Targeting CD123 in blastic plasmacytoid dendritic cell neoplasm using allogeneic anti-CD123 CAR T cells

BH3 Mimetics Augment Cytotoxic T Cell Killing of Acute Myeloid Leukemia via Mitochondrial Apoptotic Mechanism

Adoptive cell therapy (ACT) can address an unmet clinical need for patients with relapsed/refractory acute myeloid leukemia (AML), but its effect is often modest in the setting of high tumor burden. In this study, we postulated that strategies to lower the AML apoptotic threshold will augment T cell killing of AML cells. BH3 mimetics, such as venetoclax, are a clinically approved class of compounds that predispose cells to intrinsic apoptosis by inhibiting anti-apoptotic mitochondrial proteins. We explored the anti-leukemic efficacy of BH3 mimetics combined with WT1-specific CD8 + T cells on AML cell lines and primary samples from patients with a diverse array of disease characteristics to evaluate if lowering the cellular apoptotic threshold via inhibition of anti-apoptotic mitochondrial proteins can increase leukemic cell sensitivity to T cell therapy. We found that the combination approach of BH3 mimetic and CD8 + T cells led to significantly increased killing of established AML lines as well as of adverse-risk primary AML leukemic blast cells. In contrast to the hypothesis that enhanced killing would be due to combined activation of the intrinsic and extrinsic apoptotic pathways, we found that CTL-mediated killing of AML cells was accomplished primarily through activation of the intrinsic/mitochondrial apoptotic pathway. This highly effective combinatorial activity due to convergence on the same apoptotic pathway was conserved across multiple AML cell lines and primary samples, suggesting that mitochondrial priming may represent a novel mechanism of optimizing adoptive cell therapy for AML patients.

Ulcerating skin lesions from blastic plasmacytoid dendritic cell neoplasm responding to low-dose radiotherapy-a case report and literature review

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematologic malignancy that can manifest with skin nodules and erythematous plaques. In most cases BPDCN progresses rapidly, causing multiple skin lesions and also affecting internal organs and bone marrow, warranting initiation of systemic therapies or hematopoietic stem cell transplantation (HCT). Although not curative, radiotherapy for isolated lesions might be indicated in case of (imminent) ulceration and large or symptomatic lesions. To this end, doses of 27.0-51.0 Gy have been reported. Here, we present the case of an 80-year-old male with BPDCN with multiple large, nodular, and ulcerating lesions of the thorax, abdomen, and face. Low-dose radiotherapy of 2 × 4.0 Gy was administered to several lesions, which resolved completely within 1 week with only light residual hyperpigmentation of the skin in affected areas and reliably prevented further ulceration. Radiotoxicity was not reported. Therefore, low-dose radiotherapy can be an effective and low-key treatment in selected cases of BPDCN, especially in a palliative setting, with a favorable toxicity profile.

Overcoming Antigen Escape and T-Cell Exhaustion in CAR-T Therapy for Leukemia

Leukemia is a prevalent pediatric cancer with significant challenges, particularly in relapsed or refractory cases. Chimeric antigen receptor T-cell (CAR-T) therapy has emerged as a personalized cancer treatment, modifying patients' T cells to target and destroy resistant cancer cells. This study reviews the current therapeutic options of CAR-T therapy for leukemia, addressing the primary obstacles such as antigen escape and T-cell exhaustion. We explore dual-targeting strategies and their potential to improve treatment outcomes by preventing the loss of target antigens. Additionally, we examine the mechanisms of T-cell exhaustion and strategies to enhance CAR-T persistence and effectiveness. Despite remarkable clinical successes, CAR-T therapy poses risks such as cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS). Our findings highlight the need for ongoing research to optimize CAR-T applications, reduce toxicities, and extend this innovative therapy to a broader range of hematologic malignancies. This comprehensive review aims to provide valuable insights for improving leukemia treatment and advancing the field of cancer immunotherapy.

