AIDS vaccine developments

Nonhuman primate models for cell-associated simian immunodeficiency virus transmission: the need to better understand the complexity of HIV mucosal transmission

Nonhuman primates are extensively used to assess strategies to prevent infection from sexual exposure to human immunodeficiency virus (HIV) and to study mechanisms of mucosal transmission. However, although semen represents one of the most important vehicles for the virus, the vast majority of preclinical challenge studies have used cell-free simian immunodeficiency virus (SIV) or simian/human immunodeficiency virus (SHIV) viral particles inoculated as diluted culture supernatants. Semen is a complex body fluid containing many factors that may facilitate or decrease HIV infectiousness. The virus in semen is present in different forms: as free virus particles or as cell-associated virus (ie, within infected leukocytes). Although cell-to-cell transmission of HIV is highly efficient, the role of cell-associated virus in semen has been surprisingly poorly investigated in nonhuman primate models. Mucosal exposure of macaques to cell-associated SIV by using infected peripheral blood mononuclear cells or spleen cells has been shown to be an efficient means of infection; however, it has yet to be shown that SIV- or SHIV-infected seminal leukocytes can transmit infection in vivo. Improvement of animal models to better recapitulate the complex microenvironment at portals of HIV entry is needed for testing candidate antiretrovirals, microbicides, and vaccines.

Cytoskeletal proteins bound to heat-shock protein 70 may elicit resistance to simian immunodeficiency virus infection of CD4(+) T cells

This study is based on the evidence that immunization of macaques with human CD4(+) T cells elicits prevention of simian immunodeficiency virus (SIV) infection. We hypothesized that heat-shock protein 70 (HSP70) isolated from CD4(+) T cells may act as a chaperone and carry the protective host proteins. Two moieties of HSP70 were affinity-purified from human CD4(+) T cells; an ADP preparation with HSP70-bound proteins (ADP-HSP) and an ATP control preparation. Immunization of rhesus macaques with these preparations showed significant inhibition of SIVmac251 infectivity ex vivo in CD4(+) T cells only with the ADP-HSP (P = 0.01). Proteomic analysis identified three cytoskeletal elements, cofilin, profilin and gamma-actin, exclusively in the ADP-HSP preparation. Investigation of the mechanism of prevention of SIV replication suggests that antibodies to the cytoskeletal proteins may inhibit actin depolymerization and facilitate viral degradation by the innate antiviral APOBEC3G. As cytoskeletal proteins are critical in the formation of virological and immunological synapses, finding specific antibodies and anti-SIV/human immunodeficiency virus (HIV) factors suggests a novel insight into HIV-1 immunopathogenesis.

Innate immunity in experimental SIV infection and vaccination

Innate immunity represents the first line of defence to pathogens besides the physical barrier and seems to play a role in protection against HIV/SIV infection and disease progression. High production of beta-chemokines and CD8+ T cell anti-viral factors in naive as well as in vaccinated macaques has been associated with complete or partial protection against SIV infection indicating that genetic or environmental factors may influence their production. This innate immunity may help in generating HIV/SIV-specific responses upon the first exposure to HIV/SIV. SIV subunit vaccines given by the targeted iliac lymph node route have been shown to induce an increased production of CD8+ T cell suppressor factors and beta-chemokines. Only a few vaccine studies have focused on enhancing the innate immune response against HIV/SIV. The use of unmethylated CpG motifs, HSP and GM-CSF as adjuvants in SIV vaccines has been shown to induce production of HIV/SIV-inhibiting cytokines and beta-chemokines, which seem to be important in modulating and steering the adaptive immune responses. HSP has also been shown to induce gammadelta+ T cells, which contribute to the innate immunity. More knowledge about the interplay between the innate and adaptive immune responses is important to develop new HIV/SIV vaccine strategies.

Induction of inhibitory antibodies to the CCR5 chemokine receptor and their complementary role in preventing SIV infection in macaques

The seven-transmembrane G-protein-linked CCR5 molecule functions as a major coreceptor for HIV or simian immunodeficiency virus (SIV) infection. Antibodies to CCR5 were studied in rhesus macaques immunized with SIV grown in human CD4(+) T cells. These macaques were completely protected against i.v. challenge with live SIV. Sera from the protected macaques showed significantly greater inhibition of SIV replication (p < 0.001) and macrophage inflammatory protein-1beta-generated CCR5-dependent chemotaxis (p < 0.01) than sera from unprotected macaques, in the absence of significant neutralizing antibodies to SIV. These two functional assays demonstrate serum antibodies to the CCR5 receptors which were specifically inhibited by CCR5-transfected HEK-293 cells. We postulate that anti-CCR5 antibodies may be complementary to beta-chemokines in blocking CCR5 coreceptors to HIV or SIV binding and fusion of CD4(+) cells.

