Background
Antigens are large molecules such as chemicals, toxins, and drugs that are found on the surface of cells, bacteria, fungi, viruses, and non-living substances. The immune system detects antigens and releases antibodies that recognize and initiate the destruction of foreign substances that contain antigens. Antigens can be produced by a variety of bacteria, viruses, and cells.
Human antibodies consist of 5 isotypes (IgM, IgD, IgG, IgA, and IgE) based on their heavy (H) chains, which give each isotype distinct characteristics and roles. IgG is the most prevalent antibody in the blood, making up around 70% of human antibodies. It helps detoxify substances and recognize antigens. IgM and IgA are also fairly abundant, each making up 10% of immunoglobins in the body.
Antibody production is triggered by the detection of antigens. For example, the recognition of pollen or molecules from food can result in an allergic response by the body. Upon entering a cell, an antigen is coupled to a histocompatibility complex and presented on the surface of the cell to be recognized by antibodies. Each antibody matches an antigen like a key to a lock. The fit of the antibody can be precise, while other times it can be more general. The role of antibodies is to target an antigen and mark it for termination.
Antibodies reside various bodily fluids and are gamma globulin proteins. The body uses antibodies to identify and neutralize foreign objects in the body, such as viruses or bacteria. This mechanism is like a built-in antibiotic for the immune system. Antibodies are classified as a family of large molecules known as immunoglobulins. Globulins consist of polypeptide chains or amino acids. Each antibody is constructed of 2 light chains and 2 heavy polypeptide chains that form the arms of a “Y” shape. These arms are antigen specific and vary from one antibody to another.
Other types of antibodies include:
Autoantibodies – rather than fighting foreign antigens, autoantibodies attack the body’s own cells
Antinuclear antibodies – a group of autoantibodies that attack structures inside the nucleus of the cell.
Therapeutic Antibodies
Antibodies can be used in humans for therapeutic purposes – introducing specific antibodies can help fight viral infections, cancers, and a variety of other problematic conditions. Despite their promising nature, antibody therapies have been progressing rather slowly, even with recent advances in approved medicines. One of the most promising applications has been the development of monoclonal antibodies, which present a highly specific use of antibodies that can be used to target specific cancer cells. Limitations of antibody therapy include antibody size, problems with efficiency, and in vivo penetration for the treatment of specific cancers.
Therapeutic antibodies can be categorized into two general groups: the direct use of a naked antibody or the modification of an antibody for therapeutic enhancement. The alteration of antibodies is used in chimeric antigen receptor T cell (CAR-T) therapy, where a gene for a chimeric T cell receptor-antibody that targets a specific cancer marker is inserted into T cells. This leads to the cells becoming engineered to target and kill cancer cells. This approach has gained major traction in recent years and patients have even gained remission from their cancer through CAR-T.
Monoclonal antibodies are created by combining single antibody-forming cells with tumor cells that are grown in culture. The new cell is called a hybridoma cell and each one of the new cells produces a large quantity of identical antibody molecules. Growing these cells in culture makes it possible to produce large quantities of identical antibody molecules. This can be used to target highly specific foreign particles should they enter an organism. There are several potential issues though, for example, the antibodies may be targeted by an organism’s immune system. This specific problem can be resolved by changing the origin of the hybridoma to be that of a recipient organism.
Currently, there are several antibody therapeutics in the market. Some are now undergoing clinical testing, while others have been approved as standard of care therapies. These include monoclonal antibodies such as ipilimumab, pembrolizumab, and nivolumab.