What Is Cytokine Release Syndrome?


Cytokine release syndrome refers to a condition that may occur after treatment with some types of immunotherapy, such as monoclonal antibodies and CAR-T cells. Cytokine release syndrome is caused by a large, rapid release of cytokines into the blood from immune cells affected by the immunotherapy.

Cytokines are immune substances that have many different actions in the body. Signs and symptoms of cytokine release syndrome include fever, nausea, headache, rash, rapid heartbeat, low blood pressure, and trouble breathing.

Most patients have a mild reaction, but sometimes, the reaction may be severe or life threatening. Severe cases have been called “cytokine storms”.

The term “cytokine storm” appears to have been first used in 1993 in a discussion of graft vs. host disease; CRS as an adverse effect has been known since the approval of the first monoclonal antibody drug, muromonab-CD3, which causes CRS, but people working in the field of drug development at biotech and pharmaceutical companies, regulatory agencies, and academia began to more intensely discuss methods to classify it and how to mitigate its risk following the disastrous 2006 Phase I clinical trial of TGN 1412, in which the six subjects experienced severe CRS. CRS is sometimes referred to as an infusion-related reaction (IRR) or infusion reaction.

Cause Of Cytokine Release Syndrome

CRS occurs when large numbers of white blood cells, including B cells, T cells, and natural killer cells, macrophages, dendritic cells, and monocytes are activated and release inflammatory cytokines, which in turn activate yet more white blood cells.

This can occur when the immune system is fighting pathogens, as cytokines signal immune cells such as T-cells and macrophages to travel to the site of infection. In addition, cytokines activate those cells, stimulating them to produce more cytokines.

CRS has also arisen with biotherapeutics intended to suppress or activate the immune system through receptors on white blood cells. Muromonab-CD3, an anti-CD3 monoclonal antibody, was intended to suppress the immune system to prevent rejection of organ transplants, alemtuzumab against CD52 and used to treat blood cancers as well as multiple sclerosis in organ transplants, rituximab against CD20 also used to treat blood cancers and auto-immune disorders, all cause CRS. Adoptive T-cell therapies with T-cells modified with chimeric antigen receptors (CAR-T) also causes CRS.

It appears that interleukin 6 is a key mediator of CRS.

Severe CRS or cytokine storms can occur in a number of infectious and non-infectious diseases including graft-versus-host disease (GVHD), acute respiratory distress syndrome (ARDS), sepsis, Ebola, avian influenza, smallpox, and systemic inflammatory response syndrome (SIRS).

Cytokine storm may also be induced by certain medications, such as the CD20 antibody rituximab and the CD19 CAR T cell tisagenlecleucel. The experimental drug TGN1412 caused extremely serious symptoms when given to six participants in a Phase I trial.


Treatment for less severe CRS is supportive, addressing the symptoms like fever, muscle pain, or fatigue. Moderate CRS requires oxygen therapy and giving fluids and antihypotensive agents to raise blood pressure.

For moderate to severe CRS, the use of immunosuppressive agents like corticosteroids may be necessary, but judgement must be used to avoid negating the effect of drugs intended to activate the immune system.

Tocilizumab, an anti-IL6 monoclonal antibody, has been used in some medical centers to treat severe CRS.

Although frequently used to treat severe CRS in people with ARDS, corticosteroids and NSAIDs have been evaluated in clinical trials and have shown no effect on lung mechanics, gas exchange, or beneficial outcome in early established ARDS.

Daniel W. Lee, et al
Current concepts in the diagnosis and management of cytokine release syndrome
Blood. 2014 Jul 10; 124(2): 188–195.