Self-inactivating lentiviral vectors with U3 and U5 modifications

Lentiviral vectors have gained much attention in recent years mainly because they integrate into nondividing host-cell genomes. For clinical applications, a safe and efficient lentiviral vector system is required. Previously, we have established a human immunodeficiency virus type 1 (HIV-1)-derived three-plasmid lentiviral vector system for viral vector production which includes a packaging vector pHP, a transducing vector pTV, and an envelope-encoding plasmid pHEF-VSVG. Cotransfection of these three plasmids into TE671 human rhabdomyosarcoma cells routinely yields 10(5)-10(6) infectious units per milliliter in 24 h. Here we have extensively modified long terminal repeats (LTRs) of pTV to generate a safer lentiviral vector system. The 5' U3 was replaced with a truncated cytomegalovirus (CMV) immediate early (IE) enhancer/TATA promoter and the 3' U3 (except for the integration attachment site) was also deleted. These modifications resulted in a vector with 80% wild-type vector efficiency. Further deletion of 3' U5 impaired vector function; however, this problem was solved by replacing the 3' U5 with bovine growth hormone polyadenylation (bGHpA) sequence. The pTV vector containing all these modifications including the 5' promoter substitution, the 3' U3 deletion, and the substitution of 3' U5 with bGHpA exhibited a self-inactivating (SIN) phenotype after transduction, transduced both dividing and nondividing cells at similar efficiencies, and produced vector titers twice as high as that of the wild-type construct. Thus, both safety and efficacy of the HP/TV vector have been improved by these LTR modifications. Further deletion of 5' U5 impaired vector efficiency, suggesting that the 5' U5 has critical roles in vector function.

Contributions of viral splice sites and cis-regulatory elements to lentivirus vector function

The mobile transgene constructs of most human immunodeficiency virus (HIV)-based lentivirus vectors currently in use contain viral long terminal repeats, a 5' untranslated region, gag sequences, and env sequences that include the Rev-responsive element (RRE). In this study, we examined the possibility of deleting HIV splice sites and gag and env sequences from an HIV type 1 recombinant vector established in our laboratory as part of our ongoing efforts to improve this vector system. Mutations in the major splice donor site (SD) markedly reduced viral RNA expression but had little effect on vector titer. Deletion of gag or env sequences, excluding RRE, led to a moderate reduction in vector titer. Interestingly, deletion of RRE slightly reduced viral RNA expression but markedly impaired vector function. Combined deletions of RRE, gag (except for the first 40 nucleotides), env, and the SD mutation resulted in a twofold increase in cytoplasmic viral RNA expression and a recovery of vector efficiency to approximately 50% of the wild-type level. This increase in cytoplasmic RNA levels is likely to be due, at least in part, to effects of the TE671 host cells, a human rhabdomyosarcoma cell line used for vector production in our system, on the cytoplasmic distribution of spliced and unspliced viral RNA. These results show that optimal lentivirus vector function can be maintained in the absence of multiple essential viral elements.

Efficacy and safety analyses of a recombinant human immunodeficiency virus type 1 derived vector system

Lentiviruses infect both dividing and nondividing cells. In this study we characterized a lentiviral vector system consisting of a packaging vector (pHP) and a transducing vector (pTV) derived from a recombinant human immunodeficiency virus type 1 (HIV-1). In pHP, the long terminal repeats (LTRs), the 5' untranslated leader and portions of the env and nef genes were deleted. The leader sequence of pHP was substituted with a modified Rous sarcoma virus (RSV) 59 bp leader containing a mutated RSV gag AUG and a functional 5' splice site. The pHP construct was found to direct Gag-Pol synthesis as efficiently as wild-type HIV-1. The pTV construct contains sequences required for RNA packaging, reverse transcription and integration, but lacks viral genes. Co-transfection of pHP, pTV and a vesicular stomatitis virus G (VSV-G) envelope plasmid produced vectors at titers of 10(5)-10(6) transducing units per milliliter in 48 h. Replication-competent virus (RCV) was not detected when deletions were made in the env gene in pHP. The ability of this vector system to transduce dividing and nondividing cell in vitro and in vivo was also demonstrated. Compared with a Moloney murine leukemia virus (MLV) vector, the HP/TV vectors transduced human muscle-, kidney-, liver-derived cell lines and CD34+ primary hematopoietic progenitor cells more efficiently. Although the levels of the pTV transgene expression were high soon after transduction, the expression tended to decrease with time due either to the loss of proviral DNA or to the inactivation of promoter activity, which was found to be cell type-dependent. Analyses of extrachromosomal DNA showed that the unintegrated proviral DNA of lentiviral vectors survived much longer than that of the retroviral vectors. We demonstrate that the HP/TV vector is capable of high efficiency transduction and that long-term expression of lentiviral vectors is dependent on target cell type, the internal promoter and the transgene itself in the transducing vector.

