Historical perspective and clinical implications of the Pelger-Hüet cell

Targeting SRSF2 mutations in leukemia with RKI-1447: A strategy to impair cellular division and nuclear structure

Spliceosome machinery mutations are common early mutations in myeloid malignancies; however, effective targeted therapies against them are still lacking. In the current study, we used an in vitro high-throughput drug screen among four different isogenic cell lines and identified RKI-1447, a Rho-associated protein kinase inhibitor, as selective cytotoxic effector of SRSF2 mutant cells. RKI-1447 targeted SRSF2 mutated primary human samples in xenografts models. RKI-1447 induced mitotic catastrophe and induced major reorganization of the microtubule system and severe nuclear deformation. Transmission electron microscopy and 3D light microscopy revealed that SRSF2 mutations induce deep nuclear indentation and segmentation that are apparently driven by microtubule-rich cytoplasmic intrusions, which are exacerbated by RKI-1447. The severe nuclear deformation in RKI-1447-treated SRSF2 mutant cells prevents cells from completing mitosis. These findings shed new light on the interplay between microtubules and the nucleus and offers new ways for targeting pre-leukemic SRSF2 mutant cells.

Septic shock caused by Capnocytophaga canimorsus in a patient with heterozygous Pelger-Huët anomaly

Capnocytophaga canimorsus is a Gram-negative bacillus of the commensal flora of dogs and cats that can cause infections in humans through bites, scratches or contact with oral secretions. It can be difficult to identify in clinical microbiology laboratories because of the need for specific culture media. We present the case of a patient with no relevant medical history who was admitted with septic shock, where blood smear examination was crucial for the etiologic diagnosis of Capnocytophaga canimorsus infection. The patient was also diagnosed Pelger-Huët anomaly, a condition causing a defect in neutrophil chemotaxis, which may have contributed to the severity of the infection.

Lamin B1 deletion in myeloid neoplasms causes nuclear anomaly and altered hematopoietic stem cell function

Abnormal nuclear morphology is a hallmark of malignant cells widely used in cancer diagnosis. Pelger-Huët anomaly (PHA) is a common abnormality of neutrophil nuclear morphology of unknown molecular etiology in myeloid neoplasms (MNs). We show that loss of nuclear lamin B1 (LMNB1) encoded on chromosome 5q, which is frequently deleted in MNs, induces defects in nuclear morphology and human hematopoietic stem cell (HSC) function associated with malignancy. LMNB1 deficiency alters genome organization inducing in vitro and in vivo expansion of HSCs, myeloid-biased differentiation with impaired lymphoid commitment, and genome instability due to defective DNA damage repair. Nuclear dysmorphology of neutrophils in patients with MNs is associated with 5q deletions spanning the LMNB1 locus, and lamin B1 loss is both necessary and sufficient to cause PHA in normal and 5q-deleted neutrophils. LMNB1 loss thus causes acquired PHA and links abnormal nuclear morphology with HSCs and progenitor cell fate determination via genome organization.

Protean Regulation of Leukocyte Function by Nuclear Lamins

The leukocyte nucleus must be sufficiently elastic to squeeze through tissue barriers during migration, but not so collapsible as to risk damaging chromatin. The proper balance is struck in part by the composition of the nuclear lamina, a flexible meshwork composed mainly of intermediate filaments woven from type A and type B lamin proteins, that is located subjacent to the inner nuclear membrane. There is now increasing evidence that, in addition to influencing nuclear shape and stiffness and cell migration, lamins and lamin-interacting proteins may also interact functionally with chromatin to influence leukocyte gene expression, differentiation, and effector function, including T cell differentiation, B cell somatic hypermutation, and the formation of neutrophil extracellular traps (NETosis).

Peripheral Blood Examination Findings in SARS-CoV-2 Infection

OBJECTIVES

Peripheral blood abnormalities in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have not been fully elucidated. We report qualitative and quantitative peripheral blood findings in coronavirus disease 2019 (COVID-19) patients and compare them with a control group.

