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Purpose: The purpose of this study was to investigate the remodeling of the multiple myeloma microenvironment after B-cell maturation antigen (BCMA)-targeted chimeric antigen receptor T (CAR-T) cell therapy., Experimental Design: We performed single-cell RNA sequencing on paired bone marrow specimens (n = 14) from seven patients with multiple myeloma before (i.e., baseline, "day -4") and after (i.e., "day 28") lymphodepleted BCMA CAR-T cell therapy., Results: Our analysis revealed heterogeneity in gene expression profiles among multiple myeloma cells, even those harboring the same cytogenetic abnormalities. The best overall responses of patients over the 15-month follow-up are positively correlated with the abundance and targeted cytotoxic activity of CD8+ effector CAR-T cells on day 28 after CAR-T cell infusion. Additionally, favorable responses are associated with attenuated immunosuppression mediated by regulatory T cells, enhanced CD8+ effector T-cell cytotoxic activity, and elevated type 1 conventional dendritic cell (DC) antigen presentation ability. DC re-clustering inferred intramedullary-originated type 3 conventional DCs with extramedullary migration. Cell-cell communication network analysis indicated that BCMA CAR-T therapy mitigates BAFF/GALECTIN/MK pathway-mediated immunosuppression and activates MIF pathway-mediated anti-multiple myeloma immunity., Conclusions: Our study sheds light on multiple myeloma microenvironment dynamics after BCMA CAR-T therapy, offering clues for predicting treatment responsivity., (©2024 The Authors; Published by the American Association for Cancer Research.)

Purpose: This study aimed to report the 5-year clinical outcomes of anti-B-cell maturation antigen chimeric antigen receptor (CAR) T-cell (HDS269B) therapy in patients with relapsed/refractory multiple myeloma (RRMM), including those with poor performance status [Eastern Cooperative Oncology Group (ECOG) scores 3 to 4], and to identify factors influencing long-term outcomes., Patients and Methods: Forty-nine patients with RRMM enrolled from 2016 to 2020 received HDS269B (9 × 106 cells/kg) after receiving a conditioning chemotherapy consisting of cyclophosphamide and fludarabine. The overall response, long-term outcomes, and safety were assessed, as were their associations with clinical and disease characteristics., Results: With a median follow-up of 59.0 months, the overall response rate was 77.55%. The median progression-free survival (PFS) and overall survival (OS) were 9.5 months [95% confidence interval (CI), 5.01-13.99] and 20.0 months (95% CI, 11.26-28.74), respectively. The 5-year PFS and OS rates were 21.3% (95% CI, 12.3%-36.7%) and 34.1% (95% CI, 22.7%-51.3%), respectively. Patients with ECOG 0 to 2 had marked longer survival, with a median PFS of 11.0 months and a median OS of 41.8 months. Early minimal residual disease negativity, higher and persistent CAR T-cell expansion, and the absence of extramedullary disease were associated with better survival outcomes. No new CAR T-cell therapy-associated toxicities were observed. Importantly, ECOG scores 0 to 2, prior therapy lines <4, and CAR T-cell persistence at ≥6 months were independently associated with longer OS., Conclusions: HDS269B is effective and safe, especially for patients with ECOG scores 0 to 2. Early CAR T-cell intervention may improve prognosis in patients with RRMM., (©2024 The Authors; Published by the American Association for Cancer Research.)

