AIDS virus env Protein Expressed from a Recombinant Vaccinia Virus

Immunopotentiation of the antibody response against influenza HA with apoptotic bodies generated by rabies virus G-ERA protein-driven apoptosis

Apoptosis is considered to be a way of eliminating unwanted cells without causing major inflammation. Nevertheless, several lines of evidence show that apoptotic cell-derived antigens can be strong immunogens. The rabies virus glycoprotein G-ERA is an apoptotic molecule. We tested the ability of G-ERA to potentiate a B cell response against an exogenous antigen (influenza hemagglutinin, HA). We found that co-expression of G-ERA and HA in apoptotic bodies increased both the primary and memory HA-specific immune responses. The immunopotentiation of G-ERA is apoptosis-mediated but not necrosis-mediated. Our data indicate that G-ERA-mediated apoptosis might be useful to improve the immunogenicity of live vaccines.

Recombinant CD63/ME491/neuroglandular/NKI/C-3 antigen inhibits growth of established tumors in transgenic mice

Attempts to vaccinate against tumors can be hindered by the induction of immunological tolerance to the target Ag as a result of Ag expression on normal tissues. In this study, we find that transgenic mice expressing the melanoma-associated Ag CD63/ME491/neuroglandular/NKI/C-3 on their normal tissues do, in fact, exhibit immunological tolerance to the Ag, recapitulating the conditions in cancer patients. In these mice, growth of murine melanoma cells expressing the Ag after gene transfer was inhibited by immunization with Ag-expressing recombinant vaccinia virus combined with IL-2, but not by immunization with the protein alone, anti-idiotypic Abs, or irradiated tumor cells. The effect of the recombinant virus was demonstrated both for nonestablished and established tumors. Infiltration with both CD4(+) and CD8(+) T lymphocytes was significantly more extensive in tumors from experimental mice than in tumors from control mice. MHC class I-positive, but not class I-negative, tumors were inhibited by the vaccine, suggesting that MHC class I-restricted T lymphocytes play a role in the antitumor effects. Abs did not appear to be involved in the vaccine effects. CD63 was immunogenic in 2 of 13 melanoma patients, pointing to the potential of this Ag, combined with IL-2, as a vaccine for melanoma patients.

Folding of HIV-1 envelope glycoprotein involves extensive isomerization of disulfide bonds and conformation-dependent leader peptide cleavage

Human immunodeficiency virus binds and enters cells via the Envelope glycoprotein gp160 at its surface. In infected cells, gp160 is found not only on the plasma membrane but also in the endoplasmic reticulum (ER). Our aim was to establish rate-determining steps in the maturation process of gp160, using a radioactive pulse-chase approach. We found that gp160 has an intricate folding process: disulfide bonds start to form during synthesis but undergo extensive isomerization until the correct native conformation is reached. Removal of the leader peptide critically depends on formation of at least some disulfide bonds in subunit gp120 during folding. Envelope folds extremely slowly and therefore resides in the ER longer than other proteins, but the yield of properly folded molecules is high and degradation is undetectable. The large quantity of gp160 in the ER hence is a result of its slow transit through this compartment. We show here that newly synthesized HIV-1 Envelope glycoprotein apparently follows a slow but high-yield folding path in which co- and post-translational formation of disulfide bonds in gp120, disulfide isomerization and conformation dependent removal of the leader sequence are determining and intertwined events.

Construction and characterisation of infectious recombinant HIV-1 clones containing CTL epitopes from structural proteins in Nef

In this study the construction is described of HIV-1 molecular clones in which CTL epitopes from RT or Env late proteins were inserted into the Nef early protein. The ectopic epitopes were efficiently processed from the recombinant Nef proteins, were recognized by their cognate CTL in cytolytic assays, and did not perturb virus replication or viral protein expression in vitro. These recombinant viruses will therefore be an important tool in studying the effect of distinct epitope expression kinetics on the efficiency of CTL-mediated suppression of HIV-1 replication.

Generation of monoclonal antibodies to native human immunodeficiency virus type 1 envelope glycoprotein by immunization of mice with naked RNA

The Semliki Forest virus (SFV) vector system is a new approach for in vivo expression of heterologous proteins and can also be used to generate specific immune responses in animal models. HIV-1 envelope glycoprotein produced using the SFV expression system is correctly folded, cleaved, transported to the cell surface and exhibits functional activity. We evaluated a recombinant Semliki Forest virus naked RNA-based immunization protocol for generation of monoclonal antibodies against the HIV-1 envelope glycoprotein. In vitro-transcribed RNA encoding for the SFV replicase complex and Env protein of HIV-1 (HXB2 strain) was injected intramuscularly to mice. This approach elicited an Env-specific antibody response in four mice out of five and a monoclonal antibody, 12H2, directed against gp41 was produced. Our results show that recombinant SFV RNA immunization can potentially be used as a quick and direct method to produce monoclonal antibodies, with the particular advantage that vectored RNA, rather than purified antigen, delivers a complex oligomer produced correctly.

The optimization of helper T lymphocyte (HTL) function in vaccine development

Helper T lymphocyte (HTL) responses play an important role in the induction of both humoral and cellular immune responses. Therefore, HTL epitopes are likely to be a crucial component of prophylactic and immunotherapeutic vaccines. For this reason, Pan DR helper T cell epitopes (PADRE), engineered to bind most common HLA-DR molecules with high affinity and act as powerful immunogens, were developed. Short linear peptide constructs comprising PADRE and Plasmodium-derived B cell epitopes induced antibody responses comparable to more complex multiple antigen peptides (MAP) constructs in mice. These antibody responses were composed mostly of the IgG subclass, reactive against intact sporozoites, inhibitory of schizont formation in liver invasion assays, and protective against sporozoite challenge in vivo. The PADRE HTL epitope has also been shown to augment the potency of vaccines designed to stimulate a cellular immune response. Using a HBV transgenic murine model, it was found that CTL tolerance was broken by PADRE-CTL epitope lipopeptide, but not by a similar construct containing a conventional HTL epitope. There are a number of prophylactic vaccines that are of limited efficacy, require multiple boosts, and/or confer protection to only a fraction of the immunized population. Also, in the case of virally infected or cancerous cells, new immunotherapeutic vaccines that induce strong cellular immune responses are desirable. Therefore, optimization of HTL function by use of synthetic epitopes such as PADRE or pathogen-derived, broadly crossreactive epitopes holds promise for a new generation of highly efficacious vaccines.