Engineering immune-evasive allogeneic cellular immunotherapies

Allogeneic cellular immunotherapies hold a great promise for cancer treatment owing to their potential cost-effectiveness, scalability and on-demand availability. However, immune rejection of adoptively transferred allogeneic T and natural killer (NK) cells is a substantial obstacle to achieving clinical responses that are comparable to responses obtained with current autologous chimeric antigen receptor T cell therapies. In this Perspective, we discuss strategies to confer cell-intrinsic, immune-evasive properties to allogeneic T cells and NK cells in order to prevent or delay their immune rejection, thereby widening the therapeutic window. We discuss how common viral and cancer immune escape mechanisms can serve as a blueprint for improving the persistence of off-the-shelf allogeneic cell therapies. The prospects of harnessing genome editing and synthetic biology to design cell-based precision immunotherapies extend beyond programming target specificities and require careful consideration of innate and adaptive responses in the recipient that may curtail the biodistribution, in vivo expansion and persistence of cellular therapeutics.

Impact of scFv on Functionality and Safety of Third-Generation CD123 CAR T Cells

Chimeric antigen receptor (CAR) T cells express an extracellular domain consisting of a single-chain fragment variable (scFv) targeting a surface tumor-associated antigen. scFv selection should involve safety profiling with evaluation of the efficacy/toxicity balance, especially when the target antigen also is expressed on healthy cells. Here, to assess differences in terms of efficacy and on-target/off-tumor effects, we generated five different CARs targeting CD123 by substituting only the scFv. In in vitro models, T cells engineered to express three of these five CD123 CARs were effectively cytotoxic on leukemic cells without increasing lysis of monocytes or endothelial cells. Using the IncuCyte system, we confirmed the low cytotoxicity of CD123 CAR T cells on endothelial cells. Hematotoxicity evaluation using progenitor culture and CD34 cell lysis showed that two of the five CD123 CAR T cells were less cytotoxic on hematopoietic stem cells. Using a humanized mouse model, we confirmed that CD123- cells were not eliminated by the CD123 CAR T cells. Two CD123 CAR T cells reduced tumor infiltration and increased the overall survival of mice in three in vivo models of blastic plasmacytoid dendritic cell neoplasm. In an aggressive version of this model, bulk RNA sequencing analysis showed that these CD123 CAR T cells upregulated genes associated with cytotoxicity and activation/exhaustion a few days after the injection. Together, these results emphasize the importance of screening different scFvs for the development of CAR constructs to support selection of cells with the optimal risk-benefit ratio for clinical development.

Blastic Plasmacytoid Dendritic Cell Neoplasm Presenting as a Mammary Gland Tumor in a Pediatric Patient: A Case Report

Emanating from a discrete category within the lympho-hematopoietic tumor system, as established by the World Health Organization in 2008, the blastic plasmacytoid dendritic cell neoplasm constitutes an uncommon malignant hematological disorder. It is routinely misidentified on account of its conspicuous dermatological manifestation, yet may insidiously permeate bone marrow and lymph nodes, involving peripheral blood and diverse extra-nodal tissues. Instances of mammary gland encroachment are extraordinarily infrequent. The current document delineates a case of a 14-year-old female patient contending with blastic plasmacytoid dendritic cell neoplasm, whose primary symptom was a mammary nodule, and whose breast and bone marrow/blood involvement were synchronous, in attempt to increase clinical vigilance.

IL-3: key orchestrator of inflammation

Interleukin (IL)-3 has long been known for its hematopoietic properties. However, recent evidence has expanded our understanding of IL-3 function by identifying IL-3 as a critical orchestrator of inflammation in a wide array of diseases. Depending on the type of disease, the course of inflammation, the cell or the tissue involved, IL-3 promotes either pathologic inflammation or its resolution. Here, we describe the cell-specific functions of IL-3 and summarize its role in diseases. We discuss the current treatments targeting IL-3 or its receptor, and highlight the potential and the limitations of targeting IL-3 in clinics.

A systematic literature review of 74 Chinese blastic plasmacytoid dendritic cell neoplasm patients

Background

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive hematological cancer. Due to its low incidence, researchers struggle to gather sufficient prospective data to inform clinical treatment.

