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Rheumatoid arthritis (RA) is a chronic inflammatory condition where the immune system attacks the lining of joints. While there currently is no cure for RA, many classes of drugs have been developed to help manage symptoms and flares. Biologic drugs work to lower inflammation by interacting with immune cells or other inflammatory mediators to slow joint damage associated with RA.
Biologics are drugs made of proteins, sugars, or nucleic acids. Unlike other drugs that are chemically synthesized, biologics are derived from living organisms. Examples of biologics include vaccines, gene therapy, and monoclonal antibodies used to treat cancer and RA. Biologics that are disease-modifying antirheumatic drugs (DMARDs) can be used to treat rheumatic diseases, including RA.
All biologics are given as injections — either subcutaneous (under the skin) or intramuscular (into muscle) — or as IV infusions. Biologics cannot be taken by mouth because they would be broken down in the stomach and intestines before being absorbed into the bloodstream.
To understand how biologic DMARDs are used to treat RA, it is important to know a little more about the immune system, inflammation, and a class of biologics known as monoclonal antibodies.
Antibodies are an important component of the body’s immune system. They are usually made by specialized immune cells, known as B cells, when there is a bacterial or viral infection. The human body is capable of making almost 100 billion different types of B cells, and each type of B cell produces only one type of antibody. Each antibody is a protein that recognizes and interacts with a very specific target.
B cells can also be genetically altered in a lab to produce specific antibodies that will attach to a target protein. These are known as monoclonal antibodies because they are produced from one type of B cell.
Every antibody made by that B cell will have the same properties. Researchers have designed monoclonal antibodies to target specific proteins on the outside of immune cells, cancer cells, and more.
There are four main classes of biologics used to treat RA, including B-cell inhibitors, tumor necrosis factor alpha (TNF-alpha) inhibitors, selective costimulation modulators, and interleukin inhibitors. Each class of biologics interferes with different aspects of the immune system involved in inflammation and joint damage in RA.
B cells are an important part of an immune system response. These cells are responsible for making antibodies that are used to fight off infections and build immunity. In the case of autoimmune diseases, B cells make autoantibodies that attack the body’s own healthy tissues. This eventually leads to joint damage and inflammation.
In RA, autoantibodies attack the lining of joints, known as the synovium. B cells can also release tumor necrosis factor alpha, a cytokine (signaling protein) which is responsible for causing damage in RA.
B-cell inhibitors are biologics used to kill B cells in the blood, stopping them from making autoantibodies and TNF-alpha. This helps prevent the immune system from attacking the synovium in joints and lowers inflammation.
The U.S. Food and Drug Administration (FDA) has approved Rituxan (rituximab) to treat RA in cases when other treatments have not worked. Rituxan was originally approved for treating B-cell lymphoma, but it is also effective in treating RA.
Tumor necrosis factor alpha is an inflammatory cytokine responsible for causing inflammation and bone degradation in RA. TNF-alpha can be found in high levels in the joints of people with RA, where it binds to receptors on the outside of cells. Monoclonal antibodies have been developed to block TNF-alpha. These biologics work in a few different ways.
The first is by blocking TNF-alpha's access to its receptors on a cell. If TNF-alpha cannot bind to its receptors, then it cannot turn on an inflammatory response. Drugs that block receptors from other proteins are called antagonists. One example of a TNF-alpha antagonist is Humira (adalimumab).
The second way a biologic can inhibit TNF-alpha is by binding directly to the protein and neutralizing (destroying) it, so it cannot bind to its receptor. Examples of TNF-alpha-neutralizing antibodies include Remicade (infliximab), Simponi (golimumab), and Cimzia (certolizumab pegol).
The third and final way TNF-alpha inhibitors work is by mimicking the TNF receptor. Enbrel (etanercept) is a genetically engineered protein that is the same shape as the TNF receptor. When injected, Enbrel “soaks up” free TNF-alpha in the joints so it cannot bind to its receptors.
Selective costimulation modulators are biologics that work by blocking the function of a group of immune cells known as antigen-presenting cells (APCs). APCs activate other immune cells, like T cells, by binding to special receptors called costimulation receptors. Once turned on, the T cells will then increase inflammation. In the case of RA and other autoimmune diseases, APCs may activate autoreactive T cells, which attack the body’s own tissues.
Orencia (abatacept) is a biologic that works by binding to the costimulatory receptors on APCs. This blocks T cells and APCs from interacting with one another and shuts down any immune response between the two cells.
Interleukins (ILs) are a group of cytokines that help turn on and off various immune cells. They bind to receptors on the outside of cells to trigger inflammatory signaling pathways. Specifically, IL-1 and IL-6 contribute to inflammation in RA.
Interleukin inhibitors are biologics created to block these cytokines from creating more inflammation. Kineret (anakinra) is an IL-1 receptor antagonist that works by blocking IL-1 binding to cells. Actemra (tocilizumab) works similarly, blocking IL-6 binding to cells.
Biologic DMARDs have been shown to prevent and slow irreversible joint damage, similarly to other RA drugs like JAK inhibitors. In studies, biologics begin working quickly and often relieve symptoms of RA within a few weeks. TNF-alpha inhibitors may begin working as early as a few days after the first dose.
In clinical trials studying RA, drugs are rated using the ACR20, ACR50, ACR70 scale. This scale was developed by the American College of Rheumatology, and measures a 20 percent, 50 percent, or 70 percent improvement in RA symptoms. In multiple trials, biologic DMARDs worked better than other drugs, such as methotrexate alone. Participants who were treated with biologics saw more improvement in their ACR20, ACR50, ACR70 scores than those who did not receive biologics.
Unfortunately, there is currently no cure available for RA. The overall goal of treatment is to stop or reduce inflammation to the lowest levels possible in order to relieve symptoms and slow further joint damage.
If RA continues to progress, it can lead to permanent joint damage and disability. DMARDs, like biologics, can control active rheumatoid arthritis and reduce inflammation, helping you lead a healthier life.
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