Cytokine Release Syndrome

Cytokine release syndrome is a serious inflammatory response that happens when your immune system releases too many signaling proteins into your bloodstream, causing widespread inflammation that can damage organs and tissues throughout the body.

Table of contents

• What is Cytokine Release Syndrome?
• Signs and Symptoms
• Causes and Risk Factors
• Possible Complications
• How Doctors Diagnose This Condition
• Severity Grading
• Treatment Options
• Recovery and Outlook

CRS, infusion reaction, cytokine storm

What is Cytokine Release Syndrome?

Cytokine release syndrome (CRS) occurs when your immune system releases large amounts of cytokines (proteins that help control blood cells and immune cells) into your bloodstream^[1]. While cytokines are normally part of a healthy immune system, too many of them can cause serious problems.

The condition happens when large numbers of white blood cells are activated and release inflammatory cytokines, which then activate even more white blood cells in a cycle of increasing inflammation^[5]. This flood of cytokines may cause widespread inflammation throughout your body, leading to serious and sometimes life-threatening conditions, including organ failure^[1].

Cytokine release syndrome is most commonly seen as a side effect of certain types of immunotherapy (cancer treatment that uses your immune system), especially CAR-T cell therapy and bispecific antibodies^[6]. The syndrome can also result from infections or autoimmune diseases^[1].

Signs and Symptoms

Cytokine release syndrome symptoms can range from mild to severe. In mild cases, you may feel like you have the flu. The condition can affect different areas of your body, causing various symptoms^[1]:

• Chills and high fever
• Confusion and dizziness
• Diarrhea
• Difficulty swallowing
• Headaches
• Joint and muscle pain
• Nausea and vomiting
• Skin rash
• Tiredness

More severe symptoms can develop as the condition progresses. These include fast breathing, rapid heartbeat, low blood pressure, seizures, hallucinations, tremor, and loss of coordination^[5]. In serious cases, CRS can lead to low blood oxygen levels, shock, and heart or lung problems^[8].

Causes and Risk Factors

The syndrome happens when your immune system overreacts and releases large amounts of cytokines. Immunotherapy for cancer, particularly CAR-T cell therapy and bispecific antibodies, is the most common trigger^[1].

When you receive certain immunotherapies, immune cells become activated and release inflammatory cytokines. Important cytokines involved include IL-6, IFN-γ, IL-8, IL-10, and others^[5]. Many of these cytokines are not produced by the treatment cells themselves, but by other immune cells that become activated in response^[5].

After CAR-T cell therapy, the frequency of cytokine release syndrome varies between different products, with any grade occurring in 37-93% of patients and severe cases (grade 3-4) occurring in 1-23%^[8]. Symptoms may appear within 24 hours or up to two weeks after treatment^[1].

Certain factors may increase your risk of developing cytokine release syndrome. Having an autoimmune disease or certain genetic conditions that affect your immune system may make you more vulnerable^[1]. Hemophagocytic lymphohistiocytosis (HLH) is an example of a genetic condition that can lead to cytokine release syndrome. High tumor burden and higher doses of CAR-T cells also appear to be associated with a higher risk of CRS^[8].

Severe reactions occur more commonly during the first infusion in patients with blood cancers who have not received prior chemotherapy, and these severe reactions are marked by their rapid onset and the intensity of associated symptoms^[7].

Possible Complications

Cytokine release syndrome can cause severe inflammation in your kidneys, liver, or lungs. It may also damage your blood vessels or heart. Without prompt treatment, CRS may cause serious medical issues, some of which may be life-threatening^[1]:

• Capillary leak syndrome (a condition where fluid leaks from blood vessels into surrounding tissues)
• Cardiomyopathy (disease of the heart muscle) and heart failure
• Kidney failure
• Liver failure
• Lung failure and very low oxygen levels

The condition can rapidly progress to shock and failure of multiple organs, with symptoms including low blood oxygen, fast shallow breathing, rapid heartbeat, low blood pressure, and irregular heart rhythms^[8].

How Doctors Diagnose This Condition

Healthcare providers diagnose CRS in different ways depending on the cause. If you receive immunotherapy, your provider will watch for CRS symptoms closely. The diagnosis is based on the presence of compatible clinical symptoms, elevated biomarkers, and recent treatment with a biological agent^[17].

If you develop symptoms, your provider may do several tests, including^[1]:

• Complete blood count (CBC) to check your blood cells
• Cytokine levels to measure specific proteins in your blood
• C-reactive protein test and other tests to check inflammation levels
• Kidney and liver function tests

Although laboratory tests cannot definitively establish or rule out the diagnosis of CRS, they can be used to monitor organ function^[8]. CRS symptoms and laboratory findings closely mimic infection, so infectious workup and treatment are of primary importance^[8]. Differentiating CRS from infections and other inflammatory conditions can be challenging^[11].

Severity Grading

Cytokine release syndrome grades range from 1 to 4. The higher the number, the more serious the condition. Your healthcare provider will consider several factors to establish a grade for your condition^[1]:

• Whether you have a high fever, low blood pressure, or a fast heartbeat
• Whether they need to take steps to keep your vital signs stable
• Whether you need mechanical ventilation to help you breathe
• Whether you have organ failure symptoms, like weakness and fast, shallow breathing

Mild CRS (grade 1) can be managed conservatively with simple supportive care. All higher grades require intensive monitoring and intervention. Starting from grade 2, admission to an intensive care unit should be considered^[8].

Treatment Options

Your treatment will vary depending on the reason why you have CRS and how severe it is. The first sign of CRS is usually fever^[8]. Mild cases can be managed through symptomatic treatment and fluids^[17].

Treatment for severe CRS from immunotherapy may include^[1]:

• Corticosteroids (medications that reduce inflammation)
• Medication that targets specific cytokines, like siltuximab (Sylvant®), tocilizumab (Actemra®), and anakinra (Kineret®)
• Medication for very low blood pressure
• Mechanical ventilation to support breathing

Tocilizumab is approved by regulatory agencies for the treatment of CRS^[8]. Although corticosteroids are also effective, they suppress the activity of the immune cells used in treatment, so they should only be considered as second-line therapy or in cases of severe neurological involvement. This is because tocilizumab does not cross the blood-brain barrier^[17].

Supportive therapy consists of fluids and antipyretics (medications to reduce fever). The use of medications to support blood pressure automatically indicates higher-grade CRS^[8]. Patients receiving CAR-T cells should be monitored continuously or at regular intervals for cardiovascular function and temperature^[8].

Recovery and Outlook

Your recovery time depends on your situation. People with mild CRS symptoms after immunotherapy usually recover within one to two weeks. Your recovery may take longer if complications develop^[1].

Cytokine release syndrome generally has a good outlook when recognized and treated promptly^[17]. Effective CRS management requires early recognition, differentiation from infectious conditions that may look similar, and collaboration between cancer specialists and infectious disease specialists^[11].

A structured approach with close monitoring and prompt intervention is essential for optimizing outcomes for patients who develop this condition^[11].