Expression of ribozymes in gene transfer systems to modulate target RNA levels

The possibility of designing ribozymes to cleave any specific target RNA has rendered them valuable tools in both basic research and therapeutic applications. In the therapeutics area, they have been exploited to target viral RNAs in infectious diseases, dominant oncogenes in cancers and specific somatic mutations in genetic disorders. Most notably, several ribozyme gene therapy protocols for HIV patients are already in Phase 1 trials. More recently, ribozymes have been used for transgenic animal research, gene target validation and pathway elucidation.

Development of novel cell surface CD34-targeted recombinant adenoassociated virus vectors for gene therapy

Recombinant adenoassociated virus (rAAV) type 2 vectors have been used to transduce a wide variety of cell types, including hematopoietic progenitor cells. For in vivo gene transfer, it is desirable to have an rAAV vector that specifically transduces selected target cells. As a first step toward generating an rAAV vector capable of targeting delivery in vivo, we have engineered a chimeric protein combining the AAV capsid protein and the variable region of a single-chain antibody against human CD34 molecules, a cell surface marker for hematopoietic stem/progenitor cells. Inclusion of the chimeric CD34 single-chain antibody-AAV capsid proteins within an rAAV virion significantly increased the preferential infectivity of rAAV for the CD34+ human myoleukemia cell line KG-1, which is normally refractory to rAAV transduction. Antibodies against the single-chain antibody and the CD34 protein blocked this transduction. This chimeric vector represents a significant improvement in the host range of rAAV and the first step toward specific gene delivery by rAAV vectors to cells of choice, in this case, hematopoietic progenitor cells, for the treatment of human disease.

Ribozyme gene therapy for hepatitis C virus infection

BACKGROUND

The development of antiviral drugs for hepatitis C virus (HCV) infection represents a substantial challenge. Similar to human immunodeficiency virus (HIV), HCV is highly prone to mutation. It is, therefore, expected that potential HCV therapeutics currently under development, such as protease inhibitors, will suffer from the same shortcomings of HIV therapeutic drugs; the emergence of drug resistant viral mutants. Ribozymes (Rz) are enzymatic RNA molecules that can be engineered to specifically target any given RNA molecule. A therapeutic Rz can be manufactured and administered as a drug, or a Rz gene can be delivered and expressed intracellularly by gene therapy. For HCV therapeutics, we favour the gene therapy approach as delivery and in vivo expression of Rz genes will result in a constant and continuous supply of multiple intracellular Rz, offering less opportunity for the development of drug-resistant viral variants.

OBJECTIVES

To utilise direct intravenous injection of hepatotropic viral vectors to transfer Rz genes directly into the hepatocytes of HCV-infected patients, resulting in degradation of the HCV positive strand RNA genome, the viral mRNAs, and even the negative strand RNA replication intermediate. We plan to circumvent the emergence of drug-resistant viral mutants by targeting multiple, highly conserved HCV RNA sequences simultaneously with multiple Rz genes expressed from a single vector.

STUDY DESIGN

Rzs targeting conserved regions of the HCV positive and negative RNAs were transcribed in vitro and used to cleave HCV target RNAs. The most effective Rzs identified were then incorporated into adeno associated viral (AAV) vectors and adenoviral (AV) vectors and tested for their ability to inhibit HCV core expression in a tissue culture model.

RESULTS

Several Rzs targeting highly conserved HCV sequences effectively degraded positive and negative strands of HCV RNA in vitro. Furthermore, substantial inhibition of HCV gene expression was observed in tissue culture using viral vectors to deliver and express Rz genes.

CONCLUSIONS

Rz gene therapy has potential for the production of anti-viral drugs directed against HCV. Initial studies employing Rz gene therapy to produced anti-viral drugs against HCV have proved successful. Rz gene therapy may be a useful approach to overcome problems associated with anti-HCV drug design, such as the emergence of drug-resistant mutants.

A Phase I clinical trial of immunotherapy with interferon-gamma gene-modified autologous melanoma cells: monitoring the humoral immune response

BACKGROUND

Tumor cells transduced with cytokine genes provide immunogenic vaccines for cancer immunotherapy.

METHODS

A Phase I clinical trial was conducted for the specific active immunization of melanoma patients with interferon-gamma (IFN-gamma) gene-modified autologous melanoma tumor cells. Short term melanoma cultures were transduced retrovirally with the gene for human IFN-gamma. The genetically modified melanoma cells secreted biologically active IFN-gamma and showed enhanced expression of major histocompatibility complex class I and class II surface antigens. These cells were inactivated by irradiation (50 gray) and were cryopreserved for the vaccine. Twenty melanoma patients were enrolled in this clinical trial. The immunizations were administered in escalating doses once every 2 weeks for 3 months. The first and second injections consisted of 2 million cells, followed by 6 million for the third and fourth injections, and then 18 million for the fifth and sixth injections. The humoral immune responses of the patients were assessed by enzyme-linked immunoadsorbent assay, radioimmunoassay, and radioimmunoprecipitation.

