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Abstract Introduction: Cilta-cel is a BCMA-directed CAR T-cell therapy that has shown remarkable efficacy in patients with RRMM. As real-world (RW) experience with cilta-cel continues to expand, and with the recent FDA guidance reducing the recommended proximity to the CAR T center from four to two weeks post-infusion, there is growing interest in identifying patients at low risk for severe early complications who may be safely managed in the outpatient setting and potentially ‘discharged’ home earlier. Methods Data were collected from 769 patients with RRMM treated with cilta-cel at 15 institutions in the U.S. via the Multiple Myeloma Immunotherapy Consortium.Logistic regression was used to identify predictors of patients who could be managed in the outpatient setting (low-risk group). Based on expert consensus within the Consortium, low-risk patients were defined as: grade ≤1 CRS, no ICANS, and no IEC-HS. The remaining patients were categorized as high-risk. We evaluated baseline characteristics with missingness < 20% as predictors, including age, sex, race, and ethnicity, ECOG performance status (PS) at time of lymphodepletion (LD), extramedullary disease, bone marrow plasma cell (BMPC) percentage, high-risk cytogenetics, bridging therapy including response, penta-refractory status, number of prior lines of therapy, prior anti-BCMA therapy, baseline C-reactive protein (CRP), and baseline ferritin. The cohort was restricted to patients with complete data on all predictors (n=455) and split into a training and testing cohort (80/20 split, n=364/91). Bidirectional stepwise regression was used to build the predictive model using variables with significance of p<0.15 selected for entry. The best model was selected based on the AIC (Akaike Information Criterion) and a significance level of p<0.05. Results Among the 455 patients with complete data included in the final model, 290 (64%) were categorized as low-risk and 165 (36%) as high-risk. Compared to the low-risk group, high-risk patients were more likely to have an ECOG PS ≥2 at time of LD (20% vs 9%, p<0.001), high-risk cytogenetics (47% vs 35%, p=0.009), and penta-refractory disease status (34% vs 24%, p=0.031). High-risk patients also had a higher median BMPC percentage (15% vs 5%, p<0.001), and higher baseline pre-LD CRP and ferritin. Overall response rates were high, at 95% vs 90% (p=0.047) for the low vs high risk groups, with complete response or better achieved in 73% vs 66% of patients, respectively (p=0.14). With a median follow-up of approximately 11 months, median progression-free survival was not reached (95% CI: 27-NA) in the low-risk group and 18.2 months (95% CI: 13.1-NA) in the high-risk group. In terms of safety, non-ICANS neurotoxicity (NINT) occurred less frequently in the low-risk group (6.6% vs 13%, p=0.015). Specifically, Parkinsonism was observed in 1.7% vs 6.1% (p=0.013), and cranial nerve palsy in 4.5% vs 5.5% (p=0.7), respectively. Non-relapse mortality (NRM) was lower in the low-risk group (4.2%) compared to the high-risk group (14%; p < 0.001). The most common causes of NRM in the low- and high-risk groups were acute toxicities (0% vs 36%, including CRS, IEC-HS, and ICANS), delayed toxicities (0% vs 8%, including colitis, NINT, and Parkinsonism), infections (50% vs 48%), and other unrelated causes (50% vs 8%). The best model to predict low-risk patients that could be managed in the outpatient settingincluded BMPC percentage and ECOG PS at LD. In the training cohort, patients with a higher pre-LD BMPC percentage and an ECOG PS ³2 were less likely to be in the low-risk group(OR per 1-unit change in BMPC percentage = 0.99, 95% CI=0.98-0.99, p<0.001 and OR for ECOG PS 2-4 = 0.38, 95% CI=0.20-0.72, p=0.003). The AUC for this model was 0.663 in the training cohort and 0.659 in the testing cohort. Conclusion In this large, multi-institutional cohort of patients with RRMM treated with cilta-cel, we identified clinical factors associated with lower risk for early severe toxicities, supporting outpatient administration and the potential for earlier discharge in selected patients, particularly those who are fit and have low disease burden. Our findings provide a practical framework to guide risk stratification and outpatient CAR T management strategies, particularly in light of evolving regulatory guidance and growing RW experience with cilta-cel.