Course of specific T lymphocyte cytotoxicity, plasma and cellular viral loads, and neutralizing antibody titers in 17 recently seroconverted HIV type 1-infected patients

Relationships were sought between specific anti-HIV cytotoxic T lymphocyte (CTL) responses (against structural and regulatory proteins of the HIV-1 LAI isolate) and plasma and cellular viral loads (VLs) in 17 recently HIV-1-infected patients including 3 displaying asymptomatic primary infection (PI) followed up for 12 months. Plasma VL was correlated directly with CD8 counts and inversely with CD4 counts. Cytotoxic reactions were observed in all patients and directed mainly against structural proteins. The earliest CTL responses were against Gag and Env proteins detected in 87 and 75% of the subjects, respectively, within the first month following PI. Anti-Env and Gag cytotoxic responses were inversely correlated with the plasma VL. Reactions against the pol gene products were thought to be either less involved in or less efficient for the initial decrease of viremia. Responses against regulatory gene products were weak and variable, apart from Nef, which was recognized by half of the subjects. Neutralizing antibodies were not detected before month 3, and were found only in six patients at subsequent times. Two of three patients with asymptomatic PI had a low viral burden and either a delayed response or one limited to a few protein CTL responses, suggesting that the magnitude of the CTL response depends on the initial plasma VL. The third patient displayed viral and CTL parameters identical to those of the patients with symptomatic PI. However, two subjects with symptomatic PI exhibited similarly low plasma VL and moderate CTL responses. Overall, the results suggest that the CTL response may not be the sole factor controlling viremia.

Induction of rat CD4+ proliferative and mouse CD8+ cytotoxic T-cell lines specific for human papillomavirus type 16 antigens

Infection by human papillomavirus type 16 (HPV16) has been associated with cervical dysplasia and carcinoma. To detect a possible cellular immune response against HPV16, we investigated the induction of T cells specific for antigens encoded by the virus. Two CD4+ T-cell lines with a specific proliferative response were isolated from the spleens of rats vaccinated using vaccinia virus vectors expressing E6 or E7 and challenged with syngeneic HPV-transformed cells. Two CD8+ T-cell lines with a specific cytotoxic activity were obtained from mice immunized using a syngeneic squamous cell tumour cell line transfected with the full-length HPV16 DNA. These results demonstrate that both CD8-mediated cytotoxic responses and CD4-mediated delayed-type hypersensitivity responses are involved in immunologic reactions to HPV antigens.

High-titer immune responses elicited by recombinant vaccinia virus priming and particle boosting are ineffective in preventing virulent SIV infection

Eighteen rhesus monkeys were vaccinated with recombinant vaccinia viruses expressing SIVmac antigens in 3 separate rounds of experiments. Twelve of the monkeys were primed with a trivalent vaccinia virus recombinant expressing Gag, Pol, and Env polypeptides that can assemble into SIV pseudovirion particles and boosted with SIV particles in adjuvant. Four of the monkeys were primed with different vaccinia virus recombinants expressing env or gag+env followed by SIV particle boosts; two received vaccinia virus recombinants alone (env or env+gag). Despite the induction of vigorous immune responses, 17 of 18 rhesus monkeys became infected on challenge with a low dose of virulent SIVmac. The single protected animal was one of three challenged with homologous cloned SIV exactly matched to the clone used for construction of trivalent vaccinia virus recombinant and particles. Vaccination may have diminished SIV burdens and rates of CD4+ cell declines in some of the animals, but vaccinated/challenge/infected animals eventually developed fatal disease similar to control animals. These results highlight the extreme difficulty in achieving vaccine protection against virulent SIVmac infection even under idealized laboratory conditions.

Multiepitope polypeptide of the HIV-1 envelope induces neutralizing monoclonal antibodies against V3 loop

A gene encoding a multiepitope polypeptide (MEP) has been synthesized. It contains the information for (1) an 11-amino acid (aa) epitope from the C1 region of gp120 of HIV-1 and (2) 3 epitopes of 15 amino acids each, from the central part of the V3 loop of isolates MN, SC, and WMJII. These four segments are linked by the short spacer peptide AGGGA. This gene was cloned in a plasmid vector and expressed in Escherichia coli as a fusion product with a 62-aa fragment of human IL-2. The recombinant protein TAB1 was purified by washed pellet procedures and reversed-phase HPLC. TAB1 was recognized in ELISAs by 25 of 27 sera from seropositive individuals. Mice were immunized and several hybridomas were obtained. Two of them secrete monoclonal antibodies that react with synthetic peptides from isolates MN, WMJI, WMJIII, and SC with an affinity constant in the range of 10(8) M-1. They also recognized peptides from isolates SF2 and WMJII, but at much lower affinity. The results obtained from peptide ELISAs indicate that the putative epitope recognized by these MAbs lies within the sequence IHIGPGRAFYT. Classic neutralization assays demonstrated that MAb 2C4 neutralizes 50% of the MN isolate at 0.6 micrograms/ml but fails to neutralize IIIB and SF2 strains. The presence of antibodies directed against every one of the component peptides in the sera of rabbits immunized with TAB1 was also documented.

Use of the recombinant chimera proteins, LacZ-Env and Gag-Env, for immunological studies on HIV-1 infection

To use Env proteins as antigens for detection of the human immunodeficiency virus type-1 (HIV-1) antibodies, we attempted to overexpress the Env proteins in Escherichia coli. To study the epitopes in the Env proteins recognized by the sera of HIV carriers, various regions of the proviral DNA encoding the Env region were fused to the 3' end of the lacZ gene. The immunoblotting analysis of the LacZ-Env(512-611) and LacZ-Env(721-826) proteins with the 41 positive sera revealed that the former and the latter immunologically reacted with 100 and 78% of the sera, respectively. To avoid rare false-positive reactions due to the LacZ moiety of the fusion protein, we attempted to express the Env(512-611) alone or Gag-Env(512-611) under the control of bacteriophage T7 promoter. Although we could express only a low level of the Env(512-611) peptide in E. coli, we succeeded in producing large amounts of the Gag(121-406)-Env(512-611) and Gag(308-406)-Env(512-611) proteins as chimeric proteins. Both of these chimera proteins strongly reacted with the 41 positive sera. We purified these proteins and analyzed the immunological reactivity by dot blot with the 60 positive sera and the 84 normal sera. As little as 20 ng of the dotted proteins was enough for the reaction with the positive sera, whereas as much as 320 ng of them did not show false-positive reactions with the normal sera. We obtained highly purified Gag-Env proteins with highly specific seroreactivity, which should be useful for diagnosis and prognosis.