Objectives

We sought to summarize the clinical characteristics and current treatment methods of BPDCN and provide more specific guidance on treatment options.

Design

A systematic literature review using data from 74 Chinese BPDCN patients.

Date resources and methods

We retrospectively analyzed the clinical manifestations, treatment response, survival outcomes, and prognostic factors of six BPDCN patients treated at the First Affiliated Hospital of Zhengzhou University and 68 patients described in 28 articles published in the China Knowledge Network database since 2019.

Results

In Chinese patients, the disease occurred with a male-to-female ratio of 2.52 and a median age of onset of 50 years in adults and 10 years in pediatric patients. Immunohistochemical analysis revealed distinctive immune phenotypes of BPDCN cells, characterized by high expression levels of CD4, CD56, CD123, and HLA-DR, while showing minimal to no expression of myeloperoxidase (MPO), CD20, and CD79a. There was no significant difference in the initial complete remission (CR) rate, relapse rate, and the overall survival (OS) time of patients receiving acute myeloid leukemia-like, acute lymphocytic leukemia-like, or non-Hodgkin's lymphoma-like chemotherapy regimens. Univariate analysis identified CD3 expression, male gender, and central nervous system infiltration as hazardous factors. In multivariate analysis, age proved to be an independent prognostic indicator, indicating better prognosis and longer OS time in younger patients. Notably, hematopoietic stem cell transplantation (HSCT) emerged as a significant factor in improving the survival outcomes for individuals diagnosed with BPDCN. However, further investigation is needed to explore the role of HSCT and the best timing for its implementation in pediatric BPDCN patients.

Conclusion

Administering HSCT during the initial CR state following inductive chemotherapy might extend the OS and improve the prognosis of patients with BPDCN.

Peptide-scFv antigen recognition domains effectively confer CAR T cell multiantigen specificity

The emergence of immune escape is a significant roadblock to developing effective chimeric antigen receptor (CAR) T cell therapies against hematological malignancies, including acute myeloid leukemia (AML). Here, we demonstrate feasibility of targeting two antigens simultaneously by combining a GRP78-specific peptide antigen recognition domain with a CD123-specific scFv to generate a peptide-scFv bispecific antigen recognition domain (78.123). To achieve this, we test linkers with varying length and flexibility and perform immunophenotypic and functional characterization. We demonstrate that bispecific CAR T cells successfully recognize and kill tumor cells that express GRP78, CD123, or both antigens and have improved antitumor activity compared to their monospecific counterparts when both antigens are expressed. Protein structure prediction suggests that linker length and compactness influence the functionality of the generated bispecific CARs. Thus, we present a bispecific CAR design strategy to prevent immune escape in AML that can be extended to other peptide-scFv combinations.

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.

Pediatric Blastic Plasmacytoid Dendritic Cell Neoplasm: A Case Report

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive neoplastic process of precursor plasmacytoid dendritic cells. The diagnostic evaluation of this heterogenous entity is challenging, requiring a comprehensive approach of incorporating clinical, morphologic, immunohistochemical, and molecular/cytogenetic evaluations. Optimal management of BPDCN remains controversial, and clinical outcomes continues to be poor. Pediatric cases of BPDCN are rare and to our knowledge, this is the second case of BPDCN described in a Hispanic child, first one was described outside the US in Peru. Here, we report a case of a juvenile patient of Hispanic origin presenting with cutaneous and bone marrow involvement and initially misdiagnosed as a cutaneous infection that resulted in subsequent delaying of necessary chemotherapy for 2 months. Biopsy of the lesion showed diffuse infiltration of immature cells involving the dermis with classical sparring of epidermis. A huge panel of immunohistochemical stains were performed to reach the diagnosis of BPDCN. Staging bone marrow biopsy also revealed involvement by BPDCN. Treatment was not only delayed in this patient but also due to the rarity of BPDCN in pediatric population, the subsequent therapeutic decisions were challenging for the primary oncology team as it was based solely on published literature on adult population. Our case report will not only add one more case in the pediatric age group, but also will also emphasize that although BPDCN has a grave prognosis in the elderly, timely diagnosis with prompt treatment is the key to complete remission in pediatric BPDCN population.

