Ribozyme-mediated inhibition of HIV 1 suggests nucleolar trafficking of HIV-1 RNA.

The HIV regulatory proteins Tat and Rev have a nucleolar localization property in human cells. However, no functional role has been attributed to this localization. Recently it has been demonstrated that expression of Rev induces nucleolar relocalization of some protein factors involved in Rev export. Because the function of Rev is to bind HIV RNA and facilitate transport of singly spliced and unspliced RNA to the cytoplasm, it is likely that the nucleolus plays a critical role in HIV-1 RNA export. As a test for trafficking of HIV-1 RNAs into the nucleolus, a hammerhead ribozyme that specifically cleaves HIV-1 RNA was inserted into the body of the U16 small nucleolar RNA, resulting in accumulation of the ribozyme within the nucleoli of human cells. HeLa CD4(+) and T cells expressing this nucleolar localized ribozyme exhibit dramatically suppressed HIV-1 replication. The results presented here suggest a trafficking of HIV-1 RNA through the nucleoli of human cells, thus posing a different paradigm for lentiviral RNA processing.

Structures of five components of the actinomycin Z complex from Streptomyces fradiae, two of which contain 4-chlorothreonine.

Structure elucidation of five components of the actinomycin Z complex (Z(1)-Z(5)) isolated from Streptomyces fradiae is described. The components were separated by Si gel column chromatography and TLC/PLC and analyzed by ESIMS, FABMS, LC-MS of derivatized hydrolysates, and 2D NMR techniques. This permitted determination of the complete structures of actinomycins Z(1)-Z(5). In Z(3) and Z(5,) site 1 of the beta-depsipeptide is occupied by the rare 4-chloro-L-threonine, an amino acid not previously found in an actinomycin. The structural variants of the actinomycin Z complex have the molecular architecture typical of other actinomycins but possess greater structural diversity resulting from the presence of several highly unusual amino acids. Actinomycins Z(3) and Z(5,) but not Z(1), were more potent than actinomycin D in cytotoxicity assays against three tumor cell lines.

A clinical trial of retroviral-mediated transfer of a rev-responsive element decoy gene into CD34(+) cells from the bone marrow of human immunodeficiency virus-1-infected children.

Genetic modification of hematopoietic stem cells with genes that inhibit replication of human immunodeficiency virus-1 (HIV-1) could lead to development of T lymphocytes and monocytic cells resistant to HIV-1 infection after transplantation. We performed a clinical trial to evaluate the safety and feasibility of this procedure, using bone marrow from four HIV-1-infected pediatric subjects (ages 8 to 17 years). We obtained bone marrow, isolated CD34(+) cells, performed in vitro transduction with a retroviral vector carrying a rev-responsive element (RRE) decoy gene, and reinfused the cells into these subjects with no evidence of adverse effects. The levels of gene-containing leukocytes in peripheral blood samples in the 1 year after gene transfer/cell infusion have been extremely low. These observations support the potential of performing gene therapy for HIV-1 using hematopoietic cells, but emphasize the need for improved gene transfer techniques.

Gene transfer into human umbilical cord blood-derived CD34+ cells by particle-mediated gene transfer.

Delivery of genes into hematopoietic progenitor cells offers an attractive means for the introduction of corrective or protective genes into cells of both the myeloid and lymphoid lineage. Previously, investigators have often used murine retroviral vectors for gene delivery which require cells to be cycling for efficient delivery. We describe a nonviral method of gene delivery using particle-mediated gene transfer to obviate many disadvantages of viral vectors related to safety, production costs and the need for cell cycle proliferation. Using a CMV-CAT reporter plasmid, we show transfection of highly purified CD34+ cells isolated from umbilical cord blood. Effective gene transfer was shown in unstimulated and in growth-stimulated cells. Following transfection with a neomycin resistance gene, differentiation into cells of the myeloid lineage was observed, assayed by CFU-GM in the presence of G-418. Both unstimulated and stimulated cells gave rise to CFU-GM in the presence of G-418, indicating that stable expression of the neomycin resistance gene was maintained in early progenitors. These results demonstrate that particle-mediated gene transfer into human hematopoietic cells from umbilical cord blood can be achieved without affecting their CFU-GM differentiation potential. This gene transfer method offers an alternative approach to gene therapy studies involving human hematopoietic progenitor cells.

Infection of human marrow stroma by human immunodeficiency virus-1 (HIV-1) is both required and sufficient for HIV-1-induced hematopoietic suppression in vitro: demonstration by gene modification of primary human stroma.

