Shi, Chang‐Xin

Abstract Introduction High disease burden has been associated with reduced efficacy and resistance to BCMA CAR-T therapy in relapsed/refractory multiple myeloma (van de Donk, Blood Cancer Discov, 2021; Martin, J Clin Oncol, 2023). While CAR-T cells can still induce remissions in these patients, outcomes are often worse compared to those with a lower tumor load. In addition to tumor debulking, novel strategies are needed to improve responses and durability of CAR-T cells in these patients. We previously demonstrated that immunomodulatory drugs (IMiDs) improve in vivo responses to T cell engagers (TCE) in high tumor burden setting by boosting T cell activation (Meermeier, Blood Cancer Discov, 2021; Meermeier, Blood, in press). IMiDs have also been shown to promote CAR-T cell antitumor activity in moderate to low tumor burden conditions (E:T ratios ≥1:1) (Yan, J Transl Med, 2024; Wang, Clin Cancer Res, 2018). We hypothesized that combining CAR-T with an IMiD may improve CAR-T function in high tumor burden setting. Methods We generated murine anti-BCMA.CD28 CAR-T cells by transducing Con-A stimulated T lymphocytes extracted from hCRBN+ mice, expanded with IL-7 and IL-15 to express a memory phenotype. We then tested CAR-T, or untransduced T cells, ability to kill in vitro IMiD resistant, hCRBN-, Vk*MYC myeloma cells in low (E:T 1:1) and high (E:T 1:≥5) tumor burden, with and without pomalidomide (POM) and IL-2. Tumor killing and T cell phenotype were assessed by flow cytometry at 24-72 hours. This controlled system allowed us to focus on putative CAR-T cell intrinsic impact of IMiDs. Results In low tumor burden setting, CAR-T effectively killed tumor at all timepoints, with or without POM; addition of POM increased T cell number, confirming that IMiDs support CAR-T expansion. Unexpectedly, in high tumor burden (E:T 1:≥5), adding POM diminished CAR-T mediated killing over time and hindered CAR-T expansion. Moreover, combination with POM decreased granzyme B, while increased expression of exhaustion marker TOX, ultimately leading to CAR-T apoptosis. This phenotype was further intensified by increasing concentrations of IL-2 in the co-culture, resulting in increased expression of CAR-T expressing LAG-3, TIM-3, and TIGIT, suggesting that CAR-T cells may be overactivated by POM and IL-2. Our manufacturing protocol preferentially expands memory CAR-T cells, favored for their durability, proliferative capacity, and considered to rapidly expand upon encounter with antigen. We reasoned that CAR-T are already sufficiently activated by CAR/CD3z stimulation, especially with a CD28 co-stimulatory domain (versus 4-1BB), known promote rapid, effector memory expansion upon activation (Kawalekar, Immunity, 2016). Activation is intensified by high tumor burden where antigen is highly abundant. We hypothesize under intense, sustained antigen exposure in high tumor burden, the addition of POM paradoxically triggers activation induced cell death (AICD). Conclusion Although it is well accepted that POM can boost T cell function and proliferation, we demonstrate that in high tumor burden, POM drives memory CAR-T to increase exhaustion markers and apoptotic cell death by overactivation, further exacerbated by exogenous IL-2. Interestingly, we have shown opposite effects of preclinically combining POM with TCE therapy in high tumor burden, based on dosing schedule. Concomitant administration transiently boosted T cell activation improving response rates but rapidly led to T cell exhaustion (Meermeier, Blood Cancer Discov, 2021). In contrast, IMiD pretreatment in the context of step-up dosing TCE administration improved T cell fitness and longevity (Meermeier, Blood, in press).The effect of IMiDs on T cells transcriptional program is likely to differ depending on differentiation stage and mode of T cell activation. Memory cells have more sensitive TCR signaling (Kumar, Immunity, 2011) and can be hyperactivated, leading to AICD. Thus, timing of IMiD administration, when tumor burden is low, may be a critical consideration as different T cell subsets require different levels of activation. Conversely, TCE provide only initial activation via TCR signaling, therefore POM may help in providing necessary co-stimulation in this setting. Future studies will evaluate different co-stimulatory domains and test in vivo effects of POM on CAR-T expansion and persistence, particularly as CAR-T cells diminish over time as tumor burden increases.

