CD303 (BDCA-2) - a potential novel target for therapy in hematologic malignancies

Plasmacytoid dendritic cells at the forefront of anti-cancer immunity: rewiring strategies for tumor microenvironment remodeling

Plasmacytoid dendritic cells (pDCs) are multifaceted immune cells executing various innate immunological functions. Their first line of defence consists in type I interferons (I-IFN) production upon nucleic acids sensing through endosomal Toll-like receptor (TLR) 7- and 9-dependent signalling pathways. Type I IFNs are a class of proinflammatory cytokines that have context-dependent functions on cancer immunosurveillance and immunoediting. In the last few years, different studies have reported that pDCs are also able to sense cytosolic DNA through cGAS-STING (stimulator of interferon genes) pathway eliciting a potent I-IFN production independently of TLR7/9. Human pDCs are also endowed with direct effector functions via the upregulation of TRAIL and production of granzyme B, the latter modulated by cytokines abundant in cancer tissues. pDCs have been detected in a wide variety of human malignant neoplasms, including virus-associated cancers, recruited by chemotactic stimuli. Although the role of pDCs in cancer immune surveillance is still uncompletely understood, their spontaneous activation has been rarely documented; moreover, their presence in the tumor microenvironment (TME) has been associated with a tolerogenic phenotype induced by immunosuppressive cytokines or oncometabolites. Currently tested treatment options can lead to pDCs activation and disruption of the immunosuppressive TME, providing a relevant clinical benefit. On the contrary, the antibody-drug conjugates targeting BDCA-2 on immunosuppressive tumor-associated pDCs (TA-pDCs) could be proposed as novel immunomodulatory therapies to achieve disease control in patients with advance stage hematologic malignancies or solid tumors. This Review integrate recent evidence on the biology of pDCs and their pharmacological modulation, suggesting their relevant role at the forefront of cancer immunity.

Plasmacytoid dendritic cell expansion in myeloid neoplasms: A novel distinct subset of myeloid neoplasm?

Plasmacytoid dendritic cells (pDCs) are a specific dendritic cell type stemming from the myeloid lineage. Clinically and pathologically, neoplasms associated with pDCs are classified as blastic plasmacytoid dendritic cell neoplasm (BPDCN), mature plasmacytoid dendritic myeloid neoplasm (MPDMN) and pDC expansion in myeloid neoplasms (MNs). BPDCN was considered a rare and aggressive neoplasm in the 2016 World Health Organization (WHO) classification. MPDMN, known as mature pDC-derived neoplasm, is closely related to MNs and was first recognized in the latest 2022 WHO classification, proposing a new concept that acute myeloid leukemia cases could show clonally expanded pDCs (pDC-AML). With the advances in detection techniques, an increasing number of pDC expansion in MNs have been reported, but whether the pathogenesis is similar to that of MPDMN remains unclear. This review focuses on patient characteristics, diagnosis and treatment of pDC expansion in MNs to gain further insight into this novel and unique provisional subtype.

Blastic plasmacytoid dendritic cell neoplasm: a comprehensive review in pediatrics, adolescents, and young adults (AYA) and an update of novel therapies

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematologic malignancy that can involve the bone marrow, peripheral blood, skin, lymph nodes, and the central nervous system. Though more common in older adults, BPDCN has been reported across all age groups, including infants and children. The incidence of pediatric BPDCN is extremely low and little is known about the disease. Pediatric BPDCN is believed to be clinically less aggressive but often with more dissemination at presentation than adult cases. Unlike adults who almost always proceed to a hematopoietic stem cell transplantation in first complete remission if transplant-eligible, the majority of children can be cured with a high-risk acute lymphoblastic leukemia-like regimen. Hematopoietic stem cell transplantation is recommended for children with high-risk disease, the definition of which continues to evolve, or those in relapse and refractory settings where outcomes continue to be dismal. Novel agents used in other hematologic malignancies and CD123 targeted agents, including chimeric antigen receptor T-cells and monoclonal/bispecific antibodies, are being brought into research and practice. Our goal is to provide a comprehensive review of presentation, diagnosis, and treatment by review of pediatric cases reported for the last 20 years, and a review of novel targeted therapies and therapies under investigation for adult and pediatric patients.