Decreased brain protein levels of cytochrome oxidase subunits in Alzheimer's disease and in hereditary spinocerebellar ataxia disorders: a nonspecific change?

Controversy exists as to the clinical importance, cause, and disease specificity of the cytochrome oxidase (CO) activity reduction observed in some patients with Alzheimer's disease (AD). Although it is assumed that the enzyme is present in normal amount in AD, no direct measurements of specific CO protein subunits have been conducted. We measured protein levels of CO subunits encoded by mitochondrial (COX I, COX II) and nuclear (COX IV, COX VIc) DNA in autopsied brain of patients with AD whom we previously reported had decreased cerebral cortical CO activity. To assess disease specificity, groups of patients with spinocerebellar ataxia type I and Friedreich's ataxia were also included. As compared with the controls, mean protein concentrations of all four CO subunits were significantly decreased (-19 to -47%) in temporal and parietal cortices in the AD group but were not significantly reduced (-12 to -17%) in occipital cortex. The magnitude of the reduction in protein levels of the CO subunits encoded by mitochondrial DNA (-42 to -47%) generally exceeded that encoded by nuclear DNA (-19 to -43%). In the spinocerebellar ataxia disorders, COX I and COX II levels were significantly decreased in cerebellar cortex (-22 to -32%) but were normal or close to normal in cerebral cortex, an area relatively unaffected by neurodegeneration. We conclude that protein levels of mitochondrial- and nuclear-encoded CO subunits are moderately reduced in degenerating but not in relatively spared brain areas in AD and that the decrease is not specific to this disorder. The simplest explanation for our findings is that CO is decreased in human brain disorders as a secondary event in brain areas having reduced neuronal activity or neuronal/synaptic elements consequent to the primary neurodegenerative process.

Genetically modified dermal keratinocytes express high levels of transforming growth factor-beta1

In an attempt to genetically modify cultured keratinocytes with transforming growth factor-beta1 (TGF-beta1), which has been proven to be one of the most important cytokines involved in wound healing, two constructs were made. One, designated pG3Z:K14-TGF-beta1, is a plasmid in which the expression of TGF-beta1 is driven by the keratin 14 promoter. The other, designated pLin-TGF-beta1, is a retroviral vector in which the retroviral 5' long-terminal repeat promoter drives expression. In both constructs, the deletion of a small fragment of the noncoding region of the TGF-beta1 gene was made to differentiate the transcript from that for endogenously expressed TGF-beta1. Different types of cells were transfected with the pG3Z:K14-TGF-beta1 construct using the calcium phosphate method. The pLin-TGF-beta1 construct was propagated in a retroviral packaging cell line and conditioned medium that contained high titers of the virus was used to transduce keratinocytes or other types of cells grown in standard culture. Northern analysis, used to evaluate the expression of TGF-beta1 mRNA in the pG3Z:K14-TGF-beta1 transfected keratinocyte C1-177 cell line, showed a smaller TGF-beta1 transcript compared with that endogenously expressed by dermal fibroblasts. The level of TGF-beta1 protein evaluated by enzyme-linked immunosorbent assay was significantly higher in medium conditioned by either the K14-TGF-beta1 transfected or the pLin-TGF-beta1 transduced keratinocytes, compared with that obtained from control cells; however, the level of TGF-beta1 protein was unchanged in cultures of pG3Z:K14-TGF-beta1 transfected nonkeratinocyte cells such as fetal and adult fibroblasts. Using the mink lung epithelial cell growth inhibition assay, we found an increase in TGF-beta1 activity in conditioned medium from the pG3Z:K14-TGF-beta1 transfected cells. To evaluate possible paracrine effects of the keratinocyte derived TGF-beta1, a coculture system was established with pLin-TGF-beta1 transduced keratinocytes grown in the upper chamber and dermal fibroblasts in the lower chamber. The results showed that TGF-beta1 released from keratinocytes diffused to the lower chamber where it stimulated collagen production by dermal fibroblasts. In summary, we demonstrate here that primary cultured keratinocytes can be genetically modified to express high levels of TGF-beta1 and suggest that this offers a potential approach for the therapy of dermal lesions such as nonhealing wounds.

