Absolute Lymphocyte Count and Outcomes of Multiple Myeloma Patients Treated with Idecabtagene Vicleucel: The U.S. Myeloma Immunotherapy Consortium Real World Experience

Background Idecabtagene vicleucel (ide-cel) has shown impressive efficacy in relapsed-refractory multiple myeloma (RRMM). The aim of this study was to investigate the impact of absolute lymphocyte count (ALC) on the survival outcomes of RRMM patients treated with standard of care (SOC) ide-cel. Methods Data were retrospectively collected from 11 institutions in the U.S. Impact of ALC parameters including pre-apheresis (pre-A), pre-lymphodepletion (pre-LD), absolute and percent difference from pre-A to pre-LD on clinical outcomes after ide-cel were examined using survival analysis. A new ALC profile was created based on univariate analysis and included three groups: Normal (≥1 × 109/L) pre-LD ALC (LDN), low (<1 × 109/L) pre-LD ALC (LDL) + percent reduction <37.5 (%RL), and LDL ALC + percent reduction ≥37.5 (%RH). Results 214 SOC ide-cel recipients were included in this analysis, median age (IQR) was 64 (57-69) years, median number of prior therapies was 6 (5-9), and median (IQR) follow up time was 5.4 (2.1-8.3) months. Most patients had both low pre-A (75.3%) and pre-LD (77.2%) ALC, and the reduction from pre-A to pre-LD (median 0.65 to 0.55 × 109/L) was statistically significant. Univariate analysis showed that the LDL + %RH group had significantly worse progression-free survival (PFS) and overall survival (OS) compared to the LDL + %RL and LDN ALC groups (6-month PFS: 40% vs 67.6% and 60.9%; 6-month OS: 69.5% vs 87% and 94.3%). In multivariable analysis, after adjusting for age, performance status, cytogenetic risk, use of bridging therapy, and extramedullary disease, PFS did not maintain its statistical significance. However, OS remained significantly worse for LDL + %RH group compared to the LDN ALC group (HR, 95% CI: 4.3, 1.1-17), but the difference between the LDL + %RH vs %RL groups was not statistically significant (HR, 95% CI: 1.7, 0.8-4.0). Conclusion Our findings indicate that low pre-LD ALC with high percent reduction from pre-A to pre-LD was associated with inferior survival outcomes, particularly OS, in patients who received SOC ide-cel.