Characteristics of the principal neutralizing determinant of HIV-1 prevalent in Japan

The principal neutralizing determinants (PNDs) of 29 human immunodeficiency virus type 1 (HIV-1) isolates in Japan were analyzed using polymerase chain reactions. The viruses were isolated from 16 hemophiliacs, 11 individuals infected by their sexual transmission and 1 patient infected by blood transfusion (total 28 patients). Two virus isolates which were obtained from the same individual at different periods were also analyzed. All individuals were Japanese except one. The results produced 32 different PND sequences. A highly conserved central core sequence (GPG) was present in 27 of 32 patients, similar to the number reported in the United States, despite the marked heterogeneity in flanking regions of PNDs. The PNDs of all the 16 HIV-1 isolates obtained from patients with coagulation disorders had GPG sequences. Secondary structure prediction of PNDs by a joint method suggested that they were composed of coil-beta strand-coil-beta strand-alpha helix. It is suggested that the conserved core sequence has a type I turn. These findings may be useful in planning further clinical trials for passive vaccination.

Identification of a uniquely immunodominant, cross-reacting site in the human immunodeficiency virus endonuclease protein

One of the features of the life cycle of retroviruses is insertion of the proviral DNA into host chromosomes. A protein encoded by the 3' end of the pol gene of the virus genome has been shown to possess endonuclease activity (D. P. Grandgenett, A. C. Vora, and R. D. Schiff, Virology 89:119-132, 1978), which is necessary for DNA integration. Sera from the majority of human immunodeficiency virus (HIV)-infected individuals react with endonuclease protein p31 in serological tests (J. S. Allan, J. E. Coligan, T.-H. Lee, F. Barin, P. J. Kanki, S. M'Boup, M. F. McLane, J. E. Groopman, and M. Essex, Blood 69:331-333, 1987; E. F. Lillehoj, F. H. R. Salazar, R. J. Mervis, M. G. Raum, H. W. Chan, N. Ahmad, and S. Venkatesan, J. Virol. 62:3053-3058, 1988; K. S. Steimer, K. W. Higgins, M. A. Powers, J. C. Stephans, A. Gyenes, G. George-Nascimento, P. A. Liciw, P. J. Barr, R. A. Hallewell, and R. Sanchez-Pescador, J. Virol. 58:9-16, 1986). It is not known, however, which part of the protein represents the target(s) for antibody response. To study this, we synthesized peptides and used them in an enzyme-linked immunosorbent assay system to map the reactivity of human immunodeficiency virus type 1 (HIV-1) antibody-positive sera to the different regions of the HIV endonuclease. A uniquely antigenic, HIV-1- and HIV-2-cross-reacting site was identified in the central part of this protein from Phe-663 to Trp-670.

HIV-specific humoral and cellular immunity in rabbits vaccinated with recombinant human immunodeficiency virus-like gag-env particles

Recombinant human immunodeficiency virus type-1 (HIV-1)-like gag-env particles produced in mammalian cells were inoculated into two New Zealand white rabbits. In parallel, two control rabbits were inoculated with the homologous HIV-1 virions inactivated by ultra violet light (uv) and psoralen treatments. The humoral and cellular immune responses to HIV-1 were evaluated for both groups of animals. Recombinant particles elicited humoral immunity that was specific for all the viral structural proteins. The antibodies recognized both denatured and nondenatured proteins. Moreover, the sera neutralized the in vitro infectivity of the homologous virus in CEM cells. Importantly, the recombinant particles also generated a T helper response by priming with the HIV proteins. Similar results were observed with inactivated virus immunization. Therefore, our results suggest that the recombinant HIV-like particles elicit functional humoral immunity as well as cellular immunity and represent a novel vaccine candidate for AIDS.

New use of BCG for recombinant vaccines

BCG, a live attenuated tubercle bacillus, is the most widely used vaccine in the world and is also a useful vaccine vehicle for delivering protective antigens of multiple pathogens. Extrachromosomal and integrative expression vectors carrying the regulatory sequences for major BCG heat-shock proteins have been developed to allow expression of foreign antigens in BCG. These recombinant BCG strains can elicit long-lasting humoral and cellular immune responses to foreign antigens in mice.

