Plasmacytoid Dendritic Cell Precursors Research Articles

Blastic Plasmacytoid Dendritic Cell Neoplasm, from a Dermatological Point of View.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an aggressive hematological malignancy derived from the precursors of plasmacytoid dendritic cells. Although disease awareness has increased over time, BPDCN represents a rare disease with an aggressive clinical course and a dismal prognosis. Due to the overlap in clinical and histological features with a large spectrum of inflammatory and neoplastic diseases, BPDCN is difficult to diagnose. Furthermore, given the rarity of the disease, treatment options for BPDCN are limited, sometimes changing by practitioner and hospitals. Treatment options range from conventional chemotherapy to the recently approved biologic agent tagraxofusp and stem cell transplantation. Therefore, a multidisciplinary approach with coordination among dermatologists, pathologists, and hematologists is ultimately imperative to reach the correct diagnosis and management of BPDCN.

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.

Epidemiology and Survival Outcomes in Blastic Plasmacytoid Dendritic Cell Neoplasm (BPDCN): A US Population-Based Study

Background: Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare, clinically aggressive hematological malignancy arising from plasmacytoid dendritic cell precursors. BPDCN remains poorly understood due to its rarity, constantly changing nomenclature, and defining criteria. This study using the Surveillance, Epidemiology, and End Results Program (SEER) database is the largest and most recent population-based study in BPDCN. We aimed to determine the incidence, clinical characteristics, overall survival, and prognostic factors in BPDCN. Methods: Patients diagnosed with BPDCN from 2000-2019 were identified from the SEER 17 database using the International Classification of Disease for Oncology, 3 rd edition (ICD-O-3) code 9727. Patient characteristics, treatment, and survival information were obtained. Age-adjusted incidence rate per 100,000 population and incidence rate ratio (IRR) were calculated using SEER stat software with the year 2000 US population as the reference standard. Overall survival and prognostic factors were evaluated based on univariate survival analysis using Kaplan-Meier plot with log-rank test, and Cox proportional hazard regression model for multivariate survival analysis. All statistical analyses were conducted with a two-sided significant p value of <0.05 using SEER stat software and STATA software version 15.1. Results: A total of 844 patients with BPDCN were included in the study. The median age at diagnosis was 40 (IQR: 15-68) with majority < 20 years (32.5%) or > 60 years (34.3%) . Majority were males (68.1%) and Caucasians (83.5%). The lymph node was the most common primary site of involvement (56.6%) followed by the bone marrow (19.1%) and skin (13%). . Eighteen percent of the cohort received radiation therapy and 83.6% received chemotherapy. The overall incidence of BPDCN was found to be 0.05 cases per 100,000 population. Incidence was significantly lower in females than males (IRR 0.62, p < 0.01) and in African Americans compared to Caucasians (IRR 0.70m, p<0.01). There was no significant change in disease incidence from 2005 to 2019. Survival rates at 1 year, 2 years and 5 years were found to be 70%, 56% and 41% respectively. On univariate analysis, age > 60 years (p <0.01) and male gender (p< 0.01) was associated with significantly worse overall survival while survival did not differ by race (p=0.10). On multivariate analysis after adjusting for age, sex, race, marital status, radiation therapy, chemotherapy and disease primary site, age > 60 years (HR 2.70; 95% CI 2.01-3.54, p<0.01) and African American race (HR 1.44; 95% CI 1.01-2.04, p<0.04) was associated with worse overall survival. Conclusion: To our knowledge, this is the largest and most recent population-based study in BPDCN. Our study revealed a population level incidence of 0.05 cases per 100,000 population. Majority are Caucasian males with bimodal age distribution (<20 years and above 60 years). The lymph nodes are the most common site of involvement. Older age and African American ethnicity are negative prognostic factors for overall survival. Racial disparities in OS warrant further prognosis. More prospective studies are needed to determine disease characteristics and optimal treatment approaches for this rare life-threatening hematological malignancy.