Patients with human immunodeficiency virus-1 (HIV-1) infection often present with bone marrow (BM) failure that may affect all hematopoietic lineages. It is presently unclear whether this failure reflects a direct viral impairment of the CD34+ hematopoietic progenitor cells or whether the virus affects the BM microenvironment. To study the effects of HIV-1 on the BM microenvironment, we examined the stromal cell monolayers in long-term BM culture (LTBMC), which are the in vitro equivalent of the hematopoietic microenvironment. We assessed the hematopoietic support function (HSF) of human stromal layers by determining the cellular proliferation and colony-forming ability of hematopoietic progenitors from BM cells grown on the stromal layers. We show that the HSF is reduced by in vitro infection of the human stromal cell layer by a monocytotropic isolate of HIV-1 (JR-FL). There is no loss of HSF when the stromal cell layer is resistant to HIV-1 replication, either using murine stromal cell layers that are innately resistant to HIV-1 infection or using human stromal cells genetically modified to express a gene that inhibits HIV-1 replication (an RRE decoy). Decreased HSF was seen using either human or murine hematopoietic cells, if the stromal cells were human cells that were susceptible to HIV-1 infection. These in vitro studies implicate HIV-1 replication in the stroma as the essential component causing decreased hematopoietic cell production in HIV-1 infection.

Inhibition of human immunodeficiency virus-1 (HIV-1) replication after transduction of granulocyte colony-stimulating factor-mobilized CD34+ cells from HIV-1-infected donors using retroviral vectors containing anti-HIV-1 genes.

Transfer of "anti-HIV-1 genes" into hematopoietic stem cells of human immunodeficiency virus-1 (HIV-1)-infected individuals may be a potent therapeutic approach to render mature cells arising from transduced stem cells resistant to the destructive events associated with HIV-1 infection. To determine the feasibility of gene therapy for acquired immunodeficiency syndrome in individuals already infected with HIV-1, granulocyte colony-stimulating factor mobilized peripheral blood CD34+ cells were isolated from HIV-1-infected individuals and transduced with retroviral vectors containing three different anti-HIV-1-genes: the Rev binding domain of the Rev Responsive Element (RRE decoy) (L-RRE-neo), a double hammerhead ribozyme vector targeted to cleave the tat and rev transcripts (L-TR/TAT-neo), and the trans-dominant mutant of rev (M10) (L-M10-SN). As a control, a vector mediating only neomycin resistance (LN) was used. After 3 days of transduction on allogeneic stroma in the presence of stem cell factor, interleukin-6 (IL-6), and IL-3, the cultures were G418-selected, and then challenged with HIV-1(JR-FL) and a primary HIV-1 isolate. Compared with the control cultures, the L-RRE-neo-, L-TR/TAT-neo-, and L-M10-SN-transduced cultures displayed up to 1,000-fold inhibition of HIV-1 replication after challenge with HIV-1(JR-FL) and the primary HIV-1 isolate. Growth of the hematopoietic cells in long-term bone marrow culture was not perturbed by the presence of any of the anti-HIV-1 genes. This study shows that anti-HIV-1 genes can be introduced into CD34+ cells from individuals already infected with HIV-1, and strongly inhibit HIV-1 replication in primary monocytes derived from the CD34+ progenitors.

Suitability of bone marrow from HIV-1-infected donors for retrovirus-mediated gene transfer.

