Expression of human immunodeficiency virus type 1 Gag protein precursor and envelope proteins from a vesicular stomatitis virus recombinant: high-level production of virus-like particles containing HIV envelope

Recombinant vesicular stomatitis viruses have been developed as high-level expression vectors which serve as effective vaccine vectors in animals (Roberts et al., 1998, J. Virol. 72, 4704-4711; Roberts et al., 1999, J. Virol. 73, 3723-3732). Here we show that two genes can be expressed simultaneously from a single, live-attenuated VSV recombinant. The genes used encode the Pr55(gag) protein precursor of HIV-1 (1.7-kb gene) and an HIV-1 envelope (Env) protein (2.4 kb gene). Our results show that VSV can accommodate up to a 40% increase in genome size with only a threefold reduction in virus titer. Recombinants expressing the Pr55(gag) protein precursor with or without Env protein produced abundant HIV virus-like particles (VLPs) in addition to bullet-shaped VSV particles. HIV Env protein expressed from a VSV recombinant also expressing Gag was specifically incorporated into the HIV VLPs but not into the VSV particles. In contrast, VSV G protein was found in both VSV particles and in HIV VLPs. Such VSV/HIV recombinants producing HIV VLPs with Env protein could be an effective source of HIV-like particles inducing both cellular and antibody-mediated immunity to HIV-1.

Auxin-regulated genes encoding cell wall-modifying proteins are expressed during early tomato fruit growth

An expansin gene, LeExp2, was isolated from auxin-treated, etiolated tomato (Lycopersicon esculentum cv T5) hypocotyls. LeExp2 mRNA expression was restricted to the growing regions of the tomato hypocotyl and was up-regulated during incubation of hypocotyl segments with auxin. The pattern of expression of LeExp2 was also studied during tomato fruit growth, a developmental process involving rapid cell enlargement. The expression of genes encoding a xyloglucan endotransglycosylase (LeEXT1) and an endo-1, 4-beta-glucanase (Cel7), which, like LeExp2, are auxin-regulated in etiolated hypocotyls (C. Catalá, J.K.C. Rose, A.B. Bennett [1997] Plant J 12: 417-426), was also studied to examine the potential for synergistic action with expansins. LeExp2 and LeEXT1 genes were coordinately regulated, with their mRNA accumulation peaking during the stages of highest growth, while Cel7 mRNA abundance increased and remained constant during later stages of fruit growth. The expression of LeExp2, LeEXT1, and Cel7 was undetectable or negligible at the onset of and during fruit ripening, which is consistent with a specific role of these genes in regulating cell wall loosening during fruit growth, not in ripening-associated cell wall disassembly.

Replication-competent rhabdoviruses with human immunodeficiency virus type 1 coats and green fluorescent protein: entry by a pH-independent pathway

We describe a replication-competent, recombinant vesicular stomatitis virus (VSV) in which the gene encoding the single transmembrane glycoprotein (G) was deleted and replaced by an env-G hybrid gene encoding the extracellular and transmembrane domains of a human immunodeficiency virus type 1 (HIV-1) envelope protein fused to the cytoplasmic domain of VSV G. An additional gene encoding a green fluorescent protein was added to permit rapid detection of infection. This novel surrogate virus infected and propagated on cells expressing the HIV receptor CD4 and coreceptor CXCR4. Infection was blocked by SDF-1, the ligand for CXCR4, by antibody to CD4 and by HIV-neutralizing antibody. This virus, unlike VSV, entered cells by a pH-independent pathway and thus supports a pH-independent pathway of HIV entry. Additional recombinants carrying hybrid env-G genes derived from R5 or X4R5 HIV strains also showed the coreceptor specificities of the HIV strains from which they were derived. These surrogate viruses provide a simple and rapid assay for HIV-neutralizing antibodies as well as a rapid screen for molecules that would interfere with any stage of HIV binding or entry. The viruses might also be useful as HIV vaccines. Our results suggest wide applications of other surrogate viruses based on VSV.