Advancing CART therapy for acute myeloid leukemia: recent breakthroughs and strategies for future development

Chimeric antigen receptor (CAR) T therapies are being developed for acute myeloid leukemia (AML) on the basis of the results obtained for other haematological malignancies and the need of new treatments for relapsed and refractory AML. The biggest challenge of CART therapy for AML is to identify a specific target antigen, since antigens expressed in AML cells are usually shared with healthy haematopoietic stem cells (HSC). The concomitant expression of the target antigen on both tumour and HSC may lead to on-target/off-tumour toxicity. In this review, we guide researchers to design, develop, and translate to the clinic CART therapies for the treatment of AML. Specifically, we describe what issues have to be considered to design these therapies; what in vitro and in vivo assays can be used to prove their efficacy and safety; and what expertise and facilities are needed to treat and manage patients at the hospital.

Allogeneic hematopoietic cell transplantation for blastic plasmacytoid dendritic cell neoplasm: a CIBMTR analysis

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematological malignancy with a poor prognosis and considered incurable with conventional chemotherapy. Small observational studies reported allogeneic hematopoietic cell transplantation (allo-HCT) offers durable remissions in patients with BPDCN. We report an analysis of patients with BPDCN who received an allo-HCT, using data reported to the Center for International Blood and Marrow Transplant Research (CIBMTR). We identified 164 patients with BPDCN from 78 centers who underwent allo-HCT between 2007 and 2018. The 5-year overall survival (OS), disease-free survival (DFS), relapse, and nonrelapse mortality (NRM) rates were 51.2% (95% confidence interval [CI], 42.5-59.8), 44.4% (95% CI, 36.2-52.8), 32.2% (95% CI, 24.7-40.3), and 23.3% (95% CI, 16.9-30.4), respectively. Disease relapse was the most common cause of death. On multivariate analyses, age of ≥60 years was predictive for inferior OS (hazard ratio [HR], 2.16; 95% CI, 1.35-3.46; P = .001), and higher NRM (HR, 2.19; 95% CI, 1.13-4.22; P = .02). Remission status at time of allo-HCT (CR2/primary induction failure/relapse vs CR1) was predictive of inferior OS (HR, 1.87; 95% CI, 1.14-3.06; P = .01) and DFS (HR, 1.75; 95% CI, 1.11-2.76; P = .02). Use of myeloablative conditioning with total body irradiation (MAC-TBI) was predictive of improved DFS and reduced relapse risk. Allo-HCT is effective in providing durable remissions and long-term survival in BPDCN. Younger age and allo-HCT in CR1 predicted for improved survival, whereas MAC-TBI predicted for less relapse and improved DFS. Novel strategies incorporating allo-HCT are needed to further improve outcomes.

Expanding the Immunophenotypic Spectrum of Neoplastic and Reactive Plasmacytoid Dendritic Cells

OBJECTIVES

Targeted therapies for blastic plasmacytoid dendritic cell neoplasm (BPDCN) have presented a diagnostic dilemma for differentiating residual BPDCN from reactive plasmacytoid dendritic cells (pDCs) because these conditions have a similar immunoprofile, necessitating discovery of additional diagnostic markers.

METHODS

Fifty cases of BPDCN involving bone marrow (26/50) and skin (24/50) as well as other hematologic malignancies (67) and nonneoplastic samples (37) were included. Slides were stained using a double-staining protocol for the following immunohistochemical marker combinations: TCF4/CD123, TCF4/CD56, SOX4/CD123, and IRF8/CD123.

RESULTS

The nuclear marker SOX4 is expressed in neoplastic pDCs; in our cohort, SOX4/CD123 showed 100% sensitivity and 98% specificity in distinguishing BPDCN from reactive pDCs and other neoplasms. TCF4/CD56 had a 96% sensitivity and 100% specificity for BPDCN. IRF8 is a nonspecific marker that is positive in BPDCN and pDCs as well as other myeloid malignancies.