Abstract Introduction: Ciltacabtagene autoleucel (cilta-cel) is a highly effective BCMA-redirected CAR T-cell therapy for RRMM. While the pivotal CARTITUDE-1 trial established a target dose of 0.75 x 10^6 CAR+ viable T-cells/kg, the approved cell dose is 0.5-1.0 x 10^6 and the optimal dosing strategy to balance efficacy and toxicity remains unclear. This question is of interest given that a dose-response association has been demonstrated for idecabtagene vicleucel (a related BCMA-directed CAR T product). It has also been hypothesized that lower doses of cilta-cel may be associated with reduced toxicity. This study aims to evaluate the association between cilta-cel dose and key efficacy and toxicity outcomes using a large, real-world dataset from the US Multiple Myeloma Immunotherapy Consortium. Methods: We conducted a multicenter, retrospective analysis of 751 RRMM patients treated with commercial cilta-cel across 15 US academic centers. The administered cilta-cel dose (million cells/kg) was categorized into four groups: low (<0.5), standard-low (0.5 to <0.6), standard (0.6 to <0.8), and standard-high (0.8 to 1.0). We compared incidence rates of cytokine release syndrome (CRS), immune effector cell-associated neurotoxicity syndrome (ICANS), delayed neurotoxicity (DNT), and immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome (IEC-HS) across these dose categories using logistic regression. Best response rates and progression-free survival (PFS), estimated using the Kaplan-Meier method, were also compared, with differences assessed using the log-rank test for the latter. Results presented are derived from multivariable models adjusting for extramedullary disease, ECOG status, penta-refractory disease and receipt of bridging therapy. Results: Among 751 infused patients, the dose distribution was: <0.5 (n=33), 0.5 to <0.6 (n=131), 0.6 to <0.8 (n=550), and 0.8 to 1.0 (n=37). The four dose groups were well-balanced in terms of baseline patient and disease characteristics, including age, high-risk cytogenetics, and extramedullary disease, with the exception of t(14;16), which was more common in the standard-low and standard dose groups (p=0.006). There were no statistically significant differences in the rates of any grade CRS (p=0.11), any grade ICANS (p=0.84), grade ≥3 ICANS (p=0.36), duration of CRS (p=0.18) or ICANS (p=0.64), or IEC-HS (p=0.16) across the four dose categories. Time to onset of CRS was shorter for the standard-high dose compared to the low dose (6 days vs. 8 days; p=0.08). Importantly, there was no significant difference in the rate of DNT (3.0%, 9.2%, 8.8%, 5.4%; p=0.24). Similarly, there was no significant difference in overall response rates (97%, 96%, 96%, 88%; p=0.50) or complete response rates (75%, 65%, 75%, 66%; p=0.10) by dose. The median follow-up was 12.3 months (IQR: 6.9, 20.5). For patients who received a standard-low dose (0.5, 0.6), the median PFS was 17.5 (IQR: 13.5, NR) months. For the standard dose range of (0.6, 0.8), the median PFS was 28.7 (95% CI: 19.8, NR) months, while the median PFS for the standard-high dose (0.8, 1.0) was not reached. For the low dose range of <0.5, the median follow up was only 8.7 months, which did not allow reliable estimation of the median PFS. While the overall difference in PFS among the groups did not reach statistical significance by the log rank test, there was a clear trend toward improved PFS with higher cell doses in the multivariable model, with outcomes clearly ordered in the same direction as the cell dose categories. A similar trend was also evident in the rates of 12-month PFS which showed an improvement with increasing dose (62% ,67%, 73%, 80%). Conclusions: In this large, real-world cohort of RRMM patients treated with cilta-cel, a lower cell dose was not associated with reduced incidence or severity of CRS, ICANS, DNT, or IEC-HS. Conversely, a dose-response correlation with PFS was observed, with higher doses trending toward longer median and 12-month PFS. It remains unknown if a lower cell dose in the commercial setting reflects poor T cell quality, yet these findings suggest that dose reduction of cilta-cel may not be an effective strategy to mitigate toxicities and might be associated with a trend toward lower efficacy. Therefore, the standard target dose should be utilized to maximize patient outcomes and further prospective dose exploration is warranted.

