The most common side effect of CAR T-cell therapy is called cytokine release syndrome, or CRS. It’s also known as a “cytokine storm.” About 70-90% of patients experience it, but it generally only lasts about five to seven days. Most patients describe it as having a severe case of the flu, with high fever, fatigue and body aches. It usually starts around the second or third day after the infusion. It happens because the T cells have been multiplying and attacking the cancer, causing an immune response in the body. There’s a very effective remedy for CRS called tocilizumab, which reverses this side effect in most patients fairly quickly. The medicine was originally used to treat rheumatoid arthritis, but has since been approved by the U.S. Food and Drug Administration (FDA) to treat CRS.
The other side effect is known as “CRES,” which stands for “CAR T-cell-related encephalopathy syndrome.” It typically starts around day five after the infusion. Patients can become confused and disoriented, and sometimes may not be able to speak at all for a few days. CRES can be upsetting for patients and their families, but it typically is completely reversible.