RESULTS

Thirteen of the 20 patients completed the immunization protocol. Eight of these 13 patients showed a humoral immunoglobulin (Ig)G response against autologous and allogeneic melanoma cells. The other five patients either had no detectable antimelanoma antibodies or showed a weak IgG response that did not rise significantly above the preimmune level. All the sera contained low or undetectable levels of antimelanoma IgM antibodies. The IgG response increased progressively in titer during the course of immunization. The positive sera showed preferentially strong binding to melanoma cell lines and some cross-reactivity to nonmelanoma tumors. A 75-80 kD antigen on melanoma cells was immunoprecipitated by postimmune sera of 3 of the responding patients. Preimmune sera from these three patients and sera from other patients immunized with a standard nontransduced melanoma cell vaccine failed to precipitate this antigen. Two patients with significant increases in serum IgG had clinical tumor regression, and two additional patients with low serum IgG response had transient shrinkage of nodular disease during therapy.

CONCLUSIONS

These data suggest that gene therapy with IFN-gamma-transduced melanoma cells is safe and worthy of further investigation in patients with less advanced stage malignant melanoma. The ability to monitor changes in the humoral responses of the immunized patients has been demonstrated.

Sustained cytokine production and immunophenotypic changes in human neuroblastoma cell lines transduced with a human gamma interferon vector

The majority of human neuroblastomas express low to undetectable levels of major histocompatibility complex (MHC) class I and II antigens (MHC-I and -II). We studied the effects of gamma interferon (gamma-IFN) transduction on expression of these antigens in six human neuroblastoma cell lines with and without genomic amplification of the N-myc oncogene. All six were stably transduced with an MoMLV-based gamma-IFN retroviral vector (DAh gamma-IFN). G418-resistant cells were assayed for MHC-I, MHC-II, B7-1, and neuroblastoma-associated antigen expression, as well as for gamma-IFN levels in cell culture supernatants. Sustained gamma-IFN production, 2 to > 1000 units/10(6) cells/d, was attained for five of six transduced cell lines and persisted for up to 9 months. This resulted in marked upregulation of MHC-I and MHC-II expression in LA-N-1, LA-N-6, and CHLA-127 cells and moderate upregulation in SK-N-Fi and SK-N-AS cells. One cell line (LA-N-1) had marked induction of MHC-I and MHC-II despite marginal levels of gamma-IFN production. Expression of CD28 ligand B7-1 (as determined by BB1 antibody) remained unchanged in all gamma-IFN-transduced cell lines tested. Expression of several neuroblastoma-associated antigens (NKH1A, 126-4, HSAN 1.2, HNK, 459, and 390) was upregulated in some of the gamma-IFN-transduced cell lines. These results demonstrate that preparation of gamma-IFN expressing neuroblastoma cells for immunotherapeutic purposes is feasible and that gamma-IFN transduction results in phenotypic changes that may improve immunogenicity of human neuroblastoma cells.

Cytotoxic T-lymphocyte induction in asymptomatic HIV-1-infected patients immunized with Retrovector-transduced autologous fibroblasts expressing HIV-1IIIB Env/Rev proteins

OBJECTIVE

To demonstrate the safety and enhancement of HIV-1-specific immune responses in HIV-infected asymptomatic patients following treatment with retroviral vector (Retrovector)-transduced autologous fibroblasts (VTAF) expressing HIV-1IIIB Env/Rev proteins.

DESIGN

A non-placebo-controlled, single arm Phase I study.

PARTICIPANTS

Four HIV-1-seropositive asymptomatic volunteers were selected based on age (18-50 years), CD4/CD3 lymphocyte counts (> 600 x 10(6)/l or > 40%), and positive delayed-type hypersensitivity test to at least one recall antigen.

INTERVENTIONS

Patients were treated at 2-week intervals with a total of three intramuscular injections of irradiated autologous fibroblasts transduced with a molecularly engineered, non-replicating amphotropic murine retrovector encoding the HIV-1IIIB Env/Rev proteins.

