CD123 Positivity Research Articles

Flow cytometric immunophenotypic features of acute myeloid leukemia with mast cell differentiation.

Acute myeloid leukemia (AML) with mast cell (MC) differentiation was recently described as an aggressive subgroup of AML cases. The objectives of this study were to assess the flow cytometric immunophenotypic features of AML-MC cases. We characterized the immunophenotypic features of 21 AML-MC cases by flow cytometry and compared them to 20 reactive/regenerating bone marrow specimens. The number of MCs detected by flow cytometry in AML-MC cases ranged from 0.4% to 21.1%, with a median of 3.5%, significantly higher than that of normal/reactive bone marrow (BM) (median, 0.01%; range, 0.000%-0.396%; P < .0001). Immunophenotypically, MCs in AML-MC cases demonstrated immaturity, differing from MCs in normal/reactive BMs, including dimmer CD45 (100% vs 0%), lower side scatter (100% vs 0%), more frequent CD34 (81% vs 20%), and CD123 (100% vs 10%) positivity, and more frequent uniform/increased CD38 expression (95% vs 20%) (all P ≤ .0001). CD2 (0/5) and CD25 (2/6, 1 uniform and 1 partial) were assessed in a subset of cases. The myeloblasts in AML-MC were typically CD34+CD117+HLA-DR+ with unusually frequent expression of CD56 (57%, all partial) and CD25 (63%, mostly partial), increased CD117 (62%), and decreased CD38 (86%). The MC percentage determined by flow cytometry correlated well with MCs detected by tryptase immunohistochemistry (r = 0.76, P < .001). The MCs in AML-MC cases are characterized by dim CD45, low side scatter, CD34 and CD123 positivity, and uniform and increased CD38 expression. Flow cytometry is an excellent tool for identifying AML-MC cases.

Frontline Hyper-CVAD Plus Venetoclax for Pediatric Blastic Plasmacytoid Dendritic Cell Neoplasm.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematologic malignancy, especially in pediatrics, that can involve the bone marrow, skin, lymph nodes, and central nervous system (CNS). Given its variable clinical presentation, coupled with an immunohistochemistry pattern (CD4, CD56, TCF4, TCL-1, and CD123 positivity) that differs from other myeloid neoplasms, the diagnosis of BPDCN can be missed. Limited data are available to guide the treatment of pediatric BPDCN. Herein, we report a case of a pediatric patient who had BPDCN with central nervous system, orbital, and skin involvement. This patient achieved complete remission after receiving modified hyper-CVAD (hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone with venetoclax and intrathecal chemotherapy. He remains disease-free 200 days after receiving a stem cell transplant. This represents the first known published pediatric case using a modified hyper-CVAD plus venetoclax regimen for treating a pediatric BPDCN patient in the frontline setting.

Ameli-01: A Phase I Trial of UCART123v1.2, an Anti-CD123 Allogeneic CAR-T Cell Product, in Adult Patients with Relapsed or Refractory (R/R) CD123+ Acute Myeloid Leukemia (AML)