METHODS

We reviewed electronic medical records, complete blood counts, peripheral blood smears, and flow cytometry data in 12 patients with SARS-CoV-2. These were compared with 10 control patients with symptoms suspicious for SARS-CoV-2 but who tested negative.

RESULTS

No significant differences were noted in blood counts, except that absolute lymphopenia was present frequently in the control group (P < .05). Acquired Pelger-Huët anomaly (APHA) was noted in all COVID-19 cases, in most cases affecting over 5% of granulocytes. This contrasted with APHA in only 50% of control cases, affecting fewer than 5% of granulocytes in all cases (P < .05). Monolobate neutrophils were exclusive to COVID-19 cases. COVID-19 patients had greater frequency of plasmacytoid lymphocytes (P < .05). Flow cytometry data revealed absolute CD3+ T-cell count reduction in 6 of 7 patients; all of them required mechanical ventilation.

CONCLUSIONS

Lymphopenia was infrequent in our COVID-19 cohort; however, flow cytometric analysis revealed absolute T-cell count reduction in most cases. COVID-19 cases had significant APHA with monolobate neutrophils and plasmacytoid lymphocytes as compared to controls.

Acquired Pelger-Huët anomaly in a patient treated with valganciclovir

A follow-up blood count was performed on a 74-year-old woman diagnosed with colitis due to cytomegalovirus and under treatment with valganciclovir. The automated complete blood count revealed an abnormal white blood cells (WBC) scattergram together with WBC alert flags. The peripheral blood smear showed neutrophils with markedly hyposegmented nuclei or bilobed nuclei and very condensed chromatin or clumping chromatin all consistent with Pelger-Huët anomaly (PHA). We checked previous blood counts, ruling out an inherited PHA. We assessed the haematological, infectious and iatrogenic aetiologies for an acquired PHA. Once the valganciclovir treatment was completed and the drug was withdrawn, without changing the rest of the treatment, the morphological abnormalities of neutrophils were completely resolved. We conclude therefore that the acquired PHA presented by our patient is probably related to valganciclovir treatment.

Analysis of hematopathology and alteration of JAK1/STAT3/STAT5 signaling axis in experimental myelodysplastic syndrome

Hematological disorders like myelodysplastic syndrome (MDS) may arise due to cumulative dysregulation of various signalling pathways controlling proliferation, differentiation, maturation and apoptosis of bone marrow cells. This devastating bone marrow condition can be due to consequential abnormalities in haematopoiesis as well as its supportive microenvironment. Although mutations related to JAK/STAT pathway are common in myeloproliferative neoplasms, further studies are required to fully explore the myelodysplastic scenario regarding the concerned pathway. In this study, we have investigated the JAK-STAT signalling pathway which inevitably plays a crucial role in haematopoiesis. MDS was mimicked in a mouse model with an induction of ENU in adult mice. The bone marrow of the control and MDS groups of animals were subjected to a variety of tests, including cell morphology study in peripheral blood and bone marrow, cytochemistry and histochemistry of bone marrow smears, karyotyping and flowcytometric expression analysis of the phosphorylated forms of proteins like JAK1, STAT3 and STAT5 (denoted as pJAK1, pSTAT3 and pSTAT5) and the phenotypic expression of proteins like CD45 and CD71. The results revealed that the morphology of the blood and bone marrow cells were dysplastic compared to the affected blast populations of different lineages. The expression of common leucocyte antigen CD45 was less in comparison to the expression of transferrin receptor CD71 which was increased in the ENU induced MDS mouse model. Moreover, we have observed an upregulated expression of JAK1 followed by STAT5. Therefore, we can conclude that downregulation of CD45 may have helped in the upregulation of JAK-STAT signaling and CD71 expression. This aberrant signaling may be among one of the activated signaling axes that lead to affected hematopoietic lineages in Myelodysplastic syndrome.

