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

An assessment of the role of chimpanzees in AIDS vaccine research

Prior to Simian Immunodeficiency Virus (SIV)-infected macaques becoming the 'model of choice' in the 1990s, chimpanzees were widely used in AIDS vaccine research and testing. Faced with the continued failure to develop an effective human vaccine, some scientists are calling for a return to their widespread use. To assess the past and potential future contribution of chimpanzees to AIDS vaccine development, databases and published literature were systematically searched to compare the results of AIDS vaccine trials in chimpanzees with those of human clinical trials, and to determine whether the chimpanzee trials were predictive of the human response. Protective and/or therapeutic responses have been elicited in chimpanzees, via: passive antibody transfer; CD4 analogues; attenuated virus; many types and combinations of recombinant HIV proteins; DNA vaccines; recombinant adenovirus and canarypox vaccines; and many multi-component vaccines using more than one of these approaches. Immunogenicity has also been shown in chimpanzees for vaccinia-based and peptide vaccines. Protection and/or significant therapeutic effects have not been demonstrated by any vaccine to date in humans. Vaccine responses in chimpanzees and humans are highly discordant. Claims of the importance of chimpanzees in AIDS vaccine development are without foundation, and a return to the use of chimpanzees in AIDS research/vaccine development is scientifically unjustifiable.

Safety and immunogenicity of a live recombinant canarypox virus expressing HIV type 1 gp120 MN MN tm/gag/protease LAI (ALVAC-HIV, vCP205) followed by a p24E-V3 MN synthetic peptide (CLTB-36) administered in healthy volunteers at low risk for HIV infection. AGIS Group and L'Agence Nationale de Recherches sur Le Sida

A live recombinant canarypox vector expressing HIV-1 gpl20 MN tm/gag/protease LAI (ALVAC-HIV, vCP205) alone or boosted by a p24E-V3 MN synthetic peptide (CLTB-36) was tested in healthy volunteers at low risk for HIV infection for their safety and immunogenicity. Both antigens were well tolerated. ALVAC-HIV (vCP205) induced low levels of neutralizing antibodies against HIV-1 MN in 33% of the volunteers. None of them had detectable neutralizing antibodies against a nonsyncytium-inducing HIV-1 clade B primary isolate (Bx08). After the fourth injection of vCP205, CTL activity was detected in 33% of the volunteers and was directed against Env, Gag, and Pol. This activity was mediated by both CD4+ and CD8+ lymphocytes. On the other hand, the CLTB-36 peptide was poorly immunogenic and induced no neutralizing antibodies or CTLs. Although the ALVAC-HIV (vCP205) and CLTB-36 prime-boost regimen was not optimal, further studies with ALVAC-HIV (vCP205) are warranted because of its clear induction of a cellular immune response and utility as a priming agent for other subunit antigens such as envelope glycoproteins, pseudoparticles, or new peptides.

Cytotoxic and proliferative T cell responses in HIV-1-infected Macaca nemestrina

Macaca nemestrina has been described as an animal model for acute HIV-1 infection. This animal, unlike most infected humans, appears to contain HIV-1 replication. Therefore analysis of HIV-1-specific proliferative and cytotoxic T lymphocyte (CTL) responses following HIV-1 challenge of M. nemestrina may provide information into the role of such responses in both the control of acute HIV infection and protective immunity. Although CD4+ T cell responses to HIV-1 are generally difficult to detect in HIV-1-infected humans, early and persistent CD4+ T cell proliferative responses to HIV-1 antigens were detected in all HIV-1-inoculated M. nemestrina. HIV-1-specific CD8+ CTL responses were evaluated in PBMC by stimulation with autologous cells expressing HIV-1 genes, limiting dilution precursor frequency analysis, and T cell cloning. CTL reactive with gag, env, and nef were present 4-8 wk after infection, and persisted to 140 wk after infection. The presence of both CD4+ and CD8+ T cell responses before and after clearance of HIV-1 viremia is consistent with a role for these responses in the successful control of HIV-1 viral replication observed in M. nemestrina. Further studies of T cell immunity in these animals that resist disease should provide insights into the immunobiology of HIV-1 infection.

Primary in vitro sensitization of human T-helper lymphocytes by peptides derived from the V3 loop of human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein

To generate CD4+ T-helper cell lines, lymphocytes from HIV-seronegative subjects were primed in vitro with peptides derived from the V3 loop of HIV-1 gp120. Antigen-specific reactivity was inhibited by an anti-DR monoclonal antibody, indicating HLA-class II dependency, but peptides could be recognized in different HLA-class II contexts. Three sites on V3LAI and two on V3MN were identified as targets of the respective V3LAI- and V3MN-specific lines. Recognition of V3 peptides was isolate-specific. The lines did not react against whole gp160, which suggests that V3 may be differently presented when used as such rather than as part of the entire glycoprotein. Similar results were obtained in chimpanzees immunized in vivo against V3LAI.