Introduction: UCART123v1.2 is a genetically modified allogeneic T-cell product manufactured from healthy donor cells. Donor-derived T-cells are transduced using a lentiviral vector to express the anti-CD123 chimeric antigen receptor and are further modified using Cellectis' TALEN® technology to disrupt the T-cell receptor alpha constant (TRAC) and CD52 genes to minimize risk of graft-vs-host disease (GvHD) and allow use of anti-CD52-directed therapy as part of lymphodepletion (LD). AMELI-01 (NCT04106076) is a phase 1, open-label, dose-escalation trial evaluating the safety, tolerability, expansion, and persistence of UCART123v1.2 given at escalating dose levels after LD with either fludarabine and cyclophosphamide (FC) or FC with alemtuzumab (FCA) in patients (pts) with R/R CD123+ AML. Alemtuzumab was added to the LD regimen to sustain host T- and NK-cell depletion and to promote UCART123v1.2-cell expansion and persistence. Methods: Key eligibility criteria include pts 18-65 yrs, adequate organ function, ECOG PS ≤ 1, and blasts positive for CD123 by flow cytometry. Pts must have received ≥2 cycles of chemotherapy (one with standard dose cytarabine), ≥ 1 cycle of a high/intermediate dose cytarabine containing regimen, ≥ 2 cycles of an HMA combination regimen, or prior allogeneic HSCT. After LD with FC or FCA, pts received UCART123v1.2 at one of the following dose levels: 2.5x105 cells/kg (DL1); 6.25x105 cells/kg (DL2); 1.5x106 cells/kg (DL2i); or 3.03x106 cells/kg (DL3). The primary endpoint is the safety, tolerability, and MTD/RP2D of UCART123v1.2. DLTs are assessed over a 28d observation period after UCART123v1.2 infusion. Additional endpoints include investigator assessed anti-leukemic activity per 2017 ELN criteria, and expansion, trafficking, and persistence of UCART123v1.2 (assessed in peripheral blood [PB] and bone marrow [BM] by flow cytometry and vector copy number [VCN]). Measurable residual disease (MRD) was analyzed by local multiparameter flow cytometry with a sensitivity of 0.02%. Results: As of July 1, 2022, 16 pts received LD and UCART123v1.2; 8 pts received UCART123v1.2 after FC (DL1 [n=2]; DL2 [n=3]; DL2i [n=2]; DL3 [n=1]), and 8 pts received UCART123v1.2 after FCA (DL2). Pts were high risk and heavily pretreated with disease characteristics outlined in Table 1. Median baseline BM and PB % blasts was 37% (0-88%) and 19% (0-79%), and median baseline CD123 positivity by central flow cytometry in the FC and FCA arms was 82% (17-98%) and 84% (25-97%), respectively. Four pts experienced DLTs: 3 pts in FC arm (G4 CRS [1pt in DL2i and 1pt in DL3] and G3 ICANS [1pt in DL2i]); and 1 pt in FCA arm (G5 CRS in DL2). Cytokine release syndrome (CRS) occurred in 15/16 pts (FC arm [n=7]; FCA arm [n=8]), of which 3 pts experienced ≥ G3 CRS which were classified as DLTs as noted above (FC arm G4 [n=2]; FCA arm G5 [n=1]). Responses were assessed beginning on D28. Evidence of UCART123v1.2 activity was observed in 4/16 pts with best overall responses as follows: FC arm (DL2: 1 SD; DL2i: 1 MLFS); FCA arm (DL2: 1 SD and 1 MRD-negative CR). The pt in the DL2 FCA arm with SD achieved greater than 90% BM blast reduction (60% to 5%) at D28. The pt with CR, who had failed 5 prior lines of therapy including HSCT and had baseline G4 cytopenias, had CRi at D28 with full count recovery at D56 and remains in an MRD-negative CR beyond the 8-month f/u visit. Adequate lymphodepletion was not achieved in the FC arm, as host lymphocyte recovery was observed in 7/8 pts prior to D28, and only 3/8 pts had UCART123v1.2 expansion (Cmax ranged from 3,757 to 27,828 copies/μg DNA). In contrast, FCA LD resulted in robust lymphodepletion for greater than 28 days in all pts, and 6/8 demonstrated UCART123v1.2 expansion, with Cmax ranging from 13,177 to 330,530 copies/μg DNA, an almost 9-fold increase compared with FC LD. An increase in inflammatory markers, notably serum ferritin, and serum cytokines (including IL-2, IL-6, IL-10, IL-15, IFN-γ, and TNF-α) in the FCA arm correlated with both UCART123v1.2 expansion and CRS. Conclusions: Adding alemtuzumab to the FC regimen was associated with improved LD and significantly higher UCART123v1.2 cell expansion and persistence, which correlated with improved activity and safety, including one pt in the DL2 FCA arm who achieved a durable MRD-negative CR. Overall, these data support the safety and activity of UCART123v1.2 after FCA LD in pts with CD123+ R/R AML. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Phase I Study of Tagraxofusp with or without Chemotherapy in Pediatric Patients with Relapsed or Refractory CD123-Expressing Hematologic Malignancies: A Therapeutic Advances in Childhood Leukemia and Lymphoma (TACL) Consortium Trial