Expression of functional human recombinant interleukin-12 and development of a new reliable bioassay by interferon-gamma ELISPOT

Interleukin-12 (IL-12) is one of the important cytokines for promoting the differentiation and maturation of type 1 T helper cells and facilitating the initiation of cell-mediated immune responses. Because of its multi-functional roles in anti-tumor and anti-viral immunity, IL-12 is considered a promising therapeutic cytokine in immunotherapy against cancer and infectious diseases. To evaluate the therapeutic efficacy, an easy and reliable quantitative assay for functional IL-12 is essential. Presently, IL-12 concentration is often determined by ELISA or RIA, which may or may not correlate with IL-12 biological function. Established IL-12 bioassays are based on a time-consuming lymphocyte proliferation assay and require freshly isolated peripheral blood lymphocytes.

Development of replicative and nonreplicative hepatitis B virus vectors

To investigate the possibility of using hepatitis B virus (HBV) as a vector, the tat gene from human immunodeficiency virus type 1 (HIV-1) was inserted into the full-length HBV genome in-frame with the polymerase (pol) open reading frame in the tether region and downstream of the preS1 promoter. We demonstrated that the tat gene was expressed with full activity in transactivating the HIV-1 long terminal repeat (LTR). The expression of the tat gene in the context of the HBV genome in chicken hepatoma and human cervical carcinoma cells, however, was not as efficient as that in human hepatoblastoma cells, which reflects the cellular and species specificity of promoters of hepadnaviruses. Detection of RNA expressed from this HBVtat recombinant revealed transcription of the tat gene by two promoters: the core/pol promoter and the preS1 promoter. A Pol-Tat fusion protein expressed by the core/pol promoter did not seem to contribute to the tat transactivation activity of the HBVtat recombinant since a frameshift mutation in the pol gene did not affect the recombinant tat function. The functional tat protein, therefore, was most likely expressed as a Tat-Pol fusion product. Endogenous polymerase assays showed that the pol protein expressed from the HBVtat recombinant was still active although at a reduced level. Hepatitis B surface antigens and e antigen produced from this recombinant were detected at similar levels as those produced from the wild type. Notably, the capability of forming complete HBV particles was still retained. These studies indicate the potential of constructing HBV as a replicative vector. We also showed that manipulation of a nonreplicative HBV vector was possible. Expression of the HBV polymerase could be completely eliminated and replication of the nonreplicative HBV recombinant could be supported by Pol transcomplementation.

Placental trophoblasts resist infection by multiple human immunodeficiency virus (HIV) type 1 variants even with cytomegalovirus coinfection but support HIV replication after provirus transfection

Whether cell-free human immunodeficiency virus type 1 (HIV-1) can productively infect placental trophoblasts (which in turn could transmit the virus into the fetal circulation) is controversial but essential to know for the evaluation of alternative routes (such as cell-mediated infection or trophoblast damage). We have addressed infection factors such as cell purity, source, culture methods, and activation states as well as virus variant and detection methods to conclusively determine the outcome of trophoblast challenge by free virus. Pure (> 99.98%) populations of trophoblasts from 11 different placentas were challenged at a multiplicity of infection (MOI) as high as 6 with five different HIV-1 variants, three of which are non-syncytium-forming, macrophage-tropic isolates from infected infants, with and without coinfection with cytomegalovirus; these preparations were monitored for productive infection for up to 3 weeks after challenge by five different criteria, the most sensitive of which were cocultivation with target cells that can detect virus at an MOI of 10(-7) and HIV DNA PCR that detects 30 virus copies per 10(5) cells. Infection was never detected. However, molecularly cloned T-cell (pNL4-3)- and macrophage (pNLAD8)-tropic provirus plasmids, when transfected into primary trophoblasts, yielded productive infections, indicating that trophoblasts do not suppress late-stage virus replication and assembly. Because of the purity of the trophoblast preparations, the extended length of the infection culture period, the number of trophoblast preparations and virus types examined, the sensitivity of the bioassays and molecular detection assays, and the observations that trophoblasts can support virus replication from provirus, the results of this study strongly argue that free virus cannot infect primary villous trophoblasts.

