Aberrant Expression Of CD56 Research Articles

Aberrant Expression of CD Markers in Acute Leukemia with Hematological Parameters Correlation: A Single Center Experience

ABSTRACT Background: Immunophenotyping by flowcytometry improves both the accuracy and reproducibility of an acute leukemia (AL) diagnosis. The morphologically similar blast cells can be easily differentiated by immunophenotyping based on expression and different CD (cluster of differentiation) markers. It also plays a crucial role in the identification of aberrant antigens. The present study was conducted to determine the frequency of aberrant phenotypes in newly diagnosed cases of acute leukemia and its correlation with hematological parameters. Methods: We retrospectively investigated the phenotype of blast cells from 72 patients with acute leukemia diagnosed over a one and half year period. Diagnosis of acute leukemia was based on morphology, cytochemistry, and immunophenotyping by flow cytometry. Results: Out of the total 72 cases of Acute leukemia, 40 (55.6%) cases showed aberrant expression. 12/27 cases (44.4%) of AML and 28/45 cases (62.2%) of ALL showed aberrant phenotypes in the present study. Aberrant expression of CD7, 6/27 cases (22.2%) was very frequent in AML. Among the ALL cases, CD13, 14/45 cases (31.1%) were most commonly expressed. The mean total leukocyte count (TLC) and percentage of blasts in peripheral blood were significantly higher in AML and ALL cases with aberrant phenotypes as compared to their conventional phenotypes with no aberrancy. Conclusions: It is of clinical importance to detect aberrant phenotypes for accurate diagnosis and when looking for minimal residual disease during morphologic remission. In addition, aberrant phenotypes in AML and ALL cases are associated with unfavorable hematological features in our study.

Extranodal NK/T cell lymphoma with aberrant CD20 expression: a clinicopathological analysis of two cases

Extranodal NK/T cell lymphoma with aberrant CD20 expression: a clinicopathological analysis of two cases

A-173 Evaluation of Artificial Intelligence (AI)-assisted Flow Cytometry Analysis for Plasma Cell Neoplasms

Abstract Background Flow cytometry plays a critical role in diagnosing hematologic disorders, yet manual analysis is time-consuming and prone to variability. Significant advancements in artificial intelligence (AI) within healthcare have occurred in recent years. Previously, we developed and evaluated an AI-assisted automated system for diagnosing acute leukemia. This study aims to assess the effectiveness of the AI system in diagnosing plasma cell neoplasms. Methods A total of 76 bone marrow samples were analyzed using a panel of antibodies (CD38, CD56, CD138, Kappa, and Lambda) to determine plasma cell percentages and immunophenotype. All samples were used for initial diagnosis of plasma cell neoplasm or therapeutic monitoring. Manual analysis using Kaluza™ software served as the gold standard. The same flow cytometry data was processed by the AI software (DeepFlow™) for comparison. Pearson correlation coefficients were used to compare AI and manual analysis for diagnosis and plasma cell count. Results Among the 76 cases, manual analysis identified 57 positive cases for monoclonal plasma cells (36 cases of CD38+/CD138+/Kappa+ and 21 cases of CD38+/CD138+/Lambda+), with 89% showing aberrant CD56 expression. AI identified 49 monoclonal cases, missing 8 cases with low plasma cell levels (<0.07%) or brighter fluorescence. AI accurately matched 97% of immunophenotypes with manual analysis. Pearson correlation coefficients demonstrated excellent correlation (r=1.0) between manual and AI plasma cell percentages. Furthermore, AI has also enhanced laboratory efficiency, reducing analysis time per case from 10 minutes with manual methods to just 3 minutes with AI analysis. Conclusions This study shows promise for AI-assisted flow software in diagnosing plasma cell neoplasms. AI has enhanced operational efficiency by reducing the manual processing and analysis time. Further training is needed to improve the identification of variations in fluorescence intensity and low plasma cell levels.

