Removal of cryptic poxvirus transcription termination signals from the human immunodeficiency virus type 1 envelope gene enhances expression and immunogenicity of a recombinant vaccinia virus

Characterization of human immunodeficiency virus type 1 gp120 binding to liposomes containing galactosylceramide

Human immunodeficiency virus type 1 (HIV-1) infects some cell types which lack CD4, demonstrating that one or more alternative viral receptors exist. One such receptor is galactosylceramide (GalCer), a glycosphingolipid distributed widely in the nervous system and in colonic epithelial cells. Using a liposome flotation assay, we found that the HIV-1 surface glycoprotein, gp120, quantitatively bound to liposomes containing GalCer but not to liposomes containing phospholipids and cholesterol alone. Binding was saturable and was inhibited by preincubating liposomes with anti-GalCer antibodies. We observed less efficient binding of gp120 to liposomes containing lactosylceramide, glucosylceramide, and galactosylsulfate, whereas no binding to liposomes containing mixed gangliosides, psychosine, or sphingomyelin was detected. Binding to GalCer was rapid, largely independent of temperature and pH, and stable to conditions which remove most peripheral membrane proteins. By contrast, gp120 bound to lactosylceramide could be removed by 2 M potassium chloride or 3 M potassium thiocyanate, demonstrating a less stable interaction. Removal of N-linked oligosaccharides on gp120 did not affect binding efficiency. However, as previously observed for CD4 binding, heat denaturation of gp120 prevented binding to GalCer. Finally, binding was critically dependent on the concentration of GalCer in the target membrane, suggesting that binding to glycolipid-rich domains occurs and that GalCer conformation may be important for gp120 recognition.

Expression of HIV-1 envelope gene by recombinant avipox viruses

Recombinant canarypox (CP) and fowlpox (FP) viruses that contained two forms of the HIV-1 (SF2 strain) env gene were engineered and their expression analysed in chick, simian and human cells. These vectors can efficiently replicate in avian but not in mammalian cells, in which infection is abortive. The two forms, consisting of the entire env open reading frame (IS+) or of the same gene lacking the putative immunosuppressive (IS-) region (amino acids 583-599), were individually inserted into the two virus vector backgrounds. In order to avoid premature transcription termination of the foreign gene and to improve protein expression, a mutagenesis was also performed within the T5NT motif without altering the amino acid sequence. By immunoprecipitation analyses, cells infected with CP and FP recombinants expressed HIV-1 env polypeptides of the appropriate molecular weight. We observed that the gp160 precursor was proteolytically cleaved except in MRC-5 cells infected with the IS- recombinants and that these polypeptides were glycosylated. Further analysis of these recombinant viruses by indirect immunofluorescence and syncytia inhibition assays indicated that the gp120 gp41 complex was present on the surface of infected cells, the number of syncytia being significantly lower when cells were infected by the CPIS- or FPIS- recombinants. Moreover, sera of immunized rabbits revealed the presence of specific antibodies in animals inoculated either with CP or with FP recombinants. These new constructs, which are unable to support a productive infection in human cells, might therefore also be a good anti-HIV-1 candidate vaccine in seropositive hosts.

Major expansion of CD8+ T cells with a predominant V beta usage during the primary immune response to HIV

A SIGNIFICANT proportion (up to 70%) of individuals experience an acute clinical syndrome of varying severity associated with primary infection with the human immunodeficiency virus (HIV). We report here studies on six individuals who showed an acute HIV syndrome which generally resolved within four weeks, concomitant with a dramatic downregulation of viraemia. To characterize the T-cell-mediated primary immune response to HIV, we used combined semiquantitative polymerase chain reaction assay and cytofluorometry to analyse the T-cell antigen receptor repertoire in sequential peripheral blood mononuclear cells from the patients. We found major oligoclonal expansions in a restricted set of variable-domain beta-chain (V beta) families. Cells expressing the expanded V beta s predominantly expressed the CD8 T-cell differentiation antigen and mediated HIV-specific cytotoxicity. Major oligoclonal expansions of these CD8+ T lymphocytes may represent an important component of the primary immune response to viral infections and may help to clarify both the immunopathogenic and the protective mechanisms of HIV infection.

A trans-dominant mutation in human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp41 inhibits membrane fusion when expressed in target cells

A recombinant vaccinia virus was used to express a mutation in the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120-gp41. In this mutant protein, the second amino acid in the N-terminal region of gp41 has been converted from a hydrophobic valine residue to the polar glutamate. When recombinant vaccinia viruses encoding wild-type HIV-1 envelope glycoprotein infect a lymphocyte cell line lacking CD4, the cells express the HIV-1 envelope glycoprotein gp120-gp41 and are able to fuse with a CD4(4) T lymphocyte cell line. Cells expressing the mutant envelope glycoprotein are unable to fuse with CD4(4) T lymphocytes. When both viruses infect CD4- cells simultaneously, there is an inhibition of fusion to CD4+ cells with an increasing fraction of the virus encoding the mutated envelope glycoprotein. Interestingly, when the opposing, or CD4+ target cells are infected with the mutation-expressing virus, while CD4- cells are infected with wild-type envelope-expressing virus, a similar inhibition of fusion is observed. This suggests that the mutated envelope glycoprotein does not need to reside in the same membrane as the wild-type protein it inhibits.