Granulocyte-macrophage colony-stimulating factor and B7-2 combination immunogene therapy in an allogeneic Hu-PBL-SCID/beige mouse-human glioblastoma multiforme model

Glioblastoma multiforme is the most common primary central nervous system neoplasm. Its dismal prognosis has led to investigation of new treatment strategies such as immunogene therapy. We transduced the human glioblastoma cell line D54MG in vitro with genes encoding the proinflammatory cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF), the T cell co-stimulatory molecule B7-2, or both (in a bicistronic vector) via retroviral vectors. Therapeutic gene expression by D54MG was high after transduction and selection (30 ng/10(6) cells/day for GM-CSF and > 2 orders of magnitude fluorescence shift on flow cytometry for B7-2). The effect of GM-CSF and/or B7-2 transduction on D54MG tumor growth in vivo was monitored in a novel allogeneic human peripheral blood lymphocyte-severe combined immunodeficiency mouse (Hu-PBL-SCID) model. GM-CSF- or B7-2-transduced tumors showed growth suppression in hu-PBL-reconstituted mice compared to untransduced and/or unreconstituted controls. Growth suppression was greatest for B7-2. Furthermore, vaccination with irradiated GM-CSF/B7-2-transduced tumor cells markedly inhibited growth of wild-type tumors at distant sites. Thus, this study illustrates a potential gene therapy strategy for glioblastoma multiforme patients using GM-CSF and/or B7-2 transduced tumor vaccines. Although extension of these allogeneic studies to an autologous system is critical, this is the first demonstration of in vivo efficacy of combination GM-CSF and B7-2 immunogene therapy for human glioblastoma multiforme.

Computer-assisted, quantitative cytokine enzyme-linked immunospot analysis of human immune effector cell function

Originally developed for detecting antibody production from B lymphocytes, the enzyme-linked immunospot (ELISPOT) assay was later modified to assess cytokine production from various immune effector cells. Although the ELISPOT assay can detect antibody or cytokine production at the single-cell level, the visual counting of spots in a 96-well plate under a microscope makes this method unsuitable for handling large sample sizes. Here, we introduce a computer-assisted image analysis system to overcome this problem. This system makes the data analysis step of the ELISPOT assay convenient, objective, sensitive and suitable for handling large sample pools. Studies requiring lymphocyte proliferation assay, cytotoxic lymphocyte assay and precursor frequency assay can be conducted through the ELISPOT assay. This is demonstrated here using examples such as mixed lymphocyte allogeneic reactions and human immunodeficiency virus antigen-specific, cell-mediated immune responses.

Striatal dopamine nerve terminal markers but not nigral cellularity are reduced in spinocerebellar ataxia type 1

We previously reported markedly reduced (-76%) dopamine (DA) levels in the putamen of seven patients with spinocerebellar ataxia type 1 (SCA1) who had no evidence of nigral cell loss or parkinsonism. To determine whether the DA reduction was accompanied by loss of DA nerve terminals, we measured levels of the DA transporter ([3H]WIN, 35,428 binding; DA transporter protein) and the vesicular monoamine transporter ([3H]DTBZ binding) in the putamen of these patients. As compared with the controls (n = 14), mean putamen concentrations of [3H]WIN 35,428 binding (-45%), dopamine transporter protein (-61%), and [3H]DTBZ binding (-48%) were significantly reduced in this SCA1 subgroup. We conclude that the degeneration in nigrostriatal DA neurons begins at the nerve ending in SCA1.

