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Chimeric antigen receptor (CAR) T cell therapy has shown unprecedented response rates in patients with relapsed/refractory (R/R) multiple myeloma (MM). However, the factors associated with immediate response and durable remission have not been fully elucidated. This study aimed to investigate the impact of prelymphodepletion (pre-LD) absolute lymphocyte count (ALC) on the outcomes of CAR T cell therapy and cytokine release syndrome (CRS). A receiver operating characteristic curve was used to determine the optimal cutoff value of pre-LD ALC. The correlation of pre-LD ALC with deep response (defined as very good partial response or better), CRS, and long-term outcomes was analyzed in 85 patients with R/R MM who received CAR T cell treatment. The median pre-LD ALC was 1.0 × 10 9 /L (range, 0.1 to 2.9× 10 9 /L). The optimal cutoff value of pre-LD ALC was 0.75 × 10 9 /L. Twenty-two patients (26%) had a low pre-LD ALC (<0.75 × 10 9 /L), and 63 patients (74%) had a high pre-LD ALC (≥0.75 × 10 9 /L). The deep response rate was significantly higher in patients with a high pre-LD ALC compared with patients with a low pre-LD ALC (76% versus 41%; P = .002). Patients with a low pre-LD ALC had significantly inferior overall survival (OS) and progression-free survival (PFS) compared with those with a high pre-LD ALC (median OS, 15.4 months versus not reached [P < .001]; median PFS, 8.4 months versus 27.3 months [P < .001]). No correlation between pre-LD ALC and CRS was observed. Our data indicate that pre-LD ALC may be a useful indicator to predict the outcomes of CAR T cell therapy in patients with R/R MM. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc., Competing Interests: Declaration of Competing Interest There are no conflicts of interest to report., (Copyright © 2021. Published by Elsevier Inc.)