Alteration of V3 loop context within the envelope of human immunodeficiency virus type 1 enhances neutralization

Neutralization of a chimeric human immunodeficiency virus (HIV) type 1, containing the V3 loop of the MN isolate substituted within the HXB2 envelope, was enhanced up to 20-fold compared with the HXB2 or MN parental isolates by human HIV-positive sera. MN V3 loop-specific monoclonal antibodies were better able to recognize the chimeric virus compared with MN, staining a greater percentage of infected cells and exhibiting slight increases in relative affinity with a concomitant increase in neutralization titer. Competition analysis revealed that enhanced neutralization by human HIV-positive sera of the chimera was attributable in some cases to better reactivity with the linear V3 loop epitope but in others to conformational loop epitopes or previously cryptic or poorly recognized epitopes outside the loop region. Mice primed with a vaccinia virus-chimeric envelope recombinant and boosted with gp160 developed a spectrum of antibodies different from that of mice similarly immunized with HXB2 or MN recombinants or that of naturally infected humans. The chimeric envelope elicited antibodies with enhanced binding to the native MN V3 loop; however, the sites seen by the BALB/c mice were not neutralizing epitopes. Nevertheless, similar to the observations made with use of human sera, the chimeric virus was more readily neutralized by all of the immune mouse sera, an effect apparently mediated by non-V3 loop epitopes. These studies illustrate that not only the V3 loop sequence and conformation but also its context within the viral envelope influence neutralization.

Expression of foreign genes in cultured human primary macrophages using recombinant vaccinia virus vectors

Recombinant vaccinia viruses (re-VVs) provide an extremely versatile method for the expression of foreign genes in a wide range of cultured cell types of different lineages and species. In the present report, we examine the utility of re-VV vectors for re-protein production in cultured human primary macrophages obtained through in vitro differentiation of peripheral blood monocytes. Primary macrophages supported early stages of the VV infection cycle, including morphologic cytopathic effect, shut-off of host protein synthesis and activation of early viral protein synthesis; however, late stages of infection were blocked, including synthesis of late viral proteins, replication of viral DNA, and production of infectious progeny virions. Abortive infection was observed with several independent VV strains. Using re-VVs containing Escherichia coli lacZ as a reporter gene, we assayed the activities of different classes of VV promoters. Consistent with the results noted above, human primary macrophages supported reporter gene expression driven by an early or intermediate VV promoter, but not by a late promoter; expression was obtained with synthetic bifunctional promoters containing early and/or intermediate components. Primary macrophages also supported the VV/bacteriophage T7 RNA polymerase hybrid gene expression system. The utility of re-VV vectors for production of proteins of biological interest in human primary macrophages was demonstrated using re-VVs encoding human CD4 and the human immunodeficiency virus type-1 envelope glycoprotein.

Native oligomeric human immunodeficiency virus type 1 envelope glycoprotein elicits diverse monoclonal antibody reactivities

We synthesized and purified a recombinant human immunodeficiency virus type 1 (HIV-1) envelope (Env) glycoprotein, lacking the gp120/gp41 cleavage site as well as the transmembrane domain, that is secreted principally as a stable oligomer. Mice were immunized with separated monomeric and oligomeric HIV-1 Env glycoproteins to analyze the repertoire of antibody responses to the tertiary and quaternary structure of the protein. Hybridomas were generated and assayed for reactivity by immunoprecipitation of nondenatured Env protein. A total of 138 monoclonal antibodies (MAbs) were generated and cloned, 123 of which were derived from seven animals immunized with oligomeric Env. Within this group, a significant response was obtained against the gp41 ectodomain; 49 MAbs recognized epitopes in gp41, 82% of which were conformational. The influence of conformation on gp120 antigenicity was less pronounced, with 40% of the anti-gp120 MAbs binding to conformational epitopes, many of which blocked CD4 binding. Surprisingly, less than 7% of the MAbs derived from mice immunized with oligomeric Env recognized the V3 loop. In addition, MAbs to linear epitopes in the C-terminal domain of gp120 were not obtained, suggesting that this region of the protein may be partially masked in the oligomeric molecule. A total of 15 MAbs were obtained from two mice immunized with monomeric Env. Nearly half of these recognized the V3 loop, suggesting that this region may be a less predominant epitope in the context of oligomeric Env than in monomeric protein. Thus, immunization with oligomeric Env generates a large proportion of antibodies to conformational epitopes in both gp120 and gp41, many of which may be absent from monomeric Env.

Major histocompatibility complex-restricted CD8+ cytotoxic T lymphocytes from horses with equine infectious anemia virus recognize Env and Gag/PR proteins

Cytotoxic T lymphocytes (CTL) can control some viral infections and may be important in the control of lentiviruses, including human immunodeficiency virus type 1. Since there is limited evidence for an in vivo role of CTL in control of lentiviruses, dissection of immune mechanisms in animal lentiviral infections may provide needed information. Horses infected with equine infectious anemia virus (EIAV) a lentivirus, have acute plasma viremia which is terminated in immunocompetent horses. Viremic episodes may recur, but most horses ultimately control infection and become asymptomatic carriers. To begin dissection of the immune mechanisms involved in EIAV control, peripheral blood mononuclear cells (PBMC) from infected horses were evaluated for CTL to EIAV-infected cells. By using noninfected and EIAV-infected autologous equine kidney (EK) cells in 51Cr-release assays, EIAV-specific cytotoxic activity was detected in unstimulated PBMC from three infected horses. The EIAV-specific cytotoxic activity was major histocompatibility complex (MHC) restricted, as determined by assaying EIAV-infected heterologous EK targets, and was mediated by CD8+ T lymphocytes, as determined by depleting these cells by a panning procedure with an anti-CD8 monoclonal antibody. MHC-restricted CD8+ CTL in unstimulated PBMC from infected horses caused significant specific lysis of autologous EK cells infected with recombinant vaccinia viruses expressing EIAV genes, either env or gag plus 5' pol. The EIAV-specific MHC-restricted CD8+ CTL were detected in two EIAV-infected horses within a few days after plasma viremia occurred and were present after viremia was terminated. The detection of these immune effector cells in EIAV-infected horses permits further studies to determine their in vivo role.