Background: Tagraxofusp is a protein-drug conjugate consisting of a human interleukin-3 fused to a truncated diphtheria toxin payload and is the first CD123 targeted agent approved by the FDA. Tagraxofusp is approved as a single agent for the treatment of individuals age 2 years and above with Blastic Plasmacytoid Dendritic Cell Neoplasm (BPDCN) based on a 90% overall response rate and favorable toxicity profile (Pemmaraju et al. NEJM 2019; 380:1628-1637). CD123 is widely expressed on a variety of other hematologic malignancies, including the majority of patients with acute myeloid leukemia (AML) and some subtypes of B- and T-cell acute lymphoblastic leukemia (ALL). The potent activity of tagraxofusp in BPDCN, coupled with the favorable toxicity profile, makes tagraxofusp a compelling agent for study in other CD123-expressing malignancies with high unmet needs. Our proposal to study this agent represents the first trial of tagraxofusp as a single agent and in combination with other agents for children and young adults with CD123-expressing hematologic malignancies. Study Design and Methods: This is a non-randomized, open-label, multicenter phase I dose-determination trial for children < 21 years of age with relapsed and/or refractory CD123-expressing hematologic malignancies (NCT05476770). The study is conducted through the Therapeutic Advances in Childhood Leukemia and Lymphoma (TACL) Consortium and consists of 2 sequential parts. Tagraxofusp is administered intravenously once daily over 5 days for both parts. In Part 1, tagraxofusp monotherapy is initiated at the FDA-approved dose of 12 mcg/kg and incorporates a single dose escalation and de-escalation. In Part 2, tagraxofusp will be initiated at one dose level below the Part 1 recommended dose in combination with other agents in three cohorts: Cohort A incorporates myeloid-directed combination therapy (fludarabine, high-dose cytarabine); Cohort B incorporates lymphoid-directed combination therapy (vincristine, dexamethasone); and Cohort C incorporates the hypomethylating agent azacitidine. Each cohort includes a single dose escalation of tagraxofusp. Cohort allocation is determined by investigator preference but patients with measurable residual disease (defined as 1% to < 5%) are only eligible for Cohort C. Depending on response, patients in both parts and all cohorts are eligible to receive subsequent cycles of tagraxofusp monotherapy (maximum of 5 additional cycles). Key Eligibility: Patients age 1 to 21 years with two or more relapses or refractory CD123-expressing hematologic malignancies are eligible for Part 1 and patients with hematologic malignancies in first relapse or refractory to de novotreatment are eligible for Part 2. Patients with Down Syndrome are eligible to receive tagraxofusp as monotherapy at the same dose level as patients with non-Down Syndrome. Patients with BPDCN in first relapse are eligible for both parts. Confirmation of qualitative CD123 positivity at the treating site is required. Objectives: The primary objectives are to assess safety and tolerability of tagraxofusp monotherapy (Part 1) and in combination with chemotherapy (Part 2) in pediatric and young adult patients with relapsed/refractory CD123-expressing hematologic malignancies. Secondary objectives include pharmacokinetics and anti-tumor activity within the context of a phase I study. Correlative studies will assess for biomarkers of tagraxofusp response and explore potential mechanisms of resistance. Sample Size and Statistical Design: Part 1 utilizes a standard 3+3 dose escalation/de-escalation design and, based on safety and tolerability, is planned to enroll between 4 and 18 patients with 3 dose levels. Part 2 also utilizes astandard 3+3 design but with a single escalation and is planned to enroll between 6 and 36 patients. The study is open to accrual at select TACL sites. Support: This study is conducted by the TACL Consortium with financial support from Stemline Therapeutics. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Efficacy of Flotetuzumab in Combination with Cytarabine in Patient-Derived Xenograft Models of Pediatric Acute Myeloid Leukemia.

Children with acute myeloid leukemia (AML) have a poor prognosis despite the intensification of chemotherapy. Future efforts to improve outcomes should focus on more precise targeting of leukemia cells. CD123, or IL3RA, is expressed on the surface of nearly all pediatric AML samples and is a high-priority target for immunotherapy. The efficacy of an investigational dual-affinity retargeting antibody (DART) molecule (CD123 × CD3; MGD006 or flotetuzumab) was assessed in two distinct patient-derived xenograft (PDX) models of pediatric AML. MGD006 simultaneously binds to CD123 on target cells and CD3 on effector T cells, thereby activating T cells and redirecting them to induce cytotoxicity in target cells. The concurrent treatment of cytarabine and MGD006 was performed to determine the effect of cytarabine on T-cell counts and MGD006 activity. Treatment with MGD006 along with an allogeneic human T-cell infusion to act as effector cells induced durable responses in both PDX models, with CD123 positivity. This effect was sustained in mice treated with a combination of MGD006 and cytarabine in the presence of T cells. MGD006 enhanced T-cell proliferation and decreased the burden of AML blasts in the peripheral blood with or without cytarabine treatment. These data demonstrate the efficacy of MGD006 in prolonging survival in pediatric AML PDX models in the presence of effector T cells and show that the inclusion of cytarabine in the treatment regimen does not interfere with MGD006 activity.