Aberrant Expression of CD56 in Hematologic Malignancies

Aberrant Expression of CD56 in Hematologic Malignancies

Point of care CD19 chimeric antigen receptor (CAR) T-cells for relapsed/refractory acute myeloid leukemia (AML) with aberrant CD19 antigen expression

Relapsed/refractory (r/r) acute myeloid leukemia (AML) is associated with poor prognosis. CD19 is a B-cell marker, is aberrantly expressed in AML, mostly with t(8; 21)(q22; q22.1). Here we report the results of a phase 2 study giving point of care produced CD19 CAR T- cells for r/r AML with aberrant expression of CD19 (NCT04257175). Lymphodepletion included fludarabine and cyclophosphamide The response was evaluated by bone marrow (BM) aspiration on day 28. Six patients (5 adults and 1 child) were included. Median number of previous chemotherapy lines was 4 (range, 3–8) and four patients received CAR T-cells 8–18 months post allogeneic hematopoietic stem cell transplantation (allo-HSCT). Cytokine release syndrome (CRS) of any grade occurred in all patients, and 1 patient had grade 3 CRS. Immune effector cell-associated neurotoxicity syndrome (ICANS) occurred in 2 patients at low grades. Tocilizumab was administered to 2 patients and corticosteroids to 3 patients. Four patients achieved a complete remission (CR), while 2/6 progressed (PD). Three patients (2 with CR and 1 with PD) underwent allo-HSCT (it was the second transplant in 2) 2–5 months post CAR T-cells infusion. The median duration of response in patients achieving CR was 8.5 (range; 3–14) months. However, all patients eventually died within 5 (1–18) months.In conclusion, CD19 CAR T- cell treatment for AML is feasible and safe. However, the response is short and should be followed by allo-HSCT. Hopefully, future long term results will be improved by combining the CAR T- cell therapy with the emerging novel effective anti-leukemic compounds.

Current Knowledge about CD3+CD20+ T Cells in Patients with Multiple Sclerosis.

Multiple sclerosis (MS) is a disease of the central nervous system (CNS) characterized by inflammation and autoimmune responses. This review explores the participation of T cells, particularly certain CD3+CD20+ T cells, in the clinical manifestations of MS and highlights their presence in diagnosed patients. These T cells show aberrant expression of CD20, normally considered a B-cell marker. In this review, relevant journal articles available in PubMed and CINAHL were identified by employing diverse search terms, such as MS, CD3+CD20+ T cells, the incidence and significance of CD3+CD20+ T cells in MS patients, and the impact of rituximab treatment. The search was limited to articles published in the ten-year period from 2014 to 2024. The results of this review suggest that most scholars agree on the presence of CD3+CD20+ T cells in cerebrospinal fluid. Emerging concepts relate to the fundamental role of CD20-expressing T cells in determining the target and efficacy of MS therapeutics and the presence of T cells in the cerebrospinal fluid of MS patients. The results clearly show that CD20+ T cells indicate disease chronicity and high disease activity.

A comprehensive study on aberrant CD20+ mycosis fungoides: clinical and prognostic insights.

As the majority of T-cell lymphomas lack CD20 expression, cases of mycosis fungoides (MF) exhibiting aberrant CD20 expression are exceedingly uncommon. To comprehensively evaluate the clinical, histopathological and prognostic features of seven patients diagnosed with CD20+ MF. This retrospective study involved seven cases of MF with aberrant CD20 expression. The study provides details of demographics, clinical features, histopathology and treatment outcomes. Key timepoints include initial diagnosis of MF, detection of CD20 expression and follow-up, with a mean follow-up of 46 months. Aberrant CD20+ MF was diagnosed at an average age of 58.6 years, approximately 5.6 years after the first MF diagnosis. Following CD20 detection, patients presented with advanced disease stages, requiring treatments such as chemotherapy, brentuximab vedotin and allogeneic haematopoietic stem cell transplantation. Four patients died from lymphoma, with an average survival time of 52 months. Aberrant CD20 expression in MF is rare but indicates a progressive course associated with poor prognosis. This often requires systemic chemotherapy and, in certain instances, allogeneic haematopoietic stem cell transplantation. This study provides important insights into the clinical attributes, disease progression and treatment options for patients with MF with aberrant CD20 expression. Further research is necessary to validate the effectiveness of emerging therapies and enhance our understanding of the underlying mechanisms and prognostic determinants specific to this unique MF subgroup.

Clinical and pathological characteristics of blastoid mantle cell lymphoma: a single institution experience.

