Yes, Tecfidera does suppress the immune system. Although experts are not sure exactly how Tecfidera does this, Tecfidera has been associated with reductions in lymphocyte counts, and several serious opportunistic viral infections, such as progressive multifocal leukoencephalopathy and herpes zoster, as well as uncommon fungal and bacterial infections. Tecfidera belongs to the class of medicines called selective immunosuppressants.

Tecfidera (dimethyl fumarate) is an oral medication that may be used to treat relapsing forms of multiple sclerosis (MS) in adults, which includes clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease.

How does Tecfidera suppress the immune system?

Experts aren’t sure exactly how Tecfidera suppresses the immune system, and initial reports suggested it did not appear to increase overall infection rates nor vaccination responses.

However, since it was approved in 2013, it is apparent that it can be associated with several secondary immune-related complications. These include:

• Pronounced lymphocytopenia (decreased lymphocytes) of below 500/µl have been reported in 4–6% of patients that may persist for several weeks or months (mostly CD8 counts and to a lesser extent, CD4 counts)
• Progressive multifocal leukoencephalopathy (PML) an opportunistic viral infection of the brain caused by the JC virus (JCV) that usually only occurs in patients who are immunocompromised and is often fatal or leaves the person severely disabled. Symptoms include progressive weakness on one side of the body or clumsiness of limbs, disturbance of vision, and changes in thinking, memory, and orientation leading to confusion and personality changes
• Severe herpes zoster including disseminated herpes zoster, herpes zoster ophthalmicus, herpes zoster meningoencephalitis, and herpes zoster meningomyelitis
• Serious viral infections, such as those caused by herpes simplex virus, West Nile virus, or cytomegalovirus; serious fungal infections (Candida and Aspergillus), and serious bacterial infections, such as those caused by Nocardia, Listeria monocytogenes, or Mycobacterium tuberculosis)
• Eosinophilic gastroenteritis, a rare gastrointestinal disease that may be autoimmune in origin. Investigate any cases of protracted and severe GI symptoms.

How does Tecfidera work?

Experts are not sure exactly how Tecfidera (dimethyl fumarate) works but there is evidence that it activates a pathway that is involved in oxidative stress, called the Nrf2 (Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway. A metabolite of Tecfidera, monomethyl fumarate (MMF), acts as a nicotinic acid receptor agonist which can affect nerve firing.

Research has shown Tecfidera reduces inflammation and protects nerve cells from damage caused by the immune system attacking the myelin sheath.