Abstract Introduction: Ciltacabtagene autoleucel (cilta-cel) has shown high efficacy in relapsed MM, but further efforts are needed to mitigate non-ICANS delayed neurotoxicity (DNT) and non-relapse mortality (NRM). Identifying risk factors associated with DNT and NRM may help with risk mitigation by aiding the development of interventions for potentially modifiable risk factors and also help with clinical decision making. Methods: In this multi-center retrospective study from the US MM Immunotherapy Consortium, we evaluated 761 patients treated at 15 centers receiving standard of care cilta-cel for relapsed MM between May 2022 to December 2024. Risk factors for DNT, particularly Parkinsonism and NRM were evaluated in by univariable and multivariable analysis. Any NRM events occurring after disease progression were censored for NRM evaluation. Results: The median age of the cohort was 65 years old (range: 30-88), median prior lines of therapy (pLoT) were 5 (range: 1-23). Cilta-cel was used in earlier relapse (1-3 pLOT) in 16% (n=120) patients. High-risk cytogenetics [del 17p, t(14;16) or t(4;14)] were present in 39%, with extramedullary disease (EMD) in 27% and R-ISS stage III in 18% of patients, respectively. Majority of patients (86%) received bridging therapy with response to bridging (≥ partial response, PR) seen in 33% of patients, respectively. Median follow up was 10.1 months, with response rate of 92% and CR rate of 70%. DNT was seen in 10% (n=75) of patients, with distribution as follows: Parkinsonism in 2.9% (n=22), cranial nerve palsy in 4.6% (n=35) and other DNT in 2.4% (n=18), with some patients manifesting more than one type of DNT. Risk of DNT was higher in patients who did not respond to bridging therapy (Any DNT: 12% vs 6%; Parkinsonism: 5% vs 0.5%, both p<0.05) Of the 22 cases of Parkinsonism, 21 patients (95%) did not respond to bridging, even though they achieved a post CAR-T response with ORR of 91% and ≥ CR in 68%. Absolute lymphocyte count (ALC), a surrogate measure of CAR expansion was higher in patients who developed DNT, particularly Parkinsonism, including ALC at days 7,14,21,28 and as peak ALC in the first month post cilta-cel (p<0.05 for all). Median peak ALC for patients with vs without Parkinsonism was: 5.88 vs 1.17/uL (p<0.001). We evaluated risk of Parkinsonism with various thresholds of peak ALC expansion. Amongst patients who developed Parkinsonism vs. not, peak ALC was as follows, > 1000/uL: 100% vs 57%, > 2500/uL: 73% vs 19% and > 3000/uL: 68% vs 14% (all p<0.001). The absolute risk of Parkinsonism with ALC > 3000 vs ≤ 3000/uL was 12% vs 1%, p<0.001; for ALC 2500 vs ≤ 2500uL was 9% vs 1%, p<0.001. On multivariable analysis, peak ALC > 3000/uL (OR: 12.7, p<0.001) and non-response to bridging therapy (OR: 9.9, p=0.03) were independent risk factors for developing Parkinsonism after cilta-cel. After cilta-cel, 1 and 2 year NRM estimates were 9% and 10%, respectively. Amongst 63 (8%) patients experiencing NRM events, the most common cause of NRM was infectious complications (35, 56%), followed by acute immune-mediated adverse events (AEs) like CRS, ICANS, IEC-HS in 14 (22%), delayed immune mediated AEs like DNT and colitis in 6 (9.5%), second cancers in 5 (8%) and other causes in 3 (5%) patients, respectively. When evaluating the timing of NRM events, the risk of infection related mortality remained relatively stable in the first year, though immune mediated toxicty deaths were uncommon after 6 months, while SPMs were uncommon within the first 6 months. On multivariable analysis, non-response to bridging (HR 2.41, p=0.046), poor performance status ≥ 2, high-risk cytogenetics and age ≥ 70 years were independent predictors for NRM. Conclusion: In a large cohort of over 750 patients receiving cilta-cel, we identified potentially modifiable risk factors for Parkinsonism and NRM. Non-response to bridging therapy and peak ALC > 3000/uL were independent predictors of developing Parkinsonism. Peak ALC of > 2500/uL and > 3000/uL were associated with 9% and 12% absolute risk of Parkinsonism. This indicates that peak ALC of 2500/uL or 3000/uL in the first month after cilta-cel may be a potential biomarker to identify patients for pre-emptive interventions such as steroids that can suppress rapid CAR expansion and perhaps decrease the risk of Parkinsonism. In addition, we need to focus on effective bridging strategies to further decrease the risk of Parkinsonism, as well as NRM with cilta-cel.