CD123 Expression Patterns and Potential of IMGN632, a CD123-Targeted Antibody Drug Conjugate, in Acute Lymphoblastic Leukemia

Background: The interleukin (IL)-3 receptor α-chain, CD123, is the primary low-affinity subunit of the IL-3 receptor. CD123 is expressed at various levels in hematologic malignancies and has thus become an attractive target of therapy. While CD123 expression in precursor B-lymphoblastic leukemia/lymphoma (B-ALL) has been reported, only limited data in T-ALL exists. Furthermore, the potential of CD123-targeted therapies in ALL remains largely unexplored. In this study, we examine CD123 expression levels in a large cohort of ALL patients and assess the impact of IMGN632, a conjugate of a CD123-binding antibody with the novel DNA-alkylating IGN payload DGN549, on in vitro viability of patient ALL cells and cell lines.Methods: The study cohort (n=188) included 162 B-ALL and 26 T-ALL patients diagnosed and treated at the University of Texas MD Anderson Cancer Center between 12/2012 and 1/2017. Among B-ALL patients, 59 (36%) were Philadelphia chromosome-positive (Ph+). T-ALL patients were further subtyped into the following immunophenotypic categories: early, early T precursor (ETP), thymic, and mature. CD123 expression was evaluated using multiparameter flow cytometry (MFC). Blasts were defined by lineage markers as well as CD45dim blast gate, and CD123 expression was measured for the percentage of positivity and mean fluorescence intensity (MFI) ratio over controls. An arbitrary cutoff of 20% was used for expressing nominal MFC results. Median follow up duration was 21.1 months. CD123 expression was correlated with clinical, laboratory, and outcomes results. The number of binding sites for IMGN632 on ALL blast and cell lines was quantified by QuantiBRITE method. Cytotoxicity of IMGN632 was evaluated after continuous exposure up to five days by WST-8 assays on cell lines or by MFC on primary ALL patient samples.Results: Patients had a median age of 46 years (range, 16-88 years) and included 117 (62%) men. The median CD123 positivity on ALL blasts was 78% (range, 0.3-100) with a median MFI ratio of 11 (range, 0-203). For categorical analysis purposes, we used a standard cutoff of 20% to define positive CD123 expression. Prevalence of CD123 expression was overall higher in B-ALL compared to T-ALL [145 (90%) vs. 11 (42%); p<0.001]. Expression prevalence was highest in Ph+ B-ALL (57/59; 97%) followed by Ph- B-ALL (88/103; 85%) and T-ALL (11/26; 42%). In Ph- B-ALL, CD123 expression correlated with CD34 expression (p=0.002) and lower bone marrow blast count (p=0.003). In T-ALL, CD123 expression correlated with immunophenotypic subtypes (early) (p=0.006). To test the potential of targeting CD123 in ALL, B-ALL cell lines (n=12) which express CD123 at levels similar to AML patient samples were exposed to titrated IMGN632 levels. IMGN632 IC50 values ranged between 0.6 and 20 pM, and the conjugate cytotoxicity was highly CD123-specific, as masking CD123 with a competing anti-CD123 antibody reduced the potency more than 1000-fold. To test the anti-leukemia activity of IMGN632 on primary B-ALL cells, bone marrow cells from B-ALL patients were exposed to IMGN632 following which blasts and non-malignant cells were enumerated by MFC. Notably, IMGN632 eliminated more than 90% of B-ALL blasts in 6 out of 8 samples from newly-diagnosed as well as relapsed-refractory patients at low pico-molar concentrations. Normal cells were not affected by IMGN632 at 100-fold higher concentrations.Conclusions: CD123 expression is prevalent across ALL subtypes, including 90% of B-ALL and 42% of T-ALL. CD123 expression was associated with CD34 expression in B-ALL and immunophenotype in T-ALL. The CD123 targeted antibody-drug conjugate IMGN632 demonstrates promising activity and safety in pre-clinical models of B-ALL._ [Display omitted] DisclosuresDaver:Incyte Corporation: Honoraria, Research Funding; Daiichi-Sankyo: Research Funding; Immunogen: Research Funding; Karyopharm: Consultancy, Research Funding; Jazz: Consultancy; Pfizer Inc.: Consultancy, Research Funding; Sunesis Pharmaceuticals, Inc.: Consultancy, Research Funding; Kiromic: Research Funding; Bristol-Myers Squibb Company: Consultancy, Research Funding; Otsuka America Pharmaceutical, Inc.: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy. Zweidler-McKay:ImmunoGen: Employment. Kantarjian:ARIAD: Research Funding; Amgen: Research Funding; Delta-Fly Pharma: Research Funding; Bristol-Meyers Squibb: Research Funding; Pfizer: Research Funding; Novartis: Research Funding. Jabbour:Bristol-Myers Squibb: Consultancy. Khoury:Stemline Therapeutics: Research Funding; Kiromics: Research Funding; Pfizer: Research Funding; Angle: Research Funding.

