Flotetuzumab as salvage immunotherapy for refractory acute myeloid leukemia

Immunotherapies in acute leukemia

In the past decade, immunotherapy has emerged as one of the most promising field of therapeutic progress in acute leukemia. Antibody-drug conjugates are now combined to standard chemotherapy backbones in both acute myeloid (AML) and lymphoblastic leukemia (ALL). CD19 targeting immune cell engagers and chimeric antigen receptor (CAR) T-cells have been approved in relapsed/refractory B-cell acute lymphoblastic leukemia and pave the way to promising developments in acute myeloid leukemia. Next generation immune checkpoint inhibitors targeting TIM-3 or CD47 binding by SIRPα on macrophages are tested in combination to hypomethylating agents to improve survival of unfit AML patients with acceptable safety profiles. This review summarizes the antibody-derived strategies developed in the field of acute leukemias with a specific focus on recently approved drugs.

Phase II Trial of Pembrolizumab after High-Dose Cytarabine in Relapsed/Refractory Acute Myeloid Leukemia

Immune suppression, exhaustion, and senescence are frequently seen throughout disease progression in acute myeloid leukemia (AML). We conducted a phase II study of high-dose cytarabine followed by pembrolizumab 200 mg i.v. on day 14 to examine whether PD-1 inhibition improves clinical responses in relapsed/refractory (R/R) AML. Overall responders could receive pembrolizumab maintenance up to 2 years. Among 37 patients enrolled, the overall response rate, composite complete remission (CRc) rate (primary endpoint), and median overall survival (OS) were 46%, 38%, and 11.1 months, respectively. Patients with refractory/early relapse and those receiving treatment as first salvage had encouraging outcomes (median OS, 13.2 and 11.3 months, respectively). Grade ≥3 immune-related adverse events were rare (14%) and self-limiting. Patients who achieved CRc had a higher frequency of progenitor exhausted CD8⁺ T cells expressing TCF-1 in the bone marrow prior to treatment. A multifaceted correlative approach of genomic, transcriptomic, and immunophenotypic profiling offers insights on molecular correlates of response and resistance to pembrolizumab.

Significance

Immune-checkpoint blockade with pembrolizumab was tolerable and feasible after high-dose cytarabine in R/R AML, with encouraging clinical activity, particularly in refractory AML and those receiving treatment as first salvage regimen. Further study of pembrolizumab and other immune-checkpoint blockade strategies after cytotoxic chemotherapy is warranted in AML.See related commentary by Wei et al., p. 551. This article is highlighted in the In This Issue feature, p. 549.

Haploidentical Stem Cell Transplantation for Acute Myeloid Leukemia: Current Therapies, Challenges and Future Prospective

Haploidentical stem cell transplantation (haplo-SCT), an alternative donor source, offers a curative therapy for patients with acute myeloid leukemia (AML) who are transplant candidates. Advances in transplantation techniques, such as donor selection, conditioning regimen modification, and graft-versus-host disease prophylaxis, have successfully improved the outcomes of AML patients receiving haplo-SCT and extended the haploidentical transplant indictions for AML. Presently, treating de novo AML, secondary AML, therapy-related AML and refractory and relapsed AML with haplo-SCT can achieve comparable outcomes to those of human leukocyte antigen (HLA)-matched sibling donor transplantation (MSDT), unrelated donor transplantation or umbilical cord blood transplantation. For some subgroups of AML subjects, such as patients with positive pretransplantation minimal/measurable residual disease, recent studies suggest that haplo-SCT might be superior to MSDT in decreasing relapse and improving survival. Unfortunately, for patients with AML after haplo-SCT, relapse and infections remain the causes of death that restrict further improvement in clinical outcomes. In this review, we discuss the recent advances and challenges in haplo-SCT for AML treatment, mainly focusing on unmanipulated haplo-SCT protocols. We provide an outlook on future prospects and suggest that relapse prophylaxis, intervention, and treatment, as well as infection prevention and therapy, are areas of active research in AML patients who receive haploidentical allografts.

Management of Acute Myeloid Leukemia: Current Treatment Options and Future Perspectives

Treatment of acute myeloid leukemia (AML) has improved in recent years and several new therapeutic options have been approved. Most of them include mutation-specific approaches (e.g., gilteritinib for AML patients with activating FLT3 mutations), or are restricted to such defined AML subgroups, such as AML-MRC (AML with myeloid-related changes) or therapy-related AML (CPX-351). With this review, we aim to present a comprehensive overview of current AML therapy according to the evolved spectrum of recently approved treatment strategies. We address several aspects of combined epigenetic therapy with the BCL-2 inhibitor venetoclax and provide insight into mechanisms of resistance towards venetoclax-based regimens, and how primary or secondary resistance might be circumvented. Furthermore, a detailed overview on the current status of AML immunotherapy, describing promising concepts, is provided. This review focuses on clinically important aspects of current and future concepts of AML treatment, but will also present the molecular background of distinct targeted therapies, to understand the development and challenges of clinical trials ongoing in AML patients.

Dual Targeting of Multiple Myeloma Stem Cells and Myeloid-Derived Suppressor Cells for Treatment of Chemotherapy-Resistant Multiple Myeloma

Here we review the insights and lessons learned from early clinical trials of T-cell engaging bispecific antibodies (BsABs) as a new class of biotherapeutic drug candidates with clinical impact potential for the treatment of multiple myeloma (MM). BsABs are capable of redirecting host T-cell cytotoxicity in an MHC-independent manner to malignant MM clones as well as immunosuppressive myeloid-derived suppressor cells (MDSC). T-cell engaging BsAB targeting the BCMA antigen may help delay disease progression in MM by destroying the MM cells. T-cell engaging BsAB targeting the CD38 antigen may help delay disease progression in MM by depleting both the malignant MM clones and the MDSC in the bone marrow microenvironment (BMME). BsABs may facilitate the development of a new therapeutic paradigm for achieving improved survival in MM by altering the immunosuppressive BMME. T-cell engaging BsiABs targeting the CD123 antigen may help delay disease progression in MM by depleting the MDSC in the BMME and destroying the MM stem cells that also carry the CD123 antigen on their surface.

