Isolation and Characterization of a Cell Line from the Epithelial Cells of the Human Fetal Pancreas

Pancreatic cell lines are useful for basic studies of pancreatic biology and for possible application to cell transplantation therapies for diabetes. A retroviral vector expressing simian virus 40 (SV40) T antigen and H-rasval12 was used to infect a monolayer culture of epithelial cells from an 18-wk human fetal pancreas. Infected cells gave rise to a clonal epithelial cell line, designated TRM-1. This cell line expresses epithelial markers as well as glut2 and small amounts of insulin and glucagon. TRM-1 is the first cell line to be generated from the human fetal pancreas and also the first cell line derived directly from the fetal pancreas of any species. The approach that we have used to develop TRM-1 should be applicable to isolating cell lines from other stages of human pancreatic development. Copyright © 1997 Elsevier Science, Inc.

Pharmacological induction of pancreatic islet cell transdifferentiation: relevance to type I diabetes

Type I diabetes (T1D) is an autoimmune disease in which an immune response to pancreatic β-cells results in their loss over time. Although the conventional view is that this loss is due to autoimmune destruction, we present evidence of an additional phenomenon in which autoimmunity promotes islet endocrine cell transdifferentiation. The end result is a large excess of δ-cells, resulting from α- to β- to δ-cell transdifferentiation. Intermediates in the process of transdifferentiation were present in murine and human T1D. Here, we report that the peptide caerulein was sufficient in the context of severe β-cell deficiency to induce efficient induction of α- to β- to δ-cell transdifferentiation in a manner very similar to what occurred in T1D. This was demonstrated by genetic lineage tracing and time course analysis. Islet transdifferentiation proceeded in an islet autonomous manner, indicating the existence of a sensing mechanism that controls the transdifferentiation process within each islet. The finding of evidence for islet cell transdifferentiation in rodent and human T1D and its induction by a single peptide in a model of T1D has important implications for the development of β-cell regeneration therapies for diabetes.

Antipsychotics activate the TGFβ pathway effector SMAD3

Although effective in treating an array of neurological disorders, antipsychotics are associated with deleterious metabolic side effects. Through high-throughput screening, we previously identified phenothiazine antipsychotics as modulators of the human insulin promoter. Here, we extended our initial finding to structurally diverse typical and atypical antipsychotics. We then identified the transforming growth factor beta (TGFβ) pathway as being involved in the effect of antipsychotics on the insulin promoter, finding that antipsychotics activated SMAD3, a downstream effector of the TGFβ pathway, through a receptor distinct from the TGFβ receptor family and known neurotransmitter receptor targets of antipsychotics. Of note, antipsychotics that do not cause metabolic side effects did not activate SMAD3. In vivo relevance was demonstrated by reanalysis of gene expression data from human brains treated with antipsychotics, which showed altered expression of SMAD3 responsive genes. This work raises the possibility that antipsychotics could be designed that retain beneficial CNS activity while lacking deleterious metabolic side effects.

Adult human beta-cell neogenesis?

Prospects for inducing endogenous beta-cell regeneration in the pancreas, one of the most attractive approaches to reverse type 1 and type 2 diabetes, have gained substantially from recent evidence that cells in the adult pancreas exhibit more plasticity than previously recognized. There are two major pathways to beta-cell regeneration, beta-cell replication and beta-cell neogenesis. Substantial evidence for a role for both processes exists in different models. While beta-cell replication clearly occurs during development and early in life, the potential for replication appears to decline substantially with age. In contrast, we have demonstrated that the exocrine compartment of the adult human pancreas contains a facultative stem cell that can differentiate into beta-cells under specific circumstances. We have favoured the idea that, similar to models described in liver regeneration, beta-cell mass can be increased either by neogenesis or replication, depending on the intensity of different stimuli or stressors. Understanding the nature of endocrine stem/progenitor cells and the mechanism by which external stimuli mobilize them to exhibit endocrine differentiation is central for success in therapeutic approaches to induce meaningful endogenous beta-cell neogenesis.

NeuroD1 in the endocrine pancreas: Localization and dual function as an activator and repressor

The basic helix-loop-helix transcription factor NeuroD1 regulates cell fate in the nervous system but previously has not been considered to function similarly in the endocrine pancreas due to its reported expression in all islet cell types in the newborn mouse. Because we found that NeuroD1 potently represses somatostatin expression in vitro, its pattern of expression was examined in both strains of mice in which lacZ has been introduced into the NeuroD1 locus by homologous recombination. Analysis of adult transgenic mice revealed that NeuroD1 is predominantly expressed in beta-cells and either absent or expressed below the limit of lacZ detection in mature alpha-, delta-, or PP cells. Consistent with a previous report, NeuroD1 colocalizes with glucagon as well as insulin in immature islets of the newborn mouse. However, no colocalization of NeuroD1with somatostatin was detected in the newborn. In vitro, ectopic expression of NeuroD1 in TRM-6/PDX-1, a human pancreatic delta-cell line, resulted in potent repression of somatostatin concomitant with induction of the beta-cell hormones insulin and islet amyloid polypeptide. Additionally, NeuroD1 induced expression of Nkx2.2, a transcription factor expressed in beta- but not delta-cells. Transfection studies using insulin and somatostatin promoters confirm the ability of NeuroD1 to act as both a transcriptional repressor and activator in the same cell, suggesting a more complex role for NeuroD1 in the establishment and/or maintenance of mature endocrine cells than has been recognized previously.

Current and future treatment strategies for type 2 diabetes: the beta-cell as a therapeutic target

Diabetes affects millions of people worldwide. The most common variants are type 1 diabetes with autoimmune destruction of the pancreatic beta-cells and type 2 diabetes with peripheral insulin resistance and beta-cell dysfunction. In spite of tremendous research, current pharmacological regimens are still sub-optimal for adequate blood glucose control. As a consequence, patients with diabetes are at significant risk for development of serious long-term complications, such as blindness and kidney disease. This review will discuss present and future strategies for the treatment of type 2 diabetes with a focus on the more recently recognized problems of beta-cell dysfunction and loss. The treatment strategies presented include promotion of beta-cell proliferation and differentiation by glucagon-like peptide 1 receptor agonists.

