Neutralization of HTLV-III/LAV replication by antiserum to thymosin alpha 1

Effects of overexpression and inhibited expression of thymosin, an actin-interacting protein from Bombyx mori, on BmNPV proliferation and replication

Previous study showed that exogenously applied recombinant thymosin from Bombyx mori (BmTHY) reduces B. mori nucleopolyhedrovirus (BmNPV) proliferation in silkworm. Which stands to reason that BmTHY in B. mori is crucial for the defense against BmNPV. However, little is known about the effect of endogenously overexpressed or repressed BmTHY on B. mori resistance to virus infection. To study this issue, we constructed an overexpression and inhibited expression systems of BmTHY in BmN cells. The viral titer and the analysis from the quantitative real-time polymerase chain reaction (PCR) revealed that overexpression of BmTHY decreased the copies of BmNPV gene gp41, which goes over to inhibit the proliferation of BmNPV in BmN cells, while the inhibited expression of BmTHY significantly enhanced viral proliferation in infected BmN cells. These results indicated that endogenous BmTHY can inhibit BmNPV proliferation and replication in infected BmN cells. Furthermore, Co-IP showed that BmTHY could bind to actin in BmN cells. Also, the overexpression or inhibited expression of BmTHY shifted the ratio of F/G-actin in infected BmN cells. Lastly, the BmTHY, an actin-interacting protein, might be one of the key host factors against BmNPV, which inhibits viral proliferation and replication in BmN cells.

Flt3 ligand enhances the immunogenicity of a gag-based HIV-1 vaccine

Liposomes and Flt3 ligand (Flt3L), a ligand for the fms-like tyrosine kinase receptor Flt3/ FLK2, can augment the immune response to an HIV peptide vaccine. The HGP-30 peptide used in these studies is a synthetic peptide that corresponds to a highly conserved region of HIV-1 p17 gag (amino acids 86-115). Mice were immunized with HGP-30 or HGP-30 conjugated to keyhole limpet hemocyanin (KLH) and delayed-type hypersensitivity (DTH) responses, antibody (IgG) amount and antigen-specific proliferative responses by spleen cells were used to monitor the immune response. Daily injections of Flt3L prior to HGP-30 administration enhanced significantly an antigen-specific lymphocyte proliferation response when compared with Flt3L, HGP-30 alone or HGP-30 containing liposomes. Intravenous administration of HGP-30 was superior to intramuscular (i.m.) immunization for the induction of DTH responses. The HGP-30/KLH containing liposomes enhanced both DTH and antibody responses, while liposomes containing HGP-30 peptide elicited only T cell responses. In these studies, either Flt3L or liposomes increased DTH responses compared with the i.m. injection of the HGP-30 vaccine alone.

Characterization of a novel human immunodeficiency virus type 1 neutralizable epitope within the immunodominant region of gp41

Previously, we generated human monoclonal antibodies using peripheral blood mononuclear cells from an asymptomatic human immunodeficiency virus type 1 (HIV-1)-seropositive donor. One of these monoclonal antibodies (designated clone 3, CL3) recognized 10 amino acids (GCSGKLICTT) within the immunodominant region (cluster I) of the transmembrane envelope glycoprotein gp41 and neutralized infection of target cells with different laboratory isolates. Because the epitope recognized by CL3 has two cysteine residues that could potentially produce a disulfide loop in gp41, we analyzed binding of our monoclonal antibody to the cyclic and linear motif of the peptide sequence IWGCSGKLICTTAVP (residues 600-614). The CL3 antibody did not bind to the synthetic cyclic peptide but did recognize the linear form. Two polyclonal rabbit sera against both the linear and cyclic peptides were then generated. Both antisera bound to viral glycoproteins gp41 and gp160, but neither sera neutralized HIV-1 laboratory isolates. Using a set of alanine-substituted IWGCSGKLICTTAV peptides, we analyzed binding of polyclonal antisera and CL3. The profile of binding of polyclonal antisera to these peptides was different from that of CL3 to the same peptides. This suggests that CL3 recognized a unique neutralizable core epitope, which was not immunogenic in either the cyclic or the linear IWGCSGKLICTTAVP peptides used as immunogens in the rabbits.

Anti-P30-52 monoclonal antibody cross-reacted to Env V3 and inhibited the viral multiplication of HIV-1-infected MT-4 cells

It is well known that the anti-p17 antibody titer decreases with the disease progression among human immunodeficiency virus type 1 (HIV-1) carriers. We previously established several murine anti-p17 monoclonal antibodies (MAbs) to investigate the immunological role of p17, and to further characterize these MAbs, we examined the anti-p17 antibody titer in serum of a patient who was a long-term nonprogressor with hemophilia, and found that the antibody for the p17-derivative peptide from amino acid residues 30 to 52 (P30-52) cross-reacted to the third variable region of the envelope glycoprotein of HIV-1, Env V3. In the present study, we primed mice with P30-52 to establish anti-P30-52 MAbs (P30-52 MAbs), and examined their affinity and whether they suppressed the viral multiplication of HIV-1-infected MT-4 (HTLV-1-transformed CD4+ T-cell line) cells, in a TCID50 assay. At the same time, an anti-Env V3 MAb (Env V3 MAb) was also established and examined as above. The IgM-type P30-52 MAb and Env V3 MAb showed heteroclitic binding, and the IgM-type P30-52 MAb inhibited the viral multiplication. We also found that an increase of fragmented DNA of HIV-1-infected MT-4 cells co-cultured with P30-52 MAbs. Because DNA fragmentation is one of the features of programmed cell death, the viral multiplication may be suppressed by the apoptosis of HIV-1-infected MT-4 cells co-cultured with P30-52 MAbs. Though the relationship between cross-reactivity and the inhibition mechanism of multiplication of HIV-1 is unclear, P30-52 of p17 may well be a useful region of viral proteins for the development of therapeutic and vaccination strategies.

