High levels of human gamma-globin gene expression in adult mice carrying a transgene of deletion-type hereditary persistence of fetal hemoglobin

Corrected cerebral blood flow and reduced cerebral inflammation in berk sickle mice with higher fetal hemoglobin

Fetal hemoglobin (HbF) is known to lessen the severity of sickle cell disease (SCD), through reductions in peripheral vaso-occlusive disease and reduced risk for cerebrovascular events. However, the influence of HbF on oxygen delivery to high metabolism tissues like the brain, or its influence on cerebral perfusion, metabolism, inflammation or function have not been widely studied. We employed a Berkley mouse model (BERK) of SCD with gamma transgenes q3 expressing exclusively human α- and β^S-globins with varying levels of γ globin expression to investigate the effect of HbF expression on the brain using magnetic resonance imaging (MRI), MRI diffusion tensor imaging (DTI) and spectroscopy (MRS) and hematological parameters. Hematological parameters improved with increasing γ level expression, as did markers for brain metabolism, perfusion and inflammation. Brain microstructure assessed by DTI fractional anisotropy improved, while myo-inositol levels increased, suggesting improved microstructural integrity and reduced cell loss. Our results suggest that increasing γ levels not only improves sickle peripheral disease, but also improves brain perfusion and oxygen delivery while reducing brain inflammation while protecting brain microstructural integrity.

In vivo hematopoietic stem cell gene therapy ameliorates murine thalassemia intermedia

Current thalassemia gene therapy protocols require the collection of hematopoietic stem/progenitor cells (HSPCs), in vitro culture, lentivirus vector transduction, and retransplantation into myeloablated patients. Because of cost and technical complexity, it is unlikely that such protocols will be applicable in developing countries, where the greatest demand for a β-thalassemia therapy lies. We have developed a simple in vivo HSPC gene therapy approach that involves HSPC mobilization and an intravenous injection of integrating HDAd5/35++ vectors. Transduced HSPCs homed back to the bone marrow, where they persisted long-term. HDAd5/35++ vectors for in vivo gene therapy of thalassemia had a unique capsid that targeted primitive HSPCs through human CD46, a relatively safe SB100X transposase-based integration machinery, a micro-LCR-driven γ-globin gene, and an MGMT(P140K) system that allowed for increasing the therapeutic effect by short-term treatment with low-dose O6-benzylguanine plus bis-chloroethylnitrosourea. We showed in "healthy" human CD46-transgenic mice and in a mouse model of thalassemia intermedia that our in vivo approach resulted in stable γ-globin expression in the majority of circulating red blood cells. The high marking frequency was maintained in secondary recipients. In the thalassemia model, a near-complete phenotypic correction was achieved. The treatment was well tolerated. This cost-efficient and "portable" approach could permit a broader clinical application of thalassemia gene therapy.

Pharmacologic induction of fetal hemoglobin production

Reactivation of fetal hemoglobin (HbF) expression is an important therapeutic option in adult patients with hemoglobin disorders. The understanding of the developmental regulation of γ-globin gene expression was followed by the identification of a number of chemical compounds that can reactivate HbF synthesis in vitro and in vivo in patients with hemoglobin disorders. These HbF inducers can be grouped in several classes based on their mechanisms of action. This article focuses on pharmacologic agents that were tested in humans and discusses current knowledge about the mechanisms by which they induce HbF.

Persistent fetal gamma-globin expression in adult transgenic mice following deletion of two silencer elements located 3' to the human Agamma-globin gene

Natural deletions of the human gamma-globin gene cluster lead to specific syndromes characterized by increased production of fetal hemoglobin in adult life and provide a useful model to delineate novel cis-acting elements involved in the developmental control of hemoglobin switching. A hypothesis accounting for these phenotypic features assumes that silencers located within the Agamma-to delta-gene region are deleted in hereditary persistence of fetal hemoglobin (HPFH) and deltabeta-thalassemias, leading to failure of switching. In the present study, we sought to clarify the in vivo role of two elements, termed Enh and F, located 3' to the Agamma-globin, in silencing the fetal genes. To this end, we generated three transgenic lines using cosmid constructs containing the full length of the globin locus control region (LCR) linked to the 3.3-kb Agamma-gene lacking both the Enh and F elements. The Enh/F deletion resulted in high levels of Agamma-globin gene expression in adult mice in all single copy lines, whereas, the LCR-Agamma single copy lines which retain the Enh and F elements exhibited complete normal switching of the fetal Agamma-gene. Our study documents directly for the first time the in vivo role of these two gene-proximal negative regulatory elements in silencing the fetal globin gene in the perinatal period, and thus these data may permit their eventual exploitation in therapeutic approaches for thalassemias.