Recovery of human mesenchymal stem cells following dehydration and rehydration

As cell therapies advance from research laboratories to clinical application, there is the need to transport cells and tissues across long distances while maintaining cell viability and function. Currently cells are successfully stored and shipped under liquid nitrogen vapor. The ability to store these cells in the desiccated state at ambient temperature would provide tremendous economic and practical advantage. Human mesenchymal stem cells (hMSCs) have broad potential uses in tissue engineering and regeneration since they can differentiate along multiple lineages and support hematopoeisis. The current research applied recent technological advances in the dehydration and storage of human fibroblasts to hMSCs. Three conditions were tested: air-dried, air-dried and stored under vacuum (vacuum only), and incubated with 50 mM trehalose + 3% glycerol and then air-dried and stored under vacuum (vacuum + trehalose). Plates containing dehydrated hMSCs were shipped from San Diego to Baltimore overnight in separate FedEx cardboard boxes. The hMSCs were rehydrated with 3 ml of hMSC medium and were able to regain their spindle-shaped morphology and adhesive capability. In addition, they maintained high viability and proliferation capacity. Rehydrated and passaged cells continued to express the characteristic hMSC surface antigen panel. Additionally, cells showed constitutive levels of mRNA for a stromal factor and, when exposed to reagents known to induce differentiation, demonstrated upregulation of two tissue-specific messages indicative of differentiation potential for fat and bone. While our preliminary findings are encouraging, we still need to address consistency and duration of storage by considering factors such as cell water content, oxygen concentration, and the presence of free radicals.

Overexpression of trehalose synthase and accumulation of intracellular trehalose in 293H and 293FTetR:Hyg cells

A humanized clone containing the trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase (otsA/B) has been constructed. Using the Gateway Cloning System (Invitrogen, Inc.), the otsA/B genes have been placed under the control of the CMV promoter (pEXPcmv-otsA/B) or the CMV promoter and the tet operator (pEXP cmv TetO-otsA/B). The pEXPcmv-otsA/B clone has been introduced into 293H cells using LIPOFECTAMINE 2000 and the intracellular concentration of trehalose has been evaluated. The 293H cells accumulate 4-5 microg trehalose/mg dry weight and this concentration increases to 7-10 microg trehalose/mg dry weight if trehalose is included in the growth medium. The pEXPcmv TetO-otsA/B clone has been transfected into 293FTetR:Hyg cells which contain the tet repressor integrated into the genome. When these transfected cells are grown in the absence of tetracycline, no intracellular trehalose is detected. Inclusion of 0.3 microg/ml tetracycline in the growth medium results in the accumulation of 11-14 microg trehalose/mg dry weight, a value which increases to 19-20 microg trehalose/mg dry weight if trehalose is included in the growth medium. The data for the 293FTetR:Hyg cells indicate that intracellular trehalose accumulates in response to the addition of tetracycline. This system will allow us to manipulate the intracellular concentration of trehalose and to evaluate the desiccation tolerance of these cells as a function of intracellular trehalose concentration.

Diabetes mellitus-cell transplantation and gene therapy approaches

Diabetes mellitus affects millions of people in the United States and worldwide. It has become clear over the past decade that the chronic complications of diabetes result from lack of proper blood glucose concentration regulation, and particularly the toxic effects of chronic hyperglycemia on organs and tissues. Pancreas transplants can cure insulin-dependent diabetes mellitus (IDDM). Furthermore, recent advances in pancreatic islet isolation and immunosuppressive regimens have resulted in dramatic improvements in the survival and function of islet allografts. Therefore, islet replacement strategies are becoming increasingly attractive options for patients at risk for severe diabetic complications. A major limitation of these approaches is the small number of organs available for transplantation or islet isolation. Thus, an important next step in developing curative treatments for type I diabetes will be the generation of a replenishable source of glucose-responsive, insulin-secreting cells that can be used for beta cell replacement. This review focuses on approaches to developing robust and widely applicable beta-cell replacement strategies with an emphasis on manipulating beta-cell growth and differentiation by genetic engineering.

Desiccation tolerance in human cells

The ability to desiccate mammalian cells while maintaining a high degree of viability would have implications for many areas of biological science, including tissue engineering. Previously, we reported that introduction of the genes for trehalose biosynthesis allowed human cells in culture to be reversibly desiccated for up to 5 days. Here, we have further investigated the factors that allow human cells to survive in the desiccated state. The most important finding is that vacuum greatly enhances the ability of human cells in culture to withstand desiccation. In fact, cells dried slowly and stored under vacuum are able to withstand desiccation even in the absence of added carbohydrates or polyols. In addition to vacuum, the rate of desiccation, the temperature at which cells are maintained, the degree of confluence when dried, and the presence or absence of light have a large effect on the ability to retain viability in the desiccated state. Our data are consistent with a model in which cells can retain viability if they are desiccated in such a way that cellular structures are maintained. However, gradual loss of viability may be due to damage that occurs over time in the desiccated state, perhaps due to free radicals. Further optimization of the process for desiccating and maintaining cells is required before long-term storage of desiccated cells can be achieved.

Beta-cell differentiation from a human pancreatic cell line in vitro and in vivo

Cell transplantation therapy for diabetes is limited by an inadequate supply of cells exhibiting glucose-responsive insulin secretion. To generate an unlimited supply of human beta-cells, inducibly transformed pancreatic beta-cell lines have been created by expression of dominant oncogenes. The cell lines grow indefinitely but lose differentiated function. Induction of beta-cell differentiation was achieved by stimulating the signaling pathways downstream of the transcription factor PDX-1, cell-cell contact, and the glucagon-like peptide (GLP-1) receptor. Synergistic activation of those pathways resulted in differentiation into functional beta-cells exhibiting glucose-responsive insulin secretion in vitro. Both oncogene-expressing and oncogene-deleted cells were transplanted into nude mice and found to exhibit glucose-responsive insulin secretion in vivo. The ability to grow unlimited quantities of human beta-cells is a major step toward developing a cell transplantation therapy for diabetes.