Expression of foreign proteins in a human neuronal system

The NT2N cell system offers an attractive way to overcome some of the technical limitations inherent in working with primary neuronal cultures. In particular, it is possible to obtain large quantities of neurons with which to perform biochemical experiments, and the growth of neurites can be synchronized and controlled by varying the substrate on which the cells grow. In addition, because the differentiated NT2N neurons are derived from a mitotically active precursor cell line in vitro, it is possible to employ a variety of techniques, that are not otherwise available when working directly with postmitotic neurons, to obtain expression of foreign proteins. Because they are fully polarized, NT2N cells offer a way to study protein sorting to axons and dendrites at both the biochemical and the morphological level. Further characterization of NT2N cells is underway, and more efficient ways to obtain expression of foreign proteins will no doubt be found.

Recombinant vaccinia viruses co-expressing dengue-1 glycoproteins prM and E induce neutralizing antibodies in mice

Four recombinant vaccinia viruses expressing different portions of the dengue type 1 virus (DEN-1) genome (C-prM-E-NS1-NS2A-NS2B; prM-E; prM-E-NS1-NS2A-NS2B; or NS1-NS2A) were constructed in order to establish the most immunogenic configuration of DEN-1 proteins. Both recombinants producing prM and E in the absence of C induced the synthesis of extracellular forms of E in vitro. Mice inoculated with these two recombinants produced DEN-1 neutralizing (NEUT) and haemagglutination inhibiting (HAI) antibodies. The other two recombinant vaccinia viruses, which did not induce the production of extracellular forms of E, did not induce E-specific immune responses. These results support our previous studies on the design of flavivirus-vaccinia vaccine candidates by showing the importance of co-expressing prM and E in order to induce the synthesis of extracellular E and to elicit NEUT and HAI antibodies.

An endogenously synthesized decamer peptide efficiently primes cytotoxic T cells specific for the HIV-1 envelope glycoprotein

The immunodominant H-2Dd-restricted cytotoxic T lymphocyte (CTL) response to the HIV-1 gp160 envelope glycoprotein maps to a single determinant in the V3 loop, designated p18. Using a series of peptides synthesized on pins we have determined that the minimal core sequence of this determinant required for CTL recognition comprises 8 amino acids (residues 320-327). However, 9mer and 10mer peptides containing this core sequence were more effective than the 8mer peptide at sensitizing Dd-expressing target cells. To analyze the antigenicity of endogenously synthesized p18, minigenes encoding a 10-amino acid determinant (residues 318-327) and a 67-amino acid peptide (residues 281-348; containing the V3 loop) were expressed using vaccinia virus (Vac) recombinants. Both peptides were as effective as wild-type gp160 in their ability to sensitize target cells for lysis by gp160-specific CTL. Immunization of BALB/c mice with Vac recombinants encoding both gp160 peptides elicited gp160-specific CTL. These data demonstrate that both the V3 loop itself and a 10-residue epitope are sufficient to prime CTL in vivo and strongly support the potential use of minigene-encoded CTL epitopes for recombinant vaccines designed to induce protective T cell-mediated immunity against HIV-1.

Immunogenicity of the Plasmodium falciparum serine repeat antigen (p126) expressed by vaccinia virus

cDNA encoding the serine repeat antigen (SERA) (also called p126) of Plasmodium falciparum has been isolated from the FCR3 strain and inserted into a recombinant vaccinia virus designated vP870. Expression analysis of vP870-infected Vero cells by immunoprecipitation has demonstrated several intracellular forms of SERA and a single secreted SERA peptide. Endoglycosidase digestion of these immunoprecipitated SERA peptides indicated that the intracellular SERA peptides contain simple, high-mannose N-linked oligosaccharides and that the secreted SERA peptide contains complex N-linked oligosaccharides. Pulse-chase experiments indicate that the multiple intracellular SERA peptides in infected Vero cells represent a trafficking pathway whereby the smallest SERA peptide is converted into larger peptides by co- and posttranslational modifications, including glycosylation, and eventually secreted from the cell with complex N-linked oligosaccharides. To study the immunogenicity of vaccinia virus-expressed SERA, rabbits were immunized with vP870 and their sera were analyzed for reactivity with authentic, parasite-derived SERA protein. The anti-vP870 rabbit sera reacted with P. falciparum-infected erythrocytes by immunofluorescence analysis, recognized authentic SERA from schizonts by both immunoprecipitation and Western blot (immunoblot) analyses, and recognized proteolytically processed fragments of SERA secreted into the culture medium by Western blot analysis. These results indicate that when expressed by vaccinia virus, SERA is glycosylated and secreted from infected cells and that in immunized rabbits, vaccinia virus-expressed SERA can stimulate a humoral immune response against SERA derived from blood-stage parasites.

Reactivation of transcription from a vaccinia virus early promoter late in infection

We have studied the kinetics of RNA synthesis from the vaccinia virus 7,500-molecular-weight gene (7.5K gene) which is regulated by early and late promoters arranged in tandem. Unexpectedly, after a first burst of RNA synthesis early in infection, transcription was reactivated late in infection. Reactivation was not dependent on the location of the promoter in the genome or on the presence of the upstream late regulatory sequences. The mRNA synthesized from the reactivated promoter in the late phase had the same 5' and 3' ends as the molecules transcribed in the early phase. Interestingly, these molecules were efficiently translated despite the absence of the poly(A) leader characteristic of late mRNAs. Reactivation appears to be dependent on virus assembly since it is prevented by rifampin, a specific inhibitor of morphogenesis. Finally, analysis of various other early genes showed that reactivation is not unique to the 7.5K early promoter.