Induction of inflammatory cytokines in placental monocytes of gravidae infected with the human immunodeficiency virus type 1

Placental mononuclear cells (PMC) are susceptible to infection with the human immunodeficiency virus (HIV). PMC secreted tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta), and IL-6 among other factors, which, in turn, regulate HIV replication in latently infected cells. We assessed the induction of these cytokines in PMC from HIV-infected (HIV+) and uninfected (control) gravidae following exposure to lipopolysaccharide (LPS), HIV lysate (iHIV), recombinant HIV env (GP160) and HIV gag (gag55), and synthetic HIV p17 (HGP30) antigens. In comparison to control PMC, HIV+ PMC constitutively secreted higher levels of IL-1beta and IL-6 and were refractory to stimulation by iHIV, GP160, gag55, and HGP30. Control PMC IL-1 beta levels were boosted by LPS; gag55 and HGP30 augmented IL-6 but not IL-1 beta. Both groups exhibited low basal TNF-alpha production that was augmented by LPS. HIV+ PMC exhibited higher constitutive levels of IL-1 beta, IL-6, and TNF-alpha gene transcription than control PMC. These levels could be further augmented by LPS, yet the incremental levels were lower than those obtained from PMC of uninfected women. The high basal constitutive secretion of cytokines by HIV+ PMC and their refractoriness to activation may reflect a virus-mediated dysregulation of cytokine expression culminating in compromised host defenses against secondary opportunistic infections associated with AIDS.

Characterization of human immunodeficiency virus type 1 p17 matrix protein motifs associated with mother-to-child transmission

In order to determine if viral selection occurs during mother-to-child transmission of human immunodeficiency virus type 1 (HIV-1), we used a direct solid-phase sequencing method to sequence the p17 matrix protein-encoding regions of viral isolates from 12 HIV-1-infected mother-and-child pairs, 4 infected infants, 4 transmitting mothers, and 22 nontransmitting mothers and compared the sequences. The blood samples were collected during the delivery period for the mothers and during the first month of life for most of the children. The p17 nucleic sequences were distributed among several clades corresponding to the HIV-1 A, B, and G subtypes. At the amino acid level, no significant differences within the known p17 functional regions were observed among the subtypes. Statistical analyses could be performed with the B subtype. Within the major p17 antibody binding site, a constant KIEEEQN motif (amino acids 103 to 109) was found in all mother-and-child isolates from the B subtype. On the other hand, 9 of 17 nontransmitting mother isolates were variable in this 103 to 109 region. Thus, this motif was significantly associated with the transmitting status (chi square, P = 0.0034). A valine residue at position 104 was significantly associated with the nontransmitting phenotype (chi square, P = 0.014), suggesting that it has a protective role during vertical transmission. The C-terminal end of p17 was globally conserved among nontransmitting mother isolates (chi square, P = 0.0037). These results might improve the understanding of the pathogenesis of HIV-1 vertical transmission and might allow the screening of seropositive mothers by a rapid molecular or peptide test.

Aspects of molecular interaction between HIV p17 and human gamma interferon

We describe the specific interaction between high-purity recombinant human immunodeficiency virus (HIV) type 1 p17 and human gamma interferon (hIFN-gamma) proteins. This interaction was found to be dose dependent and to involve conformational epitopes on both sides. Specificity was confirmed by competition ELISA, using monoclonal antibodies (MAbs) to hIFN-gamma as specific reagents. By competition experiments we also identified the epitope(s) on the hIFN-gamma molecule involved in p17 binding, very close to the receptor binding site. The kinetic constants were determined by surface plasmon resonance (SPR) analysis. The affinity constant (KA) of the complex was 2.78 x 10(8) M-1, that is, the ratio between a low dissociation rate constant (Koff)(1 x 10(-5)sec-1) and a high association rate constant (Kon) (3 x 10(3) M-1sec-1). However, p17 did not displace the binding of hIFN-gamma to its cellular receptor, nor did it interfere with the capability of the lymphokine to induce de novo expression of HLA-DR antigens on human monocytic cells or to inhibit the proliferation of tumor cells.

Three antigenic regions in p17 of human immunodeficiency virus type 1 (HIV-1) revealed by mouse monoclonal antibodies and human antibodies in HIV-1 carrier sera

We investigated the murine antibody response to recombinant p17 (rp17) of human immunodeficiency virus type 1 (HIV-1) and the human antibody response directed to p17 in HIV-1 infection. Three large peptides covering residues 12-29, 53-87 and 87-115 of p17 were synthesized. The cysteine residues 57 and 87 of peptide 53-87 were reoxidized to form a disulfide bridge. Eighteen out of 19 murine monoclonal anti-rp17 antibodies had relatively high affinities (KA = 1.9 x 10(5)-1.4 x 10(8) M-1) with one of the 3 p17 peptides in the liquid phase. Each monoclonal antibody reacted only with one particular peptide and had no reactivity with the other 2 p17 peptides. All the monoclonal antibodies reacted with rp17 in the liquid phase with a reasonable degree of affinity (KA = 2.0 x 10(5)-1.8 x 10(7) M-1). Four HIV-1 carrier sera, which were positive in ELISA using rp17 as the antigen, reacted positively in an ELISA using 3 p17 peptides which were used to titrate murine monoclonal antibodies. Murine monoclonal antibodies having specificity for the 3 p17 peptides stained live HIV-1-infected cells by means of indirect membrane immunofluorescence, irrespective of their specificity. This suggests that the various portions of p17 (at least 3 regions of p17) were exposed on the surface of live infected cells, probably as short polypeptide chains.