Gene therapy for diabetes

For more than eighty years, insulin injection has been the only treatment option for all type I and many type II diabetic individuals. Whole pancreas transplantation has been a successful approach for some patients, but is a difficult and complex operation. Recently, it was demonstrated that a glucocorticoid-free immunosuppressive regimen led to remarkably successful islet transplantation. However, both pancreas and islet cell transplantation are limited by the tremendous shortage of cadaveric pancreases that are available for transplantation. Therefore, a major goal of diabetes research is to generate an unlimited source of cells exhibiting glucose-responsive insulin secretion that can be used for transplantation, ideally without the need for systemic immunosuppression. The focus of this review is on how gene therapy can be used in beta cell replacement strategies. Gene transfer to beta cells as well as recent advances in beta cell growth and development will be discussed.

Characterization of ataxia telangiectasia fibroblasts with extended life-span through telomerase expression

Ataxia-telangiectasia (A-T) is an autosomal recessive disease characterized by progressive cerebellar degeneration, immunodeficiencies, genomic instability and gonadal atrophy. A-T patients are hypersensitive to ionizing radiation and have an elevated cancer risk. Cells derived from A-T patients require higher levels of serum factors, exhibit cytoskeletal defects and undergo premature senescence in culture. We show here that expression of the catalytic subunit of telomerase (hTERT) in primary A-T patient fibroblasts can rescue the premature senescence phenotype. Ectopic expression of hTERT does not rescue the radiosensitivity or the telomere fusions in A-T fibroblasts. The hTERT+AT cells also retain the characteristic defects in cell-cycle checkpoints, and show increased chromosome damage before and after ionizing radiation. Although A-T patients have an increased susceptibility to cancer, the expression of hTERT in A-T fibroblasts does not stimulate malignant transformation. These immortalized A-T cells provide a more stable cell system to investigate the molecular mechanisms underlying the cellular phenotypes of Ataxia-telangiectasia.

Accelerated telomere shortening and senescence in human pancreatic islet cells stimulated to divide in vitro

Widespread application of beta-cell replacement strategies for diabetes is dependent upon the availability of an unlimited supply of cells exhibiting appropriate glucose-responsive insulin secretion. Therefore, a great deal of effort has been focused on understanding the factors that control beta-cell growth. Previously, we found that human beta-cell-enriched islet cultures can be stimulated to proliferate, but expansion was limited by growth arrest after 10-15 cell divisions. Here, we have investigated the mechanism behind the growth arrest. Our studies, including analyses of the expression of senescence-associated beta-galactosidase, p16(INK4a) levels, and telomere lengths, indicate that cellular senescence is responsible for limiting the number of cell divisions that human beta-cells can undergo. The senescent phenotype was not prevented by retroviral transduction of the hTERT gene, although telomerase activity was induced. These results have implications for the use of primary human islet cells in cell transplantation therapies for diabetes.

PDX-1 and cell-cell contact act in synergy to promote delta-cell development in a human pancreatic endocrine precursor cell line

Cell lines from the fetal and adult pancreas that were developed by retroviral transfer of the SV40T and ras(val12) oncogenes lose insulin expression but retain extremely low levels of somatostatin and glucagon mRNA. In contrast to expanded populations of primary human islet cells, none of them express the homeodomain transcription factor PDX-1. When that factor was expressed in the cell lines by retroviral-mediated gene transfer, one of the cell lines, TRM-6, derived from human fetal islets, exhibited a 10- to 100-fold increase in somatostatin gene expression. This is the first report of induction of the endogenous somatostatin gene by PDX-1. Promotion of cell-cell contact by aggregation of TRM-6/PDX-1 into islet-like clusters produced a further 10- to 100-fold increase in somatostatin mRNA, to a level similar to that of freshly isolated islets, which resulted in production of somatostatin protein. Thus, we demonstrate here that signals induced by cell-cell contact act in synergy with PDX-1 to up-regulate the endogenous somatostatin promoter in an immortalized cell line from human fetal islets. This system provides a powerful model for studying human islet cell development and, particularly, the role of cell-cell contact in the differentiation process.

Protection from cell death in cultured human fetal pancreatic cells

Endocrine cells from the human fetal pancreas will proliferate in vitro on extracellular matrix but lose hormone expression, and redifferentiation requires removal of the expanded cells from the matrix and reaggregation into cell aggregates. However, extensive cell death occurs during manipulation and culture. The mechanism of cell death was examined at each stage throughout the process under different experimental conditions to determine optimal protocols to increase cell viability. During shipment, the addition of trehalose to the media to prevent necrosis increased yield 17-fold, while during culture as islet-like cell clusters the apoptosis inhibitor Z-VAD increased yield 1.8-fold. Following disruption of cell matrix interactions and reaggregation, there was marked evidence of apoptotic bodies by the TUNEL assay. Addition of nicotinamide or Z-VAD, or removal of arginine from the media during reaggregation, reduced the number of apoptotic bodies and the effect was additive. However, a combination of treatments was necessary to significantly increase the yield of viable cells. We conclude that cell death of human fetal pancreatic tissue in culture results from both necrosis and apoptosis and that understanding the mechanisms at the cellular level will lead to protocols that will improve cell viability and promote beta-cell growth.

Trehalose expression confers desiccation tolerance on human cells

Many organisms that withstand desiccation express the disaccharide trehalose. We have now expressed the otsA and otsB genes of Escherichia coli, which encode trehalose biosynthetic enzymes, in human primary fibroblasts using a recombinant adenovirus vector. Infected cells produced increased amounts of trehalose with increasing multiplicity of infection (MOI). Human primary fibroblasts expressing trehalose could be maintained in the dry state for up to five days. Fourier transform infrared spectroscopy indicated that dry, but viable, human cells contained no detectable water. This study shows that mammalian cells can be engineered to retain viability in the absence of water.

