Clonal hematopoiesis related TET2 loss-of-function impedes IL1β-mediated epigenetic reprogramming in hematopoietic stem and progenitor cells

Clonal hematopoiesis (CH) is defined as a single hematopoietic stem/progenitor cell (HSPC) gaining selective advantage over a broader range of HSPCs. When linked to somatic mutations in myeloid malignancy-associated genes, such as TET2-mediated clonal hematopoiesis of indeterminate potential or CHIP, it represents increased risk for hematological malignancies and cardiovascular disease. IL1β is elevated in patients with CHIP, however, its effect is not well understood. Here we show that IL1β promotes expansion of pro-inflammatory monocytes/macrophages, coinciding with a failure in the demethylation of lymphoid and erythroid lineage associated enhancers and transcription factor binding sites, in a mouse model of CHIP with hematopoietic-cell-specific deletion of Tet2. DNA-methylation is significantly lost in wild type HSPCs upon IL1β administration, which is resisted by Tet2-deficient HSPCs, and thus IL1β enhances the self-renewing ability of Tet2-deficient HSPCs by upregulating genes associated with self-renewal and by resisting demethylation of transcription factor binding sites related to terminal differentiation. Using aged mouse models and human progenitors, we demonstrate that targeting IL1 signaling could represent an early intervention strategy in preleukemic disorders. In summary, our results show that Tet2 is an important mediator of an IL1β-promoted epigenetic program to maintain the fine balance between self-renewal and lineage differentiation during hematopoiesis.

MYC Promotes Bone Marrow Stem Cell Dysfunction in Fanconi Anemia

Bone marrow failure (BMF) in Fanconi anemia (FA) patients results from dysfunctional hematopoietic stem and progenitor cells (HSPCs). To identify determinants of BMF, we performed single-cell transcriptome profiling of primary HSPCs from FA patients. In addition to overexpression of p53 and TGF-β pathway genes, we identified high levels of MYC expression. We correspondingly observed coexistence of distinct HSPC subpopulations expressing high levels of TP53 or MYC in FA bone marrow (BM). Inhibiting MYC expression with the BET bromodomain inhibitor (+)-JQ1 reduced the clonogenic potential of FA patient HSPCs but rescued physiological and genotoxic stress in HSPCs from FA mice, showing that MYC promotes proliferation while increasing DNA damage. MYC-high HSPCs showed significant downregulation of cell adhesion genes, consistent with enhanced egress of FA HSPCs from bone marrow to peripheral blood. We speculate that MYC overexpression impairs HSPC function in FA patients and contributes to exhaustion in FA bone marrow.

Extrahepatic deficiency of transferrin receptor 2 is associated with increased erythropoiesis independent of iron overload

Transferrin receptor 2 (TFR2) is a transmembrane protein expressed mainly in hepatocytes and in developing erythroid cells and is an important focal point in systemic iron regulation. Loss of TFR2 function results in a rare form of the iron-overload disease hereditary hemochromatosis. Although TFR2 in the liver has been shown to be important for regulating iron homeostasis in the body, TFR2's function in erythroid progenitors remains controversial. In this report, we analyzed TFR2-deficient mice in the presence or absence of iron overload to distinguish between the effects caused by a high iron load and those caused by loss of TFR2 function. Analysis of bone marrow from TFR2-deficient mice revealed a reduction in the early burst-forming unit-erythroid and an expansion of late-stage erythroblasts that was independent of iron overload. Spleens of TFR2-deficient mice displayed an increase in colony-forming unit-erythroid progenitors and in all erythroblast populations regardless of iron overload. This expansion of the erythroid compartment coincided with increased erythroferrone (ERFE) expression and serum erythropoietin (EPO) levels. Rescue of hepatic TFR2 expression normalized hepcidin expression and the total cell count of the bone marrow and spleen, but it had no effect on erythroid progenitor frequency. On the basis of these results, we propose a model of TFR2's function in murine erythropoiesis, indicating that deficiency in this receptor is associated with increased erythroid development and expression of EPO and ERFE in extrahepatic tissues independent of TFR's role in the liver.

LMTK3 is essential for oncogenic KIT expression in KIT-mutant GIST and melanoma

Certain cancers, including gastrointestinal stromal tumor (GIST) and subsets of melanoma, are caused by somatic KIT mutations that result in KIT receptor tyrosine kinase constitutive activity, which drives proliferation. The treatment of KIT-mutant GIST has been revolutionized with the advent of KIT-directed cancer therapies. KIT tyrosine kinase inhibitors (TKI) are superior to conventional chemotherapy in their ability to control advanced KIT-mutant disease. However, these therapies have a limited duration of activity due to drug-resistant secondary KIT mutations that arise (or that are selected for) during KIT TKI treatment. To overcome the problem of KIT TKI resistance, we sought to identify novel therapeutic targets in KIT-mutant GIST and melanoma cells using a human tyrosine kinome siRNA screen. From this screen, we identified lemur tyrosine kinase 3 (LMTK3) and herein describe its role as a novel KIT regulator in KIT-mutant GIST and melanoma cells. We find that LMTK3 regulated the translation rate of KIT, such that loss of LMTK3 reduced total KIT, and thus KIT downstream signaling in cancer cells. Silencing of LMTK3 decreased cell viability and increased cell death in KIT-dependent, but not KIT-independent GIST and melanoma cell lines. Notably, LMTK3 silencing reduced viability of all KIT-mutant cell lines tested, even those with drug-resistant KIT secondary mutations. Furthermore, targeting of LMTK3 with siRNA delayed KIT-dependent GIST growth in a xenograft model. Our data suggest the potential of LMTK3 as a target for treatment of patients with KIT-mutant cancer, particularly after failure of KIT TKIs.

The tumor suppressor phosphatase PP2A-B56α regulates stemness and promotes the initiation of malignancies in a novel murine model

Protein phosphatase 2A (PP2A) is a ubiquitously expressed Serine-Threonine phosphatase mediating 30–50% of protein phosphatase activity. PP2A functions as a heterotrimeric complex, with the B subunits directing target specificity to regulate the activity of many key pathways that control cellular phenotypes. PP2A-B56α has been shown to play a tumor suppressor role and to negatively control c-MYC stability and activity. Loss of B56α promotes cellular transformation, likely at least in part through its regulation of c-MYC. Here we report generation of a B56α hypomorph mouse with very low B56α expression that we used to study the physiologic activity of the PP2A-B56α phosphatase. The predominant phenotype we observed in mice with B56α deficiency in the whole body was spontaneous skin lesion formation with hyperproliferation of the epidermis, hair follicles and sebaceous glands. Increased levels of c-MYC phosphorylation on Serine62 and c-MYC activity were observed in the skin lesions of the B56α^hm/hm mice. B56α deficiency was found to increase the number of skin stem cells, and consistent with this, papilloma initiation was accelerated in a carcinogenesis model. Further analysis of additional tissues revealed increased inflammation in spleen, liver, lung, and intestinal lymph nodes as well as in the skin lesions, resembling elevated extramedullary hematopoiesis phenotypes in the B56α^hm/hm mice. We also observed an increase in the clonogenicity of bone marrow stem cells in B56α^hm/hm mice. Overall, this model suggests that B56α is important for stem cells to maintain homeostasis and that B56α loss leading to increased activity of important oncogenes, including c-MYC, can result in aberrant cell growth and increased stem cells that can contribute to the initiation of malignancy.

