Characteristics of the phenotypic abnormalities of bone marrow cells in childhood myelodysplastic syndromes and juvenile myelomonocytic leukemia

Phenotypic profiling of CD34+ cells by advanced flow cytometry improves diagnosis of juvenile myelomonocytic leukemia

Diagnostic criteria for juvenile myelomonocytic leukemia (JMML) are currently well defined, however in some patients diagnosis still remains a challenge. Flow cytometry is a well established tool for diagnosis and follow-up of hematological malignancies, nevertheless it is not routinely used for JMML diagnosis. Herewith, we characterized the CD34+ hematopoietic precursor cells collected from 31 children with JMML using a combination of standardized EuroFlow antibody panels to assess the ability to discriminate JMML cells from normal/reactive bone marrow cell as controls (n=29) or from cells of children with other hematological diseases mimicking JMML (n=9). CD34+ precursors in JMML showed markedly reduced B-cell and erythroid-committed precursors compared to controls, whereas monocytic and CD7+ lymphoid precursors were significantly expanded. Moreover, aberrant immunophenotypes were consistently present in CD34+ precursors in JMML, while they were virtually absent in controls. Multivariate logistic regression analysis showed that combined assessment of the number of CD34+CD7+ lymphoid precursors and CD34+ aberrant precursors or erythroid precursors had a great potential in discriminating JMMLs versus controls. Importantly our scoring model allowed highly efficient discrimination of truly JMML versus patients with JMML-like diseases. In conclusion, we show for the first time that CD34+ precursors from JMML patients display a unique immunophenotypic profile which might contribute to a fast and accurate diagnosis of JMML worldwide by applying an easy to standardize single eight-color antibody combination.

Childhood Myelodysplastic Syndrome

Myelodysplastic syndrome (MDS) in children is rare, accounting for < 5% of all childhood hematologic malignancies. With the advent of next-generation sequencing, the etiology of many childhood MDS (cMDS) cases has been elucidated with the finding of predisposing germline mutations in one-quarter to one-third of cases; somatic mutations have also been identified, indicating that cMDS is different than adult MDS. Herein, cMDS classification schema, clinical presentation, laboratory values, bone marrow histology, differential diagnostic considerations, and the recent molecular findings of cMDS are described.

Immunophenotypic changes in juvenile myelomonocytic leukaemia after treatment with hypomethylating agent: Do they help to evaluate dept of response?

5-Azacitidine has been used before stem cell transplantation in juvenile myelomonocytic leukaemia (JMML) patients. Recently, we have described immunophenotypic features in JMML at diagnosis. Here, our aim was to examine the changes in the immunophenotypic features during azacitidine treatment, correlating it with clinical response. Patients treated with 5-azacitidine were evaluated at diagnosis and after three and six cycles of medication. Among 32 patients entering the study, 28 patients were examined after three cycles and 25 patients after six. Patients showed a reduction in CD34/CD117⁺ cells: median 3.35% at diagnosis, 2.8% after three cycles and 1.63% after six. B-cell progenitors were decreased at diagnosis and decreased after treatment. Monocytes decreased: 11.91% to 6.4% and 4.18% respectively. Complete response was associated with increase in classical monocytes. T lymphocytes, reduced at diagnosis, increased in patients responding to 5-azacitidine. Immunophenotypic aberrancies including expression of CD7 in myeloid progenitors remained after treatment. This feature was associated with a worse response to treatment, as well as presence of NF1. Immunophenotyping was feasible in all patients. Clinical response was associated with a decrease of myeloid progenitors and monocytes and a rise in T lymphocytes although phenotypic aberrancies persisted. The largest effect was observed after three cycles.

A Case of Myelofibrosis and Myelodysplasia Identified Following Exposure to Isotretinoin

A 15-year-old male individual treated with isotretinoin for acne vulgaris presented with persistent pancytopenia and circulating myeloblasts after discontinuation of the drug. Marrow assessment revealed myelofibrosis (MF) and myeloblasts exhibiting monosomy 7, diagnostic of myelodysplastic syndrome (MDS). Although a popular website seems to associate isotretinoin with MF, no published cases of MF or MDS attributable to this drug were identified. Although we expect that he would eventually have developed MDS and MF, this patient was perhaps identified sooner due to cytopenias accelerated by isotretinoin. This case illustrates that patients exhibiting cytopenias persisting following isotretinoin therapy merit evaluation for underlying hematopoietic disorders.

