Vaccine-induced CD8+ T cells control AIDS virus replication.

Developing a vaccine for human immunodeficiency virus (HIV) may be aided by a complete understanding of those rare cases in which some HIV-infected individuals control replication of the virus. Most of these elite controllers express the histocompatibility alleles HLA-B*57 or HLA-B*27 (ref. 3). These alleles remain by far the most robust associations with low concentrations of plasma virus, yet the mechanism of control in these individuals is not entirely clear. Here we vaccinate Indian rhesus macaques that express Mamu-B*08, an animal model for HLA-B*27-mediated elite control, with three Mamu-B*08-restricted CD8(+) T-cell epitopes, and demonstrate that these vaccinated animals control replication of the highly pathogenic clonal simian immunodeficiency virus (SIV) mac239 virus. High frequencies of CD8(+) T cells against these Vif and Nef epitopes in the blood, lymph nodes and colon were associated with viral control. Moreover, the frequency of the CD8(+) T-cell response against the Nef RL10 epitope (Nef amino acids 137-146) correlated significantly with reduced acute phase viraemia. Finally, two of the eight vaccinees lost control of viral replication in the chronic phase, concomitant with escape in all three targeted epitopes, further implicating these three CD8(+) T-cell responses in the control of viral replication. Our findings indicate that narrowly targeted vaccine-induced virus-specific CD8(+) T-cell responses can control replication of the AIDS virus.

Vaccination with Gag, Vif, and Nef gene fragments affords partial control of viral replication after mucosal challenge with SIVmac239.

UNLABELLED: Broadly targeted cellular immune responses are thought to be important for controlling replication of human and simian immunodeficiency viruses (HIV and SIV). However, eliciting such responses by vaccination is complicated by immunodominance, the preferential targeting of only a few of the many possible epitopes of a given antigen. This phenomenon may be due to the coexpression of dominant and subdominant epitopes by the same antigen-presenting cell and may be overcome by distributing these sequences among several different vaccine constructs. Accordingly, we tested whether vaccinating rhesus macaques with "minigenes" encoding fragments of Gag, Vif, and Nef resulted in broadened cellular responses capable of controlling SIV replication. We delivered these minigenes through combinations of recombinant Mycobacterium bovis BCG (rBCG), electroporated recombinant DNA (rDNA) along with an interleukin-12 (IL-12)-expressing plasmid (EP rDNA plus pIL-12), yellow fever vaccine virus 17D (rYF17D), and recombinant adenovirus serotype 5 (rAd5). Although priming with EP rDNA plus pIL-12 increased the breadth of vaccine-induced T-cell responses, this effect was likely due to the improved antigen delivery afforded by electroporation rather than modulation of immunodominance. Indeed, Mamu-A*01(+) vaccinees mounted CD8(+) T cells directed against only one subdominant epitope, regardless of the vaccination regimen. After challenge with SIVmac239, vaccine efficacy was limited to a modest reduction in set point in some of the groups and did not correlate with standard T-cell measurements. These findings suggest that broad T-cell responses elicited by conventional vectors may not be sufficient to substantially contain AIDS virus replication. IMPORTANCE: Immunodominance poses a major obstacle to the generation of broadly targeted, HIV-specific cellular responses by vaccination. Here we attempted to circumvent this phenomenon and thereby broaden the repertoire of SIV-specific cellular responses by vaccinating rhesus macaques with minigenes encoding fragments of Gag, Vif, and Nef. In contrast to previous mouse studies, this strategy appeared to minimally affect monkey CD8(+) T-cell immundominance hierarchies, as seen by the detection of only one subdominant epitope in Mamu-A*01(+) vaccinees. This finding underscores the difficulty of inducing subdominant CD8(+) T cells by vaccination and demonstrates that strategies other than gene fragmentation may be required to significantly alter immunodominance in primates. Although some of the regimens tested here were extremely immunogenic, vaccine efficacy was limited to a modest reduction in set point viremia after challenge with SIVmac239. No correlates of protection were identified. These results reinforce the notion that vaccine immunogenicity does not predict control of AIDS virus replication.

A strategy for high antibody expression with low anti-drug antibodies using AAV9 vectors.