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.

Introduction/Background: Bispecific T cell engagers (TCE) targeting BCMA and CD3 induce deep hematologic responses in approximately 60% of heavily pre-treated multiple myeloma (MM) patients. There is an unmet need to overcome primary resistance, as this off-the-shelf therapy is readily available to patients with aggressive disease relapse and has the potential to be delivered in the community. We and others found that high tumor burden leads to primary resistance to TCE 1,2,3,4 and that combination with immunomodulatory drugs (IMiDs) transiently improves responses yet exacerbates T cell exhaustion2. Here, we present preclinical strategies to overcome primary resistance which are tolerable and provide more durable responses specifically for the high tumor burden setting. Methods: We evaluated response and survival to a murine surrogate BCMA/CD3 TCE in the Vk*MYC immunocompetent mouse model of MM expressing human CRBN to investigate tumor burden as a mechanism underpinning primary resistance. We evaluated dosing methods and combination strategies with IMiDs or novel CELMoDs, checkpoint inhibitors, and dexamethasone to improve response rates while maintaining a manageable safety profile. Results: We investigated primary resistance in an expanded panel of Vk*MYC models reflecting differing genomic heterogeneity and confirmed that a threshold of tumor burden limits T cell activation and correlates with resistance to TCE. BCMA is cleaved from the tumor cell surface by gamma-secretase and thus, high density of shed BCMA may act as a sponge to BCMA TCE. However, we found that administration of gamma-secretase inhibitors, while stabilizing BCMA expression on MM cells, is not sufficient to overcome high tumor burden-driven resistance to TCE. We previously reported the combinatorial activity of BCMA TCE with IMiDs and revealed a role for tumor-extrinsic effects of IMiDs in allowing mice with a high tumor burden to transiently respond to BCMA-TCE before T cell exhaustion prevailed2. To build on that combination strategy, we first hypothesized that the addition of a PD1 checkpoint inhibitor could reduce T cell exhaustion that occurs in response the BCMA-TCE in the resistant setting. We found that this triple combination provides more persistent activation and expansion of cytolytic T cells and sustains remission but leads to toxic cytokine release syndrome and early mortality in half of the cohort. Next, to address the acute toxicity from the hyperactivated T cell response and reduce tumor burden, we combined the triple combination with dexamethasone (Dex). To our surprise, concurrent Dex, even in the absence of IMiDs/CELMoDs, boosts responses to TCE. We observe that Dex moderates T cell proliferation in response to the TCE and leads to a moderate sustained cytokine production (IFN-γ, TNF, and IL-2R) systemically and in the bone marrow compared with a high transient burst seen with TCE alone or the concurrent treatment with IMiD + PD1 blockade. We determined that incremental step-up TCE dosing allows the combination of IMiDs or CELMoDs (iberdomide or mezigdomide) with Dex to be completely tolerated. To investigate whether delivering IMiD or CELMoDs before or during TCE administration altered efficacy, we tested pre-treatment with IMiDs/CELMoDs + Dex compared with concurrent dosing and found pre-treatment led to superior durable responses. Pre-treatment with iberdomide + Dex followed by step-up dosed TCE generated 100% response rate and the highest overall survival in subjects bearing a high tumor burden. This was accompanied by a more favorable T cell profiling over time, with limited expansion of regulatory T cells and reduced accumulation of exhausted T cells. Conclusion: Modelling the dosing and combination strategies of a BCMA-TCE in our immunocompetent system has allowed us to understand the dynamic changes in T cell fitness that are required for effective, tolerable, and durable TCE therapy for MM. We illustrate how improvements to TCE therapy mitigate T cell exhaustion and overcome primary resistance, and importantly, suggest a strong immunotherapeutic strategy for MM patients with challenging-to-treat actively progressing disease. 1. Lee et al., Nat Med 29, 2295-2306 (2023) 2. Meermeier et al. Blood Cancer Discov. 2021 Jul;2(4):354-369. 3. Rees et al. Blood Cancer J. 2024 Jul 23;14(1):122. 4. Girgis et al. Blood Adv. 2023 Feb 28;7(4):644-648

