Sidana, Surbhi

Abstract Background Patients (pts) with plasma cell leukemia (PCL) were excluded from key trials, so we assessed their outcomes with standard of care bispecific antibodies (BsAbs). Methods Our multicenter retrospective US Myeloma consortium study included PCL pts treated with BsAbs. PCL was defined as ≥5% circulating plasma cells, including primary PCL, secondary PCL, historical PCL, and active PCL within 30 days of BsAb initiation. Endpoints were toxicity rates, overall response (ORR), progression-free survival (PFS), and overall survival (OS). Results Our study involved 122 PCL pts from 15 US centers with: 27% primary PCL, 65% secondary PCL, 51% active PCL, 53% women, median age of 65 years (range 31-83), 77% white, 15% black, 60% high-risk cytogenetics, 45% high bone marrow burden (≥50% plasma cells), 5% CNS myelomatosis, and 20% EMD. Median prior lines of therapy (tx) were 6 (IQR 5-9), 94% triple-refractory, 57% penta-refractory, 73% prior transplant, and 57% prior BCMA tx (70% in talquetamab group, 41% in BCMA BsAb group). Treatments included 4 cohorts: 37% teclistamab, 11% elranatamab, 42% talquetamab definitive tx, and 11% talquetamab bridge to CAR-T. BsAb was used either as monotherapy (94%) or in combination (6%) with other agents. CRS grade (G) 1 was 41%, G2 14.8%, G3 2.5%, and G4 1.6%, while ICANS G1 was 8.2%, G2 7.4%, G3 3.3%, and G4 1.6%. Infections occurred in 34% and median hospitalization was 10 days (IQR 8-15). Of 110 evaluable pts, ORR was 54.5%, with 24.5% CR, 13.6% VGPR, and 16.4% PR. The ORR was 60.8% for talquetamab definitive tx (21.6% CR, 23.5% VGPR, 15.7% PR), 46.2% for elranatamab (38.5% CR, 7.7% PR), and 33.3% for teclistamab (20% CR, 4.4% VGPR, 8.9% PR). Talquetamab bridge to CAR-T in 12 evaluable pts had a pre-CAR-T day 30 ORR of 58.3% (16.7% CR, 8.3% VGPR, 33.3% PR). With a median follow-up of 8.3 months (mo), the median (m) PFS was 3.2 mo, and mOS was 9.2 mo, with similar outcomes between primary vs. secondary PCL (p=0.37 for PFS, p=0.18 for OS). Talquetamab definitive tx had better outcomes with a mPFS of 5.5 mo, mOS of 11.5 mo, 10-mo PFS of 31.2%, and 10-mo OS of 55.7%, and further improved when used as a bridge to CAR-T, with unreached mPFS, unreached mOS, 10-mo PFS of 53.8%, and 10-mo OS of 62.7%. BCMA BsAbs had inferior outcomes, with teclistamab yielding a mPFS of 1.2 mo, mOS of 8.1 mo, 10-mo PFS of 15.3%, and 10-mo OS of 44.3%, while elranatamab showed a mPFS of 1.6 mo and mOS of 3.6 mo (p=0.007 for PFS, p=0.023 for OS). In BCMA naive pts, BCMA BsAbs' outcomes remained inferior to talquetamab with a mPFS of 1.2 mo and mOS of 3.4 mo (p=0.003, 0.001). Sixty pts with active PCL had a poor mPFS (1.6 vs. 4.4 mo, p=0.036) and mOS (5.3 vs. 10.7 mo, p=0.004) compared to pts with only historical PCL. However, in active PCL, talquetamab definitive tx (n=29) showed superior outcomes with a mPFS of 6.9 mo and mOS of 12.2 mo (p=0.003, 0.012). Talquetamab bridge to CAR-T (n=3) showed a mPFS of 3.2 mo and mOS of 5.2 mo. BCMA BsAbs had inferior outcomes: teclistamab with a mPFS of 0.7 mo and mOS of 1.4 mo, while elranatamab showed a mPFS of 1.0 mo and mOS of 3.1 mo (p=0.003, 0.012). In BCMA naive pts, BCMA BsAbs' efficacy remained poor with a mPFS of 0.7 mo and mOS of 1.4 mo (p=0.006, 0.002). While in pts with only historical PCL (without active PCL), BCMA BsAbs in BCMA naive pts led to similar outcomes with a mPFS of 5.2 mo and mOS of 8.5 mo, compared to a mPFS of 3.7 mo and mOS of 10.4 mo with talquetamab (p=0.90, 0.86). Multivariable analysis (MVA) associated active PCL with worse PFS (p=0.035, HR=1.93, CI 1.05-3.55) and OS (p=0.017, HR=2.3, CI 