Introduction: Use of adeno-associated virus (AAV) vectors is complicated by host immune responses that can limit transgene expression. Recent clinical trials using AAV vectors to deliver HIV broadly neutralizing antibodies (bNAbs) by intramuscular administration resulted in poor expression with anti-drug antibodies (ADA) responses against the bNAb. Methods: Here we compared the expression of, and ADA responses against, an anti-SIV antibody ITS01 when delivered by five different AAV capsids. We first evaluated ITS01 expression from AAV vectors three different 2A peptides. Rhesus macaques were selected for the study based on preexisiting neutralizing antibodies by evaluating serum samples in a neutralization assay against the five capsids used in the study. Macaques were intramuscularly administered AAV vectors at a 2.5x10^12 vg/kg over eight administration sites. ITS01 concentrations and anti-drug antibodies (ADA) were measured by ELISA and a neutralization assay was conducted to confirm ex vivo antibody potency. Results: We observed that ITS01 expressed three-fold more efficiently in mice from AAV vectors in which heavy and light-chain genes were separated by a P2A ribosomal skipping peptide, compared with those bearing F2A or T2A peptides. We then measured the preexisting neutralizing antibody responses against three traditional AAV capsids in 360 rhesus macaques and observed that 8%, 16%, and 42% were seronegative for AAV1, AAV8, and AAV9, respectively. Finally, we compared ITS01 expression in seronegative macaques intramuscularly transduced with AAV1, AAV8, or AAV9, or with the synthetic capsids AAV-NP22 or AAV-KP1. We observed at 30 weeks after administration that AAV9- and AAV1-delivered vectors expressed the highest concentrations of ITS01 (224 µg/mL, n=5, and 216 µg/mL, n=3, respectively). The remaining groups expressed an average of 35-73 µg/mL. Notably, ADA responses against ITS01 were observed in six of the 19 animals. Lastly, we demonstrated that the expressed ITS01 retained its neutralizing activity with nearly the same potency of purified recombinant protein. Discussion: Overall, these data suggest that the AAV9 capsid is a suitable choice for intramuscular expression of antibodies in nonhuman primates.

Dengue virus-specific CD4+ and CD8+ T lymphocytes target NS1, NS3 and NS5 in infected Indian rhesus macaques.

Every year, Dengue virus (DENV) infects approximately 100 million people. There are currently several vaccines undergoing clinical studies, but most target the induction of neutralizing antibodies. Unfortunately, DENV infection can be enhanced by subneutralizing levels of antibodies that bind virions and deliver them to cells of the myeloid lineage, thereby increasing viral replication (termed antibody-dependent enhancement [ADE]). T lymphocyte-based vaccines may offer an alternative that avoids ADE. The goal of our study was to describe the cellular immune response generated after primary DENV infection in Indian rhesus macaques. We infected eight rhesus macaques with 105 plaque-forming units (PFU) of DENV serotype 2 (DENV2) New Guinea C (NGC) strain, and monitored viral load and the cellular immune response to the virus. Viral replication peaked at day 4 post-infection and was resolved by day 10. DENV-specific CD4+ and CD8+ T lymphocytes targeted nonstructural (NS) 1, NS3 and NS5 proteins after resolution of peak viremia. DENV-specific CD4+ cells expressed interferon-gamma (IFN-γ) along with tumor necrosis factor-alpha (TNF-α), interleukin-2 (IL-2), and macrophage inflammatory protein-1 beta (MIP-1ß). In comparison, DENV-specific CD8+ cells expressed IFN-γ in addition to MIP-1ß and TNF-α and were positive for the degranulation marker CD107a. Interestingly, a fraction of the DENV-specific CD4+ cells also stained for CD107a, suggesting that they might be cytotoxic. Our results provide a more complete understanding of the cellular immune response during DENV infection in rhesus macaques and contribute to the development of rhesus macaques as an animal model for DENV vaccine and pathogenicity studies.

The role of MHC class I allele Mamu-A*07 during SIV(mac)239 infection.

Virus-specific CD8(+) T cells play an important role in controlling HIV/SIV replication. These T cells recognize intracellular pathogen-derived peptides displayed on the cell surface by individual MHC class I molecules. In the SIV-infected rhesus macaque model, five Mamu class I alleles have been thoroughly characterized with regard to peptide binding, and a sixth was shown to be uninvolved. In this study, we describe the peptide binding of Mamu-A1*007:01 (formerly Mamu-A*07), an allele present in roughly 5.08% of Indian-origin rhesus macaques (n = 63 of 1,240). We determined a preliminary binding motif by eluting and sequencing endogenously bound ligands. Subsequently, we used a positional scanning combinatorial library and panels of single amino acid substitution analogs to further characterize peptide binding of this allele and derive a quantitative motif. Using this motif, we selected and tested 200 peptides derived from SIV(mac)239 for their capacity to bind Mamu-A1*007:01; 33 were found to bind with an affinity of 500 nM or better. We then used PBMC from SIV-infected or vaccinated but uninfected, A1*007:01-positive rhesus macaques in IFN-γ Elispot assays to screen the peptides for T-cell reactivity. In all, 11 of the peptides elicited IFN-γ(+) T-cell responses. Six represent novel A1*007:01-restricted epitopes. Furthermore, both Sanger and ultradeep pyrosequencing demonstrated the accumulation of amino acid substitutions within four of these six regions, suggestive of selective pressure on the virus by antigen-specific CD8(+) T cells. Thus, it appears that Mamu-A1*007:01 presents SIV-derived peptides to antigen-specific CD8(+) T cells and is part of the immune response to SIV(mac)239.