Overexpression of CD200 and CD123 is a major influential factor in the clinical course of pediatric acute myeloid leukemia

Acute myeloid leukemia (AML) accounts for approximately 20% of all pediatric acute leukemias. The outcome of AML is still unsatisfactory. CD123 and CD200 were demonstrated to play important roles in hematological malignancies. The aim of this study was to investigate the impact of CD200 and CD123 overexpression and the influence of both proteins on the clinical presentation and disease outcome. Bone marrow (BM) samples from 89 pediatric AML patients were obtained at presentation and after therapy. Cells from the bulk population and from the leukemia stem cell (LSC) compartment were examined by multi parametric flow cytometry. In the bulk population, CD200 was positive in 64/89 (71.9) samples, CD123 was positive in 62/89 (69.7%) samples, and dual CD200 and CD123 positivity was observed in 54/89 (60.7%) samples. CD200/CD123 expressions were observed in LSCs in 64/60 samples respectively (71.9%/67.4%), and co-expressed in 51 samples (57.3%). CD200 was overexpressed in secondary AML (p < 0.05). A multivariate analysis revealed that minimal residual disease (MRD) and lymphadenopathy were associated with CD200 overexpression. Moreover, lymphadenopathy, low platelet count, and MRD were independently associated with CD123 expression. The co-expression of CD200 and CD123 demonstrated a statistically significant relationship with unfavorable cytogenetic karyotypes and high total leucocyte count (TLC). The expression of CD200 and CD123 alone and together had an adverse impact on complete remission (CR), MRD positivity, and overall survival (OS). Cases with MRD on day 28 after induction displayed stable expression patterns of CD200 and CD123. CD200 and CD123 both had a negative influence on clinical presentation and treatment outcome, which remarkably worsened when both were concomitantly overexpressed. CD200 and CD123 can therefore be used as markers of MRD in AML and may also serve as therapeutic targets.

A Real-world Perspective of CD123 Expression in Acute Leukemia as Promising Biomarker to Predict Treatment Outcome in B-ALL and AML

IntroductionCD123 is overexpressed in many hematologic malignancies and found to be useful in characterizing leukemic blasts of both acute myeloid leukemia (AML) and B-acute lymphoblastic leukemia (B-ALL). CD123 has been recently found to be a marker of leukemic stem cells, and its utility to measure residual disease and potential role in disease relapse is under evaluation. Materials and MethodsHerein, we have evaluated the expression of CD123 in 757 samples of acute leukemia including 479 treatment-naive and 278 follow-up samples and compared with post-induction morphologic complete remission and measurable residual disease (MRD) status. Multiparametric flow cytometry was used for assessment of CD123 expression and immunophenotypic characterization of leukemic blasts at diagnostic and MRD assessment time points. ResultsUsing variable cutoffs of 5%, 10%, and 20% to define a case as CD123-positive, expression of CD123 was observed in 75.6%, 66.2%, and 50% of AML and 88.6%, 81.8%, and 75% of B-ALL, respectively. Of 11 patients, 7 (63.63%) had mixed phenotype acute leukemia, but none of the 12 patients with T-acute lymphoblastic leukemia showed positivity for CD123. CD123 expression at diagnosis was associated with post-induction MRD-positive status in both B-ALL (P < .001) and AML (P = .001). We also evaluated the utility of CD123 as a leukemia-associated aberrant immunophenotype and found it to be useful in both patients with AML (baseline, 50.6%; follow-up, 53%) and B-ALL (baseline, 75%; follow-up, 73.07%). ConclusionsIn conclusion, CD123 may be considered as a cardinal marker for residual disease assessment and response evaluation in AML and B-ALL.