Erythropoietin blockade inhibits the induction of tumor angiogenesis and progression

Background

The induction of tumor angiogenesis, a pathologic process critical for tumor progression, is mediated by multiple regulatory factors released by tumor and host cells. We investigated the role of the hematopoietic cytokine erythropoietin as an angiogenic factor that modulates tumor progression.

Methodology/Principal Findings

Fluorescently-labeled rodent mammary carcinoma cells were injected into dorsal skin-fold window chambers in mice, an angiogenesis model that allows direct, non-invasive, serial visualization and real-time assessment of tumor cells and neovascularization simultaneously using intravital microscopy and computerized image analysis during the initial stages of tumorigenesis. Erythropoietin or its antagonist proteins were co-injected with tumor cells into window chambers. In vivo growth of cells engineered to stably express a constitutively active erythropoietin receptor EPOR-R129C or the erythropoietin antagonist R103A-EPO were analyzed in window chambers and in the mammary fat pads of athymic nude mice. Co-injection of erythropoietin with tumor cells or expression of EPOR-R129C in tumor cells significantly stimulated tumor neovascularization and growth in window chambers. Co-injection of erythropoietin antagonist proteins (soluble EPOR or anti-EPO antibody) with tumor cells or stable expression of antagonist R103A-EPO protein secreted from tumor cells inhibited angiogenesis and impaired tumor growth. In orthotopic tumor xenograft studies, EPOR-R129C expression significantly promoted tumor growth associated with increased expression of Ki67 proliferation antigen, enhanced microvessel density, decreased tumor hypoxia, and increased phosphorylation of extracellular-regulated kinases ERK1/2. R103A-EPO antagonist expression in mammary carcinoma cells was associated with near-complete disruption of primary tumor formation in the mammary fat pad.

Conclusions/Significance

These data indicate that erythropoietin is an important angiogenic factor that regulates the induction of tumor cell-induced neovascularization and growth during the initial stages of tumorigenesis. The suppression of tumor angiogenesis and progression by erythropoietin blockade suggests that erythropoietin may constitute a potential target for the therapeutic modulation of angiogenesis in cancer.

Characterization of a novel deletion causing (deltabeta)0-thalassemia in a Thai family

A novel deletion of the human beta-globin gene cluster associated with the increased level of fetal hemoglobin (Hb F) in adult life has been demonstrated in a Thai family. A Thai girl who was mistakenly diagnosed as beta-thalassemia/HbE is found to be the compound heterozygote of this mutation and Hb E. The heterozygous father had mild hypochromic and microcytic red blood cells and a high level of Hb F (23.2%). Polymorphic restriction sites in the beta-globin gene cluster identified the homozygous alleles, which localized the deletion region between the psibeta-globin and the 3' beta-globin genes. DNA polymerase that can amplify a long DNA template was employed to examine DNA fragment encompassing this deletion. A 11.3 kilobases (kb) of DNA deletion, beginning approximately 3.1 kb 5' to the delta-globin gene and end in the intron 2 of the beta-globin gene was detected. DNA analysis revealed that this is a case of (deltabeta)(0)-thalassemia with a novel mutation, which can lead to a mild form of beta-thalassemia upon interaction with Hb E.