1.16-4.60), talquetamab with improved PFS (p=0.009, HR=0.41, CI 0.21-0.81) and OS (p=0.012, HR=0.40, CI 0.19-0.82), and talquetamab bridge to CAR-T with improved PFS (p=0.042, HR 0.28, CI 0.08-0.95) without reaching statistical significance for OS (p=0.11, HR 0.29, HR 0.07-1.3). MVA results remained similar when the talquetamab bridge to CAR-T cohort was excluded. Conclusions Despite PCL's poor prognosis, talquetamab was superior to BCMA BsAbs in active PCL, with a mPFS of 6.9 mo and mOS of 12.2 mo, aligning with the broader cohort. BCMA BsAbs had poor efficacy in active PCL, even in BCMA naive pts, with a mPFS of 0.7 mo and mOS of 1.4 mo. In historical PCL without active PCL, BCMA BsAbs in BCMA-naive pts showed comparable outcomes to talquetamab. In the overall cohort, talquetamab bridge to CAR-T improved PFS without reaching significance for OS benefit in MVA.

Abstract Background: Talquetamab (Talq), a GPRC5D-targeting bispecific antibody, shows promising activity in relapsed/refractory multiple myeloma (RRMM). However, outcomes in patients (pts) with soft tissue plasmacytoma (STP) remain poorly characterized. Method: We retrospectively analyzed 463 RRMM pts treated with Talq at 15 U.S. centers by Dec 2024. Pts were grouped by presence of STP at Talq start: (1) extramedullary disease (EMD; lesions not contiguous with bone), (2) paraskeletal disease (PSK; bone-contiguous), (3) EMD + PSK, and (4) No-STP. Those receiving Talq as a bridge-to-CAR T (n=103, 22%) were censored at CAR T infusion if progression had not occurred. Time-to-event endpoints were calculated from Talq step-up, using Kaplan-Meier/Cox models. Result: Median age was 66 years (y) (35–89); 54 (11.7%) had EMD, 26 (5.6%) PSK, 60 (13%) EMD+PSK, and 320 (69%) No-STP. EMD pts were younger than No-STP (62 vs 66 y, p=.009), while PSK (66.5) and EMD+PSK (64.5) were similar to No-STP. Median prior lines were higher in PSK (7) vs EMD (5), EMD+PSK (6) and No-STP (6) (p=.035). Median time from diagnosis to Talq was shortest in EMD (3.8 y), followed by EMD+PSK (4.6 y), vs PSK (6.4 y), and No-STP (5.9 y) (p=.015). Among pts with any EMD (EMD or EMD+PSK), 81 (69%) had visceral involvement and 85 (73%) had multiple lesions. Rates of prior BCMA- or GPRC5D-directed therapy, plasma cell leukemia (≥5% circulating plasma cells at the time of Talq), and penta-refractoriness were similar across groups. ECOG ≥ 2 at Talq was more common in EMD (42%), PSK (39%), EMD+ PSK (37%) than in No-STP (23%) (p = .002). Other baseline features were similar. Cytokine release syndrome (CRS) rate/severity were similar across groups. The immune effector cell–associated neurotoxicity syndrome (ICANS) was more frequent in PSK (38%) vs EMD (11%), EMD + PSK (18%), and No-STP (11%), with the most PSK cases (60%, 6/10) being grade ≥2 (p=.006). No difference in CRS/ICANS onset or duration. Infection rates were lower in No-STP (36%) vs EMD (55%), PSK (46%), and EMD+ PSK (48%) (p=.025). Best overall response rates (ORR) were 71% in EMD, 68% in PSK, 67% in EMD+PSK, and 71% in No-STP (p=.9). Complete response (CR) rates were 14% in EMD, 20% in PSK, 13% in EMD+ PSK, and 25% in No-STP (p=.1) [CRs were not required to be confirmatory, which may not meet full IMWG criteria]. Radiographic response was evaluable in 41 EMD (86%), 16 PSK (61.5%), and 48 EMD+PSK (80%) pts, with partial response (PR) or better observed in 48%, 27%, and 38%, respectively. Among pts with any STP, 34% received radiation (XRT) (4 as bridge-to-CAR T), 24 (51%) were evaluable, and 71% (n=17) achieved ≥PR. The median follow-up from Talq initiation was 10.1 months (mo) (95% CI: 8.8–11.4) and was longest in EMD (13.9 