Linear epitopes of HIV-1, presented as hybrids with Escherichia coli beta-galactosidase or synthetic peptides

HIV-1 B cell epitopes from gp41, the T cell epitope of p34pol, and a cluster of B and T epitopes from p17gag were selected. The epitopes were presented as synthetic peptides and as either N- or C-terminal insertions into beta-galactosidase. Hybrids were efficiently expressed in E. coli and easily purified when epitopes were inserted at the beta-galactosidase C terminus. Sera from HIV-1-infected individuals reacted in peptide- and hybrid protein-based enzyme-linked immunosorbent assays (ELISAs) mostly with the immunodominant site of gp41. The second site of gp41 and also sites from p17 and p34 appeared to be immunorecessive. A few of the HIV-1-positive sera exhibited several immunorecessive reactivities. HIV-1-positive sera from the former Soviet Union and Cuba had reactivities similar to those of American, African, and west European sera. Some sera could not be evaluated as specifically HIV-1 seropositive because of their broad reactivities with a multitude of peptides and proteins, unrelated to HIV-1. Extensive tests were performed to define unspecific reactivities by absorption, blocking, and sandwich ELISAs. The application of the hybrid protein assay substantially improved the specificity of the ELISA tests. Thus, hybrid protein-based ELISAs appeared to be more suitable than peptide-based ELISAs, especially for the evaluation of immunorecessive reactivities.

Can AIDS be prevented by T-cell vaccination?

T-cell vaccination as a specific prophylactic and therapeutic procedure has been shown to be effective in animal models of autoimmune disease. As autoimmunopathogenic components have been implicated in HIV infection, the authors propose a therapeutic test utilizing T-cell vaccination and suggest that AIDS could be prevented by such a procedure.

Thymic pathology in primary and secondary immunodeficiencies

For the sake of clarity and in agreement with the World Health Organization immunodeficiency classification, it is important to distinguish the congenital, inherited malformative lesions called generically 'thymic dysplasia' from the secondary, acquired changes, designated under the broad term of 'severe thymic atrophy'. Thymic dysplasia represents the archetype of thymic changes in cellular immunodeficiency, since there is no example of a thymic dysplasia associated with a normal T-cell function. Thymic dysplasia is observed in several inherited diseases, the most frequent of them being severe combined immunodeficiency. More than the depletion of lymphoid cells, the lack of differentiation of the thymic epithelium, responsible for the absence of Hassal's corpuscles, is the main and constant feature of this condition. Thymic dysplasia underscores the crucial role of the thymic epithelium in the normal differentiation of the T-cell population. Severe thymic atrophy is secondary to various causes, including prolonged protein malnutrition and immunosuppressive or cytotoxic drugs, graft versus host reaction and, chiefly today, chronic viral infection, especially with HIV-1. The morphological changes are similar and are characterized by a partial lymphoid depletion, involving mainly the CD1+ population, necrosis and calcification of epithelial cells, the frequent presence of plasma cells and, more significantly, fibrohyaline changes of the basement membrane of the vessels and thymic epithelium. The severity of the atrophic changes and the immunodeficiency-related manifestations depend on the duration of the aetiological factors and, more significantly, with their early occurrence, within the first months of life. The mechanisms underlying thymic atrophy are poorly understood. A primary impairment of lymphoid cells seems at present to be the most likely hypothesis.

The human immunodeficiency virus (HIV) gag gene product p18 is responsible for enhanced fusogenicity and host range tropism of the highly cytopathic HIV-1-NDK strain

Formation of large syncytia and rapid cell killing are characteristics of the Zairian human immunodeficiency virus type 1 isolate HIV-1-NDK, which is highly cytopathic for CD4+ lymphocytes in comparison with the HIV-1-LAV prototype. Chimeric viruses containing different combinations of HIV-1-NDK genetic determinants corresponding to the splice donor, the packaging signal, and the coding sequence of the p18gag protein together with the HIV-1-NDK EcoRI5278-XhoI8401 fragment were obtained by polymerase chain reaction-directed recombination. Phenotypic analysis of recombinant viruses indicated that 75 amino acids from the N-terminal part of HIV-1-NDK p18gag protein together with the HIV-1-NDK envelope glycoprotein are responsible for enhanced fusogenicity of HIV-1-NDK in CD4+ lymphocytes as well as for enhanced infectivity of HIV-1-NDK in some CD4- cells lines. The HIV-1-NDK splice donor/packaging sequence and the sequence encoding the gag protein p25 were not important for the variation observed in HIV-1 fusogenicity.