Accelerated viraemia in cats vaccinated with fixed autologous FIV-infected cells

We have vaccinated cats with fixed autologous FIV infected PBMC to determine whether autologous presentation of antigen is capable of inducing a protective immune response against homologous challenge. To this end autologous PBMC were infected with a FIV molecular clone (19k1). When infection was established, cells were inactivated by dialysis against paraformaldehyde. Upon vaccination, cats developed a virus specific immune response as measured by ELISA against the Gag protein of FIV. No antibodies against the envelope protein were detected with a peptide ELISA. Virus neutralizing antibodies however could be detected with a neutralization assay based on infection of CrFK cells, but not in an assay based on infection of primary T-cells. Although vaccination led to the induction of these virus-specific immune responses, vaccinated cats were not protected against homologous challenge but showed an accelerated viraemia upon infection. This was shown both by PCR and cell-associated viral load. The possible mechanisms underlying this observation are discussed in this paper.

Generation of CD8 suppressor factor and beta chemokines, induced by xenogeneic immunization, in the prevention of simian immunodeficiency virus infection in macaques

Previous xenogeneic immunization experiments in rhesus macaques with simian immunodeficiency virus (SIV) grown in human CD4(+) T cells consistently elicited protection from challenge with live SIV. However, the mechanism of protection has not been established. We present evidence that xenogeneic immunization induced significant CD8 suppressor factor, RANTES (regulated upon activation, normal T cell expressed and secreted), macrophage inflammatory protein (MIP) 1alpha, and MIP-1beta (P < 0.001 - P < 0.02). The concentrations of these increased significantly in protected as compared with infected macaques (P < 0.001). Xenogeneic stimulation in vitro also up-regulated CD8 suppressor factors (SF; P < 0.001) and the beta chemokines which were neutralized by antibodies to the 3 beta chemokines. Recombinant human RANTES, MIP-1alpha and MIP-1beta which bind to simian CCR5, suppressed SIV replication in a dose-dependent manner, with RANTES being more effective than the other two chemokines. The results suggest that immunization with SIV grown in human CD4(+) T cells induces CD8-suppressor factor, RANTES, MIP-1alpha and MIP-1beta which may block CCR5 receptors and prevent the virus from binding and fusion to CD4(+) cells.

Utility of SHIV for testing HIV-1 vaccine candidates in macaques

SUMMARY

Intravenous injection of SHIV (simian/human immunodeficiency virus, chimeric virus) into rhesus macaques resulted in a viremia in peripheral blood lymphocytes (PBL) and the generation of anti-HIV-1 (human immunodeficiency virus type 1) envelope immune responses. A challenge stock of a SHIV containing HIV-1 HXBc2 envelope glycoproteins was prepared from infected rhesus monkey peripheral blood mononuclear cells (PBMC). The minimum animal infectious dose of the SHIV stock was determined and used in a challenge experiment to test protection. The vaccination of two rhesus monkeys with whole inactivated HIV-1 plus polydicarboxylatophenoxy phosphazene (PCPP) as the adjuvant protected the animals from becoming infected by a SHIV challenge. This experiment demonstrated for the first time that monkeys immunized with HIV-1 antigens can be protected against an HIV-1 envelope-containing virus. As the challenge virus was prepared from monkey PBMC, human antigens were unlikely to be involved in the protection. Protection of rhesus monkeys from SHIV challenge may help,define protective immune responses stimulated by HIV-1 vaccine candidates.