Expression and immunogenicity of the V3 loop from the envelope of human immunodeficiency virus type 1 in an attenuated aroA strain of Salmonella typhimurium upon genetic coupling to two Escherichia coli carrier proteins

A peptide comprising residues glu293 to ser334 from the principal neutralization determinant (V3 loop) of the envelope of human immunodeficiency virus type 1 (HIV1 LAVBRU isolate) has been inserted within internal permissive sites of either LamB or MalE, two envelope proteins from Escherichia coli K12. The MalE hybrid protein (MalE133-V3 loop) was stably expressed in the periplasm of Escherichia coli K12, and the V3 loop peptide was detectable on the surface of the native protein by an anti-gp160 monoclonal antibody (mAb 110-A). The disulfide bridge between the two cysteines of the loop was formed. In contrast, genetic coupling to the outer membrane protein LamB did not allow the expression of a stable hybrid protein, and major proteolytic cleavage products of the LamB153-V3 loop were detected by mAb 110-A. The two plasmid-encoded hybrid genes were transferred to an aroA mutant of Salmonella typhimurium. Constitutive expression of the MalE133-V3 loop had no detectable effect on cell growth and on the survival in vivo of the recipient strain. The LamB153-V3 loop was not stably expressed in Salmonella, either in vitro or in vivo. Live recombinant salmonellas expressing MalE-V3 and LamB-V3 loop hybrids were used to immunize mice. The MalE-V3 loop hybrid induced anti-HIV1 envelope antibodies detectable by Western blot and ELISA, while the anti-HIV1 envelope antibodies induced by the LamB-V3 loop hybrid were only detectable by Western blot. In addition, purified MalE-V3 loop hybrid protein was able to stimulate in vitro and induce in vivo a V3 loop-specific T-cell proliferative response.

Immunogenicity of HILDA/LIF either in a soluble or in a membrane anchored form expressed in vivo by recombinant vaccinia viruses

Insertion of various cDNAs in the genome of the vaccinia virus (VV) enables the in vivo and in vitro study of the functional role and/or the immunogenicity of the virally encoded recombinant proteins. We have prepared a recombinant VV expressing the cDNA of the human cytokine HILDA/LIF (human interleukin for DA cells/leukaemia inhibitory factor), and used this virus to immunize mice against this protein, which is very homologous to its murine counterpart (approximately 80% homology). We also constructed and expressed by the same system a chimeric gene encoding the HILDA/LIF protein fused to the 37 COOH-terminal amino-acids of the human decay accelerating factor (DAF). This sequence proved to be sufficient for the targeting of the fusion protein to the cell membrane, where it is linked to the phosphatidylinositols. Both recombinant VVs induced cytokine-specific antibodies in mice as analysed with an ELISA where the recombinant HILDA/LIF was plastic-coated and a cytofluorometric assay where the LIF-DAF molecule was present at the cell surface of stably transfected P815. In the latter case HILDA/LIF remained biologically active suggesting that it was expressed in its native form. The LIF-DAF fusion protein was found to exhibit a better capacity to elicit an antibody response against the native form of the cytokine as detected in cytofluorometric assays. Whatever the recombinant virus used to immunize the mice, the MoAbs obtained were positive either in the ELISA or in the cytofluorometric assays but one, which suggested that the plastic coating induced a conformational change of HILDA/LIF.

A peptide substitution in HIV-1 gp120 first hypervariable domain enhances its immunogenicity in mice

The envelope (Env) protein from HIV-1 is the focus of several vaccine trials in humans. It could be considered for the optimization of Env vaccinal preparations to add within the molecule defined epitopes, for instance epitopes conserved among viral isolates from HIV-1, such as from Gag or Nef proteins. As a first step to this approach, we have constructed by in vitro mutagenesis HIV-1(LAI) Env gp120 molecules in which a 12-amino acid sequence in the first (V1) or the third (V3) hypervariable region was substituted by the hemagglutinin (HA) 307-318 peptide from the influenza virus, a dominant T helper cell epitope in humans. The proteins were produced by recombinant vaccinia viruses. They had kept their structural properties in terms of serological recognition and binding to CD4. Of note, we observed that the gp120 protein substituted in the V1 domain elicited a stronger serological immune response in mice compared to native or V3 substituted gp120. This indicates that gp120 can accommodate large substitutions without major structural perturbations and that, on the contrary, some of them could prove beneficial in terms of immunogenicity.

Membrane expression of HIV envelope glycoproteins triggers apoptosis in CD4 cells

The cytopathic effect of HIV-1 and HIV-2 in CD4+ lymphocytes has been shown to be associated with apoptosis or programmed cell death. Using different experimental conditions, we demonstrate here that apoptosis is triggered by cell membrane expression of the mature HIV envelope glycoproteins, gp120-gp41 complex, and their interaction with CD4 receptor molecules. Viral entry alone did not induce apoptosis but virus replication was required in order to produce the gp120-gp41 complex. Indeed, expression of the HIV env gene alone in the CD4+ T cell line (CEM) was sufficient for the induction of apoptosis. In general, syncytium formation and apoptosis induction were closely associated as both events require functional envelope glycoproteins and CD4 molecules. Nevertheless, apoptosis but not syncytium formation was suppressed by a monoclonal antibody against CD4 that does not affect gp120 binding. Furthermore, single-cell killing by apoptosis was observed in infected cell cultures treated with a monoclonal antibody against gp41, which completely abolishes the formation of syncytia. These results indicate that apoptosis is not the consequence of toxic effects induced by the formation of syncytia but is triggered by the HIV envelope glycoproteins. Therefore, cell death during HIV infection in CD4+ lymphocyte cultures is due to a specific event triggered by the gp120-gp41 heterodimer complex programming death in metabolically active cells.