Transporter-independent processing of HIV-1 envelope protein for recognition by CD8+ T cells

CD8+ cytolytic T lymphocytes (CTL) identify virally infected cells by recognizing processed viral antigen in association with class I major histocompatibility complex (MHC) molecules on infected cells. Processing begins in the cytosol with the generation of peptides, possibly by a protease complex with MHC-encoded subunits, known as the proteasome. Transport of the resulting cytosolic peptides into the endoplasmic reticulum for association with class I molecules is essential and probably involves a heterodimer of the MHC-encoded proteins, Tap-1 and Tap-2. The site of processing of viral envelope proteins is uncertain. These proteins are not present in the cytosol because of cotranslational translocation into the endoplasmic reticulum. We show here that the HIV-1 envelope (env) protein is processed in infected cells by a novel Tap-1/Tap-2-independent pathway that seems to be localized to the endoplasmic reticulum.

The impact of HIV-1 infection on phenotypic and functional parameters of cellular immunity in chimpanzees

As a means of assessing the immunological impact of HIV infection in the chimpanzee, as well as the participation of the cellular components in the control of HIV infection in these animals, various aspects of cellular immunity were investigated in chronically HIV-infected chimpanzees. Eight HIV-1-infected chimpanzees were included in this study; two of them were infected for more than 5 years and six for nearly 3 years at the time of study. All of the chimpanzees received either 40 or 100 TCID50 of HTLV-IIIB. Circulating peripheral blood lymphocytes were studied by flow cytofluorimetric analysis in order to reveal possible alterations in the CD4:CD8 ratio, as well as in specific CD4+ and CD8+ cell subpopulations. Chronically infected chimpanzees did not present significant alterations in the percentage of CD4+ or CD8+ lymphocyte subsets. Interestingly, the CD8+/CD57+ cell subset was not detectable. The expression of markers for activation on circulating lymphocytes, usually higher in the HIV-infected patients, was not altered in infected animals. The functional aspects of specific anti-HIV-1 non-MHC and MHC-restricted cellular cytotoxic reactivities were also investigated. The results were compared with the findings in normal uninfected chimpanzees and in HIV-infected humans. Only one chimpanzee (881) developed a detectable, specific non-MHC-restricted anti-HIV-1- reactivity. Compared to that seen in humans, the ontogeny of this activity is delayed. Among the other infected chimpanzees, no specific anti-HIV cellular reactivities were detectable in the peripheral blood. In chimpanzees, HIV-1 infection evidently does not elicit the same strong cellular reactivity as that detected in infected patients. The absence of chronic cellular activation, despite continued viral replication, may highlight a key determinant in HIV-1-induced pathogenesis that is likewise absent in infected chimpanzees.

Mutational analysis of the assembly domain of the HIV-1 envelope glycoprotein

The amino-terminal 129 amino acids of gp41 of the human immunodeficiency virus type 1 (HIV-1) envelope (Env) glycoprotein constitute the assembly domain required for efficient oligomer formation and stability. Point mutations in highly conserved structural features including cysteine residues, potential N-linked glycosylation sites, and a leucine zipper motif have been made in a soluble secreted form of Env (Envsec). No single point mutation had adverse effects on Env protein oligomerization. However, truncation of the C terminus of gp41 from 129 amino acids to 68 amino acids drastically reduced oligomerization efficiency, indicating that amino acids 68-129 are essential for assembly.

Calcium ions are required for cell fusion mediated by the CD4-human immunodeficiency virus type 1 envelope glycoprotein interaction

Calcium ions are required for fusion of a wide variety of artificial and biological membranes. To examine the role of calcium ions for cell fusion mediated by interactions between CD4 and the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (gp120-gp41), we used two experimental systems: (i) cells expressing gp120-gp41 and its receptor CD4, both encoded by recombinant vaccinia viruses, and (ii) chronically infected cells producing low levels of HIV-1. Fusion was measured by counting the number of syncytia and by monitoring the redistribution of fluorescence dyes by video microscopy. Syncytia did not form in solutions without calcium ions. Addition of calcium ions partially restored the formation of syncytia. EDTA and EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid] blocked syncytium formation in culture media containing calcium ions. Membrane fusion as monitored by fluorescence dye redistribution also required calcium ions. Cell fusion increased with an increase in calcium ion concentration from 100 microM to 10 mM but was not affected by magnesium ions in the concentration range from 0 to 30 mM. Fibrinogen and fibronectin did not promote fusion in the absence or presence of Ca2+. Binding of soluble CD4 to gp120-gp41-expressing cells was not affected by Ca2+ and Mg2+. We conclude that Ca2+ is involved in postbinding steps in cell fusion mediated by the CD4-HIV-1 envelope glycoprotein interaction.

CD4 molecules with a diversity of mutations encompassing the CDR3 region efficiently support human immunodeficiency virus type 1 envelope glycoprotein-mediated cell fusion

