Vij, Ravi

The bone marrow immune microenvironment (BMME) is a critical factor in multiple myeloma (MM) pathogenesis. Despite higher incidence of MM among self-identified African Americans, the relationship between African genetic similarity and the BMME remains unclear. We present the largest analysis to date assessing the impact of Ancestry on the BMME in myeloma (N=320, including 64 with ≥50% African genetic similarity, AFR-High) leveraging our recently generated Immune Atlas. AFR-High was associated with enrichment of late T-effector cells, driven by rare cytotoxic CD4⁺ T cells, suggesting a distinct adaptive BMME. AFR-High exhibited expansion of late-differentiated adaptive NK cells with high cytotoxic GNLY and GZMH expression. AFR-High depicted reduced CD14⁺ monocytes, increased CD16⁺ non-classical monocytes, and expansion of macrophage-like monocyte populations with enrichment of metabolic adaptation, efferocytosis and phagocytic clearance programs, and immunoregulatory pathways. These findings reveal a shift from an innate inflammatory immune landscape toward adaptive cytotoxic and immunoregulatory remodeling associated with African genetic similarity in MM.

Abstract Background: Clonotypic peptide detection by mass spectrometry (MS) leverages monoclonal protein (M-protein) de novo sequencing and peptide quantification to enable ultra-sensitive blood-based monitoring of multiple myeloma (MM) patient M-protein kinetics. Etentamig is a 2nd generation BCMA x CD3 bispecific antibody that has shown promising efficacy and a favorable safety profile in heavily pre-treated patients with relapsed or refractory (RR) MM (Journal of Clinical Oncology, 43;16:suppl.7527). In the current study, we explored the depth and kinetics of MS M-protein response to etentamig monotherapy in serum samples from Phase 1 M22-466 (NCT03933735) study patients. The correlation between blood-based MS M-protein levels and bone marrow minimal residual disease (MRD) negativity as determined by next generation sequencing (NGS) was also evaluated. Method: Clonotypic peptide MS using M-Insight (Sebia/Corgenix) was performed on serum samples from a subset of MRD evaluable patients enrolled into the Phase 1 (NCT03933735) clinical trial of etentamig monotherapy in patients with RRMM. Bone marrow MRD negativity (<10-5 and 10-6) analysis was determined by NGS (clonoSEQ, Adaptive Biotechnologies). Patient pre-treatment (Cycle [C] 1 Day [D] 1) serum samples were digested with proteolytic enzymes to permit sequencing of the M-protein heavy and light chain. Clonotypic peptides specific to the patient's complementarity-determining regions were selected for quantification by MS. Clonotypic peptide quantification by MS was performed on available tracking peripheral blood samples at C2D1, C3D1, C4D1, and C5D1 time points post etentamig monotherapy treatment. Results: Twenty patients who were MRD evaluable and treated with 40 mg and 60 mg doses of etentamig with available serum samples collected from C1D1–C5D1 time points were selected for M-Insight evaluation. Of the 20 patients, 16 (80%) had at least one clonotypic peptide identified prior to etentamig treatment that was utilized for tracking at subsequent time points. Rapid decline in MS M-protein levels was observed in patients treated with etentamig, which strongly correlated with the patients' best International Myeloma Working Group (IMWG) response. At C3D1 post etentamig treatment, patients with complete response (CR)/stringent CR (n=9) demonstrated a significant decline from MS M-protein levels (median: 1.8±0.9 g/dL at C1D1 to 0.03±0.2 g/dL at C3D1) (P<0.001). All evaluable subjects (n=16) had detectable MS M-protein at all time points (n=80). The lowest detectable M-protein level observed in the current dataset was 44 mg/dL (lower limit of quantitation of assay: 10 mg/dL). Subsequent analysis of differences in kinetics between MRD-negative (<10-5) (n=8) and MRD-positive (n=8) patients revealed a deeper reduction in M-protein levels for MRD-negative patients (median 0.02±0.2 g/dL at C3D1 compared with 0.4±0.3 g/dL at C3D1 for MRD-positive patients). Among the 8 patients who achieved MRD negativity at 10-5 threshold, 5 patients also achieved <10-6 threshold, and serum MS M-protein levels remained detectable in these patients (0.07±0.2 g/dL). Conclusions: Using MS-based clonotypic peptide detection, rapid and deep decline in serum M-protein levels was observed in RRMM patients treated with etentamig. Strong concordance was observed between MS M-protein levels and IMWG response, including in patients achieving MRD-negative CR at <10-5 and 10-6thresholds. Non-invasive and ultra-sensitive M-protein detection is feasible in MM and may serve as a key biomarker for enhancing the detection of residual disease in the future.