Identification of immunoreactive forms of thymosin alpha 1 in serum and supernatants by combining HPLC and RIA

Thymosin alpha 1 (T alpha 1) is a biologically active peptide, originally isolated from the thymus and currently undergoing clinical trials as an immunomodulator in cancer patients, in individuals with chronic active hepatitis, and as an immunoenhancer of vaccines in immunocompromised individuals. Absorption of rabbit antibody to thymosin alpha 1 with a synthetic C-14 fragment of T alpha 1 results in an antiserum with increased affinity for the amino terminal region of T alpha 1 and the precursor protein prothymosin alpha (ProT alpha). Using HPLC methodologies, the predominant form of immunoreactivity in serum and thymus was T alpha 1 not the precursor. Using this assay we detected a decline in mouse serum T alpha 1 following irradiation but not thymectomy, an observation consistent with the existence of an important radiation sensitive lymphoid source of serum T alpha 1. The secretion of authentic T alpha 1 but not the precursor into culture medium by thymic epithelial cells as well as in mitogen-stimulated peripheral blood lymphocytes was also demonstrated by HPLC/RIA. HPLC analysis by molecular weight sizing columns demonstrated that unlike thymic epithelial cells or peripheral blood lymphocytes, the immunoreactive T alpha 1 (IRT alpha 1) form in the supernatants from tumor cells such as MCF-7 breast carcinoma was of a lower molecular weight than authentic T alpha 1. These studies suggest that the authentic form of T alpha 1 is the major immunoreactive form in normal serum and that it is secreted by the medullary thymic epithelial cells as well as by peripheral blood lymphocytes. An additional immunoreactive form, secreted by tumor cells has also been identified and is the subject of future studies.

A prospective study on correlation between the decrease in anti-P17 antibody level and progression to AIDS in asymptomatic carriers of HIV

As the majority of human immunodeficiency virus (HIV) carriers are in asymptomatic stage for a long period of time, it is important to investigate the factors or surrogate markers for conversion from asymptomatic to symptomatic stage. Our study is designed to evaluate the relationship among virus isolation rate, anti-p17 antibody status and progression to AIDS. We studied anti-p17 antibody status along with virus isolation in 56 asymptomatic carriers and 46 AIDS cases. Progression to AIDS was markedly associated with high rate of virus isolation and loss of anti-p17 antibody. In order to know the meaning of loss of anti-p17 antibody during the clinical course, 15 anti-p17 antibody positive and 16 anti-p17 antibody negative cases were followed up prospectively for the development of AIDS. None of the anti-p17 antibody positive cases developed AIDS while 6 out of 16 anti-p17 negative cases developed AIDS during observation period (P < 0.05). Progression to AIDS was associated with loss of anti-p17 antibody. Identification of cases losing anti-p17 antibody in peripheral blood during asymptomatic period may help high-risk group who are in need of chemoprophylaxis. Moreover, study of anti-p17 antibody may be helpful in designing vaccine in future if it works as a neutralizing antibody to HIV in vivo.

A phase I study of HGP-30, a 30 amino acid subunit of the human immunodeficiency virus (HIV) p17 synthetic peptide analogue sub-unit vaccine in seronegative subjects

HGP-30-KLH vaccine in alum at doses of 10, 25, 50, and 100 micrograms/kg administered intramuscularly at weeks 0, 4, and 10 appear well-tolerated clinically. Local pain at the injection site, appears to be the main clinical toxicity. Laboratory parameters are not affected by administration of the vaccine candidate except for perhaps mild urinalysis abnormalities at the highest dose. This vaccine candidate has no apparent immunotoxicity and does not appear to affect lymphocyte populations or T-cell functional studies. Low levels and transient antibodies develop in a minority of subjects early after immunization with the vaccine candidate. These responses were observed in the lowest dose range. Higher doses, and longer follow-up will be needed to confirm this observation. T-cell proliferative responses to KLH and KLH-HGP-30 are consistent and may not be dose dependent, but the proliferative responses are variable and more data need to be accumulated. Preliminary, there appears to be an HGP-30-induced CTL response of HGP-30-coated EBV-transformed autologous B cell lines. This study was approved under an IND for the California Department of Health Services' Food and Drug Branch. They have provided excellent support and regulatory guidelines for this project. Future work will extend and confirm these initial observations.

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.

Clonal analysis of murine B cell response to the human immunodeficiency virus type 1 (HIV1)-gag p17 and p25 antigens

The antigenicity of HIV-gag p17 and p25 proteins was analyzed using a panel of 52 monoclonal antibodies (mAb) derived from 17 independent fusion experiment protocols performed in 12 different laboratories. These mAb were tested for their capacity to bind peptides corresponding to sequences of HIV1-BRU-gag p17 and p25. Thirty-five overlapping peptides (P1 to P35) totally covering the p17 and p25 proteins were used. This study allowed us to identify four immunodominant regions inducing B cell response, two on p17 corresponding to P2 and P13 (amino acids 11-25 and 121-132, respectively) and two on p25 corresponding to P21 and P28-P29-P30 (a.a. 201-218 and 285-320 respectively). According to secondary structure predictions, peptides P2 and P21 contained hydrophilic alpha helix folded regions whereas P13 sequence presented a beta turn propensity. These regions and the P28-30 region were also predicted to be easily accessible to mAb. Several other p25-derived peptides: P15 (a.a. 142-156), P16 (a.a. 148-162), P19 (a.a. 176-192), P22 (a.a. 219-233) and P23 (a.a. 233-253) were recognized by mAb. No p17-derived peptide other than P2, P13 and P12 (a.a. 111-123) was found to react with mAb. Cross-blocking studies between mAb, suggested the existence of more than four distinct epitopic areas on p17 and eight on p25.

