What is cytokine release syndrome (CRS)?

Cytokine release syndrome (CRS) is characterized as a systemic inflammatory reaction that can be life-threatening. It occurs when the immune system is activated, typically in response to certain therapies, such as some forms of immunotherapy or CAR T-cell therapy. During this process, immune cells release cytokines, which are signaling proteins that help mediate and regulate immunity, inflammation, and the production of blood cells.

In CRS, the overproduction of these cytokines can lead to a cascade of inflammatory responses throughout the body, causing symptoms that range from fever and fatigue to more severe complications, such as hypotension, organ dysfunction, or even multi-organ failure. This condition highlights the importance of monitoring patients receiving treatments that can trigger CRS, as timely recognition and management are critical in preventing serious outcomes.

Other options reflect different concepts, such as mild side effects of chemotherapy, allergic reactions, and localized infections, but they do not accurately capture the systemic and potentially severe nature of CRS.