MAIN OUTCOME MEASURES

The clinical status of patients was assessed by history, physical examination, serum chemistry and hematology, CD4/CD3 lymphocyte counts, HIV viral burden, and monitored throughout the study to detect potentially treatment-induced toxic or unwanted side-effects. In addition, HIV-1-specific cytotoxic T-lymphocyte (CTL) activity was measured to determine the biological activity of VTAF.

RESULTS

No acute local or systemic adverse events occurred following three injections with VTAF. Furthermore, a statistically significant increase of CD8+ CTL activity against HIV-1IIIB Env/Rev-expressing targets was observed in peripheral blood mononuclear cells from two out of four patients.

CONCLUSIONS

This is the first report of the administration of a gene transfer treatment to HIV-1-infected patients and provides initial support for the safety and activity of retrovector-transduced fibroblasts administered to asymptomatic patients. This treatment resulted in the detection of increased HIV-1IIIB Env/Rev-specific CTL activity in two HIV-seropositive patients and could provide a better understanding of the role of CTL activity in HIV disease progression.

Transduction of human melanoma cells with the gamma interferon gene enhances cellular immunity

Human tumor cells transduced with the gamma interferon (gamma IFN) gene are currently used in specific active immunotherapy protocols to enhance the antitumor immune responses of cancer patients. This in vitro study was undertaken to examine the initial events in the cellular immune response that may occur following the administration of the gamma IFN-transduced cell vaccine. Human melanoma tumor cell lines were transduced with a MoMLV-based retroviral vector carrying the human gamma IFN gene. The transduced cells expressed the cytokine gene, secreted biologically active gamma IFN, and exhibited enhanced expression of MHC class I and class II (HLA-DR), and ICAM-1 surface antigens. The gamma IFN-transduced and corresponding parental melanoma cells were used for the induction of short-term lymphocyte cultures. Peripheral blood lymphocytes or lymph node cells from 20 melanoma patients were stimulated for 5 to 15 days with autologous or MHC class I-matched allogeneic parental or gamma IFN-transduced melanoma cells. Seven of the 20 lymphocyte cultures showed substantial increases in lytic activity following stimulation with the transduced melanoma cells in comparison to control lymphocyte cultures stimulated with unmodified parental melanoma. The cytolytic activity stimulated with gamma IFN-modified melanomas was mediated partly by MHC-restricted cytotoxic T lymphocytes and partly by NK cells. Lymphocyte cultures that displayed increases in cytotoxicity after stimulation with the gamma IFN-transduced melanoma cells also exhibited enhanced expression or induction of one or more of the following lymphokines: IL-4, IL-1 alpha, IL-1 beta, gamma IFN, and TNF-alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Proto-oncogene fos: factors affecting expression and covalent modification of the gene product

Expression of proto-oncogene fos is induced in response to a variety of growth factors and differentiation-specific agents. However, the induction of fos gene expression is not influenced by inhibition of protein synthesis. We, therefore, entertained the notion that expression of the fos gene may be governed by posttranslational modification of cellular transcriptional factors. We report here that transcription of the human c-fos gene is modulated by negatively and positively acting cellular factors. The nuclear protein products of the resident oncogene of the FBJ-murine osteosarcoma virus (v-fos) and its corresponding cellular proto-oncogene (c-fos) are stoichiometrically phosphorylated on serine and threonine residues. The c-fos protein is more highly phosphorylated than the v-fos protein due to the phosphorylation of unique sites tentatively localized to the c-terminal 20 amino acid residues. The protein kinase C agonist, TPA, stimulates phosphorylation of the c-fos, but not the v-fos protein.

Modification of fos proteins: phosphorylation of c-fos, but not v-fos, is stimulated by 12-tetradecanoyl-phorbol-13-acetate and serum

We have investigated the covalent modification of the proteins encoded by the murine fos proto-oncogene (c-fos) and that of the corresponding gene product of FBJ murine osteosarcoma virus (v-fos). Both proteins are posttranslationally processed in the cell, resulting in forms with lower electrophoretic mobilities than that of the initial translation product on sodium dodecyl sulfate-polyacrylamide gels. Treatment with alkaline phosphatase indicates that most, if not all, of this electrophoretic shift is due to phosphoesterification of both proteins. These phosphoryl groups stoichiometrically modify the v-fos and c-fos proteins on serine residues and turn over rapidly in vivo in the presence of protein kinase inhibitors (half-life, less than 15 min). Direct quantitative comparison of steady-state labeling studies with L-[35S]methionine and [32P]phosphate reveals that the c-fos protein is four- to fivefold more highly phosphorylated than the v-fos protein is. Comparison of tryptic fragments from [32P]phosphate-labeled proteins indicates that although the two proteins have several tryptic phosphopeptides in common, the c-fos protein contains unique major tryptic phosphopeptides that the v-fos protein lacks. These unique sites of c-fos phosphorylation have been tentatively localized to the carboxy-terminal 20 amino acid residues of the protein. Phosphorylation of the c-fos protein, but not the v-fos protein, can be stimulated at least fivefold in vivo by the addition of either 12-tetradecanoyl-phorbol-13-acetate or serum. This increase in the steady-state degree of phosphorylation of c-fos appears to be independent of protein kinase C since phosphorylation is Ca2+ and diacylglycerol independent. The possible role of phosphorylation of these proteins in cellular transformation is discussed.