Vaccine-induced virus-neutralizing antibodies and cytotoxic T cells do not protect macaques from experimental infection with simian immunodeficiency virus SIVmac32H (J5)

To gain further insight into the ability of subunit vaccines to protect monkeys from experimental infection with simian immunodeficiency virus (SIV), two groups of cynomolgus macaques were immunized with either recombinant SIVmac32H-derived envelope glycoproteins (Env) incorporated into immune-stimulating complexes (iscoms) (group A) or with these SIV Env iscoms in combination with p27gag iscoms and three Nef lipopeptides (group B). Four monkeys immunized with recombinant feline immunodeficiency virus Env iscoms served as controls (group C). Animals were immunized intramuscularly at weeks 0, 4, 10, and 16. Two weeks after the last immunization, monkeys were challenged intravenously with 50 monkey 50% infectious doses of virus derived from the J5 molecular clone of SIVmac32H propagated in monkey peripheral blood mononuclear cells. High titers of SIV-neutralizing antibodies were induced in the monkeys of groups A and B. In addition, p27gag-specific antibodies were detected in the monkeys of group B. Vaccine-induced cytotoxic-T-lymphocyte precursors against Env, Gag, and Nef were detected on the day of challenge in the monkeys of group B. Env-specific cytotoxic-T-lymphocyte precursors were detected in one monkey from group A. In spite of the observed antibody and T-cell responses, none of the monkeys was protected from experimental infection. In addition, longitudinal determination of cell-associated virus loads at weeks 2, 4, 6, 9, and 12 postchallenge revealed no significant differences between vaccinated and control monkeys. These findings illustrate the need to clarify the roles of the different arms of the immune system in conferring protection against primate lentivirus infections.

Antigenicity and immunogenicity of recombinant envelope glycoproteins of SIVmac32H with different in vivo passage histories

Shortly after infection of two rhesus monkeys (Macaca mulatta) either with a SIVmac32H challenge stock or with the same virus that had been passaged in another rhesus monkey for 11 months, SIV-envelope genes were cloned from their peripheral blood mononuclear cells and subsequently expressed by recombinant vaccinia viruses. The molecular weights and antigenicities of the thus produced envelope glycoproteins were largely identical to those of the native SIV. The envelope glycoprotein derived from the in vivo passaged virus proved to be poorly recognized by virus neutralizing monoclonal antibodies directed against one of the seven antigenic sites for which monoclonal antibodies were available. Immunization studies in rats showed that this protein was also less efficient in inducing antibodies against this antigenic site, and that it induced significantly lower levels of virus neutralizing antibodies than the other SIV-envelope glycoprotein. The immunogenicity of the SIV-envelope glycoprotein incorporated into immune stimulating complexes (iscoms) was compared to that of the same protein presented with Quil A or MDP-tsl.

Studies of complement-activating antibodies in the SIV/macaque model of acute primary infection and vaccine protection

Questions regarding the potential impact of complement-activating antibodies on lentivirus pathogenesis and vaccine development were addressed in the SIV/macaque model by evaluating sera for activity related to complement-mediated, antibody-dependent enhancement (C'-ADE) of SIV infection in vitro. C'-ADE activity in sera obtained during acute primary infection in macaques inoculated with SIVmac251 appeared before neutralizing antibodies and coincided with the initial peak and decline of plasma antigenemia. The power of C'-ADE activity (i.e., virus production measured by p24 immunoassay) decreased as titers of neutralizing antibodies increased in these animals, suggesting a balance in the net effect between C'-ADE and neutralizing activities in vitro. Antibodies with C'-ADE activity were also induced in macaques immunized with live-attenuated SIVmac239/nef-deletion or primed with recombinant SIVmne gp120 vaccinia virus and boosted with SIVmne rgp160. The titer (i.e., last serum dilution to show enhancement), peak (i.e., serum dilution producing the greatest enhancement as measured by p24 production), and power (i.e., magnitude of p24 production at the peak titer) of C'-ADE activity in sera obtained from vaccinated macaques on the day of challenge were comparable to those of sera from infected macaques and showed no correlation with vaccine outcome, where some protected animals had C'-ADE profiles that resembled those of unprotected animals. The results of these studies suggest that antibodies having C'-ADE activity in vitro could contribute to virus replication or, alternatively, to virus clearance during the acute stage of SIV infection in macaques.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of feline immunodeficiency virus infection after immunization with envelope glycoprotein subunit vaccines