The Corepressor Rcor1 Is Essential for Normal Myeloerythroid Lineage Differentiation

Based on its physical interactions with histone-modifying enzymes, the transcriptional corepressor Rcor1 has been implicated in the epigenetic regulation blood cell development. Previously, we have demonstrated that Rcor1 is essential for the maturation of definitive erythroid cells and fetal survival. To determine the functional role of Rcor1 in steady-state hematopoiesis in the adult, we used a conditional knockout approach. Here, we show that the loss of Rcor1 expression results in the rapid onset of severe anemia due to a complete, cell autonomous block in the maturation of committed erythroid progenitors. By contrast, both the frequency of megakaryocyte progenitors and their capacity to produce platelets were normal. Although the frequency of common lymphoid progenitors and T cells was not altered, B cells were significantly reduced and showed increased apoptosis. However, Rcor1-deficient bone marrow sustained normal levels of B-cells following transplantation, indicating a non-cell autonomous requirement for Rcor1 in B-cell survival. Evaluation of the myelomonocytic lineage revealed an absence of mature neutrophils and a significant increase in the absolute number of monocytic cells. Rcor1-deficient monocytes were less apoptotic and showed ∼100-fold more colony-forming activity than their normal counterparts, but did not give rise to leukemia. Moreover, Rcor1(-/-) monocytes exhibited extensive, cytokine-dependent self-renewal and overexpressed genes associated with hematopoietic stem/progenitor cell expansion including Gata2, Meis1, and Hoxa9. Taken together, these data demonstrate that Rcor1 is essential for the normal differentiation of myeloerythroid progenitors and for appropriately regulating self-renewal activity in the monocyte lineage.

The triterpenoid RTA 408 is a robust mitigator of hematopoietic acute radiation syndrome in mice

Bone marrow suppression due to exposure to ionizing radiation is a significant clinical problem associated with radiation therapy as well as with nonmedical radiation exposure. Currently, there are no small molecule agents available that can enhance hematopoietic regeneration after radiation exposure. Here, we report on the effective mitigation of acute hematopoietic radiation syndrome in mice by the synthetic triterpenoid, RTA 408. The administration of a brief course of RTA 408 treatment, beginning 24 h after lethal doses of radiation to bone marrow, significantly increased overall survival. Importantly, treatment with RTA 408 led to the full recovery of steady state hematopoiesis with normalization of the frequency of hematopoietic stem and progenitor cells. Moreover, hematopoietic stem cells from RTA 408-mitigated mice showed lineage-balanced, long-term, multilineage potential in serial transplantation assays, indicative of their normal self-renewal activity. The potency of RTA 408 in mitigating radiation-induced bone marrow suppression makes it an attractive candidate for potential clinical use in treating both therapy-related and unanticipated radiation exposure.

HCMV infection of humanized mice after transplantation of G-CSF-mobilized peripheral blood stem cells from HCMV-seropositive donors

Human cytomegalovirus (HCMV) infection, including primary infection resulting from transmission from a seropositive donor to a seronegative recipient (D(+)/R(-)), remains a significant problem in the setting of peripheral blood stem cell transplantation (PBSCT). The lack of a suitable animal model for studying HCMV transmission after PBSCT is a major barrier to understanding this process and, consequently, developing novel interventions to prevent HCMV infection. Our previous work demonstrated that human CD34(+) progenitor cell-engrafted NOD-scid IL2Rγc(null) (NSG) mice support latent HCMV infection after direct inoculation and reactivation after treatment with granulocyte colony-stimulating factor. To more accurately recapitulate HCMV infection in the D(+)/R(-) PBSCT setting, granulocyte colony-stimulating factor-mobilized peripheral blood stem cells from seropositive donors were used to engraft NSG mice. All recipient mice demonstrated evidence of HCMV infection in liver, spleen, and bone marrow. These findings validate the NSG mouse model for studying HCMV transmission during PBSCT.

Endothelial cells mitigate DNA damage and promote the regeneration of hematopoietic stem cells after radiation injury

Endothelial cells (ECs) are an essential component of the hematopoietic microenvironment, which maintains and regulates hematopoietic stem cells (HSCs). Although ECs can support the regeneration of otherwise lethally-irradiated HSCs, the mechanisms are not well understood. To further understand this phenomenon, we studied HSC regeneration from irradiated bone marrow using co-culture with human aortic ECs (HAECs). Co-culture with HAECs induced a 24-fold expansion of long-term HSCs (CD150(+), lineage(lo), Sca-1(+), c-Kit(+); CD150(+)LSK cells) in vitro. These cells gave rise to functional hematopoietic stem and progenitor cells (HSPCs) with colony-forming activity, multilineage reconstitution and serial transplantation potential. Furthermore, HAECs significantly reduced DNA damage in irradiated LSK cells within 24h. Remarkably, we were able to delay the exposure of irradiated bone marrow to the regenerative, HAEC-derived signals for up to 48h and still rescue functional HSCs. G-CSF is the gold standard for promoting hematopoietic regeneration in vivo. However, when compared to HAECs, in vitro G-CSF treatment promoted lineage differentiation and regenerated 5-fold fewer CD150(+)LSK cells. Together, our results show that HAECs are powerful, direct mitigators of HSC injury and DNA damage. Identification of the HAEC-derived factors that rescue HSCs may lead to improved therapies for hematopoietic regeneration after radiation injury.

Kinase pathway dependence in primary human leukemias determined by rapid inhibitor screening

Kinases are dysregulated in most cancers, but the frequency of specific kinase mutations is low, indicating a complex etiology in kinase dysregulation. Here, we report a strategy to rapidly identify functionally important kinase targets, irrespective of the etiology of kinase pathway dysregulation, ultimately enabling a correlation of patient genetic profiles to clinically effective kinase inhibitors. Our methodology assessed the sensitivity of primary leukemia patient samples to a panel of 66 small-molecule kinase inhibitors over 3 days. Screening of 151 leukemia patient samples revealed a wide diversity of drug sensitivities, with 70% of the clinical specimens exhibiting hypersensitivity to one or more drugs. From this data set, we developed an algorithm to predict kinase pathway dependence based on analysis of inhibitor sensitivity patterns. Applying this algorithm correctly identified pathway dependence in proof-of-principle specimens with known oncogenes, including a rare FLT3 mutation outside regions covered by standard molecular diagnostic tests. Interrogation of all 151 patient specimens with this algorithm identified a diversity of kinase targets and signaling pathways that could aid prioritization of deep sequencing data sets, permitting a cumulative analysis to understand kinase pathway dependence within leukemia subsets. In a proof-of-principle case, we showed that in vitro drug sensitivity could predict both a clinical response and the development of drug resistance. Taken together, our results suggested that drug target scores derived from a comprehensive kinase inhibitor panel could predict pathway dependence in cancer cells while simultaneously identifying potential therapeutic options.

A novel human cytomegalovirus locus modulates cell type-specific outcomes of infection

Clinical strains of HCMV encode 20 putative ORFs within a region of the genome termed ULb' that are postulated to encode functions related to persistence or immune evasion. We have previously identified ULb'-encoded pUL138 as necessary, but not sufficient, for HCMV latency in CD34+ hematopoietic progenitor cells (HPCs) infected in vitro. pUL138 is encoded on polycistronic transcripts that also encode 3 additional proteins, pUL133, pUL135, and pUL136, collectively comprising the UL133-UL138 locus. This work represents the first characterization of these proteins and identifies a role for this locus in infection. Similar to pUL138, pUL133, pUL135, and pUL136 are integral membrane proteins that partially co-localized with pUL138 in the Golgi during productive infection in fibroblasts. As expected of ULb' sequences, the UL133-UL138 locus was dispensable for replication in cultured fibroblasts. In CD34+ HPCs, this locus suppressed viral replication in HPCs, an activity attributable to both pUL133 and pUL138. Strikingly, the UL133-UL138 locus was required for efficient replication in endothelial cells. The association of this locus with three context-dependent phenotypes suggests an exciting role for the UL133-UL138 locus in modulating the outcome of viral infection in different contexts of infection. Differential profiles of protein expression from the UL133-UL138 locus correlated with the cell-type dependent phenotypes associated with this locus. We extended our in vitro findings to analyze viral replication and dissemination in a NOD-scid IL2Rγ(c) (null)-humanized mouse model. The UL133-UL138(NULL) virus exhibited an increased capacity for replication and/or dissemination following stem cell mobilization relative to the wild-type virus, suggesting an important role in viral persistence and spread in the host. As pUL133, pUL135, pUL136, and pUL138 are conserved in virus strains infecting higher order primates, but not lower order mammals, the functions encoded likely represent host-specific viral adaptations.