Presenilin 1 facilitates the constitutive turnover of beta-catenin: differential activity of Alzheimer's disease-linked PS1 mutants in the beta-catenin-signaling pathway

Although an association between the product of the familial Alzheimer's disease (FAD) gene, presenilin 1 (PS1), and beta-catenin has been reported recently, the cellular consequences of this interaction are unknown. Here, we show that both the full length and the C-terminal fragment of wild-type or FAD mutant PS1 interact with beta-catenin from transfected cells and brains of transgenic mice, whereas E-cadherin and adenomatous polyposis coli (APC) are not detected in this complex. Inducible overexpression of PS1 led to increased association of beta-catenin with glycogen synthase kinase-3beta (GSK-3beta), a negative regulator of beta-catenin, and accelerated the turnover of endogenous beta-catenin. In support of this finding, the beta-catenin half-life was dramatically longer in fibroblasts deficient in PS1, and this phenotype was completely rescued by replacement of PS1, demonstrating that PS1 normally stimulates the degradation of beta-catenin. In contrast, overexpression of FAD-linked PS1 mutants (M146L and DeltaX9) failed to enhance the association between GSK-3beta and beta-catenin and interfered with the constitutive turnover of beta-catenin. In vivo confirmation was demonstrated in the brains of transgenic mice in which the expression of the M146L mutant PS1 was correlated with increased steady-state levels of endogenous beta-catenin. Thus, our results indicate that PS1 normally promotes the turnover of beta-catenin, whereas PS1 mutants partially interfere with this process, possibly by failing to recruit GSK-3beta into the PS1-beta-catenin complex. These findings raise the intriguing possibility that PS1-beta-catenin interactions and subsequent activities may be consequential for the pathogenesis of AD.

Sustained proliferation of PDX-1+ cells derived from human islets

Ex vivo expansion of human beta-cells is an important step toward the development of cell-based insulin delivery systems in type 1 diabetes. Here, we report that human pancreatic endocrine cells can be expanded through 15 cell doublings in vitro for an estimated total 30,000-fold increase in cell number. We believe that the cells resulting from these cultures are of beta-cell origin, since they uniformly express the transcription factor PDX-1 (STF-1, IDX-1, IPF-1), which is initially seen only in cells positive for insulin and negative for the ductal cell marker cytokeratin (CK)-19. To rule out the possibility that PDX-1 expression might be induced by the culture conditions used here, cells from isolated human pancreatic ducts were cultured under the same conditions as the islet cells. Cells in these cultures expressed CK-19 but not PDX-1. Although the expanded beta-cells continued to express PDX-1, insulin expression was lost over time. Whether reexpression of islet-specific genes in vitro is essential for successful cell transplantation remains to be determined.

Towards gene therapy of diabetes mellitus

A definitive treatment for diabetes mellitus will be one that maintains a normal blood glucose concentration in the face of fluctuating dietary intake. To accomplish this, there must be mechanisms to sense the amount of blood glucose coupled to rapid release of the right amount of insulin. While mechanical devices to accomplish this are being developed, ultimately the best approach is likely to be based on genetic modification of cells. These could be pancreatic beta-cells, which are the only cells that produce insulin, or other cells that are involved in the pathogenesis of diabetes. Although definitive treatment of diabetes using genetically modified cells is a long-term goal, much progress is being made. This review discusses various approaches to modifying cells genetically, both in vitro and in vivo, for the treatment of diabetes.

Gene transfer to human pancreatic endocrine cells using viral vectors

We have studied the factors that influence the efficiency of infection of human fetal and adult pancreatic endocrine cells with adenovirus, murine retrovirus, and lentivirus vectors all expressing the green fluorescent protein (Ad-GFP, MLV-GFP, and Lenti-GFP, respectively). Adenoviral but not retroviral vectors efficiently infected intact pancreatic islets and fetal islet-like cell clusters (ICCs) in suspension. When islets and ICCs were plated in monolayer culture, infection efficiency with all three viral vectors increased. Ad-GFP infected 90-95% of the cells, whereas infection with MLV-GFP and Lenti-GFP increased only slightly. Both exposure to hepatocyte growth factor/scatter factor (HGF/SF) and dispersion of the cells by removal from the culture dish and replating had substantial positive effects on the efficiency of infection with retroviral vectors. Studies of virus entry and cell replication revealed that cell dispersion and stimulation by HGF/SF may be acting through both mechanisms to increase the efficiency of retrovirus-mediated gene transfer. Although HGF/SF and cell dispersion increased the efficiency of infection with MLV-GFP, only rare cells with weak staining for insulin were infected, whereas approximately 25% of beta-cells were infected with Lenti-GFP. We conclude that adenovirus is the most potent vector for ex vivo overexpression of foreign genes in adult endocrine pancreatic cells and is the best vector for applications where high-level but transient expression is desired. Under the optimal conditions of cell dispersion plus HGF/SF, infection with MLV and lentiviral vectors is reasonably efficient and stable, but only lentiviral vectors efficiently infect pancreatic beta-cells.

EDITS: development of questionnaires for evaluating satisfaction with treatments for erectile dysfunction

OBJECTIVES

To develop Patient and Partner versions of a psychometrically sound questionnaire, the EDITS (Erectile Dysfunction Inventory of Treatment Satisfaction), to assess satisfaction with medical treatments for erectile dysfunction.

METHODS

Treatment satisfaction differs from treatment efficacy as it focuses on a person's subjective evaluation of treatment received. Twenty-nine items representing the domain of treatment satisfaction for men and 20 representing partner satisfaction were generated. Two independent samples of 28 and 29 couples completed all items at two points in time. Spearman rank-order correlations were derived to assess test-retest reliability and couple coefficients of validity. Internal consistency coefficients were calculated for both Patient and Partner versions and a content validity panel was used to analyze content validity.

RESULTS

Only items that met all the following criteria were selected to comprise the final questionnaires: (a) range of response four or more out of five; (b) test-retest reliability greater than 0.70; (c) ratings by at least 70% of the content validity panel as belonging in and being important for the domain; and (d) significant correlation between the subjects' and partners' responses. Eleven patient items met criteria and formed the Patient EDITS; five partner items met criteria and formed the Partner EDITS. Scores on the two inventories were normally distributed with internal consistencies of 0.90 and 0.76, respectively. Test-retest reliability for the Patient EDITS was 0.98; for the Partner EDITS, it was 0.83.