Cats were immunized three times with different recombinant feline immunodeficiency virus (FIV) candidate vaccines. Recombinant vaccinia virus (rVV)-expressed envelope glycoprotein with (vGR657) or without (vGR657 x 15) the cleavage site and an FIV envelope bacterial fusion protein (beta-Galactosidase-Env) were incorporated into immune-stimulating complexes or adjuvanted with Quil A. Although all immunized cats developed antibodies against the envelope protein, only the cats vaccinated with the rVV-expressed envelope glycoproteins developed antibodies which neutralized FIV infection of Crandell feline kidney cells. These antibodies failed to neutralize infection of thymocytes with a molecularly cloned homologous FIV. After the third immunization the cats were challenged with homologous FIV. Two weeks after challenge the cell-associated viral load proved to be significantly higher in the cats immunized with vGR657 and vGR657 x 15 than in the other cats. The cats immunized with vGR657 and vGR657 x 15 also developed antibodies against the Gag proteins more rapidly than the cats immunized with beta-Galactosidase-Env or the control cats. This suggested that immunization with rVV-expressed glycoprotein of FIV results in enhanced infectivity of FIV. It was shown that the observed enhancement could be transferred to naive cats with plasma collected at the day of challenge.

Can live attenuated virus work as post-exposure treatment?

Simple mathematical models for the competition between different virus variants in the presence of a crossreactive immune response show that, contrary to expectation, selection can favour variants that induce low viral loads. Here, Sebastian Bonhoeffer and Martin Nowak suggest that such 'competitively superior', but 'less pathogenic', mutants may be a possibility for post-exposure treatment of persistent virus infections.

An experimental chemically inactivated HIV-1 vaccine induces antibodies that neutralize homologous and heterologous viruses

We have developed a unique multiple step procedure to inactivate human immunodeficiency virus chemically with a very high safety margin while retaining antigenically active structural virion proteins, including gp120, in the final immunogen. The whole virus preparation (1-10 micrograms per dose) was highly immunogenic in a variety of small mammals and induced antibodies that recognized homologous and heterologous strains of HIV-1. Sera from immunized animals bound to peptides representing the entire sequence of the external glycoprotein gp120. Neutralizing antibodies active against the homologous immunizing strain and against heterologous HIV-1 strains were also elicited. Sera with virus neutralizing activity did not bind to MHC class I proteins derived from the human cell line used to grow the virus.

Protection of rhesus macaques from SIV infection by immunization with different experimental SIV vaccines

The immunogenicity and efficacy of an inactivated whole SIVmac (32H) preparation adjuvanted with muramyl dipeptide (SIV-MDP) and a gp120-enriched SIVmac (32H) ISCOM preparation (SIV-ISCOM), were compared by immunizing four rhesus macaques (Macaca mulatta) four times with SIV-MDP and four others in the same way with SIV-ISCOM. Two monkeys immunized with whole inactivated measles virus (MV) adjuvanted with MDP (MV-MDP) and two monkeys immunized with MV-ISCOM served as controls. In the SIV-ISCOM-immunized monkeys higher SIV-specific serum antibody titres were found than in the SIV-MDP-immunized monkeys. In contrast to the MV-immunized monkeys all SIV-MDP- and SIV-ISCOM-immunized monkeys were protected against intravenous challenge 2 weeks after the last immunization with 10 median monkey infectious doses (MID50) of a cell-free SIVmac (32H) challenge stock propagated in the human T-cell line C8166. After 43 weeks the protected monkeys were reboosted and 2 weeks later rechallenged with 10 MID50 of the same virus produced in peripheral blood mononuclear cells (PBMC) from a rhesus macaque. None of these animals proved to be protected against this challenge. In a parallel experiment in which the same numbers of monkeys were immunized in the same way, the animals were challenged intravenously with 10 MID50 of PBMC from an SIVmac (32H)-infected rhesus macaque. Two out of four SIV-MDP- and two out of four SIV-ISCOM-immunized monkeys proved to be protected from SIV infection.

Some statistical issues in HIV vaccine trials

Efficacy trials of prophylactic HIV vaccines will be among the most difficult clinical trials ever attempted. Not only will there be challenges with the recruitment and retention of high-risk uninfected individuals, there will be many statistical challenges to the design, conduct, analysis, and interpretation of these trials. General features of an efficacy trial are described, including choice for the primary endpoint and testing for and estimating vaccine efficacy. Secondary objectives of trials are also discussed. These include determining the correlates of protective immunity, assessing the impact of HIV genetic variation on vaccine efficacy, and using biological markers such as viral load and CD4+ lymphocyte cell count to gain insight on a vaccine's ability to prevent or delay disease. The use of biological markers as surrogates for disease outcome is discussed. Last, trial designs for studying several candidate vaccines or other HIV prevention strategies in a single trial are examined.

