IL6 and congenital rubella syndrome: Severe CRS (≥ grade 3) occurs in 15–30% of CAR‐T recipients, driven by excessive release of IL‐6 and IFN‐γ from activated T cells.[179] ICANS affects 5–12% of patients and is linked to disruption of the blood‐brain barrier by inflammatory cytokines.[180] 4) Complex manufacturing and high costs.