Granulocyte-colony stimulating factor reactivates human cytomegalovirus in a latently infected humanized mouse model

Human cytomegalovirus (HCMV) is a significant cause of morbidity and mortality in organ transplant recipients. The use of granulocyte-colony stimulating factor (G-CSF)-mobilized stem cells from HCMV seropositive donors is suggested to double the risk of late-onset HCMV disease and chronic graft-versus-host disease in recipients when compared to conventional bone marrow transplantation with HCMV seropositive donors, although the etiology of the increased risk is unknown. To understand mechanisms of HCMV transmission in patients receiving G-CSF-mobilized blood products, we generated a NOD-scid IL2Rγ(c)(null)-humanized mouse model in which HCMV establishes latent infection in human hematopoietic cells. In this model, G-CSF induces the reactivation of latent HCMV in monocytes/macrophages that have migrated into organ tissues. In addition to establishing a humanized mouse model for systemic and latent HCMV infection, these results suggest that the use of G-CSF mobilized blood products from seropositive donors pose an elevated risk for HCMV transmission to recipients.

Endothelial cells mediate the regeneration of hematopoietic stem cells

Recent studies suggest that endothelial cells are a critical component of the normal hematopoietic microenvironment. Therefore, we sought to determine whether primary endothelial cells have the capacity to repair damaged hematopoietic stem cells. Highly purified populations of primary CD31(+) microvascular endothelial cells isolated from the brain or lung did not express the pan hematopoietic marker CD45, most hematopoietic lineage markers, or the progenitor marker c-kit and did not give rise to hematopoietic cells in vitro or in vivo. Remarkably, the transplantation of small numbers of these microvascular endothelial cells consistently restored hematopoiesis following bone marrow lethal doses of irradiation. Analysis of the peripheral blood of rescued recipients demonstrated that both short-term and long-term multilineage hematopoietic reconstitution was exclusively of host origin. Secondary transplantation studies revealed that microvascular endothelial cell-mediated hematopoietic regeneration also occurs at the level of the hematopoietic stem cell. These findings suggest a potential therapeutic role for microvascular endothelial cells in the self-renewal and repair of adult hematopoietic stem cells.

Hematopoietic stem cells contribute to lymphatic endothelium

Background

Although the lymphatic system arises as an extension of venous vessels in the embryo, little is known about the role of circulating progenitors in the maintenance or development of lymphatic endothelium. Here, we investigated whether hematopoietic stem cells (HSCs) have the potential to give rise to lymphatic endothelial cells (LEC).

Methodology/Principal Findings

Following the transfer of marked HSCs into irradiated recipients, donor-derived LEC that co-express the lymphatic endothelial markers Lyve-1 and VEGFR-3 were identified in several tissues. HSC-derived LEC persisted for more than 12 months and contributed to ∼3–4% of lymphatic vessels. Donor-derived LECs were not detected in mice transplanted with common myeloid progenitors and granulocyte/macrophage progenitors, suggesting that myeloid lineage commitment is not a requisite step in HSC contribution to lymphatic endothelium. Analysis of parabiotic mice revealed direct evidence for the existence of functional, circulating lymphatic progenitors in the absence of acute injury. Furthermore, the transplantation of HSCs into Apc^Min/+ mice resulted in the incorporation of donor-derived LEC into the lymphatic vessels of spontaneously arising intestinal tumors.

Conclusions/Significance

Our results indicate that HSCs can contribute to normal and tumor associated lymphatic endothelium. These findings suggest that the modification of HSCs may be a novel approach for targeting tumor metastasis and attenuating diseases of the lymphatic system.

Transvection mediated by the translocated cyclin D1 locus in mantle cell lymphoma

In mantle cell lymphoma (MCL) and some cases of multiple myeloma (MM), cyclin D1 expression is deregulated by chromosome translocations involving the immunoglobulin heavy chain (IgH) locus. To evaluate the mechanisms responsible, gene targeting was used to study long-distance gene regulation. Remarkably, these targeted cell lines lost the translocated chromosome (t(11;14)). In these MCL and MM cells, the nonrearranged cyclin D1 (CCND1) locus reverts from CpG hypomethylated to hypermethylated. Reintroduction of the translocated chromosome induced a loss of methylation at the unrearranged CCND1 locus, providing evidence of a transallelic regulatory effect. In these cell lines and primary MCL patient samples, the CCND1 loci are packaged in chromatin-containing CCCTC binding factor (CTCF) and nucleophosmin (NPM) at the nucleolus. We show that CTCF and NPM are bound at the IgH 3′ regulatory elements only in the t(11;14) MCL cell lines. Furthermore, NPM short hairpin RNA produces a specific growth arrest in these cells. Our data demonstrate transvection in human cancer and suggest a functional role for CTCF and NPM.

Myeloid lineage progenitors give rise to vascular endothelium

Despite an important role in vascular development and repair, the origin of endothelial progenitors remains unknown. Accumulating evidence indicates that cells derived from the hematopoietic system participate in angiogenesis. However, the identity and functional role of these cells remain controversial. Here we show that vascular endothelial cells can differentiate from common myeloid progenitors and granulocyte/macrophage progenitors. Endothelial cells derived from transplanted bone marrow-derived myeloid lineage progenitors expressed CD31, von Willebrand factor, and Tie2 but did not express the hematopoietic markers CD45 and F4/80 or the pericyte markers desmin and smooth muscle actin. Lineage tracing analysis in combination with a Tie2-driven Cre/lox reporter system revealed that, in contrast to bone marrow-derived hepatocytes, bone marrow-derived endothelial cells are not the products of cell fusion. The establishment of both hematopoietic and endothelial cell chimerism after parabiosis demonstrates that circulating cells can give rise to vascular endothelium in the absence of acute radiation injury. Our findings indicate that endothelial cells are an intrinsic component of myeloid lineage differentiation and underscore the close functional relationship between the hematopoietic and vascular systems.

Mouse models of hematopoietic engraftment: limitations of transgenic green fluorescent protein strains and a high-performance liquid chromatography approach to analysis of erythroid chimerism

Transgenic mouse strains ubiquitously expressing green fluorescent protein (GFP) have enabled investigators to develop in vivo transplant models that can detect donor contributions to many different tissues. However, most GFP transgenics lack expression of the reporter in the erythroid lineage. We evaluated expression of GFP in the bone marrow of the OsbY01 transgenic mouse (B6-GFP) in the context of CD71 and TER-119 expression and found that GFP fluorescence is lost prior to the basophilic erythroblast stage of development. However, platelets in B6-GFP mice were found to be uniformly positive for GFP. We therefore used the GFP transgenic model in combination with allelic variants of CD45 and the hemoglobin beta (Hbb) chain to develop a model system that allows all blood lineages to be followed in a mouse model of bone marrow transplantation (BMT). To detect Hbb variant molecules, we developed a new protocol based on high-performance liquid chromatography that is sensitive and precise, allowing rapid and quantitative analysis of erythroid chimerism. Platelet and leukocyte engraftment were detected by flow cytometry. BMT into sublethally irradiated (4 Gy) recipients demonstrated the failure of B6-GFP-derived cells to engraft relative to B6-CD45(a)-derived cells, suggesting that an immune barrier may prevent efficient engraftment of the transgenic cells in a setting of minimal ablation. These results establish limitations in the use of transgenic GFP expression as a donor marker in transplantation models.