CONCLUSIONS

Reliability and validity were well established, enabling the EDITSs to be used to assess satisfaction with treatment modalities for erectile dysfunction and to explore the impact of patient and partner satisfaction on treatment continuation.

Telomerase activity is sufficient to allow transformed cells to escape from crisis

The introduction of simian virus 40 large T antigen (SVLT) into human primary cells enables them to proliferate beyond their normal replicative life span. In most cases, this temporary escape from senescence eventually ends in a second proliferative block known as "crisis," during which the cells cease growing or die. Rare immortalization events in which cells escape crisis are frequently correlated with the presence of telomerase activity. We tested the hypothesis that telomerase activation is the critical step in the immortalization process by studying the effects of telomerase activity in two mortal SVLT-Rasval12-transformed human pancreatic cell lines, TRM-6 and betalox5. The telomerase catalytic subunit, hTRT, was introduced into late-passage cells via retroviral gene transfer. Telomerase activity was successfully induced in infected cells, as demonstrated by a telomerase repeat amplification protocol assay. In each of nine independent infections, telomerase-positive cells formed rapidly dividing cell lines while control cells entered crisis. Telomere lengths initially increased, but telomeres were then maintained at their new lengths for at least 20 population doublings. These results demonstrate that telomerase activity is sufficient to enable transformed cells to escape crisis and that telomere elongation in these cells occurs in a tightly regulated manner.

Interaction of vesicular stomatitis virus-G pseudotyped retrovirus with CD34+ and CD34+ CD38- hematopoietic progenitor cells

Retroviral vectors have had limited success in mediating gene transfer to hematopoietic stem cells, particularly in primates, due in part to low or absent expression of the amphotropic receptor (RAM-1). We have been interested in determining whether retrovirus pseudotyped with vesicular stomatitis virus G protein (VSV-G) would allow more efficient gene delivery to hematopoietic stem cells as the VSV-G receptors appear to be ubiquitously present phospholipids. However, we previously found that completion of retroviral vector reverse transcription does not occur in CD34+ CD38- hematopoietic stem cells that were exposed to VSV-G pseudotyped retrovirus. To determine at which stage the block to infection of CD34+ CD38- cells occurs, we confirmed by FACS analysis that VSV-G pseudotyped viral particles could bind to CD34+ CD38- cells. Virus binding to CD34+ cells was saturable at 4 degrees C but nonsaturable at 37 degrees C, up to a multiplicity of infection of 1080. This suggests that surface levels of phospholipid receptors available for viral binding are limiting on CD34+ cells. Cytokine stimulation increased virus binding to CD34+ cells. However, no increase in the level of surface phosphatidylserine (PS), a strong candidate for the VSV-G receptor, was seen as detected by the PS-specific reagent, annexin V. This suggests that another molecule is serving as the VSV-G receptor on CD34+ cells. Here, we show that once virus binding to cytokine-stimulated CD34+ CD38- cells has occurred, virus fusion proceeds efficiently as determined by octadecyl rhodamine (R18) fusion assays. Taken together with our previous observation that reverse transcription does not occur in CD34+ CD38- cells, we suggest that there are intracellular mechanisms leading to blockage of complete reverse transcription of the retrovirus in CD34+ CD38- cells. This has important implications for retrovirus-mediated gene transfer to quiescent stem cells.

Isolation and characterization of a cell line from the epithelial cells of the human fetal pancreas

Pancreatic cell lines are useful for basic studies of pancreatic biology and for possible application to cell transplantation therapies for diabetes. A retroviral vector expressing simian virus 40 (SV40) T antigen and H-rasval12 was used to infect a monolayer culture of epithelial cells from an 18-wk human fetal pancreas. Infected cells gave rise to a clonal epithelial cell line, designated TRM-1. This cell line expresses epithelial markers as well as gult2 and small amounts of insulin and glucagon. TRM-1 is the first cell line to be generated from the human fetal pancreas and also the first cell line derived directly from the fetal pancreas of any species. The approach that we have used to develop TRM-1 should be applicable to isolating cell lines from other stages of human pancreatic development.

Development of a VSV-G protein pseudotyped retroviral vector system expressing dominant oncogenes from a lacO-modified inducible LTR promoter

We report the development of a retroviral vector system in which two dominant oncogenes are expressed inducibly in human cells using the lac repressor/lac operator regulatable promoter system. First, the parent vector, pLoCRNLo, was constructed to contain a retroviral long terminal repeat (LTR) promoter that has been modified by incorporation of a lac operator sequence (lacO). This promoter, LTRo, was shown to mediate IPTG-inducible cat expression in rat cells expressing the lac repressor. The pLoCRNLo backbone was used to develop the retroviral vector LoTPRRNLo which expresses SV40 T antigen and H-ras val12 oncogenes as a dicistronic unit separated by a poliovirus internal ribosome entry sequence (PO-IRES). LoPRRNLo retrovirus was produced as a VSV-G protein pseudotype and used to infect primary human cells, resulting in the efficient formation of transformed cell lines. Subsequent introduction into the transformed cells of the lac repressor, expressed from a second retroviral vector, MSCV-In(S), resulted in IPTG-responsive oncogene expression and cell growth. This vector system is useful for introducing multiple genes under inducible control into mammalian cells.

E2A gene products are not required for insulin gene expression

Transcripts for E2A gene products, ubiquitous basic helix-loop-helix transactivating proteins, are expressed at high levels in the pancreatic epithelium. E2A proteins have been shown to bind the cognate E box sequence (CANNTG) of the insulin promoter/enhancer. E2A gene products dimerize with cell-specific basic helix-loop-helix proteins and synergize with the homeodomain transcription factor, PDX-1, in insulin gene transactivation. PDX-1 is also required for normal pancreatic development in mice. We investigated whether pancreatic development and insulin production could occur in the absence of E2A gene products by studying mice with a null mutation for the gene. E2A(-/-) mice demonstrated normal formation of pancreatic endocrine and exocrine tissue in histochemical sections as well as positive and distinct immunostaining for insulin and glucagon in islet tissue, signifying development of mature beta- and alpha-cells. Moreover, E2A(-/-) mice displayed no significant difference in blood glucose levels or pancreatic insulin content compared with wild-type littermates. These data show that although E2A gene products probably play an important role in insulin gene expression, pancreatic development and insulin production can proceed in their absence.

