CD33 target validation and sustained depletion of AML blasts in long-term cultures by the bispecific T-cell-engaging antibody AMG 330

A review of immunotargeted therapy for Philadelphia chromosome positive acute lymphoblastic leukaemia: making progress in chemotherapy-free regimens

Philadelphia chromosome-positive acute lymphoblastic leukemia (PH + ALL) is the most common cytogenetic abnormality of B-ALL in adults and is associated with poor prognosis. Previously, the only curative treatment option in PH + ALL was allogeneic hematopoietic stem cell transplantation (Allo-HSCT). Since 2000, targeted therapy combined with chemotherapy, represented by the tyrosine kinase inhibitor Imatinib, has become the first-line treatment for PH + ALL. Currently, the remission rate and survival rate of Imatinib are superior to those of simple chemotherapy, and it can also improve the efficacy of transplantation. More recently, some innovative immune-targeted therapy greatly improved the prognosis of PH + ALL, such as Blinatumomab and Inotuzumab Ozogamicin. For patients with ABL1 mutations and those who have relapsed or are refractory to other treatments, targeted oral small molecule drugs, monoclonal antibodies, Bispecific T cell Engagers (BiTE), and chimeric antigen receptor (CAR) T cells immunotherapy are emerging as potential treatment options. These new therapeutic interventions are changing the treatment landscape for PH + ALL. In summary, this review discusses the current advancements in targeted therapeutic agents shift in the treatment strategy of PH + ALL towards using more tolerable chemotherapy-free induction and consolidation regimens confers better disease outcomes and might obviate the need for HSCT.

Industry Perspective on First-in-Human and Clinical Pharmacology Strategies to Support Clinical Development of T-Cell Engaging Bispecific Antibodies for Cancer Therapy

T-cell-engaging bispecific antibodies (TCEs) that target tumor antigens and T cells have shown great promise in treating cancer, particularly in hematological indications. The clinical development of TCEs often involves a lengthy first-in-human (FIH) trial with many dose-escalation cohorts leading up to an early proof of concept (POC), enabling either a no-go decision or dose selection for further clinical development. Multiple factors related to the target, product, disease, and patient population influence the efficacy and safety of TCEs. The intricate mechanism of action limits the translatability of preclinical models to the clinic, thereby posing challenges to streamline clinical development. In addition, unlike traditional chemotherapy, the top dose and recommended phase II doses (RP2Ds) for TCEs in the clinic are often not guided by the maximum tolerated dose (MTD), but rather based on the integrated dose-response assessment of the benefit/risk profile. These uncertainties pose complex challenges for translational and clinical pharmacologists (PK/PD scientists), as well as clinicians, to design an efficient clinical study that guides development. To that end, experts in the field, under the umbrella of the American Association of Pharmaceutical Scientists, have reviewed learnings from published literature and currently marketed products to share perspectives on the FIH and clinical pharmacology strategies to support early clinical development of TCEs.

Targeting the membrane-proximal C2-set domain of CD33 for improved CAR T cell therapy

Current CD33-targeted immunotherapies typically recognize the membrane-distal V-set domain of CD33. Here, we show that decreasing the distance between T cell and leukemia cell membrane increases the efficacy of CD33 chimeric antigen receptor (CAR) T cells. We therefore generated and optimized second-generation CAR constructs containing single-chain variable fragments from antibodies raised against the membrane-proximal C2-set domain, which bind CD33 regardless of whether the V-set domain is present (CD33PAN antibodies). CD33PAN CAR T cells resulted in efficient tumor clearance and improved survival of immunodeficient mice bearing human AML cell xenografts and, in an AML model with limited CD33 expression, forced escape of CD33neg leukemia. Compared to CD33V-set CAR T cells, CD33PAN CAR T cells showed greater in vitro and in vivo efficacy against several human AML cell lines with differing levels of CD33 without increased expression of exhaustion markers. CD33PAN moieties were detected at a higher frequency on human leukemic stem cells, and CD33PAN CAR T cells had greater in vitro efficacy against primary human AML cells. Together, our studies demonstrate improved efficacy with CAR T cells binding CD33 close to the cell membrane, providing the rationale to investigate CD33PAN CAR T cells further toward possible clinical application.

Safety and tolerability of AMG 330 in adults with relapsed/refractory AML: a phase 1a dose-escalation study

AMG 330, a bispecific T-cell engager (BiTE®) that binds CD33 and CD3 on T cells facilitates T-cell-mediated cytotoxicity against CD33+ cells. This first-in-human, open-label, dose-escalation study evaluated the safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy of AMG 330 in adults with relapsed/refractory acute myeloid leukemia (R/R AML). Amongst 77 patients treated with AMG 330 (0.5 µg/day-1.6 mg/day) on 14-day or 28-day cycles, maximum tolerated dose was not reached; median duration of treatment was 29 days. The most frequent treatment-related adverse events were cytokine release syndrome (CRS; 78%) and rash (30%); 10% of patients experienced grade 3/4 CRS. CRS was mitigated with stepwise dosing of AMG 330, prophylactic dexamethasone, and early treatment with tocilizumab. Among 60 evaluable patients, eight achieved complete remission or morphologic leukemia-free state; of the 52 non-responders, 37% had ≥50% reduction in AML bone marrow blasts. AMG 330 is a promising CD33-targeted therapeutic strategy for R/R AML.

Bispecific antibodies: advancing precision oncology

Bispecific antibodies (bsAbs) are engineered molecules designed to target two different epitopes or antigens. The mechanism of action is determined by the bsAb molecular targets and structure (or format), which can be manipulated to create variable and novel functionalities, including linking immune cells with tumor cells, or dual signaling pathway blockade. Several bsAbs have already changed the treatment landscape of hematological malignancies and select solid cancers. However, the mechanisms of resistance to these agents are understudied and the management of toxicities remains challenging. Herein, we review the principles in bsAb engineering, current understanding of mechanisms of action and resistance, data for clinical application, and provide a perspective on ongoing challenges and future developments in this field.

Breaking Boundaries: Immunotherapy for Myeloid Malignancies

Immunotherapy has revolutionized the treatment of myeloid oncologic diseases, particularly for patients resistant to chemotherapy or ineligible for allogeneic stem cell transplantation due to age or fitness constraints. As our understanding of the immunopathogenesis of myeloid malignancies expands, so too do the treatment options available to patients. Immunotherapy in myeloid malignancies, however, faces numerous challenges due to the dynamic nature of the disease, immune dysregulation, and the development of immune evasion mechanisms. This review outlines the progress made in the field of immunotherapy for myeloid malignancies, addresses its challenges, and provides insights into future directions in the field.

Advances and clinical applications of immune checkpoint inhibitors in hematological malignancies

Immune checkpoints are differentially expressed on various immune cells to regulate immune responses in tumor microenvironment. Tumor cells can activate the immune checkpoint pathway to establish an immunosuppressive tumor microenvironment and inhibit the anti-tumor immune response, which may lead to tumor progression by evading immune surveillance. Interrupting co-inhibitory signaling pathways with immune checkpoint inhibitors (ICIs) could reinvigorate the anti-tumor immune response and promote immune-mediated eradication of tumor cells. As a milestone in tumor treatment, ICIs have been firstly used in solid tumors and subsequently expanded to hematological malignancies, which are in their infancy. Currently, immune checkpoints have been investigated as promising biomarkers and therapeutic targets in hematological malignancies, and novel immune checkpoints, such as signal regulatory protein α (SIRPα) and tumor necrosis factor-alpha-inducible protein 8-like 2 (TIPE2), are constantly being discovered. Numerous ICIs have received clinical approval for clinical application in the treatment of hematological malignancies, especially when used in combination with other strategies, including oncolytic viruses (OVs), neoantigen vaccines, bispecific antibodies (bsAb), bio-nanomaterials, tumor vaccines, and cytokine-induced killer (CIK) cells. Moreover, the proportion of individuals with hematological malignancies benefiting from ICIs remains lower than expected due to multiple mechanisms of drug resistance and immune-related adverse events (irAEs). Close monitoring and appropriate intervention are needed to mitigate irAEs while using ICIs. This review provided a comprehensive overview of immune checkpoints on different immune cells, the latest advances of ICIs and highlighted the clinical applications of immune checkpoints in hematological malignancies, including biomarkers, targets, combination of ICIs with other therapies, mechanisms of resistance to ICIs, and irAEs, which can provide novel insight into the future exploration of ICIs in tumor treatment.