Characterization of neutrophils and macrophages from ex vivo-cultured murine bone marrow for morphologic maturation and functional responses by imaging flow cytometry

Neutrophils and macrophages differentiate from common myeloid progenitors in the bone marrow, where they undergo nuclear morphologic changes during maturation. During this process, both cell types acquire critical innate immune functions that include phagocytosis of pathogens, and for neutrophils the release of nuclear material called nuclear extracellular traps (NETs). Primary cells used to study these functions are typically purified from mature mouse tissues, but bone marrow-derived ex vivo cultures provide more abundant numbers of progenitors and functionally mature cells. Routine analyses of these cells use conventional microscopy and flow cytometry, which present limitations; microscopy is laborious and subjective, whereas flow cytometry lacks spatial resolution. Here we describe methods to generate enriched populations of neutrophils or macrophages from cryopreserved mouse bone marrow cultured ex vivo, and to use imaging flow cytometry that combines the resolution of microscopy with flow cytometry to analyze cells for morphologic features, phagocytosis, and NETosis.

A review of blood diseases and cytopenias associated with human parvovirus B19 infection

Parvovirus B19 is a single-stranded DNA virus which preferentially targets the erythroblast resulting in red cell aplasia, which is temporary in immunocompetent persons. Since the discovery of B19 virus in 1975, a wide variety of blood diseases and cytopenias affecting several blood cell lineages have been documented during or following B19 infection. These include cytopenias affecting the erythroid, megakaryoblastoid, myeloid and lymphoid lineages, as well as a variety of bicytopenias, pancytopenia, bone marrow necrosis / fat embolism syndrome, myelodysplastic syndrome, leucoerythroblastopenia, and hemophagocytic lymphohistiocytosis. B19 infection may also complicate and precede the course of acute leukemia, the significance of which remains to be determined. This review describes the current state of knowledge of the abnormalities of individual blood cell lineages encountered during parvovirus B19 infection, over the almost 40 years since its discovery, and reveals some very interesting themes, which improve our understanding of the pathogenesis of B19 infection with particular reference to the bone marrow.

Pseudo-Pelger-Huët anomaly and granulocytic dysplasia associated with human granulocytic anaplasmosis

Pseudo-Pelger-Huët anomaly (PHA) refers to mono- or bi-lobed granulocytes, reportedly observed in patients with severe infections and inflammation or hematological malignancies including myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). Dysplastic changes in granulocytes are typical manifestations in MDS and granulocytic leukemias. Here, we report the unique case of a patient found to have human granulocytic anaplasmosis (HGA), a tick-borne disease caused by Anaplasma phagocytophilum, a Gram-negative coccobacillus. This patient showed striking hematological manifestations including a large number of pseudo-PHA, a severe degree of left shift, and dysplastic granulocytes. These hematological presentations on the peripheral smear all resolved with doxycycline treatment, implying that the changes were most likely reactive manifestations secondary to HGA, rather than underlying hematological malignancies such as MDS or AML.

Acquired myelodysplasia or myelodysplastic syndrome: clearing the fog

Myelodysplastic syndromes (MDS) are clonal myeloid disorders characterized by progressive peripheral blood cytopenias associated with ineffective myelopoiesis. They are typically considered neoplasms because of frequent genetic aberrations and patient-limited survival with progression to acute myeloid leukemia (AML) or death related to the consequences of bone marrow failure including infection, hemorrhage, and iron overload. A progression to AML has always been recognized among the myeloproliferative disorders (MPD) but occurs only rarely among those with essential thrombocythemia (ET). Yet, the World Health Organization (WHO) has chosen to apply the designation myeloproliferative neoplasms (MPN), for all MPD but has not similarly recommended that all MDS become the myelodysplastic neoplasms (MDN). This apparent dichotomy may reflect the extremely diverse nature of MDS. Moreover, the term MDS is occasionally inappropriately applied to hematologic disorders associated with acquired morphologic myelodysplastic features which may rather represent potentially reversible hematological responses to immune-mediated factors, nutritional deficiency states, and disordered myelopoietic responses to various pharmaceutical, herbal, or other potentially myelotoxic compounds. We emphasize the clinical settings, and the histopathologic features, of such AMD that should trigger a search for a reversible underlying condition that may be nonneoplastic and not MDS.

