What is cell sorting?Cell sorting is a process of cell identification and selection, and subsequent separation of the different cell species. Cells can be sorted by different characteristics such as morphology but also based on markers. For many cell sorting methods, fluorescently labeled antibodies, which only bind to specific cell types or cells in certain stages of cellular development, are being applied to identify the cells of interest and thus to distinguish target cells from unwanted cells.
What is cell sorting used for?Cell sorting is widely used to obtain a homogenous cell population from mixed cell samples. Bone marrow extracts, for example, contain various different immune cells at various stages of development and differentiation, however, for most research projects, only a certain type of immune cells is relevant. B-cells, for example, can be identified via CD19/CD20 markers and then be separated from other immune cells in the bone marrow extract.
In oncology and cancer research, it has been shown that tumors not only contain tumor cells, but also immune cells are invading the tumor tissue. Moreover, the tumor cells also vary amongst each other regarding their genomic information due to acquired cancer mutations and thus contribute to tumor heterogeneity. Molecular pathologists are therefore interested in cell sorting technologies for liquid biopsies to be able to make a better informed diagnosis.
In addition to human and animal organs, also plants consist of specialized cell types which play different roles in development and disease. Crop science specifically is interested in understanding cellular processes to grow crops that are better adapted to the changing climate and to become resistant against predators and pathogens.
For many studies, a homogeneous cell population or even single cells are an essential pre-requisite to obtain meaningful results from the experiments. Therefore, cell sorting is one of the most important steps in sample preparation.
What are the primary methods of cell sorting?One of the most commonly used methods in cell sorting is FACS (fluorescence activated cell sorting). This method relies on cell suspensions which contain a decent number of fluorescent target cells. Thus, target cells need to be specifically labeled with a fluorescent dye via antibodies or they need to express fluorescent proteins to be detected by the FACS cell sorter. A similar method to FACS is Magnetic Activated Cell Sorting (MACS), where antibody-coated magnetic beads specifically bind to the target cells to be able to separate them with a strong magnet from non-labeled cells.
In addition to FACS and MACS cell sorters, there are several other cell sorting methods based on microfluidics or on filter technologies. These methods are ideal for cellular enrichment of one certain cell type or of a specific cell population. They also require a relatively high number of cells and suspension volume.
In contrast, cell picking and micromanipulation systems, which are typically installed on microscopes, are highly selective and can work with small amounts of sample. Intriguingly, these systems are able to isolate even rare and single cells. Initially, these devices for microscope cell sorting heavily relied on the manual handling capabilities of the individual users. Today, fully automated cell picking instruments are available that allow for selective cell picking and medium-throughput cell sorting.