Expression in yeast of a cDNA clone encoding a transmembrane glycoprotein gp41 fragment (a.a. 591-642) bearing the major immunodominant domain of human immunodeficiency virus

A cDNA clone corresponding to the gp41 gene fragment nucl. 7573-7730 of the human immunodeficiency virus type 1 (HIV-1) was selected from a random HIV-1 genomic library expressed in yeast. This clone encodes a 52-residue long peptide (amino acid (a.a.)) 591-642) bearing the major immunodominant domain (a.a. 598-609) of the HIV-1 transmembrane glycoprotein gp41. Expression of the recombinant peptide pSE-env591-642 was driven by the alpha-mating factor leader sequence contained in a plasmid pSE-x allowing the synthesis and secretion of foreign gene product in Saccharomyces cerevisiae. Time-course analysis of the secretion into culture medium revealed an optimal production of the glycoprotein fragment at 28-30 h with no observable cytotoxicity. The secreted peptide is highly glycosylated with NH2-terminal heterogeneity probably due to different post-translational modifications. The secreted peptide shows an extreme antigenicity since in ELISA assays, as few as 5 microliters/well of crude supernatant are sufficient to obtain a strong detection by monoclonal antibodies or by 100% of sera from HIV-infected individuals. The purified glycopeptide pSE-env591-642 binds to a monoclonal antibody directed against the immunodominant epitope (a.a. 603-609) with an affinity similar to that of the complete glycoprotein gp160 (Kd values within the 10(-10) M range) and with a 100-fold higher affinity than that of a linear peptide fragment SP-env584-609. These results indicate that overexpression in yeast can efficiently provide an abundant source of highly antigenic gp41 protein fragment pSE-env591-642 which retains the antigenic properties of the native gp160 protein. Such a recombinant peptide should therefore be considered as a good candidate for antigen in HIV detection tests.

A peptide library expressed in yeast reveals new major epitopes from human immunodeficiency virus type 1

In order to characterize novel human immunodeficiency virus type 1 (HIV-1) continuous epitopes, we designed a simple method, based on recombinant DNA, providing a complete set of peptides derived from HIV-1. A library (4 x 10(4) clones) was first constructed in a new expression/secretion vector, using as inserts small fragments of HIV-1 DNA (50-150 bp) generated by random DNAse I cleavage. This peptide library, expressed in the yeast Saccharomyces cerevisiae, was screened with sera of HIV-1 infected individuals and human and murine anti-HIV-1 monoclonal antibodies. Plasmids from immunoreactive colonies were recovered and the sequences of the HIV-1 derived inserts were determined. By using human sera, we have detected classical HIV-1 epitopes and identified two novel major epitopes, which may be used to improve diagnostic tests, localized in the p24 core protein and in the endonuclease. In addition, four minor epitopes were also defined by screening the library with monoclonal antibodies: in the protease, in the p17 core protein, in gp120 and near the C-terminal of gp41. This method is general and can be used for any protein from which a cloned cDNA is available.

Poliovirus antigen chimeras

Poliovirus, the aetiological agent of paralytic poliomyelitis, is arguably the best characterized of all animal viruses. Using recombinant-DNA technology, this information, together with the availability of infectious cDNA clones of the notably safe and efficacious live attenuated Sabin 1 vaccine strains of poliovirus, has enabled the creation of hybrid viruses (chimeras) possessing novel antigenicity. The potential applications of these 'epitope-presentation systems' include their use as immunogens, as antigens for serodiagnosis, and as vaccines.