The third complementarity-determining region (CDR3) within domain 1 of the human CD4 molecule has been suggested to play a critical role in membrane fusion mediated by the interaction of CD4 with the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein. To analyze in detail the role of CDR3 and adjacent regions in the fusion process, we used cassette mutagenesis to construct a panel of 30 site-directed mutations between residues 79 and 96 of the full-length CD4 molecule. The mutant proteins were transiently expressed by using recombinant vaccinia virus vectors and were analyzed for cell surface expression, recombinant gp120-binding activity, and overall structural integrity as assessed by reactivity with a battery of anti-CD4 monoclonal antibodies. Cells expressing the CD4 mutants were assayed for their ability to form syncytia when mixed with cells expressing the HIV-1 envelope glycoprotein. Surprisingly in view of published data from others, most of the mutations had little effect on syncytium-forming activity. Normal fusion was observed in 21 mutants, including substitution of human residues 85 to 95 with the corresponding sequences from either chimpanzee, rhesus, or mouse CD4; a panel of Ser-Arg double insertions after each residue from 86 to 91; and a number of other charge, hydrophobic, and proline substitutions and insertions within this region. The nine mutants that showed impaired fusion all displayed defective gp120 binding and disruption of overall structural integrity. In further contrast with results of other workers, we observed that transformant human cell lines expressing native chimpanzee or rhesus CD4 efficiently formed syncytia when mixed with cells expressing the HIV-1 envelope glycoprotein. These data refute the conclusion that certain mutations in the CDR3 region of CD4 abolish cell fusion activity, and they suggest that a wide variety of sequences can be functionally tolerated in this region, including those from highly divergent mammalian species. Syncytium formation mediated by several of the CDR3 mutants was partially or completely resistant to inhibition by the CDR3-directed monoclonal antibody L71, suggesting that the corresponding epitope is not directly involved in the fusion process.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparative clonal analysis of human immunodeficiency virus type 1 (HIV-1)-specific CD4+ and CD8+ cytolytic T lymphocytes isolated from seronegative humans immunized with candidate HIV-1 vaccines

The lysis of infected host cells by virus-specific cytolytic T lymphocytes (CTL) is an important factor in host resistance to viral infection. An optimal vaccine against human immunodeficiency virus type 1 (HIV-1) would elicit virus-specific CTL as well as neutralizing antibodies. The induction by a vaccine of HIV-1-specific CD8+ CTL in humans has not been previously reported. In this study, CTL responses were evaluated in HIV-1-seronegative human volunteers participating in a phase I acquired immune deficiency syndrome (AIDS) vaccine trial involving a novel vaccine regimen. Volunteers received an initial immunization with a live recombinant vaccinia virus vector carrying the HIV-1 env gene and a subsequent boost with purified env protein. An exceptionally strong env-specific CTL response was detected in one of two vaccine recipients, while modest but significant env-specific CTL activity was present in the second vaccinee. Cloning of the responding CTL gave both CD4+ and CD8+ env-specific CTL clones, permitting a detailed comparison of critical functional properties of these two types of CTL. In particular, the potential antiviral effects of these CTL were evaluated in an in vitro system involving HIV-1 infection of cultures of normal autologous CD4+ lymphoblasts. At extremely low effector-to-target ratios, vaccine-induced CD8+ CTL clones lysed productively infected cells present within these cultures. When tested for lytic activity against target cells expressing the HIV-1 env gene, CD8+ CTL were 3-10-fold more active on a per cell basis than CD4+ CTL. However, when tested against autologous CD4+ lymphoblasts acutely infected with HIV-1, CD4+ clones lysed a much higher fraction of the target cell population than did CD8+ CTL. CD4+ CTL were shown to recognize not only the infected cells within these acutely infected cultures but also noninfected CD4+ T cells that had passively taken up gp120 shed from infected cells and/or free virions. These results were confirmed in studies in which CD4+ lymphoblasts were exposed to recombinant gp120 and used as targets for gp120-specific CD4+ and CD8+ CTL clones. gp120-pulsed, noninfected targets were lysed in an antigen-specific fashion by CD4+ but not CD8+ CTL clones. Taken together, these observations demonstrate that in an in vitro HIV-1 infection, sufficient amounts of gp120 antigen are produced and shed by infected cells to enable uptake by cells that are not yet infected, resulting in the lysis of these noninfected cells by gp120-specific, CD4+ CTL.(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro infection of human placental trophoblast by wild-type vaccinia virus and recombinant virus expressing HIV envelope glycoprotein

Short-time (< or = 7 days) cultures of trophoblast mononuclear cells isolated from term placentae were challenged with vaccinia virus. Cytopathic effects were induced in crude placental cell preparations as well as in cultures established after negative immunosorting of major histocompatibility complex class I epitope-expressing cells, i.e. cultures exclusively derived from villous cytotrophoblast according to our present state of knowledge. The trophoblast in vitro supported a full replicative cycle of both wild-type viruses and a recombinant clone serving as a vector for the human immunodeficiency virus type 1 envelope gene. Results may shed light on mechanisms involved in the rarely observed foetal damage caused by smallpox vaccination during pregnancy.

Quantitative assessment of poxvirus promoters in fowlpox and vaccinia virus recombinants

A comparison was undertaken of poxvirus promoters in vaccinia and fowlpox virus (FPV) recombinants using the level of beta-galactosidase expressed from the LacZ gene as a measure of promoter function. In this study a comparison was made of the vaccinia virus promoters, P 7.5 and P L11, the major late promoter of cowpox virus, P CPX (expressing the abundant inclusion body protein), and the FPV promoters, P E/L and P L. In vaccinia virus recombinants the FPV P E/L promoter expressed one-third to one-half the level of beta-galactosidase expressed by the P L11 promoter. In comparison with the P 7.5 promoter, the FPV P E/L promoter expressed four to five times the level of beta-galactosidase. In FPV recombinants beta-galactosidase activity expressed was equal for the P E/L and P CPX promoters. Levels expressed by P L11 and P L were one-half and one-fifth that level, respectively. The temporal regulation of the promoters was maintained in both vaccinia virus and FPV recombinants. The P E/L promoter of FPV has the TAAATG sequence characteristic of late poxvirus promoters at the transcription initiation site. In an attempt to enhance the utility of this promoter for the expression of foreign genes in FPV and vaccinia virus recombinants, the effect upon promoter function of changing the G of the ATG to A, T, or C was determined using transient expression assays with vaccinia virus. Substitution of A, T, or C for the G abolished promoter function. Because of its early/late function, the level of expression and the presence of the oppositely oriented late P L promoter, the FPV P E/L promoter will be valuable for the expression of foreign genes in poxvirus recombinants.