Identification of novel candidate genes for globin regulation in erythroid cells containing large deletions of the human β-globin gene cluster

The genetic mechanisms underlying the continued expression of the gamma-globin genes during the adult stage in deletional hereditary persistence of fetal hemoglobin (HPFH) and deltabeta-thalassemias are not completely understood. Herein, we investigated the possible involvement of transcription factors, using the suppression subtractive hybridization (SSH) method as an initial screen to identify differentially expressed transcripts in reticulocytes from a normal and a HPFH-2 subject. Some of the detectable transcripts may participate in globin gene regulation. Quantitative real-time PCR (qRT-PCR) experiments confirmed the downregulation of ZHX2, a transcriptional repressor, in two HPFH-2 subjects and in a carrier of the Sicilian deltabeta-thalassemia trait. The chromatin remodeling factors ARID1B and TSPYL1 had a very similar pattern of expression with an incremental increase in HPFH and decreased expression in deltabeta-thalassemia. These differences suggest a mechanism to explain the heterocellular and pancellular distribution of fetal hemoglobin in deltabeta-thalassemia and deletional HPFH, respectively. Interestingly, alpha-globin mRNA levels were decreased, similar to beta-globin in all reticulocyte samples analyzed.

Effects of human gamma-globin in murine beta-thalassaemia

Murine models of beta-thalassaemia have been used to test therapeutic globin gene vectors. However, the level of gamma-globin expression necessary to achieve full phenotypic correction in these models is unclear. In order to address this issue, we carried out breeding and transplantation studies in murine models of beta-thalassaemia intermedia (Hbb(th-3)/+) and severe beta-thalassaemia major (Hbb(th-3)/Hbb(th-3)) using transgenic lines expressing various levels of human gamma-globin. Expression of gamma-globin RNA at a modest 7-14% of total alpha-globin RNA resulted in the selective survival of HbF(+) erythrocytes, a fivefold increase in total HbF, and a phenotypic improvement in the beta-thalassaemia intermedia model. Full normalisation of erythrocyte indices in this model required gamma-globin RNA expression at 27% of alpha-globin, resulting in an average 40% (6.8 g/dl) HbF. Studies using the homozygous Hbb(th-3) model of lethal beta-thalassaemia major demonstrated that even this high level of gamma-globin expression, for reasons related to the function of the hybrid globin tetramers, could only prolong, but not fully support, survival. Taken together, these results indicate that only the heterozygous Hbb(th-3) model of beta-thalassaemia intermedia can be reliably used for the pre-clinical assessment of gamma-globin gene therapy vectors, as well as other means of gamma-globin gene induction.

Use of the hereditary persistence of fetal hemoglobin 2 enhancer to increase the expression of oncoretrovirus vectors for human gamma-globin

The development of oncoretrovirus vectors for human gamma-globin has been hampered by problems of low expression and gene silencing. In order to address these problems, we investigated an enhancer element identified from individuals with deletional hereditary persistence of fetal hemoglobin 2 (HPFH2), a genetic condition characterized by elevated levels of gamma-globin in adults. Plasmid transfection studies in erythroid MEL (murine erythroleukemia) cells demonstrated the HPFH2 element could function synergistically with the beta-globin locus control region to enhance the expression of an Agamma-globin gene with a truncated -382 bp promoter. A series of oncoretrovirus vectors were subsequently generated that contain an expression cassette for Agamma-globin linked to various combinations of the HPFH2 enhancer, the alpha-globin HS40 enhancer, and several versions of the promoter from Agamma-globin or beta-globin. Expression analysis in transduced MEL cell clones revealed very high levels of promoter-autonomous silencing that was at least partially abrogated by the HPFH2 enhancer. The vector containing a combination of a -201 bp Agamma-globin gene promoter with the Greek HPFH -117 point mutation and both the HPFH2 and HS40 enhancers exhibited no signs of vector silencing and was expressed at 248+/-99% per copy of mouse alpha-globin (62% of total alpha-globin). This represents a significant improvement over previously reported oncoretrovirus vectors for Agamma-globin, and demonstrates the capacity of the HPFH2 enhancer to abrogate sequence-autonomous silencing of the Agamma-globin promoter in the context of a gene transfer vector.