Bone marrow-derived cells fuse with normal and transformed intestinal stem cells

Transplanted adult bone marrow-derived cells (BMDCs) have been shown to adopt the phenotype and function of several nonhematopoietic cell lineages and promote tumorigenesis. Beyond its cancer enhancing potential, cell fusion has recently emerged as an explanation of how BMDCs regenerate diseased heptocytes, contribute to Purkinje neurons and skeletal and cardiac muscle cells, and participate in skin and heart regeneration. Although bone marrow-derived epithelial cells also have been observed in the intestine, fusion as a mechanism has not been investigated. Here, we show that transplanted BMDCs fuse with both normal and neoplastic intestinal epithelium. Long-term repopulation by donor-derived cells was detected in all principal intestinal epithelial lineages including enterocytes, goblet cells, Paneth cells, and enteroendocrine cells, suggesting that the fusion partners of the BMDCs are long-lived intestinal progenitors or stem cells. Fusion of BMDCs with neoplastic epithelium did not result in tumor initiation. Our findings suggest an unexpected role for BMDCs in both regeneration and tumorigenesis of the intestine.

In Vivo Genetic Selection of Renal Proximal Tubules

Repopulation by transplanted cells can result in effective therapy for several regenerative organs including blood, liver, and skin. In contrast, cell therapies for renal diseases are not currently available. Here we developed an animal model in which cells genetically resistant to a toxic intermediate of tyrosine metabolism, homogentisic acid (HGA), were able to repopulate the damaged proximal tubule epithelium of mice with fumarylacetoacetate hydrolase (Fah) deficiency. HGA resistance was achieved by two independent mechanisms. First, Fah+ transplanted bone marrow cells produced significant replacement of damaged proximal tubular epithelium (up to 50%). The majority of bone marrow-derived epithelial cells were generated by cell fusion, not transdifferentiation. In addition to regeneration by fusion-derived epithelial cells, proximal tubular repopulation was also observed by host epithelial cells, which had lost the homogentisic acid dioxygenase gene. These data demonstrate that extensive regeneration of the renal proximal tubule compartment can be achieved through genetic selection of functional cells.

Donor marker infidelity in transgenic hematopoietic stem cells

Transgenic marking approaches are increasingly used to evaluate the developmental potential of stem cells. However, cell fate mapping studies using different transgenic marking systems have produced conflicting results. These disparate findings may be due in part to the infidelity of donor marker gene expression. Analysis of hematopoietic stem cells (c-Kit+, Sca-1+, lineage marker- [KSL]) from a transgenic mouse (1Osb) engineered to ubiquitously express the enhanced green fluorescent protein (EGFP) reveals two distinct populations. Forty percent of KSL cells demonstrate intermediate levels of EGFP fluorescence and differentiate into subpopulations of B cells, T cells, and myeloid cells that do not express EGFP. By contrast, progeny of the remaining 60% of KSL cells are almost exclusively EGFP bright. Long-term multilineage hematopoietic reconstitution and serial transplantation experiments show that these differences in EGFP are a property of self-renewing stem cells. Furthermore, both the transgene integration site and the activation status of a cell are important determinants of EGFP expression. These results indicate that a combination of donor cell markers is required to reliably track the full differentiation potential of transgenic stem cells.

Transplanted human bone marrow contributes to vascular endothelium

Recent evidence indicates that bone marrow is a source of endothelial progenitor cells that are mobilized into the peripheral blood in response to cytokines or tissue injury. Previously, we showed that functional endothelial cells (ECs) can be clonally derived from phenotypically defined hematopoietic stem cells. To determine the EC potential of human bone marrow and peripheral blood stem cells, blood vessels in sex-mismatched transplant recipients were evaluated. EC outcomes were identified by using a combination of immunohistochemistry and XY interphase FISH. Donor-derived ECs were detected in the skin and gut of transplant recipients with a mean frequency of 2% and could readily be distinguished from CD45-expressing hematopoietic stem cells. None of the >4,000 ECs examined had more than two sex chromosomes, consistent with an absence of cell fusion. Y chromosome signals were not detected in sex-matched female recipients, excluding the vertical transmission of male cells. None of the recipients evaluated before hematopoietic engraftment demonstrated donor-derived ECs, indicating a close linkage between the recovery of hematopoiesis and EC outcomes. Transplantable bone marrow-derived endothelial progenitor cells may represent novel therapeutic targets for hematopoietic and vascular disease.

The hereditary hemochromatosis protein, HFE, lowers intracellular iron levels independently of transferrin receptor 1 in TRVb cells

Hereditary hemochromatosis (HH) is an autosomal recessive disease that leads to parenchymal iron accumulation. The most common form of HH is caused by a single amino acid substitution in the HH protein, HFE, but the mechanism by which HFE regulates iron homeostasis is not known. In the absence of transferrin (Tf), HFE interacts with transferrin receptor 1 (TfR1) and the 2 proteins co-internalize, and in vitro studies have shown that HFE and Tf compete for TfR1 binding. Using a cell line lacking endogenous transferrin receptors (TRVb cells) transfected with different forms of HFE and TfR1, we demonstrate that even at low concentrations Tf competes effectively with HFE for binding to TfR1 on living cells. Transfection of TRVb cells or the derivative line TRVb1 (which stably expresses human TfR1) with HFE resulted in lower ferritin levels and decreased Fe2+ uptake. These data indicate that HFE can regulate intracellular iron storage independently of its interaction with TfR1. Earlier studies found that in HeLa cells, HFE expression lowers Tf-mediated iron uptake; here we show that HFE lowers non-Tf-bound iron in TRVb cells and add to a growing body of evidence that HFE may play different roles in different cell types.

Myelomonocytic cells are sufficient for therapeutic cell fusion in liver

Liver repopulation with bone marrow-derived hepatocytes (BMHs) can cure the genetic liver disease fumarylacetoacetate hydrolase (Fah) deficiency. BMHs emerge from fusion between donor bone marrow-derived cells and host hepatocytes. To use such in vivo cell fusion efficiently for therapy requires knowing the nature of the hematopoietic cells that fuse with hepatocytes. Here we show that the transplantation into Fah(-/-) mice of hematopoietic stem cells (HSCs) from lymphocyte-deficient Rag1(-/-) mice, lineage-committed granulocyte-macrophage progenitors (GMPs) or bone marrow-derived macrophages (BMMs) results in the robust production of BMHs. These results provide direct evidence that committed myelomonocytic cells such as macrophages can produce functional epithelial cells by in vivo fusion. Because stable bone marrow engraftment or HSCs are not required for this process, macrophages or their highly proliferative progenitors provide potential for targeted and well-tolerated cell therapy aimed at organ regeneration.

PECAM-1 is expressed on hematopoietic stem cells throughout ontogeny and identifies a population of erythroid progenitors

Platelet endothelial cell adhesion molecule-1 (PECAM-1) (CD31) is an adhesion molecule expressed on endothelial cells and subsets of leukocytes. Analysis of phenotypically defined hematopoietic stem cells (HSCs) from the yolk sac, fetal liver, and adult bone marrow demonstrates CD31 expression on these cells throughout development. CD31+ c-kit+ cells, but not CD31- c-kit+ cells, isolated from day-9.5 yolk sac give rise to multilineage hematopoiesis in vivo. Further evaluation of the CD31+ lineage marker-negative fraction of adult bone marrow reveals functionally distinct cell subsets. Transplantation of CD31+ Lin- c-kit- cells fails to protect lethally irradiated recipients, while CD31+ Lin- c-kit+ Sca-1- cells (CD31+ Sca-1-) provide radioprotection in the absence of long-term donor-derived hematopoiesis. Although donor-derived leukocytes were not detected in CD31+ Sca-1- recipients, donor-derived erythroid cells were transiently produced during the initial phases of bone marrow recovery. These results demonstrate CD31 expression on hematopoietic stem cells throughout ontogeny and identify a population of CD31+ short-term erythroid progenitors cells that confer protection from lethal doses of radiation.