High viremia is associated with high levels of in vivo major histocompatibility complex class I Downregulation in rhesus macaques infected with simian immunodeficiency virus SIVmac239.

Human and simian immunodeficiency viruses (HIV and SIV) downregulate major histocompatibility complex class I (MHC-I) molecules from the surface of infected cells. Although this activity is conserved across viral isolates, its importance in AIDS pathogenesis is not clear. We therefore developed an assay to detect the level of MHC-I expression of SIV-infected cells directly ex vivo. Here we show that the extent of MHC-I downregulation is greatest in SIVmac239-infected macaques that never effectively control virus replication. Our results suggest that a high level of MHC-I downregulation is a hallmark of fast disease progression in SIV infection.

Patterns of CD8+ immunodominance may influence the ability of Mamu-B*08-positive macaques to naturally control simian immunodeficiency virus SIVmac239 replication.

Certain major histocompatibility complex (MHC) class I alleles are strongly associated with control of human immunodeficiency virus and simian immunodeficiency virus (SIV). CD8(+) T cells specific for epitopes restricted by these molecules may be particularly effective. Understanding how CD8(+) T cells contribute to control of viral replication should yield important insights for vaccine design. We have recently identified an Indian rhesus macaque MHC class I allele, Mamu-B*08, associated with elite control and low plasma viremia after infection with the pathogenic isolate SIVmac239. Here, we infected four Mamu-B*08-positive macaques with SIVmac239 to investigate why some of these macaques control viral replication. Three of the four macaques controlled SIVmac239 replication with plasma virus concentrations below 20,000 viral RNA copies/ml at 20 weeks postinfection; two of four macaques were elite controllers (ECs). Interestingly, two of the four macaques preserved their CD4(+) memory T lymphocytes during peak viremia, and all four recovered their CD4(+) memory T lymphocytes in the chronic phase of infection. Mamu-B*08-restricted CD8(+) T-cell responses dominated the acute phase and accounted for 23.3% to 59.6% of the total SIV-specific immune responses. Additionally, the ECs mounted strong and broad CD8(+) T-cell responses against several epitopes in Vif and Nef. Mamu-B*08-specific CD8(+) T cells accounted for the majority of mutations in the virus at 18 weeks postinfection. Interestingly, patterns of viral variation in Nef differed between the ECs and the other two macaques. Natural containment of AIDS virus replication in Mamu-B*08-positive macaques may, therefore, be related to a combination of immunodominance and viral escape from CD8(+) T-cell responses.

The major histocompatibility complex class II alleles Mamu-DRB1*1003 and -DRB1*0306 are enriched in a cohort of simian immunodeficiency virus-infected rhesus macaque elite controllers.

The role of CD4(+) T cells in the control of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) replication is not well understood. Even though strong HIV- and SIV-specific CD4(+) T-cell responses have been detected in individuals that control viral replication, major histocompatibility complex class II (MHC-II) molecules have not been definitively linked with slow disease progression. In a cohort of 196 SIVmac239-infected Indian rhesus macaques, a group of macaques controlled viral replication to less than 1,000 viral RNA copies/ml. These elite controllers (ECs) mounted a broad SIV-specific CD4(+) T-cell response. Here, we describe five macaque MHC-II alleles (Mamu-DRB*w606, -DRB*w2104, -DRB1*0306, -DRB1*1003, and -DPB1*06) that restricted six SIV-specific CD4(+) T-cell epitopes in ECs and report the first association between specific MHC-II alleles and elite control. Interestingly, the macaque MHC-II alleles, Mamu-DRB1*1003 and -DRB1*0306, were enriched in this EC group (P values of 0.02 and 0.05, respectively). Additionally, Mamu-B*17-positive SIV-infected rhesus macaques that also expressed these two MHC-II alleles had significantly lower viral loads than Mamu-B*17-positive animals that did not express Mamu-DRB1*1003 and -DRB1*0306 (P value of <0.0001). The study of MHC-II alleles in macaques that control viral replication could improve our understanding of the role of CD4(+) T cells in suppressing HIV/SIV replication and further our understanding of HIV vaccine design.

