How do CAR-T therapies like Kymriah and Yescarta differ, and why is cytokine release syndrome such a concern with them?

Both Kymriah (tisagenlecleucel) and Yescarta (axicabtagene ciloleucel) are groundbreaking CAR-T cell therapies, but they differ in their design, the specific conditions they treat, and their underlying biology.

Key Differences

• Targeting and Signaling: Both therapies work by genetically modifying a patient’s T cells to recognize the CD19 protein found on B-cell cancers. However, they use different "costimulatory domains" to signal the T cell to activate.
  • Kymriah uses a 4-1BB costimulatory domain. This generally leads to slower, more sustained T-cell proliferation and persistence in the body.
  • Yescarta uses a CD28 costimulatory domain. This typically results in a more rapid, aggressive expansion of T cells, which can be highly effective but also contributes to a different safety profile.
• Approved Uses: While both are used for various B-cell lymphomas and leukemias, they have distinct regulatory approvals. For example, Kymriah was the first CAR-T therapy approved (initially for pediatric ALL), whereas Yescarta is often utilized in aggressive non-Hodgkin lymphomas like diffuse large B-cell lymphoma (DLBCL).

Why Cytokine Release Syndrome (CRS) is a Concern

Cytokine Release Syndrome (CRS) is the most common and potentially severe systemic side effect of CAR-T therapy. It is essentially a "storm" of inflammatory proteins.

1. Mechanism of Action: When CAR-T cells are infused into the patient, they encounter cancer cells expressing CD19. The T cells activate, multiply rapidly, and release large amounts of cytokines (such as Interleukin-6, or IL-6).
2. The "Storm": In a healthy immune response, these cytokines help coordinate an attack on a pathogen. With CAR-T, the sheer volume of cytokines released during the massive destruction of tumor cells triggers a systemic inflammatory response.
3. Clinical Impact: Because CRS acts systemically, it can affect the entire body. It often starts with flu-like symptoms (fever, fatigue, muscle aches) but can quickly escalate to dangerous levels, including dangerously low blood pressure (hypotension), high fever, capillary leak, and organ dysfunction (such as respiratory or kidney failure).

Because these therapies are so potent, they are administered in specialized centers where medical teams are trained to monitor for these symptoms. If CRS occurs, physicians can intervene with therapies like tocilizumab (an IL-6 receptor antagonist) to calm the inflammatory response without necessarily destroying the therapeutic CAR-T cells.

Because the mechanisms of Kymriah (4-1BB) and Yescarta (CD28) differ, the onset and severity of CRS can vary between them—Yescarta’s rapid T-cell expansion is often associated with a faster onset of high-grade CRS compared to Kymriah.