Blastic Plasmacytoid Dendritic Cell Neoplasm (BPDCN):Multi-Center Collaboration and Global Registry Program

Background BPDCN is a rare, aggressive hematologic malignancy derived from the precursors of plasmacytoid dendritic cells (pDC), typically presenting with primary cutaneous dissemination and involvement of bone marrow (BM) as well as extramedullary sites including central nervous system (CNS). In 2008, it was recognized by WHO as a distinct entity and is now recognized under Myeloid/Histiocytic/Dendritic neoplasms in the 2022 5th edition update of WHO Classification. Since the recognition of this unique entity, recent efforts have been put forward for greater understanding and international collaboration, however usually focused on North America and Europe(Pemmaraju at al and Pagano et al), with this current effort representing the largest known international efforts including more parts of the world, including Asia, Middle East and Africa. Objective Due to its historical rarity and heterogeneous presentation of disease, as well as differences in availability of therapies across geo-locations, at present there is no worldwide consensus on the management of BPDCN. The outcomes remain poor, and the optimal therapy of disease remains to be determined. Launched on July 1st, 2022, the aim of our global registry is through a multi-center international collaboration to build a large database of patients with BPDCN in order to generate data-driven diagnostic and treatment recommendations. Materials and Methods The registry collects retrospective and prospective data on clinical presentation, diagnostics, treatment regimens and outcomes of patients diagnosed with BPDCN after January 1st, 2010. The data is collected globally through eCRF and Excel form. The Registry is included in ClinicalTrials.gov database (NCT05430971). Results Through July 15 th, 2023, 15 centers from 11 countries (Armenia, Canada, Cyprus, Egypt, Georgia, India, Italy, Taiwan, Turkey, UK and USA) have joined the registry and another 13 centers from USA, UK, Egypt, Iraq, Canada, Netherlands, Tajikistan, Czech Republic, Guatemala, Brazil, Serbia, Germany are onboarding. 27 retrospective and 2 prospective pts are currently included in the registry. 76 % of pts are male, in keeping with historical expectation BPDCN. Median age at diagnosis was 62 years (4-97). In 90 % of patients the tumor cells were triple positive with CD4+, CD56+, CD123+ immunophenotype. 53.6% of patients presented with cutaneous manifestation. 21% of pts received the initial treatment with AML-based regimens, 66% with ALL-based and 7% with lymphoma-based regimens. 21% of pts underwent alloSCT. 35% of pts were diagnosed after 2018, only 1 patient has received tagraxofusp, a CD123-directed therapy that received FDA approval for previously untreated or relapsed/refractory BPDCN in 2018(Pemmaraju N et al NEJM 2019). 69 % of patients achieved complete response (CR), from which 90 % were treated with ALL-based regimens. 52% of patients experienced relapse. Conclusion Current analysis of a 29-patient worldwide cohort of BPDCN demonstrates a high degree of heterogeneity in treatment regimens based on a multitude of considerations including geographic, socio-economic, drug availability, and varied clinical preferences. The outcome of ALL-based treatment was superior as compared to AML-based, but relapse rate remained high. Further global collaboration is needed to collect additional data and to identify the best diagnostic and therapeutic approaches for this challenging disease.

Comparison and Development of Immunohistochemical Diagnostic Criteria for Blastic Plasmacytoid Dendritic Cell Neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematological malignancy derived from the precursors of plasmacytoid dendritic cells. Diagnostic criteria for BPDCN have not been fully established. BPDCN is often diagnosed without other BPDCN markers than the 3 conventional markers (CD4, CD56, and CD123) in practice and case reports, although acute myeloid leukemia/myeloid sarcoma (AML/MS), which is always considered in the differential diagnosis of BPDCN, can express them. We reviewed published case reports on BPDCN and found that the diagnosis was made without any other BPDCN markers than the conventional markers in two-thirds of the cases. Next, 4 representative existing diagnostic criteria were applied to 284 cases of our cohort of BPDCN and mimics. The results differed in 20% (56/284) of the cases. The criterion based on the 3 conventional markers alone had a low concordance rate (80%-82%) with the other 3 criteria, which were almost concordant with each other. However, newly found minor limitations in these criteria prompted us to devise new diagnostic criterion for BPDCN composed of TCF4, CD123, TCL1, and lysozyme. We also revealed that CD123-positive AML/MS patients had a significantly poorer outcome than those with BPDCN and that 12% (24/205) of the cases were non-BPDCN even if all 3 conventional markers were positive, thus clarifying the risk of diagnosing BPDCN without more specific markers. In addition, histopathological features, such as the reticular pattern, which is not seen in BPDCN and suggests AML/MS, were also identified.

Acute Myeloid Leukemia, Version 3.2023, NCCN Clinical Practice Guidelines in Oncology.