Purpose: Bispecific antibodies (BsAb) directed against B-cell maturation antigen (teclistamab) or the orphan G protein-coupled receptor GPRC5D (talquetamab) induce deep and durable responses in heavily pretreated patients with multiple myeloma. However, mechanisms underlying primary and acquired resistance remain poorly understood., Experimental Design: The anti-multiple myeloma activity of teclistamab and talquetamab was evaluated in bone marrow (BM) samples from patients with multiple myeloma. T-cell phenotype and function were assessed in BM/peripheral blood samples obtained from patients with multiple myeloma who were treated with these BsAb., Results: In ex vivo killing assays with 41 BM samples from BsAb-naive patients with multiple myeloma, teclistamab- and talquetamab-mediated multiple myeloma lysis was strongly correlated (r = 0.73, P < 0.0001). Both BsAb exhibited poor activity in samples with high regulatory T-cell (Treg) numbers and a low T-cell/multiple myeloma cell ratio. Furthermore, comprehensive phenotyping of BM samples derived from patients treated with teclistamab or talquetamab revealed that high frequencies of PD-1+ CD4+ T cells, CTLA4+ CD4+ T cells, and CD38+ CD4+ T cells were associated with primary resistance. Although this lack of response was linked to a modest increase in the expression of inhibitory receptors, increasing T-cell/multiple myeloma cell ratios by adding extra T cells enhanced sensitivity to BsAb. Further, treatment with BsAb resulted in an increased proportion of T cells expressing exhaustion markers (PD-1, TIGIT, and TIM-3), which was accompanied by reduced T-cell proliferative potential and cytokine secretion, as well as impaired antitumor efficacy in ex vivo experiments., Conclusions: Primary resistance is characterized by a low T-cell/multiple myeloma cell ratio and Treg-driven immunosuppression, whereas reduced T-cell fitness due to continuous BsAb-mediated T-cell activation may contribute to the development of acquired resistance., (©2024 American Association for Cancer Research.)

In February 2022, the FDA approved ciltacabtagene autoleucel, a chimeric antigen receptor (CAR) T-cell therapy targeting the B-cell maturation antigen, for adult patients with relapsed/refractory multiple myeloma after ≥4 lines of therapy, including an immunomodulatory agent, a proteasome inhibitor, and an anti-CD38 monoclonal antibody. Approval was based on overall response rate (ORR), complete response (CR) rate, and duration of response (DoR) in 97 adult patients in a single-arm, open-label, multicenter phase 2 trial (CARTITUDE-1 [NCT03548207]). Patients received a single infusion of ciltacabtagene autoleucel, preceded by lymphodepleting chemotherapy. Of the 97 patients evaluable, ORR was 97.9% [95% confidence interval (CI), 92.7-99.7] with a stringent CR rate of 78.4% (95% CI, 68.8-86.1). After median follow-up of 18 months, the median DoR was 21.8 months (95% CI, 21.8-not estimable [NE]) in responders (PR or better) and NE (95% CI, 21.8 months-NE) in patients who achieved stringent CR. Serious adverse reactions occurred in 55% of the 97 patients evaluated for safety. Grade 3 or higher cytokine release syndrome (CRS) and neurologic toxicities occurred in 5% and 11% of the patients, respectively, leading to a Risk Evaluation and Mitigation Strategy. Neurologic toxicities included immune effector cell-associated neurologic syndrome, typically seen with CAR-T products, parkinsonism, peripheral neuropathy, cranial nerve palsies, and Guillain-Barré syndrome. One fatal case of hemophagocytic lymphohistiocytosis/macrophage activation syndrome occurred. Prolonged and recurrent grade 3 or 4 cytopenias occurred; a single patient required hematopoietic stem-cell rescue., (©2024 American Association for Cancer Research.)

Purpose: B-cell maturation antigen (BCMA)-chimeric antigen receptor T-cells (CART) improve results obtained with conventional therapy in the treatment of relapsed/refractory multiple myeloma. However, the high demand and expensive costs associated with CART therapy might prove unsustainable for health systems. Academic CARTs could potentially overcome these issues. Moreover, response biomarkers and resistance mechanisms need to be identified and addressed to improve efficacy and patient selection. Here, we present clinical and ancillary results of the 60 patients treated with the academic BCMA-CART, ARI0002h, in the CARTBCMA-HCB-01 trial., Patients and Methods: We collected apheresis, final product, peripheral blood and bone marrow samples before and after infusion. We assessed BCMA, T-cell subsets, CART kinetics and antibodies, B-cell aplasia, cytokines, and measurable residual disease by next-generation flow cytometry, and correlated these to clinical outcomes., Results: At cut-off date March 17, 2023, with a median follow-up of 23.1 months (95% CI, 9.2-37.1), overall response rate in the first 3 months was 95% [95% confidence interval (CI), 89.5-100]; cytokine release syndrome (CRS) was observed in 90% of patients (5% grades ≥3) and grade 1 immune effector cell-associated neurotoxicity syndrome was reported in 2 patients (3%). Median progression-free survival was 15.8 months (95% CI, 11.5-22.4). Surface BCMA was not predictive of response or survival, but soluble BCMA correlated with worse clinical outcomes and CRS severity. Activation marker HLA-DR in the apheresis was associated with longer progression-free survival and increased exhaustion markers correlated with poorer outcomes. ARI0002h kinetics and loss of B-cell aplasia were not predictive of relapse., Conclusions: Despite deep and sustained responses achieved with ARI0002h, we identified several biomarkers that correlate with poor outcomes., (©2024 American Association for Cancer Research.)

