Efficacy of a SHIV 89.6 proviral DNA vaccine against mucosal SIVmac239 challenge

Innate protection against intrarectal SIV acquisition by a live SHIV vaccine

Identifying immune correlates of protection is a major challenge in AIDS vaccine development. Anti-Envelope antibodies have been considered critical for protection against SIV/HIV (SHIV) acquisition. Here, we evaluated the efficacy of an SHIV vaccine against SIVmac251 challenge, where the role of antibody was excluded, as there was no cross-reactivity between SIV and SHIV envelope antibodies. After 8 low-dose intrarectal challenges with SIVmac251, 12 SHIV-vaccinated animals demonstrated efficacy, compared with 6 naive controls, suggesting protection was achieved in the absence of anti-envelope antibodies. Interestingly, CD8+ T cells (and some NK cells) were not essential for preventing viral acquisition, as none of the CD8-depleted macaques were infected by SIVmac251 challenges. Initial investigation of protective innate immunity revealed that protected animals had elevated pathways related to platelet aggregation/activation and reduced pathways related to interferon and responses to virus. Moreover, higher expression of platelet factor 4 on circulating platelet-leukocyte aggregates was associated with reduced viral acquisition. Our data highlighted the importance of innate immunity, identified mechanisms, and may provide opportunities for novel HIV vaccines or therapeutic strategy development.

SIV infection of rhesus macaques of Chinese origin: a suitable model for HIV infection in humans

Simian immunodeficiency virus (SIV) infection of Indian-origin rhesus macaques (RM) has been widely used as a well-established nonhuman primate (NHP) model for HIV/AIDS research. However, there have been a growing number of studies using Chinese RM to evaluate immunopathogenesis of SIV infection. In this paper, we have for the first time reviewed and discussed the major publications related to SIV or SHIV infection of Chinese RM in the past decades. We have compared the differences in the pathogenesis of SIV infection between Chinese RM and Indian RM with regard to viral infection, immunological response, and host genetic background. Given AIDS is a disease that affects humans of diverse origins, it is of importance to study animals with different geographical background. Therefore, to examine and compare results obtained from RM models of Indian and Chinese origins should lead to further validation and improvement of these animal models for HIV/AIDS research.

Envelope determinants of equine lentiviral vaccine protection

Lentiviral envelope (Env) antigenic variation and associated immune evasion present major obstacles to vaccine development. The concept that Env is a critical determinant for vaccine efficacy is well accepted, however defined correlates of protection associated with Env variation have yet to be determined. We reported an attenuated equine infectious anemia virus (EIAV) vaccine study that directly examined the effect of lentiviral Env sequence variation on vaccine efficacy. The study identified a significant, inverse, linear correlation between vaccine efficacy and increasing divergence of the challenge virus Env gp90 protein compared to the vaccine virus gp90. The report demonstrated approximately 100% protection of immunized ponies from disease after challenge by virus with a homologous gp90 (EV0), and roughly 40% protection against challenge by virus (EV13) with a gp90 13% divergent from the vaccine strain. In the current study we examine whether the protection observed when challenging with the EV0 strain could be conferred to animals via chimeric challenge viruses between the EV0 and EV13 strains, allowing for mapping of protection to specific Env sequences. Viruses containing the EV13 proviral backbone and selected domains of the EV0 gp90 were constructed and in vitro and in vivo infectivity examined. Vaccine efficacy studies indicated that homology between the vaccine strain gp90 and the N-terminus of the challenge strain gp90 was capable of inducing immunity that resulted in significantly lower levels of post-challenge virus and significantly delayed the onset of disease. However, a homologous N-terminal region alone inserted in the EV13 backbone could not impart the 100% protection observed with the EV0 strain. Data presented here denote the complicated and potentially contradictory relationship between in vitro virulence and in vivo pathogenicity. The study highlights the importance of structural conformation for immunogens and emphasizes the need for antibody binding, not neutralizing, assays that correlate with vaccine protection.