Acute myeloid leukemia (AML) is a heterogeneous hematologic malignancy characterized by the clonal expansion of myeloid blasts in the peripheral blood, bone marrow, and/or other tissues. It is the most common form of acute leukemia among adults and accounts for the largest number of annual deaths from leukemias in the United States. Like AML, blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a myeloid malignancy. It is a rare malignancy characterized by the aggressive proliferation of precursors of plasmacytoid dendritic cells that frequently involves the bone marrow, skin, central nervous system, and other organs and tissues. This discussion section focuses on the diagnosis and management of BPDCN as outlined in the NCCN Guidelines for AML.

Clinical Insights into the Management of Blastic Plasmacytoid Dendritic Cell Neoplasm.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is aggressive hematologic malignancy derived from plasmacytoid dendritic cell precursors of myeloid cell lineage. Patients frequently present with bruise-like skin lesions, which typically are followed months later by progressive cytopenias. Historically, BPDCN prognosis has been dismal, with median overall survival ranging from 9 to 13 months. In the past 2 decades, our understanding of BPDCN pathogenesis has led to the successful development of novel therapeutics. In December 2018, the FDA approved tagraxofusp-erzs for adults and pediatric patients older than 2 years who have either treatment-naïve or relapsed/refractory BPDCN. Acute lymphoblastic leukemia (ALL)-based chemotherapy regimens also provide comparable outcomes to tagraxofusp. In our practice, for patients with good performance status, we use tagraxofusp, ALL-based chemotherapy regimens, or clinical trials as frontline induction therapy, followed by consolidation with allogeneic stem cell transplant once the first complete response has been achieved. Our induction regimen also includes intrathecal chemotherapy for central nervous system prophylaxis. Patients with poor performance status who are treatment-naïve or patients with relapsed/refractory disease have limited therapeutic options, and we strongly recommend enrollment in clinical trials; several novel agents and combinations are currently under clinical investigation for both treatment-naïve and relapsed/refractory BPDCN.

Education on Blastic Plasmacytoid Dendritic Cell Neoplasm Significantly Impacts the Interdisciplinary Physician Team

Education on Blastic Plasmacytoid Dendritic Cell Neoplasm Significantly Impacts the Interdisciplinary Physician Team

Immunophenotypic and Single-Cell Transcriptional Profiling of CD34+ Hematopoietic Stem and Progenitor Cells Mobilized with Motixafortide (BL-8040) and G-CSF Versus Plerixafor and G-CSF Versus Placebo and G-CSF: A Correlative Study of the Genesis Trial