Protection against Friend retrovirus-induced leukemia by recombinant vaccinia viruses expressing the gag gene

High sequence variability in the envelope gene of human immunodeficiency virus has provoked interest in nonenvelope antigens as potential immunogens against retrovirus infection. However, the role of core protein antigens encoded by the gag gene in protective immunity against retroviruses is unclear. By using recombinant vaccinia viruses expressing the Friend murine leukemia helper virus (F-MuLV) gag gene, we could prime CD4+ T-helper cells and protectively immunize susceptible strains of mice against Friend retrovirus infection. Recovery from leukemic splenomegaly developed more slowly after immunization with vaccinia virus-F-MuLV gag than with vaccinia virus-F-MuLV env; however, genetic nonresponders to the envelope protein could be partially protected with Gag vaccines. Class switching of F-MuLV-neutralizing antibodies from immunoglobulin M to immunoglobulin G after challenge with Friend virus complex was facilitated in mice immunized with the Gag antigen. Sequential deletion of the gag gene revealed that the major protective epitope was located on the N-terminal hydrophobic protein p15.

Production of human monoclonal antibodies specific for conformational and linear non-V3 epitopes of gp120

Three IgG1 human monoclonal antibodies (MAbs) directed against conformational epitopes of the gp120 envelope protein of HIV-1 were produced, as was a single human MAb to a linear epitope spanning amino acids 487-509 in the C-terminal portion of gp120. All three conformation-dependent MAbs reacted optimally with recombinant gp120 (rgp120) captured on plastic via its carbohydrate moieties with Concanavalin A. These MAbs were able to block the interaction between recombinant CD4 (rCD4) and rgp120; they were also able to achieve 50% neutralization of HTLV-IIIB and MN strains of HIV-1 in a concentration range of 0.5-12.8 micrograms/mL. The MAb to the linear determinant is the first reported human MAb specific for the immunodominant portion of gp120; this MAb was most reactive with rgp120 when it was coated directly on plastic. It could neither inhibit rCD4-rgp120 binding nor neutralize either HTLV-IIIB or MN. The binding affinities of the four human MAbs for rgp120 in solution, reflected by their dissociation constants (Kd), ranged from 0.5 x 10(-8) to 7.5 x 10(-8) M.

Insertion of the human immunodeficiency virus CD4 receptor into the envelope of vesicular stomatitis virus particles

Enveloped virus particles carrying the human immunodeficiency virus (HIV) CD4 receptor may potentially be employed in a targeted antiviral approach. The mechanisms for efficient insertion and the requirements for the functionality of foreign glycoproteins within viral envelopes, however, have not been elucidated. Conditions for efficient insertion of foreign glycoproteins into the vesicular stomatitis virus (VSV) envelope were first established by inserting the wild-type envelope glycoprotein (G) of VSV expressed by a vaccinia virus recombinant. To determine whether the transmembrane and cytoplasmic portions of the VSV G protein were required for insertion of the HIV receptor, a chimeric CD4/G glycoprotein gene was constructed and a vaccinia virus recombinant which expresses the fused CD4/G gene was isolated. The chimeric CD4/G protein was functional as shown in a syncytium-forming assay in HeLa cells as demonstrated by coexpression with a vaccinia virus recombinant expressing the HIV envelope protein. The CD4/G protein was efficiently inserted into the envelope of VSV, and the virus particles retained their infectivity even after specific immunoprecipitation experiments with monoclonal anti-CD4 antibodies. Expression of the normal CD4 protein also led to insertion of the receptor into the envelope of VSV particles. The efficiency of CD4 insertion was similar to that of CD4/G, with approximately 60 molecules of CD4/G or CD4 per virus particle compared with 1,200 molecules of VSV G protein. Considering that (i) the amount of VSV G protein in the cell extract was fivefold higher than for either CD4 or CD4/G and (ii) VSV G protein is inserted as a trimer (CD4 is a monomer), the insertion of VSV G protein was not significantly preferred over CD4 or CD4/G, if at all. We conclude that the efficiency of CD4 or CD4/G insertion appears dependent on the concentration of the glycoprotein rather than on specific selection of these glycoproteins during viral assembly.

Recombinant vaccinia virus producing the prM and E proteins of yellow fever virus protects mice from lethal yellow fever encephalitis

Four recombinant vaccinia viruses were constructed for expression of different portions of the 17D yellow fever virus (YFV-17D) open reading frame. A recombinant, vP869, expressing prM and E induced high titers of neutralizing and hemagglutination inhibiting antibodies in mice and was protective against intracranial challenge with the French neurotropic strain of YFV. Levels of protection were equivalent to those achieved by immunization with the YFV-17D vaccine virus. Recombinant vaccinia viruses expressing E and NS1, C prM, E, NS1, or only NS1 failed to protect mice against challenge with YFV despite eliciting antibodies to NS1. The vP869-infected HeLa cells produced a particulate extracellular hemagglutinin (HA) similar to that produced by YFV-infected cells, supporting previous studies with Japanese encephalitis virus (Mason et al., 1991), suggesting that the ability of recombinant vaccinia virus to produce extracellular HA particles is important for effective flavivirus immunity.

Priming of anti-human immunodeficiency virus (HIV) CD8+ cytotoxic T cells in vivo by carrier-free HIV synthetic peptides

The generation of antiviral cytotoxic T lymphocytes (CTLs) is a critical component of the immune response to viral infections. A safe and nontoxic vaccine for AIDS would optimally use a carrier-free synthetic peptide immunogen containing only components of HIV necessary for induction of protective immune responses. We report that hybrid synthetic peptides containing either a HIV envelope gp120 T-cell determinant (T1) or the envelope gp41 fusion domain (F) N-terminal to HIV CTL determinants are capable of priming murine CD8+, major histocompatibility complex class I-restricted anti-HIV CTLs in vivo. These data demonstrate that carrier-free, nonderivatized synthetic peptides can be used in vivo to induce anti-HIV CTL responses.