Blastoid mantle cell lymphoma (B-MCL) is a rare aggressive lymphoma. It is characterized by blastoid morphology with high proliferation and inconsistent immunohistochemistry (IHC), making it a diagnostic challenge for the pathologist. This is a retrospective analytical cohort study. We reviewed biopsy confirmed cases of B-MCL diagnosed over a period of 10 years (January 2012 to December 2022). The clinical presentation, histopathological and IHC findings, treatment received, and survival outcomes were studied. Randomly selected cases of classic MCL (n=12), diagnosed during the same period served as controls. A total of 12 cases were studied. Four cases were transformed from previously diagnosed MCL; 8 cases arose de novo. Mean age was 61.17 years and the male: female ratio was 5:1. Half of the cases showed extra nodal extension and 81.8% had bone marrow involvement. Gastrointestinal tract was the most common site of extra nodal involvement. Histopathological examination showed diffuse involvement of the lymph node with medium sized cells. On immunohistochemistry, one of the cases showed loss of CD5 expression while the other had aberrant CD10 expression. Mean Ki-67 index was 58.09% in the cases and 16.33% in controls and was statistically significant ( p=0.005). The median overall survival (OS) for cases was 2 years vs 8 years in controls. The p53 over expression (>30% nuclear positivity) was seen in 66.6% cases (4/6). There are several factors that contribute to the aggressiveness of B-MCL, and new treatment approaches might be required to improve patient outcomes.

Characteristics and outcomes of acute myeloid leukaemia patients with baseline CD7 expression.

Targeted therapy development for acute myeloid leukaemia (AML) requires an understanding of specific expression profiles. We collected flow cytometry data on 901 AML patients and recorded aberrant CD7 expression on leukaemic blasts. 263 (29.2%) had blasts positive for CD7. CD7+ AML was more likely to be adverse risk (64.6% vs. 55.6%, p = 0.0074) and less likely to be favourable risk (15.2% vs. 24.1%, p = 0.0074) by European LeukemiaNet 2022 criteria. Overall survival was inferior (11.9 [95% CI, 9.7-15.9] vs. 19.0 months [95% CI, 16.1-23.0], p = 0.0174). At relapse, 30.4% lost and 19.0% gained CD7, suggesting moderate instability over time.

ALK-positive large B-cell lymphoma (ALK + LBCL) with aberrant CD3 expression

ALK-positive ( +) large B cell lymphoma (ALK + LBCL) is a rare distinct subtype of diffuse large B cell lymphoma presenting with high stage and aggressive behavior. Although B cell markers such as CD20, CD19, and CD22 are generally negative, plasmacytic markers including CD138, CD38, and MUM1 are positive. T cell markers are negative with rare exceptions. We report an unusual case of ALK1 + LBCL in a 58-year-old man with partial expression of CD3 without other T cell antigen expression. The tissue was evaluated with flow cytometry, immunohistochemistry, fluorescent in situ hybridization, and gene rearrangement studies. Gene rearrangement studies for IGH and TCR gamma were performed. Flow cytometry did not demonstrate any abnormal lymphoid populations. Tissue sectioning shows a malignant plasmacytic large cell neoplasm which expresses CD45 but is negative for CD20, CD79a, and PAX5. Plasmacytic markers CD138 and MUM1 are positive with kappa light chain restriction. Strong granular cytoplasmic expression of ALK is present. FISH showing disrupted ALK supports the diagnosis while MYC, BCL6, and BCL2 are intact. Gene rearrangement studies show coexisting IGH and TCR gamma clones; however, the TCR peak was present within a polyclonal background suggesting the disputed cells are likely only a subset of the T cell population. ALK + LBCL can present with an ambiguous immunophenotype, which warrants the use of multiple B cell, T cell, and plasmacytic antibodies. CD3 expression in this entity is rare and of uncertain clinical significance, but warrants further study.

Primary cutaneous aggressive epidermotropic CD8+ cytotoxic T-cell lymphoma with aberrant CD56 expression: a rare case report.

Primary cutaneous aggressive epidermotropic CD8+ cytotoxic T-cell lymphoma with aberrant CD56 expression: a rare case report.

EBV positive plasmacytoma in immunocompetent patients: A diagnostically challenging rare entity