Involvement of human leukocyte antigen class I molecules in human immunodeficiency virus infection of CD4-positive cells

We have studied the putative roles of human immunodeficiency virus (HIV)-associated and cell surface-expressed major histocompatibility complex class I (MHC-I) molecules in the course of the HIV life cycle by the combined use of MHC-I molecule-positive and MHC-I molecule-negative virus particles and MHC-I molecule-positive and MHC-I molecule-negative CD4+ human cells. We found (i) that several anti-MHC-I monoclonal antibodies neutralize cell infection by direct interaction with HIV-associated MHC-I antigens, (ii) that these HIV-associated MHC-I antigens are however dispensable for cell infection, and (iii) that the cell surface-expressed MHC-I molecules are unnecessary for productive infection of CD4+ human cells. These results clarify further the functions of MHC-I molecules during the HIV life cycle.

Vaccine-induced neutralizing antibodies directed in part to the simian immunodeficiency virus (SIV) V2 domain were unable to protect rhesus monkeys from SIV experimental challenge

The potential of the simian immunodeficiency virus (SIV) variable 2 (V2) domain as an effective region to boost SIV-neutralizing antibodies and to protect against live SIV challenge was tested in rhesus macaques. In this study, two rhesus macaques were primed with vaccinia virus recombinants expressing the surface glycoprotein gp140 of SIVmac and were given booster injections with the SIVmac V2 domain presented by a highly immunogenic carrier, the hepatitis B surface antigen (HBsAg). The two vaccinated macaques exhibited SIV-neutralizing antibodies after primer injections that were enhanced by the V2/HBsAg injections. Part of these SIV-neutralizing antibodies were directed specifically to the V2 region, as shown by neutralization-blocking experiments. However, despite having consistent SIV-neutralizing antibody titers, animals were not protected against homologous challenge with BK28, the molecular clone of SIVmac251. No SIV envelope-specific cellular cytotoxic response was detected throughout the immunization protocol, suggesting that neutralizing antibodies directed to SIV envelope gp140 and especially to the V2 domain were unable on their own to protect against SIV challenge. Furthermore, the vaccinees seemed to have higher viral loads than control animals after challenge, raising the question of whether neutralizing antibodies induced by vaccination and directed to the SIV envelope selected viral escape mutants, as shown previously in SIV-infected macaques. This mechanism is certainly worthy of intensive investigation and raises some concern for SIV envelope-targeted immunization.

Incomplete protection, but suppression of virus burden, elicited by subunit simian immunodeficiency virus vaccines

We compared the efficacy of immunization with either simian immunodeficiency virus (SIV) Env glycoprotein (Env), Env plus Gag proteins (Gag-Env), or whole inactivated virus (WIV), with or without recombinant live vaccinia vector (VV) priming, in protecting 23 rhesus macaques (six vaccine and two control groups) from challenge with SIVmac251 clone BK28. Vaccination elicited high titers of syncytium-inhibiting and anti-Env (gp120/gp160) antibodies in all vaccinated macaques and anti-Gag (p27) antibodies in groups immunized with WIV or Gag-Env. Only WIV-immunized macaques developed anticell (HuT78) antibodies. After homologous low-dose intravenous virus challenge, we used frequency of virus isolation, provirus burden, and change in antibody titers to define four levels of resistance to SIV infection as follows. (i) No infection ("sterilizing" immunity) was induced only in WIV-immunized animals. (ii) Abortive infection (strong immunity) was defined when virus or provirus were detected early in the postchallenge period but not thereafter and no evidence of virus or provirus was detected in terminal tissues. This response was observed in two animals (one VV-Env and one Gag-Env). (iii) Suppression of infection (incomplete or partial immunity) described a gradient of virus suppression manifested by termination of viremia, declining postchallenge antibody titers, and low levels (composite mean = 9.1 copies per 10(6) cells) of provirus detectable in peripheral blood mononuclear cells or lymphoid tissues at termination (40 weeks postchallenge). This response occurred in the majority (8 of 12) of subunit-vaccinated animals. (iv) Active infection (no immunity) was characterized by persistent virus isolation from blood mononuclear cells, increasing viral antibody titers postchallenge, and high levels (composite mean = 198 copies per 10(6) cells) of provirus in terminal tissues and blood. Active infection developed in all controls and two of three VV-Gag-Env-immunized animals. The results of this study restate the protective effect of inactivated whole virus vaccines produced in heterologous cells but more importantly demonstrate that a gradient of suppression of challenge virus growth, reflecting partial resistance to SIV infection, is induced by subunit vaccination. The latter finding may be pertinent to studies with human immunodeficiency virus vaccines, in which it is plausible that vaccination may elicit significant suppression of virus infection and pathogenicity rather than sterilizing immunity.