Novel Vpx virus-like particles to improve cytarabine treatment response against acute myeloid leukemia

Knowledge of the molecular pathogenesis of acute myeloid leukemia has advanced in recent years. Despite novel treatment options, acute myeloid leukemia remains a survival challenge for elderly patients. We have recently shown that the triphosphohydrolase SAMHD1 is one of the factors determining resistance to Ara-C treatment. Here, we designed and tested novel and simpler virus-like particles incorporating the lentiviral protein Vpx to efficiently and transiently degrade SAMHD1 and increase the efficacy of Ara-C treatment. The addition of minute amounts of lentiviral Rev protein during production enhanced the generation of virus-like particles. In addition, we found that our 2nd generation of virus-like particles efficiently targeted and degraded SAMHD1 in AML cell lines with high levels of SAMHD1, thereby increasing Ara-CTP levels and response to Ara-C treatment. Primary AML blasts were generally less responsive to VLP treatment. In summary, we have been able to generate novel and simpler virus-like particles that can efficiently deliver Vpx to target cells.

The Immunotherapy of Acute Myeloid Leukemia: A Clinical Point of View

The potential of the immune system to eradicate leukemic cells has been consistently demonstrated by the Graft vs. Leukemia effect occurring after allo-HSCT and in the context of donor leukocyte infusions. Various immunotherapeutic approaches, ranging from the use of antibodies, antibody-drug conjugates, bispecific T-cell engagers, chimeric antigen receptor (CAR) T-cells, and therapeutic infusions of NK cells, are thus currently being tested with promising, yet conflicting, results. This review will concentrate on various types of immunotherapies in preclinical and clinical development, from the point of view of a clinical hematologist. The most promising therapies for clinical translation are the use of bispecific T-cell engagers and CAR-T cells aimed at lineage-restricted antigens, where overall responses (ORR) ranging from 20 to 40% can be achieved in a small series of heavily pretreated patients affected by refractory or relapsing leukemia. Toxicity consists mainly in the occurrence of cytokine-release syndrome, which is mostly manageable with step-up dosing, the early use of cytokine-blocking agents and corticosteroids, and myelosuppression. Various cytokine-enhanced natural killer products are also being tested, mainly as allogeneic off-the-shelf therapies, with a good tolerability profile and promising results (ORR: 20-37.5% in small trials). The in vivo activation of T lymphocytes and NK cells via the inhibition of their immune checkpoints also yielded interesting, yet limited, results (ORR: 33-59%) but with an increased risk of severe Graft vs. Host disease in transplanted patients. Therefore, there are still several hurdles to overcome before the widespread clinical use of these novel compounds.

The present and future of bispecific antibodies for cancer therapy

Bispecific antibodies (bsAbs) enable novel mechanisms of action and/or therapeutic applications that cannot be achieved using conventional IgG-based antibodies. Consequently, development of these molecules has garnered substantial interest in the past decade and, as of the end of 2023, 14 bsAbs have been approved: 11 for the treatment of cancer and 3 for non-oncology indications. bsAbs are available in different formats, address different targets and mediate anticancer function via different molecular mechanisms. Here, we provide an overview of recent developments in the field of bsAbs for cancer therapy. We focus on bsAbs that are approved or in clinical development, including bsAb-mediated dual modulators of signalling pathways, tumour-targeted receptor agonists, bsAb-drug conjugates, bispecific T cell, natural killer cell and innate immune cell engagers, and bispecific checkpoint inhibitors and co-stimulators. Finally, we provide an outlook into next-generation bsAbs in earlier stages of development, including trispecifics, bsAb prodrugs, bsAbs that induce degradation of tumour targets and bsAbs acting as cytokine mimetics.

CD8 + T cell-based molecular subtypes with heterogeneous immune landscapes and clinical significance in acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy. Although high-dose chemotherapy is the primary treatment option, it cannot cure the disease, and new approaches need to be developed. The tumor microenvironment (TME) plays a crucial role in tumor biology and immunotherapy. CD8 + T cells are the main anti-tumor immune effector cells, and it is essential to understand their relationship with the TME and the clinicopathological characteristics of AML.

METHODS

In this study, we conducted a systematic analysis of CD8 + T cell infiltration through multi-omics data and identified molecular subtypes with significant differences in CD8 + T cell infiltration and prognosis. We aimed to provide a comprehensive evaluation of the pathological factors affecting the prognosis of AML patients and to offer theoretical support for the precise treatment of AML.

RESULTS

Our results indicate that CD8 + T cell infiltration is accompanied by immunosuppression, and that there are two molecular subtypes, with the C2 subtype having a significantly worse prognosis than the C1 subtype, as well as less CD8 + T cell infiltration. We developed a signature to distinguish molecular subtypes using multiple machine learning algorithms and validated the prognostic predictive power of molecular subtypes in nine AML cohorts including 2059 AML patients. Our findings suggest that there are different immunosuppressive characteristics between the two subtypes. The C1 subtype has up-regulated expression of immune checkpoints such as CTLA4, PD-1, LAG3, and TIGITD, while the C2 subtype infiltrates more immunosuppressive cells such as Tregs and M2 macrophages. The C1 subtype is more responsive to anti-PD-1 immunotherapy and induction chemotherapy, as well as having higher immune and cancer-promoting variant-related pathway activity. Patients with the C2 subtype had a higher FLT3 mutation rate, higher WBC counts, and a higher percentage of blasts, as indicated by increased activity of signaling pathways involved in energy metabolism and cell proliferation. Analysis of data from ex vivo AML cell drug assays has identified a group of drugs that differ in therapeutic sensitivity between molecular subtypes.

CONCLUSIONS

Our results suggest that the molecular subtypes we constructed have potential application value in the prognosis evaluation and treatment guidance of AML patients.

Preclinical Characterization of the Anti-Leukemia Activity of the CD33/CD16a/NKG2D Immune-Modulating TriNKET® CC-96191

Increasing efforts are focusing on natural killer (NK) cell immunotherapies for AML. Here, we characterized CC-96191, a novel CD33/CD16a/NKG2D immune-modulating TriNKET®. CC-96191 simultaneously binds CD33, NKG2D, and CD16a, with NKG2D and CD16a co-engagement increasing the avidity for, and activation of, NK cells. CC-96191 was broadly active against human leukemia cells in a strictly CD33-dependent manner, with maximal efficacy requiring the co-engagement of CD16a and NKG2D. A frequent CD33 single nucleotide polymorphism, R69G, reduced CC-96191 potency but not maximal activity, likely because of reduced CD33 binding. Similarly, the potency, but not the maximal activity, of CC-96191 was reduced by high concentrations of soluble CD33; in contrast, the soluble form of the NKG2D ligand MICA did not impact activity. In the presence of CD33+ AML cells, CC-96191 activated NK cells but not T cells; while maximum anti-AML efficacy was similar, soluble cytokine levels were 10- to >100-fold lower than with a CD33/CD3 bispecific antibody. While CC-96191-mediated cytolysis was not affected by ABC transporter proteins, it was reduced by anti-apoptotic BCL-2 family proteins. Finally, in patient marrow specimens, CC-96191 eliminated AML cells but not normal monocytes, suggesting selectivity of TriNKET-induced cytotoxicity toward neoplastic cells. Together, these findings support the clinical exploration of CC-96191 as in NCT04789655.