Cell cycle inhibitory effects of HIV and SIV Vpr and Vpx in the yeast Schizosaccharomyces pombe

The Vpr gene of human immunodeficiency virus type 1 and type 2 (HIV-1, HIV-2) and simian immunodeficiency virus (SIV) encodes a small nuclear protein which is virion-associated and assists nuclear transport of the preintegration complex. Expression of HIV-1 Vpr has been shown to induce differentiation and prevent proliferation of human cells. HIV-1 Vpr has also been shown to arrest cell growth and cause morphological defects in yeast. In contrast, the Vpx gene of HIV-2 and SIV, which shares sequence homology with Vpr, does not seem to inhibit proliferation of human cells. It has been suggested that the cell cycle arrest effect of Vpr and Vpx is species and cell-type dependent. In this study, we have taken advantage of a conditional expression system to characterize the growth inhibitory effects of Vpr and Vpx of HIV-1, HIV-2, and SIV in the fission yeast Schizosaccharomyces pombe. Our results show that both Vpr and/or Vpx of HIV-1, HIV-2, and SIV arrest cell growth in S. pombe, and HIV-1 Vpr is more cytotoxic than HIV-2 or SIV Vpr or Vpx. Flow cytometry analysis indicated that yeast cells cease proliferating with DNA contents indicative of arrest in G1 and G2, with some cells showing signs of overreplication of DNA. While the observed cell cycle arrest phenotype was not identical to that observed in mammalian cells, there were similarities of growth arrest phenotype caused by Vpr and Vpx in yeast and mammalian cells. Specifically, the observation that yeast and mammalians cell both arrest in G2 with reduced p34/cdc2 kinase activity indicates that Vpr and Vpx interact with conserved target(s) in yeast and mammalian cells. The ability to use genetic analysis to elucidate the mechanisms involved makes S. pombe an excellent model system in which to study the effects of Vpr and Vpx on cellular function.

Protective immunity to HIV-1 in SCID/beige mice reconstituted with peripheral blood lymphocytes of exposed but uninfected individuals

Immunodeficiency typically appears many years after initial HIV infection. This long, essentially asymptomatic period contributes to the transmission of HIV in human populations. In rare instances, clearance of HIV-1 infection has been observed, particularly in infants. There are also reports of individuals who have been frequently exposed to HIV-1 but remain seronegative for the virus, and it has been hypothesized that these individuals are resistant to infection by HIV-1. However, little is known about the mechanism of immune clearance or protection against HIV-1 in these high-risk individuals because it is difficult to directly demonstrate in vivo protective immunity. Although most of these high-risk individuals show an HIV-1-specific cell-mediated immune response using in vitro assays, their peripheral blood lymphocytes (PBLs) are still susceptible to HIV infection in tissue culture. To study this further in vivo, we have established a humanized SCID mouse infection model whereby T-, B-, and natural killer-cell defective SCID/beige mice that have been reconstituted with normal human PBLs can be infected with HIV-1. When the SCID/beige mice were reconstituted with PBLs from two different multiply exposed HIV-1 seronegative individuals, the mice showed resistance to infection by two strains of HIV-1 (macrophage tropic and T cell tropic), although the same PBLs were easily infected in vitro. Mice reconstituted with PBLs from non-HIV-exposed controls were readily infected. When the same reconstituted mice were depleted of human CD8 T cells, however, they became susceptible to HIV-1 infection, indicating that the in vivo protection required CD8 T cells. This provides clear experimental evidence that some multiply exposed, HIV-1-negative individuals have in vivo protective immunity that is CD8 T cell-dependent. Understanding the mechanism of such protective immunity is critical to the design and testing of effective prophylactic vaccines and immunotherapeutic regimens.

Myopathy and spontaneous Pasteurella pneumotropica-induced abscess formation in an HIV-1 transgenic mouse model

In an effort to augment human immunodeficiency virus type 1 (HIV-1) gene expression in transgenic mice, an infectious proviral DNA clone was modified by deleting the two NF kappa B binding sites and some adjacent upstream LTR sequences and replacing them with the core enhancer of Moloney murine leukemia virus (MLV). Two independent lines of MLV/HIV transgenic mice were established that expressed HIV-1-specific RNA in lymphoid tissue, striated skeletal muscle, and the eye lens. Heterozygous animals from each transgenic line spontaneously developed an inflammatory disease of the eye associated with the production of copious amounts of purulent lacrimal secretions beginning at 2 weeks of age. Periorbital abscess formation became grossly apparent by 2 months of age and Pasteurella pneumotropica was cultured from the harderian glands and conjunctival surfaces of many of the MLV/HIV animals but not their nontransgenic, cohabiting littermates. This gram-negative commensal bacterium has been previously associated with a similar disease phenotype in immunocompromised (e.g., nude mice) rodent colonies. MLV/HIV mice developed normally until 15 weeks of age, when weight loss and wasting occurred, culminating in premature death (as earlier as 6 months of age). The cachexia was associated with an initially focal and subsequently progressive myopathy, coinciding with age-related increases of HIV gene expression in muscle.

