On Thursday, Nov. 19, Mayo Clinic began offering an experimental therapy to patients who test positive for COVID-19 and are at high risk for serious illness. The therapy uses a type of drug called a monoclonal antibody. But what are monoclonal antibodies? To understand this type of drug, Richard Kennedy, Ph.D., an immunologist and co-director of Mayo Clinic's Vaccine Group, explains how antibodies are used in the body's natural immune response.

Natural Antibody Response

The body naturally produces immune proteins, called antibodies, that fight infection. Antibodies are made by B cells, with each B cell making millions of copies of a single antibody. When needed, each B cell will divide into two daughter B cells that are essentially clones of the parent. These clones produce the same antibody. Each antibody is keyed to a particular target, or bad actor, in the body, such as a cancer cell or a virus particle. During an infection, the body has many B cells producing a collection of antibodies that recognize different targets on the same cancer cell or virus particle. This response is called polyclonal ― "poly" because you have many different antibodies and "clonal" because each type of antibody comes from a set of cloned B cells.

Antibodies as a Treatment

Antibodies also can be manufactured if researchers know the structure of what the antibody will target. Once the target is clarified, a single antibody can be copied over and over to develop an effective dose to treat diseases. These drugs are called monoclonal antibodies, meaning one (mono) antibody. They are currently used for cancer treatment, autoimmune disorders, and viral infections.

Mayo Clinic began offering a monoclonal antibody therapy at some locations to minimize the effects of COVID-19 in a limited number of patients who have tested positive for the disease and are at risk for severe illness. This monoclonal antibody therapy, bamlanivimab, is designed to attach to the spike protein on the SARS-CoV-2 virus, the virus that causes COVID-19. It is administered in an IV.

The virus that causes COVID-19 is called SARS-CoV-2. It is in a family called coronavirus, so named for the way their spike (S) protein appears, under the microscope. That spike protein, along with other proteins (M and E) are embedded in a protective, fatty coating called a lipid envelope. It keeps the viral RNA, which is in turn protected in a nucleocapsid, protected until the RNA can be injected into a host cell.

The Food and Drug Administration issued an emergency use authorization to use bamlanivimab to treat confirmed COVID-19 in adults, and children over age 12, who have mild or moderate symptoms but have a high risk of progression to severe disease and hospitalization. Clinicians will weigh these factors, along with the known and potential risks and benefits on a patient-by-patient basis.

For updates on clinical use of bamlanivimab, stay tuned to the Mayo Clinic News Network.

— Sara Tiner, Nov. 19, 2020