▪Background: CD34 expression remains the most common immunophenotypic cell surface marker defining human hematopoietic stem and progenitor cells (HSPCs). Recently, use of multicolor fluorescence-activated cell sorting (mFACS) and single-cell RNA sequencing (scRNA seq) has illustrated the heterogenous nature of CD34+ HSPCs, with immunophenotypically and transcriptionally distinct subsets ranging from primitive hematopoietic stem cells (HSCs) capable of long-term multilineage potential to differentiated, lineage-committed progenitors. Meanwhile, the addition of CXCR4 inhibitors (CXCR4i) to G-CSF (G) has increased mobilization of CD34+ HSPCs for stem cell transplantation (SCT). Yet, the effect of CXCR4i +/- G on mobilization of specific immunophenotypic and transcriptional CD34+ HSPC subsets is not well-characterized. Motixafortide (M) is a novel cyclic peptide CXCR4i with a low receptor off rate and extended in vivo action vs plerixafor (Px). M was recently evaluated in the phase 3, double blind, placebo controlled GENESIS Trial as an HSPC mobilizer prior to autologous SCT (ASCT) in multiple myeloma (MM).Methods: GENESIS Trial patients were prospectively randomized (2:1) to receive either M+G or placebo (P)+G for HSPC mobilization. Demographically similar patients undergoing mobilization with Px+G prior to ASCT for MM were prospectively enrolled on a parallel tissue banking protocol. All patients received G (10 mcg/kg) on days 1-5 (and 6-8 if needed). Patients also received either M (1.25 mg/kg) or P on day 4 (and 6 if needed); or Px (0.24 mg/kg) on day 4 (and 5-7 if needed). Apheresis began day 5 (and 6-8 if needed). HSPCs were purified from apheresis product on day 5 via CD34+ immunomagnetic selection. CD34+ HSPC subset profiling was performed via mFACS and scRNA seq. CXCR4 expression and receptor occupancy was evaluated by antibody binding capacity of 12G5 and 1D9 clones.Results: Demographics were similar between the M+G (n=24), P+G (n=13) and Px+G (n=14) cohorts. By mFACS, M+G mobilized a 5.5 fold higher absolute number (#) of HSCs, multipotent progenitors (MPP) and common myeloid progenitors (CMP) vs P+G (p<0.0001); and a 2.6 fold higher # of these subsets vs Px+G (p=0.0327) (Figure 1A). M+G mobilized a 10.5 fold higher absolute # of primitive HSCs vs P+G (p<0.0001) and a 1.1 fold higher # vs Px+G (p=0.7876) (Figure 1B). M+G and Px+G mobilized a 7-8 fold higher # of plasmacytoid dendritic cell precursors vs P+G (p-values >0.05). 1D9 binding to CXCR4 on CD34+ HSPCs was similar between all 3 arms (p-values 0.45-0.75). 12G5 binding (which competes with CXCR4i's for binding to CXCR4) was significantly lower with M+G (MFI:11) vs P+G (MFI:74; p<0.0001) and Px+G (MFI:271; p<0.0001).By scRNA seq, UMAP clustering identified 3 transcriptionally similar HSC sub-clusters (HSC-I, -II and -III) mobilized by all 3 regimens; and 1 distinct HSC-PL cluster mobilized by P+G expressing heat shock protein genes (HSPA1 A/B) (Figure 1C). Differentially expressed genes (DEGs) of HSCs I-III included CD52, FTH1, HLA-E, KLF2 and LMNA. AVP was unique to HSC-I while EGR1, JUN and ZFP36 were unique to HSC-III. MPPs clustered into 3 sub-clusters (MPP-I, -II and -III). MPP-I clustered closely to HSC-II/III with low expression of genes of differentiation. MPP-II expressed DEGs (PLEK) on a continuum toward megakaryocyte-erythroid progenitors (MEP-I/II), which expressed DEGs of erythroid differentiation (HBD/HBB). MPP-I and -II contained cells from all 3 regimens. However, MPP-III was specific to M+G with DEGs (MT-ATP8, HIST1H1) associated with monocyte, lymphocyte and NK cell differentiation.Conclusions: Extended CXCR4i with M+G mobilized significantly higher #s of combined CD34+ HSCs, MPPs and CMPs vs Px+G and P+G (p-values <0.05). Additionally, M+G mobilized a 10.5 fold higher # of immunophenotypically primitive CD34+ HSCs capable of broad multilineage hematopoietic reconstitution vs P+G (p<0.0001) and similar #s vs Px+G. CXCR4 expression on CD34+ HSPCs by 1D9 binding was similar across all arms. Whereas, 12G5 binding was much lower with M+G vs P+G and Px+G, consistent with extended CXCR4 receptor occupancy by M. All regimens mobilized transcriptionally similar HSC-I-III subsets. However, lack of CXCR4i (M or Px) resulted in mobilization of more-differentiated HSCs (HSC-PL subset). Whereas extended CXCR4i with M+G (but not Px+G) mobilized a unique MPP-III subset with DEGs related to leukocyte differentiation. [Display omitted] DisclosuresCrees: BioLineRx Ltd.: Research Funding. Retting: BioLineRx Ltd.: Research Funding. Jayasinghe: WUGEN: Consultancy; MMRF: Consultancy. Vainstein: BioLineRx LTD: Current Employment. Sorani: BioLineRx LTD: Current Employment. Ickowicz: BioLineRx Ltd.: Current Employment. Shemesh-Darvish: BioLineRx LTD: Current Employment. Kadosh: BioLineRx Ltd.: Current Employment.

Immunohistochemistry Aids in the Diagnosis of Blastic Plasmacytoid Dendritic Cell Neoplasm in a Patient with Multiple Cutaneous Plaques and Nodules

