Tocilizumab is a humanized monoclonal antibody that blocks the action of interleukin-6 (IL-6) receptors. The IL-6 receptor has two forms: the membrane form mIL6R and the soluble form sIL-6R. Tocilizumab can bind specifically to sIL-6R and mIL-6R and inhibit the transduction signal. It is commonly used in rheumatoid arthritis as it is immunosuppressive.

Since the beginning of the COVID-19 pandemic, it has been shown that in patients severely affected by COVID-19 caused by the SARS-CoV-2 virus, there was a "cytokine storm" that would be a major cause of mortality as the inflammatory overreaction would destroy tissues.

IL-6 is thought to be one of the mediators of the inflammation that follows the immune response against SARS-CoV-2 in the pulmonary alveoli and thus one of the cytokines responsible for this "cytokine storm" phenomenon.  Tocilizumab may therefore be a good candidate for treatment of COVID-19.