Cell-cycle kinetics and VSV-G pseudotyped retrovirus-mediated gene transfer in blood-derived CD34+ cells

As hematopoietic stem and progenitor cells have a low mitotic index, we have quantitated the impact of cytokine combinations on cell cycling of CD34+ cells and, using VSV-G pseudotyped retroviral vectors, correlated our findings with ex vivo gene transfer. We tested nine different combinations of cytokines for induction of human peripheral blood CD34+ cells into cell cycle over 72 hours. Using the 5-bromodeoxyuridine-Hoechst 33258 (BrdU-Hoechst) assay, we measured the cell-cycle kinetics. The combinations of cytokines tested that were most efficient in inducing the CD34+ cells into cycle were stem cell factor (SCF) plus one of the following: interleukin-1 (IL-1), IL-3, granulocyte colony-stimulating factor (G-CSF). The maximum numbers of cells in S+G2M phase were observed after 48 hours of culture. At least 35 +/- 5% of the CD34+ cells remained quiescent in the first G0/G1 phase, however, no matter which cytokine combination was used. Cell-cycle analysis of the CD34+CD38- subset by 7-amino actinomycin D staining did not detect cycling cells during 72 hours of culture with any of the cytokines tested. To investigate whether the cells could be infected by the VSV-G pseudotyped virus containing the neomycin phospho-transferase gene (neo), we exposed CD34+ cells to the virus for 7-8 hours after 0, 36, and 48 hours of cytokine stimulation. Total CD34+ cells and the CD34+CD38- subset were analyzed by polymerase chain reaction (PCR) for reverse-transcribed viral DNA of the neomycin resistance gene (RT-neoDNA). Immediately after exposure to the virus, RT-neoDNA was detectable in CD34+ cells that have been cultured with or without cytokines for 36 to 48 hours. Forty-eight hours postinfection, however, RT-neoDNA could be detected only with cytokine combinations that induced mitosis of the CD34+ cells, consistent with the requirement for mitotic activity for retroviral integration. Similar experiments performed with the 34+CD38- subset showed that RT-reoDNA could not be detected at any time point. Thus, postinfection RT-neoDNA could be immediately detected in noncycling CD34+ cells but not in CD34+CD38- cells. These results suggest during short-term liquid culture, there may be blocks for reverse transcription of retroviral RNA in CD34+CD38-cells in addition to the lack of mitotic activity.

Differential integrin expression facilitates isolation of human fetal pancreatic epithelial cells

We have studied the expression of the beta 1 family of integrins in fetal and adult human pancreas. Immunohistochemical staining with a monoclonal anti-beta 1 antibody revealed that the epithelial cells of the human fetal pancreas express high amounts of beta 1 integrin, while the pancreatic stromal cells express substantially lower amounts. Islets of Langerhans from human adult pancreas also expressed high amounts of beta 1 integrin. Taking advantage of the extremely high affinity binding between the invasin protein of Yersinia pseudotuberculosis and many beta 1 integrins, we have been able to isolate highly enriched populations of fetal pancreatic epithelial cells. Epithelial-enriched cell populations retain the ability to differentiate into mature endocrine cells following transplantation into nude mice.

Acid beta-galactosidase: a developmentally regulated marker of endocrine cell precursors in the human fetal pancreas

Isolation of endocrine cell precursors from the human fetal pancreas will be important to the study of islet cytodifferentiation and eventually for islet transplantation in insulin-dependent diabetes. These precursor cells, from which all four islet endocrine cell types arise, are present within fetal pancreatic ductal epithelium. After enzymatic digestion and culture of the fetal pancreas, we obtained cell clusters resembling islets, but with a high content of undifferentiated cells. Histochemical staining revealed very high acid beta-galactosidase activity in over 70% of cells within the clusters. After transplantation into athymic nude mice, the islet-like cell clusters gave rise to tissue rich in differentiated endocrine cells, but low in beta-galactosidase activity. The histochemical finding of high acid beta-galactosidase activity in endocrine precursor cells was confirmed by direct measurement of lysosomal enzyme activities. In addition, we found that the expression of acid beta-galactosidase was developmentally regulated, peaking at 18-24 weeks gestation and declining to low levels in adult islets. Using a fluorogenic beta-galactosidase substrate, we were able to isolate a subpopulation of cells high in acid beta-galactosidase activity using fluorescence-activated flow cytometry. Evidence identifying these cells as potential islet cell precursors includes, besides the transplantation experiments, the colocalization in vitro of tyrosine hydroxylase, a marker of embryonic islet cells. Thus, our results indicate that high acid beta-galactosidase activity serves as a marker for a population of fetal pancreatic cells with the potential to differentiate and grow into mature pancreatic endocrine cells.

High efficiency retroviral-mediated gene transduction into CD34+ cells purified from peripheral blood of breast cancer patients primed with chemotherapy and granulocyte-macrophage colony-stimulating factor

The hematopoietic system has been one of the major targets for designing human gene therapy protocols. In the present system, we have transduced LNL6, one of the most commonly used retroviral vectors in gene therapy, into purified CD34+ cells from peripheral blood of patients primed with chemotherapy and granulocyte-macrophage colony-stimulating factor (GM-CSF). Purification of CD34+ cells was achieved by incubation with a murine anti-CD34 monoclonal antibody (9C5), and subsequently with paramagnetic microspheres (Dynal) coated with sheep anti-mouse IgG1 (Fc). The CD34+ cells were released from the beads by treatment with chymopapain. Flow cytometry analysis using the anti-CD34 antibody HPCA-2-FITC targeted at another epitope of CD34 showed that 78-97.5% of the cells thus purified were CD34+. After retroviral-mediated gene transfer, polymerase chain reaction (PCR) analysis revealed that 67-100% of the hematopoietic colonies contained the marker gene neo, indicating that CD34+ cells purified by immunomagnetic microsphere method from peripheral mononuclear cells primed with hematopoietic growth factors are highly susceptible to retroviral-mediated gene transfer. The expression of neo as determined by reverse transcription (RT)-PCR appeared to be unstable and not persistent. Taken together, our data suggest that LNL6 is a suitable vector for gene marking of hematopoietic progenitors but not for gene therapy protocols based on persistent gene expression.