Abstract Introduction Ciltacabtagene autoleucel (cilta-cel) has demonstrated unprecedented response rates and progression-free survival (PFS) in relapsed/refractory multiple myeloma (RRMM), but a proportion of patients experience early relapse. Identifying these patients is essential to guide future therapeutic strategies, such as enhanced bridging therapy or consolidation, while avoiding overtreatment in those likely to achieve durable disease control. Methods We conducted a multi-center study of patients treated with cilta-cel at 15 U.S. academic centers. Outcomes were evaluated based on high-risk (HR) features, including functional HR disease (FHR; relapse within 18 months of first-line therapy initiation), true extramedullary disease (EMD), traditional HR cytogenetics as defined in CARTITUDE-1 [deletion 17p, t(4;14), t(14;16)], and a 2024 IMS-IMWG-adapted HR definition (deletion 17p; t(4;14) or t(14;16) with gain 1q or deletion 1p; and gain 1q with deletion 1p). Multivariable Cox regression was used to examine the association of HR features (FHR, adapted IMS-IMWG HR, and EMD, individually and collectively) with PFS while adjusting for baseline ferritin, prior BCMA, and ECOG performance status (PS ≥2). Among patients with ≥18 months of follow-up, we evaluated predictors of early relapse (≤18 months post infusion) using logistic regression. Results Our cohort included 598 patients treated with cilta-cel between 5/2022 and 12/2024 who had available data on all HR features. The median age was 65 years (range 33-83), and the median prior lines of therapy (pLOT) was 5 (range: 1-18, 84% with >3 pLOT); 8% had received prior BCMA-directed therapy, and 27% were penta-refractory. Most patients (88%) received bridging therapy and 30% achieved ≥ partial response. In our cohort, 33% (n=195) had FHR, 43% (n=258) had traditional HR cytogenetics, 42% (n=253) had adapted IMS-IMWG HR disease, and 11% (n=64) had EMD. Median follow up was 10.6 months (range 0.4-34.1). Overall response rate (ORR) and complete response (CR) rates were lower in patients with vs without HR features: FHR (ORR: 89% vs 94%, CR: 61% vs 75%), traditional HR (ORR: 90% vs 94%, CR: 65% vs 74%), adapted IMS-IMWG HR (ORR: 91% vs 94%, CR: 64% vs 75%) and EMD (ORR: 77% vs 94%, CR: 61% vs 71%). Corresponding 12-month PFS was also lower in patients with vs without HR features: FHR (55% vs 79%), traditional HR (63% vs 78%), adapted IMS-IMWG HR (61% vs 80%) and EMD (59% vs 73%). ORR, CR rate, and 12-month PFS in patients without any HR features compared to those with ≥1 HR feature were 96% vs 90%, 81% vs 64%, and 83% vs 65%, respectively. In multivariable models, each HR feature (FHR, adapted IMS-IMWG HR, and EMD) was independently associated with inferior PFS after adjusting for baseline ferritin, prior BCMA, and ECOG PS ≥ 2. However, because early relapse cannot always be identified a priori based on traditional risk factors, we sought to identify predictors of relapse within 18 months of cilta-cel in a subset of patients with ≥18 months of follow-up (N=247; infused by 12/2023). Notably, while FHR (OR=3.04, 95% CI=1.59-5.89) and adapted IMS-IMWG HR (OR=2.07, 95% CI=1.10-3.89) were independently associated with odds of relapse within 18 months, EMD was not (OR=0.90, 95% CI=0.32, 2.40) when accounting for prior BCMA, ECOG PS ≥ 2, and baseline ferritin. We also used a time-varying Cox model to examine each HR feature associated with PFS at two time periods, <18 and ≥18 months, while adjusting for baseline ferritin, ECOG PS, and prior BCMA. We confirmed that FHR and adapted IMS-IMWG HR were both associated with relapse <18 months (HR=2.05, 95% CI=1.48-2.83 and HR=1.56, 95% CI=1.11-2.19) but not in the ≥18-month time period (HR=0.70, 95% CI=0.19-2.59 and HR=0.76, 95% CI=0.24-2.40). The magnitude of the association for EMD with PFS was similar across both time periods (<18 months HR=1.67, 95% CI=1.09-2.57 and ≥18 months HR=2.17, 95% CI=0.45-10.40). Conclusion While cilta-cel leads to high response rates and durable PFS in RRMM, a subset of patients with FHR and adapted IMS-IMWG HR remains at increased risk for early relapse. In this large multi-center cohort, we describe PFS outcomes across high-risk subgroups and identify key predictors of relapse within 18 months of cilta-cel. These findings inform risk-adapted therapeutic strategies and interventional trials, including bridging, consolidation, or maintenance approaches, to improve outcomes in the highest-risk RRMM patients.