Innate Immune Mechanisms and Immunotherapy of Myeloid Malignancies

Similar to other cancers, myeloid malignancies are thought to subvert the immune system during their development. This subversion occurs via both malignant cell-autonomous and non-autonomous mechanisms and involves manipulation of the innate and adaptive immune systems. Multiple strategies are being studied to rejuvenate, redirect, or re-enforce the immune system in order to fight off myeloid malignancies. So far, the most successful strategies include interferon treatment and antibody-based therapies, though chimeric antigen receptor (CAR) cells and immune checkpoint inhibitors are also promising therapies. In this review, we discuss the inherent immune mechanisms of defense against myeloid malignancies, currently-approved agents, and agents under investigation. Overall, we evaluate the efficacy and potential of immuno-oncology in the treatment of myeloid malignancies.

Targeting CD123 in BPDCN: an emerging field

INTRODUCTION

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive hematologic malignancy with historically poor outcomes for patients, often refractory to traditional chemotherapy. Recent research has focused on targeted therapy to improve responses and limit potential toxicity.

AREAS COVERED

CD123 (also known as IL-3 Rα) is a cell surface marker and attractive therapeutic target for many myeloid malignancies, particularly BPDCN, whose cells ubiquitously overexpress CD123. We review the history of CD123 research regarding BPDCN, recent advances including FDA approval of tagraxofusp (formerly SL-401) for BPDCN, and ongoing clinical studies utilizing novel therapeutic strategies to target CD123.

EXPERT OPINION

The approval of tagraxofusp for the treatment of BPDCN in December 2018 drastically changed the treatment landscape for patients with this rare neoplasm. While tagraxofusp is better tolerated than traditional multi-agent chemotherapy regimens, it requires close monitoring and sound clinical judgment by providers to prevent and mitigate severe treatment-related complications with special attention to the recognition and management of capillary leak syndrome (CLS). Several other promising strategies for targeting CD123 in BPDCN are currently under investigation, including antibody-drug conjugates, T-cell engagers, and CAR-T cellular therapeutics. These CD123 targeted approaches may soon become standard of care for patients with this difficult to treat malignancy.

IL-3 in the development and function of basophils

The β common chain (βc) cytokine family includes granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3) and IL-5, all of which use βc as key signaling receptor subunit. GM-CSF, IL-3 and IL-5 have specific roles as hematopoietic growth factors. IL-3 binds with high affinity to the IL-3 receptor α (IL-3Rα/CD123) and then associates with the βc subunit. IL-3 is mainly synthesized by different subsets of T cells, but is also produced by several other immune [basophils, dendritic cells (DCs), mast cells, etc.] and non-immune cells (microglia and astrocytes). The IL-3Rα is also expressed by immune (basophils, eosinophils, mast cells, DCs, monocytes, and megacaryocytes) and non-immune cells (endothelial cells and neuronal cells). IL-3 is the most important growth and activating factor for human and mouse basophils, primary effector cells of allergic disorders. IL-3-activated basophils and mast cells are also involved in different chronic inflammatory disorders, infections, and several types of cancer. IL-3 induces the release of cytokines (i.e., IL-4, IL-13, CXCL8) from human basophils and preincubation of basophils with IL-3 potentiates the release of proinflammatory mediators and cytokines from IgE- and C5a-activated basophils. IL-3 synergistically potentiates IL-33-induced mediator release from human basophils. IL-3 plays a pathogenic role in several hematologic cancers and may contribute to autoimmune and cardiac disorders. Several IL-3Rα/CD123 targeting molecules have shown some efficacy in the treatment of hematologic malignancies.

Immunotherapy for Acute Myeloid Leukemia: Allogeneic hematopoietic cell transplantation is here to stay

Acute Myeloid Leukemia (AML) represents 1 % of all new cancer diagnosis made annually in the US and has a five-year survival of 30 %. Traditional treatment includes aggressive induction therapy followed by consolidation therapy that may include a hematopoietic stem cell transplant (HSCT). Thus far, HSCT remains the only potentially curative therapy for many patients with AML owing to the graft-versus-leukemia effect elicited by this treatment. The use of novel therapies, specifically immunotherapy, in the treatment of AML has been limited by the lack of appropriate target antigens, therapy associated toxicities and variable success with treatment. Antigenic variability on leukemia cells and the sharing of antigens by malignant and non-malignant cells makes the identification of appropriate antigens problematic. While studies with immunotherapeutic agents are underway, prior investigations have demonstrated a mixed response with some studies prematurely discontinued due to associated toxicities. This review presents a discussion of the envisioned role of immunotherapy in the treatment of AML in the setting of mixed therapeutic success and potentially lethal toxicities.

Risk, Characteristics and Biomarkers of Cytokine Release Syndrome in Patients with Relapsed/Refractory AML or MDS Treated with CD3xCD123 Bispecific Antibody APVO436

We evaluate the risk, characteristics and biomarkers of treatment-emergent cytokine release syndrome (CRS) in patients with relapsed/refractory acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) who received APVO436 during the dose-escalation phase of a Phase 1B study (ClinicalTrials.gov, identifier: NCT03647800). Of four patients who developed Grade ≥ 3 CRS, two received steroid prophylaxis. The dose level, gender, race, obesity, or baseline hematologic parameters in peripheral blood did not predict the risk of CRS. Patients with a higher leukemia burden as determined by a higher total WBC, higher percentage of blasts in bone marrow, or higher percentage of blasts in peripheral blood (by hematopathology or immunophenotyping) did not have a higher incidence of CRS. There was an age difference between patients who did versus patients who did not develop CRS (72.9 ± 1.6 years (Median 73.5 years) vs. 63.3 ± 2.3 years (Median: 65.0 years), which was borderline significant (p = 0.04). Premedication with steroids did not eliminate the risk of CRS. Cytokine profiling in patients who developed CRS after APVO436 infusion indicates that the predominant cytokine in this inflammatory cytokine response was IL-6. APVO436-associated CRS was generally manageable with tocilizumab with or without dexamethasone. Notably, the development of CRS after APVO436 therapy did not appear to be associated with a response. The prolonged stabilization of disease, partial remissions and complete remissions were achieved in both patients who experienced CRS, as well as patients who did not experience CRS after APVO436 infusions.

