Combination of Tagraxofusp and Azacitidine Is an Effective Option for Relapsed Blastic Plasmacytoid Dendritic Cell Neoplasm After Allogeneic Hematopoietic Stem-Cell Transplantation

Tagraxofusp, a first-in-class CD123-targeted agent: Five-year postapproval comprehensive review of the literature

Tagraxofusp is a first-in-class CD123-directed conjugate of an amended diphtheria toxin platform and recombinant interleukin 3. Binding and subsequent internalization of the drug result in cell death via disruption of intracellular protein synthesis. CD123 is a surface marker that is expressed in several hematological malignancies, especially blastic plasmacytoid dendritic cell neoplasm (BPDCN), where its expression is ubiquitous. A pivotal study of tagraxofusp in BPDCN resulted in its approval for the treatment of BPDCN, the first treatment approved for this indication. Since the introduction of tagraxofusp, research has focused on the management of adverse effects, combination therapy to improve outcomes in fit patients, and dosing and combination strategies to mitigate toxicities while preserving efficacy, especially among older patients. The successful targeting of CD123 in BPDCN has also encouraged research into a variety of other CD123-positive hematological neoplasms, including acute myeloid leukemia (AML), and informed the development of other novel agents targeting CD123. This review examines the clinical data leading to the development and approval of tagraxofusp in BPDCN, how it is being used in combination to improve outcomes in BPDCN and AML, and its developing role in other hematological malignancies.

Recent Advances in the Biology and CD123-Directed Treatment of Blastic Plasmacytoid Dendritic Cell Neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an aggressive myeloid malignancy of the dendritic cell lineage that affects patients of all ages, though the incidence appears to be highest in patients over the age of 60 years. Diagnosis is based on the presence of plasmacytoid dendritic cell precursors expressing CD123, the interleukin-3 (IL-3) receptor alpha, and a distinct histologic appearance. Timely diagnosis remains a challenge, due to lack of disease awareness and overlapping biologic and clinical features with other hematologic malignancies. Prognosis is poor with a median overall survival of 8 to 14 months, irrespective of disease presentation pattern. Historically, the principal treatment was remission induction therapy followed by a stem cell transplant (SCT) in eligible patients. However, bridging to SCT is often not achieved with induction chemotherapy regimens. The discovery that CD123 is universally expressed in BPDCN and is considered to have a pathogenetic role in its development paved the way for the successful introduction of tagraxofusp, a recombinant human IL-3 fused to a truncated diphtheria toxin payload, as an initial treatment for BPDCN. Tagraxofusp was approved in 2018 by the United States Food and Drug Administration for the treatment of patients aged 2 years and older with newly diagnosed and relapsed/refractory BPDCN, and by the European Medicines Agency in 2021 for first-line treatment of adults. The advent of tagraxofusp has opened a new era of precision oncology in the treatment of BPDCN. Herein, we present an overview of BPDCN biology, its diagnosis, and treatment options, illustrated by clinical cases.

Breakthrough in Blastic Plasmacytoid Dendritic Cell Neoplasm Cancer Therapy Owing to Precision Targeting of CD123

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive hematologic cancer originating from the malignant transformation of plasmacytoid dendritic cell precursors. This malignancy progresses rapidly, with frequent relapses and a poor overall survival rate, underscoring the urgent need for effective treatments. However, diagnosing and treating BPDCN have historically been challenging due to its rarity and the lack of standardized approaches. The recognition of BPDCN as a distinct disease entity is recent, and standardized treatment protocols are yet to be established. Traditionally, conventional chemotherapy and stem cell transplantation have been the primary methods for treating BPDCN patients. Advances in immunophenotyping and molecular profiling have identified potential therapeutic targets, leading to a shift toward CD123-targeted immunotherapies in both clinical and research settings. Ongoing developments with SL-401, IMGN632, CD123 chimeric antigen receptor (CAR) T-cells, and bispecific antibodies (BsAb) show promising advancements. However, the therapeutic effectiveness of CD123-targeting treatments needs improvement through innovative approaches and combinations of treatments with other anti-leukemic drugs. The exploration of combinations such as CD123-targeted immunotherapies with azacitidine and venetoclax is suggested to enhance antineoplastic responses and improve survival rates in BPDCN patients. In conclusion, this multifaceted approach offers hope for more effective and tailored therapeutic interventions against this challenging hematologic malignancy.