Transplanted adult hematopoietic stems cells differentiate into functional endothelial cells

During early embryogenesis, blood vessels and hematopoietic cells arise from a common precursor cell, the hemangioblast. Recent studies have identified endothelial progenitor cells in the peripheral blood, and there is accumulating evidence that a subset of these cells is derived from precursors in the bone marrow. Here we show that adult bone marrow-derived, phenotypically defined hematopoietic stem cells (c-kit+, Sca-1+, lineage-) give rise to functional endothelial cells. With the exception of the brain, donor-derived cells are rapidly integrated into blood vessels. Durably engrafted endothelial cells express CD31, produce von Willebrand factor, and take up low-density lipoprotein. Analysis of DNA content indicates that donor-derived endothelial cells are not the products of cell fusion. Self-renewal of stem cells with hematopoietic and endothelial cell potential was revealed by serial transplantation studies. The clonal origin of both hematopoietic and endothelial cell outcomes was established by the transfer of a single cell. These results suggest that adult bone marrow-derived hematopoietic stem cells may serve as a reservoir for endothelial cell progenitors.

Converging roads: evidence for an adult hemangioblast

Classical studies of the developing embryo first suggested the existence of the hemangioblast, a precursor cell with the potential to differentiate into both blood and blood vessels. Several lines of investigation demonstrated that many of the genes activated during early hematopoietic development are also expressed in the vascular endothelium. Gene-targeting studies using embryonic stem cells have identified Flk-1, SCL, and Runx-1 as important regulatory molecules that specify both hematopoietic and vascular outcomes. Although it was anticipated that the hemangioblast would be present only during the earliest stages of vascular development in the yolk sac, accumulating evidence now indicates that hematopoietic cells with hemangioblast activity persist into adulthood. In the adult, bone marrow-derived, circulating endothelial progenitors contribute to postnatal neovascularization and enhance vascular repair following ischemic injury. Highly purified populations of hematopoietic stem cells from humans and mice can differentiate into both blood cells and vascular tissue at the single cell level. These recent findings suggest that bone marrow-derived hematopoietic stem cells or their progeny may contribute to the maintenance and repair of both the hematopoietic and the vascular systems during adult life.

Activation of the G-CSF and Flt-3 receptors protects hematopoietic stem cells from lethal irradiation

OBJECTIVE

Synergy between Flt-3 ligand and G-CSF produces a marked expansion of hematopoietic progenitor cells and mobilizes large numbers of stem cells into the peripheral blood. To determine if the activation of the Flt-3 and G-CSF receptors enhances the regenerative capacity of the hematopoietic compartment, we evaluated whether activation of these receptors augments stem cell recovery following lethal doses of radiation.

METHODS

C57BL/6 mice received a single injection of the bi-functional Flt-3 and G-GSF agonist progenipoietin-1, 24 hours prior to exposure to 1100 cGy of gamma radiation. Survival, hematopoietic reconstitution, and competitive repopulation potential were evaluated.

RESULTS

All cytokine-treated mice survived for up to 9 months. Radioprotected recipients exhibited stable multilineage hematopoiesis and recovered normal numbers of T cells, B cells, and myelomonocytic cells in the blood, bone marrow, and thymus. Between 2 and 3 weeks following radiation, cytokine-treated mice demonstrated threefold higher serum hemoglobin levels, 10-fold higher nucleated blood cell counts, and 20-fold higher platelet counts compared to controls. Radioprotection of self-renewing hematopoietic stem cells was revealed by multilineage hematopoietic reconstitution following transplantation in a competitive repopulation assay. To further evaluate the extent of cytokine-induced radioprotective activity, a cohort of mice received a second cycle of cytokine treatment and a second exposure to radiation (1100 cGy). Survival of this serially irradiated group was 70% and analysis of the peripheral blood revealed sustained multilineage hematopoiesis.

CONCLUSION

These results demonstrate that activation of both the Flt-3 and G-CSF receptors provides a high degree of radioprotection to the hematopoietic progenitor cell and stem cell compartment.

Toxic megacolon: a life-threatening complication of high-dose therapy and autologous stem cell transplantation among patients with AL amyloidosis

AL amyloidosis is a plasma cell disorder in which tissue deposition of immunoglobulin light chains leads to organ dysfunction. Recent reports of high-dose therapy with autologous stem cell transplantation for amyloidosis suggest higher response rates and extended survival compared to those seen with conventional chemotherapy. However, substantial treatment-related toxicity has been observed. This case series describes our institutional experience with autologous transplantation in four patients with amyloidosis with an emphasis on unique gastrointestinal toxicities, including toxic megacolon.

Adult blood vessels restore host hematopoiesis following lethal irradiation

OBJECTIVE

Accumulating evidence indicates a common stem cell may be responsible for both vasculogenesis and blood cell production during early embryologic development, yet little is known about the fate of these cells during ontogeny. We sought to determine whether hematopoietic potential is associated with normal blood vessels in the adult.

MATERIALS AND METHODS

Segments of adult thoracic aorta or inferior vena cava were transplanted under the kidney capsule of lethally irradiated recipients (1100 cGy). Radioprotection, colony-forming units (CFUs), and the extent of donor-derived hematopoietic constitution were evaluated using both Ly5 congenic and ROSA26 donor mice.

RESULTS

As little as 10 mg of transplanted vascular tissue radioprotected 80% of recipients, gave rise to similar numbers of CFUs as 10(5) bone marrow cells and prevented the development of severe anemia. Bromodeoxyuridine labeling studies revealed cell proliferation within the intima of donor vascular tissue within 48 hours of transplantation. ROSA26 donor-derived vascular cells migrated to the recipient spleen; however, CFUs were of host origin, a finding confirmed using sex-mismatched transplants. Although donor-derived cells were readily detected in the peripheral blood 2 to 3 weeks after transplant, they rapidly declined in frequency to approximately 1.0% by 4 weeks and persisted at these levels for more than 1 year. Bone marrow from rescued primary recipients provided radioprotection after transplantation into secondary recipients; however, only CD3(+) donor-derived cells were detected.

CONCLUSION

These findings demonstrate the presence of a population of cells within normal adult vascular tissue that has the capacity to protect host hematopoietic stem cells from radiation-induced death.

Progenipoietin-1: a multifunctional agonist of the granulocyte colony-stimulating factor receptor and fetal liver tyrosine kinase-3 is a potent mobilizer of hematopoietic stem cells

OBJECTIVE

Progenipoietin-1 is an agonist of both the granulocyte colony-stimulating factor and fetal liver tyrosine kinase-3 receptors capable of inducing the proliferation of multiple hematopoietic cell lineages. The potential of progenipoietin-1 to mobilize transplantable hematopoietic stem cells into the peripheral blood was evaluated.

METHODS

Cohorts of donor mice were treated with either progenipoietin-1, fetal liver tyrosine kinase-3 ligand, granulocyte colony-stimulating factor, or a vehicle control. Hematopoietic progenitor/stem-cell activity in donor blood was assayed by radioprotection, multilineage reconstitution, secondary transplantation, and competitive repopulation.

RESULTS

Only 1 microL of peripheral blood from progenipoietin-1-treated donors was required to protect 80% of lethally irradiated mice, while in contrast 1 microL of peripheral blood from granulocyte colony-stimulating factor-treated donors failed to protect any recipients. The radioprotected recipients of progenipoietin-1-treated donor cells showed donor-derived (Ly5.2) multilineage hematopoietic reconstitution for up to 6 months. Serial transplantation studies using bone marrow from radioprotected, chimeric recipients demonstrated long-term donor-derived hematopoiesis, indicating the successful transplantation of multipotent hematopoietic stem cells. The engraftment potential of progenipoietin-1 donor-derived cells was directly compared with donors treated with granulocyte colony-stimulating factor or fetal liver tyrosine kinase-3 ligand alone or in combination. Both spleen colony-forming activity and competitive repopulating activity was highest in the blood from progenipoietin-1-treated donors.