Development of a vaccine for the prevention of AIDS, a critical appraisal

The pathogenesis and clinical expression of HIV-1 infection in humans is considered in terms of classical pathogenetic studies of viral infections for which successful vaccines have been produced. The unique features of HIV pathogenesis are defined, and gaps in knowledge identified as a framework for considering designs for immune intervention. Envelope-derived candidate vaccines have been used in immunization and challenge experiments in SIV/macaque or HIV/chimpanzee models, presented either as vaccinia recombinant vectors or as subunits, singly or in sequence. These studies have been paralleled by clinical trials for safety and immunogenicity in seronegative individuals. Data generated will permit comparison of immune responses to specific antigens and delivery systems in animal models and in humans. In limited studies conducted under optimized conditions, non-human primates have been protected against virus challenge when immunized with some candidate vaccines or following passive transfer of high-titred antibody. Consideration of current information suggests that in order to prevent HIV infection it may be necessary to devise new strategies capable of inducing and maintaining high threshold titres of biologically relevant antibody as well as persistence of active cytotoxic T cells recognizing multiple epitopes.

Cell-mediated immunity against HGP-30, a group-specific peptide of HIV p17 in individuals infected with the AIDS virus

HGP-30, the synthetic peptide analogue and active component in an HIV-1 (human immunodeficiency virus, type 1) p 17 core-based experimental vaccine, has previously been shown to induce cytotoxic and helper T-lymphocyte responses. In order to further define the T-helper cell responses which are known to play a role in enhancing the immunological response to foreign antigens, we studied the response of individuals infected with HIV to HGP-30 at various stages of disease progression. We have investigated the proliferative cellular response of peripheral blood mononuclear cells (PBMCs) derived from individuals infected with HIV-1 to HGP-30. We have found a PBMC proliferative response to HGP-30 in 40% of the healthy seroconverted patients, in 35% of the CDC stage III patients and in 18% of the CDC stage IV patients. There was no correlation between the proliferative response to HGP-30 and other antigens such as HIV-like proteins or tetanus toxoid not to CD4 cell count. HLA-DR typing revealed the possible presentation of HGP-30 by several different class II molecules. Since these class II molecules occur frequently in the general population, HGP-30 appears to contain broadly reactive epitopes and thus is not restricted as are many peptide vaccines. Due to its broad reactivity and extreme conservation in many HIV-1 strains. HGP-30 is one of the promising candidates for inclusion as a subunit vaccine against HIV-1.

Neutralization of divergent HIV-1 isolates by conformation-dependent human antibodies to Gp120

The spectrum of human immunodeficiency virus type 1 (HIV-1) isolates neutralized by antibodies from HIV-1-infected humans is broader than the spectrum of isolates neutralized by sera from animals immunized with purified gp120 subunits. This broader neutralization was due, in part, to the presence of antibodies to conserved gp120 conformational epitopes. Purified conformation-dependent gp120-specific human antibodies neutralized a wider range of virus isolates than human antibodies directed to linear determinants in gp120 and were also responsible for the majority of the gp120-specific CD4-blocking activity of HIV-1-infected human sera. A gp120 subunit vaccine that effectively presents these conformation-dependent neutralization epitopes should protect against a broader range of HIV-1 variants than a vaccine that presents exclusively linear determinants.

Characterization of monoclonal antibodies against the human immunodeficiency virus matrix protein, p17gag: identification of epitopes exposed at the surfaces of infected cells

Eight monoclonal antibodies reactive with the matrix protein of human immunodeficiency virus type 1 (HIV-1), p17gag, were isolated from rats which had been immunized with solubilized HIV-1 lysate. The epitope specificities of these antibodies were determined with a series of synthetic peptides representing overlapping regions of p17. Six of the antibodies were mapped to three distinct regions of p17, while two antibodies (G11g1 and G11h3) reacted only with intact recombinant p17, suggesting that they were directed against conformational or discontinuous epitopes. All the antibodies bound to HIV-infected cells which had been permeabilized with acetone, but only G11g1 and G11h3 reacted with live HIV-infected cells. Specificity studies with diverse virus strains demonstrated that these two antibodies recognized distinct epitopes, one which was group specific for HIV-1, and one which was shared with HIV type 2 and simian immunodeficiency virus. Binding competition studies indicated that these epitopes were proximal in native p17. Despite their reactivity with intact cells, these two antibodies did not possess appreciable virus-neutralizing activity. These results indicate that a form of p17 is expressed on the surfaces of live HIV-infected cells which is accessible to some, but not all, antibodies against p17. These cell surface molecules may play a role in the generation of antibodies against p17gag that are characteristic of early stages of HIV infection, and they may act as natural targets for the immune system and as potential targets for immunotherapy of HIV-infected cells.

Characterization of antibodies reacting with HIV gag proteins occasionally found in the serum of non-infected subjects

The use of serological tests for the diagnosis of HIV infection has revealed that some non-infected persons have antibodies that react with HIV-1 gag proteins. Here, the sera of three non-infected subjects reacting with p17 and 11 non-infected subjects reacting with p24 were investigated, using an enzyme immunoassay (EIA) with six recombinant gag antigens and Western blot analysis of proteolytic peptides of two of these gag antigens. The results indicate that whereas all p17-reactive sera could react with an unique epitope, individual p24-reactive sera recognize different epitopes. Investigations by EIA also demonstrated the role of sequences located far from the epitopes in making these epitopes accessible to the antibodies or in providing them with an antigenic conformation. In addition to the 14 subjects mentioned above, another subject was shown to have antibodies reacting with the p9 (NC) gag protein. Several proteins are known as having homology with HIV-1 gag proteins. Their possible role in eliciting cross-reactive antibodies is discussed.