Antitermination of vaccinia virus early transcription: possible role of RNA secondary structure

Transcription of vaccinia early genes by the viral RNA polymerase terminates downstream of a signal sequence TTTTTNT in the nontemplate DNA strand. Signal recognition occurs at the level of the sequence UUUUUNU in nascent RNA and depends on a virus-encoded termination factor (VTF). The presence of TTTTTNT elements within protein encoding regions of some early genes requires that these 5' proximal signals be ignored in order to achieve early expression of the full-sized proteins. In the case of the A18R gene, which contains a proximal terminator that is not utilized in vivo (Pacha et al., J. Virol. 64, 3853-3863 (1990)), the TTTTTNT sequence can be folded into a potential hairpin structure such that UUUUUNU would be part of a duplex stem in the nascent RNA. We find that the A18R putative hairpin is unable to promote factor-dependent termination in a purified in vitro transcription system. Sequence manipulations that abrogate the potential to form an RNA hairpin restore the activity of the TTTTTNT motif. The in vitro studies suggest that antitermination at the proximal site of the A18R gene may be mediated by secondary structure in the nascent RNA, and that early termination involves recognition by VTF and/or RNA polymerase of the UUUUUNU sequence in single-stranded form.

Stimulation of glycoprotein gp120 dissociation from the envelope glycoprotein complex of human immunodeficiency virus type 1 by soluble CD4 and CD4 peptide derivatives: implications for the role of the complementarity-determining region 3-like region in membrane fusion

We have used a recombinant vaccinia virus vector encoding the envelope glycoprotein of human immunodeficiency virus type 1 to study receptor-induced structural changes related to membrane fusion. A truncated soluble form of human CD4 (sCD4) was found to stimulate dissociation of the external subunit (gp120) from the envelope glycoprotein complex of human immunodeficiency virus type 1 expressed at the cell surface. sCD4 stimulation of gp120 release was time- and concentration-dependent and was associated with specific binding of sCD4 to gp120. Synthetic peptide derivatives corresponding to residues 81-92 of human CD4 (overlapping the complementarity-determining region 3-like region) inhibited cell-cell fusion mediated by the interaction between recombinant vaccinia-encoded CD4 and human immunodeficiency virus envelope glycoprotein. These peptide derivatives also stimulated gp120 release from the envelope glycoprotein complex. An analogous peptide derivative from chimpanzee CD4 (containing a single Glu----Gly substitution at the position corresponding to CD4 residue 87) was considerably less active at inhibition of cell-cell fusion and stimulation of gp120 release, consistent with the known inhibitory effect of this substitution on the ability of membrane-associated CD4 to mediate cell fusion. These results suggest that the sCD4-induced release of gp120 reflects postbinding structural changes in the envelope glycoprotein complex involved in membrane fusion, with the complementarity-determining region 3-like region playing a critical role.

Vaccinia virus: a tool for research and vaccine development

Vaccinia virus is no longer needed for smallpox immunization, but now serves as a useful vector for expressing genes within the cytoplasm of eukaryotic cells. As a research tool, recombinant vaccinia viruses are used to synthesize biologically active proteins and analyze structure-function relations, determine the targets of humoral- and cell-mediated immunity, and investigate the immune responses needed for protection against specific infectious diseases. When more data on safety and efficacy are available, recombinant vaccinia and related poxviruses may be candidates for live vaccines and for cancer immunotherapy.

Folding, interaction with GRP78-BiP, assembly, and transport of the human immunodeficiency virus type 1 envelope protein

A detailed kinetic and quantitative analysis of the early and late biosynthetic events undergone by the human immunodeficiency virus type 1 envelope protein expressed by a recombinant vaccinia virus was performed. Early folding events that occurred in the endoplasmic reticulum included disulfide bond formation (t1/2 approximately 10 min), folding of envelope protein into a form competent to bind CD4 (t1/2 approximately 15 min), and specific and transient association and dissociation with GRP78-BiP (t1/2 approximately 25 min). After initial folding, envelope protein monomers formed noncovalently associated dimers with high efficiency (t1/2 approximately 30 min). Studies with brefeldin A, a compound that inhibits endoplasmic reticulum-to-Golgi transport, suggested that assembly occurred in the endoplasmic reticulum while cleavage of gp160 into gp120/gp41 subunits occurred in a post-endoplasmic reticulum compartment. Transport to the Golgi was monitored by modification of N-linked sugars to forms partially resistant to endoglycosidase H. The kinetics of endoglycosidase H resistance were nearly identical to the kinetics of gp160 cleavage (t1/2 approximately 80 min). Cleavage efficiency was strongly cell type dependent, ranging from 13 to 70%. By contrast, approximately 50% of the gp120 generated by the cleavage event was shed (t1/2 approximately 120 min) regardless of the cell type used. The results are discussed in terms of the overall biosynthetic pathway of the envelope protein and provide a framework with which to assess the effects of mutations on structure and function.

Cellular immunity to HIV activated by CD4 fused to T cell or Fc receptor polypeptides

We describe functional simplified T cell and Fc receptor chimeras that are capable of directing CD8+ cytotoxic T lymphocytes (CTLs) to specifically recognize and lyse cells expressing HIV envelope proteins. Target cells bearing HLA-DR molecules are not recognized by CTL armed with the chimeras. The variety of cell types in which the native receptors are active suggests multiple possibilities for antiviral intervention through genetic means.