Background: Clonal hematopoiesis (CH) of indeterminate potential (CHIP) is a risk factor for cardiovascular disease. The relationship between CHIP and coronary microvascular dysfunction (CMD) is unknown. The current study examines the association between CHIP and CH with CMD and the potential relationships in risk for adverse cardiovascular outcomes. Methods: In this retrospective observational study, targeted next-generation sequencing was performed for 177 participants with no coronary artery disease who presented with chest pain and underwent routine coronary functional angiogram. Patients with somatic mutations in leukemia-associated driver genes in hematopoietic stem and progenitor cells were examined; CHIP was considered at a variant allele fraction ≥2%; CH was considered at a variant allele fraction ≥1%. CMD was defined as coronary flow reserve to intracoronary adenosine of ≤2. Major adverse cardiovascular events considered were myocardial infarction, coronary revascularization, or stroke. Results: A total of 177 participants were examined. Mean follow-up was 12±7 years. A total of 17 patients had CHIP and 28 had CH. Cases with CMD (n=19) were compared with controls with no CMD (n=158). Cases were 56±9 years, were 68% women, and had more CHIP (27%; P =0.028) and CH (42%; P =0.001) than controls. CMD was associated with independent risk for major adverse cardiovascular events (hazard ratio, 3.89 [95% CI, 1.21–12.56]; P =0.023), and 32% of this risk was mediated by CH. The risk mediated by CH was ≈0.5× as large as the direct effect of CMD on major adverse cardiovascular events. Conclusions: In humans, we observe patients with CMD are more likely to have CHIP, and nearly one-third of major adverse cardiovascular events in CMD are mediated by CH.

AbstractIdentifying biomarkers associated with disease progression and drug resistance are important for personalized care. We investigated the expression of 121 curated genes, related to immunomodulatory drugs (IMiDs) and proteasome inhibitors (PIs) responsiveness. We analyzed 28 human multiple myeloma (MM) cell lines with known drug sensitivities and 130 primary MM patient samples collected at different disease stages, including newly diagnosed (ND), on therapy (OT), and relapsed and refractory (RR, collected within 12 months before the patients’ death) timepoints. Our findings led to the identification of a subset of genes linked to clinical drug resistance, poor survival, and disease progression following combination treatment containing IMIDs and/or PIs. Finally, we built a seven‐gene model (MM‐IMiD and PI sensitivity‐7 genes [IP‐7]) using digital gene expression profiling data that significantly separates ND patients from IMiD‐ and PI‐refractory RR patients. Using this model, we retrospectively analyzed RNA sequcencing (RNAseq) data from the Mulltiple Myeloma Research Foundation (MMRF) CoMMpass (n = 578) and Mayo Clinic MM patient registry (n = 487) to divide patients into probabilities of responder and nonresponder, which subsequently correlated with overall survival, disease stage, and number of prior treatments. Our findings suggest that this model may be useful in predicting acquired resistance to treatments containing IMiDs and/or PIs.

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 Aims We aimed to test the hypothesis that the presence of clonal hematopoiesis of indeterminate potential (CHIP) in peripheral blood cells is associated with coronary endothelial dysfunction, enhanced inflammatory markers, and major adverse cardiovascular events (MACE).Methods and results We compared targeted next generation sequencing (35 CHIP related genes) between patients with coronary endothelial dysfunction (n = 123) and controls (n=65). Coronary endothelial dysfunction was defined by ≥ 20% decrease in coronary artery diameter (CAD) or ≤ 50% increase in coronary blood flow (CBF) in response to acetylcholine injection compared to baseline. Plasma cytokine levels of Interleukin (IL)-6 and IL-8 were also assessed. Patients were subsequently followed for 12.2 ± 4.3 years. Clonal hematopoiesis relevant gene mutations were found in 1 individual in normal endothelial function group (1.5%) and 11 cases in endothelial dysfunction group (9.3%) (p = 0.04). Additionally, CHIP mutations were associated with an increased risk of MACE (OR = 4.08, P = 0.04). Mutations in ASXL1, DNMT3A and TET2 in the endothelial dysfunction group were also associated with increased levels of IL-6 and IL-8 (P = 0.001, P = 0.003; respectively).Conclusion The current study demonstrates a high frequency of CHIP in patients with coronary endothelial dysfunction as well as an association between mutations in three most common epigenetic regulator genes and increased levels of IL-6 and IL-8. Therefore it infers a probable relationship between CHIP, endothelial dysfunction and cardiovascular adverse events.

