Dexamethasone prophylaxis for excessive lymphocyte expansion after cilta-cel in multiple myeloma

Increased absolute lymphocyte count (ALC) may predict risk of treatment-related mortality and atypical neurologic events among patients receiving chimeric antigen receptor (CAR) T-cell therapies for relapsed/refractory multiple myeloma. In this study, we analyzed the clinical outcomes of patients receiving ciltacabtagene autoleucel (cilta-cel) at the Colorado Blood Cancer Institute, from September 2023 to January 2025. Baseline data were collected pre/post-CAR T-cell therapy. Patients were stratified into preintervention (treated September 2023 to July 2024) and intervention (treated August 2024 to January 2025; those with ALC >5 × 103/μL received 3 days of dexamethasone prophylaxis on first identification of elevated ALC). In the preintervention group, 9 of 30 patients had peak ALC >5 × 103/μL; 5 of 9 (55.6%) experienced atypical neurologic events and all 5 died (cilta-cel therapy-related complications). In the intervention group, 7 of 23 patients had peak ALC >5 × 103/μL and received dexamethasone; 1 of 7 had an atypical neurologic event; and 1 death occured (infectious complication, 9 months posttreatment). Dexamethasone prophylaxis in patients with ALC of >5 × 103/μL resulted in rapid ALC reduction. Overall survival (OS) was significantly lower in preintervention patients with ALC of >5 × 103/μL vs intervention patients with ALC of >5 × 103/μL and patients with ALC of ≤5 × 103/μL (P = .0013). ALC >5 × 103/μL (vs ALC ≤ 5 × 103/μL) was significantly associated with atypical neurologic events (odds ratio, 6.8; P = .0157) and lower OS (hazard ratio, 6.2; P = .0106). In conclusion, ALC >5 × 103/μL after cilta-cel treatment predicted severe early neurologic events and high mortality risk. Dexamethasone prophylaxis demonstrated promise for risk mitigation.