Abstract Introduction/Objective Blastic Plasmacytoid Dendritic Cell Neoplasm (BPDCN) is a rare hematologic malignancy of plasmacytoid dendritic cell precursors with an estimated incidence of 0.04 cases per 100,000 in the US. Given the cutaneous tropism of BPDCN, it should be differentiated from other CD56+ hematopoietic neoplasms with skin involvement such as CD56+ AML, extranodal NK/T-cell lymphoma, and other T-cell lymphomas. Methods/Case Report A 71-year-old male presented to the emergency department with asymptomatic, pink- violaceous plaques/nodules on the trunk for 3 months. One month prior, a dermatologist diagnosed epidermal inclusion cysts that were left untreated. The nodules progressed and a course of steroids prescribed by a primary care physician provided short term improvement before the lesions flared again. Review of systems and vitals were normal. Biopsies of representative lesions sent for histologic examination showed a diffuse dermal infiltrate of small to medium atypical cells with irregular nuclear contours, fine chromatin, one to several nucleoli and scant cytoplasm. Immunohistochemistry showed these cells were positive for CD2, CD4, CD56 and CD45 with strong expression of BCL2 and focal CD123. The cells were negative for CD3, CD20, CD79a, CD8, CD30, ALK-1, MUM-1, CD10, Cyclin- D1, C-MYC, EBER, BCL6, Langerin, Granzyme, TIA1, CD68, CD163, MPO, and Lysozyme. The histology and immunoprofile were consistent with BPDCN. A bone marrow biopsy showed cells with similar morphology and staining pattern, including expression of CD123.Treatment with chemotherapy and Tagraxofusp, was initiated. Within a week, the patient showed near resolution of cutaneous lesions. Repeat bone marrow aspirate and flow cytometry a month later showed no malignant cells. Results (if a Case Study enter NA) NA Conclusion We present this case as a rare hematologic malignancy with a challenging clinical and histopathologic diagnosis. The histologic findings suggested either a high grade myeloid or lymphoid malignancy. The combination of CD3-/CD56+/CD4+/CD123+ in the lesional cells helped establish the diagnosis of BPDCN, allowing for prompt treatment.

Tre-P-29 - Vindesine dexamethasone as a therapeutic option in elderly blastic plasmacytoid dendritic cell neoplasms: a monocentric experience

Tre-P-29 - Vindesine dexamethasone as a therapeutic option in elderly blastic plasmacytoid dendritic cell neoplasms: a monocentric experience

26508 Blastic plasmacytoid dendritic cell neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematologic neoplasm that arises from precursors of plasmacytoid dendritic cells. Clinical findings of BPDCN may be nondescript, making histologic evaluation, with the aid of immunohistochemical stains, essential. We present a case of a 76-year-old male with no known medical history who presented with chief complaint of a lesion on his chest. He previously thought the lesion was a bruise; however, when it failed to resolve, he sought medical evaluation. The patient denied personal or family history of hematologic malignancy. Thorough review of systems was negative with the exception of recent onset fatigue. Physical examination revealed a solitary, well-defined erythematous-to-violaceous plaque with a central nodular component on the patient’s chest. A 4-mm punch biopsy was obtained from the nodular component. Hematoxylin–eosin evaluation demonstrated dermal nodules of tumor cells extending into the fat with sparing of the overlying epidermis. Individual cells were oval in shape with dispersed nuclear chromatin and eccentric pink plasmacytoid-like cytoplasm. Immunohistochemistry staining was positive for CD123, CD56, and CD4, but negative for CD3, supporting a diagnosis of BPDCN. Subsequently, the patient was referred to hematology and oncology for systemic evaluation and treatment. Our case highlights a rare entity as well as underscores the importance of immunohistochemical stains in accurately diagnosing hematologic neoplasms with cutaneous manifestations. While rare, BPDCN represents an important diagnostic consideration for dermatologists as it most commonly presents in the integumentary system and early identification may impact treatment course and outcome.

Toll-like receptor-9 stimulated plasmacytoid dendritic cell precursors suppress autoimmune neuroinflammation in a murine model of multiple sclerosis

Early innate education of hematopoietic progenitors within the bone marrow (BM) stably primes them for either trained immunity or instead immunoregulatory functions. We herein demonstrate that in vivo or in vitro activation within the BM via Toll-like receptor-9 generates a population of plasmacytoid dendritic cell (pDC) precursors (CpG-pre-pDCs) that, unlike pDC precursors isolated from PBS-incubated BM (PBS-pre-pDCs), are endowed with the capacity to halt progression of ongoing experimental autoimmune encephalomyelitis. CpG activation enhances the selective migration of pDC precursors to the inflamed spinal cord, induces their immediate production of TGF-β, and after migration, of enhanced levels of IL-27. CpG-pre-pDC derived TGF-β and IL-27 ensure protection at early and late phases of the disease, respectively. Spinal cords of CpG-pre-pDC-protected recipient mice display enhanced percentages of host-derived pDCs expressing TGF-β as well as an accumulation of IL-10 producing B cells and of CD11c+ CD11b+ dendritic cells. These results reveal that pDC precursors are conferred stable therapeutic properties by early innate activation within the BM. They further extend to the pDC lineage promising perspectives for cell therapy of autoimmune diseases with innate activated hematopoietic precursor cells.

