{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,11,12]],"date-time":"2026-11-12T09:14:19Z","timestamp":1794474859917,"version":"4.9.1"},"reference-count":22,"publisher":"American Society of Hematology","issue":"16","content-domain":{"domain":["ashpublications.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2026,10,15]]},"abstract":"<jats:sec>\n                    <jats:title>Abstract<\/jats:title>\n                    <jats:p>The impact of chimeric antigen receptor (CAR) T-cell expansion and persistence on clinical outcomes and treatment-related morbidity in patients with relapsed\/refractory (R\/R) multiple myeloma (MM) remains undefined, partly due to limited availability of standardized CAR T-cell quantification assays. We evaluated CAR T-cell kinetics and their association with efficacy and toxicity in patients with R\/R MM treated with idecabtagene vicleucel (ide-cel) or ciltacabtagene autoleucel (cilta-cel). Using a uniform flow cytometry\u2013based platform (N = 90; cilta-cel, n = 54; ide-cel, n = 36), we observed greater CAR T-cell expansion with cilta-cel than with ide-cel (median, 106 vs 49 cells per \u03bcL). Peak CAR T-cell expansion was associated with clinical response in the ide-cel cohort but not in the cilta-cel cohort, in which rapid and excessive expansion was associated with an increased risk of delayed neurotoxicities (DNTs), a complication with potential long-term functional consequences (median peak, 1009 vs 96 cells per \u03bcL). To identify clinically accessible biomarkers of CAR T-cell expansion, we analyzed absolute lymphocyte count (ALC) as a surrogate biomarker in a multicenter cohort (N = 532; cilta-cel, n = 256; ide-cel, n = 276). Higher peak ALC was significantly associated with the development of DNTs, particularly parkinsonism after cilta-cel. A peak ALC \u22653 \u00d7 10\u00b3\/\u03bcL, or \u22652.5 \u00d7 10\u00b3\/\u03bcL following an increase of twofold or more, predicted elevated DNT risk (sensitivity, 81%; specificity, 59%). Together, these findings delineate distinct expansion-toxicity relationships in cilta-cel and ide-cel therapy, establish ALC as a practical, uniformly available surrogate for CAR T-cell expansion, and define quantitative thresholds that may enable early recognition of patients at risk of DNT, informing preemptive strategies to mitigate morbidity after cilta-cel.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1182\/blood.2025032844","type":"journal-article","created":{"date-parts":[[2026,7,8]],"date-time":"2026-07-08T18:59:09Z","timestamp":1783537149000},"page":"1961-1972","update-policy":"https:\/\/doi.org\/10.1182\/blood.2019cm0000","source":"Crossref","is-referenced-by-count":3,"title":["Rapid peak cilta-cel expansion is associated with delayed neurotoxicity in multiple myeloma"],"prefix":"10.1182","volume":"148","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0475-9666","authenticated-orcid":false,"given":"Hitomi","family":"Hosoya","sequence":"first","affiliation":[{"name":"1Division of Blood and Marrow Transplant and Cell Therapy, Stanford University, Stanford, CA"},{"name":"2Division of Hematology and Cell Therapy, Cedars-Sinai Medical Center, Los Angeles, CA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Arash","family":"Velayati","sequence":"additional","affiliation":[{"name":"1Division of Blood and Marrow Transplant and Cell Therapy, Stanford University, Stanford, CA"},{"name":"3Division of Malignant Hematology, Cell Therapy and Transplantation, University of California Davis, Sacramento, CA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3587-7975","authenticated-orcid":false,"given":"Danai","family":"Dima","sequence":"additional","affiliation":[{"name":"4Clinical Research 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