Morphogenesis of recombinant HIV-2 gag core particles

The gag-pol coding region of the HIV-2BEN genome was expressed in CV-1 cells infected with four recombinant vaccinia viruses (VV). These recombinant VV encoded either the whole gag-pol region or the gag gene including the protease-coding region of the pol gene or the gag gene truncated at its 3'-end or only the pol gene. The HIV-2BEN gag precursor p55, its mature cleavage products p24 and p17 as well as the pol reverse transcriptase (RT) p66 were detected in VV-infected CV-1 cells. The p55 and two intermediate cleavage products p40 and p35 were myristilated. Comparison to lysates of permanently HIV-2BEN-infected Molt 4 clone 8 cells revealed that several additional gag and pol proteins were present in the VV-infected CV-1 cells. Deletion of the gag and pol overlapping region coding for the viral protease prevented cleavage of the recombinant gag precursor. Electron microscopy of VV-infected CV-1 cells revealed budding structures and immature as well as mature retroviral particles formed by the recombinant gag proteins. Striking differences in the ability to form complete particles were observed between the different recombinant VV. Expression of the truncated gag gene led to the formation of budding structures, but completely budded circular particles were not detectable. Such particles were produced by expression of the whole gag gene and the protease. Mature virions with an internal core structure were only detected in VVgagpol-infected cells. From these findings we conclude that the 3'-end of the gag gene coding for the p16 protein is essential for the formation of complete HIV-2 particles and that the pol proteins support the assembly of the viral core.

Studies on compartmentation and turnover of murine retrovirus envelope proteins

Several aspects of turnover and degradation of cell membrane proteins were studied in an NIH 3T3 cell clone expressing the env gene of Moloney murine leukemia virus ts1. Both internalization and shedding of the extracellular domain of the envelope protein gp70 occurred at the cell surface, albeit, in the case of shedding, only a very small fraction of gp70 was shed. The turnover rate of gp70 at the cell surface was similar to that of the same protein in the postendoplasmic reticulum intracellular compartment. In the presence of L-methionine methyl ester, the transmembrane domain of the envelope protein Prp15E was degraded faster than gp70.

Study of the interaction of HIV-1 and HIV-2 envelope glycoproteins with the CD4 receptor and role of N-glycans

In order to further characterize the interaction of human immunodeficiency viruses (HIV) with the CD4 receptor at the molecular level, a binding test was performed using iodine-labeled glycoproteins, 125I-gp160 from HIV-1 and 125I-gp140 from HIV-2, to bind to lymphoid cells expressing the CD4 receptor. The inhibition of binding of the radiolabeled glycoproteins to CD4+ cells by increasing concentrations of nonradiolabeled gp160 or gp140 was used to determine the affinity of the interaction between the glycoproteins and CD4. The gp-CD4 association occurs with a high affinity: K0.5 gpHIV-1 = 9 x 10(-9) M and K0.5 gpHIV-2 = 7 x 10(-8) M, indicating that the affinity of the interaction between HIV-2 gp140 and CD4 is 10 times lower than that observed with HIV-1 gp160. The N-linked glycans of the HIV-1 and HIV-2 glycoproteins account for a high proportion of their molecular mass (about 50%). Total deglycosylation of gp160 and gp140 by enzymatic treatment with Endo F-N glycanase occurred under nondenaturing conditions, indicating the high accessibility of the N-linked glycan chains in the three-dimensional structure of the molecule. Moreover, the deglycosylated proteins retained a significant binding capacity to CD4. These results show that the carbohydrate chains of HIV-2 gp140, as those of HIV-1 gp160, do not play a major role in the gp-CD4 interaction.

Immunological analysis of human immunodeficiency virus type 1 envelope glycoprotein proteolytic cleavage

Two potential cleavage sites have been identified on precursor gp 160 of human immunodeficiency virus type 1. Using antibodies directed against the C-terminus of gp 120, including the sequence between the two sites, we have shown that nonmutated viral and recombinant gp 160 are cleaved at both sites: the great majority of molecules are cleaved at site 1 (Arg-Glu-Lys-Arg), and gp41 can then associate as an oligomer; a minority of molecules are cleaved at site 2 (Lys-Ala-Lys-Arg-Arg) and the corresponding gp41 appears to present as a monomer. This could reflect two different processing pathways for gp41 biosynthesis, one of which only may result in biologically active molecules according to the literature.

Specificity of anti-peptide antibodies elicited against synthetic peptides mimicking conserved regions of HIV1 envelope glycoprotein

Comparison of HIV1Bru and HIV2Rod external envelope glycoprotein sequences enabled us to select ten highly conserved peptide sequences. The corresponding peptides were chemically synthesized, then coupled to bovine serum albumin before injection in rabbits. Although all peptides were immunogenic, only antibodies directed against peptides P1 (amino acid residues 33-55), P22 (418-462), P8 (487-508) and P21 (487-534) were able to interact with significant affinity (K0.5 about 10(-6) to 10(-8) M) with the native glycoprotein by radioimmunoassay. Noteworthy was the capacity of anti-P1 antibodies to also recognize the glycoprotein of HIV2. Anti-peptide antibodies were tested for their ability to interfere with the gp120-CD4 interaction, membrane fusion and virus replication. Preincubation of gp120 with antibodies directed to the region previously described as the putative CD4-binding site, P22 (418-462), did not abolish gp120 binding to CD4-positive cells.

Vaccinia recombinants expressing secreted and transmembrane forms of breast cancer-associated epithelial tumour antigen (ETA)

Monoclonal antibody H23 identifies a polymorphic epithelial tumour antigen (ETA) that is aberrantly expressed in breast cancer and which may afford a target for active immunotherapy. We recently reported the cloning of H23-ETA genomic and cDNA clones. H23-ETA contains a multiple internal tandem repetition of a 20 amino acid motif and sequence analysis predicted two mRNA species encoding different ETA proteins, one harbouring a C-terminal potentially transmembrane hydrophobic zone (T) and a second form (S) that lacks this zone. We report that both RNA species can be detected in breast cancer cells. To further characterize the encoded proteins we have constructed vaccinia virus recombinants, VV-ETA-S and VV-ETA-T, separately expressing the alternative forms. Despite selective loss of internal tandem repeat elements during propagation of recombinant vaccinia, the encoded polypeptides were efficiently recognized by H23 monoclonal antibody. Immunoprecipitation revealed that ETA encoded by the S recombinant was secreted into the culture medium whereas the T form remained tethered at the cell surface. Both forms were readily detected in infected cells by immunofluorescence. Abnormal mobility of the T polypeptide indicated post-translational cleavage that may permit the extracellular domain of the T-polypeptide to be shed from the cell surface. Further, fluorescence-activated cell sorting analysis shows that the S form of the polypeptide is also partly present at the cell surface. Vaccinia recombinants expressing ETA may be of utility in the active immunotherapy of breast cancer.