Expression and characterization of genetically engineered human immunodeficiency virus-like particles containing modified envelope glycoproteins: implications for development of a cross-protective AIDS vaccine

Noninfectious human immunodeficiency virus type 1 (HIV-1) viruslike particles containing chimeric envelope glycoproteins were expressed in mammalian cells by using inducible promoters. We engineered four expression vectors in which a synthetic oligomer encoding gp120 residues 306 to 328 (amino acids YNKRKRIHIGP GRAFYTTKNIIG) from the V3 loop of the MN viral isolate was inserted at various positions within the endogenous HIV-1LAI env gene. Expression studies revealed that insertion of the heterologous V3(MN) loop segment at two different locations within the conserved region 2 (C2) of gp120, either 173 or 242 residues away from the N terminus of the mature subunit, resulted in the secretion of fully assembled HIV-like particles containing chimeric LAI/MN envelope glycoproteins. Both V3 loop epitopes were recognized by loop-specific neutralizing antibodies. However, insertion of the V3(MN) loop segment into other regions of gp120 led to the production of envelope-deficient viruslike particles. Immunization with HIV-like particles containing chimeric envelope proteins induced specific antibody responses against both the autologous and heterologous V3 loop epitopes, including cross-neutralizing antibodies against the HIV-1LAI and HIV-1MN isolates. This study, therefore, demonstrates the feasibility of genetically engineering optimized HIV-like particles capable of eliciting cross-neutralizing antibodies.

Transient increases in numbers of infectious cells in an HIV-infected chimpanzee following immune stimulation

Efficient replication and production of human immunodeficiency virus (HIV) has been shown to be influenced greatly not only by the activation state of the infected cell but also by a variety of cytokines. Thus, it seems reasonable to assume, as has been hypothesized, that any stimulus to the immune system, whether by intercurrent infection, exposure to new or recall antigens, or injury with inflammation, could enhance HIV expression in infected individuals. To test this hypothesis, we subjected an HIV-1-infected chimpanzee to repeated specific and nonspecific immune stimulation by inoculation of various vaccine preparations, adjuvant alone, or HIV-specific immune globulin. Transient increases both in numbers of infectious peripheral blood cells and in some HIV-specific immune responses occurred within 1 to 2 weeks after most inoculations, including administration of the immune globulin. These results have important implications for the use of immunotherapy as a treatment for HIV-infected persons and for immunization of HIV-infected infants and children against other pathogens. They suggest that both immunotherapy and vaccination of HIV-infected individuals should be accompanied by administration of an antiviral drug(s).

Human immunodeficiency virus

A successful AIDS vaccine must elicit an immune state that will prevent the establishment of an HIV-1 persistent infection. This is a unique and difficult goal for a vaccine. Most vaccines elicit or prime for immune responses that prevent or attenuate the expression of clinical disease following infection with the pathogen. However, current evidence suggest that, following persistent infection with HIV-1, antiviral immune responses do not prevent the long-term progression to disease. Hence, it seems that the development of the persistent infection must be prevented. The ability of the immune response to accomplish this goal depends upon the efficiency with which the virus establishes persistence in the host. This is unknown for HIV-1. As a result, early efforts at vaccine development have focused on humoral immune responses directed against the virus particle in the attempt to prevent any infection of the host's cells. Studies with chimpanzees, as a model for HIV-1 infection, suggest that virus-neutralizing antibodies directed against the third hypervariable (V3) domain of the viral gp120 envelope glycoprotein may be particularly effective in preventing this infection. Studies also are in progress, both in chimpanzees and humans, to define the immunogenicity and effectiveness of various immunogens derived from the viral envelope and core structural proteins. Efforts that have concentrated on the gp120 V3 domain (or PND) have defined the extent of this region's variability and have established elements of generally conserved structure and sequence. The construction of these elements into practical and effective immunogens is an important goal. Finally, it is essential that basic studies be performed to determine if humoral or cellular immune responses directed against virus-infected cells would aid in preventing the establishment of an HIV-1 persistent infection. Such immune responses, if effective and in conjunction with specific virus-neutralizing antibody responses, would enhance the probability that an effective HIV-1 vaccine could be developed.