CONCLUSIONS

These studies demonstrate that progenipoietin-1 is a potent mobilizer of transplantable hematopoietic stem cells and indicate that this dual-receptor agonist has greater biologic activity than its constituent molecules.

In vivo selection of wild-type hematopoietic stem cells in a murine model of Fanconi anemia

Fanconi anemia (FA) is an autosomal recessive disorder characterized by birth defects, increased incidence of malignancy, and progressive bone marrow failure. Bone marrow transplantation is therapeutic and, therefore, FA is a candidate disease for hematopoietic gene therapy. The frequent finding of somatic mosaicism in blood of FA patients has raised the question of whether wild-type bone marrow may have a selective growth advantage. To test this hypothesis, a cohort radio-ablated wild-type mice were transplanted with a 1:1 mixture of FA group C knockout (FACKO) and wild-type bone marrow. Analysis of peripheral blood at 1 month posttransplantation showed only a moderate advantage for wild-type cells, but upon serial transplantation, clear selection was observed. Next, a cohort of FACKO mice received a transplant of wild-type marrow cells without prior radio-ablation. No wild-type cells were detected in peripheral blood after transplantation, but a single injection of mitomycin C (MMC) resulted in an increase to greater than 25% of wild-type DNA. Serial transplantation showed that the selection occurred at the level of hematopoietic stem cells. No systemic side effects were observed. Our results show that in vivo selection for wild-type hematopoietic stem cells occurs in FA and that it is enhanced by MMC administration.

Administration of daniplestim and granulocyte colony-stimulating factor for the mobilization of hematopoietic progenitor cells in nonhuman primates

We investigated the effects of administering a high-affinity interleukin-3 receptor agonist (daniplestim) and granulocyte colony-stimulating factor (G-CSF) on the mobilization of primitive hematopoietic progenitor cells into peripheral blood (PB). Groups of five rhesus monkeys were treated with 100 mg/kg of daniplestim for 5 days followed by 10 microg/kg of G-CSF for 5 days (D/G), daniplestim and G-CSF administered concurrently for 10 days (D+G), or G-CSF alone for 10 days. Phenotypic PB analysis indicated that the number of CD34+ cells in the G-CSF group had increased to 28 x 10(6)/L by Day 3 and then declined. In contrast, CD34+ cell counts of up to 68 x 10(6)/L were maintained until Day 10 in both the D/G and D+G groups. On Day 5, the total number of colony-forming cells in the PB had increased 15-fold in the D+G group and eightfold in both the D/G group and the G-CSF groups. By Day 7, the numbers of colony-forming units granulocyte/macrophage were comparable in all three groups, and 45-fold increases in the numbers of burst-forming units-erythroid and 12-fold increases in the numbers of multipotent colony-forming units were seen in both the D+G and the D/G groups. The frequency of circulating primitive progenitor cells in long-term stromal cultures was highest with D+G and lowest with G-CSF alone. These results indicate that the combination of daniplestim and G-CSF produces higher and more sustained levels of circulating stem cells than does G-CSF alone. D+G may offer advantages over D/G because it generates more long- and short-term clonogenic cells.

MHC class II gene silencing in trophoblast cells is caused by inhibition of CIITA expression

PROBLEM

Major histocompatibility complex (MHC) class II molecule expression is specifically suppressed on fetal trophoblasts, even in response to interferon (IFN)-gamma, a potent inducer of MHC class II genes. The suppression of class II induction has been suggested to play a role in preventing rejection of the fetal allograft. The mechanism of this suppression is unknown.

METHOD OF STUDY

Human trophoblast cell lines were examined for expression of MHC class II transcription factors and for activity of the IFN-gamma signaling pathway. Additionally, trophoblast cells were transfected with a vector expressing the class II transactivator, CIITA, and assayed for class II expression.

RESULTS

The MHC class II transcription factors RFX and X2BP and the IFN-gamma signaling pathway components are expressed constitutively and are functional in trophoblasts. However, CIITA expression was absent in trophoblasts and could not be induced by IFN-gamma. Transfection of CIITA into trophoblast cells resulted in derepression of class II gene expression.

CONCLUSIONS

The lack of induction of MHC class II genes in response to IFN-gamma in trophoblast cells is caused neither by the absence of factors that bind class II promoters, nor by a lesion in the IFN-gamma signaling pathway, but results from a specific inhibition of the CIITA gene.

In utero transplantation of human fetal haemopoietic cells in NOD/SCID mice

We have previously demonstrated that high levels of allogeneic, donor-derived mouse haemopoietic progenitor cells engraft following in utero transplantation in NOD/SCID mice. To evaluate whether the fetal NOD/SCID haemopoietic microenvironment supports the growth and development of human fetal haemopoietic progenitor cells, we injected fetal liver mononuclear cells (FL) or fetal bone marrow (FBM) derived CD34+ cells into NOD/SCID mice on day 13/14 of gestation. At 8 weeks of age 12% of FBM recipients and 10% of FL recipients were found to have been successfully engrafted with CD45+ human cells. CD45+ cells were present in the BM of all chimaeric animals; 5/6 recipients showed engraftment of the spleen, and 4/6 recipients had circulating human cells in the peripheral blood (PB). The highest levels of donor cells were found in the BM, with up to 15% of the nucleated cells expressing human specific antigens. Multilineage human haemopoietic engraftment, including B cells (CD19), myelomonocytic cells (CD13/33) and haemopoietic progenitor cells (CD34), was detected in the BM of chimaeric mice. In contrast, no human CD3+ cells were detected in any of the tissues evaluated. When the absolute number of engrafted human cells in the PB, BM and spleens of chimaeric mice was determined, a mean 16-fold expansion of human donor cells was observed. Although multilineage engraftment occurs in these fetal recipients, both the frequency and the levels of engraftment are lower than those previously reported when human cells are transplanted into adult NOD/SCID recipients.

Lymphoid reconstitution after autologous PBSC transplantation with FACS-sorted CD34+ hematopoietic progenitors

T-cell and B-cell reconstitution was studied in nine patients who received fluorescence activated cell sorter (FACS)-sorted autologous CD34+ hematopoietic progenitor cells (HPC). The mean numbers of T cells (CD3+), B cells (CD19+) and CD34+ HPC administered to each patient were .004, .002, and 1.8 x 10(6) cells/kg, respectively. After high-dose myeloablative chemotherapy (busulfan, cyclophosphamide, etoposide) CD34+) HPC were infused and lymphoid reconstitution was monitored using flow cytometry and reverse transcriptase-polymerase chain reaction (RT-PCR) amplification of VDJ T-cell receptor (TcR) sequences. Restoration of normal numbers of peripheral blood T cells and B cells among recipients of FACS-sorted CD34+ HPC was delayed compared to recipients of non-T-cell-depleted PBSC autografts. In both patient groups, the circulating T cells were primarily CD4-, CD8+, alphabeta TcR+, and CD45RO+, CD45RA- during the first 2 months after transplant. Subsequent increases in the frequency of CD45RA+ CD45RO- T cells occurred at 2 to 3 months after transplant, suggesting maturation of CD34+ hematopoietic progenitors to "naive" T cells. Analysis of the TcR repertoire after hematopoietic reconstitution demonstrated decreased diversity of Vbeta TcR expression associated with global decreases in the absolute number of total peripheral blood T cells and most Vbeta TcR+ subsets. Three of nine recipients of FACS-sorted CD34+ HPC demonstrated significant increases in the percentage of gammadelta+ peripheral T cells and CD5+ B cells at 3 to 9 weeks after transplantation, and all patients had transient oligoclonal expansions of T cells expressing specific Vbeta TcR. Transplantation with highly purified CD34+ HPC results in reduced diversity of the peripheral T-cell repertoire during the early post-transplant period compared with patients receiving unmanipulated or MoAb-depleted transplants.