Precision Medicine in Systemic Mastocytosis

Mastocytosis is a rare hematological neoplasm characterized by the proliferation of abnormal clonal mast cells (MCs) in different cutaneous and extracutaneous organs. Its diagnosis is based on well-defined major and minor criteria, including the pathognomonic dense infiltrate of MCs detected in bone marrow (BM), elevated serum tryptase level, abnormal MCs CD25 expression, and the identification of KIT D816V mutation. The World Health Organization (WHO) classification subdivides mastocytosis into a cutaneous form (CM) and five systemic variants (SM), namely indolent/smoldering (ISM/SSM) and advanced SM (AdvSM) including aggressive SM (ASM), SM associated to hematological neoplasms (SM-AHN), and mast cell leukemia (MCL). More than 80% of patients with SM carry a somatic point mutation of KIT at codon 816, which may be targeted by kinase inhibitors. The presence of additional somatic mutations detected by next generation sequencing analysis may impact prognosis and drive treatment strategy, which ranges from symptomatic drugs in indolent forms to kinase-inhibitors active on KIT. Allogeneic stem cell transplant (SCT) may be considered in selected SM cases. Here, we review the clinical, diagnostic, and therapeutic issues of SM, with special emphasis on the translational implications of SM genetics for a precision medicine approach in clinical practice.

Evolving Therapeutic Approaches for Older Patients with Acute Myeloid Leukemia in 2021

Simple Summary

The better understanding of disease biology, the availability of new effective drugs and the increased awareness of patients’ heterogeneity in terms of fitness and personal expectations has made the current treatment paradigm of AML in the elderly very challenging. Here, we discuss the evolving criteria used to define eligibility for induction chemotherapy and transplantation, the introduction of new agents in the treatment of patients with very different clinical conditions, the implications of precision medicine and the importance of quality of life and supportive care, proposing a simplified algorithm that we follow in 2021.

Abstract

Acute myeloid leukemia (AML) in older patients is characterized by unfavorable prognosis due to adverse disease features and a high rate of treatment-related complications. Classical therapeutic options range from intensive chemotherapy in fit patients, potentially followed by allogeneic hematopoietic cell transplantation (allo-HCT), to hypomethylating agents or palliative care alone for unfit/frail ones. In the era of precision medicine, the treatment paradigm of AML is rapidly changing. On the one hand, a plethora of new targeted drugs with good tolerability profiles are becoming available, offering the possibility to achieve a prolonged remission to many patients not otherwise eligible for more intensive therapies. On the other hand, better tools to assess patients’ fitness and improvements in the selection and management of those undergoing allo-HCT will hopefully reduce treatment-related mortality and complications. Importantly, a detailed genetic characterization of AML has become of paramount importance to choose the best therapeutic option in both intensively treated and unfit patients. Finally, improving supportive care and quality of life is of major importance in this age group, especially for the minority of patients that are still candidates for palliative care because of very poor clinical conditions or unwillingness to receive active treatments. In the present review, we discuss the evolving approaches in the treatment of older AML patients, which is becoming increasingly challenging following the advent of new effective drugs for a very heterogeneous and complex population.

Immune Therapies for Myelodysplastic Syndromes and Acute Myeloid Leukemia

Myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) are hematologic malignancies arising from the bone marrow. Despite recent advances in treating these diseases, patients with higher-risk MDS and AML continue to have a poor prognosis with limited survival. It has long been recognized that there is an immune component to the pathogenesis of MDS and AML, but until recently, immune therapies have played a limited role in treating these diseases. Immune suppressive therapy exhibits durable clinical responses in selected patients with MDS, but the question of which patients are most suitable for this treatment remains unclear. Over the past decade, there has been remarkable progress in identifying genomic features of MDS and AML, which has led to an improved discernment of the molecular pathogenesis of these diseases. An improved understanding of immune and inflammatory molecular mechanisms of MDS and AML have also recently revealed novel therapeutic targets. Emerging treatments for MDS and AML include monoclonal antibodies such as immune checkpoint inhibitors, bispecific T-cell-engaging antibodies, antibody drug conjugates, vaccine therapies, and cellular therapeutics including chimeric antigen receptor T-cells and NK cells. In this review, we provide an overview of the current understanding of immune dysregulation in MDS and AML and an update on novel immune therapies for these bone marrow malignancies.

New Drugs Bringing New Challenges to AML: A Brief Review

The better understanding of the genomic landscape in acute myeloid leukaemia (AML) has progressively paved the way for precision medicine in AML. There is a growing number of drugs with novel mechanisms of action and unique side-effect profiles. This review examines the impact of evolving novel therapies on survival in AML and the challenges that ensue.

CD123-Directed Bispecific Antibodies for Targeting MDS Clones and Immunosuppressive Myeloid-Derived Suppressor Cells (MDSC) in High-Risk Adult MDS Patients

There is an urgent need to identify effective strategies to prevent leukemic transformation and induce sustained deep remissions in adult high-risk myelodysplastic syndrome (MDS) patients. This article discusses the clinical impact potential of bispecific antibodies (BiAB) capable of redirecting host T-cell cytotoxicity in an MHC-independent manner to malignant clones as well as immunosuppressive myeloid-derived suppressor cells (MDSC) as a new class of anti-MDS drug candidates. T-cell engaging BiAB targeting the CD123 antigen may help delay disease progression in high-risk adult MDS and potentially reduce the risk of transformation to secondary AML.

