Meermeier, Erin W

Abstract Purpose: Naturally occurring tumor-specific T cells derived from peripheral blood (PB) offer a clinically accessible source for adoptive immunotherapy. However, the expansion of these T cells from patients with cancer remains a challenge. We hypothesized that mimicking innate immune activation could optimally stimulate antigen-driven T-cell expansion in vitro, unlocking the therapeutic potential of PB-derived T cells. Patients and Methods: We previously developed an ex vivo culture system that selectively expands tumor antigen–activated T cells from PB mononuclear cells (PBMC), generating multiclonal effector and central memory T cells. In this hypothesis-generating study, we evaluated the therapeutic potential of MUC1-activated T cells in patients with relapsed and/or refractory multiple myeloma (r/rMM) in a phase I clinical trial (NCT05411497). MUC1 is an oncoprotein overexpressed in r/rMM. We translated our small-scale culture into GMP-compliant, large-scale manufacturing, which achieved expansion of T cells from heavily pretreated patients’ PBMCs without exhaustion. Five patients were treated with escalating doses of up to 1 × 1010 T cells. Results: Although the cell infusions were well tolerated, no objective responses occurred. One patient, who received the highest dose, has had stable disease for 2 years after infusion. This patient exhibited transient dermatitis with localized MUC1 and CD3 staining, as potential evidence of on-target, off-tumor T-cell reactivity, perhaps contributing to disease stabilization. T-cell receptor sequencing revealed the T-cell product in four of the patients’ blood, which correlated with the product’s degree of polyfunctionality and MUC1 reactivity. Conclusions: These findings demonstrate the feasibility, safety, and biological activity of PB-derived, MUC1-specific T cells as adoptive immunotherapy. Significance: Expanding tumor antigen–specific T cells for clinical use from the blood of heavily pretreated patients with cancer remains a significant hurdle. We scale up a novel culture method that integrates innate immune signals to stimulate T-cell expansion and demonstrate safety, feasibility, and a case of long-term disease stabilization upon treatment of patients with multiple myeloma in a phase I clinical trial.

Abstract Glutamine dependence of cancer cells reduces local glutamine availability, which hinders antitumor T-cell functionality and facilitates immune evasion. We thus speculated that glutamine deprivation might be limiting efficacy of chimeric antigen receptor (CAR) T-cell therapies in patients with cancer. We have seen that antigen-specific T cells are unable to proliferate or produce interferon gamma (IFN-γ) in response to antigen stimulation when glutamine concentration is limited. Using multiple myeloma (MM) as a glutamine-dependent disease model, we found that murine CAR T cells selectively targeting B-cell maturation antigen (Bcma) in MM cells were sensitive to glutamine deprivation. However, CAR T cells engineered to increase glutamine uptake by expression of the glutamine transporter Asct2 exhibited enhanced proliferation and responsiveness to antigen stimulation, increased production of IFN-γ, and heightened cytotoxic activity, even under conditions of low glutamine concentration. Mechanistically, Asct2 overexpression reprogrammed the metabolic fitness of CAR T cells by upregulating the mechanistic target of rapamycin complex 1 gene signature, modifying the solute carrier transporter repertoire, and improving both basal oxygen consumption rate and glycolytic function, thereby enhancing CAR T-cell persistence in vivo. Accordingly, expression of Asct2 increased the efficacy of Bcma-CAR T cells in syngeneic and genetically engineered mouse models of MM, which prolonged mouse survival. In patients, higher-level expression of ASCT2 by MM cells predicted poor outcome to combined immunotherapy and BCMA-CAR T-cell therapy. Our results indicate that reprogramming glutamine metabolism may enhance antitumor CAR T-cell functionality in MM. This approach may also be effective for other cancers that depend on glutamine as a key energy source and metabolic hallmark.

Abstract Bispecific T-cell engagers (TCEs) targeting B-cell maturation antigen (BCMA) and CD3, induce deep hematologic responses in ∼60% of heavily pretreated patients with multiple myeloma (MM). We and others found that high tumor burden leads to resistance to TCE and novel strategies are urgently needed to improve responses in this setting. Ikaros degraders, including immunomodulatory drugs (IMiDs) and cereblon E3 ligase modulatory drugs (CELMoDs), represent logical partners for TCEs due to their direct anti-MM effects and additional immune-stimulatory activity; however, it is unclear how to optimally combine them with TCEs. Taking advantage of the immunocompetent IMiD-sensitive Vk∗MYChCRBN murine model of MM, we optimized strategies to overcome primary resistance to BCMA-TCEs and achieve sustained remission, while maintaining a manageable safety profile. The addition of anti–programmed cell death protein 1 (PD1) and pomalidomide reduced the T-cell exhaustion that occurs in response to TCEs in high tumor burden settings. This allowed for a higher degree of T-cell activation and significant improvement in response rates but also increased risk of lethal cytokine release syndrome (CRS). To moderate the response and prevent CRS, we evaluated Ikaros degraders and dexamethasone (DEX) with step-up–dosed TCEs. Pretreatment with iberdomide and DEX reshaped the bone marrow T-cell compartment, promoted infiltration of naïve T cells, and generated 100% response rates and the longest survival in subjects with high tumor burden. This was accompanied by more favorable T-cell profiling, with limited expansion of regulatory T cells and exhaustion. Overall, administering a TCE after DEX and iberdomide treatments provided deeper and more durable responses with a reduced risk of CRS.