Models of HIV type 1 proviral gene expression in wild-type HIV and MLV/HIV transgenic mice

Two proviral HIV transgenic mouse models, one bearing wild-type HIV proviral DNA and the other a modified provirus in which the viral LTRs contained the core enhancer of the Moloney murine leukemia virus (MLV), were compared. The MLV/HIV chimeric LTR, in which the MLV enhancer replaced the NF-kappa B-binding motifs, was transcriptionally active in human and murine cells in vitro and virus containing the chimeric LTR was replication competent in human cell cultures. Transgenic mice derived from microinjections of chimeric MLV/HIV proviral DNA transcribed HIV genes at a greater frequency and at higher levels than wild-type HIV proviral transgenic mice. MLV/HIV mice were also more apt to develop disease; wasting, periocular infections, and a degenerative myopathy characterized the most predominant phenotype. The tissue specificities of the wild-type and chimeric LTRs in transgenic mice were remarkably similar, but a significant difference was apparent in lymphoid cells. Basal level and LPS-inducible HIV gene expression occurred in peritoneal and bone marrow-derived macrophages from wild-type HIV transgenic mice. In contrast, HIV gene expression in macrophages from MLV/HIV mice was undetectable, even following LPS induction. However, cultured splenocytes from MLV/HIV mice supported HIV proviral gene transcription better than splenocytes from HIV mice, particularly after induction with LPS or anti-IgD antibody but not with concanavalin A. These data suggest that in transgenic mice, the HIV and MLV/HIV LTRs display a differential tropism for macrophages and B cells, respectively. HIV and MLV/HIV transgenic mice represent alternative models amenable to in vivo studies of HIV gene regulation in lymphoid cells, the induction of HIV-related disease and the evaluation of anti-HIV therapies.

Infection and replication of Tat- human immunodeficiency viruses: genetic analyses of LTR and tat mutations in primary and long-term human lymphoid cells

Tat is an essential regulatory protein for the replication of human immunodeficiency virus (HIV). Mutations in the tat gene have been shown to block HIV replication in human T cells. Several studies have established that Tat releases an elongation block to the transcription of HIV long terminal repeat (LTR); however, it is not known whether this mechanism alone is sufficient to explain the block to HIV replication in human T cells when Tat is absent. It is possible that Tat is also needed for other functions during HIV replication. To test these hypotheses, we studied several tat mutants, including two stop codon mutants and one deletion mutant using replication-competent HIV-1 constructs carrying wild-type or mutant LTRs with modifications in the NF-kappa B and/or Sp1 binding sites. In this study, we show that Tat- HIV-1 with wild-type LTRs can replicate in HeLa cells, and the virus produced from HeLa cells can infect primary peripheral blood lymphocytes and macrophages. It was found that the propagation of the Tat mutants containing wild-type LTRs was less efficient than that of the LTR-modified Tat mutants. Large amounts of viral RNA and particles were synthesized in infections established using the tat mutants that contain modified LTRs. However, this efficient propagation of the LTR-modified tat mutants was restricted to some lymphoid cell lines that have been transformed with other viruses. Thus, despite its essential role for releasing an elongation block, Tat is not otherwise absolutely required for synthesis of full-length HIV transcripts and assembly of virus particles. Direct sequencing of the viral genomes and reinfection kinetics showed no evidence of wild-type reversion even after prolonged infection with the Tat- virus. The implications for in vivo HIV-1 replication and potential application of this system to the study of alternative Tat function are discussed.