Blastic plasmacytoid dendritic cell neoplasm with genetic mutations in multiple epigenetic modifiers: a case report

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare, aggressive hematodermic malignancy derived from plasmacytoid dendritic cell precursors. Despite advances in our understanding of tumor cell surface markers, the pathogenesis of BPDCN remains largely unknown. No standard or optimal treatments are available for BPDCN, and the prognosis is usually poor. We report herein a case of BPDCN that harbored multiple genetic mutations in epigenetic modifiers such as TET2 and ZRSR2. Genetic studies in patients with BPDCN may provide insights into the underlying pathogenesis, prediction of clinical prognosis, and development of better targeted therapeutics for this rare clinical entity.

A case series of blastic plasmacytoid dendritic cell neoplasia

Blastic plasmacytoid dendritic cell neoplasm (BPDCN), an extremely rare and aggressive tumor, derives from plasmacytoid dendritic cell precursors and is characterized by CD4 and CD56 positivity accompanied by the expression of isolated myeloid, B- or T-cell lineage markers. Despite the recent introduction of specific targeted therapies, prognosis is still poor with a median overall survival of one year, and allogeneic bone marrow transplantation remains the only curative treatment in eligible patients. In this series, we described two cases of adult BPDCN treated with high dose cytarabine and methotrexate and autologous hematopoietic stem cell transplantation, or fludarabine, cytarabine, and idarubicin achieving the first a complete lasting remission, while the second only a transient improvement in skin lesions.

Whole-genome analysis uncovers recurrent IKZF1 inactivation and aberrant cell adhesion in blastic plasmacytoid dendritic cell neoplasm.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and highly aggressive hematological malignancy with a poorly understood pathobiology and no effective therapeutic options. Despite a few recurrent genetic defects (eg, single nucleotide changes, indels, large chromosomal aberrations) have been identified in BPDCN, none are disease‐specific, and more importantly, none explain its genesis or clinical behavior. In this study, we performed the first high resolution whole‐genome analysis of BPDCN with a special focus on structural genomic alterations by using whole‐genome sequencing and RNA sequencing. Our study, the first to characterize the landscape of genomic rearrangements and copy number alterations of BPDCN at nucleotide‐level resolution, revealed that IKZF1, a gene encoding a transcription factor required for the differentiation of plasmacytoid dendritic cell precursors, is focally inactivated through recurrent structural alterations in this neoplasm. In concordance with the genomic data, transcriptome analysis revealed that conserved IKZF1 target genes display a loss‐of‐IKZF1 expression pattern. Furthermore, up‐regulation of cellular processes responsible for cell‐cell and cell‐ECM interactions, which is a hallmark of IKZF1 deficiency, was prominent in BPDCN. Our findings suggest that IKZF1 inactivation plays a central role in the pathobiology of the disease, and consequently, therapeutic approaches directed at reestablishing the function of this gene might be beneficial for patients.

Features of non-activation dendritic state and immune deficiency in blastic plasmacytoid dendritic cell neoplasm (BPDCN)

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare, male-predominant hematologic malignancy with poor outcomes and with just one recently approved agent (tagraxofusp). It is characterized by the abnormal proliferation of precursor plasmacytoid dendritic cells (pDCs) with morphologic and molecular similarities to acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS)/chronic myelomonocytic leukemia (CMML) in its presentation within the bone marrow and peripheral blood. To identify disease-specific molecular features of BPDCN, we profiled the bone marrow, peripheral blood, and serum samples from primary patient samples using an in-house hematologic malignancy panel (“T300” panel), transcriptome microarray, and serum multiplex immunoassays. TET2 mutations (5/8, 63%) were the most prevalent in our cohort. Using the transcriptome microarray, genes specific to pDCs (LAMP5, CCDC50) were more highly expressed in BPDCN than in AML specimens. Finally, the serum cytokine profile analysis showed significantly elevated levels of eosinophil chemoattractants eotaxin and RANTES in BPDCN as compared with AML. Along with the high levels of PTPRS and dendritic nature of the tumor cells, these findings suggest a possible pre-inflammatory context of this disease, in which BPDCN features nonactivated pDCs.