Abstract Background Patients (pts) with multiple myeloma and CNS involvement (CNS MM) have poor outcomes, and we recently showed that CAR-T has activity and is reasonable in this population (Gaballa et al., 2025). We sought to evaluate the safety and efficacy of Bispecific T-cell engagers (BsAbs) in CNS MM pts, with specific interest in evaluating ICANS. Methods We conducted a retrospective study of CNS MM pts treated with BsAbs via the MM immunotherapy consortium. Primary endpoints were toxicity rates, with a specific focus on ICANS. Secondary endpoints were systemic responses, CNS responses, and survival outcomes. CNS MM was defined as involvement of the brain parenchyma, spinal cord tissue, leptomeningeal disease, or CSF positivity. CNS response was determined based on CSF and imaging, as complete CNS response, partial CNS response, and non-response/progression. Results The study included 24 pts from 13 US institutions treated with teclistamab (33%), talquetamab (50%), elranatamab (17%), and were used as monotherapy in 83% while 17% received them in combination with either daratumumab or IMiDs. The median age was 64.5 (range 41-82), 50% female, 79% white, and 17% black. High-risk cytogenetics were identified in 39%, 4% had prior primary PCL, and 21% had secondary PCL (2 active within 30 days of BsAb initiation). All pts were triple-refractory, 33% were penta-refractory, and 39% had non-CNS EMD. Pts received a median of 5 prior lines of therapy (IQR 4-7), 71% prior transplant, and 21% prior CAR-T. Prior BCMA therapy was received in 83% of the talquetamab group and 17% of the BCMA BsAbs group (teclistamab and elranatamab). CNS disease was determined based on both imaging and CSF findings in 58%, imaging only in 33%, and CSF only in 8%. Site of CNS disease included 42% brain/cranial nerves, 13% spinal cord, or 46% with both. CNS disease was diagnosed prior to BsAb in 19 pts, with a median interval of 46 days (IQR 7-234), and 3 pts were identified within 2 weeks after BsAb initiation. Two pts identified at days 68 and 121 were included in the safety evaluation but excluded from the efficacy assessments. One pt received teclistamab and intrathecal chemotherapy (IT chemo) as a bridge to CAR-T and achieved a complete CNS response before CAR-T. CNS-directed therapy consisted of: 30% radiotherapy (RT), 30% IT chemo, 13% RT + IT chemo, 9% RT + surgery, and 4% steroids. CRS grade (G) 1-2 occurred in 50%, with no G3-4 CRS. ICANS G 1, 2, and 3 occurred in 13%, 21%, and 4%, respectively, with no G 4 ICANS. One pt developed delayed parkinsonism, and another developed leukoencephalopathy; both had CNS MM diagnosed pre-BsAbs and achieved a CNS response (1 complete, 1 partial). Infections occurred in 67% of pts, with 42% being severe, and 1 infection-related death. The systemic ORR of 18 evaluable pts was 67%, including 22% CR, 17% VGPR, and 28% PR. The overall CNS response of 19 evaluable pts was 58%, including 37% complete CNS response and 21% partial CNS response. Of 11 pts achieving a CNS response, 82% didn't have subsequent CNS progression. In 9 pts achieving CNS response after BsAb initiation, the median time to CNS response was 0.9 months (range 0.03-2.8), with an unreached median duration of CNS response. With a median follow-up of 11 months, the median PFS was 5.0 months (95% CI 2.5-NA) and OS was 12.2 months (95% CI 7.7-NA). No significant difference in median PFS (10.6 vs 4.6 months, p=0.11) or OS (20.2 vs 9.3 months, p=0.37) was observed between BCMA BsAbs (n=11) and talquetamab (n=11). Due to small sample limitation, no significant difference was observed in the median PFS (4.6 vs 8.2 months, p=0.48) or OS (20.2 vs 9.9 months, p=0.73) between BsAb monotherapy (n=19) and BsAb combination therapy (n=3). One pt who received teclistamab as a bridge to CAR-T achieved a complete CNS response and remains progression-free to date, demonstrating the best long-term outcome with a PFS of 674 days. Conclusions Our study demonstrates that BsAb use in pts with CNS MM is safe without increased incidence of ICANS. The use of BsAbs in combination with a multimodal CNS-directed approach led to an overall CNS response rate of 58% and an unreached median duration of CNS response. Previous studies (Gaballa et al., 2025) reported a 100% CNS response rate with CAR-T. In this study, 1 pt treated with BsAb as a bridge to CAR-T had the longest PFS, warranting further research to evaluate this combination's efficacy in this very high-risk population.