Attenuated vesicular stomatitis viruses as vaccine vectors

We showed previously that a single intranasal vaccination of mice with a recombinant vesicular stomatitis virus (VSV) expressing an influenza virus hemagglutinin (HA) protein provided complete protection from lethal challenge with influenza virus (A. Roberts, E. Kretzschmar, A. S. Perkins, J. Forman, R. Price, L. Buonocore, Y. Kawaoka, and J. K. Rose, J. Virol. 72:4704-4711, 1998). Because some pathogenesis was associated with the vector itself, in the present study we generated new VSV vectors expressing HA which are completely attenuated for pathogenesis in the mouse model. The first vector has a truncation of the cytoplasmic domain of the VSV G protein and expresses influenza virus HA (CT1-HA). This nonpathogenic vector provides complete protection from lethal influenza virus challenge after intranasal administration. A second vector with VSV G deleted and expressing HA (DeltaG-HA) is also protective and nonpathogenic and has the advantage of not inducing neutralizing antibodies to the vector itself.

Cooperative disassembly of the cellulose-xyloglucan network of plant cell walls: parallels between cell expansion and fruit ripening

Modification of the plant primary cell wall is required for both cell expansion and for developmental events, such as fruit softening, where cell size remains static but where wall loosening is an important feature. Recent studies suggest that the cellulose-xyloglucan network is targeted by similar enzymatic activities in both expanding cells and ripening fruit but that unique isoforms are expressed in each process. Disassembly of this structural network probably involves the concerted and synergistic action of suites of these enzyme families, where one family of cell wall modifying proteins might mediate the activity of another, providing the basis for orchestrating ordered cell wall restructuring and turnover.

Recombinant vesicular stomatitis virus expressing respiratory syncytial virus (RSV) glycoproteins: RSV fusion protein can mediate infection and cell fusion

The genes encoding the respiratory syncytial virus (RSV) attachment (G) and fusion (F) envelope glycoproteins were expressed separately as additional genes in recombinant vesicular stomatitis viruses (VSV). Cells infected with the VSV-RSV F recombinant formed large syncytia illustrating the fusion activity of F in absence of other RSV proteins. Both F and G glycoproteins were expressed at the cell surface and incorporated into virions. Incorporation of these proteins did not require cytoplasmic tail sequences of VSV G. Using a compound, ammonium chloride, that raises the endosomal pH, we showed that presence of the RSV F glycoprotein in the envelope of recombinant VSV allowed for infectivity through a low-pH-independent pathway. Recombinant VSV expressing RSV glycoproteins could be useful as an RSV vaccine.

A plasma membrane localization signal in the HIV-1 envelope cytoplasmic domain prevents localization at sites of vesicular stomatitis virus budding and incorporation into VSV virions

Previous studies showed that the HIV-1 envelope (Env) protein was not incorporated into vesicular stomatitis virus (VSV) virions unless its cytoplasmic tail was replaced with that of the VSV glycoprotein (G). To determine whether the G tail provided a positive incorporation signal for Env, or if sequences in the Env tail prevented incorporation, we generated mutants of Env with its 150-amino-acid tail shortened to 29, 10, or 3 amino acids (Envtr mutants). Cells infected with VSV recombinants expressing these proteins or an Env-G tail hybrid showed similar amounts of Env protein at the surface. The Env-G tail hybrid or the Envtr3 mutant were incorporated at the highest levels into budding VSV virions. In contrast, the Envtr29 or Envtr10 mutants were incorporated poorly. These results defined a signal preventing incorporation within the 10 membrane-proximal amino acids of the Env tail. Confocal microscopy revealed that this signal functioned by causing localization of human immunodeficiency virus type 1 Env to plasma membrane domains distinct from the VSV budding sites, where VSV proteins were concentrated.

Generation of mucosal cytotoxic T cells against soluble protein by tissue-specific environmental and costimulatory signals