LINEAGE-SPECIFIC RUNX2 SUPER-ENHANCER ACTIVATES MYC VIA TRANSLOCATION (6;8) AND PROMOTES THE DEVELOPMENT OF BLASTIC PLASMACYTOID DENDRITIC CELL NEOPLASM

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an aggressive subtype of acute leukemia, the cell of origin of which is considered to be precursors of plasmacytoid dendritic cells (pDCs). BPDCN cells show high frequencies of mutations in TET2 and p53; however, the molecular mechanisms underlying the pathogenesis of BPDCN have not yet been elucidated. Since translocation (6;8)(p21;q24) is a recurrent anomaly for BPDCN, we demonstrate that a pDC-specific super-enhancer of RUNX2 is associated with the MYC promoter due to t(6;8). RUNX2 ensures the expression of pDC-signature genes in leukemic cells, but also confers survival and proliferative properties in BPDCN cells. Furthermore, the pDC-specific RUNX2 super-enhancer is hijacked to activate MYC in addition to RUNX2 expression, thereby promoting the proliferation of BPDCN, which is reversed by the deletion of super-enhancer of RUNX2 or the inhibition of BRD4 function. We also demonstrate that the transduction of MYC and RUNX2 is sufficient to initiate the transformation of BPDCN in mice lacking Tet2 and Tp53. Since BPDCN cells show lower expression levels of pDCs-signature genes than mature pDCs in patients and mice, we find that macrophage-dendritic cell progenitors, but not mature pDCs, are at least one of the cells of origin of BPDCN by examining the in vivo tumor initiating capacity of those cells. This study provides a model that accurately recapitulates the aggressive human disease and gives an insight into the molecular mechanisms underlying the pathogenesis of BPDCN.

Lineage-specific RUNX2 super-enhancer activates MYC and promotes the development of blastic plasmacytoid dendritic cell neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an aggressive subtype of acute leukemia, the cell of origin of which is considered to be precursors of plasmacytoid dendritic cells (pDCs). Since translocation (6;8)(p21;q24) is a recurrent anomaly for BPDCN, we demonstrate that a pDC-specific super-enhancer of RUNX2 is associated with the MYC promoter due to t(6;8). RUNX2 ensures the expression of pDC-signature genes in leukemic cells, but also confers survival and proliferative properties in BPDCN cells. Furthermore, the pDC-specific RUNX2 super-enhancer is hijacked to activate MYC in addition to RUNX2 expression, thereby promoting the proliferation of BPDCN. We also demonstrate that the transduction of MYC and RUNX2 is sufficient to initiate the transformation of BPDCN in mice lacking Tet2 and Tp53, providing a model that accurately recapitulates the aggressive human disease and gives an insight into the molecular mechanisms underlying the pathogenesis of BPDCN.