Gemtuzumab ozogamicin for relapsed or primary refractory acute myeloid leukemia in children-the Polish Pediatric Leukemia and Lymphoma Study Group experience

Background

Gemtuzumab ozogamicin (GO), one of the first targeted drugs used in oncology, consists of an anti-cluster of differentiation 33 (CD33) monoclonal antibody bound to a derivative of cytotoxic calicheamicin. After the drug withdrawn in 2010 due to a significantly higher rate of early deaths, GO regained approval in 2017 for the treatment of newly diagnosed, refractory, or relapsed acute myeloid leukemia (AML) in adults and children over 15 years of age. The objective of the study was a retrospective analysis of clinical characteristics, treatment outcomes, and GO toxicity profile in children with primary refractory or relapsed (R/R) AML treated in Poland from 2008 to 2022.

Methods

Data were collected through the Polish Registry of Acute Myeloid Leukemia. From January 2008 to December 2022, 35 children with R/R AML were treated with GO in seven centers of the Polish Pediatric Leukemia and Lymphoma Study Group.

Results

Most of the children (30 of 35) received only one GO cycle in combination with various chemotherapy cycles (IDA-FLA, DOXO-FLA, FLA, FLAG, and others). Eighteen children (51%) achieved complete remission (CR), 14 did not respond to treatment, and three progressed. GO therapy was followed by allogeneic hematopoietic stem cell transplantation (allo-HSCT) in 18 children in CR. The 5-year overall survival (OS) after GO therapy was 37.1% ± 8.7% for the total cohort. There was a trend toward a superior outcome in patients with strong expression of CD33 expression (over 50% positive cells) compared with that in patients with lower expression of CD33 (OS, 41.2% ± 11.9% versus 27.8% ± 13.2%; p = 0.5; 5-year event-free survival, 35.4% ± 11.6% versus 25.7% ± 12.3%; p = 0.5, respectively). Children under 15 years have better outcome (OS, 34.9% ± 10.4% versus 30% ± 14.5%, p = 0.3). The most common adverse events were bone marrow aplasia, fever of unknown origin, infections, and elevated liver enzyme elevation. Sinusoidal obstruction syndrome occurred in two children.

Conclusions

The use of GO in severely pretreated children, including those under 15 years of age, with previous failure of AML treatment is a feasible and effective bridging therapy to allo-HSCT with an acceptable toxicity profile.

Chimeric Antigen Receptor T Cell Therapy in Acute Myeloid Leukemia: Trials and Tribulations

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy that is often associated with relapse and drug resistance after standard chemotherapy or targeted therapy, particularly in older patients. Hematopoietic stem cell transplants are looked upon as the ultimate salvage option with curative intent. Adoptive cell therapy using chimeric antigen receptors (CAR) has shown promise in B cell malignancies and is now being investigated in AML. Initial clinical trials have been disappointing in AML, and we review current strategies to improve efficacy for CAR approaches. The extensive number of clinical trials targeting different antigens likely reflects the genetic heterogeneity of AML. The limited number of patients reported in multiple early clinical studies makes it difficult to draw conclusions about CAR safety, but it does suggest that the efficacy of this approach in AML lags behind the success observed in B cell malignancies. There is a clear need not only to improve CAR design but also to identify targets in AML that show limited expression in normal myeloid lineage cells.

Harnessing autologous immune effector mechanisms in acute myeloid leukemia: 2023 update of trials and tribulations

Numerous recent advances have been made in therapeutic approaches toward acute myeloid leukemia (AML). Since 2017, we have seen eleven novel Food & Drug Administration (FDA)-approved medications for AML, all of which extend beyond the classical cytarabine-based cytostatic chemotherapy. In the recent two decades, the role of immune surveillance in AML has been intensively investigated. The power of one's own innate and adaptive immunity has been harnessed pharmacologically toward the goal of clearance of AML cells. Specifically, pre-clinical studies have shown great promise for antibodies that disinhibit T cells and macrophages by blocking checkpoint receptors within the immunologic synapse, thereby resulting in the elimination of AML cells. Anti-CD33 CAR-T therapies and anti-CD3/CD123 bispecific antibodies have also exhibited encouraging results in pre-clinical and early clinical studies. However, despite these translational efforts, we currently have no immune-based therapies for AML on the market, with the exception of gemtuzumab ozogamicin. In this focused review, we discuss molecular target validation and the most relevant clinical updates for immune-based experimental therapeutics including anti-CD47 monoclonal antibodies, CAR-T therapies, and bispecific T cell engagers. We highlight barriers to the clinical translation of these therapies in AML, and we propose solutions to optimize the manufacturing and delivery of the most novel immune-based therapies in the pipeline.

Bispecific Antibodies in Hematological Malignancies: A Scoping Review

Bispecific T-cell engagers (BiTEs) and bispecific antibodies (BiAbs) have revolutionized the treatment landscape of hematological malignancies. By directing T cells towards specific tumor antigens, BiTEs and BiAbs facilitate the T-cell-mediated lysis of neoplastic cells. The success of blinatumomab, a CD19xCD3 BiTE, in acute lymphoblastic leukemia spearheaded the expansive development of BiTEs/BiAbs in the context of hematological neoplasms. Nearly a decade later, numerous BiTEs/BiAbs targeting a range of tumor-associated antigens have transpired in the treatment of multiple myeloma, non-Hodgkin's lymphoma, acute myelogenous leukemia, and acute lymphoblastic leukemia. However, despite their generally favorable safety profiles, particular toxicities such as infections, cytokine release syndrome, myelosuppression, and neurotoxicity after BiAb/BiTE therapy raise valid concerns. Moreover, target antigen loss and the immunosuppressive microenvironment of hematological neoplasms facilitate resistance towards BiTEs/BiAbs. This review aims to highlight the most recent evidence from clinical trials evaluating the safety and efficacy of BiAbs/BiTEs. Additionally, the review will provide mechanistic insights into the limitations of BiAbs whilst outlining practical applications and strategies to overcome these limitations.

Adapter CAR T cells to counteract T-cell exhaustion and enable flexible targeting in AML

Although the landscape for treating acute myeloid leukemia (AML) patients has changed substantially in recent years, the majority of patients will eventually relapse and succumb to their disease. Allogeneic stem cell transplantation provides the best anti-AML treatment strategy, but is only suitable in a minority of patients. In contrast to B-cell neoplasias, chimeric antigen receptor (CAR) T-cell therapy in AML has encountered challenges in target antigen heterogeneity, safety, and T-cell dysfunction. We established a Fab-based adapter CAR (AdCAR) T-cell platform with flexibility of targeting and control of AdCAR T-cell activation. Utilizing AML cell lines and a long-term culture assay for primary AML cells, we were able to demonstrate AML-specific cytotoxicity using anti-CD33, anti-CD123, and anti-CLL1 adapter molecules in vitro and in vivo. Notably, we show for the first time the feasibility of sequential application of adapter molecules of different specificity in primary AML co-cultures. Importantly, using the AML platform, we were able to demonstrate that chronic T-cell stimulation and exhaustion can be counteracted through introduction of treatment-free intervals. As T-cell exhaustion and target antigen heterogeneity are well-known causes of resistance, the AdCAR platform might offer effective strategies to ameliorate these limitations.