Abstract Introduction/Objective Epstein-Barr Virus (EBV)-positive plasmacytoma is a rare entity that shows morphological and immunophenotypic overlap with plasmablastic lymphoma and can cause a diagnostic dilemma. Here we discuss a unique case of EBER-positive plasmacytoma arising from nasal polyps. Methods/Case Report A 61-year-old immunocompetent male presented with nasal polyps, right maxillary sinus lesions, and an enlarging sternal lesion. Multiple biopsies were obtained which revealed a diffuse infiltration by atypical plasma cells, that were positive for CD138, MUM1, CD79a, CD56, lambda-in situ hybridization, and Ki67- proliferation index of 20-30%. In situ, hybridization for EBV-encoded viral RNA (EBER) was positive in the neoplastic cells. B- and T- cell markers were negative. The flow cytometry studies detected monotypic lambda-restricted CD38/CD138 positive plasma cells with an aberrant expression of CD56 and CD117. Molecular studies for B-and T- cell gene rearrangement were also negative. A final diagnosis of EBER-positive plasmacytoma was made. The patient was treated with cyclophosphamide, vincristine, doxorubicin, and carboplatin followed by four cycles of RVD, and is doing well. Results (if a Case Study enter NA) NA Conclusion EBER-positive plasmacytoma poses a diagnostic challenge with plasmablastic lymphoma, specifically in immunocompetent individuals. The useful differentiating clues pointing towards EBER positive plasmacytoma could be a spectrum of morphology ranging from mature to anaplastic, low Ki67 proliferation index, aberrant CD56 and CD117 positivity, and high M- spike on protein studies. Comprehensive clinical, morphologic phenotypic, and genetic investigations are necessary to make a specific diagnosis as the two entities differ in their management.

Untangling the Strands of Hairy Cell Leukemia: The Clinicopathological Spectrum over Eleven Years at a Tertiary Care Center.

Hairy Cell Leukemia (HCL) is an uncommon, indolent lymphoproliferative disorder of mature B lymphoid cells, accounting for 2% of all lymphoid tumors. The present study evaluated the clinical-hematological profile of HCL patients diagnosed at a single tertiary care center over a 11-year period. The retrospective observational study was done between October 2010 and September 2021. The relevant clinical and laboratory information were retrieved from hospital medical records and electronic databases. The statistical analysis was performed using version 23.0 of SPSS. 66 (5.9%) of 1125 cases of chronic lymphoproliferative disorder were HCL. Splenomegaly was found in 47 (71.2%), hepatomegaly in 26 (39.5%), and lymphadenopathy in 17 (25.7%) of the cases. The mean hemoglobin, total leukocytes count, and platelets count were 8.04 g/dl, 6.76 X 109/L, and 77 X 109/L, respectively. Pancytopenia was detected in 40 cases (60.61 %). Bone marrow biopsies were majorly hypercellular and showed predominantly diffuse infiltration by atypical lymphoid cells. In two patients, initially thought of having refractory/hypoplastic anemia, the bone marrow biopsy and flow cytometry revealed HCL involvement. 42 cases of HCL underwent flow cytometry. CD20, CD 11c, CD 25 and CD 103 were positive in all the cases. The aberrant expression of CD5, CD10, and CD23 was found in frequencies of 5.71 %, 31.42 %, and 19.35%, respectively. In 40 cases for which follow-up information was available, there was full remission in 26 patients (65%), and later three showed relapse (7.5%) of which one died, and persistent leukemic activity in five (10%). Eight patients (20%) died even before the initiation of treatment. One patient died within one month of therapy. No patient was examined for BRAF V600E mutation analysis. CD 10+ HCL was the most prevalent atypical immunophenotypic subgroup. Bone marrow biopsy and flow cytometry are crucial diagnostic tools to rule out hairy cell leukemia. However, BRAF V600E mutation analysis should be performed in cases with unusual presentation or resistance to treatment.

Co-occurring mutations in ASXL1, SRSF2, and SETBP1 define a subset of myelodysplastic/ myeloproliferative neoplasm with neutrophilia

Identification of genomic signatures with consistent clinicopathological features in myelodysplastic/myeloproliferative neoplasm (MDS/MPN) is critical for improved diagnosis, elucidation of biology, inclusion in clinical trials, and development of therapies. We describe clinical and pathological features with co-existence of mutations in ASXL1 (missense or nonsense), SRSF2, and SKI homologous region of SETBP1, in 18 patients. Median age was 68 years with a male predominance (83%). Leukocytosis and neutrophilia were common at presentation. Marrow features included hypercellularity, granulocytic hyperplasia with megakaryocytic atypia, while the majority had myeloid hyperplasia and/or erythroid hypoplasia, myeloid dysplasia, and aberrant CD7 expression on blasts. Mutations in growth signaling pathways (RAS or JAK2) were noted at diagnosis or acquired during the disease course in 83% of patients. Two patients progressed upon acquisition of FLT3-TKD (acute myeloid leukemia) or KIT (aggressive systemic mastocytosis) mutations. The prognosis is poor with only two long-term survivors, thus far, who underwent blood or marrow transplantation. We propose that the presence of co-occurring ASXL1, SRSF2, and SETBP1 mutations can be diagnostic of a subtype of MDS/MPN with neutrophilia if clinical and morphological findings align. Our report underscores the association between genotype and phenotype within MDS/MPN and that genomic signatures should guide categorization of these entities.