Retroviral vector with a CMV-IE/HIV-TAR hybrid LTR gives high basal expression levels and is up-regulated by HIV-1 Tat

We have constructed a new retroviral vector by making modifications to the commonly used Moloney murine leukemia virus (MoMLV) based vector in the long terminal repeat (LTR). The changes include replacement of a portion of the U3 region of the MoMLV LTR with a hybrid regulatory element consisting of the human cytomegalovirus immediate-early enhancer/promoter (CMV-IE) together with the human immunodeficiency virus transactivation response element (HIV-TAR). Transfection of chloramphenicol acetyl transferase (CAT) reporter constructs into a variety of human cell lines showed that the hybrid LTR with the CMV-IE/HIV-TAR enhancer/promoter exhibited basal expression levels which were 10- to 50-fold higher than those obtained from the wild-type MoMLV-LTR enhancer/promoter. Expression from the recombinant LTR was further increased in the presence of the HIV-Tat protein, and surprisingly, Tat up-regulated transcription from both the HIV and the MoMLV TATA boxes. In contrast, a MoMLV enhancer/promoter containing only the HIV-TAR element in the LTR did not respond to Tat. When stably transfected into an amphotropic packaging cell line, the modified retroviral vector containing the hybrid LTR plus an extended packaging signal consistently gave higher titres of retrovirus than did the parental MoMLV based vector. Higher basal expression levels which can be further upregulated by Tat, together with more efficient virion production, suggests that the modified vector should be superior for anti-HIV gene therapy applications as well as for other more general applications in human gene therapy.

Vascular smooth muscle cells express a constitutive NF-kappa B-like activity

The NF-kappa B/Rel family of transcription factors is commonly expressed in non-hematopoietic cells in an inactive form within the cytoplasm, complexed with an inhibitor I kappa B protein. Thus, it was surprising that NF-kappa B element-driven heterologous promoter-reporter gene constructs were active upon transient transfection into vascular smooth muscle cells (VSMCs). Here, we report that VSMCs express a constitutive nuclear NF-kappa B-like activity. In electrophoretic mobility shift assays, nuclear extracts demonstrated binding to a wild type NF-kappa B element but not to those mutated at nucleotides critical for Rel-protein DNA interaction. Binding was abrogated by the presence of I kappa B-alpha. Furthermore, addition of an antibody to the p50 subunit of classical NF-kappa B (but not p65, c-Rel, or RelB) resulted in supershifted complexes. Transactivation of element-driven constructs was negatively affected by co-transfection of a vector expressing a dominant negative p50 subunit, which can dimerize with other Rel subunits but not bind DNA. The long terminal repeat of the human immunodeficiency virus-1, which is driven in part by two NF-kappa B elements, displayed strong activity within VSMCs. This activity was abrogated upon co-transfection of the vector expressing the dominant negative p50 mutant. Taken together, these experiments indicate that VSMCs constitutively express a functional NF-kappa B-like trans-acting factor, which may play a significant role in the regulation of proliferation and viral infection of these cells.

Presence of negative and positive cis-acting RNA splicing elements within and flanking the first tat coding exon of human immunodeficiency virus type 1

The human immunodeficiency virus type 1 (HIV-1) RNA follows a complex splicing pathway in which a single primary transcript either remains unspliced or is alternatively spliced to more than 30 different singly and multiply spliced mRNAs. We have used an in vitro splicing assay to identify cis elements within the viral genome that regulate HIV-1 RNA splicing. A novel splicing regulatory element (SRE) within the first tat coding exon has been detected. This element specifically inhibits splicing at the upstream 3' splice site flanking this tat exon. The element only functions when in the sense orientation and is position dependent when inserted downstream of a heterologous 3' splice site. In vivo, an HIV-1 SRE mutant demonstrated a decrease in unspliced viral RNA, increased levels of single- and double-spliced tat mRNA, and reduced levels of env and rev mRNAs. In addition to the negative cis-acting SRE, the flanking 5' splice site downstream of the first tat coding exon acts positively to increase splicing at the upstream 3' splice sites. These results are consistent with hypotheses of bridging interactions between cellular factors that bind to the 5' splice site and those that bind at the upstream 3' splice site.

Cerebellar glutamate metabolizing enzymes in spinocerebellar ataxia type I

We measured the levels of three glutamate metabolizing enzymes, namely, glutamate dehydrogenase (GDH), aspartate aminotransferase (AAT), and glutamine synthetase (GS) in cerebellar and occipital cortices of nine patients with dominantly-inherited olivopontocerebellar atrophy (OPCA; spinocerebellar ataxia type I). As compared with the controls, mean GDH activities in cerebellar cortex of the OPCA patients were normal whereas levels of AAT (-17%) and the glial enzyme GS (-27%) were significantly reduced. No statistically significant changes were observed in occipital cortex, a morphologically unaffected brain area. We suggest that the decreased GS levels could reflect impaired capacity of astrocytes to metabolize glutamate which might contribute to the degenerative processes in OPCA cerebellum.