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.

Targeted Therapies and Druggable Genetic Anomalies in Acute Myeloid Leukemia: From Diagnostic Tools to Therapeutic Interventions

Acute myeloid leukemia (AML) is a clonal disorder resulting from acquired somatic mutations in hematopoietic progenitor cells that lead to the dysregulation of differentiation and the proliferation of hematopoietic cells [...].

Targeted Therapies for the Evolving Molecular Landscape of Acute Myeloid Leukemia

Despite considerable growth in our understanding of the heterogeneous biology and pathogenesis of acute myeloid leukemia (AML) in recent decades, for nearly forty years, little progress was gained in the realm of novel therapeutics. Since 2017, however, nine agents have been FDA-approved for patients with AML in both the upfront and relapsed/refractory (R/R) settings. Most of these compounds function as inhibitors of key cell cycle enzymatic pathways or mediators of leukemic proliferation and survival. They have been approved both as single agents and in combination with conventional or reduced-intensity conventional chemotherapeutics. In this article, we review the molecular landscape of de novo vs. R/R AML and highlight the potential translational impact of defined molecular disease subsets. We also highlight several recent agents that have entered the therapeutic armamentarium and where they fit in the AML treatment landscape, with a focus on FLT3 inhibitors, IDH1 and IDH2 inhibitors, and venetoclax. Finally, we close with a survey of two promising novel agents under investigation that are poised to enter the mainstream clinical arena in the near future.

Multiparametric Flow Cytometry for MRD Monitoring in Hematologic Malignancies: Clinical Applications and New Challenges

Simple Summary

In hematologic cancers, Minimal Residual Disease (MRD) monitoring, using either molecular (PCR) or immunophenotypic (MFC) diagnostics, allows the identification of rare cancer cells, readily detectable either in the bone marrow or in the peripheral blood at very low levels, far below the limit of classic microscopy. In this paper, we outlined the state-of-the-art of MFC-based MRD detection in different hematologic settings, highlighting main recommendations and new challenges for using such method in patients with acute leukemias or chronic hematologic neoplasms. The combination of new molecular technologies with advanced flow cytometry is progressively allowing clinicians to design a personalized therapeutic path, proportionate to the biological aggressiveness of the disease, in particular by using novel immunotherapies, in view of a modern decision-making process, based on precision medicine.

Abstract

Along with the evolution of immunophenotypic and molecular diagnostics, the assessment of Minimal Residual Disease (MRD) has progressively become a keystone in the clinical management of hematologic malignancies, enabling valuable post-therapy risk stratifications and guiding risk-adapted therapeutic approaches. However, specific prognostic values of MRD in different hematological settings, as well as its appropriate clinical uses (basically, when to measure it and how to deal with different MRD levels), still need further investigations, aiming to improve standardization and harmonization of MRD monitoring protocols and MRD-driven therapeutic strategies. Currently, MRD measurement in hematological neoplasms with bone marrow involvement is based on advanced highly sensitive methods, able to detect either specific genetic abnormalities (by PCR-based techniques and next-generation sequencing) or tumor-associated immunophenotypic profiles (by multiparametric flow cytometry, MFC). In this review, we focus on the growing clinical role for MFC-MRD diagnostics in hematological malignancies—from acute myeloid and lymphoblastic leukemias (AML, B-ALL and T-ALL) to chronic lymphocytic leukemia (CLL) and multiple myeloma (MM)—providing a comparative overview on technical aspects, clinical implications, advantages and pitfalls of MFC-MRD monitoring in different clinical settings.

Pre-clinical development of a novel CD3-CD123 bispecific T-cell engager using cross-over dual-variable domain (CODV) format for acute myeloid leukemia (AML) treatment

Novel therapies are needed for effective treatment of AML. In the relapsed setting, prognosis is very poor despite salvage treatment with chemotherapy. Evidence suggests that leukemic stem cells (LSCs) cause relapse. The cell surface receptor CD123 is highly expressed in blast cells and LSCs from AML patients and is a potential therapeutic target. CD123 cross-over dual-variable domain T-cell engager (CD123-CODV-TCE) is a bispecific antibody with an innovative format. One arm targets the CD3εδ subunit of T-cell co-receptors on the surface of T cells, while the other targets CD123 on malignant cells, leading to cell-specific cytotoxic activity. Here, we describe the preclinical activity of CD123-CODV-TCE. CD123-CODV-TCE effectively binds to human and cynomolgus monkey CD3 and CD123 and is a highly potent T-cell engager. It mediates T-cell activation and T-cell-directed killing of AML cells in vitro. In vivo, CD123-CODV-TCE suppresses AML tumor growth in leukemia xenograft mouse models, where it achieves an effective half-life of 3.2 days, which is a significantly longer half-life compared to other bispecific antibodies with no associated Fc fragment. The in vitro safety profile is as expected for compounds with similar modes of action. These results suggest that CD123-CODV-TCE may be a promising therapy for patients with relapsed/refractory AML.

The state of the art of bispecific antibodies for treating human malignancies

Bispecific antibodies (bsAb) that target two independent epitopes or antigens have been extensively explored in translational and clinical studies since they were first developed in the 1960s. Many bsAbs are being tested in clinical trials for treating a variety of diseases, mostly cancer. Here, we provide an overview of various types of bsAbs in clinical studies and discuss their targets, safety profiles, and efficacy. We also highlight the current challenges, potential solutions, and future directions of bsAb development for cancer treatment.