[Cloning and expression of the CD4 receptor gene from human T-lymphocytes in Escherichia coli cells]

The gene for the CD4-membrane glycoprotein-receptor for HIV has been cloned. The 179 amino acids fragment of the CD4-receptor responsible for binding of gp120 HIV glycoprotein has been fused with beta-galactosidase and shown to be expressed in Escherichia coli cells. The recombinant protein in ELISA and immunoblotting techniques reacts with the monoclonal antibodies OKT4A and Leu3A known to block the interaction between the CD4 and gp120 HIV glycoprotein. The recombinant protein can be used for different scientific and practical purposes including studying of the mechanisms for HIV interaction with the sensitive cells as well as for viral gp120 protein purification, etc.

[The expression of a fragment of the HIV-1 Nef gene in Escherichia coli bacteria]

The presence of antibodies to p27, the product of gene Nef, may be an important diagnostic sign since some sera from subjects of the risk groups negative to HIV-1 structural proteins may contain antibody to p27. The study resulted in construction of a hybrid plasmid determining in E coli bacteria the synthesis of a hybrid protein the N-terminus part of which is represented by full-size beta-galactosidase and the C-terminus by a part of protein p27 with the main immunoreactive epitopes. The resulting polypeptide specifically interacts with sera of the infected subjects and may be used for detection of antibodies to the protein Nef in the blood of virus-carriers.

Highly immunogenic human immunodeficiency viruslike particles are produced by recombinant vaccinia virus-infected cells

CV-1 cells were infected with two recombinant vaccinia viruses carrying the gag gene with deletion of 231 bp from 3' terminus (strain vC5) and env gene (strain vE234L) of human immunodeficiency virus type 1 (HIV-1). Both recombinant proteins synthesized in the cells (p50gag and gp160/120env) were localized predominantly in cell membranes; however, some amount of p50 was found in cell nuclei. Thin-section immunoelectron microscopy showed accumulation of viruslike particles undistinguished from immature HIV-1 virions in the culture medium of the cells infected with vC5. The similar particles containing gag and env proteins were produced into the culture medium when the cells were coinfected with vC5 and vE234L strains. The particles contained heterogeneous cellular RNA, but no virus-specific RNA as shown by Northern blot hybridization. Immunization of the rabbits with purified viruslike particles produced virus-specific antibodies against gag and env proteins. The titer of antibodies was significantly higher than after immunization with cell lysate or recombinant proteins purified from the infected cells. Highly immunogenic HIV-1-like particles containing gag and env proteins but no virus-specific RNA are good candidates for potential vaccine.

Evolution of sequences encoding the principal neutralization epitope of human immunodeficiency virus 1 is host dependent, rapid, and continuous

The principal neutralization epitope of human immunodeficiency virus 1 is localized in the third variable (V3) domain of the external envelope and has been shown to bind isolate-specific antibodies. Therefore, the extent of variation within the nucleic acid sequence encoding this epitope was studied in DNA directly obtained from peripheral blood mononuclear cells of six children and their plasma donor. This revealed that the quasi-species distribution of sequences obtained after cloning varied from recipient to recipient and that the distance from the donor sequences increased over time. V3 nucleotide evolution rates averaged 9.5 x 10(-3) per site per year for silent sites and 11.4 x 10(-3) per site per year for nonsilent sites (vs. 9.7 and 9.8 x 10(-3) per site per year for a control region 5' adjacent to the V3 region) and, although individual differences were observed, did not correlate with the serum antigen levels or disease progression. Sequences of both the epitope coding region itself (V3) and the control region upstream diverted more from the donor sequence among children not progressing to AIDS than among children progressing to AIDS. The evolution of V3 sequences is apparently host dependent, rapid, and independent of the level of antigen expression.