Interaction of human epidermal Langerhans cells with HIV-1 viral envelope proteins (gp 120 and gp 160s) involves a receptor-mediated endocytosis independent of the CD4 T4A epitope

The CD4 molecule is known to be the preferential receptor for the HIV-1 envelope glycoprotein. Epidermal Langerhans cells are dendritic cells which express several surface antigens, among them CD4 antigens. To clarify the exact role of CD4 molecules in Langerhans cell infection induced by HIV-1, we investigated the possible involvement of the interactions between HIV-1 gp 120 or HIV-1 gp 160s (soluble gp 160) and Langerhans cell surface. We also assessed the expression of CD4 molecules on Langerhans cell membranes dissociated by means of trypsin from their neighbouring keratinocytes. The cellular phenotype was monitored using flow cytometry and quantitative immunoelectron microscopy. We reported that human Langerhans cells can bind the viral envelope proteins (gp 120 or gp 160s), and that this binding does not depend on CD4 protein expression. This binding is not blocked by anti-CD4 monoclonal antibodies. We show that a proportion of gp 120/gp 160s-receptor complexes enters Langerhans cells by a process identified as a receptor-mediated endocytosis. The amount of surface bound gp 120/gp 160s is not consistent with the amount of CD4 antigens present on Langerhans cell membranes. Gp 120/gp 160s binding sites on Langerhans cell suspensions appeared to be trypsin resistant, while CD4 antigens (at least the epitopes known to bind the HIV-1) are trypsin sensitive. A burst of gp 120 receptor expression was detected on 1-day cultured Langerhans cells while CD4 antigens disappeared. These findings lead to the most logical conclusion that binding of gp 120/gp 160s is due to the presence of a Langerhans cell surface molecule different from CD4 antigens.

Trypsin-resistant gp120 receptors are upregulated on short-term cultured human epidermal Langerhans cells

The CD4 molecule is known to be the preferential receptor for the HIV1 envelope glycoprotein. Epidermal Langerhans cells (LC) are dendritic cells which express several surface antigens, among them the CD4 antigens. LC infection was suggested when these cells were seen to present buddings coincident with membrane thickening of roughly 100 nm in size. These buddings were similar in ultrastructural aspect to HIV buddings on in vitro infected promonocytic cells (U937). To clarify the exact role of CD4 molecules in LC infection induced by HIV1, we investigated the possible involvement of between native and recombinant HIV1 gp120 and the LC surface. We also assessed the expression of CD4 molecules on LC membranes dissociated by means of trypsin from their neighbouring keratinocytes. The cellular phenotype was monitored using flow cytometry. We show that human LC can bind the viral envelope protein and that this binding does not depend on CD4 protein expression. The amount of surface bound gp120 was not consistent with the amount of CD4 antigens present on LC membranes. The gp120-binding sites on LC in suspension appear to be typsin-resistant while the CD4 antigens (at least the epitopes known to bind HIV1) are trypsin-sensitive. A burst of gp120 receptor expression was detected on 1-day cultured LC while the CD4 antigens disappeared. These findings lead to the logical conclusion that the binding of gp120 is due to the presence of a LC surface molecule which is different from CD4 antigens.

Immunization against human papillomavirus type 16 tumor cells with recombinant vaccinia viruses expressing E6 and E7

Papillomaviruses are etiological agents of epithelial proliferative disease. In man, neoplastic transformation of the uterine cervix has been linked to infection with specific subtypes of human papillomavirus, particularly types 16 and 18. We previously reported that live vaccinia virus recombinants expressing early transforming proteins of other tumor viruses can immunize against challenge with cognate tumor cells and we have extended this approach to HPV16. Neoplastic transformation by papillomaviruses involves expression of early open reading frames (ORFs) E5, E6, and E7, and we report the construction of vaccinia recombinants separately expressing ORFs E5-E7 of HPV16. Primary rat cell lines cotransformed with HPV16 and an activated ras oncogene were established in order to evaluate the potential of the recombinants to elicit antitumor immunity. We report that inoculation of rats with vaccinia recombinants expressing E6 or E7 retarded or prevented tumor development in a proportion of animals challenged by subcutaneous seeding of tumor cells whereas the recombinant expressing E5 was inactive.

Immunogenicity and epitope mapping of a recombinant soluble gp160 of the human immunodeficiency virus type 1 envelope glycoprotein

The human immunodeficiency virus 1 envelope glycoprotein is synthesized as a precursor, gp160, which is subsequently cleaved to generate the external gp120 and the transmembrane gp41. Both of these cleavage products are known to mediate critical functions of the virus. In order to define the best strategy for the development of a vaccine against human immunodeficiency virus 1, it could be important to map the crucial epitopes on gp160. This entire gp160 is uneasy to purify because it is readily subjected to proteolytic cleavage. Furthermore, it is anchored on the cell membrane and needs detergent treatment for purification. We thus used a recombinant gp160 which was engineered to remove the cleavage sites between gp120 and gp41 and the hydrophobic transmembrane in order to investigate the murine immune response. We selected a panel of 8 monoclonal antibodies which recognize different epitopes on the immunizing recombinant soluble gp160. The reactivity of the monoclonal antibodies was checked on virus-derived gp160, gp120, and gp41. Three antibodies reacted only with gp120 but the others were shown to react with gp41 epitopes or with discontinuous epitopes bridging gp120 and gp41. One subregion of these epitopes was located using a synthetic peptide corresponding to the sequence of gp41. This epitope is apparently part of an immunodominant site since it is recognized by three different monoclonal antibodies. We used competitive inhibition experiments to map the epitopes on recombinant gp160; therefore, the results are probably indicative of the folding of the recombinant soluble gp160 used for immunization.