Pelger-huet anomaly and a mild skeletal phenotype secondary to mutations in LBR

The Lamin B receptor (LBR) gene has been described to encode a bifunctional protein. Mutations in the LBR gene can affect neutrophil segmentation and sterol reductase activity and have been associated with two different recognized clinical conditions, Pelger-Huet anomaly (PHA) and Greenberg skeletal dysplasia. PHA is a benign autosomal co-dominant laminopathy resulting in bilobed neutrophil nuclei in heterozygotes, and unsegmented (ovoid) neutrophil nuclei in homozygotes. Some putative PHA homozygotes have been reported with minor skeletal malformations. Greenberg skeletal dysplasia is a severe autosomal recessive, perinatal lethal dwarfing disorder in which heterozygous carriers are usually without clinical manifestations. We here report a girl who has bilobed neutrophil nuclei and a mild skeletal dysplasia. Mutation analysis showed two novel mutations in the LBR gene: c.651_653 delinsTGATGAGAAA (p.Ile218Aspfs*19) and c.1757G > A (p.Arg586His). These mutations were found to be in trans, and, thus, she is a compound heterozygote. Sterol analysis found trace amounts of cholesta-8,14-dien-3beta-ol, which is normally undetected in healthy individuals. This and previously reported cases suggest that mutations in LBR can result in a continuum of phenotypic manifestations.

Nuclear mechanics in disease

Over the past two decades, the biomechanical properties of cells have emerged as key players in a broad range of cellular functions, including migration, proliferation, and differentiation. Although much of the attention has focused on the cytoskeletal networks and the cell's microenvironment, relatively little is known about the contribution of the cell nucleus. Here, we present an overview of the structural elements that determine the physical properties of the nucleus and discuss how changes in the expression of nuclear components or mutations in nuclear proteins can not only affect nuclear mechanics but also modulate cytoskeletal organization and diverse cellular functions. These findings illustrate that the nucleus is tightly integrated into the surrounding cellular structure. Consequently, changes in nuclear structure and composition are highly relevant to normal development and physiology and can contribute to many human diseases, such as muscular dystrophy, dilated cardiomyopathy, (premature) aging, and cancer.

Understanding and recognizing the Pelger-Huët anomaly

The Pelger-Huët anomaly (PHA) is a recognized morphologic variant affecting all granulocytes but is most evident in polymorphonuclear neutrophils (PMNs). PHA is caused by a decreased amount of the lamin B receptor (LBR). Recognition of PHA morphologic features serves as a marker for mutations in the LBR gene. This review summarizes the history of PHA and the current knowledge of the functions of the LBR. Guidance is given for distinguishing PHA from other hematologic disorders in which granulocytes may show similar changes. Recognition of PHA in the laboratory should prompt communication to the patient's physician about the possible clinical significance of this finding and the recommended screening for the anomaly in other family members by CBC and review of a peripheral blood smear.

Dicer1 deletion in myeloid-committed progenitors causes neutrophil dysplasia and blocks macrophage/dendritic cell development in mice

MicroRNAs (miRNAs) have the potential to regulate cellular differentiation programs; however, miRNA deficiency in primary hematopoietic stem cells (HSCs) results in HSC depletion in mice, leaving the question of whether miRNAs play a role in early-lineage decisions un-answered. To address this issue, we deleted Dicer1, which encodes an essential RNase III enzyme for miRNA biogenesis, in murine CCAAT/enhancer-binding protein α (C/EBPA)-positive myeloid-committed progenitors in vivo. In contrast to the results in HSCs, we found that miRNA depletion affected neither the number of myeloid progenitors nor the percentage of C/EBPA-positive progenitor cells. Analysis of gene-expression profiles from wild-type and Dicer1-deficient granulocyte-macrophage progenitors (GMPs) revealed that 20 miRNA families were active in GMPs. Of the derepressed miRNA targets in Dicer1-null GMPs, 27% are normally exclusively expressed in HSCs or are specific for multipotent progenitors and erythropoiesis, indicating an altered gene-expression landscape. Dicer1-deficient GMPs were defective in myeloid development in vitro and exhibited an increased replating capacity, indicating the regained self-renewal potential of these cells. In mice, Dicer1 deletion blocked monocytic differentiation, depleted macrophages, and caused myeloid dysplasia with morphologic features of Pelger-Huët anomaly. These results provide evidence for a miRNA-controlled switch for a cellular program of self-renewal and expansion toward myeloid differentiation in GMPs.