We compared peripheral and mucosal primary CD8 T cell responses to inflammatory and noninflammatory forms of antigen in a T cell-adoptive transfer system. Immunization with the soluble antigen, ovalbumin (ova), administered i.p. or orally without adjuvant, activated nonmucosal CD8 T cells but did not induce cytotoxic activity. However, after activation, the transferred cells entered the intestinal mucosa and became potent antigen-specific killers. Thus, exogenous intact soluble protein entered the major histocompatibility complex class I antigen presentation pathway and induced mucosal cytotoxic T lymphocytes. Moreover, distinct costimulatory requirements for activation of peripheral versus mucosal T cells were noted in that the CD28 ligand, B7-1, was critical for activated mucosal T cell generation but not for activation of peripheral CD8 T cells. The costimulator, B7-2, was required for optimum activation of both populations. Infection with a new recombinant vesicular stomatitis virus encoding ovalbumin induced lytic activity in mucosal as well as peripheral sites, demonstrating an adjuvant effect of inflammatory mediators produced during virus infection. Generation of antiviral cytotoxic T lymphocytes was also costimulation-dependent. The results indicated that induction of peripheral tolerance via antigen administration may not extend to mucosal sites because of distinct costimulatory and inflammatory signals in the mucosa.

Vaccination with a recombinant vesicular stomatitis virus expressing an influenza virus hemagglutinin provides complete protection from influenza virus challenge

Since the development of a system for generating vesicular stomatitis virus (VSV) from plasmid DNAs, our laboratory has reported the expression of several different glycoproteins from recombinant VSVs. In one of these studies, high-level expression of an influenza virus hemagglutinin (HA) from a recombinant VSV-HA and efficient incorporation of the HA protein into the virions was reported (E. Kretzschmar, L. Buonocore, M. J. Schnell, and J. K. Rose, J. Virol. 71:5982-5989, 1997). We report here that VSV-HA is an effective intranasal vaccine vector that raises high levels of neutralizing antibody to influenza virus and completely protects mice from bronchial pneumonia caused by challenge with a lethal dose of influenza A virus. Additionally, these recombinant VSVs are less pathogenic than wild-type VSV (serotype Indiana). This vector-associated pathogenicity was subsequently eliminated through introduction of specific attenuating deletions. These live attenuated recombinant VSVs have great potential as vaccine vectors.

Temporal sequence of cell wall disassembly in rapidly ripening melon fruit

The Charentais variety of melon (Cucumis melo cv Reticulatus F1 Alpha) was observed to undergo very rapid ripening, with the transition from the preripe to overripe stage occurring within 24 to 48 h. During this time, the flesh first softened and then exhibited substantial disintegration, suggesting that Charentais may represent a useful model system to examine the temporal sequence of changes in cell wall composition that typically take place in softening fruit. The total amount of pectin in the cell wall showed little reduction during ripening but its solubility changed substantially. Initial changes in pectin solubility coincided with a loss of galactose from tightly bound pectins, but preceded the expression of polygalacturonase (PG) mRNAs, suggesting early, PG-independent modification of pectin structure. Depolymerization of polyuronides occurred predominantly in the later ripening stages, and after the appearance of PG mRNAs, suggesting the existence of PG-dependent pectin degradation in later stages. Depolymerization of hemicelluloses was observed throughout ripening, and degradation of a tightly bound xyloglucan fraction was detected at the early onset of softening. Thus, metabolism of xyloglucan that may be closely associated with cellulose microfibrils may contribute to the initial stages of fruit softening. A model is presented of the temporal sequence of cell wall changes during cell wall disassembly in ripening Charentais melon.

Polygalacturonase gene expression in ripe melon fruit supports a role for polygalacturonase in ripening-associated pectin disassembly

Ripening-associated pectin disassembly in melon is characterized by a decrease in molecular mass and an increase in the solubilization of polyuronide, modifications that in other fruit have been attributed to the activity of polygalacturonase (PG). Although it has been reported that PG activity is absent during melon fruit ripening, a mechanism for PG-independent pectin disassembly has not been positively identified. Here we provide evidence that pectin disassembly in melon (Cucumis melo) may be PG mediated. Three melon cDNA clones with significant homology to other cloned PGs were isolated from the rapidly ripening cultivar Charentais (C. melo cv Reticulatus F1 Alpha) and were expressed at high levels during fruit ripening. The expression pattern correlated temporally with an increase in pectin-degrading activity and a decrease in the molecular mass of cell wall pectins, suggesting that these genes encode functional PGs. MPG1 and MPG2 were closely related to peach fruit and tomato abscission zone PGs, and MPG3 was closely related to tomato fruit PG. MPG1, the most abundant melon PG mRNA, was expressed in Aspergillus oryzae. The culture filtrate exponentially decreased the viscosity of a pectin solution and catalyzed the linear release of reducing groups, suggesting that MPG1 encodes an endo-PG with the potential to depolymerize melon fruit cell wall pectin. Because MPG1 belongs to a group of PGs divergent from the well-characterized tomato fruit PG, this supports the involvement of a second class of PGs in fruit ripening-associated pectin disassembly.