Selection and Characterization of Antibody Clones Are Critical for Accurate Flow Cytometry-Based Monitoring of CD123 in Acute Myeloid Leukemia

Abstract Background: CD123, the trans-membrane alpha chain of the interleukin-3 receptor (IL-3RA) is overexpressed in acute myeloid leukemia (AML) and distinguishes leukemia stem cells from their normal counterparts. There are several novel therapeutics under development to target CD123 in AML, including CD123 fused to Diphtheria toxin, a recombinant chimeric anti-CD123 MoAb, CD3/CD123 bi-specific T cell engagers, and engineered T cells that express chimeric antigen receptors (CARs). Thus, accurate detection and quantification of CD123 is critical for newly diagnosed and relapsed patients, and to follow minimal residual disease for patients in remission. Our data suggest that the evaluation of CD123 by flow cytometry varies significantly with different antibody clones. Objective: To identify the most accurate flow cytometry method for evaluation of CD123 expression in patients with AML to evaluate CD123 targeting therapies. Methods: 51 AML patient samples and 7 normal cord blood or bone marrow samples were stained with five different commercially available monoclonal antibodies to detect CD123 (7G3, 6H6, 9F5, AC145 and FAB301P), as well as CD45 and CD5, for evaluation by multiparameter flow cytometry. CD123 gene expression was also compared between these primary AML samples and bone marrow samples from healthy donors. Cell surface expression (by percentage and MFI) was evaluated relative to transcriptional expression and sensitivity to known therapeutics (cytarabine, parthenolide, and HSP90 inhibitors). Results: We observed CD123 surface expression patterns varied between the antibody clones tested. For the 9F5 and 6H6 clones, 93% and 82% of the samples, respectively, showed &gt;60% CD123+ cells whereas for the 7G3, FAB 301P and AC145 clones, 71 to 76% of the samples showed &gt;60% positivity. Also, surface expression of CD123 using 7G3, AC 145 and FAB 301P did not correlate with transcript levels for IL3RA assessed using qPCR, while surface expression of CD123 using 9F5 and 6H6 did correlate with transcript levels of IL3RA, using both mean fluorescence intensity (MFI) and percentage. For example, the correlation between CD123 surface expression as measured by percentage and IL3RA transcripts was most significant using the 9F5 and 6H6 clone (R2=0.1084, p=0.0183, R2=0.1588, p=0.0038 respectively) whereas the correlation for 7G3 (R2=0.0004, p=0.8945), FAB301P (R2=0.0027, p=0.7151) and AC145 (R2=0.0392, p=0.1638) were not significant. Surface expression of CD123 evaluated with 7G3 antibody did not correlate with overall sensitivity to in vitro treatment with cytarabine (R2=0.03767, p= 0.6451). However, using the 9F5 antibody, we found that higher levels of surface CD123 were associated with resistance to cytarabine in vitro (R2= 0.5502, p= 0.0351). Differences were noted for other experimental therapeutics including parthenolide and PU-H71. Most importantly, when we tested the ability of a novel allogeneic anti-CD123 CAR T-cell therapy (UCART123) to eliminate CD123+ AML cells, we found that CD123 positivity as measured by the 7G3 clone was not predictive of sensitivity to UCART123 in vitro or in vivo AML patient derived xenotransplants. Conclusions: Several novel therapeutic modalities targeting CD123 in AML are under development, including allogeneic anti-CD123 CAR T-cell therapy. Accurate, quantitative assessment of CD123 expression is thus of utmost importance for patient selection in clinical trials as well as disease monitoring. We found discrepancies between antibody clones, and such discrepancies may alter patient selection and data interpretation regarding patient response to CD123 based therapies. For therapies targeting CD123, protocol design and antibody selection should be done considering the results in this study. Based on our findings we recommend 9F5 or 6H6 antibody clones as well as the utilization of qPCR along side flow cytometry for adequate detection. Flow cytometry findings should be reported as percent positive cells. If utilizing the 9F5 clone, samples with &gt; 60% CD123+ should be considered positive for CD123. A comparison in a large cohort may be warranted to determine the impact of multiple CD123 measurements on disease outcome. Disclosures Galetto: Cellectis SA: Employment. Gouble:Cellectis: Employment. Smith:Cellectis SA: Employment. Roboz:Agios, Amgen, Amphivena, Astex, AstraZeneca, Boehringer Ingelheim, Celator, Celgene, Genoptix, Janssen, Juno, MEI Pharma, MedImmune, Novartis, Onconova, Pfizer, Roche/Genentech, Sunesis, Teva: Consultancy; Cellectis: Research Funding. Guzman:Cellectis: Research Funding.