Abstract 385: Synergistic effects of MIA-602 and its potential for use in ATRA/ATO Resistant APL

Abstract Introduction: Acute Myeloid Leukemia (AML) is a malignant neoplastic disease arising from myeloid cell lines. AML is characterized by the proliferation of immature, nonfunctional cells in the bone marrow. Acute Promyelocytic Leukemia (APL) is a subtype of AML characterized by proliferation of immature promyelocytes. Growth Hormone Releasing Hormone (GHRH) is a hypothalamic peptide that stimulates the release of Growth Hormone from the anterior pituitary. This study aimed to investigate the role of MIA-602, a growth hormone-releasing hormone receptor (GHRH-R) antagonist as front line-combination therapy in the K-562 in-vitro model of AML as well as its potential for treating ATRA/ATO resistant APL. Design: Western blot analysis was used to detect the GHRH-R in both K-562 and NB4 cell lines. K562 cells were maintained as a cell suspension in the RPMI medium, with 10% heat-inactivated fetal bovine serum and gentamicin. Doxorubicin treatment concentrations were 0.005, 0.01, and 0.05 μg/μl. Combination therapy concentrations were 0.005, 0.01, and 0.05 μg/μl of doxorubicin and 5 μmol/L of MIA-602. Proliferation was observed and recorded at 24h and 48h. Wild type NB4 cells and NB4 cells resistant to both ATRA and ATO (NB4-RAA) were cultured in suspension. Cell lysates were prepared after incubation with MIA-602. Cell viability was measured at 24, 48, and 72h. Flow cytometry was also performed to assess expression of CD-56. Results: Incubation of cells with doxorubicin showed a decrease in proliferation in a dose-dependent manner. Co-incubation of K562 cells with MIA-602 and doxorubicin showed a significantly greater reduction in proliferation (p<0.05). Co-administration of doxorubicin and MIA-602 was shown to have a synergistic effect, when compared to doxorubicin alone at all concentrations at 24 and 48h. Viability of both NB4 cell lines decreased at similar levels at 24 h and 48 h when exposed to concentrations of MIA-602 higher than 0.05 μmol/L (p < 0.05). No difference in cell viability was found between naïve NB4 and resistant NB4-RAA when exposed to the same concentrations of MIA-602. Results of flow cytometry revealed significantly increased expression of CD-56 (>5.8-fold; p,0.05) in NB4-RAA cells as compared to the parent cell line. Discussion: Co-administration of doxorubicin and the GHRH-R antagonist MIA-602 was shown to have a synergistic effect in reducing proliferation of the K-562 AML cell line. Use of MIA-602 in front-line combination therapy with anthracycline-based regimens may help prevent the acquisition of resistance in AML. CD-56 plays an essential role in the regulation of cell survival and stress resistance. Aberrant expression of CD-56 is also associated with reduced complete remission rates, higher relapse rates, and poor overall survival. The equal effectiveness of MIA-602 in cells with increased expression of CD-56 may provide an important therapeutic option in the setting of resistance. Citation Format: Ravinder S. Chale, Mario Rodriguez, Stephanie M. Almeida, Shelly Sclatter, Anastasia Singaready, Andrew V. Schally, Joaquin J. Jimenez. Synergistic effects of MIA-602 and its potential for use in ATRA/ATO Resistant APL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 385.

Blastoid variant mantle cell lymphoma with aberrant expression of CD10.

Blastoid variant mantle cell lymphoma with aberrant expression of CD10.

Myeloid Proliferations Associated with Down Syndrome: Clinicopathologic Characteristics of Forty Cases from Five Large Academic Institutions