Summary CD19 chimeric antigen receptor T‐cell (CAR‐T) therapy is a pivotal part of the treatment algorithm for large B‐cell lymphoma (LBCL) in the second‐ and third‐line settings based on numerous clinical trials. However, these studies included very few patients with a diagnosis of high‐grade B‐cell lymphoma, not otherwise specified (HGBCL‐NOS) and it is unclear if outcomes are similar to those observed with more common LBCL histologies. Using the Center for International Blood and Marrow Transplant Research (CIBMTR) registry, we identified 111 HGBCL‐NOS patients who received CAR‐T therapy. The cytokine release syndrome (CRS) rate was 74% (7.7% grade 3+), median onset was 4 days (1–17) and immune effector cell‐associated neurotoxicity syndrome rate was 45.2% (22.6% grade 3+), median onset was 7 days (1–17). At 2 years post‐CAR‐T infusion, the probability of overall survival and progression‐free survival were 41.6% and 28.7% respectively. The 2‐year non‐relapse mortality and relapse/progression were 3.1% (95% confidence interval [CI]: 0.6–7.6) and 68.1% (95% CI: 57.9–77.6) respectively. Our analysis illustrates that patients with HGBCL‐NOS represent a particularly difficult group to treat, even with CAR‐T therapy. We observed that one third of patients achieved a durable response; however, the overall results were less favourable, with lower overall response rate, overall survival and progression‐free survival as compared to published reports on LBCL.

7527 Background: Etentamig (etenta) is a differentiated BCMA x CD3 bispecific T-cell engager composed of high avidity bivalent BCMA-binding domains, low-affinity CD3-binding domain designed to reduce cytokine release syndrome (CRS), and silenced Fc tail for extended half-life enabling convenient dosing. We present long term results from 2 ongoing Ph 1 studies evaluating efficacy and safety of etenta in patients (pts) with RRMM. Methods: Data were from a Ph 1 multicenter, open-label, dose escalation/expansion (NCT03933735) trial and Arm A of a Ph 1b, open label (NCT05650632) trial of etenta; both enrolled pts ≥18 years with RRMM, ≥3 prior lines of therapy (LoT), and triple-class exposed. Pts received 60 mg Q4W or 40 mg Q3W, both regimens with similar dose intensity, in the Ph 1 trial; pts from Arm A of the Ph 1b trial received a step-up dose (SUD) on day 1 and full dose of 60 mg Q4W on day 4. This pooled analysis assessed long-term efficacy, safety, and tolerability. Tumor response was assessed per IMWG 2016 criteria. Results: Of 146 pts with RRMM who received etenta, 87 (60%) were male, median age (range) was 68 (40–87) years, median prior LoT were 4 (3–23), and median duration of follow-up was 13 (1–48) months (mo). ORR was achieved in 96 (66%) pts and ≥VGPR in 79 (54%) pts. Response rates across subgroups are reported in the Table. Median duration of response was not reached (NR) (NR–NR) among responders; Kaplan-Meier (KM) estimate at 12 mo was 71% (58.5%–80.5%). Median PFS (mPFS) was NR (8.7–NR) mo; KM estimate at 12 mo was 55% (44.9%–63.1%). Any grade and G3/4 treatment emergent adverse events (TEAEs) occurred in 145 (99%) pts and 116 (79%) pts. Most common G3/4 TEAEs (≥15%) were neutropenia (38%), anemia (23%), lymphopenia (25%), and thrombocytopenia (16%). Infections G3/G4 were reported in 32 (22%) pts; most common infections G3/G4 (≥5%) were pneumonia (12%) and sepsis (5%). TEAEs leading to etenta discontinuation were reported in 13 (9%) pts. Deaths from TEAEs were reported in 13 (9%) pts; 10 were not attributed to etenta treatment. In Arm A of Ph 1 study where 60mg Q4W was administered with SUD and modified dex as premedication, CRS incidence was 30% (4% G2; No ≥G3 events) with median time to CRS onset of 22.3 (5.5–29.6) hours; and median time to CRS resolution of 20.7 (1.8–131.7) hours. Conclusions: Etenta with SUD demonstrated a low CRS incidence, durable response, and tolerability in pts with heavily pretreated RRMM. Efficacy across all subgroups was comparable and maintained, suggesting therapeutic benefits among a broad population and supporting further exploration in the ongoing Ph 3 Cervino study. Subgroup ORR, n (%) ≥VGPR, n (%) mPFS, months (range) Age ≥75years 26 (72) 23 (63.9) NR (7.5–NR) Race: Black 15 (63) 13 (54.2) 13.7 (5.0–NR) High cytogenetic risk 21 (55) 18 (47.4) 7.4 (2.8–NR) 3 prior LoT 29 (64.4) 23 (51.1) 13.5 (5.6–NR) ≥4 prior LoT 67 (67) 56 (56) NR (8.3–NR)