Abstract Multiple myeloma (MM) is a malignancy that is often driven by MYC and that is sustained by IRF4, which are upregulated by super-enhancers. IKZF1 and IKZF3 bind to super-enhancers and can be degraded using immunomodulatory imide drugs (IMiD). Successful IMiD responses downregulate MYC and IRF4; however, this fails in IMiD-resistant cells. MYC and IRF4 downregulation can also be achieved in IMiD-resistant tumors using inhibitors of BET and EP300 transcriptional coactivator proteins; however, in vivo these drugs have a narrow therapeutic window. By combining IMiDs with EP300 inhibition, we demonstrate greater downregulation of MYC and IRF4, synergistic killing of myeloma in vitro and in vivo, and an increased therapeutic window. Interestingly, this potent combination failed where MYC and IRF4 expression was maintained by high levels of the AP-1 factor BATF. Our results identify an effective drug combination and a previously unrecognized mechanism of IMiD resistance. Significance: These results highlight the dependence of MM on IKZF1-bound super-enhancers, which can be effectively targeted by a potent therapeutic combination pairing IMiD-mediated degradation of IKZF1 and IKZF3 with EP300 inhibition. They also identify AP-1 factors as an unrecognized mechanism of IMiD resistance in MM. See related article by Neri, Barwick, et al., p. 56. See related commentary by Yun and Cleveland, p. 5. This article is featured in Selected Articles from This Issue, p. 4

Abstract BCMA/CD3-targeting bispecific antibodies (BsAb) are a recently developed immunotherapy class that shows potent tumor killing activity in multiple myeloma. Here, we investigated a murine BCMA/CD3-targeting BsAb in the immunocompetent Vk*MYC model and its immunomodulatory imide drug (IMiD)–sensitive derivative Vk*MYChCRBN model of multiple myeloma. The BCMA/CD3 BsAb was safe and efficacious in a subset of mice but failed in those with high tumor burden, consistent with clinical reports of BsAb in leukemia. The combination of BCMA/CD3 BsAb with pomalidomide expanded lytic T cells and improved activity even in IMiD-resistant high–tumor burden cases. Yet, survival was only marginally extended due to acute toxicity and T-cell exhaustion, which impaired T-cell persistence. In contrast, the combination with cyclophosphamide was safe and allowed for a tempered proinflammatory response associated with long-lasting complete remission. Concurrent cytotoxic therapy with BsAb actually improved T-cell persistence and function, offering a promising approach to patients with a large tumor burden. Significance: BCMA-targeted therapy induces deep but transient clinical responses. We developed an immunocompetent, IMiD-sensitive genetically engineered mouse model and show that IMiDs potentiate T-cell activation, increasing short-term efficacy of anti-BCMA/CD3 BsAb, but exacerbate T-cell exhaustion. Surprisingly, by reducing tumor burden and depleting regulatory T cells, cyclophosphamide prevents BsAb-induced T-cell exhaustion and promotes long-term multiple myeloma control. See related commentary by Louvet et al., p. 297.

Abstract The most common genetic abnormality in multiple myeloma is the deletion of chromosome 13, seen in almost half of newly diagnosed patients. Unlike chronic lymphocytic leukemia, where a recurrent minimally deleted region including MIR15A/MIR16-1 has been mapped, the deletions in multiple myeloma predominantly involve the entire chromosome and no specific driver gene has been identified. Additional candidate loci include RB1 and DIS3, but while biallelic deletion of RB1 is associated with disease progression, DIS3 is a common essential gene and complete inactivation is not observed. The Vk*MYC transgenic mouse model of multiple myeloma spontaneously acquires del(14), syntenic to human chromosome 13, and Rb1 complete inactivation, but not Dis3 mutations. Taking advantage of this model, we explored the role in multiple myeloma initiation and progression of two candidate loci on chromosome 13: RB1 and MIR15A/MIR16-1. Monoallelic deletion of Mir15a/Mir16-1, but not Rb1, was sufficient to accelerate the development of monoclonal gammopathy in wild-type mice and the progression of multiple myeloma in Vk*MYC mice, resulting in increased expression of Mir15a/Mir16-1 target genes and plasma cell proliferation, which was similarly observed in patients with multiple myeloma. Significance: In the absence of a defined, minimally deleted region the significance of del(13) in multiple myeloma has remained controversial. Here we show that haploinsufficiency of Mir15a/Mir16-1, but not Rb1, upregulates the cell cycle–regulatory network, inducing monoclonal gammopathy in mice and promoting multiple myeloma progression in both mice and men. See related commentary by Walker, p. 16. This article is highlighted in the In This Issue feature, p. 5