Immunization of chimpanzees with the HIV-1 glycoprotein gp160 induces long-lasting T-cell memory

The goal of the present study was to investigate the antigen-specific T-cell response to the recombinant HIV envelope glycoprotein (gp160) and to test the effect of various adjuvant formulations on the efficiency of T-cell priming as well as on magnitude and longevity of the gp160-specific T-cell response. Our studies revealed that, in combination with an appropriate adjuvant (lipid-based adjuvant or mineral carrier complex), immunization with recombinant gp160 led to the appearance of gp160-primed T cells. The T-cell response obtained was substantial (proliferative response of greater than 100,000 delta dpm after one primary and two booster immunizations), gp160-specific (proliferation only in response to gp160, no proliferation after addition of a mock gp160 preparation), and long-lasting (T cell responses of greater than 50,000 delta dpm were observed more than one year after the last booster). The results presented here differ from those of previous studies in that they show the presence of substantial and long-lasting T-cell memory toward the immunogen gp160. Therefore further investigations on the use of these preparations as HIV candidate vaccines appear to be justified.

Structural properties of HIV-1 Env fused with the 14-kDa vaccinia virus envelope protein

To gain insights into the structure-function relationship of the envelope (env) glycoprotein of the human immunodeficiency virus type 1 (HIV-1) we have generated a vaccinia virus (VV) recombinant (VV-14kENV) that expresses a fusion protein (14k-env) consisting of the VV 14-kDa envelope protein (110 amino acids) fused at the C-terminus with HIV-1 env protein (816 amino acids). The 14k-env protein displayed unique structural properties in virus-infected cells. This protein was recognized by 14 kDa-specific antisera as well as HIV-1 env antisera. It was not cleaved during virus infection of cultured cells of various origins, it was stable, it was not released to the medium, and it was not incorporated into virions. Instead of a predicted 174-kDa protein, two proteins of about 110 and 100 kDa were observed. The size reduction of the fusion protein was due to limited glycosylation (110 kDa) and formation of unglycosylated protein (100 kDa). The 14k-env protein formed oligomeric structures and was exposed on the cell surface after virus infection. When mice were inoculated with the recombinant virus that expresses the 14K-env fusion protein, humoral immune response against gp160 was observed. Our findings suggest that 14k-env protein might display novel immunogenic properties.

Strategy for developing a genetically-engineered whole-virus vaccine against HIV

The production of genetically-engineered, noninfectious virions of human immunodeficiency virus (HIV) represents a novel approach to the development of a safe and effective vaccine for the acquired immune deficiency syndromes (AIDS). Insofar as preparations of inactivated simian immunodeficiency virus (SIV) are now demonstrating protection in immunization-challenge studies in rhesus monkeys, a safe preparation of noninfectious HIV virions produced in a genetically-engineered cell line becomes a logical candidate vaccine for studies in humans. These particles, or pseudovirions, offer distinct advantages over the use of inactivated HIV for human AIDS vaccines. Guarantees of safety without the requirement for inactivation and their potential for structural modification for the modulation of immunogenicity are compelling reasons for the acceptance of HIV pseudovirions as a candidate vaccine in humans.

Immunization of chimpanzees confers protection against challenge with human immunodeficiency virus

Sustained high titers of neutralizing antibodies were elicited in three chimpanzees after sequential injections of different human immunodeficiency virus 1 (HIV-1) antigen preparations derived from the HIV-1 BRU strain that included whole inactivated virus or purified recombinant proteins and then synthetic peptides identical to the major HIV-1 neutralizing epitope V3. The animals were challenged i.v. with 40 chimpanzee infectious doses (equivalent to 100 tissue culture 50% infectious doses) of a stock of HIV-1 IIIB isolate. After 6 mo of follow-up, all three animals appeared uninfected by serologic and virologic criteria, including polymerase chain reaction analysis and failure to isolate virus from peripheral blood lymphocytes, bone marrow, and lymph node tissue. Of two chimpanzees monitored for 1 yr, virus was isolated initially from one animal at 32 weeks, but the second chimpanzee was virus negative by all assays through 12 mo; the third animal has remained virus negative through 9 mo of follow-up. These results indicate that it is possible to elicit protection against, or significantly delay infection of, HIV-1 by immunization, thus laying the foundation for development of an HIV-1 vaccine.