Towards precision medicine for AML

With rapid advances in sequencing technologies, tremendous progress has been made in understanding the molecular pathogenesis of acute myeloid leukaemia (AML), thus revealing enormous genetic and clonal heterogeneity, and paving the way for precision medicine approaches. The successful development of precision medicine for patients with AML has been exemplified by the introduction of targeted FLT3, IDH1/IDH2 and BCL-2 inhibitors. When used as single agents, these inhibitors display moderate antileukaemic activity. However, augmented clinical activity has been demonstrated when they are administered in combination with drugs with broader mechanisms of action targeting epigenetic and/or other oncogenic signalling pathways or with conventional cytotoxic agents. The development of immunotherapies has been hampered by the expression of antigens that are expressed by both leukaemic and non-malignant haematopoietic progenitor cells; nonetheless, a diverse range of immunotherapies are now entering clinical development. This myriad of emerging agents also creates challenges, such as how to safely combine agents with different mechanisms of action, the need to circumvent primary and secondary resistance, and new challenges in future clinical trial design. In this Review, we discuss the current state of precision medicine for AML, including both the potential to improve patient outcomes and the related challenges.

Targeted Therapy in Pediatric AML: An Evolving Landscape

The outcomes associated with pediatric acute myeloid leukemia (AML) have improved over the last few decades, with the implementation of intensive chemotherapy, hematopoietic stem cell transplant, and improved supportive care. However, even with intensive therapy and the use of HSCT, both of which carry significant risks of short- and long-term side effects, approximately 30% of children are not able to be cured. The characterization of AML in pediatrics has evolved over time and it currently involves use of a variety of diagnostic tools, including flow cytometry and comprehensive genomic sequencing. Given the adverse effects of chemotherapy and the need for additional therapeutic options to improve outcomes in these patients, the genomic and molecular architecture is being utilized to inform selection of targeted therapies in pediatric AML. This review provides a summary of current, targeted therapy options in pediatric AML.

Paving the Way for Immunotherapy in Pediatric Acute Myeloid Leukemia: Current Knowledge and the Way Forward

Simple Summary

Immunotherapy may be an attractive treatment option to increase survival, and to reduce treatment-related side effects, for children with acute myeloid leukemia (AML). While immunotherapies have shown successes in many cancer types, the development and subsequent clinical implementation have proven difficult in pediatric AML. To expedite the development of immunotherapy, it will be crucial to understand which pediatric AML patients are likely to respond to immunotherapies. Emerging research in solid malignancies has shown that the number and phenotype of immune cells in the tumor microenvironment is predictive of response to several types of immunotherapies. Such a predictive model may also be applicable for AML and, thus, knowledge on the immune cells infiltrating the bone marrow environment is needed. Here, we discuss the current state of knowledge on these infiltrating immune cells in pediatric AML, as well as ongoing immunotherapy trials, and provide suggestions concerning the way forward.

Abstract

Immunotherapeutic agents may be an attractive option to further improve outcomes and to reduce treatment-related toxicity for pediatric AML. While improvements in outcome have been observed with immunotherapy in many cancer types, immunotherapy development and implementation into patient care for both adult and pediatric AML has been hampered by an incomplete understanding of the bone marrow environment and a paucity of tumor-specific antigens. Since only a minority of patients respond in most immunotherapy trials across different cancer types, it will be crucial to understand which children with AML are likely to respond to or may benefit from immunotherapies. Immune cell profiling efforts hold promise to answer this question, as illustrated by the development of predictive scores in solid cancers. Such information on the number and phenotype of immune cells during current treatment regimens will be pivotal to generate hypotheses on how and when to intervene with immunotherapy in pediatric AML. In this review, we discuss the current understanding of the number and phenotype of immune cells in the bone marrow in pediatric AML, ongoing immunotherapy trials and how comprehensive immune profiling efforts may pave the way for successful clinical trials (and, ultimately, implementation into patient care).

A Clinical Phase 1B Study of the CD3xCD123 Bispecific Antibody APVO436 in Patients with Relapsed/Refractory Acute Myeloid Leukemia or Myelodysplastic Syndrome

APVO436 is a recombinant T cell-engaging humanized bispecific antibody designed to redirect host T cell cytotoxicity in an MHC-independent manner to CD123-expressing blast cells from patients with hematologic malignancies and has exhibited single-agent anti-leukemia activity in murine xenograft models of acute myeloid leukemia (AML). In this first-in-human (FIH) multicenter phase 1B study, we sought to determine the safety and tolerability of APVO436 in R/R AML/myelodysplastic syndrome (MDS) patients and identify a clinically active recommended phase 2 dose (RP2D) level for its further clinical development. A total of 46 R/R AML/MDS patients who had failed 1-8 prior lines of therapy received APVO436 as weekly intravenous (IV) infusions at 10 different dose levels, ranging from a Minimum Anticipated Biological Effect Level (MABEL) of 0.3 mcg to 60 mcg. APVO436 exhibited a favorable safety profile with acceptable tolerability and manageable drug-related adverse events (AEs), and its maximum tolerated dose (MTD) was not reached at a weekly dose of 60 mcg. The most common APVO436-related AEs were infusion-related reactions (IRR) occurring in 13 (28.3%) patients and cytokine release syndrome (CRS) occurring in 10 (21.7%). The single dose RP2D level was identified as 0.2 mcg/kg. Preliminary efficacy signals were observed in both AML and MDS patients: Prolonged stable disease (SD), partial remissions (PR), and complete remissions (CR) were observed in R/R AML patients as best overall responses to APVO436 at the RP2D level. Three of six evaluable MDS patients had marrow CRs. The safety and preliminary evidence of efficacy of APVO436 in R/R AML and MDS patients warrant further investigation of its clinical impact potential.