CD33 BiTE® molecule-mediated immune synapse formation and subsequent T-cell activation is determined by the expression profile of activating and inhibitory checkpoint molecules on AML cells

Bispecific T-cell engager (BiTE^®) molecules recruit T cells to cancer cells through CD3ε binding, independently of T-cell receptor (TCR) specificity. Whereas physiological T-cell activation is dependent on signal 1 (TCR engagement) and signal 2 (co-stimulation), BiTE molecule-mediated T-cell activation occurs without additional co-stimulation. As co-stimulatory and inhibitory molecules modulate the strength and nature of T-cell responses, we studied the impact of the expression profile of those molecules on target cells for BiTE molecule-mediated T-cell activation in the context of acute myeloid leukemia (AML). Accordingly, we created a novel in vitro model system using murine Ba/F3 cells transduced with human CD33 ± CD86 ± PD-L1. T-cell fitness was assessed by T-cell function assays in co-cultures and immune synapse formation by applying a CD33 BiTE molecule (AMG 330). Using our cell-based model platform, we found that the expression of positive co-stimulatory molecules on target cells markedly enhanced BiTE molecule-mediated T-cell activation. The initiation and stability of the immune synapse between T cells and target cells were significantly increased through the expression of CD86 on target cells. By contrast, the co-inhibitory molecule PD-L1 impaired the stability of BiTE molecule-induced immune synapses and subsequent T-cell responses. We validated our findings in primary T-cell-AML co-cultures, demonstrating a PD-L1-mediated reduction in redirected T-cell activation. The addition of the immunomodulatory drug (IMiD) lenalidomide to co-cultures led to stabilization of immune synapses and improved subsequent T-cell responses. We conclude that target cells modulate CD33 BiTE molecule-dependent T-cell activation and hence, combinatorial strategies might contribute to enhanced efficacy.

Hydrogel-Based Pre-Clinical Evaluation of Repurposed FDA-Approved Drugs for AML

In vivo models of acute myeloid leukemia (AML) are low throughput, and standard liquid culture models fail to recapitulate the mechanical and biochemical properties of the extracellular matrix-rich protective bone marrow niche that contributes to drug resistance. Candidate drug discovery in AML requires advanced synthetic platforms to improve our understanding of the impact of mechanical cues on drug sensitivity in AML. By use of a synthetic, self-assembling peptide hydrogel (SAPH) of modifiable stiffness and composition, a 3D model of the bone marrow niche to screen repurposed FDA-approved drugs has been developed and utilized. AML cell proliferation was dependent on SAPH stiffness, which was optimized to facilitate colony growth. Three candidate FDA-approved drugs were initially screened against the THP-1 cell line and mAF9 primary cells in liquid culture, and EC50 values were used to inform drug sensitivity assays in the peptide hydrogel models. Salinomycin demonstrated efficacy in both an 'early-stage' model in which treatment was added shortly after initiation of AML cell encapsulation, and an 'established' model in which time-encapsulated cells had started to form colonies. Sensitivity to Vidofludimus treatment was not observed in the hydrogel models, and Atorvastatin demonstrated increased sensitivity in the 'established' compared to the 'early-stage' model. AML patient samples were equally sensitive to Salinomycin in the 3D hydrogels and partially sensitive to Atorvastatin. Together, this confirms that AML cell sensitivity is drug- and context-specific and that advanced synthetic platforms for higher throughput are valuable tools for pre-clinical evaluation of candidate anti-AML drugs.

Current nonclinical approaches for immune assessments of immuno-oncology biotherapeutics

Harnessing the immune system to kill tumors has been revolutionary and, as a result, has had an enormous benefit for patients in extending life and resulting in effective cures in some. However, activation of the immune system can come at the cost of undesirable adverse events such as cytokine release syndrome, immune-related adverse events, on-target/off-tumor toxicity, neurotoxicity and tumor lysis syndrome, which are safety risks that can be challenging to assess non-clinically. This article provides a review of the biology and mechanisms that can result in immune-mediated adverse effects and describes industry approaches using in vitro and in vivo models to aid in the nonclinical safety risk assessments for immune-oncology modalities. Challenges and limitations of knowledge and models are also discussed.

A perspective of immunotherapy for acute myeloid leukemia: Current advances and challenges

During the last decade, the underlying pathogenic mechanisms of acute myeloid leukemia (AML) have been the subject of extensive study which has considerably increased our understanding of the disease. However, both resistance to chemotherapy and disease relapse remain the principal obstacles to successful treatment. Because of acute and chronic undesirable effects frequently associated with conventional cytotoxic chemotherapy, consolidation chemotherapy is not feasible, especially for elderly patients, which has attracted a growing body of research to attempt to tackle this problem. Immunotherapies for acute myeloid leukemia, including immune checkpoint inhibitors, monoclonal antibodies, dendritic cell (DC) vaccines, together with T-cell therapy based on engineered antigen receptor have been developed recently. Our review presents the recent progress in immunotherapy for the treatment of AML and discusses effective therapies that have the most potential and major challenges.

Present and Future Role of Immune Targets in Acute Myeloid Leukemia

It is now well known that the bone marrow (BM) cell niche contributes to leukemogenesis, but emerging data support the role of the complex crosstalk between AML cells and the BM microenvironment to induce a permissive immune setting that protects leukemic stem cells (LSCs) from therapy-induced death, thus favoring disease persistence and eventual relapse. The identification of potential immune targets on AML cells and the modulation of the BM environment could lead to enhanced anti-leukemic effects of drugs, immune system reactivation, and the restoration of AML surveillance. Potential targets and effectors of this immune-based therapy could be monoclonal antibodies directed against LSC antigens such as CD33, CD123, and CLL-1 (either as direct targets or via several bispecific T-cell engagers), immune checkpoint inhibitors acting on different co-inhibitory axes (alone or in combination with conventional AML drugs), and novel cellular therapies such as chimeric antigen receptor (CAR) T-cells designed against AML-specific antigens. Though dozens of clinical trials, mostly in phases I and II, are ongoing worldwide, results have still been negatively affected by difficulties in the identification of the optimal targets on LSCs.

Immune dysfunction signatures predict outcomes and define checkpoint blockade-unresponsive microenvironments in acute myeloid leukemia

BackgroundImmune exhaustion and senescence are dominant dysfunctional states of effector T cells and major hurdles for the success of cancer immunotherapy. In the current study, we characterized how acute myeloid leukemia (AML) promotes the generation of senescent-like CD8+ T cells and whether they have prognostic relevance.METHODSWe analyzed NanoString, bulk RNA-Seq and single-cell RNA-Seq data from independent clinical cohorts comprising 1,896 patients treated with chemotherapy and/or immune checkpoint blockade (ICB).ResultsWe show that senescent-like bone marrow CD8+ T cells were impaired in killing autologous AML blasts and that their proportion negatively correlated with overall survival (OS). We defined what we believe to be new immune effector dysfunction (IED) signatures using 2 gene expression profiling platforms and reported that IED scores correlated with adverse-risk molecular lesions, stemness, and poor outcomes; these scores were a more powerful predictor of OS than 2017-ELN risk or leukemia stem cell (LSC17) scores. IED expression signatures also identified an ICB-unresponsive tumor microenvironment and predicted significantly shorter OS.ConclusionThe IED scores provided improved AML-risk stratification and could facilitate the delivery of personalized immunotherapies to patients who are most likely to benefit.TRIAL REGISTRATIONClinicalTrials.gov; NCT02845297.FUNDINGJohn and Lucille van Geest Foundation, Nottingham Trent University's Health & Wellbeing Strategic Research Theme, NIH/NCI P01CA225618, Genentech-imCORE ML40354, Qatar National Research Fund (NPRP8-2297-3-494).

Current landscape and future directions of bispecific antibodies in cancer immunotherapy

Recent advances in cancer immunotherapy using monoclonal antibodies have dramatically revolutionized the therapeutic strategy against advanced malignancies, inspiring the exploration of various types of therapeutic antibodies. Bispecific antibodies (BsAbs) are recombinant molecules containing two different antigens or epitopes identifying binding domains. Bispecific antibody-based tumor immunotherapy has gained broad potential in preclinical and clinical investigations in a variety of tumor types following regulatory approval of newly developed technologies involving bispecific and multispecific antibodies. Meanwhile, a series of challenges such as antibody immunogenicity, tumor heterogeneity, low response rate, treatment resistance, and systemic adverse effects hinder the application of BsAbs. In this review, we provide insights into the various architecture of BsAbs, focus on BsAbs' alternative different mechanisms of action and clinical progression, and discuss relevant approaches to overcome existing challenges in BsAbs clinical application.