Sustained multilineage engraftment of allogeneic hematopoietic stem cells in NOD/SCID mice after in utero transplantation

Substantial barriers exist to the engraftment of hematopoietic cells in mice after in utero transplantation. Although high levels of donor-derived hematopoiesis have been reported in SCID mice, the majority of chimeric recipients exhibit decreasing levels of donor cells over time. To directly test whether the natural killer cell and macrophage activity of the recipients represents a barrier to sustained engraftment, fetal NOD/SCID mice were injected on day 13.5 of gestation with an enriched congenic hematopoietic progenitor cell population. Forty-four percent of pups showed the presence of Ly5.1+ donor cells 4 weeks after transplantation. The mean number of donor-derived nucleated cells in the peripheral blood (PB) was 30%. Although the majority of circulating donor cells were lymphocytes, up to 15% expressed myelomonocytic markers. Serial PB samples from individual mice indicated that the percentage of circulating donor cells increased from 17% to 55% between 4 and 24 weeks. At 6 months posttransplantation, an increased frequency of multilineage, donor-derived cells was also observed in the bone marrow (BM) and the spleen of chimeric recipients. The engraftment of pluripotent hematopoietic stem cells was evaluated by transplanting BM from chimeric mice into irradiated congenic recipients. Irradiated secondary recipients also exhibited multilineage donor-derived hematopoiesis in the PB, BM, and spleen for up to 6 months. These results show that the in utero transplantation of lineage-depleted BM cells into NOD/SCID recipients produces a high frequency of sustained engraftment of allogeneic hematopoietic stem cells.

Engraftment potential of different sources of human hematopoietic progenitor cells in BNX Mice

Human hematopoietic progenitor cells (HPCs) from mobilized peripheral blood mononuclear cells (PBMCs), adult bone marrow (ABM), and fetal bone marrow (FBM) were evaluated for their ability to produce multilineage human hematopoietic engraftment in vivo. Sublethally irradiated BNX (beige/nude/xid) mice were injected with either unfractionated cells or CD34+ cells purified from these sources. The presence of human cells in the mouse PB, BM, and spleen was evaluated by flow cytometry at either 6 to 8 weeks or 6 months postinjection. Recipients with > or = 1% human cells in any of these tissues were considered chimeric. Of 26 mice injected with FBM, 4 showed up to 73% human cells in the BM or spleen at 6 months. The phenotypes of these cells included CD13/33+ myelomonocytic cells (38%), CD19+ B cells (67%), and CD34+ progenitor cells (28%). In contrast, ABM gave rise to a mean of 5% human cells in the PB in 2 of 42 (4%) recipients at 6 to 8 weeks. These circulating human cells were predominantly CD3+, whereas CD13/33+ and CD34+ cells were detected in the BM for up to 6 months. A total of 18% of mice injected with PBMCs showed a mean of 36% human cells in the PB. Both the BM and spleens of PBMC-injected mice contained CD3+ cells in a proportion similar to that observed in the PB. These CD3+ cells were phenotypically mature CD4+,CD8- or CD4-,CD8+ T cells and coexpressed a variety of Vbeta T-cell receptor (TCR) genes. The percentage of CD3+ cells in the circulation of chimeric recipients injected with either FBM, ABM, or PBMCs correlated well with the input CD3+ cell dose for each of these HPC sources (r = .99). The high levels of engraftment of CD3+ cells in recipients of PBMCs and the long-term multilineage engraftment of FBM recipients have important implications for developing strategies to study the regulation of these human cells in vivo.

CD34+ progenitor cells from asymptomatic patients are not a major reservoir for human immunodeficiency virus-1

Controversy exists as to whether hematopoietic progenitor cells are infected by human immunodeficiency virus-1 (HIV-1) in vivo. Most studies have focused on patients with acquired immunodeficiency syndrome (AIDS)/AIDS-related complex, and little data are available on asymptomatic patients with well preserved CD4+ T-cell counts. To determine if CD34+ hematopoietic progenitor cells are infected early in the course of HIV-1 disease, we evaluated 10 asymptomatic HIV-1 seropositive (HIV-1+) patients. The CD34+ cell fraction was purified by a two-step procedure consisting of both affinity chromatography and fluorescence-activated cell sorting that resulted in a median purity of over 99%. Using conventional and nested polymerase chain reaction (PCR) assays, we evaluated the presence and frequency of HIV-1 proviral DNA. Both bone marrow mononuclear cells and CD34- cells from all 10 patients were strongly positive for the HIV-1 pol and/or gag gene sequences. In contrast, sorted CD34+ cells from only two of 10 patients were positive, and the number of copies of proviral DNA in these samples was estimated to be from 2 to 5 per 250,000 cells. To test the in vitro functional capacity of CD34+ progenitors, these cells were assayed in both methylcellulose and long-term stromal culture. We found no significant reduction in the number of colony-forming unit-erythroid (CFU-E), burst-forming unit-erythroid (BFU-E), or colony-forming unit-granulocyte macrophage (CFU-GM) colonies, or in the frequency of cobblestone area forming cells from limit dilution analysis in HIV-1+ asymptomatic patients. Pooled methylcellulose colonies generated from CD34+ cells were HIV-1- in nine of 10 samples. All progeny from long-term cultures of CD34+ cells were HIV-1-. We conclude that the CD34+ hematopoietic progenitor compartment is not infected in the majority of asymptomatic HIV-1+ patients, and that these cells may represent a suitable target for strategies designed to protect developing CD4+ T cells from infection.

Pulmonary resection for invasive Aspergillus infections in immunocompromised patients

Standard antifungal medical therapy of invasive pulmonary aspergillosis that occurs in immunocompromised patients with hematologic diseases with neutropenia or in liver transplant recipients results in less than a 5% survival. In view of these dismal mortality rates, we adopted an aggressive approach with resection of the involved area of lung along with systemic antifungal therapy when localized invasive pulmonary aspergillosis developed in these patients. Between January 1987 and December 1993, 14 patients with hematologic diseases and 2 liver transplant recipients underwent resection of acute localized pulmonary masses suggestive of invasive pulmonary aspergillosis a median of 7.5 days (range 1 to 45 days) after the diagnosis was clinically suggested and confirmed by chest computed tomographic scans. Operative procedures done included two pneumonectomies, one bilobectomy with limited thoracoplasty, nine lobectomies, and five wedge resections (one patient with hematologic disease had two procedures). All patients were treated before and after the operation with antifungal agents. Nine (64%) of 14 patients with hematologic disease and 2 (100%) of 2 liver transplant recipients survived the hospitalization with no evidence of recurrent Aspergillus infection after a median 8 months of follow-up (range 3 to 82 months). The five hospital deaths (all patients with hematologic diseases) occurred a median of 20 days after operation from diffuse alveolar hemorrhage in three, graft-versus-host disease in one, and multiple organ system failure with presumed disseminated Aspergillus infection in one. Four of the five deaths were in patients with allogeneic bone marrow transplants. Two of the three patients requiring resection of multiple foci of infection died, as did the only patient who was preoperatively ventilator dependent. In immunocompromised patients with hematologic diseases or liver transplantation with invasive pulmonary aspergillosis, early pulmonary resection should be strongly considered when the characteristic clinical and radiographic pictures appear.