Provirus-anchored long-range (PAL) mapping of mammalian genomes

To design a strategy for more efficient long-range physical mapping of large mammalian genomes, we have developed a method for directional mapping from anchor points of randomly integrated retroviral proviruses containing sequences that provide unique cleavage sites in the genome. Using this method, we have determined a physical map of approximately 1.6 Mb flanking an Mo MLV-proviral integration site in mouse NIH/3T3 cells. Our results indicate that this provirus-anchored long-range (PAL) mapping strategy, which uses only two proviral sequences as universal hybridization probes, can potentially allow rapid construction of physical maps for chromosomal regions devoid of other genetic markers.

Cytotoxicity of a replication-defective mutant of herpes simplex virus type 1

Replication-defective mutants of herpes simplex virus type 1 (HSV-1) may prove useful as vectors for gene transfer, particularly to nondividing cells. Cgal delta 3 is an immediate-early gene 3 (IE 3) deletion mutant of HSV-1 that expresses the lacZ gene of Escherichia coli from the human cytomegalovirus immediate-early control region but does not express viral early or late genes. This vector was able to efficiently infect and express lacZ in cells refractory to traditional methods of gene transfer. However, 1 to 3 days postinfection, Cgal delta 3 induced cytopathic effects (CPE) in many cell types, including neurons. In human primary fibroblasts Cgal delta 3 induced chromosomal aberrations and host cell DNA fragmentation. Other HSV-1 strains that caused CPE, tested under conditions of viral replication-inhibition, included mutants of the early gene UL42, the virion host shutoff function, single mutants of IE 1, IE 2, and IE 3, and double mutants of IE 3 and 4 and IE 3 and 5. Inhibition of viral gene expression by UV irradiation of virus stocks or by preexposure of cells to interferon markedly reduced the CPE. We conclude from these studies that HSV-1 IE gene expression is sufficient for the induction of CPE, although none of the five IE gene products appear to be solely responsible. After infection of human fibroblasts with Cgal delta 3 at a low multiplicity of infection, we were able to recover up to 6% of the input virus 2 weeks later by a superinfection-rescue procedure, even though the virally transduced human cytomegalovirus-lacZ transgene was not expressed at this time. It is therefore likely that inhibition or inactivation of viral IE gene expression, either for establishing latency or for the long-term transduction of foreign genes by HSV-1 vectors, is essential to avoid the death of infected cells.

Gene therapy techniques

The most dramatic event of the past year in the field of gene therapy has been the initiation of clinical trials involving the introduction of genetically altered cells into human beings. Four studies, three involving new approaches to cancer therapy and one involving the treatment of adenosine deaminase deficiency, are presently under way. There has also been significant recent progress in the technology of gene transfer relevant to gene therapy. This progress, along with the recent clinical therapy trials, is the subject of this review.

Efficient gene expression in mammalian cells from a dicistronic transcriptional unit in an improved retroviral vector

We have studied the properties of dicistronic transcriptional units in retroviral vectors. In these vectors, the promoter in the 5' retroviral long terminal repeat (LTR) controls expression of both an upstream cistron (luc) encoding firefly luciferase and a downstream cistron (neo), a selectable marker encoding neomycin phosphotransferase (NPTII). By assaying for simultaneous expression of luc and neo after transfection or infection of hamster BHK, rat 208F, and mouse retroviral packaging cell lines, we have identified important factors that affect expression from the downstream cistron, including the presence of intercistronic ATG sequences, the length of the intercistronic sequence and conformity of the sequence surrounding the downstream start codon to the eukaryotic consensus sequence. Optimized dicistronic vectors produced amounts of NPTII comparable to a vector in which neo was driven by a strong internal promoter consisting of a modified Rous sarcoma virus LTR. Additionally, they produced higher virus titers and demonstrated improved stability of gene expression in the absence of selection. By virtue of their physical compactness and elimination of the need for a separate promoter for every gene, dicistronic transcriptional units allow the introduction of larger genes into retroviral vectors and may allow for more than two genes to be placed in a single vector.

The electron-transfer site of spinach plastocyanin

Two sites for electron transfer have been proposed for plastocyanin: one near the copper ion and the other close to the acid patch formed by residues 42-45. Calculations of electrostatic properties of spinach plastocyanin and ionic strength dependences of electron-transfer reactions of this protein have been used to distinguish between these two sites. Calculations show that the electric potential field of spinach plastocyanin is highly asymmetric and that the protein has a dipole moment of 360 D. The negative end of the dipole axis emerges between the negative patches formed by residues 42-45, which is though to be the cation binding site, and residues 59-61. The angles between the dipole vector and vectors from the center of mass to the copper ion and to the acid patch are 90 degrees and 30 degrees, respectively. The angle between the dipole vector and a line from the center of mass to the site of electron transfer is evaluated from the ionic strength dependence of electron-transfer rates at pH 7.8 with the help of equations developed by Van Leeuwen et al. [van Leeuwen, J.W., Mofers, F.J.M., & Veerman, E.C.I. (1981) Biochim. Biophys. Acta 635, 434] and Van Leeuwen [van Leeuwen, J.W. (1983) Biochim. Biophys. Acta 743, 408]. The angles found are 85 degrees, 110 degrees, and 75 +/- 15 degrees for reactions with tris(1,10-phenanthroline)cobalt(III), hexacyanoferrate(III), and ferrocytochrome c, respectively. The electric potential field calculations suggest that the hexacyanoferrate(III) interaction angle corresponds to a unique site of minimum repulsion at the hydrophobic region of the protein surface, close to the copper ion.(ABSTRACT TRUNCATED AT 250 WORDS)