mo) compared with PSK (10.8 mo), EMD+PSK (12.4 mo), and No-STP (9.8 mo) (p = .040). Median progression-free survival (PFS) was 4.3 mo (95% CI: 3.6–5.06) in EMD, 4.8 mo (95% CI: 2.2–7.3) in PSK, 3.8 mo (95% CI: 3.1-4.5) in EMD+ PSK, and 8.3 mo (95% CI: 7.0–9.6) in No-STP (p <.001). Among pts receiving XRT for any STP (within 4 weeks prior to or during Talq), responders had longer PFS vs non-responders (15.4 vs. 2.4 mo; p=.009). Multivariable analysis (MVA) showed inferior PFS with EMD (Hazard Ratio (HR) 1.58; 95% CI, 1.04-2.3; p=.029), EMD+PSK (HR 1.91; 95% CI, 1.2–2.8; p = .001), ECOG ≥ 2 (HR 1.4; 95% CI, 1.04–1.9; p = .024), and del(17p) at any timepoint (HR 1.99; 95% CI, 1.1–3.5; p=.017), while longer time from diagnosis to Talq was modestly protective (HR 0.95 per year; p = .016), likely reflecting less aggressive biology in those reaching 5th+ line later. PSK alone showed a non-significant trend toward inferior PFS (HR 1.5; p = .1). Median overall survival (OS) was 13.0 mo (95% CI: not reached [NR]–NR) in EMD, 12.9 mo (95% CI: 6.9–18.9) in PSK, 10.9 mo (95% CI: NR–NR) in EMD+PSK, and NR (95% CI: NR–NR) in No-STP (p = .017). The primary cause of death was disease-related across all groups (p = .6). MVA for OS showed worse outcomes with EMD+PSK (HR 1.7; p=.033), ECOG ≥ 2 (HR 1.98; p <.001), and active PCL at Talq (HR 2.1; p =.010). Conclusion: Soft tissue plasmacytoma, particularly EMD and EMD+PSK, remain strong adverse prognostic factors in Talq-treated patients, with significantly shorter PFS and OS despite similar response rates. Radiation to STP sites was associated with improved outcomes in select cases. Prospective strategies are needed to optimize management for this high-risk population.

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.

Abstract Background Talquetamab (talq) is a GPRC5D-directed bispecific antibody (BsAb) approved for the treatment of relapsed and refractory multiple myeloma (RRMM). The pivotal monumenTAL-1 clinical trial did not include patients with renal impairment (RI, creatinine clearance<40 mL/min) and therefore, data for the use of this agent in RI is lacking. Methods We examined the outcomes of patients with RRMM treated with standard of care (SOC) talq in a multicenter, retrospective cohort study. RI was defined as creatinine clearance (CrCl) <40 mL/min. For each patient we recorded demographics, disease characteristics, prior therapies, incidence and severity of adverse events of special interest, namely cytokine release syndrome (CRS) and immune-cell associated neurotoxicity syndrome (ICANS), along with response, progression-free (PFS) and overall survival (OS). We compared binary variables between different groups using Chi-squared test and assessed progression free survival (PFS) and overall survival (OS) using Kaplan Meier and Cox proportional hazards models. Patients who received talq as a bridge therapy prior to chimeric antigen receptor T-cells (CART cells) were censored for PFS analysis at the time of subsequent therapy. Results We included 417 patients who received SOC Talq and had complete datasets. 91 (22%) had RI, including 20 (5%) on dialysis. The median age was 68 and 65 years for patients with and without RI. Patients with RI were more likely to be female (64% vs. 51%), less likely to have prior CART cells (35% vs. 48%). There were no differences in performance status, race, presence of high-risk cytogenetic abnormalities [del17p, t(4;14), t(14;16), gain/amplification 1q], lines of prior therapy (median 6 vs. 6), prior ASCT (68% vs. 72%), presence of CNS disease (4% vs. 4%), prior plasma cell leukemia (8% vs 9%), prior BCMA therapy (54% vs. 61%) and triple class refractory disease (90% vs. 94%) among patients with and without RI. Rates of CRS (63% vs. 56%, P=0.21) were similar in the two groups, while severe CRS (grade ≥3: 6% vs 2%, P=0.02) was more common in patients with RI. Any grade (20% vs 14%, P=0.21) and high grade ICANS (grade ≥3: 4% vs 4%, P=0.97) were similar in patients with and without RI. There was no difference between groups on risk of infection (P=0.65) with cumulative risk at 6 months of 39% vs. 40%. With 11.1 months of median follow up, the overall response rate (60% vs 67%; P = 0.12), and progression-free survival (median 7.3 vs. 6.5 mo.; P = 0.9) were comparable between the two groups. There was no difference in outcomes according to RI in both patients previously treated with BCMA-directed therapy and BCMA-naïve. Conversely, among patients with RI, median PFS was 4.6 and 8.5 mo. for patients with and without prior BCMA therapy. Similarly, among patients without RI, median PFS was 6.5 and 6.2 mo, respectively. Among BCMA-naïve patients, there was no difference in OS between patients with and without RI (median not reached, 12 mo. OS rate 71% vs. 73%, P=0.53), while among patients with prior BCMA-directed therapy there was a trend towards better OS for patients without RI (median 8.9 vs. 13.8 mo; 12 mo. OS rate 43% vs 59%, P=0.06). Five patients (25%) became dialysis independent following talq therapy. On multivariable analysis, ECOG >1 (HR 1.62, 95% C.I. 1.25-2.10, P<0.001) and deletion of 17p (HR 1.55, 95% C.I. 1.17-2.06, P=0.003) but not RI or prior BCMA-directed therapy affected PFS. OS was affected by ECOG >1 (HR 2.37, 95% C.I 1.71-3.30, P<0.001), triple-class refractoriness (HR 3.03, 95% C.I. 1.12-8.21, P=0.03) and prior BCMA-directed therapy (HR 1.79, 95% C.I. 1.24-2.59, P=0.002) but not by RI. Conclusion Our findings support the feasibility of talq in patients with RI, including those on dialysis, with similar safety and efficacy profile to patients without RI. While neither prior BCMA-directed therapy nor RI affect PFS, refractoriness to conventional agents and prior exposure to BCMA-directed therapy adversely affects OS. This observation likely reflects better post progression survival following talq due to the availability of efficacious therapeutic options, including those directed at BCMA.

Abstract Chimeric antigen receptor (CAR) T-cell therapy has emerged as a transformative treatment for hematological malignancies, yet its potential to drive lymphomagenesis poses significant clinical concerns. In this study, we investigated the mechanisms underlying CAR T-cell–associated lymphomagenesis in the gastrointestinal (GI) tract on a single case, focusing specifically on the role of integrin α4β7 expression and a predisposing somatic SH2B3 mutation. We observed oligoclonal CAR T cells homing to, and clonally expanding in, the GI tract, with the dominant expanded clone harboring both a pathogenic SH2B3 mutation and a CAR transgene integration within a TFCP2 locus. The clonal CAR T cells subsequently transitioned beyond the GI tract into the peripheral blood, suggesting a potential pathway for systemic dissemination. We found clinical, histological, and molecular evidence demonstrating the efficacy of cyclosporine in reducing the expanded malignant clone and achieving durable clinical remission for more than a year. Our findings highlight the complex interplay between CAR T-cell therapy, preexisting genetic vulnerabilities, and the GI microenvironment, emphasizing the need for vigilant monitoring and tailored therapeutic strategies to address the risks associated with CAR T-cell lymphomagenesis.