Bone marrow samples from 21 human immunodeficiency virus type 1 (HIV-1)-infected subjects were evaluated for their suitability for retrovirus-mediated gene transduction with anti-HIV-1 genes. The percentages of CD34+ cells that could be isolated from the mononuclear fraction of bone marrow samples were determined. Fifteen of the 21 marrow samples had normal percentages of CD34+ cells isolated by immunomagnetic methods. All seven donors with CD4 counts > 100/mm3 had normal percentages of CD34+ cells; of 14 patients with low CD4 cell counts (< 100/mm3), 5 had reduced and 9 had normal percentages of CD34+ cells. Samples of the marrow were plated in a methylcellulose colony-forming unit (CFU) assay to determine the clonogenic capacity of the progenitor cells. Overall, the marrow samples from HIV-infected donors showed a 44% reduction in CFU derived from the mononuclear cell fraction and a 75% reduction in CFU derived from the isolated CD34+ cell fraction, when compared to marrow samples from uninfected donors. Isolated CD3+ cells were transduced with retroviral vectors containing various anti-HIV-1 genes to determine their susceptibility to gene transfer. Transduction of the clonogenic CD34+ cells by retroviral vectors did not differ among marrow samples from 13 HIV-1+ donors and 9 uninfected donors. Long-term bone marrow cultures established from the transduced CD34+ cells demonstrated equivalent survival of clonogenic progenitor cells from both HIV-1-infected and uninfected marrows. Toxicity from expression of the anti-HIV-1 genes was not observed; the percentages of clonogenic progenitor cells that survived in cultures transduced by vectors carrying anti-HIV-1 genes were similar to those transduced by the control LN vectors. Stromal cells cultured from marrow samples from HIV-1-infected donors showed similar growth kinetics, hematopoietic support function, and enhancement of retrovirus-mediated transduction of CD34+ cells as seen with stromal cells cultured from uninfected marrow donors. Semi-quantitative polymerase chain reaction (PCR) was performed before and after ex vivo transduction to determine the frequency of HIV-1-containing cells in the CD34+ cell preparations. Although HIV-1+ cells were present at low levels in the mononuclear cell fractions of some of the marrow samples, the CD34+ cell preparation from only one marrow sample contained detectable HIV-1 positive cells (< 1 positive cell/100,000 by PCR) prior to transduction. None of the CD34+ cell preparations contained detectable HIV-1 after transduction. These studies demonstrate that HIV-1-infected patients are candidates for retrovirus-mediated transduction of anti-HIV-1 genes in bone marrow gene therapy clinical trials.

Transduction of human CD34+ hematopoietic progenitor cells by a retroviral vector expressing an RRE decoy inhibits human immunodeficiency virus type 1 replication in myelomonocytic cells produced in long-term culture.

Genetic modification of hematopoietic stem cells with a synthetic "anti-human immunodeficiency virus type 1 (HIV-1) gene" which inhibits replication of HIV-1 may allow production of mature lymphoid and monocytic cells resistant to HIV-1 growth after autologous transplantation. Because productive HIV-1 replication requires binding of the Rev protein to the Rev-responsive element (RRE) within the viral transcripts for the HIV-1 structural proteins, anti-HIV-1 gene products which interfere with Rev-RRE interactions may inhibit HIV-1 replication. One such strategy involves overexpression of the RRE sequences in transcripts derived from retroviral vectors to act as decoys to sequester Rev protein and prevent its binding to the RRE element in HIV-1 transcripts. We developed an in vitro model to test the efficacy of this gene therapy approach in primary human hematopoietic cells. Human CD34+ hematopoietic progenitor cells from normal bone marrow or umbilical cord blood were transduced with retroviral vectors carrying RRE decoy sequences as part of a long terminal repeat-directed transcript expressing the neo gene (L-RRE-neo) or with a control vector expressing only the neo gene (LN). The transduced progenitors were allowed to differentiate into mature myelomonocytic cells which were able to support vigorous growth of the monocytotropic isolate of HIV-1, JR-FL. HIV-1 replication was measured in unselected cell populations and following G418 selection to obtain uniformly transduced cell populations. Inhibition of HIV-1 replication in the unselected cell cultures was between 50.2 and 76.7% and was highly effective (99.4 to 99.9%) in the G418-selected cultures. Progenitors transduced by either the L-RRE-neo vector or the control LN vector were identical with respect to hematopoietic growth and differentiation. These findings demonstrate the ability of an RRE decoy strategy to inhibit HIV-1 replication in primary human myelomonocytic cells after transduction of CD34+ progenitor cells, without adverse effects on hematopoietic cell function.

Expression of hammerhead ribozymes by retroviral vectors to inhibit HIV-1 replication: comparison of RNA levels and viral inhibition.

We have analyzed expression of anti-HIV-1 hammerhead ribozymes in the context of retroviral vectors. To determine optimal vector designs for ribozyme expression, we compared three vectors, each of which contained the same pair of anti-HIV-1 hammerhead ribozymes in tandem. Despite the presence of vastly different amounts of vector-derived flanking sequences, the ribozymes produced by each vector had similar cleavage activity when assayed in vitro. The ribozyme vectors were packaged into amphotropic virion and used to transduce human CEM T lymphocytes. Analysis by Northern blot and RNAse protection assays demonstrated that the highest steady-state levels of ribozyme-containing transcripts were produced by a vector in which the ribozymes were expressed under transcriptional control of the vector MoMuLV LTR. Despite these differences in the levels of ribozyme transcripts achieved by the vectors, their ability to confer resistance to HIV-1 replication was similar. Therefore, other factors than the absolute levels of ribozymes play a role in determining the effectiveness of ribozyme vectors to inhibit HIV-1. These may include structural features of the transcripts that affect the antisense effects of the ribozyme constructs, the actual catalytic activity of the ribozymes, their RNA folding, the binding of proteins, and the intracellular localization. Greater understanding of these factors may permit more effective application of ribozymes to inhibit gene expression.