Proto-oncogene expression in regenerating liver is simulated in cultures of primary adult rat hepatocytes

Proto-oncogene fos mRNA levels are rapidly and transiently elevated 12-fold in regenerating liver 10-60 min following partial hepatectomy. This response, and the induction of fos protein synthesis, has been simulated qualitatively and quantitatively in long term primary cultures of quiescent adult rat hepatocytes where proliferative transitions can be initiated directly in serum-free medium by known hepatocyte mitogens like epidermal growth factor. Expression of a second proto-oncogene, c-rasH, in proliferatively activated hepatocyte cultures between 6 and 24 h also simulates the delayed hepatic response that occurs in vivo following partial hepatectomy. These results suggest that sequential proto-oncogene expression during liver regeneration is caused directly by hepatocellular interactions with specific mitogens. In addition, a role for monovalent cations in the regulation of hepatocyte gene expression is implicated from findings that Na+ deprivation inhibits induction of fos expression in cultured hepatocytes by epidermal growth factor under chemically defined conditions.

Metabolism of S-adenosyl-L-methionine in intact human erythrocytes

Freshly isolated human erythrocytes contain S-adenosyl-L-methionine (AdoMet) at a concentration of about 3.5 mumol/l cells. When such cells are incubated in a medium containing 30 microM L-methionine, 18 mM D-glucose and 118 mM sodium phosphate (pH 7.4), intracellular AdoMet levels continuously decrease to a value of about 0.1 microM after 24 h. This occurs in spite of the fact that the cellular concentrations of the substrates for the AdoMet synthetase reaction, ATP and L-methionine, remain relatively constant. In a search for incubation conditions that lead to stable levels of AdoMet in incubated cells, we have developed a sodium-Hepes-buffered medium which includes 1 mM adenine and a stoichiometric excess of MgCl2 over its ligand, phosphate. The inclusion of magnesium ion (and a reduction in phosphate) appears to increase intracellular free Mg2+, which is required for full activity of the erythrocyte AdoMet synthetase. Even in the presence of MgCl2, however, the AdoMet pool level can drop 4-6-fold within the first 2 h of incubation. We present evidence that suggests that this initial fall in the cellular AdoMet level may be due to the activation of AdoMet-dependent protein carboxyl methyltransferase, an enzyme which accounts for a large fraction of the total cellular AdoMet utilization. Adenine, or related compounds in the medium may prevent this activation, although the mechanism of this action is not clear at present.

Demethylation of protein carboxyl methyl esters: a nonenzymatic process in human erythrocytes?

We have compared the demethylation rate of protein carboxyl methyl esters from isolated human erythrocyte membranes with the corresponding rate of metabolic turnover of these same methyl groups in the intact erythrocyte. Surprisingly, the apparent spontaneous demethylation of these membrane protein methyl esters was significantly faster at physiological pH than the corresponding rate determined by pulse-chase analysis of intact cells incubated with L-[methyl-3H]methionine. Readdition of erythrocyte lysate to purified membranes did not increase the rate of demethylation, as might be expected if there were cytosolic or membrane-bound protein methylesterase activity, but resulted instead in an apparent stabilization of these methyl esters. Thus, the metabolic lability of these protein methyl esters in intact cells may be quantitatively explained by spontaneous, rather than enzymatic, demethylation reactions. A model is presented in which a rapid but nonenzymatic intramolecular demethylation reaction results in the formation of a polypeptide imide or anhydride intermediate. The metabolic fate of these hypothetical intermediates is unknown but may lead to the repair or degradation of protein D-aspartyl and L-isoaspartyl residues, which appear to be the substrates for the initial transmethylation reaction.