Updates on targeted therapies for acute myeloid leukaemia

In the past few years research in the underlying pathogenic mechanisms of acute myeloid leukaemia (AML) has led to remarkable advances in our understanding of the disease. Cytogenetic and molecular aberrations are the most important factors in determining response to chemotherapy as well as long-term outcome, but beyond prognostication are potential therapeutic targets. Our increased understanding of the pathogenesis of AML facilitated by next-generation sequencing has spurred the development of new compounds in the treatment of AML, particularly the creation of small molecules that target the disease on a molecular level. Many of the hopeful predictions outlined in our AML review of 2018 are now therapeutic realities: gemtuzumab ozogamicin, venetoclax, FLT3 inhibitors (midostaurin, gilteritinib), IDH inhibitors (ivosidenib, enasidenib), CPX-351, glasdegib, oral decitabine, and oral azacitidine. Others may soon be (quizartinib, APR246 magrolimab, menin inhibitors). The wealth of positive data allows reconsideration of what might soon be new standards of care in younger and older patients with AML. In this review we give an overview of recently approved therapies in AML and address present and future research directions.

Bayesian modeling of a bivariate toxicity outcome for early phase oncology trials evaluating dose regimens

Most phase I trials in oncology aim to find the maximum tolerated dose (MTD) based on the occurrence of dose limiting toxicities (DLT). Evaluating the schedule of administration in addition to the dose may improve drug tolerance. Moreover, for some molecules, a bivariate toxicity endpoint may be more appropriate than a single endpoint. However, standard dose‐finding designs do not account for multiple dose regimens and bivariate toxicity endpoint within the same design. In this context, following a phase I motivating trial, we proposed modeling the first type of DLT, cytokine release syndrome, with the entire dose regimen using pharmacokinetics and pharmacodynamics (PK/PD), whereas the other DLT (DLT_o) was modeled with the cumulative dose. We developed three approaches to model the joint distribution of DLT, defining it as a bivariate binary outcome from the two toxicity types, under various assumptions about the correlation between toxicities: an independent model, a copula model and a conditional model. Our Bayesian approaches were developed to be applied at the end of the dose‐allocation stage of the trial, once all data, including PK/PD measurements, were available. The approaches were evaluated through an extensive simulation study that showed that they can improve the performance of selecting the true MTD‐regimen compared to the recommendation of the dose‐allocation method implemented. Our joint approaches can also predict the DLT probabilities of new dose regimens that were not tested in the study and could be investigated in further stages of the trial.

Molecular Characterization and Clinical Treatment of Acute Myeloid Leukemia (AML) and Myelodysplastic Syndromes (MDS) Patients With TP53 Mutation

BACKGROUND

Mutations in TP53 in myeloid neoplasms patients have been associated with poor prognosis. Effective treatments to these patients remain unclear.

PATIENTS AND METHODS

In this study, we retrospectively analyzed diagnostic and outcomes of 31 Acute Myeloid leukemia (AML) and 9 Myelodysplastic syndromes (MDS) patients with TP53 mutation at our hospital from September 2015 to October 2020.

RESULTS

A total of 42 variants (28 unique variants) in the coding region of TP53 gene were identified, and most were missense mutation (34 of 42, 81%). The median overall survival (OS) was 8 months for the AML patients (1-32 months) and 7 months for the MDS patients (3-27 months). There were 35 and 13 patients underwent frontline chemical therapy and Allo-HSCT, respectively. The overall response rate was 45.3% (16/35) for the frontline treatment. There was no significant difference between intensive and low-intensity regimens on either response to the frontline treatment (P = .255) or overall survival (P = .078). Patients, who achieved complete or partial remission at the frontline treatment, presented a higher survival than patients in non-remission, no matter transplant or not.

CONCLUSION

This study corroborates that improving the response to the first-line treatment could prolong the survival of myeloid neoplasms patients with TP53 mutation. Allo-HSCT could be a curative option for patients with TP53 mutation, when in complete remission during the first-line treatment.

Bispecific Antibodies: A Smart Arsenal for Cancer Immunotherapies

Following the clinical success of cancer immunotherapies such as immune checkpoint inhibitors blocking B7/CTLA-4 or PD-1/PD-L1 signaling and ongoing numerous combination therapies in the clinic,3 bispecific antibodies (BsAbs) are now emerging as a growing class of immunotherapies with the potential to improve clinical efficacy and safety further. Here, we describe four classes of BsAbs: (a) immune effector cell redirectors; (b) tumor-targeted immunomodulators; (c) dual immunomodulators; and (d) dual tumor-targeting BsAbs. This review describes each of these classes of BsAbs and presents examples of BsAbs in development. We reviewed the biological rationales and characteristics of BsAbs and summarized the current status and limitations of clinical development of BsAbs and strategies to overcome limitations. The field of BsAb-based cancer immunotherapy is growing, and more data from clinical trials are accumulating. Thus, BsAbs could be the next generation of new treatment options for cancer patients.

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.

Structural and evolutionary exploration of the IL-3 family and its alpha subunit receptors

Interleukin-3 (IL-3) is a cytokine belonging to the family of common β (βc) and is involved in various biological systems. Its activity is mediated by the interaction with its receptor (IL-3R), a heterodimer composed of two distinct subunits: IL-3Rα and βc. IL-3 and its receptor, especially IL-3Rα, play a crucial role in pathologies like inflammatory diseases and therefore are interesting therapeutic targets. Here, we have performed an analysis of these proteins and their interaction based on structural and evolutionary information. We highlighted that IL-3 and IL-3Rα structural architectures are conserved across evolution and shared with other proteins belonging to the same βc family interleukin-5 (IL-5) and granulocyte-macrophage colony-stimulating factor (GM-CSF). The IL-3Rα/IL-3 interaction is mediated by a large interface in which most residues are surprisingly not conserved during evolution and across family members. In spite of this high variability, we suggested small regions constituted by few residues conserved during the evolution in both proteins that could be important for the binding affinity.

Recent progress in the treatment of cancer in children

Although significant improvements have been made in the outcomes of children with cancer, the pace of improvement has slowed in recent years as the limits of therapy intensification may have been reached for many pediatric cancers. Furthermore, with increasing numbers of pediatric cancer survivors, the long-term side effects of treatment have become increasingly apparent. Therefore, attention has shifted to the use of molecularly targeted agents and immunotherapies to improve the outcomes of children who are not cured by traditional cytotoxic chemotherapies and to decrease exposure to cytotoxic chemotherapy and reduce late effects. This review describes the recent progress in the treatment of children with cancer, focusing in particular on diseases in which targeted and immunotherapeutic agents have made an impact.