Passive immunization of cynomolgus macaques with immune sera or a pool of neutralizing monoclonal antibodies failed to protect against challenge with SIVmac251

In the first of two passive transfer experiments, three groups of four macaques were injected intraperitoneally with a normal serum pool, an immune serum pool (pool 1) collected 132-172 weeks postinfection with the 11/88 pool of SIVmac251, or with a pool of four neutralizing monoclonal antibodies (KK9, 17, 54, and 56) raised against gp120 of the 11/88 pool. Sera were given at a dose of 13 ml/kg whereas the MAb pool was given at 30 ml/kg. In a second experiment, a further four macaques were injected with an immune serum pool (pool 2) collected 12 weeks postinfection with simian-grown SIVmac251 at a dose of 19 ml/kg. Animals in both experiments were challenged with SIVmac251 grown in simian peripheral blood lymphocytes. Despite high levels of circulating antibodies in the serum of animals that received either the immune serum pools or the MAbs, all macaques became infected following challenge. The results described are in contrast to a previous report in which passive transfer of sera from animals infected with SIVsm successfully protected against challenge with the homologous virus grown in human PBMCs. Challenge with SIVmac251 grown in simian PBMCs may be the reason for these conflicting results. Nevertheless, the results suggest that in this model the presence of circulating neutralizing antibodies alone does not necessarily confer protection against challenge with SIVmac251 grown in simian cells.

Immunization with whole inactivated vaccine protects from infection by SIV grown in human but not macaque cells

Homologous SIVsm stocks were generated by passage of a macaque isolate of SIVsm (SIVsm/E660) in human CEM x 174 cells or macaque peripheral blood mononuclear cells. Macaques were immunized with whole inactivated SIV vaccine consisting of virus generated by transfection of CEM x 174 cells with the SIVsmH4 clone and were challenged with either cell-free stock. Only vaccinees challenged with virus generated in human cells were protected from infection. This confirms the species-specificity of whole inactivated vaccine-mediated protection.

Purification and characterization of simian immunodeficiency virus (SIVmac) envelope glycoprotein gp130 from virus-infected cells

A non-denaturing method has been developed for the purification of the envelope glycoprotein gp130 of the simian immunodeficiency virus (SIV) using infected cells as starting material. The procedure involves solubilization of cells infected with SIV (SIVmac251), enrichment of glycoproteins by lectin affinity chromatography, fractionation by reverse phase chromatography and purification by immunoaffinity chromatography. This procedure results in a greater than 95% purification of gp130 as assessed by polyacrylamide gel electrophoresis. There is no evidence for the presence of other virus-derived proteins after Western blot analysis using antibodies specific for virus proteins. Lectin-binding studies suggest that carbohydrate groups on the infected-cell-derived gp130 may differ from those on recombinant counterparts expressed in Chinese hamster ovary cells and Baculovirus-infected insect cells. The purified gp130 is highly immunogenic in rabbits and maintains the capacity to bind the CD4 receptor. A sufficient quantity of the infected-cell-derived gp130 has been prepared for immunization studies and subsequent live virus challenge studies in macaques.

Induction of humoral and cell-mediated anti-human immunodeficiency virus (HIV) responses in HIV sero-negative volunteers by immunization with recombinant gp160

Development of an effective vaccine for prevention of infection with HIV would provide an important mechanism for controlling the AIDS epidemic. In the current study, the first clinical trial of a candidate HIV-1 vaccine initiated in the United States, the safety and immunogenicity of escalating doses (10-1,280 micrograms) of recombinant gp160 (rgp160), were evaluated in 138 HIV-negative volunteers. Maximal antibody responses, as evaluated by ELISA, were seen after immunization with three doses of 1,280 micrograms rgp160. Responses to some specific epitopes of HIV gp160, including the second conserved domain and the CD4 binding site, were seen more frequently than after natural infection. Neutralizing antibodies to the homologous HIV strain, but not heterologous strains, were induced by this regimen. Blastogenic responses to rgp160 were seen in most volunteers receiving at least two doses of > or = 20 micrograms. These envelope-specific T cell responses were also seen against heterologous strains of HIV. No major adverse reactions were seen after immunization. Thus, rgp160 is a safe and immunogenic candidate HIV vaccine; further studies are needed to determine if it will provide any clinical benefit in preventing HIV infection.