Juxtaposition of the HPFH2 enhancer is not sufficient to reactivate the gamma-globin gene in adult erythropoiesis

Previous studies have suggested that juxtaposition of a downstream enhancer to the fetal gamma-globin gene results in reactivation of the gamma-gene in adult erythrocytes of individuals with hereditary persistence of fetal hemoglobin (HPFH). To test the hypothesis in a much stricter basis, we produced beta locus YAC transgenic mice carrying an exact beta locus replicate of a deletional HPFH mutation, HPFH 2. Although the gamma-globin gene was expressed in the HPFH 2/beta locus YAC (HPFH2/YAC) transgenic mice in the early stage of development, it was completely silenced in the adult mice. The failure of gamma-gene reactivation by the juxtaposed HPFH2 enhancer contradicts the results of previous studies. We speculate that the discrepant results reflect differences in the distance between the locus of region (LCR) and the gamma-globin gene characteristic of the plasmid, cosmid or YAC constructs used for production of transgenic mice. The difference in the phenotype of the HPFH2/YAC transgenic mice and the humans with HPFH2 mutation suggests that in addition to juxtaposition of HPFH enhancers, the upstream region that is absent in the beta-YAC construct might be involved in gamma-gene reactivation in HPFH individuals. The DNase I hypersensitive sites of the LCR were well formed and the chromatin histones were acetylated. A moderate level of pol II binding was detected in the LCR, despite the fact that no transcription occurred in the globin-genes of the adult HPFH2/YAC transgenic mice. The results suggest that formation of the LCR chromatin structure in erythroid cells is independent of globin-gene transcription in the locus.

Regulation of human fetal hemoglobin: new players, new complexities

The human globin genes are among the most extensively characterized in the human genome, yet the details of the molecular events regulating normal human hemoglobin switching and the potential reactivation of fetal hemoglobin in adult hematopoietic cells remain elusive. Recent discoveries demonstrate physical interactions between the beta locus control region and the downstream structural gamma- and beta-globin genes, and with transcription factors and chromatin remodeling complexes. These interactions all play roles in globin gene expression and globin switching at the human beta-globin locus. If the molecular events in hemoglobin switching were better understood and fetal hemoglobin could be more fully reactivated in adult cells, the insights obtained might lead to new approaches to the therapy of sickle cell disease and beta thalassemia by identifying specific new targets for molecular therapies.

Control of globin gene expression during development and erythroid differentiation

Extensive studies during the last 30 years have led to considerable understanding of cellular and molecular control of hemoglobin switching. Cell biology studies in the 1970s defined the control of globin genes during erythroid differentiation and led to development of therapies for sickle cell disease. Molecular investigations of the last 20 years have delineated the two basic mechanisms that control globin gene activity during development--autonomous silencing and gene competition. Studies of hemoglobin switching have provided major insights on the control of gene loci by remote regulatory elements. Research in this field has an impact on understanding regulatory mechanisms in general and is of particular importance for eventual development of molecular cures for sickle cell disease and beta thalassemia.

The Corfu deltabeta thalassemia deletion disrupts gamma-globin gene silencing and reveals post-transcriptional regulation of HbF expression

The 7.2 kilobase (kb) Corfu deltabeta thalassemia mutation is the smallest known deletion encompassing a region upstream of the human delta gene that has been suggested to account for the vastly different phenotypes in hereditary persistence of fetal hemoglobin (HPFH) versus beta thalassemia. Fetal hemoglobin (HbF) expression in Corfu heterozygotes and homozygotes is paradoxically dissimilar, suggesting conflicting theories as to the function of the region on globin gene regulation. Here, we measure gamma- and beta-globin gene transcription, steady-state mRNA, and hemoglobin expression levels in primary erythroid cells cultured from several patients with Corfu deltabeta thalassemia. We show through RNA fluorescence in situ hybridization that the Corfu deletion results in high-level transcription of the fetal gamma genes in cis with a concomitant reduction in transcription of the downstream beta gene. Surprisingly, we find that elevated gamma gene transcription does not always result in a corresponding accumulation of gamma mRNA or fetal hemoglobin, indicating a post-transcriptional regulation of gamma gene expression. The data suggest that efficient gamma mRNA accumulation and HbF expression are blocked until beta mRNA levels fall below a critical threshold. These results explain the Corfu paradox and show that the deleted region harbors a critical element that functions in the developmentally regulated transcription of the beta-globin genes.

Mucormycosis in hematologic patients

BACKGROUND AND OBJECTIVES

To evaluate the clinical characteristics of patients affected by hematologic malignancies who developed mucormycosis and to ascertain the factors which influenced the outcome following mycotic infection.