Synthesis, oligomerization, and biological activity of the human immunodeficiency virus type 2 envelope glycoprotein expressed by a recombinant vaccinia virus

The full-length envelope gene from an infectious human immunodeficiency virus type 2 (HIV-2) molecular clone was expressed in CD4+ and CD4- cells by a recombinant vaccinia virus vector. Pulse-chase experiments indicated that gp160 was processed into gp120 and gp41 subunits. Although large amounts of gp120 were shed into the medium, the recombinant vaccinia virus-infected cells fused with uninfected CD4+ cells. The receptor binding of HIV-2 gp120 was further analyzed using a panel composed of nine soluble CD4 mutants containing insertions of 2 amino acids within the first and second immunoglobulin-like domains. Of three mutations previously shown to interfere with HIV-1 gp120 binding, two also interfered with binding of the HIV-2 glycoprotein indicating use of the same binding site. Chemical crosslinking, sucrose gradient sedimentation, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis were employed to study the oligomerization of the envelope protein. The data indicated that gp160 assembles posttranslationally into dimers and higher oligomers that are probably tetramers.

Vaccinia recombinants expressing early bovine papilloma virus (BPV1) proteins: retardation of BPV1 tumour development

Papillomaviruses are aetiological agents of epithelial proliferative diseases in animals and in man. It was previously demonstrated that animals inoculated with live vaccinia recombinants expressing early proteins of polyoma virus resist challenge with polyoma-tumour cells, and this approach has been extended to the development of a vaccine against papillomavirus-transformed cells. Bovine papillomavirus type 1 (BPV1), a virus responsible for dermal lesions in cattle, is a prototype virus of the papillomavirus group. Independent vaccinia recombinant viruses expressing the early E1, E2, E5, E6 or E7 open reading frames of BPV1 were tested for their ability to direct the expression of the corresponding protein in cultured cells. Recombinants were then assessed for their ability to elicit anti-tumour immunity in Fischer rats seeded with BPV1-transformed syngeneic FR3T3 cells. Retardation of tumour growth was observed in animals vaccinated with recombinants expressing E5, E6 or E7.

Expression and characterization of a functional human immunodeficiency virus envelope glycoprotein in insect cells

Recombinant baculoviruses were used to express the gp160 envelope glycoprotein of the human immunodeficiency virus type 1 (HIV-1) and a truncated variant designated gp160(t) which lacks a transmembrane domain. Glycosylation, proteolytic cleavage, secretion, and biological activities of gp160 and gp160(t) 160(t) were studied in Spodoptera frugiperda cells. Both proteins were rapidly glycosylated and initially were found to be totally endo-beta-N-acetyl-D-glucosaminidase H (endo-H) sensitive. However, partial resistance to endo-H was gradually acquired by both molecules. gp160 was found to remain cell-associated, whereas gp160(t) was secreted into the culture medium in large amounts. A fraction of gp160 and gp160(t) appeared to be proteolytically cleaved, and a cleavage product corresponding in size to gp120 was identified in the culture medium. gp160(t) was found to interact specifically with CD4 receptors without any requirement for proteolytic cleavage. The gp160 protein was shown to be expressed on the surface of S. frugiperda cells by direct immunofluorescence. These surface molecules were biologically active, as demonstrated by their ability to induce syncytium formation when cocultivated with HeLa T4 cells.

High level expression of the envelope glycoproteins of the human immunodeficiency virus type I in presence of rev gene using helper-independent adenovirus type 7 recombinants

The effect of rev (art/trs) gene on the level of HIV-1 envelope (env) expression using recombinant adenovirus was investigated. Recombinant adenoviruses expressing either the envelope or the rev gene of the human immunodeficiency virus type 1 (HIV-1) were constructed by inserting the gene into an expression cassette. The expression cassette contained the adenovirus type 7 major late promoter, followed by leader 1 of the adenovirus tripartite leader and a portion of intron between leaders 1 and 2, leaders 2 and 3, and a hexon polyadenylation signal. The cassette was then inserted at the terminal region between the E4 and ITR regions of the adenovirus 7 genome with a concomitant E3 region deletion (80-87 m.u.). A549 cells infected with the recombinant virus containing the env gene produced the envelope glycoproteins gp160, gp120, and gp41. HIV-1 envelope gene expression was greatly enhanced (20- to 50-fold) in the cells that were simultaneously infected with the recombinant adenovirus containing the rev gene as measured by ELISA and Western blotting. Interestingly, this effect was observed despite the lack of the 5' down splice site for rev and seems to be post-transcriptional. Another recombinant adenovirus which contains both the rev and the env genes was constructed by inserting the rev gene in the deleted E3 region and the env gene in the terminal cassette. This double recombinant virus expressed high levels of env antigen in A549 cells similar to those attained upon co-infection with two separate recombinant viruses containing the rev or env gene. Furthermore, the rev gene nucleotide sequence could be altered without altering the amino acid sequence and its sequences truncated by 17 amino acids from the C-terminus had no effect of rev function.

In vitro binding and internalization of HIV envelope glycoproteins by human epidermal Langerhans cells does not require the CD4-gp120-binding site

Langerhans cells (LC) are epidermal dendritic cells which express several surface antigens, among them the CD4 antigens. Recent data demonstrated that LC constitute target and storage cells for HIV. To better understand the interactions between HIV and LC, we investigated, in the present work, the fate of HIV envelope glycoproteins (gp120 and gp160) incubated with healthy human trypsinized LC in suspensions. After trypsin treatment, only the epitope for OKT4 appeared to be resistant on LC. In the absence of antigenic sites identified by OKT4A, Leu3a or BL4 (epitopes implicated in HIV binding), LC bound and internalized recombinant HIV gp120 or gp160. This finding supports the hypothesis that there exists at the surface of LC a second molecule which may act as an HIV receptor.