Major antigenic domain recognized by monoclonal antibodies maps within the carboxy-terminal moiety of a recombinant human immunodeficiency virus-1 p24 protein

Antigenicity in mice of a recombinant polypeptide including the complete amino acid sequence of mature human immunodeficiency virus type 1 p24 protein was studied by induction of monoclonal antibodies (MAbs). A panel of nine recloned hybridomas secreting MAbs with anti-p24 reactivity was isolated and further characterized. Competitive inhibition experiments suggested that the MAbs could be grouped into four epitopic classes corresponding to at least two distinct determinants. Analysis of reactivity to recombinant p24 deletion variants indicated that all the recognized epitopes are localized within a carboxy-terminal domain (amino acids 168-208) which should be largely exposed in recombinant as well as authentic antigen. Lack of response to N-terminal and central portions of p24 suggests that the antigenicity of those regions in the natural polypeptide is strongly conformation-dependent.

Expression and purification of p24, the core protein of HIV, using a baculovirus-insect cell expression system

The baculovirus Autographa californica nuclear polyhedrosis virus (AcNPV) has been genetically manipulated to yield a recombinant virus capable of expressing p24, the major core protein of HIV-1, in insect cell culture. The expressed product is a p24 protein flanked by short regions of p17 at the amino terminus and p12 at the carboxy terminus. It has been identified and characterized using monoclonal antibodies on Western blots and by amino-terminal sequence analysis. The presence of p24 in the soluble fraction of infected cells following lysis by detergent or sonication, combined with a high level of expression (in excess of 50 mg/l of culture) facilitates the enrichment of large quantities of recombinant HIV antigen in a simple two-step procedure involving ammonium sulphate fractionation and gel filtration. p24 antigen purified in this way is shown to be an efficient diagnostic reagent.

Modelling of poliovirus. HIV-1 antigen chimaeras

We have used laboratory-based molecular modelling to identify structural features of antigen chimaeras of poliovirus expressing epitopes from human immunodeficiency virus (HIV-1) that may affect virus viability. Chimaeras were constructed by replacement of antigenic site 1 of VP1 by sequences corresponding to epitopes from HIV-1. Loop volume, estimated by approximating the loop to an ellipsoid was significantly (P less than 0.001) lower in viable (2062.1 A3 +/- 400.2) than in non-viable (3617 A3 +/- 650.7) constructs. Our results suggest that viable virus will only be formed when antigen chimeras modified at antigenic site of VP1 have a loop occupying a similar volume in space to that occupied by the antigenic site 1 loop. In addition, the modified loop must fit with the peptide bond angles and distances at the top of the beta-barrel of VP1.

[Effective synthesis of oligo(poly)deoxyribonucleotides using an H-phosphonate method in plastic microcolumn]

A facile technique of manual oligonucleotide synthesis via H-phosphonate approach is developed. Syntheses carried out in pipette tips with siliconised glasswool filters take 3-3.5 min per cycle with 97-98% yields per condensation. The method was used to synthesize 12-55-mers: T7 and PL promoter regions, gene of the signal peptide of the E. coli OmpA protein, oligonucleotides coding for amino acid sequences 94-105 of preS1- and 133-143 of preS2-regions of hepatitis B virus, hybridisation probes, sequencing primers, oligonucleotides for site-directed mutagenesis, etc.

[Human immunodeficiency virus (HIV): a review]

Since its discovery in 1983, a lot of knowledge about the human immunodeficiency virus (HIV) has been accumulated. Our paper gives a brief survey on what is known at present about the structure, molecular biology, and the cell tropism of this virus. We discuss its relationship to other lentiviruses as well as its possible origin; in addition, we refer to the immune response to HIV and its interactions with the infected host. We also briefly summarize the difficulties encountered in the attempts to produce a vaccine against HIV and highlight some promising approaches in the development of such a vaccine.

Immunogenicity and antigenicity of conserved peptides from the envelope of HIV-1 expressed at the surface of recombinant bacteria

We expressed peptides from the HIV-1 envelope protein at the surface of Escherichia coli by genetic insertions into an exposed loop of the outer membrane protein LamB. Recombinant bacteria expressing eight peptides from gp110 (pep1-pep8), conserved between HIV-1 and HIV-2, were used as live immunogens in rabbits by the intravenous route. The eight constructions elicited anti-LamB antibodies, showing that the hybrid proteins were immunogenic. One of them, LamB-pep8, gave rise to antibodies able to react with gp160 and to neutralize HIV-1 in vitro. We also show that this type of recombinant E. coli can provide a convenient reagent to monitor and characterize specific antibodies. Recombinant clones were used to test sera of seropositive individuals, as well as to narrow down the monoclonal antibody 110-1 recognition site to a cluster of eight residues at the carboxy-terminal end of gp110.