Targeted therapy in NPM1-mutated AML: Knowns and unknowns

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by malignant proliferation of myeloid hematopoietic stem/progenitor cells. NPM1 represents the most frequently mutated gene in AML and approximately 30% of AML cases carry NPM1 mutations. Mutated NPM1 result in the cytoplasmic localization of NPM1 (NPM1c). NPM1c interacts with other proteins to block myeloid differentiation, promote cell proliferation and impair DNA damage repair. NPM1 is a good prognostic marker, but some patients ultimately relapse or fail to respond to therapy. It is urgent for us to find optimal therapies for NPM1-mutated AML. Efficacy of multiple drugs is under investigation in NPM1-mutated AML, and several clinical trials have been registered. In this review, we summarize the present knowledge of therapy and focus on the possible therapeutic interventions for NPM1-mutated AML.

Quantitative systems pharmacology modeling sheds light into the dose response relationship of a trispecific T cell engager in multiple myeloma

In relapsed and refractory multiple myeloma (RRMM), there are few treatment options once patients progress from the established standard of care. Several bispecific T-cell engagers (TCE) are in clinical development for multiple myeloma (MM), designed to promote T-cell activation and tumor killing by binding a T-cell receptor and a myeloma target. In this study we employ both computational and experimental tools to investigate how a novel trispecific TCE improves activation, proliferation, and cytolytic activity of T-cells against MM cells. In addition to binding CD3 on T-cells and CD38 on tumor cells, the trispecific binds CD28, which serves as both co-stimulation for T-cell activation and an additional tumor target. We have established a robust rule-based quantitative systems pharmacology (QSP) model trained against T-cell activation, cytotoxicity, and cytokine data, and used it to gain insight into the complex dose response of this drug. We predict that CD3-CD28-CD38 killing capacity increases rapidly in low dose levels, and with higher doses, killing plateaus rather than following the bell-shaped curve typical of bispecific TCEs. We further predict that dose–response curves are driven by the ability of tumor cells to form synapses with activated T-cells. When competition between cells limits tumor engagement with active T-cells, response to therapy may be diminished. We finally suggest a metric related to drug efficacy in our analysis—“effective” receptor occupancy, or the proportion of receptors engaged in synapses. Overall, this study predicts that the CD28 arm on the trispecific antibody improves efficacy, and identifies metrics to inform potency of novel TCEs.

Integrated multiomic approach for identification of novel immunotherapeutic targets in AML

BACKGROUND

Immunotherapy of acute myeloid leukemia has experienced considerable advances, however novel target antigens continue to be sought after. To this end, unbiased approaches for surface protein detection are limited and integration with other data types, such as gene expression and somatic mutational burden, are poorly utilized. The Cell Surface Capture technology provides an unbiased, discovery-driven approach to map the surface proteins on cells of interest. Yet, direct utilization of primary patient samples has been limited by the considerable number of viable cells needed.

METHODS

Here, we optimized the Cell Surface Capture protocol to enable direct interrogation of primary patient samples and applied our optimized protocol to a set of samples from patients with acute myeloid leukemia (AML) to generate the AML surfaceome. We then further curated this AML surfaceome to exclude antigens expressed on healthy tissues and integrated mutational burden data from hematologic cancers to further enrich for targets which are likely to be essential to leukemia biology. Finally, we validated our findings in a separate cohort of AML patient samples.

RESULTS

Our protocol modifications allowed us to double the yield in identified proteins and increased the specificity from 54 to 80.4% compared to previous approaches. Using primary AML patient samples, we were able to identify a total of 621 surface proteins comprising the AML surfaceome. We integrated this data with gene expression and mutational burden data to curate a set of robust putative target antigens. Seventy-six proteins were selected as potential candidates for further investigation of which we validated the most promising novel candidate markers, and identified CD148, ITGA4 and Integrin beta-7 as promising targets in AML. Integrin beta-7 showed the most promising combination of expression in patient AML samples, and low or absent expression on healthy hematopoietic tissue.

CONCLUSION

Taken together, we demonstrate the feasibility of a highly optimized surfaceome detection method to interrogate the entire AML surfaceome directly from primary patient samples and integrate this data with gene expression and mutational burden data to achieve a robust, multiomic target identification platform. This approach has the potential to accelerate the unbiased target identification for immunotherapy of AML.

Cellular and Molecular Biomarkers Predictive of Response to Immunotherapy in Acute Myeloid Leukemia

Immunotherapy has without question revolutionized the treatment of both hematologic and solid malignancies. Over the last several years novel strategies are being developed to incorporate these groundbreaking therapies into the care of patients with AML. Here we present an overview of the recent developments in immunotherapy for AML with a focus on biomarkers of response. Topics reviewed include antibody drug conjugates, BiTEs, DARTs, checkpoint inhibitors, and cellular therapy as well as the development of biomarkers predictive of response in each class.

Immune-Based Therapeutic Interventions for Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive, clonally heterogeneous, myeloid malignancy, with a 5-year overall survival of approximately 27%. It constitutes the most common acute leukemia in adults, with an incidence of 3-5 cases per 100,000 in the United States. Despite great advances in understanding the molecular mechanisms underpinning leukemogenesis, the past several decades had seen little change to the backbone of therapy, comprised of an anthracycline-based induction regimen for those who are fit enough to receive it, followed by risk-stratified post-remission therapy with consolidation cytarabine or allogeneic stem cell transplantation (allo-SCT). Allo-SCT is the most fundamental form of immunotherapy in which donor cytotoxic T and NK cells recognize and eradicate residual AML in the graft-versus-leukemia (GvL) effect. Building on that, several alternative or synergistic approaches to exploit both self and foreign immunity against AML have been developed. Checkpoint inhibitors, for example, CTLA-4 inhibitors, PD-1 inhibitors, and PD-L1 inhibitors block proteins found on T cells or cancer cells that stop the immune system from attacking the cancer cells. They have been used with limited success in both the AML relapsed/refractory (R/R) and post SCT settings. AML tumor mutational burden is low compared to solid tumors and thus, it is less likely to generate neoantigens and respond to antibody-mediated checkpoint blockade that has shown unprecedented results in solid tumors. Therefore, alternative therapeutic strategies that work independently of the T cell receptor (TCR) specificity have been developed. They include bispecific antibodies, which recruit T cells through CD3 engagement, and in AML have shown an overall response rate ranging between 14 and 30% in early phase trials. Chimeric Antigen Receptor (CAR) T cell therapy is a type of treatment in which T cells are genetically engineered to produce a recombinant receptor that redirects the specificity and function of T lymphocytes. However, lack of cell surface targets exclusively expressed on AML cells including Leukemic Stem Cells (LSCs) combined with clonal heterogeneity represents the biggest challenge in developing CAR therapy for AML. Antibody-Drug Conjugates (ADC) constitute the only FDA-approved immunotherapy to treat AML with Gemtuzumab Ozogamicin, a CD33-specific ADC used in CEBPα-mutated AML. The identification of additional cell surface targets is critical for the development of other ADC's potentially useful in the induction and maintenance regimens, given the ease at which these reagents can be generated and managed. Here, we will review those immune-based therapeutic interventions and highlight active areas of research investigations toward fulfillment of the great promise of immunotherapy to AML.