PURPOSE Idecabtagene vicleucel (ide-cel) and ciltacabtagene autoleucel (cilta-cel), two B-cell maturation antigen–directed chimeric antigen receptor (CAR) T-cell therapies have demonstrated remarkable efficacy in relapsed/refractory multiple myeloma (RRMM). We compare safety, efficacy, and survival among patients with RRMM treated with standard-of-care (SOC) ide-cel or cilta-cel. METHODS Data were from a retrospective chart review of patients with RRMM leukapheresed by December 31, 2022, with the intent to receive SOC ide-cel or cilta-cel at 19 institutions. An inverse probability of treatment weighting (IPTW) approach was used to compare outcomes by therapy type. RESULTS A total of 641 patients were leukapheresed by December 31, 2022, with ide-cel (n = 386) and cilta-cel (n = 255). Five hundred eighty-six patients were infused (n = 350 for ide-cel; n = 236 for cilta-cel) with a median follow-up of 12.6 and 13.0 months for ide-cel and cilta-cel, respectively. After IPTW, patient characteristics were well balanced. Cilta-cel was associated with higher likelihood of grade ≥3 cytokine release syndrome (CRS; odds ratio [OR], 6.80 [95% CI, 2.28 to 20.33]), infections (OR, 2.03 [95% CI, 1.41 to 2.92]), second primary malignancies (OR, 1.77 [95% CI, 0.89 to 3.56]), and delayed neurotoxicity (OR, 20.07 [95% CI, 4.46 to 90.20]). Cilta-cel was also associated with better treatment responses (≥complete response: OR, 2.42 [95% CI, 1.63 to 3.60]), longer progression-free survival (hazard ratio [HR], 0.48 [95% CI, 0.36 to 0.63]), and longer overall survival (HR, 0.67 [95% CI, 0.46 to 0.97]). No associations were observed between therapy type and immune effector cell–associated neurotoxicity syndrome, any CRS, severe cytopenia at days 30 and 90, or nonrelapse mortality. We observed consistent findings when repeating the analyses restricting the ide-cel cohort to patients infused during the same time period as Food and Drug Administration approval for cilta-cel (≥March 2022). CONCLUSION Cilta-cel demonstrated superior efficacy and survival, with higher incidence of certain toxicities, compared with ide-cel.

*Authors contributed equally. Introduction. Two chimeric antigen receptor (CAR) T-cell therapies have been FDA approved for patients with relapsed/refractory multiple myeloma (RRMM): idecabtagene vicleucel (ide-cel) and ciltacabtagene autoleucel (cilta-cel). Prior work from our consortium identified racial and ethnic differences in safety and response to ide-cel among patients treated in the standard of care (SOC) setting; despite these differences, survival was similar across race and ethnicity. Here, we extend this work to investigate racial and ethnic differences in safety, efficacy, and outcomes in a larger cohort of patients treated with SOC ide-cel with longer follow-up and patients treated with SOC cilta-cel. Methods. Data for RRMM patients who underwent leukapheresis by 12/31/2022 and were treated with SOC ide-cel or cilta-cel were pooled across 19 institutions in the U.S. Multiple Myeloma Immunotherapy Consortium. We compared Non-Hispanic White, Non-Hispanic Black, and Hispanic (any race) patients, excluding other racial and ethnic groups due to small sample sizes that precluded sub-group investigations. Separately for each CAR T-cell therapy, racial and ethnic differences in baseline patient characteristics, safety, and treatment responses were examined using chi-square and Kruskal-Wallis rank sum tests. Kaplan-Meier survival curves and log-rank tests were used to examine progression-free survival (PFS) and overall survival (OS) by race and ethnicity. Results. Among 332 RRMM patients treated with ide-cel, Non-Hispanic Black and Hispanic patients comprised 17% and 10% of the cohort, respectively. Hispanic patients were younger at infusion compared to Non-Hispanic Black and Non-Hispanic White patients (55.5 vs. 63 vs. 66 years, p<0.001). Non-Hispanic Black patients had a higher disease burden (≥ 50% bone marrow plasma cell percentage) compared to Non-Hispanic White and Hispanic patients (35% vs. 20% vs. 19%, p=0.05), while a higher proportion of Non-Hispanic White patients had high-risk cytogenetics compared to Non-Hispanic Black and Hispanic patients (37% vs. 23% vs. 10%, p=0.003). Non-Hispanic Black patients were more likely to develop severe (≥ grade 3) cytopenia at day 30 (p<0.001) and day 90 (p=0.01) post-infusion, and these differences were particularly driven by higher rates of severe neutropenia among Non-Hispanic Black patients at these time points. Non-Hispanic White patients were more likely to achieve a best response of partial response (PR) or better (82%) compared to Non-Hispanic Black (75%) and Hispanic patients (63%, p=0.02). No other racial and ethnic differences in baseline patient characteristics (including cytopenias), safety, PFS, and OS were observed (p>0.05). Among 222 RRMM patients treated with cilta-cel, Non-Hispanic Black and Hispanic patients comprised 12% and 9% of the cohort, respectively. At baseline, Non-Hispanic Black and Hispanic patients were more likely to have anemia (p=0.01), and Non-Hispanic Black patients were more likely to have thrombocytopenia (p=0.02) and neutropenia (p=0.06) compared to Non-Hispanic White patients. No other differences in baseline patient characteristics were observed by race and ethnicity. While not statistically significant, a higher rate of severe (≥ grade 3) cytopenia at day 90 post-infusion was observed among Non-Hispanic Black and Hispanic patients compared to Non-Hispanic White patients (33% vs. 44% vs. 21%, p=0.07), similar to the ide-cel cohort. This finding was primarily driven by higher rates of severe neutropenia among Non-Hispanic Black patients and higher rates of anemia among Hispanic patients. No other racial and ethnic differences in safety, responses to cilta-cel, PFS, or OS were not observed in the cilta-cel cohort (p>0.05). Conclusion. In a large cohort of RRMM patients treated with SOC ide-cel or cilta-cel, we observed a higher rate of cytopenias post-infusion and inferior ide-cel responses among racial and ethnic minority patients compared to Non-Hispanic White patients. Despite these differences, survival was similar across race and ethnicity, suggesting that both available CAR T-cell therapies for RRMM patients can be utilized across all populations. Future studies that include larger patient cohorts of racially and ethnically diverse patients should be conducted to confirm these findings and additionally evaluate long-term outcomes.