Accessibility of the highly conserved amino- and carboxy-terminal regions from HIV-1 external envelope glycoproteins

Amino- and carboxy-terminal extremities of the envelope external glycoproteins are regions that have remained highly conserved between human immunodeficiency viruses HIV-1 and HIV-2. The corresponding peptides have been synthesized and their structure and function analyzed. Circular dichroism spectra showed evidence of alpha helical conformation when the peptides were dissolved in the nonpolar solvent trifuoroethanol. These two regions are indeed exposed on the molecule because they were accessible to their respective specific antibodies on the native gp160 precursor or processed gp120 glycoproteins of HIV-1. Neither the peptides nor rabbit or human antibodies directed against the N- and C-terminal peptides interfered with the interaction between HIV-1 external glycoprotein gp120 and its CD4 cellular receptor. Taken together, these results indicate that N- and C-terminal regions of gp120 are accessible on the quaternary structure of the virion as well as on the soluble form of gp120 and that these regions are not directly or indirectly involved in the binding of gp120 to CD4.

The rev gene product of the human immunodeficiency virus affects envelope-specific RNA localization

By in situ hybridization analysis and immunoprecipitations following transfection of COS cells, we show that the Rev protein of the human immunodeficiency virus is necessary for envelope protein expression, which is correlated with the appearance in the cytoplasm of envelope-specific RNA. In the absence of cotransfection with a plasmid expressing Rev, envelope-specific RNA is retained in the nucleus. Several cis-acting sites in the envelope are involved, one of which is between nucleotides 7330 and 7735 and is required for the response to Rev. Other sequences (nucleotides 5797-7330 and 7735-7989) are involved in the apparent retention of the envelope-specific RNA in the nucleus in the absence of Rev and its response element. Because Rev affects the localization of envelope RNA both in the presence and in the absence of the normal splice sites on the RNA, the mechanism of Rev action is independent of splicing.

Human cell lines stably expressing HIV env and tat gene products

A DNA fragment containing the tat, rev and env genes of the human immunodeficiency virus type 1 was inserted into the retroviral vector pZIPneoAU3. The resulting plasmid penvAU3 was transfected into HeLa and psi CRIP cells. Resulting recombinant retroviruses were used to infect HeLa and Jurkat cells. Immunoprecipitation analysis of stable transformants showed the expression of HIV env glycoproteins gp160, gp120 and gp41. Transactivation assays with a plasmid containing the gene for chloramphenicol acetyltransferase linked to HIV promoter-enhancer sequences demonstrated the expression of functional tat. These cells constitute virus-free tools for functional and structural studies of native env and tat.

HIV-1 core proteins expressed from recombinant vaccinia viruses

The sequences encoding the core proteins p55, p25, and p18 of the human immunodeficiency virus (HIV-1) have been inserted into the vaccinia virus genome. Infection of cultured cells with the live recombinant viruses led to the expression of proteins that were recognized by sera from HIV-seropositive individuals. Immunization of mice with the recombinant virus expressing the HIV p25 protein and the p55 precursor yielded high levels of antibodies directed against the corresponding HIV antigens. The data obtained are discussed in terms of the possible use of these live recombinant viruses in the development of a strategy toward an AIDS vaccine.

Large-scale production and purification of a vaccinia recombinant-derived HIV-1 gp160 and analysis of its immunogenicity

The human immunodeficiency virus (HIV-1) envelope gene was expressed in large-scale microcarrier cultures of Vero cells using a system involving coinfection with two recombinant vaccinia viruses. One recombinant contained the bacteriophage T7 RNA polymerase gene under control of a vaccinia virus promoter. The second contained the HIV-1 gp160 gene flanked by T7 promoter and termination sequences. The protein was expressed on the surface of infected cells, and it was shown to have a molecular weight of 160 kD and to react with gp41 and gp120 specific monoclonal antibodies. After purification by successive affinity and ion-exchange chromatography, the protein was demonstrated to be present in a particulate form with a diameter in the range of 15-30 nm. When injected into goats a high-titer gp160 specific antibody response was elicited and group-specific neutralizing activity could be demonstrated in vitro. The immunogenicity of the protein was also studied in conjunction with a number of adjuvant formulations, and the highest potency in mice was obtained using a preparation with 0.2% Al(OH)3 and 0.25% deoxycholate.

Cell-mediated immune proliferative responses to HIV-1 of chimpanzees vaccinated with different vaccinia recombinant viruses

The only animal that can be reproducibly infected with HIV, and that thus provides an experimental system for testing the effectiveness of prototype vaccines, is the chimpanzee. We compared proliferative responses to HIV and to vaccinia virus (VV) antigens of lymphocytes taken at various times from chimpanzees vaccinated with recombinant VV expressing different HIV genes. Animals were immunized with the original VV strain, as control, or with constructs expressing gp160 (VV160) given exclusively or in combination with one or two other constructs producing p25 (VV25), F/3'-orf (VVF), or the human interleukin-2 (IL-2) gene, which was included in an attempt to amplify immune responses. Irrespective of the HIV gene utilized, lymphocyte proliferation to HIV was usually weak and rapidly decreased after each inoculation, contrasting with strong and sustained responses to VV. Lack of adequate recall reactivity after challenge with fixed autologous lymphocytes expressing VV-produced HIV antigens indicated that vaccination resulted only in low levels of HIV-specific memory cell priming. The use of IL-2-producing VV did not lead to increased responsiveness. Reactivity to soluble purified gp160, but not to p25, could be detected in PBL from animals that had received both VV160 and VV25, while immunization with VVF resulted in a significant response to this protein in one of two animals. The transient nature of T cell reactivity to HIV might explain why, in similar studies, chimpanzees were not protected from infection with live HIV.