Abstract Outcomes are poor in triple-class–exposed (TCE) relapsed and refractory multiple myeloma (R/RMM). In the phase 3 KarMMa-3 trial, patients with TCE R/RMM and 2 to 4 prior regimens were randomized 2:1 to idecabtagene vicleucel (ide-cel) or standard regimens (SRs). An interim analysis (IA) demonstrated significantly longer median progression-free survival (PFS; primary end point; 13.3 vs 4.4 months; P < .0001) and higher overall response rate (ORR) with ide-cel vs SRs. At final PFS analysis (median follow-up, 30.9 months), ide-cel further improved median PFS vs SRs (13.8 vs 4.4 months; hazard ratio [HR], 0.49; 95% confidence interval [CI], 0.38-0.63). PFS benefit with ide-cel vs SRs was observed regardless of number of prior lines of therapy, with greatest benefit after 2 prior lines (16.2 vs 4.8 months, respectively). ORR benefit was maintained with ide-cel vs SRs (71% vs 42%; complete response, 44% vs 5%). Patient-centric design allowed crossover from SRs (56%) to ide-cel upon progressive disease, confounding overall survival (OS) interpretation. At IA of OS, median was 41.4 (95% CI, 30.9 to not reached [NR]) vs 37.9 (95% CI, 23.4 to NR) months with ide-cel and SRs, respectively (HR, 1.01; 95% CI, 0.73-1.40); median OS in both arms was longer than historical data (9-22 months). Two prespecified analyses adjusting for crossover showed OS favoring ide-cel. This trial highlighted the importance of individualized bridging therapy to ensure adequate disease control during ide-cel manufacturing. Ide-cel improved patient-reported outcomes vs SRs. No new safety signals were reported. These results demonstrate the continued favorable benefit-risk profile of ide-cel in early-line and TCE R/RMM. This trial was registered at www.ClinicalTrials.gov as #NCT03651128.

7531 Background: MM eventually becomes refractory to current treatments, and new therapeutic options with convenient dosing and improved safety are needed to enhance patient (pt) adherence, access, and outcomes. ABBV-383 is a distinctive next-generation BCMA x CD3 bispecific antibody composed of 2 high-affinity BCMA-binding domains, a low-affinity CD3-binding domain designed to reduce cytokine release syndrome (CRS) risk, and a silenced Fc tail for an extended half-life allowing convenient dosing. ABBV-383 monotherapy has shown promising activity in the ongoing first-in-human phase 1 trial in RRMM (Vij et al. Blood 2023;142[suppl 1]:3378). Here, safety and efficacy results are reported that support the RP2D of 60mg Q4W as the optimal therapeutic ABBV-383 monotherapy dose. Methods: This phase 1 open-label, dose-escalation/expansion trial (NCT03933735) enrolled pts with RRMM who received ≥3 prior lines of therapy with exposure to PI, IMiD, and anti-CD38 mAb. ABBV-383 regimens explored in the expansion phase included 60mg Q4W and 40 or 60mg Q3W. A modified dexamethasone premedication schedule and shortened CRS monitoring period were implemented in the 60mg Q4W cohort for cycle 1. IV ABBV-383 was administered as a flat dose with no step-up schedule. Treatment was continued until disease progression/unacceptable toxicity. Primary objectives were to assess safety, tolerability, PK, PD, and determine the RP2D. Efficacy evaluation was a secondary objective. TEAEs were assessed per CTCAE v5.0 and tumor response per IMWG 2016 criteria. Results: As of May 2023, 220 pts received ABBV-383 (median age: 68 yr [35–92]; median prior therapy lines: 5 [3‒23]). Median FU was 4.1 mo (0.8–5.2) at 60mg Q4W (n=21), 12.2 mo (1.3–34.4) at 40mg Q3W (n=55), and 24.2 mo (0.6–33.4) at 60mg Q3W (n=61). At 60mg Q4W, with the modified premedication regimen, CRS was reported in 43% of pts (38% G1, 5% G2), and ICANS in 5% of pts (G2). In Q3W cohorts, CRS was reported in 71% (40mg; 45% G1, 25% G2) and 70% (60mg; 51% G1, 18% G2, 2% G3) of pts. The incidence of G3/4 neutropenia, anemia, and thrombocytopenia was 14/24/10% at 60mg Q4W, 31/31/16% at 40mg Q3W, and 34/13/13% at 60mg Q3W. G3/4 infections occurred in 10/24/34% of pts at 60mg Q4W, 40mg and 60mg Q3W, respectively. ORR and ≥VGPR were 65/50% at 60mg Q4W, 64/53% at 40mg Q3W, and 60/52% at 60mg Q3W. Corresponding exposure-response (ER) analyses and correlative analyses further supported RP2D determination (separate abstract submissions). Conclusions: The optimal therapeutic dose of 60mg Q4W ABBV-383 monotherapy was selected on the basis of safety, efficacy, and ER analyses. The extended interval of Q4W, with a shortened CRS monitoring period in cycle 1 and no step-up dosing, will improve convenience and reduce the treatment burden for pts. ABBV-383 at 60mg Q4W will be investigated in the registrational phase 3 trial (NCT06158841) in RRMM. Clinical trial information: NCT03933735 .