, with the bound antibody-metal conjugates, are detected through time of flight mass spectrometry (TOF MS). TOF MS is able to distinguish ions of different atomic weights with less than 0.5% spillover into adjacent channels, yielding a high resolution that allows for a large increase in measurable parameters of the MC system. It is now considered routine to have panels of approximately 50 antibodies and up to 60 total measured ions, and this number is continuing to increase, with recent of additions of metals such as nanoparticle-tantalum–based antibody conjugation. The theoretic upper limit of parameters is approximately 120 mass channels, which may be reached as the field continues to advance. Although MC has been a significant development, the application of metal-conjugated antibodies and TOF detection has continued to develop with imaging MC (IMC) and multiplexed ion beam imaging (MIBI). , IMC and MIBI both perform the same function of allowing very high-parameter detection of antibody binding to tissues, but the systems work in different ways. All 3 systems can enable very high-dimensional characterization of both surface antigens (to define cell identity), as well as intracellular antigens that can be used to characterize cellular functional properties.