DESIGN AND METHODS

This was a retrospective study conducted over a 15-year period (1987-2001). The study included 59 patients with hematologic malignancies with a proven or probable mucormycosis admitted in 18 Hematology Divisions in tertiary care or university hospitals.

RESULTS

The most frequent sites of infection were lung (64%) and orbito-sinus-facial (24%); cerebral involvement observed in 19% of cases was always associated with other sites of infection. Antifungal treatment was empirically administered in 49 patients (83%); 7 patients underwent radical surgical debridement (12%). Therapy was successful for only 18 patients (37%). Forty-seven patients died within 3 months of the diagnosis of fungal infection: the cause of death was mucormycosis in 41 patients (87%) and progression of hematologic disease in 6 patients (13%). At univariate analysis, the factors that correlated with a positive outcome from infection were the following: male sex, amphotericin B treatment, neutrophil recovery from post-chemotherapy aplasia. At multivariate analysis, the only factor that significantly correlated with recovery from infection was the liposomal amphotericin B treatment.

INTERPRETATION AND CONCLUSIONS

Mucormycosis is a rare filamentous fungal infection that occurs most frequently in neutropenic patients with acute leukemia. It does not seem to have increased in recent years. Although a reduction of mortality has been observed recently, the mortality rate still remains high. Extensive and aggressive diagnostic and therapeutic procedures are essential in order to improve the prognosis in these patients.

Persistent gamma-globin expression in adult transgenic mice is mediated by HPFH-2, HPFH-3, and HPFH-6 breakpoint sequences

Deletions at the 3' end of the human beta-globin locus are associated with the hereditary persistence of fetal hemoglobin (HPFH) in adults, potentially through the juxtaposition of enhancer elements in the vicinity of the fetal gamma-globin genes. We have tested how sequences at the HPFH-2, HPFH-3, and HPFH-6 breakpoints, which act as enhancers in vitro, affect the silencing of a locus control region A gamma (LCRA gamma) transgene in the adult stage of mice. We found persistent A gamma expression in the adult blood of most of the multicopy HPFH-2, HPFH-3, or HPFH-6 lines, in contrast to the control LCRA gamma lines which were silenced. Cre-mediated generation of single copy lines showed persistent gamma gene expression maintained in some of the HPFH-2 and HPFH-6 lines, but not in any of the HPFH-3 or LCRA gamma lines. In the HPFH-2 and HPFH-6 lines, persistent gamma gene expression correlated with euchromatic transgene integrations. Thus, our observations provide support for a model whereby HPFH conditions arise from the juxtaposition of enhancers as well as permissive chromatin subdomains in the vicinity of the gamma-globin genes.

Analysis of the mechanism of action of non-deletion hereditary persistence of fetal hemoglobin mutants in transgenic mice

Transgenic mice carrying an (A)gamma gene construct containing a -382 5' truncation of the (A)gamma gene promoter have a phenotype of hereditary persistence of fetal hemoglobin (HPFH) but, when the CACCC box of the -382(A)gamma promoter is deleted, there is no gamma gene expression in the adult mice. We used this system to investigate the mechanism whereby human HPFH mutations result in gamma gene expression in the adult. Introduction of the -198 T-->C HPFH mutation into the CACCC-less (A)gamma gene construct re-established the HPFH phenotype, indicating that this mutation increases promoter strength, most probably by establishing a novel CACCC box sequence in the -198(A)gamma region. The HPFH phenotype was also re-established when the -117 C-->T HPFH mutation was introduced into a -141(A)gamma promoter with a destroyed CACCC box, indicating that this mutation increases gamma promoter strength in the absence of the CACCC motif. The T-->A -175 HPFH mutation failed to re-establish the HPFH phenotype when the CACCC box was deleted, indicating that gamma gene expression in this mutation is CACCC box dependent. These results provide the first in vivo experimental evidence in support of mechanistic heterogeneity of the non-deletion HPFH mutants.