A sequence related to the human gonadoliberin precursor near the N-termini of HIV and SIV gag polyproteins

A highly conserved sequence near the N-terminus of all human (HIV) and simian (SIV) immunodeficiency virus gag polyproteins appears to be a precursor for a viral mimic of the amidated C-terminus of human gonadoliberin. The gag polyproteins are known to be myristylated; processing of the amidation site would yield myristylated 23-residue peptides whose C-terminal sequences mimic gonadoliberin and presumably behave as ligands for the gonadoliberin receptor. This paper describes the discovery of conserved gonadoliberin-precursor-related sequences in HIV and SIV gag polyproteins and in the p-17 core proteins derived from them. Arguments are presented that the conserved precursor structure requires post-translational processing to a peptide amide derivative which is a ligand for the gonadoliberin receptor. A model has been developed for entry of the viral genomic RNA into host cells through the gonadoliberin receptor and experiments are suggested to confirm or refute the model. This proposed mechanism for entry of HIV genomic RNA into host cells, if it proves to be substantially correct, suggests several new approaches to prevention and treatment of acquired immunodeficiency syndrome (AIDS).

Production of site-selected neutralizing human monoclonal antibodies against the third variable domain of the human immunodeficiency virus type 1 envelope glycoprotein

Cell lines secreting IgG1 human monoclonal antibodies (mAb) to the envelope glycoprotein, gp120, of human immunodeficiency virus (HIV) have been produced by transformation of peripheral blood cells from HIV-infected individuals and by fusion of transformed cells to a human-mouse heteromyeloma cell line (SHM-D33). Two human mAbs were site-selected by means of a 23-mer synthetic peptide spanning a portion of the third variable domain of gp120 from the MN strain of HIV. The two heterohybridomas produce three times more IgG than do their parent lymphoblastoid cell lines. The specificities of these mAbs have been mapped to sequences near the tip of the disulfide loop of the gp120 third variable domain, Lys-Arg-Ile-His-Ile and His-Ile-Gly-Pro-Gly-Arg, respectively. The mAbs have dissociation constants of 3.7 x 10(-6) M and 8.3 x 10(-7) M, neutralize HIVMN in vitro at nanogram levels, and bear the characteristics of antibodies associated with protective immunity in vivo.

AIDS virus infection and autoimmunity: a perspective of the clinical, immunological, and molecular origins of the autoallergic pathologies associated with HIV disease

The acquired immune deficiency syndrome (AIDS) is a viral-induced disorder of humans that is reaching pandemic proportions. The etiologic agent responsible for AIDS is recognized as a retrovirus termed the human immunodeficiency virus (HIV). This virus is both cytotropic and cytopathic for T lymphocytes in vitro, and patients with AIDS and HIV-related conditions invariably have serious T cell abnormalities, notably a reduced number of the helper/inducer (CD4+) subpopulation. There is now a substantial body of evidence to suggest that the AIDS virus triggers a diverse range of autoimmune phenomena. The purpose of this article is to summarize the clinical and immunopathological manifestations of autoimmunity in HIV infection and to provide a perspective of the possible origins and roles autoimmune reactions play in HIV disease progression.

Antigenic mimicry and autoimmune diseases

The finding of cross-reactive autoantibodies or sequence homology does not necessarily mean that this molecular mimicry is biologically meaningful or associated with disease pathogenesis. For example, relatives of persons with putative autoimmune insulin-dependent diabetes [123], and elderly humans [124] have a high incidence of autoantibodies which are generally not associated with autoimmune disease. In addition, natural antibodies to cell constituents [125] may be present in normal sera. These antibodies need to be directed against biologically important domains of host cell proteins in order to mediate autoimmune disease [27]. In spite of extensive homology between two sequences, a cross-reactive immune response may not be generated. The dissimilar amino acids should not be radical substitutions or affect the binding properties of the molecule. For instance, antibodies to synthetic peptides with only one substitution in a 19 amino acid sequence may not bind the whole protein [126]. Despite an identical six amino acid sequence shared by HLA-B27 and an EBV protein, no cross-reactive antibodies to EBV peptides were found in HLA-B27 positive patients with AS or RS. Unless the homology and subsequent crossreactive immune response can recognize a host protein intimately involved in disease pathogenesis, autoimmune disease is unlikely to occur.

Preclinical and clinical studies on immunogenicity and safety of the HIV-1 p17-based synthetic peptide AIDS vaccine--HGP-30-KLH

Immunization with a synthetic HIV-1 p17 peptide analog (HGP-30; aa 85-115 of HIV p17), coupled to a carrier protein (KLH, keyhole limpet hemocyanin) given with alum as the adjuvant induces antibodies which cross-react with both HGP-30 and HIV p17 and clones of cytotoxic and helper T-cells which recognize HGP-30 and HIV p17. Proliferation of lymphocytes in response to HGP-30 has been observed in mice, in HIV-infected individuals and in healthy HIV-seronegative volunteers vaccinated with the p17-based synthetic peptide construct. Cytotoxic T-cell responses against EBV transformed, recombinant p17 pulsed targets were observed using antigen-expanded PBLs from HGP-30-KLH immunized individuals. These results are consistent with predictions that the HGP-30 domain of HIV p17 contains both T- and B-cell epitopes that are recognized by animals and humans. In preclinical toxicology studies in animals and in initial clinical trials in humans the synthetic peptide construct (HGP-30-KLH/alum) has been shown to be safe. This paper summarizes the preclinical immunogenicity and safety data for HGP-30-KLH and presents the initial results from the first Phase 1 clinical trial.