Requirement for a non-specific glycoprotein cytoplasmic domain sequence to drive efficient budding of vesicular stomatitis virus

The cytoplasmic domains of viral glycoproteins are often involved in specific interactions with internal viral components. These interactions can concentrate glycoproteins at virus budding sites and drive efficient virus budding, or can determine virion morphology. To investigate the role of the vesicular stomatitis virus (VSV) glycoprotein (G) cytoplasmic and transmembrane domains in budding, we recovered recombinant VSVs expressing chimeric G proteins with the transmembrane and cytoplasmic domains derived from the human CD4 protein. These unrelated foreign sequences were capable of supporting efficient VSV budding. Further analysis of G protein cytoplasmic domain deletion mutants showed that a cytoplasmic domain of only 1 amino acid did not drive efficient budding, whereas 9 amino acids did. Additional studies in agreement with the CD4-chimera experiments indicated the requirement for a short cytoplasmic domain on VSV G without the requirement for a specific sequence in that domain. We propose a model for VSV budding in which a relatively non-specific interaction of a cytoplasmic domain with a pocket or groove in the viral nucleocapsid or matrix proteins generates a glycoprotein array that promotes viral budding.

Enteral feeding intolerance: an indicator of sepsis-associated mortality in burned children

OBJECTIVE

To determine if enteral feeding intolerance (EFI) is associated with sepsis and increased mortality in children with severe burns.

DESIGN

A survey.

SETTING

A pediatric burn unit.

PATIENTS

Ninety-one children surviving longer than 5 days with greater than 80% total body surface area burns.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Enteral feeding intolerance indicated by high gastric residuals (> 150 mL/h) or uncontrollable diarrhea (> 2500 mL/d); thrombocytopenia (platelet count < 100 x 10(9)/L); hyperglycemia (glucose level > 11.1 mmol/L [> 200 mg/dL]); sepsis (pathogenic bacteremia or fungemia noted on blood culture results); and mortality.

RESULTS

Neither EFI nor sepsis developed in 71 patients, EFI alone developed in 2 patients, sepsis alone developed in 5 patients, and EFI and sepsis developed in 13 patients. Enteral feeding intolerance and sepsis were associated by contingency table analysis (P<.001). Mortality was 8% (6 patients) in those with neither EFI nor sepsis, 50% (1 patient) in those with EFI alone, 60% (3 patients) in those with sepsis alone, and 77% (10 patients) in those with EFI-associated sepsis. The 2 latter groups were different from the group with neither EFI nor sepsis (P<.05). Enteral feeding intolerance was identified in 70% of patients before sepsis; thrombocytopenia, 64%; and hyperglycemia, 66%. When compared with thrombocytopenia and hyperthermia, no variables were found to be superior to others for predicting sepsis.

CONCLUSIONS

Enteral feeding intolerance was associated with the development of sepsis and increased mortality in children with greater than 80% total body surface area burns. This sign was identified in 70% of the cases before pathogens were found in the blood; no difference could be shown between the identification of EFI, thrombocytopenia, and hyperglycemia before sepsis. These data indicate that the development of EFI should be used as an indicator of infection and should prompt a search for an inciting focus.

Construction of a novel virus that targets HIV-1-infected cells and controls HIV-1 infection

We describe a recombinant vesicular stomatitis virus lacking its glycoprotein gene and expressing instead the HIV-1 receptor CD4 and a coreceptor, CXCR4. This virus was unable to infect normal cells but did infect, propagate on, and kill cells that were first infected with HIV-1 and therefore had the HIV membrane fusion protein on their surface. Killing of HIV-1-infected cells controlled HIV infection in a T cell line and reduced titers of infectious HIV-1 in the culture by as much as 10(4)-fold. Such a targeted virus could have therapeutic value in reducing HIV viral load. Our results also demonstrate a general strategy of targeting one virus to the envelope protein of another virus to control infection.