Second generation knockout sickle mice: the effect of HbF

Sickle transgenic mice expressing exclusively human globins are desirable for studying pathophysiology and testing gene therapy strategies, but they must have significant pathology and show evidence of amelioration by antisickling hemoglobins. Mice were generated that expressed exclusively human sickle hemoglobin with 3 levels of HbF using their previously described sickle constructs (cointegrated human miniLCRalpha2 and miniLCRbeta(S) [PNAS 89:12150, 1992]), mouse alpha- and beta-globin-knockouts, and 3 different human gamma-transgenes. It was found that, at all 3 levels of HbF expression, these mice have balanced chain synthesis, nearly normal mean corpuscular hemoglobin, and, in some cases, F cells. Mice with the least adult HbF expression were the most severe. Progressive increase in HbF from less than 3% to 20% to 40% correlated with progressive increase in hematocrit (22% to 34% to 40%) and progressive decrease in reticulocyte count (from 60% to 30% to 13%). Urine concentrating ability was normalized at high HbF, and tissue damage detected by histopathology and organ weight were ameliorated by increased HbF. The gamma-transgene that produces intermediate levels of HbF was introduced into knockout sickle mice described by Pàszty and coworkers that express the miniLCRalpha1(G)gamma(A)gammadeltabeta(S) transgene and have fetal but not adult expression of HbF. It was found that the level of HbF required to ameliorate low hematocrit and normalize urine concentrating defect was different for the miniLCRalpha2beta(S) and miniLCRalpha1(G)gamma(A)gammadeltabeta(S) mice. We conclude that knockout mice with the miniLCRalpha2beta(S) transgene and postnatal expression of HbF have sufficiently faithful sickle pathology to serve as a platform for testing antisickling interventions.

Deletion of a region that is a candidate for the difference between the deletion forms of hereditary persistence of fetal hemoglobin and deltabeta-thalassemia affects beta- but not gamma-globin gene expression

The analysis of a number of cases of beta-globin thalassemia and hereditary persistence of fetal hemoglobin (HPFH) due to large deletions in the beta-globin locus has led to the identification of several DNA elements that have been implicated in the switch from human fetal gamma- to adult beta-globin gene expression. We have tested this hypothesis for an element that covers the minimal distance between the thalassemia and HPFH deletions and is thought to be responsible for the difference between a deletion HPFH and deltabeta-thalassemia, located 5' of the delta-globin gene. This element has been deleted from a yeast artificial chromosome (YAC) containing the complete human beta-globin locus. Analysis of this modified YAC in transgenic mice shows that early embryonic expression is unaffected, but in the fetal liver it is subject to position effects. In addition, the efficiency of transcription of the beta-globin gene is decreased, but the developmental silencing of the gamma-globin genes is unaffected by the deletion. These results show that the deleted element is involved in the activation of the beta-globin gene perhaps through the loss of a structural function required for gene activation by long-range interactions.

Developmental control of epsilon- and gamma-globin genes

In the last few years there have been considerable advances in the understanding of the molecular control of globin genes during development. Several insights have been obtained with studies using transgenic mice. The 5' to 3' order of the genes in the beta locus, the proximity of the genes to the locus control region and the availability of transcriptional factors have been implicated in the developmental activation of globin genes. Globin genes are turned off by two general mechanisms, autonomous gene silencing involving sequences located in the proximal and distal promoters and competition between genes for interaction with the locus control region. The current understanding of the control of embryonic (epsilon) and fetal (gamma) globin genes is reviewed.

Molecular basis of hereditary persistence of fetal hemoglobin

Increased levels of fetal hemoglobin (HbF) can ameliorate the clinical course of inherited disorders of beta-globin gene expression, such as beta thalassemia and sickle cell anemia. In a group of disorders called hereditary persistence of fetal hemoglobin (HPFH), expression of the gamma-globin gene of HbF persists at high levels in adult erythroid cells. Molecular studies of the HPFH syndromes have identified several important regulatory elements for the normal pattern of gamma-globin gene expression. Deletion as well as nondeletion types of HPFH have been identified. The nondeletion types of HPFH are characterized by the presence of point mutations, in the promoter region of one or another gamma-globin gene, that are thought to alter interactions between various transcription factors and the promoter. The deletion types of HPFH are thought to deregulate the normal developmental pattern of gamma-globin gene expression due to the juxtaposition of normally distant cis-acting factors into the vicinity of the gamma genes. These findings have provided us with a more sophisticated understanding of the molecular basis for the persistent gamma-gene expression in these syndromes and point to certain strategies for potential future attempts at gene therapy for beta-globin gene disorders.