Case Report: A case of hypertrophic lupus erythematosus with negative CD123 staining and absence oftransepidermal elimination of elastin.

We report the case of a 49-year-old male with clinical and histological findings consistent with hypertrophic lupus erythematosus (HLE). HLE must be clinically and histologically differentiated from keratoacanthoma, hypertrophic lichen planus, squamous cell carcinoma and plaque type psoriasis. CD123 positivity and transepidermal elimination of elastin have recently been reported as tools to distinguish HLE. Interestingly, in this case, biopsies of two separate lesions failed to reveal these two features. The etiology of this discrepancy is unknown and further studies are needed to clarify the utility of CD123 positivity and transepidermal elimination of elastin in the diagnosis of hypertrophic lupus erythematosus.

Case Report: A case of hypertrophic lupus erythematosus with negative CD123 staining and absence of transepidermal elimination of elastin

We report the case of a 49-year-old male with clinical and histological findings consistent with hypertrophic lupus erythematosus (HLE). HLE must be clinically and histologically differentiated from keratoacanthoma, hypertrophic lichen planus, squamous cell carcinoma and plaque type psoriasis. CD123 positivity and transepidermal elimination of elastin have recently been reported as tools to distinguish HLE. Interestingly, in this case, biopsies of two separate lesions failed to reveal these two features. The etiology of this discrepancy is unknown and further studies are needed to clarify the utility of CD123 positivity and transepidermal elimination of elastin in the diagnosis of hypertrophic lupus erythematosus.

A case of hypertrophic lupus erythematosus with negative CD123 staining and transepidermal elimination of elastin

We report the case of a 49-year-old male with clinical and histological findings consistent with hypertrophic lupus erythematosus (HLE). HLE must be clinically and histologically differentiated from keratoacanthoma, hypertrophic lichen planus, squamous cell carcinoma and plaque type psoriasis. CD123 positivity and transepidermal elimination of elastin have recently been reported as tools to distinguish HLE. Interestingly, in this case, biopsies of two separate lesions failed to reveal these two features. The etiology of this discrepancy is unknown and further studies are needed to clarify the utility of CD123 positivity and transepidermal elimination of elastin in the diagnosis of hypertrophic lupus erythematosus.

A case of hypertrophic lupus erythematosus with negative CD123 staining and transepidermal elimination of elastin

We report the case of a 49-year-old male with clinical and histological findings consistent with hypertrophic lupus erythematosus (HLE). HLE must be clinically and histologically differentiated from keratoacanthoma, hypertrophic lichen planus, squamous cell carcinoma and plaque type psoriasis. CD123 positivity and transepidermal elimination of elastin have recently been reported as tools to distinguish HLE. Interestingly, in this case, biopsies of two separate lesions failed to reveal these two features. The etiology of this discrepancy is unknown and further studies are needed to clarify the utility of CD123 positivity and transepidermal elimination of elastin in the diagnosis of hypertrophic lupus erythematosus.

Clinicopathological features and prognostic significance of CXCL12 in blastic plasmacytoid dendritic cell neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDC) is a rare hematologic neoplasm, which almost always involves the skin and shows poor prognosis. The aim of our study was to enhance BPDC diagnosis and indications for prognosis. This study involved 26 patients with BPDC. To investigate the histogenesis of BPDC, we reviewed the clinical features and stained markers of various hematopoietic lineages, chemokines, and their receptors. Bone-marrow infiltration was detected in 13 of the 19 cases examined and leukemic changes in 18. Complete remission was achieved in 14 cases, but more than half of the patients showed recurrence within a short time, and 14 patients died of the disease after 1 to 25 months (mean 8.5 months). Positivity for CD123 was detected in 18 of 24 cases and for T-cell leukemia 1 in 18 of 22 cases. Of the chemokines and their receptors, 8 of 15 skin biopsy specimens proved to be positive for CXCL12. Leukemic change subsequent to skin lesions occurred in 7 of 8 CXCL12-positive cases (87.5%) and in 3 of 6 CXCL12-negative cases (50%). Seven of the 8 CXCL12-positive patients (87.5%) and two of the 6 CXCL12-negative patients (33.3%) have died, whereas one of 8 CXCL12-positive patients (12.5%) and 4 of 6 CXCL12-negative patients (66.7%) remain alive. The number of patients was limited. We speculate that the presence of CXCL12-positive cells in the skin may be associated with leukemic change and a poor prognosis.