Purpose: Multiple myeloma (MM) patients with disease refractory to all available drugs have a poor outcome, indicating the need for new agents with novel mechanisms of action., Experimental Design: We evaluated the anti-MM activity of the fully human BCMA×CD3 bispecific antibody JNJ-7957 in cell lines and bone marrow (BM) samples. The impact of several tumor- and host-related factors on sensitivity to JNJ-7957 therapy was also evaluated., Results: We show that JNJ-7957 has potent activity against 4 MM cell lines, against tumor cells in 48 of 49 BM samples obtained from MM patients, and in 5 of 6 BM samples obtained from primary plasma cell leukemia patients. JNJ-7957 activity was significantly enhanced in patients with prior daratumumab treatment, which was partially due to enhanced killing capacity of daratumumab-exposed effector cells. BCMA expression did not affect activity of JNJ-7957. High T-cell frequencies and high effector:target ratios were associated with improved JNJ-7957-mediated lysis of MM cells. The PD-1/PD-L1 axis had a modest negative impact on JNJ-7957 activity against tumor cells from daratumumab-naïve MM patients. Soluble BCMA impaired the ability of JNJ-7957 to kill MM cells, although higher concentrations were able to overcome this negative effect., Conclusions: JNJ-7957 effectively kills MM cells ex vivo , including those from heavily pretreated MM patients, whereby several components of the immunosuppressive BM microenvironment had only modest effects on its killing capacity. Our findings support the ongoing trial with JNJ-7957 as single agent and provide the preclinical rationale for evaluating JNJ-7957 in combination with daratumumab in MM., (©2020 American Association for Cancer Research.)

Purpose: Multiple myeloma is a usually incurable malignancy of plasma cells. New therapies are urgently needed for multiple myeloma. Adoptive transfer of chimeric antigen receptor (CAR)-expressing T cells is a promising new therapy for hematologic malignancies, but an ideal target antigen for CAR-expressing T-cell therapies for multiple myeloma has not been identified. B-cell maturation antigen (BCMA) is a protein that has been reported to be selectively expressed by B-lineage cells including multiple myeloma cells. Our goal was to determine if BCMA is a suitable target for CAR-expressing T cells., Experimental Design: We conducted an assessment of BCMA expression in normal human tissues and multiple myeloma cells by flow cytometry, quantitative PCR, and immunohistochemistry. We designed and tested novel anti-BCMA CARs., Results: BCMA had a restricted RNA expression pattern. Except for expression in plasma cells, BCMA protein was not detected in normal human tissues. BCMA was not detected on primary human CD34(+) hematopoietic cells. We detected uniform BCMA cell-surface expression on primary multiple myeloma cells from five of five patients. We designed the first anti-BCMA CARs to be reported and we transduced T cells with lentiviral vectors encoding these CARs. The CARs gave T cells the ability to specifically recognize BCMA. The anti-BCMA-CAR-transduced T cells exhibited BCMA-specific functions including cytokine production, proliferation, cytotoxicity, and in vivo tumor eradication. Importantly, anti-BCMA-CAR-transduced T cells recognized and killed primary multiple myeloma cells., Conclusions: BCMA is a suitable target for CAR-expressing T cells, and adoptive transfer of anti-BCMA-CAR-expressing T cells is a promising new strategy for treating multiple myeloma.

Chimeric antigen receptors redirect T cells to surface antigens. Discovery and validation of appropriate target antigens expand the possible indications for chimeric-antigen receptor (CAR)-T cells. B-cell maturation antigen (BCMA) is expressed only on mature B cells and plasma cells and promotes their survival. BCMA is a promising target for CAR-T cells in multiple myeloma.