Inhibition of HIV-1 in human T-lymphocytes by retrovirally transduced anti-tat and rev hammerhead ribozymes.

Gene therapy for AIDS requires the identification of genes which effectively inhibit HIV-1 replication coupled to an efficient vector system for gene delivery and expression. Hammerhead ribozymes are RNA molecules capable of catalytic cleavage of complementary RNA molecules. Ribozymes targeted against two portions of the HIV-1 genome were designed to cleave HIV RNA in the tat gene (TAT) or in a common exon for tat and rev (TR). The ribozymes were cloned into the LN (LTR-neomycin) retroviral vector plasmids and expressed as part of viral LTR-driven transcripts. The vectors were packaged as amphitropic virions and used to transduce human T-lymphocytes. Expression of the vector transcripts containing the ribozyme sequences was readily detected by Northern blot analysis of the transduced T cells. The T-lymphocytes expressing the anti-HIV-1 ribozymes showed resistance to HIV-1 replication. In contrast, cells expressing mutant ribozymes, containing substitutions of a key nucleotide in the catalytic domain which cripples the cleavage activity of the ribozymes, supported replication of HIV-1, demonstrating that the functional ribozymes were cleaving the target RNAs. These studies demonstrate that retrovirally transduced ribozymes included in long, multifunctional transcripts, can inhibit HIV replication in human T-lymphocytes. The ribozyme and expression strategies described here should be useful for the gene therapy of AIDS by conferring resistance to HIV-1 replication on cells derived from transduced hematopoietic stem cells.

Comparison of trans-dominant inhibitory mutant human immunodeficiency virus type 1 genes expressed by retroviral vectors in human T lymphocytes.

trans-Dominant inhibitory mutant versions of the human immunodeficiency virus type 1 (HIV-1) regulatory genes tat and rev have previously been described. We have constructed a series of retroviral vectors to transduce these genes and compare their inhibitory activities. The inhibitory activities were measured with transient transfection assays by using a reporter which expresses an HIV-1 gag-Escherichia coli lacZ fusion protein with strict dependence on coexpression of both tat and rev. Additionally, the vectors were packaged as amphotropic virions and used to stably transduce human CEM T lymphocytes. The transduced CEM cells were challenged with HIV-1, and the effects of the mutant HIV-1 genes were determined by measuring the levels of HIV-1 p24gag produced. A tat gene substituted at amino acid 41 (tatk41a) retained partial trans-activating activity and lacked inhibitory activity. A tat gene with a premature stop codon at amino acid 54 (tat54ter) showed moderate trans-dominant inhibition of the reporter plasmid but failed to significantly inhibit HIV-1 replication. The M10 rev mutant, with a 2-amino-acid substitution, showed strong trans-dominant inhibitory activity both in the reporter plasmid and in the HIV-1 infection assay. The greatest inhibition of HIV-1 growth was seen when M10 was expressed under the transcriptional control of a human cytomegalovirus promoter; slightly less inhibition was achieved when expression of M10 was controlled by the Moloney murine leukemia virus long terminal repeat, and minimal inhibition was seen when the HIV-1 long terminal repeat controlled the M10 gene. These results demonstrate the potential utility of retroviral vectors expressing trans-dominant inhibitory mutant HIV-1 genes for gene therapy approaches to AIDS.

Retroviral-mediated transfer of the human glucocerebrosidase gene into cultured Gaucher bone marrow.

Gaucher disease, a lysosomal glycolipid storage disorder, results from the genetic deficiency of an acidic glucosidase, glucocerebrosidase (GC). The beneficial effects of allogeneic bone marrow transplantation (BMT) for Gaucher disease suggest that GC gene transduction and the transplantation of autologous hematopoietic stem cells (gene therapy) may similarly alleviate symptoms. We have constructed a retroviral vector, L-GC, produced by a clone of the amphotropic packaging cell line PA317, which transduces the normal human GC cDNA with high efficiency. Whole-marrow mononuclear cells and CD34-enriched cells from a 4-yr-old female with type 3 Gaucher disease were transduced by the L-GC vector and studied in long-term bone marrow culture (LTBMC). Prestimulation of marrow with IL-3 and IL-6, followed by co-cultivation with vector-producing fibroblasts, produced gene transfer into 40-45% of the hematopoietic progenitor cells. The levels of GC expression in progeny cells (primarily mature myelomonocytic) produced by the LTBMC were quantitatively analyzed by Northern blot, Western blot, and glucocerebrosidase enzyme assay. Normal levels of GC RNA, immunoreactive protein, and enzymatic activity were detected throughout the duration of culture. These studies demonstrate that retroviral vectors can efficiently transfer the GC gene into long-lived hematopoietic progenitor cells from the bone marrow of patients with Gaucher disease and express physiologically relevant levels of GC enzyme activity.

