Ciltacabtagene autoleucel in high-risk smoldering multiple myeloma: the CAR-PRISM phase 2 trial

High-risk smoldering multiple myeloma (HR-SMM) carries an increased risk of progression to multiple myeloma, making it an ideal setting to test whether chimeric antigen receptor (CAR) T cell therapy can achieve curative outcomes. Here in this phase 2 study, patients with HR-SMM received ciltacabtagene autoleucel (cilta-cel) at 0.3-0.5 × 10⁶ or >0.5 × 10⁶ viable CAR⁺ T cells per kilogram without induction or bridging therapy. Patients with >40% marrow involvement were excluded. Primary endpoints were dose-limiting toxicities (DLTs) and treatment-emergent adverse events; secondary endpoints included response and minimal residual disease (MRD) negativity. As of 11 February 2026, 20 patients had been treated. The trial met the prespecified endpoints. No DLTs occurred. Adverse events included transient cytopenias (90% grade 3/4) and cytokine release syndrome (100% grade 1/2). Non-immune effector cell-associated neurotoxicity syndrome neurologic toxicities (NINTs) occurred in seven patients, with four comprising cranial nerve palsies that completely resolved. Three patients had persistent grade 1 symptoms. At a median follow-up of 15.3 months, all patients achieved MRD negativity 10^-6 by 2 months and have remained MRD negative. Sixteen patients with follow-up >6 months achieved a complete response; no progression or deaths were observed. Cilta-cel produced rapid, deep, sustained MRD-negative responses in HR-SMM without induction therapy. Toxicities were consistent with the safety profile of cilta-cel. ClinicalTrials.gov: NCT05767359 .