Introduction. Ciltacabtagene autoleucel (cilta-cel) and idecabtagene vicleucel (ide-cel), two anti-B-cell maturation antigen (BCMA) CAR T therapies, have demonstrated remarkable responses and improved survival among patients with relapsed/refractory multiple myeloma (RRMM) in the clinical trials and standard of care (SOC) setting. Here, we compare safety, efficacy, and survival for patients treated with SOC ide-cel and cilta-cel. Methods. Data were from a retrospective chart review of RRMM patients leukapheresed by 12/31/2022 with the intent to receive SOC ide- or cilta-cel at 19 institutions in the US Multiple Myeloma Immunotherapy Consortium. An inverse probability of treatment weighting (IPTW) approach was used to compare outcomes by therapy type (cilta- vs. ide-cel), balancing on age, sex, race and ethnicity, performance status, extramedullary disease, high-risk cytogenetics, prior BCMA therapy, bone marrow plasma cells, penta-refractory status, lymphodepleting chemotherapy, baseline ferritin, low cell dose, and bridging therapy response. Logistic regression and Cox proportional hazard models were used to examine the association of treatment type with safety, efficacy, and survival accordingly, while adjusting for IPTW weights. We employed propensity score matching utilizing the same covariates to identify the association of treatment type with progression-free survival (PFS) within relevant patient sub-groups. Results. A total of 641 patients were leukapheresed by 12/31/2022 with ide-cel (n=386) and cilta-cel (n=255). 586 patients were infused (n=350 for ide-cel; n=236 for cilta-cel) with a median follow-up of 13.0 and 12.6 months, respectively. After IPTW, patient characteristics were well-balanced. Patients treated with cilta-cel were more likely to have grade ≥ 3 cytokine release syndrome (CRS) (OR=5.52, 95% CI=1.76-17.30, p=0.004), infections (OR=2.07, 95% CI=1.44-2.97, p<0.001), and delayed neurotoxicity (NT) (OR=20.97, 95% CI=4.75-92.42, p<0.001) compared to patients treated with ide-cel. In the cilta-cel cohort, 24 patients (10%) experienced delayed NT compared to 2 patients (1%) in the ide-cel cohort. Although not statistically significant, patients treated with cilta-cel were more likely to have any second primary malignancies (SPMs) (OR=1.87, 95% CI=0.94-3.71, p=0.08) and any SPMs excluding non-melanoma skin cancers (OR=1.78, 95% CI=0.78-4.10, p=0.2) but no association was observed for odds of hematologic SPMs (OR=0.98, 95% CI=0.26-3.61). No association was observed for therapy type with any or severe immune effector cell-associated neurotoxicity syndrome, any CRS, severe cytopenias, and non-relapse mortality. Compared to ide-cel, cilta-cel was associated with better treatment responses of ≥ complete response (OR=2.38, 95% CI=1.61-3.51, p<0.001) and ≥ partial response (OR=1.74, 95% CI=0.99-3.05, p=0.06). Patients treated with cilta-cel had a longer PFS and overall survival (OS) than ide-cel (HR=0.47, 95% CI=0.35-0.62, p<0.001 and HR=0.63, 95% CI=0.42-0.93, p=0.02, respectively), and these findings were similar in the intention to treat cohort (PFS: HR=0.44, 95% CI=0.34-0.55, p<0.001; OS: HR=0.55, 95% CI=0.41-0.73, p<0.001, respectively). We observed consistent findings when repeating the analyses restricting the ide-cel cohort to patients infused during the same time-period as FDA approval for cilta-cel (≥ March 2022), restricting to patients with data on all covariates, and restricting to sites that contributed data for both products. In a propensity matched population, (n=380; n=190 for cilta-cel and n=190 for ide-cel), patients treated with cilta-cel had superior PFS compared to those treated with ide-cel in most subgroups with respect to age and disease characteristics including extramedullary disease, high-risk cytogenetics, and elevated baseline ferritin (p<0.05). Conclusion. Our results suggest superior efficacy of cilta-cel with a higher incidence of certain toxicities compared to ide-cel in the SOC setting. This study provides valuable information for patient counseling and guiding the selection of CAR T-cell therapy for specific patient populations. Further validation through similar large-scale real-world experiences or prospective studies is needed to confirm our results and enhance applicability in the clinical setting. *DH, LP, & DD are co-first authors * YL, KP, & SS are co-last authors

