{ "abstract": "Background Chimeric antigen receptor (CAR) T cell therapy has shown promise in relapsed/refractory multiple myeloma (r/rMM). Two BCMA-targeted CAR T cell therapies, cilta-cel and ide-cel, have received FDA approval and have demonstrated deep initial responses. However, their phenotypic characteristics and relationships with outcomes remain incompletely understood. We present a comparative single-cell analysis of CAR T cells from both products in a balanced patient cohort.Methods We established a prospective cohort: 23 patients received cilta-cel and 22 received ide-cel. The cohort was intentionally balanced for short- and long-term responders. Responders (R) were defined as patients achieving a best overall response (BOR) with partial response (PR) or better; non-responders (NR) had minimum response (MR) or worse. Infusion product (IP) bags and sorted CAR+ T cells from day 14 (D14) peripheral blood mononuclear cell (PBMC) samples were profiled using single-cell RNA sequencing (scRNA-seq) and paired T cell receptor sequencing (scTCR-seq). In cases where CAR+ T cells were rare, sorting gates were manually adjusted to ensure sufficient cell capture for sequencing. CAR transcript expression was quantified by reads aligning to the CAR binder region.Results After quality control, 74,901 total cells were analyzed, including 20,346 from IP (cilta-cel median 65/pt IQR [41,232]; ide-cel 463/pt [87,1610]) and 54,555 from D14 (cilta-cel 1031/pt [524-2428]; ide-cel 967/pt [416-1471]). Cell capture was lower in cilta-cel IP, accompanied by a reduced CAR+ T cell detection (cilta-cel 8.4±4.7% vs. ide-cel 66.0±13.4%, t-test P<0.0001; measured by CAR constructs expression in single-cell data). Despite this, both products showed comparable proliferation ability (%cycling T cells: cilta-cel 67.4±11.6% vs. ide-cel 72.3±12.8%, t-test P=0.18) in IP. However, CD4/CD8 ratios diverged: cilta-cel showed broader distributions at both timepoints, while ide-cel shifted from CD4-dominant (10±7) in IP to CD8-dominant (0.3±0.3) at D14.High-quality D14 data were obtained from 23 cilta-cel and 19 ide-cel samples. Among cilta-cel patients, lack of CAR T cell expansion at D14 was strongly associated with non-response (%CAR+ in cilta-cel NR: 8.0±12.1% vs. R: 71.1±22.6%; measured by flow cytometry). Ide-cel non-responders also had lower D14%CAR+ (14.5±12.3%), but responders were split into high- and low-expansion groups (62.6±18.8% vs. 6.1±4.6%; Mann-Whitney P=0.0016), without corresponding differences in progression-free survival (PFS 384±188 vs. 324±86 days; Mann-Whitney one-side P=0.304).Conclusions Cilta-cel and ide-cel exhibit distinct CAR T cell phenotypes and kinetics. Reduced D14 CAR+ T cell expansion correlates with early relapse in cilta-cel- but not in ide-cel-treated patients, suggesting divergent mechanisms of action and potential biomarkers for response stratification.Acknowledgements This study was partially funded by Kite, a Gilead Company. Additional support was provided by NIH R01CA252940 to Dr. Marcela V. Maus (Massachusetts General Hospital).Ethics Approval Clinical data and blood samples were obtained after written informed consent under an Institutional Review Board-approved protocol at the Dana-Farber/Harvard Cancer Center (DFHCC No. 16-206).", "authors": [ { "affiliations": [ "Broad Institute of MIT and Harvard, Cambridge, MA, USA" ], "name": "Xiaomeng Sun" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "Charlotte Graham" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "Aiyana Parker" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "Maria Dolaher" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "Kevin Lindell" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "Deshea L Harris" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "Won-Ho Lee" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "Kiana Graham" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "Hannah Nolan" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "Viktoria Blumenberg" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "David J Bozym" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "Diana Cirstea" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "Andrew Branagan" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA", "Harvard Medical School, Boston, MA, USA" ], "name": "Andrew Yee" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA", "Harvard Medical School, Boston, MA, USA" ], "name": "Noopur Raje" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA", "Harvard Medical School, Boston, MA, USA" ], "name": "Mark B Leick" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA", "Harvard Medical School, Boston, MA, USA" ], "name": "Matthew Frigault" }, { "affiliations": [ "Massachusetts General Hospital Cancer Center, Boston, MA, USA" ], "name": "Kathleen M Gallagher" }, { "affiliations": [ "Broad Institute of MIT and Harvard, Cambridge, MA, USA" ], "name": "Nicholas Haradhvala" }, { "affiliations": [ "Broad Institute of MIT and Harvard, Cambridge, MA, USA", "Harvard Medical School, Boston, MA, USA" ], "name": "Gad Getz" }, { "affiliations": [ "Harvard Medical School, Boston, MA, USA", "Massachusetts General Hospital, Charlestown, MA, USA" ], "name": "Marcela V Maus" } ], "title": "365 Single-cell transcriptional profiles of cilta-cel and ide-cel associate with response in multiple myeloma", "uid": "dbcd4780-1296-599f-af1a-776d8de5a8e2" }