Divergence, not diversity of an attenuated equine lentivirus vaccine strain correlates with protection from disease

We recently reported an attenuated EIAV vaccine study that directly examined the effect of lentiviral envelope sequence variation on vaccine efficacy. The study [1] demonstrated for the first time the failure of an ancestral vaccine to protect and revealed a significant, inverse, linear relationship between envelope divergence and protection from disease. In the current study we examine in detail the evolution of the attenuated vaccine strain utilized in this previous study. We demonstrate here that the attenuated strain progressively evolved during the six-month pre-challenge period and that the observed protection from disease was significantly associated with divergence from the original vaccine strain.

Amino acid mutations in the env gp90 protein that modify N-linked glycosylation of the Chinese EIAV vaccine strain enhance resistance to neutralizing antibodies

The Chinese EIAV vaccine is an attenuated live-virus vaccine obtained by serial passage of a virulent horse isolate (EIAV(L)) in donkeys (EIAV(D)), and subsequently in donkey cells in vitro. In this study, we compare the env gene of the original horse virulent virus (EIAV(L)) with attenuated strains serially passaged in donkey MDM (EIAV(DLV)), and donkey dermal cells (EIAV(FDDV)). Genetic comparisons among parental and attenuated strains found that vaccine strains contained amino acid substitutions/deletions in gp90 that resulted in a loss of three potential N-linked glycosylation sites, designated g5, g9, and g10. To investigate the biological significance of these changes, reverse-mutated viruses were constructed in the backbone of the EIAV(FDDV) infectious molecular clone (pLGFD3). The resulting virus stocks were characterized for replication efficiency in donkey dermal cells and donkey MDM, and were tested for sensitivity to neutralization using sera from two ponies experimentally infected with EIAV(FDDV). The results clearly show that these mutations generated by site-directed mutagenesis resulted in cloned viruses with enhanced resistance to serum-neutralizing antibodies that were also able to recognize parental viruses. The results of this study indicate that these mutations play an important role in the attenuation of the EIAV vaccine strains.

Limited dissemination of pathogenic SIV after vaginal challenge of rhesus monkeys immunized with a live, attenuated lentivirus

In non-human primate models of AIDS, attenuated lentiviruses provide the most reliable protection from challenge with pathogenic virus but the extent to which the vaccine virus replicates after challenge is unclear. At 7 and 14 days after vaginal challenge with pathogenic SIVmac239, plasma SIVenv RNA levels were significantly lower in female macaques immunized 6 months earlier with live, attenuated SHIV89.6 compared to unimmunized control animals. In 2 SHIV-immunized, unprotected macaques SIV replication produced moderate-level plasma viremia with dissemination of challenge virus to all tissues on day 14 after challenge. In protected, SHIV-immunized monkeys, SIV replication was controlled in all tissues, from the day of challenge through 14 days post-challenge. Further, in CD8(+) T cell-depleted SHIV-immunized animals, SIV replication and dissemination were more rapid than in control animals. These findings suggest that replication of a pathogenic AIDS virus can be controlled at the site of mucosal inoculation by live-attenuated lentivirus immunization.

The aftermath of the Merck's HIV vaccine trial

The recently released results of the Merck's Phase IIb "test-of concept" vaccine trials have shown no protection from HIV-1 infection in the vaccinated group compared with a control group vaccinated with placebo. The study was designed to test the Merck's MRKAd5 trivalent candidate vaccine. The vaccine formulation was expected to stimulate a HIV-specific T cell immune response and to either prevent infection, or to reduce the levels of the viral load in vaccinated subjects. Upon the first evaluation of the interim data, the independent Data and Safety Monitoring Board (DSMB) underscored no protection from HIV-1 infection in the vaccine-inoculated volunteers compared with the control group; accordingly, the vaccine trial was stopped. This disappointing outcome warrants a critical analysis of the current vaccine studies and calls for a renewed effort toward a rational design of novel immunogens to be tested in large primate trials.