Characterization of human immunodeficiency virus gag/pol gene products expressed by recombinant vaccinia viruses

Recombinant vaccinia viruses containing either the entire gag/pol gene or the reverse transcriptase (RT) domain of the human immunodeficiency virus (HIV) were constructed. In mammalian cells infected with the recombinant vaccinia virus containing the gag/pol gene, major and minor polypeptides of 55 and 41 kDa were made, but processed gag products (p24/p17/p15) were not detected. In addition, none of the products of the pol open-reading frame were seen. Both the 55- and 41-kDa gag proteins were post-translationally modified by addition of myristic acid residues in recombinant vaccinia-infected cells, and were immunoprecipitated by antiserum to p24 gag, as well as by antisera from HIV-infected patients. These results indicate that neither proteolytic processing nor other HIV proteins are required for myristilation, and suggest that the 55- and 41-kDa gag precursors share the same amino terminus as p17. Cells infected with a separate vaccinia recombinant containing a truncated piece of the gag/pol gene with added start and stop codons at the 5' and 3' ends of the RT reading frame synthesized a major 61-kDa and a minor 51-kDa protein product which reacted immunologically with both a monoclonal antibody to native HIV p66/51 and antisera from HIV-infected patients. These proteins were purified from recombinant vaccinia-infected mammalian cells, and their enzyme activity was found to be similar to that of authentic HIV RT. Cells infected with the vaccinia/RT vector contained approximately 200-fold more RT per milligram of protein than cells infected with HIV. Recombinant RT was inhibited by dideoxynucleoside triphosphates and should be useful in screening for specific inhibitors of this enzyme. Mice inoculated intradermally with 10(8) plaque-forming units of the vaccinia/RT vector developed specific antibodies to the p66/51 proteins of HIV, but anti-HIV antibodies were not detected in mice inoculated with the vaccinia/gag vector.

Sensitive ELISA for the gp120 and gp160 surface glycoproteins of HIV-1

We have used a panel of polyclonal and monoclonal antibodies against gp120 and gp160, the envelope glycoproteins of human immunodeficiency virus type 1, to create rapid, simple, and sensitive twin-site sandwich ELISA specific for gp120 and gp160 or for gp160 alone. These assays can detect 500 COS cells in a population transiently transfected with a construct encoding gp120 and gp160, or 50 pg of recombinant gp160. We estimate that the mean amount of gp120 + gp160 in the transfected population is equivalent to 2.5 x 10(6) molecules per cell, 40-50% of which can be recovered from the culture medium as gp120 after 24 hours. The ELISA can be adapted to assess whether gp120 is detectable in the sera of HIV-1-infected persons: we show that gp120/gp160 is completely stable in normal human serum for at least 24 hours at 37 degrees C.

Analysis of host-virus interactions in AIDS with anti-gp120 T cell clones: effect of HIV sequence variation and a mechanism for CD4+ cell depletion

The primary human T cell response to HIV was analyzed by isolating from seronegative donors T cell clones specific for HIV gp120. T cell epitopes restricted by different MHC elements were identified within gp120, and synthetic peptides were used to address the fundamental problem of how HIV sequence variability affects T cell recognition. Even one conservative substitution can drastically reduce recognition; thus the interaction of gp120 epitopes with T cell receptors and MHC is precise and poorly crossreactive. Importantly, a subset of CD4+ gp120-specific clones manifest cytolytic activity and lyse uninfected autologous CD4+Ia+ T cells in the presence of gp120 in a process that is strictly dependent upon CD4-mediated uptake of gp120 by T cells. Assuming gp120 is shed from HIV-infected cells in vivo, this novel CD4-dependent autocytolytic mechanism may contribute to the profound depletion of CD4+ cells in AIDS.

Recombinant polyoma--vaccinia viruses: T antigen expression vectors and anti-tumor immunization agents

Live vaccinia virus recombinants expressing viral antigens have recently been developed as effective anti-viral vaccines. We have examined the possibility of extending this approach to specific anti-tumor immunity, using tumors induced by the polyoma virus (PyV) as a model system. Three recombinant vaccinia viruses, separately encoding the three early proteins of the polyoma virus (large, middle and small tumor (T) antigens) were constructed. Each recombinant efficiently expresses the appropriate T antigen, which exhibits biochemical properties and subcellular localization of the authentic PyV protein. The potential of the recombinants to elicit immunity towards PyV-induced tumors was assessed in rats by a challenge injection of syngeneic PyV-transformed cells. After prior immunization with the large-T or the middle-T viruses, small tumors developed, which later regressed and were eliminated in more than 50% of the animals. In contrast, the small-T virus failed to elicit tumor rejection. Established tumors could also be eliminated by curative vaccinations. No circulating antibodies directed against PyV large-T or middle-T antigens were detected in animals vaccinated with the large-T or middle-T viruses, suggesting that rejection may be due to a cell-mediated immune response.

Bacterial expression and characterization of nine polypeptides encoded by segments of the envelope gene of human immunodeficiency virus

Nine envelope (Env) polypeptides, encoding different regions of HIV gp120 and gp41 Env proteins, and accounting for approx. 96% of the entire Env precursor glycoprotein complex (gp160) were expressed in Escherichia coli at levels ranging from approx. 2 to 20% of total cellular protein. The recombinant polypeptides were produced either as hybrid products fused to the cII gene fragment of the lambda vector or in an unfused form without interfering cII products. Partially purified protein fractions of each polypeptide were characterized serologically by Western-blot analysis against a panel of well characterized human immunodeficiency virus (HIV)-positive human reference sera. Most of the Env polypeptides were highly immunoreactive with anti-gp120/gp41 antibodies present in the sera of patients with acquired immunodeficiency syndrome (AIDS) and AIDS-related diseases, but the patterns of reactivity were different. These results demonstrate that some of the antigenic determinants residing on the viral gp160 complex are retained on the surfaces of the recombinant Env polypeptides, and suggest that these sites are differentially immunogenic. These results are therefore interpreted in the context of an ongoing process towards using bacterially expressed HIV Env polypeptides to help define biological and structural epitopes to aid in the development of more sensitive diagnostic and therapeutic reagents in the fight against AIDS.

Delineation of a region of the human immunodeficiency virus type 1 gp120 glycoprotein critical for interaction with the CD4 receptor

The primary event in the infection of cells by HIV is the interaction between the viral envelope glycoprotein, gp120, and its cellular receptor, CD4. A recombinant form of gp120 was found to bind to a recombinant CD4 antigen with high affinity. Two gp120-specific murine monoclonal antibodies were able to block the interaction between gp120 and CD4. The gp120 epitope of one of these antibodies was isolated by immunoaffinity chromatography of acid-cleaved gp120 and shown to be contained within amino acids 397-439. Using in vitro mutagenesis, we have found that deletion of 12 amino acids from this region of gp120 leads to a complete loss of binding. In addition, a single amino acid substitution in this region results in significantly decreased binding, suggesting that sequences within this region are directly involved in the binding of gp120 to the CD4 receptor.