Myelodysplastic Syndromes in the Postgenomic Era and Future Perspectives for Precision Medicine

Simple Summary

With demographic ageing, improved cancer survivorship and increased diagnostic sensitivity, incident cases of patients with Myelodysplastic Syndromes (MDS) are continuously rising, leading to a relevant impact on health care resources. Disease heterogeneity and various comorbidities are challenges for the management of the generally elderly patients. Therefore, experienced physicians and multidisciplinary teams should be involved in the establishment of the correct diagnosis, risk-assessment and personalized treatment plan. Next-generation sequencing allows for early detection of clonal hematopoiesis and monitoring of clonal evolution, but also poses new challenges for its appropriate use. At present, allogeneic hematopoietic stem cell transplantation remains the only curative treatment option for a minority of fit MDS patients. All others receive palliative treatment and will eventually progress, having an unmet need for novel therapies. Targeting compounds are in prospect for precision medicine, however, abrogation of clonal evolution to acute myeloid leukemia remains actually out of reach.

Abstract

Myelodysplastic syndromes (MDS) represent a heterogeneous group of clonal disorders caused by sequential accumulation of somatic driver mutations in hematopoietic stem and progenitor cells (HSPCs). MDS is characterized by ineffective hematopoiesis with cytopenia, dysplasia, inflammation, and a variable risk of transformation into secondary acute myeloid leukemia. The advent of next-generation sequencing has revolutionized our understanding of the genetic basis of the disease. Nevertheless, the biology of clonal evolution remains poorly understood, and the stochastic genetic drift with sequential accumulation of genetic hits in HSPCs is individual, highly dynamic and hardly predictable. These continuously moving genetic targets pose substantial challenges for the implementation of precision medicine, which aims to maximize efficacy with minimal toxicity of treatments. In the current postgenomic era, allogeneic hematopoietic stem cell transplantation remains the only curative option for younger and fit MDS patients. For all unfit patients, regeneration of HSPCs stays out of reach and all available therapies remain palliative, which will eventually lead to refractoriness and progression. In this review, we summarize the recent advances in our understanding of MDS pathophysiology and its impact on diagnosis, risk-assessment and disease monitoring. Moreover, we present ongoing clinical trials with targeting compounds and highlight future perspectives for precision medicine.

Principles and Current Clinical Landscape of Multispecific Antibodies against Cancer

Building upon the resounding therapeutic success of monoclonal antibodies, and supported by accelerating progress in engineering methods, the field of multispecific therapeutic antibodies is growing rapidly. Over 140 different molecules are currently in clinical testing, with excellent results in recent phase 1-3 clinical trials for several of them. Multivalent bispecific IgG-modified formats predominate today, with a clear tendency for more target antigens and further increased valency in newer constructs. The strategies to augment anticancer efficacy are currently equally divided between disruption of multiple surface antigens, and additional redirection of cytotoxic T or NK lymphocytes against the tumor. Both effects complement other modern modalities, such as tyrosine kinase inhibitors and adoptive cell therapies, with which multispecifics are increasingly applied in combination or merged, for example, in the form of antibody producing CAR-T cells and oncolytics. While mainly focused on B-cell malignancies early on, the contemporary multispecific antibody sector accommodates twice as many trials against solid compared to hematologic cancers. An exciting emerging prospect is the targeting of intracellular neoantigens using T-cell receptor (TCR) fusion proteins or TCR-mimic antibody fragments. Considering the fact that introduction of PD-(L)1 inhibitors only a few years ago has already facilitated 5-year survival rates of 30-50% for per se highly lethal neoplasms, such as metastatic melanoma and non-small-cell lung carcinoma, the upcoming enforcement of current treatments with "next-generation" immunotherapeutics, offers a justified hope for the cure of some advanced cancers in the near future.

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).

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.

CAR-T Cell Therapy for Acute Myeloid Leukemia: Preclinical Rationale, Current Clinical Progress, and Barriers to Success

Chimeric antigen receptor (CAR)-T cell therapy has shown impressive results in chemorefractory B cell malignancies, raising the possibilities of using this immunotherapeutic modality for other devastating hematologic malignancies, such as acute myeloid leukemia (AML). AML is an aggressive hematologic malignancy which, like B cell malignancies, poses several challenges for clinical translation of successful immunotherapy. The antigenic heterogeneity of AML results in a list of potential targets that CAR-T cells could be directed towards, each with advantages and disadvantages. In this review, we provide an up-to-date report of outcomes and adverse effects from published and presented clinical trials of CAR-T cell therapy for AML and provide the preclinical rationale underlying these studies and antigen selection. Comparison across trials is difficult, yet themes emerge with respect to appropriate antigen selection and association of adverse effects with outcomes. We highlight currently active clinical trials and the potential improvements and caveats with these novel approaches. Key hurdles to the successful introduction of CAR-T cell therapy for the treatment of AML include the effect of antigenic heterogeneity and trade-offs between therapy specificity and sensitivity; on-target off-tumor toxicities; the AML tumor microenvironment; and practical considerations for future trials that should be addressed to enable successful CAR-T cell therapy for AML.