Protection of macaques against vaginal SHIV challenge by systemic or mucosal and systemic vaccinations with HIV-envelope

BACKGROUND

Worldwide, the majority of human immunodeficiency virus (HIV) infections occur by heterosexual transmission. Thus, the development of a vaccine that can prevent intravaginal HIV infection is an important goal of AIDS vaccine research.

OBJECTIVES

To determine which single or combination of systemic and mucosal routes of immunizations of female rhesus macaques with an HIV-1 SF162 envelope protein vaccine induced protection against intravaginal challenge with SHIV.

DESIGN

Female rhesus macaques were immunized with an HIV-1 SF162 envelope protein vaccine administered systemically (intramuscularly), or mucosally (intranasally), or as a sequential combination of both routes. The macaques were then challenged intravaginally with SHIV SF162P4, expressing an envelope that is closely matched (homologous) to the vaccine.

RESULTS

Macaques receiving intramuscular immunizations, alone or in combination with intranasal immunizations, were protected from infection, with no detectable plasma viral RNA, provirus, or seroconversion to nonvaccine viral proteins, and better preservation of intestinal CD4+ T cells. Serum neutralizing antibodies against the challenge virus appeared to correlate with protection.

CONCLUSIONS

The results of this study demonstrate that, in the nonhuman primate model, it is possible for vaccine-elicited immune responses to prevent infection after intravaginal administration of virus.

Phase I study of a candidate vaccine based on recombinant HIV-1 gp160 (MN/LAI) administered by the mucosal route to HIV-seronegative volunteers: the ANRS VAC14 study

One goal of HIV vaccination is to achieve high mucosal levels of specific secretory IgA (SIgA). In order to elicit specific SIgA antibodies against human immunodeficiency virus type-1 (HIV-1), a vaccine must be administered by the mucosal route, to the nasal or vaginal mucosa for example. We report here the results of the first phase I, randomized, open-label trial designed to assess the mucosal tolerability and immunogenicity of a candidate vaccine (recombinant protein HIV-1 gp160MN/LAI with or without DC-Chol adjuvant) administered by the nasal or vaginal route. Thirty-four female volunteers with a mean age of 46 years were vaccinated. There were 465 adverse events, of which 65 were considered related to the vaccine. No severe adverse events were related to the vaccine, and no difference in terms of tolerability was observed between the sites of vaccination or between the vaccine formulations. None of the volunteers reported that study participation affected their intimate or broader social relationships. No anti-gp160 activity was found between week 4 and week 48 in serum, saliva, or cervicovaginal and nasal secretions. These results show that a mucosal HIV vaccine can be well tolerated when administered by the nasal or vaginal route.

Depo-Provera abrogates attenuated lentivirus-induced protection in male rhesus macaques challenged intravenously with pathogenic SIVmac239

BACKGROUND

Progesterone administration prior to intravaginal challenge with pathogenic SIVmac239 decreases the protective efficacy of live attenuated vaccines in rhesus macaques.

METHODS

To determine if progesterone alters the efficacy of live attenuated vaccines through local or systemic effects, seven male rhesus macaques were immunized with SHIV89.6 and then challenged intravenously with SIVmac239. Three of these animals were treated with Depo-Provera 30 days prior to the SIV challenge.

RESULTS

The SHIV animals had significantly lower plasma viral RNA levels than the unimmunized control monkeys, but the Depo-Provera treated, SHIV-immunized animals did not. Despite the lack of protection, the Depo-Provera SHIV animals had strong SIV specific T-cell responses. However, altered patterns of NK frequency and CD38 T-cell expression prior to SIV challenge were observed in Depo-Provera SHIV animals.

CONCLUSIONS

Depo-Provera eliminates live-attenuated lentivirus vaccine efficacy in male rhesus monkeys through systemic effects on antiviral immunity and/or viral replication.