Challenges and strategies for AIDS vaccine development

The major topics covered at this conference included the relevance of the SIV-macaque model for HIV vaccine development, an evaluation of the methods for producing inactivated vaccine, and the possibility of developing attenuated retrovirus vaccines. The possibility that there might be a Graft Versus Host Disease component in human AIDS was discussed, and also the recent discovery that the 'original antigenic sin' phenomenon encountered in influenza vaccines may also be seen in AIDS. It was concluded that results from animal models were encouraging in the quest for an HIV-1 vaccine.

Protective effects of a live attenuated SIV vaccine with a deletion in the nef gene

Vaccine protection against the human immunodeficiency virus (HIV) and the related simian immunodeficiency virus (SIV) in animal models is proving to be a difficult task. The difficulty is due in large part to the persistent, unrelenting nature of HIV and SIV infection once infection is initiated. SIV with a constructed deletion in the auxiliary gene nef replicates poorly in rhesus monkeys and appears to be nonpathogenic in this normally susceptible host. Rhesus monkeys vaccinated with live SIV deleted in nef were completely protected against challenge by intravenous inoculation of live, pathogenic SIV. Deletion of nef or of multiple genetic elements from HIV may provide the means for creating a safe, effective, live attenuated vaccine to protect against acquired immunodeficiency syndrome (AIDS).

Vaccination of rhesus monkeys with synthetic peptide in a fusogenic proteoliposome elicits simian immunodeficiency virus-specific CD8+ cytotoxic T lymphocytes

An effective vaccine against the human immunodeficiency virus should be capable of eliciting both an antibody and a cytotoxic T lymphocyte (CTL) response. However, when viral proteins and peptides are formulated with traditional immunological adjuvants and inoculated via a route acceptable for use in humans, they have not been successful at eliciting virus-specific, major histocompatibility complex (MHC) class I-restricted CTL. We have designed a novel viral subunit vaccine by encapsulating a previously defined synthetic peptide CTL epitope of the simian immunodeficiency virus (SIV) gag protein within a proteoliposome capable of attaching to and fusing with plasma membranes. Upon fusing, the encapsulated contents of this proteoliposome can enter the MHC class I processing pathway through the cytoplasm. In this report, we show that after a single intramuscular vaccination, rhesus monkeys develop a CD8+ cell-mediated, MHC class I-restricted CTL response that recognizes the synthetic peptide immunogen. The induced CTL also demonstrate antiviral immunity by recognizing SIV gag protein endogenously processed by target cells infected with SIV/vaccinia recombinant virus. These results demonstrate that virus-specific, MHC class I-restricted, CD8+ CTL can be elicited by a safe, nonreplicating viral subunit vaccine in a primate model for acquired immune deficiency syndrome. Moreover, the proteoliposome vaccine formation described can include multiple synthetic peptide epitopes, and, thus, offers a simple means of generating antiviral cell-mediated immunity in a genetically heterogeneous population.