Clinical Development and Therapeutic Applications of Bispecific Antibodies for Hematologic Malignancies

Bispecific antibodies are composed of two monoclonal antibodies that engage T cells with tumor cell antigens and lead to tumor cell lysis. The most common types fall into the category of bispecific T cell engagers, or BiTEs, that have the canonical CD3-CD19 bispecific construct. Blinatumomab is the first bispecific antibody that received FDA approval for relapsed refractory B cell precursor acute lymphoblastic leukemia. Blinatumomab has been shown to have robust clinical outcomes and is associated with adverse events such as cytokine release syndrome and neurotoxicity. Other bispecific antibodies are under clinical investigation for multiple myeloma and acute myeloid leukemia. Along with immune checkpoint inhibitors and chimeric antigen T cell receptor therapies, bispecific antibodies are considered a mainstay as a therapeutic option for cancer immunotherapies for Hematologic malignancies.

Development of CAR T Cell Therapy in Children-A Comprehensive Overview

CAR T cell therapy has revolutionized immunotherapy in the last decade with the successful establishment of chimeric antigen receptor (CAR)-expressing cellular therapies as an alternative treatment in relapsed and refractory CD19-positive leukemias and lymphomas. There are fundamental reasons why CAR T cell therapy has been approved by the Food and Drug administration and the European Medicines Agency for pediatric and young adult patients first. Commonly, novel therapies are developed for adult patients and then adapted for pediatric use, due to regulatory and commercial reasons. Both strategic and biological factors have supported the success of CAR T cell therapy in children. Since there is an urgent need for more potent and specific therapies in childhood malignancies, efforts should also include the development of CAR therapeutics and expand applicability by introducing new technologies. Basic aspects, the evolution and the drawbacks of childhood CAR T cell therapy are discussed as along with the latest clinically relevant information.

An Update on Immune Based Therapies in Acute Myeloid Leukemia: 2021 and Beyond!

Despite advances in the treatment of acute myeloid leukemia (AML), relapse is still widely observed and represents the major cause of death among patients with AML. Treatment options in the relapse setting are limited, still relying predominantly on allogeneic hematopoietic stem cell transplantation (allo-HSCT) and cytotoxic chemotherapy, with poor outcomes. Novel targeted and venetoclax-based combinations are being investigated and have shown encouraging results. Immune checkpoint inhibitors in combination with low-intensity chemotherapy demonstrated encouraging response rates and survival among patients with relapsed and/or refractory (R/R) AML, especially in the pre- and post-allo-HSCT setting. Blocking the CD47/SIRPα pathway is another strategy that showed robust anti-leukemic activity, with a response rate of around 70% and an encouraging median overall survival in patients with newly diagnosed, higher-risk myelodysplastic syndrome and patients with AML with a TP53 mutation. One approach that was proven to be very effective in the relapsed setting of lymphoid malignancies is chimeric antigen receptor (CAR) T cells. It relies on the infusion of genetically engineered T cells capable of recognizing specific epitopes on the surface of leukemia cells. In AML, different CAR constructs with different target antigens have been evaluated and demonstrated safety and feasibility in the R/R setting. However, the difficulty of potently targeting leukemic blasts in AML while sparing normal cells represents a major limitation to their use, and strategies are being tested to overcome this obstacle. A different approach is based on endogenously redirecting the patient's system cells to target and destroy leukemic cells via bispecific T-cell engagers (BiTEs) or dual antigen receptor targeting (DARTs). Early results have demonstrated the safety and feasibility of these agents, and research is ongoing to develop BiTEs with longer half-life, allowing for less frequent administration schedules and developing them in earlier and lower disease burden settings.

Immune-Based Therapeutic Strategies for Acute Myeloid Leukemia

Simple Summary

This review summarizes various therapeutic immune approaches representing their targets, the efficacy and toxicity in the treatment of acute myeloid leukemia. In particular, immune checkpoint inhibitors, bispecific T-cell engager antibodies and chimeric antigen receptor-T-cell approaches are highlighted.

Abstract

The development and design of immune-based strategies have become an increasingly important topic during the last few years in acute myeloid leukemia (AML), based on successful immunotherapies in solid cancer. The spectrum ranges from antibody drug conjugates, immune checkpoint inhibitors blocking programmed cell death protein 1 (PD1), cytotoxic T lymphocyte antigen 4 (CTLA4) or T cell immunoglobulin and mucin domain containing-3 (TIM3), to T-cell based monoclonal and bispecific T-cell engager antibodies, chimeric antigen receptor-T-cell (CAR-T) approaches and leukemia vaccines. Currently, there are many substances in development and multiple phase I/II studies are ongoing. These trials will help us to deepen our understanding of the pathogenesis of AML and facilitate the best immunotherapeutic strategy in AML. We discuss here the mode of action of immune-based therapies and provide an overview of the available data.

The Role of T Cell Immunotherapy in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease associated with various alterations in T cell phenotype and function leading to an abnormal cell population, ultimately leading to immune exhaustion. However, restoration of T cell function allows for the execution of cytotoxic mechanisms against leukemic cells in AML patients. Therefore, long-term disease control, which requires multiple therapeutic approaches, includes those aimed at the re-establishment of cytotoxic T cell activity. AML treatments that harness the power of T lymphocytes against tumor cells have rapidly evolved over the last 3 to 5 years through various stages of preclinical and clinical development. These include tissue-infiltrated lymphocytes (TILs), bispecific antibodies, immune checkpoint inhibitors (ICIs), chimeric antigen receptor T (CAR-T) cell therapy, and tumor-specific T cell receptor gene-transduced T (TCR-T) cells. In this review, these T cell-based immunotherapies and the potential of TILs as a novel antileukemic therapy will be discussed.

SIRPα-αCD123 fusion antibodies targeting CD123 in conjunction with CD47 blockade enhance the clearance of AML-initiating cells

Background

Acute myeloid leukaemia (AML) stem cells (LSCs) cause disease relapse. The CD47 “don’t eat me signal” is upregulated on LSCs and contributes to immune evasion by inhibiting phagocytosis through interacting with myeloid-specific signal regulatory protein alpha (SIRPα). Activation of macrophages by blocking CD47 has been successful, but the ubiquitous expression of CD47 on healthy cells poses potential limitations for such therapies. In contrast, CD123 is a well-known LSC-specific surface marker utilized as a therapeutic target. Here, we report the development of SIRPα-αCD123 fusion antibodies that localize the disruption of CD47/SIRPα signalling to AML while specifically enhancing LSC clearance.

Methods

SIRPα-αCD123 antibodies were generated by fusing the extracellular domain of SIRPα to an αCD123 antibody. The binding properties of the antibodies were analysed by flow cytometry and surface plasmon resonance. The functional characteristics of the fusion antibodies were determined by antibody-dependent cellular phagocytosis and antibody-dependent cellular cytotoxicity assays using primary AML patient cells. Finally, an in vivo engraftment assay was utilized to assess LSC targeting.

Results

SIRPα-αCD123 fusion antibodies exhibited increased binding and preferential targeting of CD123⁺ CD47⁺ AML cells even in the presence of CD47⁺ healthy cells. Furthermore, SIRPα-αCD123 fusion antibodies confined disruption of the CD47-SIRPα axis locally to AML cells. In vitro experiments demonstrated that SIRPα-αCD123 antibodies greatly enhanced AML cell phagocytosis mediated by allogeneic and autologous macrophages. Moreover, SIRPα-αCD123 fusion antibodies efficiently targeted LSCs with in vivo engraftment potential.

Conclusions

SIRPα-αCD123 antibodies combine local CD47 blockade with specific LSC targeting in a single molecule, minimize the risk of targeting healthy cells and efficiently eliminate AML LSCs. These results validate SIRPα-αCD123 antibodies as promising therapeutic interventions for AML.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13045-021-01163-6.