Abstract Despite significant therapeutic advances in multiple myeloma (MM), outcomes in patients with plasma cell leukemia (PCL) remain dismal. We conducted a multicenter retrospective analysis of patients with PCL who were treated with the B-cell maturation antigen–directed chimeric antigen receptor T-cell (CAR-T) products idecabtagene vicleucel (ide-cel) and ciltacabtagene autoleucel (cilta-cel). We identified 34 patients; 19 patients received ide-cel and 15 received cilta-cel. With a median follow-up of 11.9 months, the overall median progression-free survival (mPFS) was 9.0 months (95% confidence interval [CI], 4-15) and the median overall survival (mOS) was 13.0 months (95% CI, 8 to not estimable [NE]). The 1-year cumulative incidence of progression or death was 72%, and the 1-year cumulative incidence of death was 47%. Patients who received cilta-cel had a longer mPFS (19.0 months vs 6.0 months) and mOS (>23 months [NE] vs 9.0 months) when compared with those treated with ide-cel. Similarly, the 1-year cumulative incidence of disease progression or death was 37.5% (95% CI, 17.4-68.5) with cilta-cel, whereas all patients treated with ide-cel progressed or died within 12 months of infusion. The rates of hematologic and nonhematologic toxicities were similar between patients treated with cilta-cel and those treated with ide-cel and were consistent with those reported in patients with MM. In this first multicenter study that evaluated patients with PCL who were treated with standard-of-care CAR-T products, we show that CAR-T is safe, feasible, and associated with improved outcomes when compared with historic standards.

Abstract Ciltacabtagene autoleucel (cilta-cel) and idecabtagene vicleucel (ide-cel), 2 B-cell maturation antigen (BCMA)–directed chimeric antigen receptor T-cell (CAR-T) therapies, have transformed outcomes for relapsed/refractory multiple myeloma; however, the 6 to 8 weeks manufacturing time risks disease progression or death in up to 10% of patients. Talquetamab, a G-protein–coupled receptor, family C, group 5, member D (GPRC5D)–targeting bispecific antibody, represents a promising option. We performed a multi-institutional retrospective analysis across 20 centers (18 United States, 2 Germany) evaluating talquetamab as a bridging therapy prior to cilta-cel or ide-cel. Among 134 patients receiving talquetamab, 119 proceeded to CAR-T (n = 98 cilta-cel, n = 21 ide-cel). Reasons for not proceeding (n = 15) included progression (n = 7), manufacturing failure (n = 6), or patient decision (n = 2). Median age was 65 years and had median 5 prior lines of therapy. Notably, 85% would not have met CARTITUDE-1/KarMMa eligibility criteria. Talquetamab was administered for a median 23 days. Toxicity was manageable: no grade ≥3 cytokine release syndrome (CRS), 2% grade 3 immune effector cell–associated neurotoxicity syndrome (ICANS) and grade 1 to 2 talquetamab unique toxicities (70% oral, 38% skin, and 17% nail; 60% resolved). Talquetamab achieved 71% response rate. After CAR-T, 88% responded (54% complete response), with low-grade toxicities (2 grade ≥3 CRS, 1 grade 3 ICANS, and 5% grade ≥3 infections). Two cases of facial palsy and 1 acute myeloid leukemia occurred. Talquetamab correlated with sustained soluble BCMA decline and peak CAR-T expansion around day 14. Talquetamab bridging appears safe, enabling the majority of difficult-to-treat patients to successfully proceed to BCMA CAR-T therapy.

Abstract Teclistamab is an anti-CD3-/B-cell maturation antigen (BCMA) bispecific antibody approved for use in relapsed/refractory multiple myeloma. We undertook a retrospective study of post-approval, real-world outcomes with teclistamab in the US Multiple Myeloma Immunotherapy Consortium. Among 509 patients, 89% would have been ineligible for the MajesTEC-1 trial, primarily due to prior BCMA-directed therapy, cytopenias, or diminished performance status. Cytokine release syndrome occurred in 54% (1.4% grade ≥3) and immune effector cell–associated neurotoxicity syndrome in 11% (2.2% grade ≥3), with no fatal events. Infections occurred in 42% and contributed to death in 5%. Partial response (PR) or better was achieved in 53% and very good PR or better in 45%. With 10.1 months of median follow-up, the estimated median progression-free survival (PFS) was 5.8 months and 12-month overall survival was 61%. Independent predictors of less than very good PR and shorter PFS included BCMA-directed chimeric antigen receptor T-cell therapy in the previous 9 months, high disease burden, lymphopenia, and elevated ferritin. Significance: T cell–engaging bispecific antibodies such as teclistamab represent an important new treatment modality for multiple myeloma and other blood cancers. This study evaluates the real-world safety and efficacy of teclistamab, including its activity in populations not represented in the initial phase I/II study, and identifies clinical variables associated with treatment response. See related commentary by Zweegman et al., p. 542