Envelope variation as a primary determinant of lentiviral vaccine efficacy

Lentiviral envelope antigenic variation and associated immune evasion are believed to present major obstacles to effective vaccine development. Although this perception is widely assumed by the scientific community, there is, to date, no rigorous experimental data assessing the effect of increasing levels of lentiviral Env variation on vaccine efficacy. It is our working hypothesis that Env is, in fact, a primary determinant of vaccine effectiveness. We previously reported that a successful experimental attenuated equine infectious anemia virus vaccine, derived by mutation of the viral S2 accessory gene, provided 100% protection from disease after virulent virus challenge. Here, we sought to comprehensively test our hypothesis by challenging vaccinated animals with proviral strains of defined, increasing Env variation, using variant envelope SU genes that arose naturally during experimental infection of ponies with equine infectious anemia virus. The reference attenuated vaccine combined with these variant Env challenge strains facilitated evaluation of the protection conferred by ancestral immunogens, because the Env of the attenuated vaccine is a direct ancestor to the variant proviral strain Envs. The results demonstrated that ancestral Env proteins did not impart broad levels of protection against challenge. Furthermore, the results displayed a significant inverse linear correlation of Env divergence and protection from disease. This study demonstrates potential obstacles to the use of single isolate ancestral Env immunogens. Finally, these findings reveal that relatively minor Env variation can pose a substantial challenge to lentiviral vaccine immunity, even when attenuated vaccines are used that, to date, achieve the highest levels of vaccine protection.

Virus-like particles: designing an effective AIDS vaccine

Viruses that infect eukaryotic organisms have the unique characteristic of self-assembling into particles. The mammalian immune system is highly attuned to recognizing and attacking these viral particles following infection. The use of particle-based immunogens, often delivered as live-attenuated viruses, has been an effective vaccination strategy for a variety of viruses. The development of an effective vaccine against the human immunodeficiency virus (HIV) has proven to be a challenge, since HIV infects cells of the immune system causing severe immunodeficiency resulting in the syndrome known as AIDS. In addition, the ability of the virus to adapt to immune pressure and reside in an integrated form in host cells presents hurdles for vaccinologists to overcome. A particle-based vaccine strategy has promise for eliciting high titer, long-lived, immune responses to a diverse number of viral epitopes against different HIV antigens. Live-attenuated viruses are effective at generating both cellular and humoral immune responses. However, while these vaccines stimulate immunity, challenged animals rarely clear the viral infection and the degree of attenuation directly correlates with protection from disease. Further, a live-attenuated vaccine has the potential to revert to a pathogenic form. Alternatively, virus-like particles (VLPs) mimic the viral particle without causing an immunodeficiency disease. VLPs are self-assembling, non-replicating, non-pathogenic particles that are similar in size and conformation to intact virions. A variety of VLPs for lentiviruses are currently in preclinical and clinical trials. This review focuses on our current status of VLP-based AIDS vaccines, regarding issues of purification and immune design for animal and clinical trials.

Immune mechanisms associated with protection from vaginal SIV challenge in rhesus monkeys infected with virulence-attenuated SHIV 89.6

Although live-attenuated human immunodeficiency virus-1 (HIV) vaccines may never be used clinically, these vaccines have provided the most durable protection from intravenous (IV) challenge in the simian immunodeficiency virus (SIV)/rhesus macaque model. Systemic infection with virulence attenuated-simian-human immunodeficiency virus (SHIV) 89.6 provides protection against vaginal SIV challenge. This paper reviews the findings related to the innate and adaptive immune responses and the role of inflammation associated with protection in the SHIV 89.6/SIVmac239 model. By an as yet undefined mechanism, most monkeys vaccinated with live-attenuated SHIV 89.6 mounted effective anti-viral CD8+ T cell responses while avoiding the self-destructive inflammatory cycle found in the lymphoid tissues of unprotected and unvaccinated monkeys.