Introduction: The incidence of myelodysplastic syndrome and acute myeloid leukemia is significantly increased in children with Down syndrome (DS). Within the revised 2016 WHO edition, these entities are jointly classified as myeloid leukemia associated with DS (ML-DS). Additionally, infants with DS may develop transient abnormal myelopoiesis (TAM) which is histomorphologically similar to ML-DS. While TAM is self-limiting, it is associated with an increased risk of subsequently developing ML-DS. Differentiating TAM and ML-DS is challenging but clinically critical. Methods: We performed a retrospective review of ML-DS and TAM cases collected from five large academic institutions in the USA. We assessed clinical, pathological, immunophenotypical, and molecular features to identify differentiating criteria. Results: Forty cases were identified: 28 ML-DS and 12 TAM. Several features were diagnostically distinct, including younger age in TAM (p < 0.05), as well as presentation with clinically significant anemia and thrombocytopenia in ML-DS (p < 0.001). Dyserythropoiesis was unique to ML-DS, as well as structural cytogenetic abnormalities aside from the constitutional trisomy 21. Immunophenotypic characteristics of TAM and ML-DS were indistinguishable, including the aberrant expression of CD7 and CD56 by the myeloid blasts. Discussion: The findings of the study confirm marked biological similarities between TAM and ML-DS. At the same time, several significant clinical, morphological, and genetic differences were observed between TAM and ML-DS. The clinical approach and the differential diagnosis between these entities are discussed in detail.

Systemic mastocytosis with an associated hematological neoplasm (acute myeloid leukaemia with RUNX1::RUNX1T1 fusion) – A case study

Systemic mastocytosis (SM) is a rare blood disorder that can affect multiple body organs. There are some patients of SM with coexpression of hematological neoplasm designated in the World Health Organization classification as SM with an associated hematological neoplasm (SM-AHN). A 13-year-old female was referred for immunophenotyping since blasts were reported in the bone marrow aspirate. On performing flow cytometry, abnormal myeloid blasts (&gt;20%) were obtained on flow cytometry suggestive of acute myeloid leukemia with aberrant expression of CD19. Furthermore, there were increased mast cells abnormally expressing CD25. The aspiration slides reviewed showed atypical mast cells Type I and Type II. Molecular analysis revealed RUNX1::RUNX1T1 fusion as well as KIT D816V mutation. Karyotyping revealed a three-way translocation involving chromosomes 8, 12, and 21 consistent with RUNX1::RUNX1T1 fusion. Fluorescence in situ hybridization (FISH) performed using a dual color dual fusion probe for RUNX1::RUNX1T1 showed atypical abnormal pattern consistent with RUNX1::RUNX1T1 fusion. This rare diagnosis could be reached as a result of a strong correlation between morphology, immunophenotyping, cytogenetics, and molecular analysis, leading to a better treatment plan for the patient.

PROSPECTOR: A Global, Prospective Study To Determine The Prevalence Of The KIT D816V Mutation In Peripheral Blood (PB) From Patients With Evidence Of Systemic Mast Cell Activation (MCA)

Systemic MCA is a defining characteristic of patients with MCA syndromes (MCAS). MCAS is a heterogeneous group of mast cell disorders that can be further classified as clonal or non-clonal based on presence or absence of KIT D816V mutation or aberrant CD25 expression on mast cells. The prevalence of clonal mast cell disease with evidence of systemic MCA is unknown. PROSPECTOR (NCT04811365) is a global, multi-center screening study determining prevalence of KIT D816V mutation in PB in patients with evidence of systemic MCA.

Aberrant myelomonocytic CD56 expression predicts response to cyclosporine therapy in pediatric patients with moderate aplastic anemia.

This study aimed to investigate the expression patterns and clinical significance of neural cell adhesion molecule-positive (CD56+) myelomonocytes in pediatric patients with moderate aplastic anemia (mAA). Fifty-six pediatric patients with mAA were enrolled in this study. The patients' clinical characteristics, laboratory data, and response to cyclosporine therapy were obtained. CD56 expression on bone marrow myelomonocytic cells was investigated using flow cytometry. The association between aberrant CD56 expression and cyclosporine response was evaluated by a multivariate analysis. CD56+ myelomonocytes were detected in 43% of the mAA cases. Aberrant CD56 expression was frequent on immature CD45dimCD16dim granulocytes and mature CD45brightCD14bright monocytes. Compared with patients with CD56- myelomonocytes (CD56- patients), patients with CD56+ myelomonocytes (CD56+ patients) were in moderate hematological condition and had a distinct bone marrow cellular composition profile, which included an increased proportion of myeloid cells and CD56bright natural killer cells and a reduced proportion of CD4+ T cells, CD8+ T cells, and B cells. The multivariate analysis determined that CD56+ myelomonocytes were a favorable factor for achieving response at 6 months after cyclosporine therapy. There was a trend towards a lower 3-year rate of evolution to severe aplastic anemia or relapse among the CD56+ patients (8%) than the CD56- patients (22%). CD56+ patients had an increased myeloid compartment and better prognosis compared with CD56- patients. The findings demonstrated the favorable role of CD56+ myelomonocytes in aplastic anemia progression.