T Regulatory Cells and Plasmocytoid Dentritic Cells in Hansen Disease: A New Insight Into Pathogenesis?

Leprosy is characterized by spectrum of histologically different granulomatous skin lesions that reflects the patient's immune response to Mycobacterium leprae. Presence, frequency, and distribution of both CD4+ CD25+ FoxP3+ T regulatory cells (T-regs) and CD123+ plasmacytoid dendritic cells in leprosy have never been investigated. We performed a retrospective immunohistochemical study on 20 cases of leprosy [tuberculoid tuberculoid (TT): 1 patient; borderline tuberculoid (BT): 3 patients; borderline lepromatous (BL): 5 patients; lepromatous lepromatous (LL): 5 patients; borderline borderline in reversal reaction (BB-RR): 1 patient; BT-RR: 2 patients; and erythema nodosum leprosum (ENL): 3 patients]. FoxP3-positive cells were present in 95% of the cases with an average density of 2.9% of the infiltrate. Their distribution was not related to granulomatous structures or special locations. There was no statistical difference of FoxP3 expression between TT, BT, BL, and LL, whereas a statistical significant increment (P = 0.042) was observed in patients affected by reversal leprosy reactions (BT-RR and BB-RR) compared with patients affected by ENL and patients with nonreactional disease forms (BL, LL, BT, TT). CD123 expression was not observed in any of the biopsy specimens evaluated; with the exception of 2 cases of ENL, in which a focal positivity for CD123 was observed. Our results show that plasmacytoid dendritic cells are not involved in the immune response against M. leprae while T-regs are present in leprosy skin lesions. These data raise the question if T-regs have a pathogenetic role in HD as previously demonstrated in Leishmania major and Mycobacterium tuberculosis.

Agranuläre CD4/CD56 positive hämato-dermale Neoplasie (CD56 positives Non-Hodgkin-Lymphom)

CD4+/CD56+ hematodermic neoplasm is a rare type of primary cutaneous T-cell lymphoma and so far the single representative of the category precursor hematologic neoplasm. The tumor cells express CD56 and have therefore been suggested to represent a natural-killer(NK)-cell-lymphoma. The finding of CD123 positivity on the tumour cells now assures the origin from plasmacytoid dendritic cells. The tumour mostly shows a clinical course with high mortality caused by lymph node and bone marrow involvement often followed by a terminal leukemic phase. We present a patient treated with systemic chemotherapy (KNOSPE-scheme) and satisfactory results until now.

CD123 Expression in Chronic Lymphocytic Leukaemia - Strong Correlation with ZAP70 and CD38 Expression.

CD123 constitutes the alpha subchain of the human interleukin 3 receptor (IL-3R). Interleukin 3 binds to its receptor with high and low affinities, induces tyrosine phosphorylation and promotes the proliferation and differentiation of haematopoietic stem cells. CD123 expression has been associated with a poor prognosis in AML and has been shown to be a useful marker in hairy cell leukaemia (HCL). However, it has been little studied in CLL, with data in the literature suggesting few cases of positivity. Here we studied CD123 expression by flow cytometry on fresh peripheral blood in 134 unselected, consecutive cases of CLL. We utilised anti CD123 PE (BD Pharminogen) in a dual combination with anti CD19 FITC (Coulter Immunotech) to target B cells. The results were correlated with expression of CD38 and ZAP70, markers of poor prognosis in CLL. CD123 was expressed in = 20% (median 33, range 20–92%) of cells in 32/134 cases (24%). Typical of CLL, the intensity of surface CD123 expression was weak-moderate, unlike HCL cases, where the intensity is moderate-strong. CD38 positivity was seen in 20/32 CD123+ cases (63%). Of the remaining 102 cases where CD123 was negative, a CD38 count was available in 92 cases and 29/92 (32%) were positive. ZAP70 positivity was seen in 18/32 CD123+ cases (56%). ZAP70 data was available in 98/102 CD123− cases and positivity was seen in 26/98 (27%). These findings represent the first account of a significant percentage of CLL cases expressing CD123 positivity. Furthermore we have been able to show that CD123 positivity strongly correlates with two known markers of poor prognosis ZAP70 (p= 0.004) and CD38 (p=0.004) (Chi-Square with Yate's correction). CD123 may therefore be of prognostic significance in CLL and should be further investigated.