Membrane protein carboxyl methylation does not appear to be involved in the response of erythrocytes to cytoskeletal stress

We have investigated the effect of changes of human erythrocyte cell shape on the degree of covalent modification by carboxyl methylation of membrane cytoskeletal proteins. The results indicate that the cell probably does not utilize carboxyl methylation to respond to cytoskeletal perturbations caused by such agents as A23187, 2,4-dinitrophenol, and chlorpromazine, all of which are known to cause large changes in cell shape. Protein carboxyl methylation also remained unchanged in the presence of cytochalasin B, which prevents such changes in cell shape. These results are not consistent with a cytoskeletal regulatory role for protein methylation reactions in the intact erythrocyte.

Inhibition of protein carboxyl methylation by S-adenosyl-L-homocysteine in intact erythrocytes. Physiological consequences

S-Adenosyl-L-homocysteine was used to inhibit the methylation of carboxylic acid residues of membrane proteins in intact human erythrocytes. Incubation of erythrocytes for 24 h with 5 mM each of adenosine and L-homocysteine resulted in the intracellular accumulation of S-adenosyl-L-homocysteine and substantially inhibited membrane protein carboxyl methylation. From the degree of inhibition and from the observed turnover of methylated proteins, we estimate that the number of protein methyl esters in cells incubated with adenosine and L-homocysteine for 20 h is less than 20% that of cells incubated without these inhibitors. No significant differences in the physical deformability properties of the membrane of these hypomethylated cells were detected. However, there was a small but significant (p less than 0.001) increase in the amount of membrane protein D-aspartyl residues in these cells compared to control cells. These observations are consistent with the hypothesis that methylation of membrane proteins at D-aspartyl residues may result in the selective removal or repair of these uncommon residues.

Nutritional support of patients with severe hepatic failure

The pathophysiology, etiology, and metabolic alterations of severe hepatic failure and nutritional support of patients with this condition are reviewed. Hepatic failure encompasses a broad range of acute and chronic processes; complications may be fatal or quite minimal. Cirrhosis refers to all types of chronic diffuse liver disease. While hepatocytes regenerate in cirrhotic patients, eventually the parenchymal and vascular architecture of the liver is disrupted, leading to a syndrome of hepatic insufficiency. Normal metabolic processes deteriorate, and serum amino acid imbalances and fat intolerance may develop. Aromatic amino acids, which are normally catabolized by the liver, accumulate in the serum, and branched-chain amino acid deficiencies develop as these amino acids are broken down for energy by peripheral muscle. Hepatic encephalopathy often develops in these patients. Successful nutritional support of the patient with severe hepatic failure depends on correction of the specific metabolic abnormalities occurring. Parenteral nutrition with Hepatamine (American McGaw), a product with more branched-chain amino acids and less aromatic amino acids than other amino acid solutions, is useful in patients with altered serum amino acid profiles who develop hepatic encephalopathy. Patients in whom factors other than altered amino acids are primary causes of encephalopathy may not respond to Hepatamine. Enteral nutritional products with amino acid compositions similar to Hepatamine [Hepatic-Aid II (McGaw), Travasorb-Hepatic (Travenol Laboratories)] may be used in patients with encephalopathy, but they must be supplemented to provide complete nutrition.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane protein carboxyl methylation increases with human erythrocyte age. Evidence for an increase in the number of methylatable sites

The level of carboxyl methylation of membrane proteins has been measured in intact human erythrocyte populations of different ages separated by density gradient centrifugation. Age separation was confirmed by measurement of cytosolic pyruvate kinase specific activity in each fraction. When cells of different ages were incubated with L-[methyl-3H]methionine, the steady state level of 3H radioactivity covalently bound to membrane proteins is observed to be at least 3-fold higher in older erythrocytes. Because the specific radioactivity of the methyl group donor S-adenosyl-L-[methyl-3H]methionine was identical in all age fractions, this represents an increase in the extent of modification of membrane proteins by carboxyl methylation. Of the three major methylated erythrocyte membrane proteins, this increase in carboxyl methylation with age is 4 to 7-fold for bands 2.1 and 3, while the increase in band 4.1 is 3 to 4-fold. This increase in the steady state level of methylation with age cannot be explained by changes in either the intrinsic rate of methyl transfer or by changes in the rate constant of methyl turnover. We, therefore, propose that the age-dependent change in carboxyl methylation is due to an increase in the number of available acceptor sites as the erythrocyte ages in vivo. Since methylation of acidic residues on erythrocyte membrane proteins has been detected exclusively on D-aspartic acid residues (McFadden, P. N., and Clarke, S. (1982) Proc. Natl. Acad. Sci. U. S. A. 79, 2460-2464), these results are consistent with an accumulation of D-aspartic acid in membrane protein due to spontaneous racemization a the cell ages. The relationship of these observations to possible functions of erythrocyte membrane protein carboxyl methylation is discussed.