CONCLUSIONS

The novel immunohistochemical combination SOX4/CD123 distinguishes BPDCN, including CD56-negative BPDCN, from both reactive pDCs and other neoplasms. Because of their high diagnostic sensitivity and specificity, the double-staining marker combinations TCF4/CD123, TCF4/CD56, and SOX4/CD123 can be used to confirm lineage in BPDCN cases and detect minimal/measurable residual disease in tissue specimens.

Plasmacytoid dendritic cell neoplasms

Plasmacytoid dendritic cells (pDCs) are type I interferon-producing cells that modulate immune responses. There are two types of pDC neoplasms: 1) mature pDC proliferation (MPDCP) associated with myeloid neoplasm and 2) blastic pDC neoplasm (BPDCN). MPDCP is a clonal expansion of mature pDCs that is predominantly associated with chronic myelomonocytic leukemia. In contrast, BPDCN is a clinically aggressive myeloid malignancy involving the skin, bone marrow, lymphatic organs, and central nervous system. There are various types of skin lesions, ranging from solitary brown or violaceous to disseminated cutaneous lesions, which often spread throughout the body. The expression of CD4, CD56, CD123, and pDC markers (TCL-1, TCF4, CD303, and CD304, etc.) are typical immunophenotype of BPDCN. Historically, BPDCN treatment has been based on acute leukemia regimens and allogeneic hematopoietic cell transplantation in selected patients. Recent advances in molecular biology and genetics have led to the development of targeted agents, such as tagraxofusp (a recombinant fusion protein targeting CD123), anti-CD123 CAR-T cells, XmAb14045, and IMGN632. Lastly, this review provides a comprehensive overview of pDC neoplasms.

Cancer stem cells: Recent insights and therapies

Tumors are intricate ecosystems containing malignant components that generate adaptive and evolutionarily driven abnormal tissues. Through self-renewal and differentiation, cancers are reconstructed by a dynamic subset of stem-like cells that enforce tumor heterogeneity and remodel the tumor microenvironment (TME). Through recent technology advances, we are now better equipped to investigate the fundamental role of cancer stem cells (CSCs) in cancer biology. In this review, we discuss the latest insights into characteristics, markers and mechanism of CSCs and describe the crosstalk between CSCs and other cells in TME. Additionally, we explore the performance of single-cell sequencing and spatial transcriptome analysis in CSCs studies and summarize the therapeutic strategies to eliminate CSCs, which could broaden the understanding of CSCs and exploit for therapeutic benefit.

Diagnosis, treatment, and genetic characteristics of blastic plasmacytoid dendritic cell neoplasm: A review

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a highly aggressive and extremely rare hematologic disease with a poor prognosis, involving mainly the skin and bone marrow. The immunophenotype of these tumor cells is characterized by the expression of CD4, CD56, CD123, TCL-1, and CD303. To date, no consensus has been reached on the standard of care for BPDCN. Currently, clinical treatment is mainly based on high-dose chemotherapy combined with hematopoietic stem cell transplantation. However, this treatment method has limitations for elderly, frail, and relapsed/refractory patients. In recent years, breakthroughs in molecular biology and genetics have not only provided new ideas for the diagnosis of BPDCN but also helped develop targeted treatment strategies for this disease. The emergence of targeted drugs has filled the gap left by traditional therapies and shown great clinical promise. This article focuses on the latest advances in genetics and targeted therapies for BPDCN, especially the emerging therapies that may provide new ideas for the clinical treatment of BPDCN.

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.

Prognostic factors of second hematopoietic allogeneic stem cell transplantation among hematological malignancy patients relapsed after first hematopoietic stem cell transplantation: A single center study

Introduction

We aimed to evaluate prognostic factors of a second allogeneic stem cell transplantation (allo-HSCT2) among hematological malignancy patients who have relapsed after the first allo-HSCT(allo-HSCT1).

Methods

We retrospectively analyzed 199 hematological malignancy patients who received allo-HSCT2 as a salvage treatment post allo-HSCT1 relapse between November 2012 and October 2021.