Therapeutic Targeting of Acute Myeloid Leukemia by Gemtuzumab Ozogamicin

Acute myeloid leukemia (AML) is a complex hematological malignancy characterized by genetic and clinical heterogeneity and high mortality. Despite the recent introduction of novel pharmaceutical agents in hemato-oncology, few advancements have been made in AML for decades. In the last years, the therapeutic options have rapidly changed, with the approval of innovative compounds that provide new opportunities, together with new challenges for clinicians: among them, on 1 September, 2017 the Food and Drug Administration granted approval for Gemtuzumab Ozogamicin (GO) in combination with daunorubicin and cytarabine for the treatment of adult patients affected by newly diagnosed CD33⁺ AML. Benefits of GO-based regimens were also reported in the pre- and post-transplantation settings. Moreover, several biomarkers of GO response have been suggested, including expression of CD33 and multidrug resistance genes, cytogenetic and molecular profiles, minimal residual disease and stemness signatures. Among them, elevated CD33 expression on blast cells and non-adverse cytogenetic or molecular risk represent largely validated predictors of good response.

Does lineage plasticity enable escape from CAR-T cell therapy? Lessons from MLL-r leukemia

The clinical success of engineered, CD19-directed chimeric antigen receptor (CAR) T cells in relapsed, refractory B-cell acute lymphoblastic leukemia (B-ALL) has generated great enthusiasm for the use of CAR T cells in patients with cytogenetics that portend a poor prognosis with conventional cytotoxic therapies. One such group includes infants and children with mixed lineage leukemia (MLL1, KMT2A) rearrangements (MLL-r), who fare much worse than patients with low- or standard-risk B-ALL. Although early clinical trials using CD19 CAR T cells for MLL-r B-ALL produced complete remission in most patients, relapse with CD19-negative disease was a common mechanism of treatment failure. Whereas CD19neg relapse has been observed across a broad spectrum of B-ALL patients treated with CD19-directed therapy, patients with MLL-r have manifested the emergence of AML, often clonally related to the B-ALL, suggesting that the inherent heterogeneity or lineage plasticity of MLL-r B-ALL may predispose patients to a myeloid relapse. Understanding the factors that enable and drive myeloid relapse may be important to devise strategies to improve durability of remissions. In this review, we summarize clinical observations to date with MLL-r B-ALL and generally discuss lineage plasticity as a mechanism of escape from immunotherapy.

Targeting intracellular WT1 in AML with a novel RMF-peptide-MHC specific T-cell bispecific antibody

Antibody-based immunotherapy is a promising strategy for targeting chemo-resistant leukemic cells. However, classical antibody-based approaches are restricted to targeting lineage-specific cell-surface antigens. By targeting intracellular antigens, a large number of other leukemia-associated targets would become accessible. In this study, we evaluated a novel T-cell bispecific (TCB) antibody, generated using CrossMab and knob-into-holes technology, containing a bivalent T-cell receptor-like binding domain that recognizes the RMFPNAPYL peptide derived from the intracellular tumor antigen Wilms' tumor 1 (WT1) in the context of human leukocyte antigen (HLA) A*02. Binding to CD3ε recruits T cells irrespective of their T-cell receptor specificity. WT1-TCB elicited antibody-mediated T-cell cytotoxicity against AML cell lines in a WT1- and HLA-restricted manner. Specific lysis of primary AML cells was mediated in ex vivo long-term co-cultures utilizing allogenic (mean specific lysis: 67±6% after 13-14 days; ±SEM; n=18) or autologous, patient-derived T cells (mean specific lysis: 54±12% after 11-14 days; ±SEM; n=8). WT1-TCB-treated T cells exhibited higher cytotoxicity against primary AML cells than an HLA-A*02 RMF-specific T-cell clone. Combining WT1-TCB with the immunomodulatory drug lenalidomide further enhanced antibody-mediated T-cell cytotoxicity against primary AML cells (mean specific lysis on day 3-4: 45.4±9.0% vs 70.8±8.3%; p=0.015; ±SEM; n=9-10). In vivo, WT1-TCB-treated humanized mice bearing SKM-1 tumors showed a significant and dose-dependent reduction in tumor growth. In summary, we show that WT1-TCB facilitates potent in vitro, ex vivo and in vivo killing of AML cell lines and primary AML cells; these results led to the initiation of a phase I trial in patients with r/r AML (NCT04580121).

T-cell-based immunotherapy of acute myeloid leukemia: current concepts and future developments

Acute myeloid leukemia (AML) is a heterogeneous disease linked to a broad spectrum of molecular alterations, and as such, long-term disease control requires multiple therapeutic approaches. Driven largely by an improved understanding and targeting of these molecular aberrations, AML treatment has rapidly evolved over the last 3-5 years. The stellar successes of immunotherapies that harness the power of T cells to treat solid tumors and an improved understanding of the immune systems of patients with hematologic malignancies have led to major efforts to develop immunotherapies for the treatment of patients with AML. Several immunotherapies that harness T cells against AML are in various stages of preclinical and clinical development. These include bispecific and dual antigen receptor-targeting antibodies (targeted to CD33, CD123, CLL-1, and others), chimeric antigen receptor (CAR) T-cell therapies, and T-cell immune checkpoint inhibitors (including those targeting PD-1, PD-L1, CTLA-4, and newer targets such as TIM3 and STING). The current and future directions of these T-cell-based immunotherapies in the treatment landscape of AML are discussed in this review.

CD33 Expression and Gentuzumab Ozogamicin in Acute Myeloid Leukemia: Two Sides of the Same Coin

Simple Summary

Roughly 85–90% of adult and pediatric acute myeloid leukemia (AML) are CD33-positive. Gemtuzumab ozogamicin (GO), a humanized murine IgG4 anti-CD33 antibody, is the first target therapy approved in AML therapeutic scenario. This review focuses on current biological information and clinical data from several studies investigating the use of GO in patients with AML. Over the years, flow cytometry, cytogenetics, molecular techniques, and genotyping studies of CD33 SNPs have provided a comprehensive analysis of promising biomarkers for GO responses and have potentially helped to identify subgroups of patients that may benefit from GO addition to standard chemotherapies. Increased understanding of molecular mutations, altered intracellular pathways, and their potential relationship with CD33 expression may open new therapeutic landscapes based on combinatorial regimens in an AML scenario.

Abstract

Acute myeloid leukemia (AML), the most frequent acute leukemia in adults, has been historically treated with infusional cytarabine (ara-c) + daunorubicin (3 + 7) for at least 40 years. The first “target therapy” to be introduced was the monoclonal anti-CD33 gemtuzumab ozogamicin (GO) in 2004. Unfortunately, in 2010 it was voluntarily withdrawn from the market both for safety reasons related to potential liver toxicity and veno-occlusive disease (VOD) and because clinical studies failed to confirm the clinical benefit during induction and maintenance. Seven years later, GO was re-approved based on new data, including insights into its mechanism of action on its target receptor CD33 expressed on myeloid cells. The present review focuses on current biological information and clinical data from several studies investigating GO. Cytogenetic, molecular, and immunophenotypic data are now able to predict the potential positive advantages of GO, with the exception of high-risk AML patients who do not seem to benefit. GO can be considered a ‘repurposed drug’ that could be beneficial for some patients with AML, mostly in combination with new drugs already approved or currently in testing.