Predictors of long-term smoking cessation in head and neck cancer patients

Cigarette smoking is a major risk factor for head and neck cancer, and individuals who continue to smoke past diagnosis and treatment are at elevated risk for further disease. In a randomized controlled trial, a state of the art provider-delivered smoking cessation intervention was compared to a usual care advice control condition. The intervention consisted of surgeon- or dentist-delivered advice to stop smoking, a contracted quit date, tailored written materials, and booster advice sessions. Subjects were 186 patients with newly diagnosed first primary squamous cell carcinomas of the upper aerodigestive tract who had smoked cigarettes within the past year. At randomization, 88.2% of subjects were current smokers. At 12-month follow-up, 70.2% of subjects completing the trial (n = 114) were continuous abstainers; among baseline smokers alone the continuous abstinence (CA) rate was 64.6%. The cotinine validation rate at 12 months was 89.6%. Modeling techniques were utilized in order to derive expected CA rates, which included noncompleter subjects (n = 72). The CA rate expected at 1 year for the entire patient population was 64.2%, and for smokers alone the expected CA rate was 59.4%. Logistic regression analysis carried out on baseline smokers identified predictors of 12-month CA status. These included medical treatment, stage of change, age, nicotine dependence, and race. The intervention effect was not significant, although the sign of the effect was positive. Based on these findings, we recommend systematic brief advice to stop smoking for head and neck cancer patients, with a stepped care approach for patients less able to quit.

Quantitation of human immunodeficiency virus type 1 infection kinetics

Tissue culture infections of CD4-positive human T cells by human immunodeficiency virus type 1 (HIV-1) proceed in three stages: (i) a period following the initiation of an infection during which no detectable virus is produced; (ii) a phase in which a sharp increase followed by a peak of released progeny virions can be measured; and (iii) a final period when virus production declines. In this study, we have derived equations describing the kinetics of HIV-1 accumulation in cell culture supernatants during multiple rounds of infection. Our analyses indicated that the critical parameter affecting the kinetics of HIV-1 infection is the infection rate constant k = Inn/ti, where n is the number of infectious virions produced by one cell (about 10(2)) and ti is the time required for one complete cycle of virus infection (typically 3 to 4 days). Of particular note was our finding that the infectivity of HIV-1 during cell-to-cell transmission is 10(2) to 10(3) times greater than the infectivity of cell-free virus stocks, the inocula commonly used to initiate tissue culture infections. We also demonstrated that the slow infection kinetics of an HIV-1 tat mutant is not due to a longer replication time but reflects the small number of infectious particles produced per cycle.

Human immunodeficiency viruses containing heterologous enhancer/promoters are replication competent and exhibit different lymphocyte tropisms

The human immunodeficiency virus (HIV) type 1 long terminal repeat (LTR) contains binding sites for nuclear factor kappa B (NF-kappa B) and the constitutively expressed transcription factor Sp1, both of which are highly conserved in HIV and simian immunodeficiency virus isolates. To delineate the effects of these motifs on the replicative capacity of HIV and to explore the possibility of extending the virus host range, known heterologous enhancer/promoters were inserted into the HIV-1 LTR in place of the NF-kappa B and Sp1 binding sites. The effects of these substitutions on viral replication in transfected HeLa cells and on HIV infection of human peripheral blood lymphocytes or continuous T-leukemia cell lines were evaluated. HIVs in which the NF-kappa B/Sp1 enhancer plus the downstream TATA element were replaced with heterologous enhancer/promoters were also constructed. Viruses containing the human cytomegalovirus immediate-early enhancer exhibited infectious kinetics similar to that of wild-type HIV in activated human peripheral blood lymphocytes and AA2 cells but replicated less efficiently in H9 and CEM cells. These studies indicate that heterologous enhancer elements are capable of restoring Tat responsiveness to the HIV LTR in the context of directing reporter gene expression as well as in the production of infectious progeny virions.