Sulfation of the human immunodeficiency virus envelope glycoprotein

Sulfation is a posttranslational modification of proteins which occurs on either the tyrosine residues or the carbohydrate moieties of some glycoproteins. In the case of secretory proteins, sulfation has been hypothesized to act as a signal for export from the cell. We have shown that the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein precursor (gp160) as well as the surface (gp120) and transmembrane (gp41) subunits can be specifically labelled with 35SO42-. Sulfated HIV-1 envelope glycoproteins were identified in H9 cells infected with the IIIB isolate of HIV-1 and in the cell lysates and culture media of cells infected with vaccinia virus recombinants expressing a full-length or truncated, secreted form of the HIV-1 gp160 gene. N-glycosidase F digestion of 35SO4(2-)-labelled envelope proteins removed virtually all radiolabel from gp160, gp120, and gp41, indicating that sulfate was linked to the carbohydrate chains of the glycoprotein. The 35SO42-label was at least partially resistant to endoglycosidase H digestion, indicating that some sulfate was linked to complex carbohydrates. Brefeldin A, a compound that inhibits the endoplasmic reticulum to Golgi transport of glycoproteins, was found to inhibit the sulfation of the envelope glycoproteins. Envelope glycoproteins synthesized in cells treated with chlorate failed to incorporate 35SO42-. However, HIV glycoproteins were still secreted from cells in the presence of chlorate, indicating that sulfation is not a requirement for secretion of envelope glycoproteins. Sulfation of HIV-2 and simian immunodeficiency virus envelope glycoproteins has also been demonstrated by using vaccinia virus-based expression systems. Sulfation is a major determinant of negative charge and could play a role in biological functions and antigenic properties of HIV glycoproteins.

Protection in simian immunodeficiency virus-vaccinated monkeys correlates with anti-HLA class I antibody response

Our earlier reports demonstrated that Cynomolgus macaques vaccinated with either inactivated partially purified simian immunodeficiency virus (SIV), fixed SIV-infected C8166 (a human T lymphoblastoid cell line) cells, or fixed uninfected C8166 cells can be protected against a challenge infection with the 32H isolate of SIVmac 251 (grown in C8166) (Stott, E. J., W. L. Chan, K. H. G. Mills, M. Page, F. Taffs, M. Cranage, P. Greenway, and P. Kitchin. 1990. Lancet. 336:1538; Stott, E. J., P. A. Kitchin, M. Page, B. Flanagan, L. F. Taffs, W. L. Chan, K. H. G. Mills, P. Silvera, and A. Rodgers. 1991. Nature [Lond.]. 353:393). Protection is correlated with the levels of antibody response to cellular antigens in the human cells from which the virus immunogen was grown. However, the mechanism of protection is unclear. We report here the analysis of sera from these protected monkeys and demonstrate that there is positive correlation of protection with antibody response to the HLA class I molecule.

Improbability of effective vaccination against human immunodeficiency virus because of its intracellular transmission and rectal portal of entry

The worldwide effort to produce a vaccine against AIDS continues to disregard the fact that even human immunodeficiency virus (HIV)-specific neutralizing antibodies and cell-mediated immunity are ineffective against virus within cells without viral antigens on the cell membrane--and that much of HIV infection is transmitted in this manner. According to a recent report, a simian immunodeficiency virus vaccine that protected monkeys against an intravenous challenge with cell-free virus was, as predicted, ineffective against an intravenous challenge with the same amount of virus in infected cells. Moreover, antibody and HIV have been found to coexist in cell-free plasma from asymptomatic and symptomatic patients. Excluding direct introduction of HIV into the blood-stream, the most common and efficient form of transmission of HIV infection is by receptive anal intercourse, and semen contains large numbers of infected cells per milliliter. Recent reports showing that colorectal cells can be persistently infected by HIV and that HIV RNA and cDNA are present in the cells of the colon of dead AIDS patients indicate that either cell-free or intracellular HIV has the capacity to multiply at the portal of entry in the colorectal area without interference from neutralizing antibodies. The available data provide no basis for testing any HIV vaccine in human beings either before or after infection. The main challenge is to find a way to kill cells with chromosomally integrated HIV cDNA without harming normal cells, perhaps by identifying repressor proteins that might be produced by the cells with integrated HIV cDNA and thus could become specific targets for cell-killing drugs.

Detection of anti-human cell antibodies in sera from macaques immunized with whole inactivated virus

More than 200 sera from macaques immunized with several different vaccine preparations were tested in various assays with cells of human and macaque origin. Only in instances where whole inactivated SIV preparations were used for immunization, were reactivities found with normal human cells, and this was the case in every instance. Such sera produced a marked clumping of several normal human cell lines and exhibited strong staining of the cell surface in FACS analysis. In the presence of SIVDeltaB670, these sera also enhanced infectivity and fusion formation. When similar tests were performed with macaque cells as targets, such phenomena were not easily discernible. Likewise, there was no trace of such activities in sera from normal animals, animals chronically infected with SIV, or in those from animals which received recombinant viral subunits as vaccines. Finally, we show that in several instances where whole inactivated virus was used as a vaccine, there is a strong correlation between the titer of anticellular activity with protection.