Auxin regulation and spatial localization of an endo-1,4-beta-D-glucanase and a xyloglucan endotransglycosylase in expanding tomato hypocotyls

Xyloglucan, the primary hemicellulosic cell wall polysaccharide in dicotyledons, undergoes substantial modification during auxin-stimulated cell expansion. To identify candidates for mediating xyloglucan turnover, the expression and auxin regulation of tomato Cel7 and LeEXT, genes encoding an endo-1,4-beta-glucanase (EGase) and a xyloglucan endotransglycosylase (XET), respectively, were examined. LeEXT mRNA was present primarily in elongating regions of the hypocotyl and was induced to higher levels by hormone treatments that elicited elongation of hypocotyl segments. Cel7 mRNA abundance was very low in both elongating and mature regions of the hypocotyl but was induced to accumulate to high levels in both hypocotyl regions by auxin application. Analysis of the time dependence of expression of Cel7 and LeEXT during auxin treatment suggested that induction of these genes is not required for rapid growth responses but may participate in the cell wall changes involved in sustained cell elongation. Localization of Cel7 and LeEXT mRNA by in situ hybridization revealed that both genes are expressed in outer cell layers of the hypocotyl. In untreated etiolated seedlings, LeEXT mRNA was detected in epidermal cells of the elongating region, a tissue considered to play a key role in auxin-induced elongation. After auxin treatment, Cel7 and LeEXT mRNA showed an overlapping spatial distribution in the epidermis and outer cortical cell layers. We conclude that LeEXT and Cel7 exhibit both unique and overlapping patterns of expression and have the potential to act cooperatively in mediating cell wall disassembly associated with expansive growth.

High-efficiency incorporation of functional influenza virus glycoproteins into recombinant vesicular stomatitis viruses

We derived recombinant vesicular stomatitis virus (VSV) expressing either influenza virus hemagglutinin (HA) or neuraminidase (NA) glycoproteins from extra genes inserted in the viral genome. The HA protein was expressed from a site downstream of the VSV glycoprotein (G) gene, while NA protein was expressed from a site upstream of the VSV G gene. The HA protein was expressed at lower levels than the VSV G protein, while the NA protein was expressed at higher levels, as expected from the gradient of VSV transcription that follows the gene order. The HA and NA proteins were transported to the cell surface and were functional as demonstrated by hemadsorption, hemolysis, and NA assays. Biochemical analysis showed that both HA and NA proteins were incorporated into VSV particles at high levels, although there was a preference for incorporation of the VSV G protein over either of the influenza virus proteins. Immunoelectron microscopy of the recombinants showed that the particles derived from the recombinants were mosaics carrying both the VSV G protein and the influenza virus membrane glycoproteins. These results extend earlier studies showing incorporation of the cellular glycoprotein CD4 and two other viral glycoproteins into VSV particles. Our results indicate that there is significant space in the VSV membrane that can accommodate foreign membrane proteins and that the foreign protein can represent as much as 35% of the total protein in the viral envelope. Incorporation of foreign proteins into VSV virions can, in many cases, occur passively in the absence of specific incorporation signals.

Specific targeting to CD4+ cells of recombinant vesicular stomatitis viruses encoding human immunodeficiency virus envelope proteins

We generated replication-competent, recombinant vesicular stomatitis viruses (VSVs) expressing the human immunodeficiency virus (HIV) envelope protein or an HIV-VSV chimeric envelope protein in which the cytoplasmic domain of the HIV envelope protein was replaced with that from the VSV glycoprotein (G). These recombinants were generated with HIV type 1 (HIV-1) envelopes from both laboratory and primary isolates of HIV-1. The replication-competent recombinant viruses were stable and expressed the foreign proteins at high levels from extra transcription units in VSV. The foreign proteins were processed appropriately and transported to the cell surface. The incorporation of HIV gp120 into VSV particles was demonstrated biochemically only for the construct expressing the chimeric envelopes containing the VSV G cytoplasmic domain. The incorporation of the chimeric HIV envelope protein into the membrane of the recombinant VSV was also demonstrated by electron microscopy with gold-conjugated antibodies. To determine whether specific infection of CD4-positive cells could be demonstrated for these recombinants, we neutralized VSV infectivity due to VSV glycoprotein with anti-VSV serum. The neutralized recombinants expressing the chimeric envelope were able to infect only HeLa cells expressing CD4, and this CD4-specific infectivity was neutralized with anti-HIV serum. This assay also detected a 100-fold-lower titer of CD4-specific infectivity for the VSV recombinant expressing the wild-type HIV envelope. Our results illustrate that it is possible to express functional HIV envelopes from the VSV genome and target the recombinant virus to an alternative receptor. The recombinants may also prove useful as HIV vaccines.