Primary structure of the membrane and nucleocapsid protein genes of feline infectious peritonitis virus and immunogenicity of recombinant vaccinia viruses in kittens

Feline infectious peritonitis virus (FIPV) causes a mostly fatal, immunologically mediated disease in cats. Previously, we demonstrated that immunization with a recombinant vaccinia virus expressing the FIPV spike protein (S) induced early death after challenge with FIPV (Vennema et al., 1990, J. Virol. 64, 1407-1409). In this paper we describe similar immunizations with the FIPV membrane (M) and nucleocapsid (N) proteins. The genes encoding these proteins were cloned and sequenced. Comparison of the amino acid sequences with the corresponding sequences of porcine transmissible gastroenteritis virus revealed 84.7 and 77% identity for M and N, respectively. Vaccinia virus recombinants expressing the cloned genes induced antibodies in immunized kittens. Immunization with neither recombinant induced early death after challenge with FIPV, strongly suggesting that antibody-dependent enhancement is mediated by antibodies against S only. Immunization with the N protein recombinant had no apparent effect on the outcome of challenge. However, three of eight kittens immunized with the M protein recombinant survived the challenge, as compared to one of eight kittens of the control group.

The induction of cytotoxic T-lymphocyte precursor cells by recombinant vaccinia virus expressing human papillomavirus type 16 L1

Expression of the major coat protein L1 of human papillomavirus type 16 by recombinant vaccinia viruses using a vaccinia late promoter and their use in generating antibodies have already been reported (Zhou et al., 1990). We have now constructed recombinant vaccinia viruses (VVs) which express the L1 protein from an early promoter with the intention of inducing cell-mediated immunity. This necessitated the removal of sequence motifs (TTTTTNT) from the L1 gene which would otherwise have caused transcription termination when expressed from a vaccinia virus early promoter. The nucleotide sequence was mutated to retain the correct amino acid sequence of the L1 protein. Full-length mRNA and L1 protein were generated in cells infected with the recombinant virus containing the mutant sequence, whereas the wild-type sequence generated only truncated mRNA and no detectable protein. Mice were immunized with VV expressing L1 from the mutant sequence and from the wild-type sequence in constructs with either early or late vaccinia virus promoters. Only the early promoter constructs were effective in priming cytotoxic T lymphocytes (CTL). Moreover the mutant sequence was significantly more effective than the wild-type sequence. The same L1 sequences, expressed from a vaccinia virus late promoter or coexpressed with MHC Class I molecules also expressed from a late promoter, produced high levels of L1 protein in both cases but nevertheless failed to elicit CTL activity. This is the first report of an HPV-specific CTL response and we have reaffirmed the importance of choosing the correct promoter and sequence expressed when using recombinant vaccinia viruses to induce cytotoxic T lymphocytes. These data are relevant for the design of vaccines to generate cell-mediated immunity against human papillomavirus infection.

Identification, sequence, and expression of the gene encoding the second-largest subunit of the vaccinia virus DNA-dependent RNA polymerase

The gene, rpo 132, encoding the second-largest subunit of the vaccinia virus DNA-dependent RNA polymerase was identified and sequenced. Two complementary approaches, involving antiserum to purified vaccinia virus RNA polymerase, were used to locate the rpo 132 gene. One method involved the screening of a lambda gt11 library of vaccinia virus genome fragments and the other was based on the immunoprecipitation and polyacrylamide gel electrophoresis of the in vitro translation products of mRNA that hybridized to immobilized vaccinia virus DNA. The deduced open reading frame of the rpo 132 gene predicted a polypeptide of 1164 amino acid residues with sequence similarities to the second-largest RNA polymerase subunits of eubacteria, archaebacteria, and eukaryotes as well as to other poxviruses. Transcriptional analyses indicated that rpo 132 has both early and late RNA start sites and is expressed throughout infection.

Biological and immunological properties of human immunodeficiency virus type 1 envelope glycoprotein: analysis of proteins with truncations and deletions expressed by recombinant vaccinia viruses

The effects of C-terminal and internal deletions on the synthesis, transport, biological properties, and antigenicity of the human immunodeficiency virus type 1 envelope protein were determined. A family of recombinant vaccinia viruses that express N-terminal overlapping env proteins of 204, 287, 393, 502 (full-length gp120), 635, 747, and 851 (full-length gp160) amino acids was constructed. All of the proteins were detected in intra- and extracellular forms which differed in the extent of glycosylation. The 747- and 851-amino-acid proteins were cleaved, were expressed on the surface of infected cells, and bound CD4. The 635-amino-acid env protein was cleaved inefficiently, and both the precursor and product were secreted, indicating absence of the transmembrane sequence. The 635- as well as the 502-amino-acid protein, which was also largely secreted, could still bind CD4. Unexpectedly, the 393-amino-acid protein was anchored in the plasma membrane, but neither it nor smaller proteins bound to soluble CD4. When amino acids at the gp120-gp41 junction were deleted, proteolytic cleavage of gp160 did not occur. Nevertheless, gp160 was inserted into the plasma membrane and bound soluble CD4. The predominant conserved B-cell epitopes were mapped to gp41 and the C terminus of gp120, whereas cytotoxic T-cell epitopes were distributed throughout the length of the glycoproteins.

Human immunodeficiency virus types 1 and 2 and simian immunodeficiency virus env proteins possess a functionally conserved assembly domain

The envelope (env) glycoproteins of human immunodeficiency viruses type 1 (HIV-1) and type 2 (HIV-2) form dimers shortly after synthesis. Analysis of the simian immunodeficiency virus (SIV) env protein expressed by a recombinant vaccinia virus revealed that it, too, forms stable homodimers. When the HIV-1 and SIV env proteins or the HIV-1 and HIV-2 env proteins were coexpressed in the same cells, heterodimers were formed. Thus, the env proteins of HIV-1, HIV-2, and SIV possess a functionally conserved domain involved in subunit-subunit recognition and assembly that likely involves the ectodomain of gp41.