Immunogenicity of seven new recombinant yellow fever viruses 17D expressing fragments of SIVmac239 Gag, Nef, and Vif in Indian rhesus macaques.

An effective vaccine remains the best solution to stop the spread of human immunodeficiency virus (HIV). Cellular immune responses have been repeatedly associated with control of viral replication and thus may be an important element of the immune response that must be evoked by an efficacious vaccine. Recombinant viral vectors can induce potent T-cell responses. Although several viral vectors have been developed to deliver HIV genes, only a few have been advanced for clinical trials. The live-attenuated yellow fever vaccine virus 17D (YF17D) has many properties that make it an attractive vector for AIDS vaccine regimens. YF17D is well tolerated in humans and vaccination induces robust T-cell responses that persist for years. Additionally, methods to manipulate the YF17D genome have been established, enabling the generation of recombinant (r)YF17D vectors carrying genes from unrelated pathogens. Here, we report the generation of seven new rYF17D viruses expressing fragments of simian immunodeficiency virus (SIV)mac239 Gag, Nef, and Vif. Studies in Indian rhesus macaques demonstrated that these live-attenuated vectors replicated in vivo, but only elicited low levels of SIV-specific cellular responses. Boosting with recombinant Adenovirus type-5 (rAd5) vectors resulted in robust expansion of SIV-specific CD8(+) T-cell responses, particularly those targeting Vif. Priming with rYF17D also increased the frequency of CD4(+) cellular responses in rYF17D/rAd5-immunized macaques compared to animals that received rAd5 only. The effect of the rYF17D prime on the breadth of SIV-specific T-cell responses was limited and we also found evidence that some rYF17D vectors were more effective than others at priming SIV-specific T-cell responses. Together, our data suggest that YF17D - a clinically relevant vaccine vector - can be used to prime AIDS virus-specific T-cell responses in heterologous prime boost regimens. However, it will be important to optimize rYF17D-based vaccine regimens to ensure maximum delivery of all immunogens in a multivalent vaccine.

Macaques vaccinated with live-attenuated SIV control replication of heterologous virus.

An effective AIDS vaccine will need to protect against globally diverse isolates of HIV. To address this issue in macaques, we administered a live-attenuated simian immunodeficiency virus (SIV) vaccine and challenged with a highly pathogenic heterologous isolate. Vaccinees reduced viral replication by approximately 2 logs between weeks 2-32 (P < or = 0.049) postchallenge. Remarkably, vaccinees expressing MHC-I (MHC class I) alleles previously associated with viral control completely suppressed acute phase replication of the challenge virus, implicating CD8(+) T cells in this control. Furthermore, transient depletion of peripheral CD8(+) lymphocytes in four vaccinees during the chronic phase resulted in an increase in virus replication. In two of these animals, the recrudescent virus population contained only the vaccine strain and not the challenge virus. Alarmingly, however, we found evidence of recombinant viruses emerging in some of the vaccinated animals. This finding argues strongly against an attenuated virus vaccine as a solution to the AIDS epidemic. On a more positive note, our results suggest that MHC-I-restricted CD8(+) T cells contribute to the protection induced by the live-attenuated SIV vaccine and demonstrate that vaccine-induced CD8(+) T cell responses can control replication of heterologous challenge viruses.

Subdominant CD8+ T-cell responses are involved in durable control of AIDS virus replication.

"Elite controllers" are individuals that durably control human immunodeficiency virus or simian immunodeficiency virus replication without therapeutic intervention. The study of these rare individuals may facilitate the definition of a successful immune response to immunodeficiency viruses. Here we describe six Indian-origin rhesus macaques that have controlled replication of the pathogenic virus SIVmac239 for 1 to 5 years. To determine which lymphocyte populations were responsible for this control, we transiently depleted the animals' CD8+ cells in vivo. This treatment resulted in 100- to 10,000-fold increases in viremia. When the CD8+ cells returned, control was reestablished and the levels of small subsets of previously subdominant CD8+ T cells expanded up to 2,500-fold above pre-depletion levels. This wave of CD8+ T cells was accompanied by robust Gag-specific CD4 responses. In contrast, CD8+ NK cell frequencies changed no more than threefold. Together, our data suggest that CD8+ T cells targeting a small number of epitopes, along with broad CD4+ T-cell responses, can successfully control the replication of the AIDS virus. It is likely that subdominant CD8+ T-cell populations play a key role in maintaining this control.