Immunophenotypic characteristics of juvenile myelomonocytic leukaemia and their relation with the molecular subgroups of the disease

The diagnosis of juvenile myelomonocytic leukaemia (JMML) is based on clinical, laboratory and molecular features but immunophenotyping [multiparametric flow cytometry (MFC)] has not been used routinely. In the present study, we describe the flow cytometric features at diagnosis with special attention to the distribution of monocytic subsets and the relation between MFC and molecular subgroups. MFC was performed with an eight-colour platform based on Euroflow. We studied 33 JMML cases. CD34⁺ /CD117⁺ /CD13⁺ cells >2% was found in 25 cases, and 51·5% presented an aberrant expression of CD7. A decrease of CD34⁺ /CD19⁺ /CD10⁺ cells was seen in eight cases and in four they were absent. The granulocytic population had a decreased side scatter in 29 cases. Bone marrow monocytic precursors were increased in 28 patients, with a decrease in classical monocytes (median 80·7%) and increase in CD16⁺ (intermediate and non-classical). A more pronounced increase in myeloid CD34⁺ cells was seen in patients with Neurofibromatosis type 1 (NF1) and tyrosine-protein phosphatase non-receptor type 11 (PTPN11), with aberrant CD7 expression in four of six and 10/12 patients respectively. Thus, JMML shows an immunophenotypic profile similar to myelodysplastic syndromes, and a different monocyte subset distribution when compared with chronic MML. MFC proved to be an important diagnostic tool that can help in differential diagnosis with other clonal diseases with monocytosis.

Clinical features and outcomes of patients with Shwachman-Diamond syndrome and myelodysplastic syndrome or acute myeloid leukaemia: a multicentre, retrospective, cohort study

BACKGROUND

Data to inform surveillance and treatment for leukaemia predisposition syndromes are scarce and recommendations are largely based on expert opinion. This study aimed to investigate the clinical features and outcomes of patients with myelodysplastic syndrome or acute myeloid leukaemia and Shwachman-Diamond syndrome, an inherited bone marrow failure disorder with high risk of developing myeloid malignancies.

METHODS

We did a multicentre, retrospective, cohort study in collaboration with the North American Shwachman-Diamond Syndrome Registry. We reviewed patient medical records from 17 centres in the USA and Canada. Patients with a genetic (biallelic mutations in the SBDS gene) or clinical diagnosis (cytopenias and pancreatic dysfunction) of Shwachman-Diamond syndrome who developed myelodysplastic syndrome or acute myeloid leukaemia were eligible without additional restriction. Medical records were reviewed between March 1, 2001, and Oct 5, 2017. Masked central review of bone marrow pathology was done if available to confirm leukaemia or myelodysplastic syndrome diagnosis. We describe the clinical features and overall survival of these patients.

FINDINGS

We initially identified 37 patients with Shwachman-Diamond syndrome and myelodysplastic syndrome or acute myeloid leukaemia. 27 patients had samples available for central pathology review and were reclassified accordingly (central diagnosis concurred with local in 15 [56%] cases), 10 had no samples available and were classified based on the local review data, and 1 patient was excluded at this stage as not eligible. 36 patients were included in the analysis, of whom 10 (28%) initially presented with acute myeloid leukaemia and 26 (72%) initially presented with myelodysplastic syndrome. With a median follow-up of 4·9 years (IQR 3·9-8·4), median overall survival for patients with myelodysplastic syndrome was 7·7 years (95% CI 0·8-not reached) and 0·99 years (95% CI 0·2-2·4) for patients with acute myeloid leukaemia. Overall survival at 3 years was 11% (95% CI 1-39) for patients with leukaemia and 51% (29-68) for patients with myelodysplastic syndrome. Management and surveillance were variable. 18 (69%) of 26 patients with myelodysplastic syndrome received upfront therapy (14 haematopoietic stem cell transplantation and 4 chemotherapy), 4 (15%) patients received no treatment, 2 (8%) had unavailable data, and 2 (8%) progressed to acute myeloid leukaemia before receiving treatment. 12 patients received treatment for acute myeloid leukaemia-including the two patients initially diagnosed with myelodysplastic who progressed- two (16%) received HSCT as initial therapy and ten (83%) received chemotherapy with intent to proceed with HSCT. 33 (92%) of 36 patients (eight of ten with leukaemia and 25 of 26 with myelodysplastic syndrome) were known to have Shwachman-Diamond syndrome before development of a myeloid malignancy and could have been monitored with bone marrow surveillance. Bone marrow surveillance before myeloid malignancy diagnosis was done in three (33%) of nine patients with leukaemia for whom surveillance status was confirmed and 11 (46%) of 24 patients with myelodysplastic syndrome. Patients monitored had a 3-year overall survival of 62% (95% CI 32-82; n=14) compared with 28% (95% CI 10-50; n=19; p=0·13) without surveillance. Six (40%) of 15 patients with available longitudinal data developed myelodysplastic syndrome in the setting of stable blood counts.