Results

The median age at allo-HSCT2 was 23 (range: 3-60) years. The median time to relapse after HSCT1 was 9 (range: 1-72) months. Prior to allo-HSCT2, patients had the following hematopoietic cell transplantation-comorbidity indexes (HCT-CI): 127 with a score of 0, 52 with a score of 1, and 20 with a score of 2 or greater. Fifty percent of patients received chimeric antigen receptor (CAR) T-cell therapy following HSCT1 relapse. Disease status was minimal residual disease (MRD)-negative complete remission (CR) among 119 patients, MRD-positive CR among 37 patients and non-remission (NR) for 43 patients prior to allo-HSCT2. Allo-HSCT2 was performed from a new donor in 194 patients (97.4%) and 134 patients (67.3%) received a graft with a new mismatched haplotype. The median follow-up time was 24 months (range: 6-98 months), and the 2-year OS and LFS were 43.8% ± 4.0% and 42.1% ± 4.1%, respectively. The 2-year cumulative incidence of relapse (CIR) and non-relapse mortality (NRM) was 30.0%±4.8% and 38.5%±3.8%, respectively. Cox regression multivariate analysis showed that disease statusof MRD-negative CR, HCT-CI score of 0 prior to allo-HSCT2, and new mismatched haplotype donor were predictive factors of improved OS and LFS compared to patients without these characteristics. Based on these three favorable factors, we developed a predictive scoring system for patients who received allo-HSCT2. Patients with a prognostic score of 3 who had the three factors showed a superior 2-year OS of 63.3% ± 6.7% and LFS of 63.3% ± 6.7% and a lower CIR of 5.5% ± 3.1% than patients with a prognostic score of 0. Allo-HSCT2 is feasible and patients with good prognostic features prior to allo-HSCT2 -disease status of CR/MRD- and HCT-CI score of 0 as well as a second donor with a new mismatched haplotype could have the maximal benefit from the second allo-HSCT.

Conclusions

Allo-HSCT2 is feasible and patients with good prognostic features prior to allo-HSCT2 -disease status of CR/MRD- and HCT-CI score of 0 as well as a second donor with a new mismatched haplotype could have the maximal benefit from the second allo-HSCT.

CD123-directed allogeneic chimeric-antigen receptor T-cell therapy (CAR-T) in blastic plasmacytoid dendritic cell neoplasm (BPDCN): Clinicopathological insights

PURPOSE

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a hematologic malignancy associated with overexpression of CD123. Allogeneic chimeric antigen receptor T cells (CAR-T) directed against CD123 in BPDCN have been studied in clinical trials. We performed post-mortem analysis of a patient treated with anti-CD123 CAR-T to elucidate cause of death, development of cytokine release syndrome (CRS), and tissue distribution of UCART123 cells.

METHODS

A post-mortem multidisciplinary clinicopathologic analysis was performed with digital droplet polymerase chain reaction of isolated blood and tissue ribonucleic acid (RNA) to evaluate tissue distribution of infused CAR-T. Multiparameter flow cytometry for detection of CAR-T was used for whole blood samples. Cytokine levels in plasma were measured using multiplex bead assay. Gene expression profiling on isolated RNA was performed using semi-custom Nanostring immune gene panel and RNA-sequence method. RNA in situ hybridization was performed using CAR-specific probe.

RESULTS

The patient developed severe clinical CRS refractory to corticosteroids, tocilizumab, and lymphodepletion. Despite significant reduction in BPDCN lesions, the patient passed away on day 9 of CAR-T. Autopsy results show that following lymphodepletion and UCART123 administration, the patient remained severely lymphopenic with few UCART123 cells detected, predominantly localized to spleen.

CONCLUSIONS

No definitive cause of death was determined, but we hypothesized that the patient may have succumbed to CAR-T-mediated cardiopulmonary toxicity. UCART123 cells displayed low overall distribution, with predominance in immune organs and tissues. Mechanism of CRS development is still poorly understood in patients receiving CAR-T therapy. Future directions in the field developing CD123-targeted agents in BPDCN are discussed.