North American Blastic Plasmacytoid Dendritic Cell Neoplasm Consortium: position on standards of care and areas of need

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematologic malignancy with historically poor outcomes and no worldwide consensus treatment approach. Unique among most hematologic malignancies for its frequent cutaneous involvement, BPDCN can also invade other extramedullary compartments, including the central nervous system. Generally affecting older adults, many patients are unfit to receive intensive chemotherapy, and although hematopoietic stem cell transplantation is preferred for younger, fit individuals, not all are eligible. One recent therapeutic breakthrough is that all BPDCNs express CD123 (IL3Rα) and that this accessible surface marker can be pharmacologically targeted. The first-in-class agent for BPDCN, tagraxofusp, which targets CD123, was approved in December 2018 in the United States for patients with BPDCN aged ≥2 years. Despite favorable response rates in the frontline setting, many patients still relapse in the setting of monotherapy, and outcomes in patients with relapsed/refractory BPDCN remain dismal. Therefore, novel approaches targeting both CD123 and other targets are actively being investigated. To begin to formally address the state of the field, we formed a new collaborative initiative, the North American BPDCN Consortium (NABC). This group of experts, which includes a multidisciplinary panel of hematologists/oncologists, hematopoietic stem cell transplant physicians, pathologists, dermatologists, and pediatric oncologists, was tasked with defining the current standard of care in the field and identifying the most important research questions and future directions in BPDCN. The position findings of the NABC's inaugural meetings are presented herein.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN): A promising future in the era of targeted therapeutics

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematologic malignancy arising from precursor dendritic cells. BPDCN cells characteristically express several markers on their cell surfaces including CD123, CD4, and CD56. Because of its rarity and challenging clinical presentation, there was no standard of care in managing BPDCN for decades and its prognosis overall was poor. However, as understanding of this rare neoplasm has increased, so have treatment options. The conventional cytotoxic chemotherapy regimens once used in the treatment of BPDCN were modest in their impact on disease relapse until paired with hematopoietic stem cell transplant. Although recent data suggest that there still remains a role for chemotherapeutic agents, targeted modalities have expanded the overall BPDCN treatment landscape. The CD123-targeted agent, tagraxofusp, was the first Food and Drug Administration-approved monotherapy in the treatment of BPDCN. Since its inception, several CD123-targeted and other cell-surface agents have been investigated, with many agents still in the preclinical stages. Although relapsed/refractory disease and central nervous system disease both remain formidable areas of research, there are several promising therapeutic approaches that could have a significant impact on the trajectory of treatment. This review will provide detailed insight on the novel drugs currently in use and those being explored in the management of BPDCN.

Characteristics and Outcomes of Patients with Blastic Plasmacytoid Dendritic Cell Neoplasm Treated with Frontline HCVAD

Given high relapse and CNS involvement of BPDCN, combination chemotherapy and prophylactic CNS-directed therapy are urgently needed.

HCVAD chemotherapy plays an important role in the treatment of BPDCN, even in the modern era of CD123-targeted therapy.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a clinically aggressive blood cancer, often involving the skin, bone marrow, lymph nodes, and central nervous system (CNS) in 20% to 30% of patients. Despite significant progress in CD123- and BCL-2–targeted therapy, most patients are not cured without hematopoietic stem cell transplant (HSCT), and CNS relapses occur quite frequently. Combination approaches with targeted and chemotherapy agents plus incorporation of prophylactic CNS-directed therapy are urgently needed. In this setting, we sought to analyze outcomes using the cytotoxic chemotherapy backbone regimen hyperfractionated cyclophosphamide, vincristine, adriamycin, and dexamethasone (HCVAD). We conducted a retrospective analysis of patients with BPDCN (n = 100), evaluating complete remission (CR) and median overall survival (OS) among 3 groups: those who received frontline HCVAD-based therapy (n = 35), SL-401 (n = 37), or other regimens (n = 28). HCVAD-based regimens yielded higher CR (80% vs 59% vs 43%; P = .01). There was no significant difference in OS (28.3 vs 13.7 vs 22.8 months; P = .41) or remission duration probability among treatment groups (38.6 vs not reached vs 10.2 months; P = .24). HSCT was performed in 51% vs 49% vs 38%, respectively (P = .455). These results suggest a continued important role for HCVAD-based chemotherapy in BPDCN, even in the modern targeted-therapy era, with high CR rates in the frontline setting. Further studies must establish the clinical activity, feasibility, and safety of doublet/triplet combinations of targeted therapies plus cytotoxic agents and the addition of CNS prophylaxis, with the ultimate goal of durable long-term remission for patients with BPDCN.