Production of immunogenic HIV-1 viruslike particles in stably engineered monkey cell lines

A proviral fragment from human immunodeficiency virus type 1 (HIV-1) (LAV-1BRU) containing only protein-coding information, was expressed in COS cells using constitutive promoters in transient and stable transfection experiments. The presence of viruslike particles in cell supernatants was verified by Western blot analysis, density gradient centrifugation, and electron microscopy. Transfection of Vero cells with a similar construct employing the human metallothionein promoter led to the isolation of stable cell lines exhibiting inducible viruslike particle expression in response to cadmium chloride treatment. Induction ratios for viruslike particle expression were in excess of 1000-fold with production levels of p24 core antigen as high as 0.6 mg/L per 24 h. HIV-1 viruslike particles were immunogenic in mice, leading to strong envelope and core-specific humoral responses after two immunizations. The development of stable cell lines expressing significant quantities of HIV-1 viruslike particles offers an alternative to the use of live virus vectors for the production and evaluation of particle-based AIDS vaccines.

In vitro characterization of a biologically active molecular clone of HIV-2NIH-Z containing a nef deletion and expressing a full-length transmembrane protein

We have previously described the cloning and sequencing of a novel stain of human immunodeficiency virus type 2 (HIV-2) called HIV-2NIH-Z. A plasmid clone, pHIV2Z, containing the full-length provirus has now been constructed, and virus particles have been obtained upon transfection into COS-1 and H-9 cells. These particles can infect a number of T-cell lines and exert a cytopathic effect on fresh human and macaque peripheral blood lymphocytes. The cloned virus is biologically and morphologically indistinguishable from its parental uncloned strain as shown by restriction enzyme analysis, electron microscopy, and kinetics of infection. However, as shown by radioimmunoprecipitation assays, the cloned virus-infected cells express a full-length gp41 protein as predicted by the nucleotide sequence, whereas the wild-type parental strain expresses a truncated gp33 protein. Both the parental strain and the cloned virus possess a deletion encompassing the end of the nef gene within the U3 region which apparently does not affect their in vitro cytopathic and replicative capacities.

Immunogenicity of the human immunodeficiency virus (HIV) recombinant nef gene product. Mapping of T-cell and B-cell epitopes in immunized chimpanzees

The nonstructural nef gene product of human immunodeficiency virus (HIV), p27, is a regulatory "early phase" protein produced by HIV-infected cells. As a possible negative regulator of transcription, it has been suggested that p27 may be involved in the control of HIV proviral latency. Immune reactivity to p27 may result in early destruction of HIV-replicating cells before viral assembly or of latently infected cells. It appeared, thus, of interest to investigate the immunogenicity of the molecule in chimpanzees immunized against HIV antigens. Two of the six chimpanzees that were injected with soluble recombinant p27 in association with other HIV proteins, displayed significant and sustained T-helper lymphocyte proliferative responses to p27 and to the other antigens. Using a set of synthetic peptides spanning the entire p27 sequence, two T-cell epitopes could be located: one within the last 20 amino-acids of the C terminus of the molecule, the other around the region of residues 118-122. Sera from the same animals also reacted to p27 in a radioimmunoassay as well as to some of the peptides in enzyme-linked immunosorbent assay. Sequential B-cell epitopes could thus be determined as being located in the regions of amino acids: 17-35, 52-66, and 185-205. The results obtained with peptides spanning the region between amino acid residues 65 and 172 indicate that at least two additional B-cell epitopes were present in the region comprised between amino acid 65 and 146. Interestingly, the extreme C terminus of the molecule encompasses both immunodominant T- and B-cell epitopes. Taken together, these observations should prove useful for the rational design of a HIV vaccine.

Response of monkeys to vaccination with recombinant vaccinia virus which coexpress HIV gp160 and human interleukin-2

Immunization of two macaque monkeys with recombinant vaccinia viruses encoding the env gene of HIV-1 (VV-gp160) resulted in demonstrable levels of gp160, gp120 and gp41-specific immunoglobulins in both animals. The virus used to immunize one of the monkeys additionally expressed the human IL-2 gene, which encoded human IL-2 (VV-gp160-IL-2). No toxic side-effects of vaccine-delivered IL-2 were observed. Despite marked attenuation of virulence by the coexpressed lymphokine, the levels of vector-specific antibodies in both animals were similar. Some differences in the HIV-specific reactivity patterns were detected. Serum reactivity of monkey #A56 (VV-gp160) was directed against gp41, whereas monkey #B58 (VV-gp160-IL-2) showed a wider range of recognition, with higher antibody titres against the HIV lysate preparation. Furthermore, this study demonstrates the capacity to boost antibody responses to the vector and coexpressed HIV antigens in primates which are already immune.