Two different genes coding for processable and nonprocessable forms of a viral envelope protein can account for the apparent hormonal stimulation of protein processing in W7MG1 lymphoma cells.

In the mouse mammary tumor virus (MMTV)-infected mouse T-lymphoma cell line W7MG1, glucocorticoid hormone regulates two aspects of MMTV gene expression: hormone stimulates MMTV gene transcription and increases the ratio of mature envelope proteins to envelope precursor protein produced. To separate these two effects and determine the mechanism by which hormone regulates the conversion of the envelope precursor Pr74 to the mature cleaved products gp52 and gp33, we constructed expression vectors in which the envelope gene is constitutively transcribed. Surprisingly, the envelope precursor protein Pr74 encoded by two independently isolated, allelic envelope genes behaved differently. Pr74-P (encoded by the ENV/P gene) was processed efficiently to the mature products gp52 and gp33, independently of the level of expression, hormonal induction of cellular genes, or the presence of other MMTV proteins. In contrast, under the same conditions, Pr74-N (encoded by the ENV/N gene) was not processed further despite being relatively stable. In sucrose gradient analyses, Pr74-P sedimented as monomers, whereas Pr74-N was found in high mol wt aggregates of heterogeneous size. Coimmunoprecipitation analysis determined that Pr74-N associated with BiP, whereas Pr74-P did not. This is indicative of improper folding of Pr74-N in the endoplasmic reticulum.(ABSTRACT TRUNCATED AT 250 WORDS)

Toward gene therapy for Gaucher disease.

We are studying the transfer and expression by retroviral vectors of the human glucocerebrosidase (GC) gene into bone marrow cells as a model of gene therapy for genetic diseases of hematopoietic cells. A simple retroviral vector (G2) was developed that contains a normal human GC cDNA under the control of the Moloney murine leukemia virus long-terminal repeat (LTR) enhancer/promoter. Murine bone marrow was transduced with the G2 vector and maintained in long-term bone marrow culture (LTBMC). Expression of the human GC gene in the transduced murine LTBMC cells exceeded the level of endogenous murine GC mRNA. Murine bone marrow cells were also transduced with G2 and transplanted into irradiated syngeneic recipients. High levels of GC gene transfer and expression were seen in day-12 CFU-S foci, and to a lesser extent in the hematopoietic organs 4 months after gene transfer/bone marrow transplant (BMT). Human bone marrow, from a patient with Gaucher disease, was also used in studies of GC gene transduction. Gene transfer into 35-40% of the Gaucher hematopoietic progenitor cells was achieved, following prestimulation of the marrow with recombinant hematopoietic growth factors. Equal rates of gene transfer were obtained using either total marrow mononuclear cells or progenitor cells enriched 100-fold by immunomagnetic bead separation. GC gene transduction corrected the enzymatic deficiency of the Gaucher marrow. Our results demonstrate the potential utility of retroviral vector-mediated gene transfer for gene therapy of Gaucher disease. Current efforts are aimed at achieving more consistent in vivo GC expression in the murine BMT model and demonstrating transduction of pluripotent human hematopoietic stem cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the genome of potato leafroll virus: readthrough of the coat protein termination codon in vivo.

An antiserum was raised against a fusion protein containing part of the 56K polypeptide (P5) encoded by the open reading frame (ORF) at the 3' end of the genome of potato leafroll virus (PLRV). This antiserum reacted specifically with 80K and 90K polypeptides in PLRV-infected protoplasts, with a 90K polypeptide in infected potato tissue and with a 53K polypeptide in protein extracted from purified particles of PLRV. Monoclonal antibodies raised against purified PLRV particles also reacted with these polypeptides, as well as with the 23K coat protein. Virus particles partially purified from infected protoplasts contained some 90K polypeptide as well as the major 23K coat protein. The ORFs of the 23K coat protein and P5 are contiguous and in frame. The results suggest that the P5 polypeptide of PLRV occurs in infected cells as part of a readthrough protein comprising the 23K coat protein joined to the P5 amino acid sequence. Moreover the readthrough protein can be assembled into virus particles as a minor component together with the main 23K component. The P5 protein may thus contribute to properties of PLRV determined by its virus particle surface.