CD123 a Therapeutic Target for Acute Myeloid Leukemia and Blastic Plasmocytoid Dendritic Neoplasm

In spite of consistent progress at the level of basic research and of clinical treatment, acute myeloid leukemia (AML) still represents an unmet clinical need for adult and pediatric patients. To improve the outcomes of these patients, it is necessary to identify new therapeutic targets. IL3RA (CD123, alpha subunit of the interleukin 3 receptor) is a cell membrane protein overexpressed in several hematologic malignancies, including AML blastic plasmocytoid dendritic cell neoplasms (BPDCN). Given the higher expression of CD123 on leukemic cells compared to normal hematopoietic cells and its low/absent expression on normal hematopoietic stem cells, it appears as a suitable and attractive target for therapy. Various drugs targeting CD123 have been developed and evaluated at clinical level: interleukin-3 conjugated with diphtheria toxin; naked neutralizing anti-CD123 antibodies; drug-antibody conjugates; bispecific antibodies targeting both CD123 and CD3; and chimeric antigen receptor (CAR) T cells engineered to target CD123. Some of these agents have shown promising results at the clinical level, including tagraxofusp (CD123 conjugated with diphtheria toxin) for the treatment of BPDCN and IMGN632 (anti-CD123 drug-conjugate), and flotetuzumab (bispecific anti-CD123 and anti-CD3 monoclonal antibody) for the treatment of AML. However, the therapeutic efficacy of CD123-targeting treatments is still unsatisfactory and must be improved through new therapeutic strategies and combined treatments with other antileukemic drugs.

Venetoclax and Azacitidine in the Treatment of Blastic Plasmacytoid Dendritic Cell Neoplasm Refractory to Conventional Therapy

Blastic plasmacytoid dendritic cell neoplasm is a rare and aggressive hematological malignancy associated with poor prognosis and limited treatment options. No guideline-directed therapy existed until the approval of tagraxofusp in 2018 by the Food and Drug Administration. Multiple clinical trials are undergoing as treatment options continue to evolve. We report a case refractory to tagraxofusp and pivekimab sunirine with subsequent remission achieved on venetoclax and azacitidine therapy.

New Frontiers in Monoclonal Antibodies for the Targeted Therapy of Acute Myeloid Leukemia and Myelodysplastic Syndromes

Acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) represent an unmet clinical need whose prognosis is still dismal. Alterations of immune response play a prominent role in AML/MDS pathogenesis, revealing novel options for immunotherapy. Among immune system regulators, CD47, immune checkpoints, and toll-like receptor 2 (TLR2) are major targets. Magrolimab antagonizes CD47, which is overexpressed by AML and MDS cells, thus inducing macrophage phagocytosis with clinical activity in AML/MDS. Sabatolimab, an inhibitor of T-cell immunoglobulin and mucin domain-containing protein 3 (TIM3), which disrupts its binding to galectin-9, has shown promising results in AML/MDS, enhancing the effector functions of lymphocytes and triggering tumor cell death. Several other surface molecules, namely CD33, CD123, CD45, and CD70, can be targeted with monoclonal antibodies (mAbs) that exert different mechanisms of action and include naked and conjugated antibodies, bispecific T-cell engagers, trispecific killer engagers, and fusion proteins linked to toxins. These novel mAbs are currently under investigation for use as monotherapy or in combination with hypomethylating agents, BCL2 inhibitors, and chemotherapy in various clinical trials at different phases of development. Here, we review the main molecular targets and modes of action of novel mAb-based immunotherapies, which can represent the future of AML and higher risk MDS treatment.

Relapse of tagraxofusp treated blastic plasmacytoid dendritic cell neoplasm with loss of CD123 expression

Tagraxofusp, a CD123-based-targeted immunotherapy, was recently approved to treat blastic plasmacytoid dendritic cell neoplasm (BPDCN) with excellent response. Also, a subset of BPDCN shows resistance to tagraxofusp. These resistant cases continue to express CD123, which forms the basis of the continued utility of tagraxofusp in newer combination chemotherapies to overcome resistance in BPDCN. Herein, we report a case of an elderly male with BPDCN that achieved complete remission on initial primary treatment with tagraxofusp. However, BPDCN relapsed after 1.5 years while on treatment, with loss of CD123 expression. At relapse, the neoplasm was comprehensively immunophenotyped by flow cytometry (performed on both peripheral blood and bone marrow specimen) and by immunohistochemical evaluation of the bone marrow clot section. The neoplasm at relapse was diagnostic of BPDCN with a lack of CD123 expression. This case highlights a potential limitation of current and upcoming tagraxofusp-based multidrug therapies, at least in a subset of refractory BPDCN. We believe our report will serve as a sentinel to incite future investigations involving alternate resistance mechanisms in BDPCN.