INTERPRETATION

Our results suggest that prognosis is poor for patients with Shwachman-Diamond syndrome and myelodysplastic syndrome or acute myeloid leukaemia owing to both therapy-resistant disease and treatment-related toxicities. Improved surveillance algorithms and risk stratification tools, studies of clonal evolution, and prospective trials are needed to inform effective prevention and treatment strategies for leukaemia predisposition in patients with Shwachman-Diamond syndrome.

FUNDING

National Institute of Health.

Hematopoietic-restricted Ptpn11E76K reveals indolent MPN progression in mice

Juvenile Myelomonocytic Leukemia (JMML) is a pediatric myeloproliferative neoplasm (MPN) that has a poor prognosis. Somatic mutations in Ptpn11 are the most frequent cause of JMML and they commonly occur in utero. Animal models of mutant Ptpn11 have probed the signaling pathways that contribute to JMML. However, existing models may inappropriately exacerbate MPN features by relying on non-hematopoietic-restricted Cre-loxP strains or transplantations into irradiated recipients. In this study we generate hematopoietic-restricted models of Ptpn11E76K-mediated disease using Csf1r-MCM and Flt3Cre. We show that these animals have indolent MPN progression despite robust GM-CSF hypersensitivity and Ras-Erk hyperactivation. Rather, the dominant pathology is pronounced thrombocytopenia with expanded extramedullary hematopoiesis. Furthermore, we demonstrate that the timing of tamoxifen administration in Csf1r-MCM mice can specifically induce recombinase activity in either fetal or adult hematopoietic progenitors. We take advantage of this technique to show more rapid monocytosis following Ptpn11E76K expression in fetal progenitors compared with adult progenitors. Finally, we demonstrate that Ptpn11E76K results in the progressive reduction of T cells, most notably of CD4+ and naïve T cells. This corresponds to an increased frequency of T cell progenitors in the thymus and may help explain the occasional emergence of T-cell leukemias in JMML patients. Overall, our study is the first to describe the consequences of hematopoietic-restricted Ptpn11E76K expression in the absence of irradiation. Our techniques can be readily adapted by other researchers studying somatically-acquired blood disorders.

Flow Cytometry in Pediatric Hematopoietic Malignancies

Utility of flow cytometry in the evaluation of pediatric hematopoietic neoplasms and the differences from adult hematopoietic neoplasms are discussed in this review. Distinction of hematogones from B-lymphoblasts, detection of residual/relapsed disease after novel targeted therapies, and evaluation of pediatric myeloid neoplasms are discussed.

Mice expressing KrasG12D in hematopoietic multipotent progenitor cells develop neonatal myeloid leukemia

Juvenile myelomonocytic leukemia (JMML) is a pediatric myeloproliferative neoplasm that bears distinct characteristics associated with abnormal fetal development. JMML has been extensively modeled in mice expressing the oncogenic KrasG12D mutation. However, these models have struggled to recapitulate the defining features of JMML due to in utero lethality, nonhematopoietic expression, and the pervasive emergence of T cell acute lymphoblastic leukemia. Here, we have developed a model of JMML using mice that express KrasG12D in multipotent progenitor cells (Flt3Cre+ KrasG12D mice). These mice express KrasG12D in utero, are born at normal Mendelian ratios, develop hepatosplenomegaly, anemia, and thrombocytopenia, and succumb to a rapidly progressing and fully penetrant neonatal myeloid disease. Mutant mice have altered hematopoietic stem and progenitor cell populations in the BM and spleen that are hypersensitive to granulocyte macrophage-CSF due to hyperactive RAS/ERK signaling. Biased differentiation in these progenitors results in an expansion of neutrophils and DCs and a concomitant decrease in T lymphocytes. Flt3Cre+ KrasG12D fetal liver hematopoietic progenitors give rise to a myeloid disease upon transplantation. In summary, we describe a KrasG12D mouse model that reproducibly develops JMML-like disease. This model will prove useful for preclinical drug studies and for elucidating the developmental origins of pediatric neoplasms.