Catalysis of superoxide dismutation by manganese aminopolycarboxylate complexes

Complexes of manganese, copper, cobalt, and iron with a variety of aminopolycarboxylates at concentrations from 2 X 10(-7) to 3 X 10(-6) M were tested for superoxide dismutase activity with horse ferricytochrome c as the competing reagent for superoxide. In the presence of excess ligand only manganous nitrilotriacetate and manganous ethylenediaminediacetate showed activity with catalytic rate constants of 2.2 X 10(7) and 1.8 X 10(7) M-1 S-1, respectively, at pH 6, 22 +/- 1 degree C, and 10 mM ionic strength. These rate constants decrease considerably at higher pH. Manganous N-hydroxyethylethylenediaminetriacetate is oxidized by superoxide, but does not appear to have catalytic activity. From the experimental conditions under which the two complexes mentioned above exhibit catalysis, and the inactivity of other metal chelates, it is concluded that an open coordination site is essential but not sufficient to catalyze the dismutation reaction.

Evidence for two trans-acting genes regulating HLA class II antigen expression

Previous studies have shown that a trans-acting regulatory factor is required for expression of HLA class II molecules in B-LCL, and that a trans-active factor derived from B-LCL induces de novo synthesis of T-LCL-encoded class II antigens in hybrids of T-LCL and B-LCL. To further examine the genetics of class II antigen regulation, we have now fused two different T-LCL with the class II antigen negative B-LCL 6.1.6, a regulatory mutant that does not synthesize a trans-acting factor necessary for transcription of class II genes. Northern blot analysis and cell surface immunofluorescence studies indicate that the hybrids express class II antigens encoded by both 6.1.6 and T-LCL parent cell lines. Thus, expression of class II antigens in these hybrids is controlled by a minimum of two trans-acting regulatory genes. One of these genes is inactivated in the 6.1.6 mutant and is provided by the T-LCL fusion partner. The second regulatory gene may still be active in 6.1.6, but it alone is insufficient for maintenance of class II antigen expression.

Evidence for two trans-acting genes regulating HLA class II antigen expression

Previous studies have shown that a trans-acting regulatory factor is required for expression of HLA class II molecules in B-LCL, and that a trans-active factor derived from B-LCL induces de novo synthesis of T-LCL-encoded class II antigens in hybrids of T-LCL and B-LCL. To further examine the genetics of class II antigen regulation, we have now fused two different T-LCL with the class II antigen negative B-LCL 6.1.6, a regulatory mutant that does not synthesize a trans-acting factor necessary for transcription of class II genes. Northern blot analysis and cell surface immunofluorescence studies indicate that the hybrids express class II antigens encoded by both 6.1.6 and T-LCL parent cell lines. Thus, expression of class II antigens in these hybrids is controlled by a minimum of two trans-acting regulatory genes. One of these genes is inactivated in the 6.1.6 mutant and is provided by the T-LCL fusion partner. The second regulatory gene may still be active in 6.1.6, but it alone is insufficient for maintenance of class II antigen expression.

Different roles for cytosine methylation in HLA class II gene expression

We studied the role of cytosine methylation in the control of HLA class II gene expression in isogenic sets of cells whose members differ in their expression of HLA class II genes. These included: T5-1, 6.1.6, and P30, which are a class II expressing B-cell line, a class II nonexpressing mutant derived from T5-1, and an HLA-DR expressing partial revertant derived from 6.1.6, respectively; the class II expressing B-cell line, SB, and the class II non-expressing T-cell line, HSB, from the same individual. The use of sets of cells that differ in the way their class II genes are regulated allows us to study how that difference is reflected in the methylation state of their class II genes. At least five out of six class II genes in nonexpressing cells have a CpG site that is demethylated, when compared with the same class II gene in the respective expressing cells. The results presented in this paper indicate that most methylation changes in and around class II genes have a correlation with their state of expression. Some of these changes reflect rather than determine the state of expression. Other methylation changes appear to directly affect expression, whereas some methylation differences neither correlate with nor influence gene expression. Although 5-azacytidine does not affect class II expression in T5-1 or 6.1.6, it does induce expression in HSB. This indicates that the basis for nonexpression of class II genes is different in 6.1.6 and HSB.

HLA class II regulation and structure. Analysis with HLA-DR3 and HLA-DP point mutants

Point mutations that affect HLA-DR structure or expression have not previously been described. In the present study, we isolated such mutants by immunoselection of an ethyl methanesulfonate-mutagenized HLA-DR3 cell line with an anti-HLA-DR3 monoclonal antibody, 16.23. To facilitate analysis, we used a parent cell line with a preexisting deletion of one haplotype encompassing DR and DQ alpha and beta. The selection yielded two sets of mutants, one with defects in DR3 structure, the other with defects in different steps leading to DR expression. Of the expression-defective mutants, one had undergone a second deletion removing the remaining DR alpha gene but no other class II genes. It had a normal abundance of DR beta mRNA but had lost binding of DR monomorphic antibodies, indicating that DR beta chains do not form noncognate dimers. A second mutant had an abnormally large DR alpha mRNA, probably resulting from a splice site mutation. Several mutants had marked reductions in DR beta mRNA levels; in two of these, the lesion appeared to be transcriptional because the reduction in DR beta mRNA was paralleled by an altered methylation pattern of one of the DR beta genes. Other expression-defective mutants had different posttranscriptional defects. Some of the mutations were similar to those that have been found in mouse strains defective in I-E expression, whereas others have no known natural counterpart. The matrix of reactivities of anti-HLA class II monomorphic antibodies with these and similar mutants allowed us to define the gene products recognized by these antibodies. A set of seven mutants were "epitope defective," that is, they expressed normal or near normal levels of HLA-DR3 but no longer bound 16.23. Unexpectedly, each of the epitope mutants had decreased DR dimer stability. These mutants should be useful in localizing the DR3 alloepitope and in elucidating its contribution as a restriction element in the presentation of soluble antigen to immune T cells.