A Double Edged Sword

Natalizumab is an injection for those with Multiple Sclerosis. It is a monoclonal antibody. An antibody is a protein produced by the body’s own immune response in response to antigens. They are your body’s personal warriors to fight off infections. With modern day science scientists are able to produce antibodies in a lab. Monoclonal antibodies are man made antibodies that bind to one antigen. They are synthesized from cloned immune cells. Hence “mono” meaning 1 antigen and “clonal” meaning cloned. These cloned immune cells often come from mice who first are injected with human genes that produce certain antibodies then the mice is vaccinated with the antigen that induces the immune cells of the mice to produce the desired antibody. The antibodies are then extracted to be used as medications.

MS impacts the central nervous system (CNS). It induces an immune mediated process that causes an abnormal response of the immune system directed at the CNS (brain, spinal cord and optic nerves). The immune system causes inflammation that damages myelin that surrounds nerve fibers which negatively impacts communication between the brain and the body.

Natalizumab impacts the acquired immune response. It decreases the number of CD4+ and CD8+ T lymphocytes, CD19+ B cells and CD138+ plasma cells in the CSF of patients natalizumab therapy. The drug is to suppress the immune response to prevent or limit the immune system from attacking the myelin sheaths of the nerves which communicate from the brain and body. It binds to the subunits on integrins expressed on the surface of leukocytes. This prevents select integrins from binding to their counter receptors. This limits the immune response within the body.

Side Effects

Increases your chance of getting Progressive Multifocal Leukoencephalopathy (PML) a rare brain infection that causes death or severe disability

Since Natalizumab is an immunosuppressant it weakens the immune response to limit the attack on self cells. However it leaves the body more susceptible to other infections as well. It is important to monitor symptoms during treatment because it can lead to UTI’s, herpes infections, increased infections of the brain and more due to the suppressed immune response. This leads patients to not be able to fight off infections they typically would with not problem. Natalizumab is not a cure for MS but a treatment to limit and or eliminate the effects of it.

PML is caused by the JC virus. Often this virus remains inactive until conditions in the body such as a weakened immune system allow it to be reactivated and begin to multiply. JC can be activated by natalizumab, an immunosuppressants that suppresses the immune system. However short term use of natalizumab has limited risk of developing PML. It is long term use past 8 months where there is risk of developing PML is substantially higher. PML is an opportunist infection therefore it caused by pathogens that would not cause illness in a healthy person. Therefore extended use of immunosuppressant drugs gives the JC virus more ability to activate and cause an even more severe infection. It is not the MS that makes a person more susceptible to PML but the drugs that fight the MS that lead to more infections and even more severe ones at that.

Medicines can be as harmful as they are helpful. Medicine is not perfect but when used properly and effectively it can be lifesaving. Decisions on treatment can be scary and intense especially when the side effects can be worse than the disease itself. This is why education and the right team of doctors is so important on making decisions best for you. With treatment there always will be pros and there will always be the cons, but in the end it is the patient’s choice if those pros outweigh the cons in the end.