Myocardial protection for acquired heart disease surgery: results of a national survey

To study current myocardial protection practices, all 4,393 United States board-certified thoracic surgeons were surveyed in 1992. Of the 1,413 respondents (32% total response), 936 are in active practice dealing with acquired heart disease. Based on their frequency of cases, respondents perform approximately 32% of all acquired heart disease operations in the United States yearly and individually average 157 patients/year. For myocardial protection, 98% of respondents routinely use cardioplegic arrest. The primary method of cardioplegia delivery is antegrade 36%, retrograde 4%, and a combination of antegrade and retrograde 60%. The types of cardioplegic solutions used are blood 72%, crystalloid 22%, and oxygenated crystalloid 6%. Continuous warm blood cardioplegia is used by 10% of respondents, whereas most (75%) have adopted a skeptical "wait and see" attitude or have abandoned it (6%). Overall, most surgeons (78%) report that they are very satisfied with their present methods of myocardial protection, whereas only 2% are dissatisfied. Still, the three areas believed most important for future research are reperfusion injury (74%), acutely infarcting myocardium (61%), and metabolic enhancers in cardioplegia (58%).

Techniques to simplify esophagogastric circular stapled anastomoses

Stapling devices for end-to-end anastomoses (EEA) have facilitated more rapid and reliable reestablishment of esophagogastric continuity following esophageal resections. Despite their ease of use, various intraoperative problems can arise, especially with the esophageal pursestring or the insertion of the anvil into the fragile, commonly contracted lumen. This paper describes various technical details that are useful adjuncts to allow creation of rapid, consistently successful EEA stapled esophagogastric anastomoses. These techniques are of particular value in the resident teaching setting.

Prevalence of multidrug resistance related to activation of the mdr1 gene in human sarcoma mutants derived by single-step doxorubicin selection

Fluctuation analysis experiments were performed in the human sarcoma cell line MES-SA to assess whether selection or induction mechanisms determine resistance to doxorubicin (DOX), mutation rates, and the nature of the surviving clones. Thirteen flasks were seeded with 2000 cells/flask and grown to confluent populations of approximately 3.3 x 10(6) cells. After reseeding in 96-well plates, each population was treated with 40 nM DOX for 2 weeks. Surviving colonies were scored and harvested. Clones were propagated and analyzed for drug resistance phenotype. Expression of the mdr1, mrp, and topoisomerase II alpha and II beta genes was analyzed by reverse transcription-polymerase chain reaction. Accumulation of the P-glycoprotein substrate rhodamine-123 was measured by flow cytometry, with and without the cyclosporin D analogue SDZ PSC 833. Cellular glutathione levels were measured by flow cytometry, and M(r) 110,000 vesicular protein (p110) expression was detected by immunohistochemistry. Analysis of variance supported the hypothesis of spontaneous mutations rather than induction conferring DOX resistance. At this stringent level (5-6 log cell killing) of drug exposure, the mutation rate was estimated at 1.8 x 10(-6) per cell generation. All 30 propagated clones demonstrated cross-resistance to vinblastine, etoposide, and paclitaxel (Taxol), but not to cisplatin or bleomycin. Increased mRNA levels of mdr1 were observed in all 27 clones tested, including at least 1 from each of the 13 populations. No alterations were found in expression or level of topoisomerase II alpha or II beta, mrp, glutathione, and p110. Expression of P-glycoprotein was confirmed by flow cytometry using the monoclonal antibody UIC2. In almost all tested clones, decreased intracellular rhodamine-123 accumulation was modulated by 2 microM SDZ PSC 833, and the vinblastine resistance in all examined clones was completely reversed by SDZ PSC 833 and verapamil. Our study demonstrates that survival of cells exposed to DOX in a single step occurs as a result of a stochastic process consistent with mutational events. Activation of the mdr1 gene is the predominant mechanism selected by DOX in these resistant clones.

Rapid and sustained hematopoietic recovery in lethally irradiated mice transplanted with purified Thy-1.1lo Lin-Sca-1+ hematopoietic stem cells

Hematopoietic stem cells (HSCs) are believed to play a critical role in the sustained repopulation of all blood cells after bone marrow transplantation (BMT). However, understanding the role of HSCs versus other hematopoietic cells in the quantitative reconstitution of various blood cell types has awaited methods to isolate HSCs. A candidate population of mouse HSCs, Thy-1.1lo Lin-Sca-1+ cells, was isolated several years ago and, recently, this population has been shown to be the only population of BM cells that contains HSCs in C57BL/Ka-Thy-1.1 mice. As few as 100 of these cells can radioprotect 95% to 100% of irradiated mice, resulting long-term multilineage reconstitution. In this study, we examined the reconstitution potential of irradiated mice transplanted with purified Thy-1.1lo Lin-Sca-1+ BM cells. Donor-derived peripheral blood (PB) white blood cells were detected as early as day 9 or 10 when 100 to 1,000 Thy-1.1lo Lin-Sca-1+ cells were used, with minor dose-dependent differences. The reappearance of platelets by day 14 and thereafter was also seen at all HSC doses (100 to 1,000 cells), with a slight dose-dependence. All studied HSC doses also allowed RBC levels to recover, although at the 100 cell dose a delay in hematocrit recovery was observed at day 14. When irradiated mice were transplanted with 500 Thy-1.1lo Lin-Sca-1+ cells compared with 1 x 10(6) BM cells (the equivalent amount of cells that contain 500 Thy-1.1lo Lin-Sca-1+ cells as well as progenitor and mature cells), very little difference in the kinetics of recovery of PB, white blood cells, platelets, and hematocrit was observed. Surprisingly, even when 200 Thy1.1lo Lin-Sca-1+ cells were mixed with 4 x 10(5) Sca-1- BM cells in a competitive repopulation assay, most of the early (days 11 and 14) PB myeloid cells were derived from the HSC genotype, indicating the superiority of the Thy-1.1lo Lin-Sca-1+ cells over Sca-1- cells even in the early phases of myeloid reconstitution. Within the Thy-1.1lo Lin-Sca-1+ population, the Rhodamine 123 (Rh123)hi subset dominates in PB myeloid reconstitution at 10 to 14 days, only to be overtaken by the Rh123lo subset at 3 weeks and thereafter. These findings indicate that HSCs can account for the early phase of hematopoietic recovery, as well as sustained hematopoiesis, and raise questions about the role of non-HSC BM populations in the setting of BMT.

Intrapleural fibrinolytic treatment of multiloculated thoracic empyemas

Acute multiloculated thoracic empyemas incompletely drained by tube thoracostomy alone usually require operation. To avoid a thoracotomy yet treat this difficult problem, intrapleural fibrinolytic agents were employed. Between April 1, 1990, and April 1, 1993, 13 consecutive patients presenting with a fibrinopurulent empyema were demonstrated to have incomplete drainage. To facilitate drainage, streptokinase, 250,000 units in 100 mL 0.9% saline solution (3 patients), or urokinase, 100,000 units in 100 mL 0.9% saline solution (10 patients), was instilled daily into the chest tube, and the tube was clamped for 6 to 12 hours followed by suction. This routine was continued daily for a mean of 6.8 +/- 3.7 days (range, 1 to 14 days) until resolution of the pleural fluid collection was demonstrated by computed chest tomography and clinical indications. This regimen was completely successful in 10 of 13 patients (77%), who had resolution of the empyema, eventual withdrawal of chest tubes, and no recurrence. Two patients, both pediatric liver transplant patients, had an initial good response but eventually required decortication. One patient with a good radiographic response became increasingly febrile during streptokinase therapy and underwent a thoracotomy, but no significant undrained fluid was found. This patient's continued fever was believed to be a streptokinase reaction. Urokinase was used subsequently. No treatment-related mortalities or complications occurred. Intrapleural fibrinolytic agents, especially urokinase, are safe, cost-effective means of facilitating complete chest tube drainage, thereby avoiding the morbidity of a major thoracotomy for 77% of a group of multiloculated empyema patients who traditionally would have required open surgical therapy.