The important role of intensive induction chemotherapy in the treatment of acute myeloid leukemia

Introduction: Intensive induction chemotherapy followed by post-remission consolidation and/or allogeneic hematopoietic transplantation has been a standard-of-care therapy for acute myeloid leukemia (AML) for decades. In recent years, a plethora of new agents have been approved for AML treatment, dramatically changing the AML treatment landscape.Areas covered: This review provides an overview of the current role of intensive chemotherapy in the changing AML treatment landscape. PubMed-indexed publications (through 2020) and abstracts presented at major national and international conferences were reviewed for inclusion.Expert opinion: While intensive chemotherapy is standard-of-care therapy for younger patients with AML, older patients were historically viewed as universally ineligible for intensive chemotherapy; however, several studies suggest many older patients benefit from intensive chemotherapy with a curative intent, and a more holistic approach to determining eligibility for intensive treatment is recommended. Intensive strategies have also been expanded to include novel chemotherapy designs and chemotherapy in combination with targeted agents for patients with certain disease characteristics, which may permit more personalized treatment decisions. Intensive chemotherapy continues to play a pivotal role for the management of many AML patients and can offer the best chance of long-term remission, especially when followed by transplantation.

Emerging agents and regimens for AML

Until recently, acute myeloid leukemia (AML) patients used to have limited treatment options, depending solely on cytarabine + anthracycline (7 + 3) intensive chemotherapy and hypomethylating agents. Allogeneic stem cell transplantation (Allo-SCT) played an important role to improve the survival of eligible AML patients in the past several decades. The exploration of the genomic and molecular landscape of AML, identification of mutations associated with the pathogenesis of AML, and the understanding of the mechanisms of resistance to treatment from excellent translational research helped to expand the treatment options of AML quickly in the past few years, resulting in noteworthy breakthroughs and FDA approvals of new therapeutic treatments in AML patients. Targeted therapies and combinations of different classes of therapeutic agents to overcome treatment resistance further expanded the treatment options and improved survival. Immunotherapy, including antibody-based treatment, inhibition of immune negative regulators, and possible CAR T cells might further expand the therapeutic armamentarium for AML. This review is intended to summarize the recent developments in the treatment of AML.

New Treatment Options for Older Patients with Acute Myeloid Leukemia

OPINION STATEMENT

The treatment of acute myeloid leukemia (AML) has evolved considerably over the past several years. Advances in the field have historically benefited younger patients; however, a growing understanding of the molecular basis of leukemogenesis has brought multiple targeted agents to the clinic for patients of all ages. These therapies have expanded the therapeutic landscape for elderly patients from more than best supportive care and low-intensity monotherapy. In general, we currently utilize a backbone regimen of a hypomethylating agent (HMA) or low-intensity chemotherapy with the BCL-2 inhibitor venetoclax for the majority of elderly patients with newly diagnosed AML. For patients with targetable mutations, we employ a doublet/triplet strategy of HMA + a targeted inhibitor +/- venetoclax, often in the context of a clinical trial. CPX-351 is reserved for patients with secondary or therapy-related AML. In this review, we will outline our approach to the treatment of elderly patients with AML, with particular emphasis on recently approved agents and emerging novel therapies.

Overcoming Challenges for CD3-Bispecific Antibody Therapy in Solid Tumors

Immunotherapy of cancer with CD3-bispecific antibodies is an approved therapeutic option for some hematological malignancies and is under clinical investigation for solid cancers. However, the treatment of solid tumors faces more pronounced hurdles, such as increased on-target off-tumor toxicities, sparse T-cell infiltration and impaired T-cell quality due to the presence of an immunosuppressive tumor microenvironment, which affect the safety and limit efficacy of CD3-bispecific antibody therapy. In this review, we provide a brief status update of the CD3-bispecific antibody therapy field and identify intrinsic hurdles in solid cancers. Furthermore, we describe potential combinatorial approaches to overcome these challenges in order to generate selective and more effective responses.

Discovery and optimization of a novel anti-GUCY2c x CD3 bispecific antibody for the treatment of solid tumors

We report here the discovery and optimization of a novel T cell retargeting anti-GUCY2C x anti-CD3ε bispecific antibody for the treatment of solid tumors. Using a combination of hybridoma, phage display and rational design protein engineering, we have developed a fully humanized and manufacturable CD3 bispecific antibody that demonstrates favorable pharmacokinetic properties and potent in vivo efficacy. Anti-GUCY2C and anti-CD3ε antibodies derived from mouse hybridomas were first humanized into well-behaved human variable region frameworks with full retention of binding and T-cell mediated cytotoxic activity. To address potential manufacturability concerns, multiple approaches were taken in parallel to optimize and de-risk the two antibody variable regions. These approaches included structure-guided rational mutagenesis and phage display-based optimization, focusing on improving stability, reducing polyreactivity and self-association potential, removing chemical liabilities and proteolytic cleavage sites, and de-risking immunogenicity. Employing rapid library construction methods as well as automated phage display and high-throughput protein production workflows enabled efficient generation of an optimized bispecific antibody with desirable manufacturability properties, high stability, and low nonspecific binding. Proteolytic cleavage and deamidation in complementarity-determining regions were also successfully addressed. Collectively, these improvements translated to a molecule with potent single-agent in vivo efficacy in a tumor cell line adoptive transfer model and a cynomolgus monkey pharmacokinetic profile (half-life>4.5 days) suitable for clinical development. Clinical evaluation of PF-07062119 is ongoing.

CD123 bi-specific antibodies in development in AML: What do we know so far?

Bispecific antibodies are synthetic molecules designed to simultaneously bind two separate antigens. Given the recent success of blinatumomab in the treatment of acute lymphoblastic leukemia, there is growing interest in the use of bispecific antibodies as T-cell redirecting antibody for the treatment of cancer. In acute myeloid leukemia (AML), CD123 (also known as the interleukin receptor 3 alpha subunit) has emerged as a promising therapeutic target for bispecific antibodies. Prior attempts to target CD123 with unconjugated antibodies and antibody-drug conjugates have been mixed. However, available data from CD123-directed bispecific antibodies currently in clinical trials have been encouraging. In this review, we discuss the biology of CD123 and prior attempts to target this cell surface marker as part of anti-leukemic therapy. We then summarize and discuss the five CD123-directed bispecific antibodies currently in clinical trials for treatment of AML and provide practical insights regarding the use of these agents.