Reduced lymphocyte longevity and homeostatic proliferation in lamin B receptor-deficient mice results in profound and progressive lymphopenia

The lamin B receptor (LBR) is a highly unusual inner nuclear membrane protein with multiple functions. Reduced levels are associated with decreased neutrophil lobularity, whereas complete absence of LBR results in severe skeletal dysplasia and in utero/perinatal lethality. We describe a mouse pedigree, Lym3, with normal bone marrow and thymic development but profound and progressive lymphopenia particularly within the T cell compartment. This defect arises from a point mutation within the Lbr gene with only trace mutant protein detectable in homozygotes, albeit sufficient for normal development. Reduced T cell homeostatic proliferative potential and life span in vivo were found to contribute to lymphopenia. To investigate the role of LBR in gene silencing in hematopoietic cells, we examined gene expression in wild-type and mutant lymph node CD8 T cells and bone marrow neutrophils. Although LBR deficiency had a very mild impact on gene expression overall, for common genes differentially expressed in both LBR-deficient CD8 T cells and neutrophils, gene upregulation prevailed, supporting a role for LBR in their suppression. In summary, this study demonstrates that LBR deficiency affects not only nuclear architecture but also proliferation, cell viability, and gene expression of hematopoietic cells.

Lamin B receptor regulates the growth and maturation of myeloid progenitors via its sterol reductase domain: implications for cholesterol biosynthesis in regulating myelopoiesis

Lamin B receptor (LBR) is a bifunctional nuclear membrane protein with N-terminal lamin B and chromatin-binding domains plus a C-terminal sterol Δ(14) reductase domain. LBR expression increases during neutrophil differentiation, and deficient expression disrupts neutrophil nuclear lobulation characteristic of Pelger-Huët anomaly. Thus, LBR plays a critical role in regulating myeloid differentiation, but how the two functional domains of LBR support this role is currently unclear. We previously identified abnormal proliferation and deficient functional maturation of promyelocytes (erythroid, myeloid, and lymphoid [EML]-derived promyelocytes) derived from EML-ic/ic cells, a myeloid model of ichthyosis (ic) bone marrow that lacks Lbr expression. In this study, we provide new evidence that cholesterol biosynthesis is important to myeloid cell growth and is supported by the sterol reductase domain of Lbr. Cholesterol biosynthesis inhibitors caused growth inhibition of EML cells that increased in EML-derived promyelocytes, whereas cells lacking Lbr exhibited complete growth arrest at both stages. Lipid production increased during wild-type neutrophil maturation, but ic/ic cells exhibited deficient levels of lipid and cholesterol production. Ectopic expression of a full-length Lbr in EML-ic/ic cells rescued both nuclear lobulation and growth arrest in cholesterol starvation conditions. Lipid production also was rescued, and a deficient respiratory burst was corrected. Expression of just the C-terminal sterol reductase domain of Lbr in ic/ic cells also improved each of these phenotypes. Our data support the conclusion that the sterol Δ(14) reductase domain of LBR plays a critical role in cholesterol biosynthesis and that this process is essential to both myeloid cell growth and functional maturation.

Why are Neutrophils Polymorphonuclear?