HGP-30, a synthetic analogue of human immunodeficiency virus (HIV) p17, is a target for cytotoxic lymphocytes in HIV-infected individuals

Evaluation of the immune response of individuals exposed to human immunodeficiency virus (HIV) is an important component of any plan designed to lead toward the development of an AIDS vaccine. Since the levels of antibodies to HIV p17 and the synthetic p17 peptide HGP-30 correlate with stages of progression to AIDS, studies were initiated to determine whether cytotoxic lymphocytes directed toward target cells pulsed with HGP-30 and radioactive chromium were present in seropositive individuals. The significance of such cells in controlling HIV viral infection has recently been enhanced by reports that HIV p17 is on the surface of infected cells and that an inactivated virus vaccine depleted of viral envelope appears to be effective in controlling expression. The selection of HGP-30 as the p17 peptide to be evaluated in early studies is based on the presence of both T-cell and B-cell epitopes as predicted by computer modeling and mouse studies and the demonstration of in vitro neutralization activity by antibodies to the epitope. By using B-lymphoblastoid cells pulsed with HGP-30 and radioactive chromium as autologous targets and mixed leukocyte culture-expanded peripheral blood lymphocytes as effectors, CD8+ cytotoxic T lymphocytes against HGP-30-coated targets were identified in seropositive individuals. In this report we demonstrate that a synthetic p17 epitope can be a target for major histocompatibility complex-restricted cytotoxic T lymphocytes in HIV-infected individuals.

Characterization of monoclonal antibodies against the p17 core protein of the human immunodeficiency virus 1

Five mouse hybridomas which produce monoclonal antibodies against the p17 core protein of HIV-1 have been isolated. Cross-competition assays and mapping with synthetic peptides demonstrate that two closely related epitopes are identified by these antibodies. Directed against two neighbouring peptides at the carboxy-terminal end of the molecule, they can be used for the selective detection of p17 polypeptide in a viral extract or in an infected cell lysate by a solid-phase sandwich enzyme immunoassay.

Evidence that HIV-1 gag precursor shares antigenic sites with the major capsid protein of human cytomegalovirus

A rabbit antiserum prepared against disrupted sucrose-banded HIV-1 virus (strain FRE-3) reacted with antigens present in nuclear inclusions, pathognomonic for human cytomegalovirus (HCMV). This cross-reactivity was observed in autopsy specimens from individuals infected with CMV, in the presence or absence of co-infection with HIV-1. A Towbin immunoassay showed that the serum reacted specifically with the HCMV major capsid protein (MCP, 153 kDa), both in the nuclear fraction of infected cells and in virions. Direct evidence that these proteins share antigenic determinants was provided by the two-way cross-reactivity of affinity-selected antibodies (i.e., anti-MCP with HIV-1 gag precursor Pr55; anti-Pr55 with MCP). All four strains of HCMV tested showed this reactivity, but the counterpart proteins of simian CMV and herpes simplex virus type 1 did not, indicating that the determinant is not common to all herpes group viruses.

Prevalence of antibodies to the core protein P17, a serological marker during HIV-1 infection

Studies on monitoring the immune response to viral structural proteins during human immunodeficiency virus (HIV-1) infection have established the significance of antibodies to the core protein p24 during the progression of the disease. We have studied the prevalence of antibodies to the core protein p17 in order to study their diagnostic and prognostic significance in the pathogenesis of HIV-1. Full-length HIV-1 p17, molecularly cloned and expressed in Escherichia coli was purified by immunoaffinity chromatography using an HIV-1 p17-specific monoclonal antibody. A highly sensitive enzyme-linked immunoassay was developed using the purified recombinant p17 as the serological target to detect antibodies to p17. The results indicated that antibodies to p17 decline during progression of disease, with the decline being more dramatic as patients moved from asymptomatic to AIDS-related complex (ARC). Patient specimens deficient in p24 antibody, but having detectable levels of antibody to p17 were almost always positive for p24 antigen. Under these conditions, p17 antibody is an important serological marker because it provides a more consistent marker for core antigens during HIV-1 infection.

In vitro studies of HIV-1 infection in thymic lymphocytes: a putative role of the thymus in AIDS pathogenesis

To ascertain whether thymic lymphocytes represent suitable targets for HIV-1 infection, we infected thymic cell suspensions from normal donors with HIV-1 (HTLV-IIIB strain). We found that, in vitro, thymic lymphocytes are readily infected and highly permissive for HIV-1 replication. In addition, immature cells with the CD4+/CD8+ phenotype, most likely the precursors of mature circulating CD4+ and CD8+ lymphocytes, showed a marked susceptibility to viral infection and replication. These findings suggest that thymus infection may play a triggering role in the pathogenesis of AIDS, particularly in pediatric cases, and may partially explain the lack of restoration of peripheral CD4+ lymphocytes killed by HIV-1.

Peptide component vaccine engineering: targeting the AIDS virus

Most of the successful vaccines developed to date induce protective immunity resembling that produced by natural infection. HIV infection does not induce protective immunity. Thus, previously successful approaches based on live- or killed-virus preparations may not yield an effective and safe AIDS vaccine and many feel that a more highly engineered vaccine will be required. Synthetic peptides represent extremely powerful tools for vaccine research and construct optimization. The theory and practice of vaccine engineering using synthetic peptide components is reviewed with special emphasis on progress towards development of a vaccine for AIDS.

Immune response and epitope mapping of a candidate HIV-1 p17 vaccine HGP30

A thirty amino acid synthetic peptide (HGP30) representing the conserved region of HIV-1 p17 induced high titer antibodies to the native p17 in rabbits. This immune sera neutralized HIV-1 replication in cell culture and one of the high titer antisera also inhibited CD4-dependent cell fusion. Pepscan analysis with overlapping nonapeptides derived from the sequence of HIV-1 p17 identified the sequence (KE) ALDKIEE (EQ) as the major antibody binding site. Sera of 9% of AIDS patients (7/76) and 18% of HIV-1 seropositive healthy homosexuals (40/223) were positive for HGP30 antibodies. Decline in HIV-1 p17 antibodies has been shown to be related to disease progression in both children and adults, suggesting that HIV-1 p17 antibodies may be protective. Hence, a synthetic HIV-1 p17 peptide, representing the immunodominant epitope, could be useful as a candidate vaccine for immunization of HIV-1 seronegative or seropositive healthy homosexuals.