Treatment for Relapsed/Refractory Acute Myeloid Leukemia

Patients with relapsed or refractory (r/r) acute myeloid leukemia (AML) have a poor prognosis and treatment remains challenging. For the majority of r/r patients, allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative treatment approach. Salvage therapy is given in order to reduce the leukemia load prior to transplantation. Patients achieving complete remission prior to allogeneic HSCT have a more favorable outcome. Intensive salvage regimens commonly consist of an anthracycline and high-dose cytarabine backbone. Donor lymphocyte infusions have shown efficacy in patients relapsing after allogeneic HSCT. For patients who cannot be intensively treated (eg, elderly AML patients), outcome is generally very poor and combinations with novel agents are currently under investigation. Mutational analysis should be repeated at the time of relapse to identify aberrations that can be targeted with new agents. For r/r AML patients with mutated fms-related tyrosine kinase 3 (FLT3), gilteritinib has shown superior results to intensive salvage regimens. The US Food and Drug Administration (FDA) and European Medicines Agency (EMA) approved gilteritinib for FLT3 mutated r/r AML patients. Ivosidenib and enasidenib, inhibitors for mutated isocitrate dehydrogenase (IDH) 1 and 2, respectively, have received approval for IDH1/IDH2 mutated r/r AML by the FDA (not EMA). APR-246 restores the function of mutated TP53 and early study results are promising. Other agents targeting CD47, menin, neural-precursor-cell-expressed developmentally down-regulated 8, as well as bispecific antibodies or chimeric antigen receptor T cells are under investigation. Further trials are needed to understand how to best combine novel agents with each other or with chemotherapy.

BiTEs, DARTS, BiKEs and TriKEs-Are Antibody Based Therapies Changing the Future Treatment of AML?

Nearly four decades after their conceptualization, antibody-based therapies are slowly being added to the treatment landscape of acute myeloid leukemia (AML). While the antibody-drug conjugate gemtuzumab ozogamicin is the only antibody-based therapy that has been approved for AML treatment thus far, several bispecific antibodies have been developed and shown early encouraging results. Bispecific antibodies comprise a wide variety of constructs that share the common concept of simultaneous binding of a surface target on malignant cells and most commonly CD3 on T cells leading to an endogenous, HLA-independent, immune response against malignant cells. However, the use of bispecific antibodies in AML has been limited by the absence of highly specific leukemia-associated antigens leading to on-target, off-leukemia side effects as well as reduced efficacy due to antigen escape. Herein, we discuss the history and evolution of bispecific T cell engagers as well as various adaptations such as dual affinity retargeting antibodies, bi- and tri-specific killer engager antibodies. Common side effects including cytokine release syndrome and management thereof are highlighted. Lastly, we expound on the future direction and integration of such antibody-based therapies with other immunotherapies (programmed cell death-1 inhibitors and chimeric antigen receptor T cells).

A novel C2 domain binding CD33xCD3 bispecific antibody with potent T-cell redirection activity against acute myeloid leukemia

CD33 is expressed in 90% of patients with acute myeloid leukemia (AML), and its extracellular portion consists of a V domain and a C2 domain. A recent study showed that a single nucleotide polymorphism (SNP), rs12459419 (C > T), results in the reduced expression of V domain-containing CD33 and limited efficacy of V domain-binding anti-CD33 antibodies. We developed JNJ-67571244, a novel human bispecific antibody capable of binding to the C2 domain of CD33 and to CD3, to induce T-cell recruitment and CD33+ tumor cell cytotoxicity independently of their SNP genotype status. JNJ-67571244 specifically binds to CD33-expressing target cells and induces cytotoxicity of CD33+ AML cell lines in vitro along with T-cell activation and cytokine release. JNJ-67571244 also exhibited statistically significant antitumor activity in vivo in established disseminated and subcutaneous mouse models of human AML. Furthermore, this antibody depletes CD33+ blasts in AML patient blood samples with concurrent T-cell activation. JNJ-67571244 also cross-reacts with cynomolgus monkey CD33 and CD3, and dosing of JNJ-67571244 in cynomolgus monkeys resulted in T-cell activation, transient cytokine release, and sustained reduction in CD33+ leukocyte populations. JNJ-67571244 was well tolerated in cynomolgus monkeys up to 30 mg/kg. Lastly, JNJ-67571244 mediated efficient cytotoxicity of cell lines and primary samples regardless of their SNP genotype status, suggesting a potential therapeutic benefit over other V-binding antibodies. JNJ-67571244 is currently in phase 1 clinical trials in patients with relapsed/refractory AML and high-risk myelodysplastic syndrome.

Immunotherapy in Acute Myeloid Leukemia: Where We Stand

In the past few years, our improved knowledge of acute myeloid leukemia (AML) pathogenesis has led to the accelerated discovery of new drugs and the development of innovative therapeutic approaches. The role of the immune system in AML development, growth and recurrence has gained increasing interest. A better understanding of immunological escape and systemic tolerance induced by AML blasts has been achieved. The extraordinary successes of immune therapies that harness the power of T cells in solid tumors and certain hematological malignancies have provided new stimuli in this area of research. Accordingly, major efforts have been made to develop immune therapies for the treatment of AML patients. The persistence of leukemia stem cells, representing the most relevant cause of relapse, even after allogeneic stem cell transplant (allo-SCT), remains a major hurdle in the path to cure for AML patients. Several clinical trials with immune-based therapies are currently ongoing in the frontline, relapsed/refractory, post-allo-SCT and minimal residual disease/maintenance setting, with the aim to improve survival of AML patients. This review summarizes the available data with immune-based therapeutic modalities such as monoclonal antibodies (naked and conjugated), T cell engagers, adoptive T-cell therapy, adoptive-NK therapy, checkpoint blockade via PD-1/PD-L1, CTLA4, TIM3 and macrophage checkpoint blockade via the CD47/SIRPa axis, and leukemia vaccines. Combining clinical results with biological immunological findings, possibly coupled with the discovery of biomarkers predictive for response, will hopefully allow us to determine the best approaches to immunotherapy in AML.

Bispecific T cell engagers: an emerging therapy for management of hematologic malignancies

Harnessing the power of immune cells, especially T cells, to enhance anti-tumor activities has become a promising strategy in clinical management of hematologic malignancies. The emerging bispecific antibodies (BsAbs), which recruit T cells to tumor cells, exemplified by bispecific T cell engagers (BiTEs), have facilitated the development of tumor immunotherapy. Here we discussed the advances and challenges in BiTE therapy developed for the treatment of hematologic malignancies. Blinatumomab, the first BiTE approved for the treatment of acute lymphocytic leukemia (ALL), is appreciated for its high efficacy and safety. Recent studies have focused on improving the efficacy of BiTEs by optimizing treatment regimens and refining the molecular structures of BiTEs. A considerable number of bispecific T cell-recruiting antibodies which are potentially effective in hematologic malignancies have been derived from BiTEs. The elucidation of mechanisms of BiTE action and neonatal techniques used for the construction of BsAbs can improve the treatment of hematological malignancies. This review summarized the features of bispecific T cell-recruiting antibodies for the treatment of hematologic malignancies with special focus on preclinical experiments and clinical studies.

A modular and controllable T cell therapy platform for acute myeloid leukemia

Targeted T cell therapy is highly effective in disease settings where tumor antigens are uniformly expressed on malignant cells and where off-tumor on-target-associated toxicity is manageable. Although acute myeloid leukemia (AML) has in principle been shown to be a T cell-sensitive disease by the graft-versus-leukemia activity of allogeneic stem cell transplantation, T cell therapy has so far failed in this setting. This is largely due to the lack of target structures both sufficiently selective and uniformly expressed on AML, causing unacceptable myeloid cell toxicity. To address this, we developed a modular and controllable MHC-unrestricted adoptive T cell therapy platform tailored to AML. This platform combines synthetic agonistic receptor (SAR) -transduced T cells with AML-targeting tandem single chain variable fragment (scFv) constructs. Construct exchange allows SAR T cells to be redirected toward alternative targets, a process enabled by the short half-life and controllability of these antibody fragments. Combining SAR-transduced T cells with the scFv constructs resulted in selective killing of CD33⁺ and CD123⁺ AML cell lines, as well as of patient-derived AML blasts. Durable responses and persistence of SAR-transduced T cells could also be demonstrated in AML xenograft models. Together these results warrant further translation of this novel platform for AML treatment.