Lineage-Specific RUNX2 Super-Enhancer Activates MYC Via Translocation (6;8) to Promote the Development of Blastic Plasmacytoid Dendritic Cell Neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive hematological malignancy, characteristic of skin lesions followed by hematopoietic organ dissemination. The cell of origin of which is considered to be precursors of plasmacytoid dendritic cells (pDCs). BPDCN cells show high frequencies of mutations in TET2 and p53; however, the molecular mechanisms underlying the pathogenesis of BPDCN have not yet been elucidated. RUNX2 transcription factor, located on chromosome 6p21, is critical for the differentiation of pDCs and the enhancer of RUNX2 is activated in pDCs. Since translocation (6;8)(p21;q24), which is a rare, but specific anomaly for BPDCN, involves regions adjacent to RUNX2 and MYC, we demonstrate that the pDC-specific RUNX2 super-enhancer activates the expression of RUNX2, which functions as a lineage-survival transcription factor, but also is hijacked to activate expression of MYC via t(6;8) in BPDCN cells, and that RUNX2 and MYC promote the initiation and propagation of BPDCN by generating a novel mouse model.In order to identify the breakpoint of t(6;8)(p21;q24), we first performed fluorescent in situ hybridization and whole genome sequencing of CAL-1 cells, a BPDCN cell line, and identified a fusion point of chromosome translocation between chromosome 8 in 69 kilobases (kb) downstream of MYC and chromosome 6, which was 58 kb centromeric to a long and clustered super-enhancer of RUNX2 (791 kb upstream of RUNX2) defined by chromatin immunoprecipitation sequencing using anti-H3K27ac or anti-BRD4 antibodies. As we observed the enhanced levels of MYC and RUNX2 expression in BPDCN cells in patients and CAL-1 cells, we knocked down expression of MYC or RUNX2 using distinct shRNA vectors in CAL-1 cells. We found that the knockdown of MYC and/or RUNX2 significantly impaired colony formation capacities. By performing microarray analysis, we found that RUNX2 knockdown significantly reduced expression of pDCs-signature genes in CAL-1 cells, accompanied with the enhanced apoptosis in CAL-1 cells, implying that RUNX2 is critical for the survival of BPDCN cells due to expressing pDCs-signature genes. To evaluate the function of RUNX2 super-enhancer, we examined how BRD4 inhibition affected the proliferative capacities of CAL-1 cells in vitro. Indeed, we found that JQ1-treated CAL-1 cells showed significantly lower H3K27ac modification levels at the RUNX2 super-enhancer and significantly decreased levels of MYC and RUNX2 expression, resulting in the impaired colony formation capacities, which were rescued by the ectopic expression of both RUNX2 and MYC. We also genetically deleted the mutant-allele super-enhancer of RUNX2 on der(8) (seRUNX2der8), but not that on chromosome 6, using CRISPR-Cas9 vectors. After establishing single cell clones, all seRUNX2der8-deleted clones showed markedly impaired colony formation capacities accompanied with the reduced expression of MYC. Taken together, the seRUNX2der8 directly activates the expression of MYC to promote the development of BPDCN, which is reversed by the inhibition of BRD4.We finally examined whether the transduction of MYC and RUNX2 was sufficient for the initiation of BPDCN in vivo in the absence of Tet2 and p53. We purified Lineage-Sca-1+c-Kit+ stem/progenitor cells from wild-type and Tet2/p53 double knockout (DKO) mice and infected them with MYC- and RUNX2-retrovirus vectors. After a 9-day culture promoting the differentiation of pDCs, we transplanted transduced cells into recipient mice together with wild-type competitor cells. MYC+RUNX2-DKO mice showed robust leukocytosis, anemia, and thrombocytopenia and died by two months post-transplantation following the expansion of immature leukemic blasts. A FACS analysis showed that these leukemic blasts were CD11b-CD11cmid/+B220+Bst2+, which was consistent with the murine pDCs immunophenotype, and massively infiltrated the spleen and liver tissues. MYC+RUNX2-DKO leukemic cells were transplantable in secondary recipient mice with the same immunophenotype. Thus, the transduction of MYC and RUNX2 is sufficient to initiate the transformation of lethal BPDCN-like disease in mice lacking Tet2 and p53. We are now exploring the molecular mechanism of how MYC and RUNX2 collaborate to initiate the formation of BPDCN by performing RNA-sequencing analysis and transplantation assay of BPDCN-initiating cells. DisclosuresAsou:Asahi Kasei Pharma Co., Ltd.: Research Funding; Eisai Co., Ltd.: Research Funding; SRL Inc.: Consultancy; Yakult Honsha Co., Ltd.: Speakers Bureau; Kyowa Hakko Kirin Co., Ltd.: Speakers Bureau; Astellas Pharma Inc.: Research Funding; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Chugai Pharmaceutical Co., Ltd.: Research Funding. Ohyashiki:Pfizer KK,: Honoraria, Research Funding; MSD,: Honoraria, Research Funding; Kyowakko Kirin KK,: Research Funding; Jansen Pharma KK,: Research Funding; Novartis KK,: Honoraria, Research Funding; Celegene KK,: Honoraria, Research Funding; Takeda Pharmaceutical KK,: Honoraria, Research Funding; Taiho Pharmaceutical KK: Honoraria, Research Funding; Asahikase: Research Funding; Asteras KK,: Research Funding; Nihon-Seiyaku,: Research Funding; Eizai,: Research Funding; Dainippon Sumitomo KK,: Honoraria, Research Funding; Nippon-shinyaku,: Honoraria, Research Funding; Bristol Meyer Squibb KK,: Honoraria, Research Funding; Ono Pharmaceutical KK,: Honoraria, Research Funding; Chugai KK,: Honoraria, Research Funding.