Myristoylation of gag proteins of HIV-1 plays an important role in virus assembly

The gag proteins of HIV-1 are modified by the addition of myristic acid to the amino terminal glycine residue. Site-directed mutagenesis was used to construct a mutant of HIV-1 in which this glycine residue was changed to an alanine. Upon transfection into cos-1 cells, the mutant genome directed the synthesis of the full complement of HIV-1 proteins, but p17 and p17-containing polyproteins were not myristoylated. The cells transfected with the mutant DNA did not release any virus particles and no viral cores were visible by electron microscopy. Furthermore, supernatant from these transfected cells failed to infect CEM cells. The expression and function of gp120 on the surface of cells transfected with the mutant DNA was unaffected as these cells formed syncytia comparable in both size and number to the ones obtained with wild-type DNA.

Mutational analysis of the human immunodeficiency virus type 1 env gene product proteolytic cleavage site

The structural requirements for proteolytic cleavage of the human immunodeficiency virus type 1 env gene product, gp160, to gp120 and gp41 have been assessed by specific mutagenesis of the sequence Lys Ala Lys Arg Arg Val Val Glu Arg Glu Lys Arg located between amino acids 500 and 511, i.e., at the putative C terminus of gp120. The basic amino acids underlined have been mutated, individually and in combination, to neutral amino acids, and the cleavability of the mutated env gene products was examined after expression in CV-1 cells. The results show that the replacement of Arg-511 (cleavage presumably occurs C terminal to this amino acid) with Ser completely abolishes recognition and cleavage by the cellular protease(s), i.e., the remaining basic amino acids in the vicinity do not serve as alternative substrates. However, Arg-508 and Lys-510 are important features of the recognition site since, when they are individually changed to neutral amino acids, cleavage is severely impaired. The basic amino acids 500, 502, and 504 are, individually, not important for cleavage, since their individual replacement by neutral amino acids does not impair cleavage. However, when all four basic amino acids 500, 502, 503, and 504 are changed to neutral amino acids, cleavage is almost completely abolished. This shows that the sequence Arg Glu Lys Arg at the cleavage site is alone not sufficient for cleavage but that a contribution of other amino acids is required, whether the other amino acids provide a basic character or a certain structure in the vicinity of the cleavage site. When noncleavable or poorly cleavable mutant env genes are expressed from the infectious plasmid pNL4-3 in CD4+ human lymphoblastoid cells, noninfectious virus, incapable of spread throughout the culture, is produced.

Genetic variability in HIV-1 gp120 affects interactions with HLA molecules and T cell receptor

The propensity of HIV-1 to undergo sequence variation, particularly in the envelope glycoprotein gp120, complicates vaccine development and may enable the virus to evade ongoing immune responses in infected individuals. We present here a molecular analysis of the effects of this variability on human T cell recognition of HIV-1 gp120. Synthetic peptides representing a defined CD4+ human T cell epitope in gp120 were used to survey gp120 molecules from various HIV-1 strains for the capacity to be recognized in the context of a single human MHC molecule, DR4. Variation affected recognition at two levels. For some strains, variation in this epitope was sufficient to alter the interaction of Ag receptors on gp120-specific human T cell clones with peptide-DR4 complexes on APC. In the case of two strains, the natural variation was sufficient to prevent the critical initial interaction between the relevant gp120 peptides and DR4 on the APC. However, these strains were highly divergent from the reference strain. Thus it is encouraging to note that the range of natural sequence variation in this T cell epitope falls, for the most part, within the range of peptide sequences that can be accommodated by the relevant human MHC molecule.

