The study analyzed tissue biopsies from multiple myeloma patients who had immune-related CAR-T cell-related adverse events (CirAEs) after treatment with commercial BCMA-targeted CAR-T cell therapy. A high ratio of CD4+ CAR-T cells to toxic CD4+ cells mediates these adverse events. These cells cause the robust earlier expansion of CAR-T cells to shut down. The development of CirAEs is independently associated with ICANS treatment and with ciltakabtagene autoleuce. The article was published in Nature Medicine on January 15, 2026.