Expression of a divergent expansin gene is fruit-specific and ripening-regulated

Expansins are proteins that induce extension in isolated plant cell walls in vitro and have been proposed to disrupt noncovalent interactions between hemicellulose and cellulose microfibrils. Because the plant primary cell wall acts as a constraint to cell enlargement, this process may be integral to plant cell expansion, and studies of expansins have focused on their role in growth. We report the identification of an expansin (LeExp1) from tomato that exhibits high levels of mRNA abundance and is specifically expressed in ripening fruit, a developmental period when growth has ceased but when selective disassembly of cell wall components is pronounced. cDNAs closely related to LeExp1 were also identified in ripening melons and strawberries, suggesting that they are a common feature of fruit undergoing rapid softening. Furthermore, the sequence of LeExp1 and its homologs from other ripening fruit define a subclass of expansin genes. Expression of LeExp1 is regulated by ethylene, a hormone known to coordinate and induce ripening in many species. LeExp1 is differentially expressed in the ripening-impaired tomato mutants Nr, rin, and nor, and mRNA abundance appears to be influenced directly by ethylene and by a developmentally modulated transduction pathway. The identification of a ripening-regulated expansin gene in tomato and other fruit suggests that, in addition to their role in facilitating the expansion of plant cells, expansins may also contribute to cell wall disassembly in nongrowing tissues, possibly by enhancing the accessibility of noncovalently bound polymers to endogenous enzymic action.

Mortality determinants in massive pediatric burns. An analysis of 103 children with > or = 80% TBSA burns (> or = 70% full-thickness)

OBJECTIVE

Survivors and nonsurvivors among 103 consecutive pediatric patients with massive burns were compared in an effort to define the predictors of mortality in massively burned children.

SUMMARY BACKGROUND DATA

Predictors of mortality in burns that are used commonly are age, burn size, and inhalation injury. In the past, burns over 80% of the body surface area that are mostly full-thickness often were considered fatal, especially in children and in the elderly. In the past 15 years, advances in burn treatment have increased rates of survival in those patients treated at specialized burn centers. The purpose of this study was to document the extent of improvement and to define the current predictors of mortality to further focus burn care.

METHODS

Beginning in 1982, 103 children ages 6 months to 17 years with burns covering at least 80% of the body surface (70% full-thickness), were treated in the authors' institution by early excision and grafting and have been observed to determine outcome. The authors divided collected independent variables from the time of injury into temporally related groups and analyzed the data sequentially and cumulatively through univariate statistics and through pooled, cross-sectional multivariate logistic regression to determine which variables predict the probability of mortality.

RESULTS

The mortality rate for this series of massively burned children was 33%. Lower age, larger burn size, presence of inhalation injury, delayed intravenous access, lower admission hematocrit, lower base deficit on admission, higher serum osmolarity at arrival to the authors' hospital, sepsis, inotropic support requirement, platelet count < 20,000, and ventilator dependency during the hospital course significantly predict increased mortality.

CONCLUSIONS

The authors conclude that mortality has decreased in massively burned children to the extent that nearly all patients should be considered as candidates for survival, regardless of age, burn size, presence of inhalation injury, delay in resuscitation, or laboratory values on initial presentation. During the course of hospitalization, the development of sepsis and multiorgan failure is a harbinger of poor outcome, but the authors have encountered futile cases only rarely. The authors found that those patients who are most apt to die are the very young, those with limited donor sites, those who have inhalation injury, those with delays in resuscitation, and those with burn-associated sepsis or multiorgan failure.