Abstract HACS1 is a SH3 (Src homology 3) and SAM (sterile alpha motif) domain containing adaptor protein that is expressed in activated B and dendritic cells, is up-regulated by Interleukin 4 in the process of B cell activation and likely serves to dampen the immune response. To elucidate the function of HACS1, we generated HACS1 gene knockout mice by deletion of the SH3 and SAM domains. HACS1−/− mice were viable and fertile and had normal bone marrow B cell development and normal splenic T and B cell populations. However, adult HACS1−/− mice had increased numbers of peritoneal B1 cells (IgM+CD5+). Upon LPS plus BCR or TCR stimulations, splenic cells from HACS1−/− mice demonstrated an upregulation of activation markers with increased intensity of CD23 expression or increased population of CD69 positive cells. Purified B220+ splenic B cells from HACS1−/− mice showed increased cell proliferation upon BCR stimulation. Both T helper type 1 (Th1) and T helper type 2 (Th2) humoral responses were enhanced in HACS1−/− mice upon immunization with T cell-dependent antigen NP-KLH, which resulted in increased production of interferon-gamma (IFN-γ), anti-NP IgG2a and IL-4, as well as anti-NP IgG1 and IgE. Upon immunization with T cell-independent antigens such as TNP-LPS and TNP-Ficoll, HACS1−/− mice had increased production of anti-TNP IgM and IgG3 as compared to normal controls. The in vitro maturation of bone marrow-derived dentritic cells from HACS1−/− mice was similar to wild-type mice but HACS1−/− dentritic cells showed increased IL-12 production upon stimulation with anti-CD40 or LPS. There was no significant difference in antigen uptake by cultured dentritic cells from non-immunized wild-type or knockout mice. However, in immunized mice, an increase in antigen uptake in HACS1−/− dentritic cells was observed. We further demonstrate that the HACS1−/− B cells had increased tyrosine phosphorylation in the resting state. As deletion of the SH3 & SAM domains of HACS1 appears to generate a hypersensitive immune response, our results collectively support that HACS1 negatively regulates adaptive immunity.

Background Encapsulating peritoneal sclerosis (EPS) is a rare complication of peritoneal dialysis. The causes of EPS are not well defined and are likely multifactorial. A suitable animal model would facilitate research into the pathophysiology and treatment of EPS. Methods We developed a helper-dependent adenovirus that expresses both green fluorescent protein (GFP) and active transforming growth factor-beta (TGF-β1; HDAdTGF-β1). Mice were administered HDAdTGF-β1 via intraperitoneal injection and the response was compared with mice administered either first-generation adenovirus expressing TGF-β1 (AdTGF-β1) or control adenovirus (AdGFP). Results HDAdTGF-β1-treated mice continued to express the GFP reporter transgene to day 74, the end of the observation period. Transgene expression lasted less than 28 days in the animals treated with first-generation adenoviruses. Animals treated with first-generation AdTGF-β1 demonstrated submesothelial thickening and angiogenesis at day 7, with almost complete resolution by day 28. The HDAdTGF-β1-treated mice demonstrated progressive peritoneal fibrosis with adhesion formation and encapsulation of bowels. Weight gain was significantly reduced in animals treated with HDAdTGF-β1 compared to both the control-treated animals and the AdTGF-β1-treated animals. Inflammation was not a major component of the fibroproliferative response. Conclusions Peritoneal administration of a first-generation AdTGF-β1 leads to transient gene expression, resulting in a resolving fibrotic response and histology similar to that seen in simple peritoneal sclerosis. Prolonged TGF-β1 expression induced by the helper-dependent HDAdTGF-β1 led to changes in peritoneal morphology resembling EPS. This suggests that TGF-β1 may be a contributing factor in both simple peritoneal sclerosis and EPS. This model will be useful for elucidation of the mechanism of EPS and evaluation of potential treatment.