Identification of conserved and variant epitopes of human immunodeficiency virus type 1 (HIV-1) gp120 by human monoclonal antibodies produced by EBV-transformed cell lines

Using Epstein-Barr virus (EBV) transformation of B cells isolated from peripheral blood of two asymptomatic human immunodeficiency virus type 1-(HIV-1) infected subjects, we have produced four IgG1 human monoclonal antibodies (HMAbs) that bind to HIV-1 gp120, as determined by Western blot analysis. Two of these HMAbs, designated N70-1.5e and N70-2.3a, react with epitopes of gp120 expressed by all strains tested thus far, and therefore, appear to identify conserved epitopes. The other two HMAbs, K24-3b and N70-1.9b, identify variant epitopes; K24-3b binds to an epitope which is absent from two strains but heterogeneously expressed in eight other strains; N70-1.9b binds to an epitope that is found in relatively few strains. We also describe a novel immunoassay in which viral glycoproteins, produced by HIV-1-infected cells grown in serum-free medium, are affinity immobilized in Concanavalin A-coated wells of enzyme-linked immunosorbent assay (ELISA) plates. This method greatly facilitates the preparation of solid-phase HIV envelope glycoproteins from multiple virus strains and screening immunoassays based on this method are highly sensitive and effective in detecting antibodies to gp120.

T- and B-lymphocyte responses to human immunodeficiency virus (HIV) type 1 in macaques immunized with hybrid HIV/hepatitis B surface antigen particles

Recombinant human immunodeficiency virus (HIV)/hepatitis B surface antigen (HBsAg) subviral particles of dual antigenicity and immunogenicity were obtained by fusing 84 amino acids of the HIV type 1 external envelope glycoprotein within the pre-S2 part of the hepatitis B middle protein (M.-L. Michel, M. Mancini, E. Sobczak, V. Favier, D. Guétard, E.-M. Bahraoui, and P. Tiollais, Proc. Natl. Acad. Sci. USA 85:7957-7961, 1988). We now describe the humoral and cellular immune response of rhesus monkeys immunized with these hybrid particles. Macaque antisera raised by subcutaneous injections of the HIV/HBsAg particles were shown to be specific for HIV in peptide-binding assays. Moreover, we were able to generate in these vaccinated animals a T-cell-proliferative response to both parts of the hybrid particle, i.e., HIV and HBsAg. These results establish the presence of a T-cell epitope in this HIV segment, which has been shown previously (L.A. Lasky, G. Nakamura, D. H. Smith, C. Fennie, C. Shimasaki, E. Patzer, P. Berman, T. Gregory, and D. J. Capon, Cell 50:975-985, 1987) to be an important domain involved in the binding of the virus to its cellular receptor, the CD4 molecule. This work demonstrates the feasibility of using the HBsAg subviral particle as a carrier protein for the presentation of foreign immunogenic epitopes to the immune system.

Sensitivity of six commercial enzyme immunoassay kits that detect both anti-HIV-1 and anti-HIV-2

The sensitivities of six commercial combined anti-HIV-1/anti-HIV-2 enzyme immunoassays (EIAs) were evaluated, one assay (ELAVIA) based on whole virion antigen, two assays (Abbott, Wellcozyme) based on antigens expressed from recombinant DNA, and three assays (Biochrom, IAF Biochem and Pharmacia) based on synthetic peptides as antigens. All the kits investigated performed well on a panel of 47 routine anti-HIV-1-positive specimens, but on series of anti-HIV-1-seroconversion specimens from seven plasmapheresis donors, two of the peptide assays, Biochrom and Pharmacia, performed less well than the other assays. On a panel of anti-HIV-2-positive specimens, all the assays except Biochrom detected all 33 positive sera, though the reactions of some of them in the Abbott assay were relatively weak. In deciding whether to introduce a combined assay in place of an anti-HIV-1 assay, cost, specificity, the availability of confirmatory tests and the prevalence of HIV-2 in the locality, as well as sensitivity, should be considered.