Abstract Ciltacabtagene autoleucel (cilta-cel) was approved in 2022 for patients with relapsed/refractory multiple myeloma (RRMM). We report outcomes with cilta-cel in the standard-of-care setting. Patients with RRMM who underwent leukapheresis for cilta-cel manufacturing between 1 March 2022 and 31 December 2022 at 16 US academic medical centers were included. Overall, 255 patients underwent leukapheresis and 236 (92.5%) received cilta-cel, of which 54% would not have met CARTITUDE-1 eligibility criteria. In treated patients (N = 236), cytokine release syndrome was seen in 75% (grade ≥3, 5%), immune effector cell–associated neurotoxicity syndrome in 14% (grade ≥3, 4%), and delayed neurotoxicity in 10%. Overall and complete response rates were as follows: all patients who received cilta-cel (N = 236), 89% and 70%; patients receiving conforming cilta-cel (n = 191), 94% and 74%; and conforming cilta-cel with fludarabine/cyclophosphamide lymphodepletion (n = 152), 95% and 76%, respectively. Nonrelapse mortality was 10%, most commonly from infection. After a median follow-up of 13 months from cilta-cel, the median progression-free survival (PFS) was not reached, with 12-month estimate being 68% (95% confidence interval, 62-74). High ferritin levels, high-risk cytogenetics, and extramedullary disease were independently associated with inferior PFS, with a signal for prior B-cell maturation antigen–targeted therapy (P = .08). Second primary malignancies excluding nonmelanoma skin cancers were seen in 5.5% and myeloid malignancies/acute leukemia in 1.7%. We observed a favorable efficacy profile of standard-of-care cilta-cel in RRMM, despite more than half the patients not meeting the CARTITUDE-1 eligibility criteria.

Abstract Background: Several immune effector cell (IEC) therapies have been approved for multiple myeloma (MM), including chimeric antigen receptor T-cell (CAR-T) therapies such as idecabtagene vicleucel (ide-cel) and ciltacabtagene autoleucel (cilta-cel). We report 14 cases of IEC-associated enterocolitis, in five cases fatal, following CAR-T therapy in MM. Methods: We performed a retrospective analysis of cases of diarrhea, enterocolitis, or colitis following commercial ide-cel or cilta-cel (including out-of-specification products) at 10 centers within the United States Myeloma Immunotherapy Consortium. Patients were treated according to the local standard of care at each participating center. Results: We identified 14 cases of IEC-associated enterocolitis out of 1159 CAR-T infusions, corresponding to a 1.2% incidence (0.2% for ide-cel and 2.3% for cilta-cel). This proportion excludes 3 cases of potential or confirmed T-cell lymphoproliferative disorders of the bowel. Patients developed acute-onset symptoms (typically non-bloody Grade 3+ diarrhea) with negative infectious workup beginning a median of 79 days (range: 22-210 days) after CAR-T therapy and a median of 74 days after cytokine release syndrome resolution (range: 2-202 days). Biopsies uniformly demonstrated inflammation, with specific findings including intra-epithelial lymphocytosis, crypt dropout on colon biopsies, and villous blunting on duodenal biopsies. Systemic corticosteroids were initiated in 10 patients (71%) a median of 26 days (range: 1-80 days) following symptom onset. Only 40% of steroid-treated patients had symptomatic improvement; subsequent infliximab or vedolizumab led to improvement in 50% and 33% of corticosteroid-refractory patients, respectively. With a median follow-up of 224 days, n = 4 have had diarrhea resolution, n = 5 have had improved or stable symptoms, and n = 5 (36%) have died from IEC-associated enterocolitis or treatment-emergent infections. Conclusions: IEC-associated enterocolitis is a distinct but rare complication of CAR-T therapy characterized by non-bloody diarrhea typically beginning 1-3 months after infusion. Thorough diagnostic workup (including evaluation for potential T-cell malignancies) and appropriate management with an expert gastroenterologist are essential. Further research is critical to understand the pathogenesis of this novel toxicity. In the interim, the early use of infliximab or vedolizumab may potentially hasten symptom resolution and lower reliance on high-dose corticosteroids during the post-CAR-T period.