Most cells in the human body have a spherical or ovoid nucleus. The mature human neutrophil, unlike most other cells exhibits a distinctly non-spherical nucleus, which is segmented into three to five lobes. The possible mechanisms underlying this segmented nuclear shape have been explored. The structure of the nuclear envelope, composition of lamins and lamin-B receptor seems to have an important role in shaping the nucleus. Being the first line of defense, neutrophils migrate rapidly to the site of infection and destroy the invading pathogen. This requires negotiation through narrow capillaries, transmigration across the vessel wall and passage through tight tissue spaces. Segmented shape confers increased nuclear flexibility, thereby easing the migration of neutrophils through narrow channels. The segmented shape of the nucleus may also play a role in intranuclear chromatin organization and gene expression. The unique shape of the neutrophil nucleus seems to be an adaptation to facilitate its function.

Pseudo-Pelger-Huët anomaly induced by medications: a clinicopathologic study in comparison with myelodysplastic syndrome-related pseudo-Pelger-Huët anomaly

Pseudo-Pelger-Huët anomaly (PPHA) has been documented in association with transplant medications and other drugs. This iatrogenic neutrophilic dysplasia is reversible with cessation or adjustment of medications but is frequently confused with myelodysplastic syndrome (MDS) based on the conventional concept that PPHA is a marker for dysplasia. We investigated the clinicopathologic features in iatrogenic PPHA and compared them with MDS-related PPHA. The 13 cases studied included 5 bone marrow/stem cell transplantations, 3 solid organ transplantations, 1 autoimmune disease, 3 chronic lymphocytic leukemias, and 1 breast carcinoma. For 12 cases, there was follow-up evaluation, and all demonstrated at least transient normalization of neutrophilic segmentation. All 9 cases of MDS demonstrated at least 2 of the following pathologic abnormalities on bone marrow biopsy: hypercellularity (8/9), morphologic dysplasia (8/9), clonal cytogenetic abnormality (7/9), and increased blasts (3/9), whereas these abnormalities were typically absent in iatrogenic PPHA. Iatrogenic PPHA displayed a higher proportion of circulating PPHA cells than in MDS (mean, 47.4%; SD, 31.6% vs mean, 12.3%; SD, 9.8; P < .01). A diagnostic algorithm is proposed in which isolated PPHA is indicative of transient or benign PPHA unless proven otherwise.

Temozolomide-induced myelodysplasia

A patient who had received temozolomide (TMZ) as a single agent in treatment of malignant glioma developed therapy-induced myelodysplasia (T-MDS). TMZ is an orally active imidazotetrazine which methylates guanine residues in DNA, ultimately causing single and double-strand DNA breaks leading to apoptotic cell death. TMZ does not chemically cross-link DNA and is considered a nonclassical alkylating agent, similar in structure and activity to dacarbazine. Observations on this patient, and on similarly treated others, suggest that the cumulative dose threshold (CDT) for TMZ that predisposes to T-MDS and which may potentially lead to acute myeloid leukemia (T-AML) is around 18000 to 20000 mg/sq m. Although the incidence of T-MDS and the predisposing CDT of TMZ may differ from that of other potentially leukemogenic compounds currently and formerly used as chemotherapeutic agents, all alkylating agents, including TMZ, should be considered potentially leukemogenic when administered long term.

Lamin B receptor: multi-tasking at the nuclear envelope

Lamin B receptor (LBR) is an integral membrane protein of the interphase nuclear envelope (NE). The N-terminal end resides in the nucleoplasm, binding to lamin B and heterochromatin, with the interactions disrupted during mitosis. The C-terminal end resides within the inner nuclear membrane, retreating with the ER away from condensing chromosomes during mitotic NE breakdown. Some of these properties are interpretable in terms of our current structural knowledge of LBR, but many of the structural features remain unknown. LBR apparently has an evolutionary history which brought together at least two ancient conserved structural domains (i.e., Tudor and sterol reductase). This convergence may have occurred with the emergence of the chordates and echinoderms. It is not clear what survival values have maintained LBR structure during evolution. But it seems likely that roles in post-mitotic nuclear reformation, interphase NE growth and compartmentalization of nuclear architecture might have provided some evolutionary advantage to preservation of the LBR gene.