Replication of the bovine immunodeficiency-like virus in diploid and aneuploid cells: permanent, latent and virus-productive infections in vitro

Bovine immunodeficiency-like virus (BIV) is an infectious and leukotropic retrovirus, the sole lentivirus candidate which has been isolated from cattle. Although BIV has recently been shown to be related to the human immunodeficiency virus, there is very limited information on the replication and the pathogenesis of BIV. It is reported here that BIV can permanently infect diploid and aneuploid cells from four different species: bovine, canine, ferret and ovine. With the exceptions of a bovine diploid and a canine aneuploid cell line, all lines were virus non-productive. However, BIV was rescued by co-cultivation of virus non-productive cells with homologous BIV-free or canine cells (Cf2Th). A permanent and BIV-productive infection was established for 90-serial subcultures in a canine cell line. A BIV titre of 1 x 10(6)/0.1 ml was observed in stationary culture and 1 x 10(10)/0.1 ml in suspension culture. The canine cell line above was used for production of BIV antigens, whereas BIV-free canine cells were routinely used to isolate BIV from BIV non-productive cells infected in vitro and from blood from experimentally BIV-infected cattle. The different steps of virus maturation were similar by electron microscopy to those of lentiviruses. BIV results are compared to those of lentiviruses.

Isolation of recombinant partial gag gene product p18 (HIV-1Bru) from Escherichia coli

The membrane-associated structural protein, p18, of the human immunodeficiency virus (HIV-1), has been expressed in Escherichia coli. The recombinant protein was purified by cation-exchange chromatography on S Sepharose followed by cation-exchange high-performance liquid chromatography (HPLC) on Sulfoethyl Aspartamide. The isolation of 28.7 mg of recombinant p18 from 16.71 of cell culture represents an overall yield of ca. 20%. Recombinant p18 was characterized by sodium dodecyl sulphate polyacrylamide gel electrophoresis, reversed-phase HPLC, amino acid composition and amino acid sequence analysis of the N-terminus. Edman degradation of peptides generated by trypsin or Staphylococcus aureus V8 proteolytic digestion, including the C-terminus, confirmed the amino acid sequence to be that predicted from the cDNA. A C-terminally cleaved form of recombinant p18, p18LM, was separated in the cation-exchange HPLC step and was partially characterized in parallel with the intact molecule. By Western blotting it was shown that recombinant p18 in addition to the cleaved form p18LM is recognized by a monoclonal antibody which was generated against the natural protein from HIV-1.

Antibodies from human immunodeficiency virus-infected individuals bind to a short amino acid sequence that elicits neutralizing antibodies in animals

A total of 18 overlapping peptides were synthesized that covered envelope amino acid sequences (amino acids 288-472 of the III-B isolate) of the human immunodeficiency virus type 1 (HIV-1). Antibodies from human immunodeficiency virus-1-infected individuals bound to three of the peptides tested. Guinea pigs were immunized with each of the overlapping peptides and the resultant sera analyzed for biologic activity. One of the peptides elicited antibodies that had both neutralizing and fusion blocking activities that were type specific. This peptide, designated 1-69, was also one of the peptides reactive with the human immunodeficiency virus type 1-positive human sera.

Preliminary results on clinical and immunological effects of thymus hormone preparations in AIDS

The human immunodeficiency virus (HIV) is the newly recognized agent of the acquired immunodeficiency syndrome (AIDS). Global defects of the immune functions, including T- and B-cell immunity, macrophage functions and cytokine production, are commonly observed among patients with HIV infection. Many studies have shown thymus involvement and endocrine function impairments among these patients. Clinical trials with thymic compounds aiming at restoring the immune dysfunctions will be reviewed.

Antigenic specificity of antibody-dependent cell-mediated cytotoxicity directed against human immunodeficiency virus in antibody-positive sera

Antibody-dependent cell-mediated cytotoxicity (ADCC) specific for human immunodeficiency virus (HIV) has been described for HIV-infected individuals. To determine the antigenic specificity of this immune response and to define its relationship to the disease state, an ADCC assay was developed using Epstein-Barr virus-transformed lymphoblastoid cell line targets infected with vaccinia virus vectors expressing HIV proteins. The vaccinia virus vectors induced appropriate HIV proteins (envelope glycoproteins gp160, gp120, and gp41 or gag proteins p55, p40, p24, and p17) in infected lymphoblastoid cell lines as demonstrated by radioimmunoprecipitation and syncytia formation with c8166 cells. Killer cell-mediated, HIV-specific ADCC was found in sera from HIV-seropositive but not HIV-seronegative hemophiliacs. This HIV-specific response was directed against envelope glycoprotein but was completely absent against target cells expressing the HIV gag proteins. The ADCC directed against gp160 was present at serum dilutions up to 1/316,000. There was no correlation between serum ADCC titer and the stage of HIV-related illness as determined by T-helper-cell numbers. These experiments clearly implicated gp160 as the target antigen of HIV-specific ADCC activity following natural infection. Vaccines which stimulate antibodies directed against gp160, which are capable of mediating ADCC against infected cells, could be important for protection against infection by cell-associated virus.