Inhibition of simian immunodeficiency virus (SIV) replication by CD8(+) T lymphocytes from macaques immunized with live attenuated SIV

CD8β Depletion Does Not Prevent Control of Viral Replication or Protection from Challenge in Macaques Chronically Infected with a Live Attenuated Simian Immunodeficiency Virus

We evaluated the contribution of CD8αβ+ T cells to control of live-attenuated simian immunodeficiency virus (LASIV) replication during chronic infection and subsequent protection from pathogenic SIV challenge. Unlike previous reports with a CD8α-specific depleting monoclonal antibody (mAb), the CD8β-specific mAb CD8β255R1 selectively depleted CD8αβ+ T cells without also depleting non-CD8+ T cell populations that express CD8α, such as natural killer (NK) cells and γδ T cells. Following infusion with CD8β255R1, plasma viremia transiently increased coincident with declining peripheral CD8αβ+ T cells. Interestingly, plasma viremia returned to predepletion levels even when peripheral CD8αβ+ T cells did not. Although depletion of CD8αβ+ T cells in the lymph node (LN) was incomplete, frequencies of these cells were 3-fold lower (P = 0.006) in animals that received CD8β255R1 than in those that received control IgG. It is possible that these residual SIV-specific CD8αβ+ T cells may have contributed to suppression of viremia during chronic infection. We also determined whether infusion of CD8β255R1 in the LASIV-vaccinated animals increased their susceptibility to infection following intravenous challenge with pathogenic SIVmac239. We found that 7/8 animals infused with CD8β255R1, and 3/4 animals infused with the control IgG, were resistant to SIVmac239 infection. These results suggest that infusion with CD8β255R1 did not eliminate the protection afforded to LASIV vaccination. This provides a comprehensive description of the impact of CD8β255R1 infusion on the immunological composition in cynomolgus macaques, compared to an isotype-matched control IgG, while showing that the control of LASIV viremia and protection from challenge can occur even after CD8β255R1 administration.IMPORTANCE Studies of SIV-infected macaques that deplete CD8+ T cells in vivo with monoclonal antibodies have provided compelling evidence for their direct antiviral role. These studies utilized CD8α-specific mAbs that target both the major (CD8αβ+) and minor (CD8αα+) populations of CD8+ T cells but additionally deplete non-CD8+ T cell populations that express CD8α, such as NK cells and γδ T cells. In the current study, we administered the CD8β-specific depleting mAb CD8β255R1 to cynomolgus macaques chronically infected with a LASIV to selectively deplete CD8αβ+ T cells without removing CD8αα+ lymphocytes. We evaluated the impact on control of virus replication and protection from pathogenic SIVmac239 challenge. These results underscore the utility of CD8β255R1 for studying the direct contribution of CD8αβ+ T cells in various disease states.

CD8+ Cytotoxic-T-Lymphocyte Breadth Could Facilitate Early Immune Detection of Immunodeficiency Virus-Derived Epitopes with Limited Expression Levels

Cytotoxic-T-lymphocyte (CTL) responses are important to control the replication of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV). Accumulating evidence suggests that the ability of a few immunodominant T-cell populations to detect and kill HIV/SIV-infected cells is important in individuals with a protective major histocompatibility complex class I (MHC-I) allele.

Cytotoxic-T-lymphocyte (CTL) responses are important to control the replication of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV). Accumulating evidence suggests that the ability of a few immunodominant T-cell populations to detect and kill HIV/SIV-infected cells is important in individuals with a protective major histocompatibility complex class I (MHC-I) allele. On the other hand, immunization with live(-attenuated) viruses may be effective against superinfection of virulent viral strains regardless of the host’s MHC-I haplotypes, although the underlying mechanisms have not been fully documented. In this article, we propose a hypothesis that the early detection of infected cells in superinfected individuals may be partly facilitated by recognition of diverse CTL epitopes with limited expression levels. We further explain the hypothesis using simple mathematics that was written based on previous in vitro viral suppression assay results and by considering the physical contact of infected cells with CTLs.

ALT-803 Transiently Reduces Simian Immunodeficiency Virus Replication in the Absence of Antiretroviral Treatment

Developing biological interventions to control human immunodeficiency virus (HIV) replication in the absence of antiretroviral therapy (ART) could contribute to the development of a functional cure. As a potential alternative to ART, the interleukin-15 (IL-15) superagonist ALT-803 has been shown to boost the number and function of HIV-specific CD8⁺ T and NK cell populations in vitro Four simian immunodeficiency virus (SIV)-positive rhesus macaques, three of whom possessed major histocompatibility complex alleles associated with control of SIV and all of whom had received SIV vaccine vectors that had the potential to elicit CD8⁺ T cell responses, were given ALT-803 in three treatment cycles. The first and second cycles of treatment were separated by 2 weeks, while the third cycle was administered after a 29-week break. ALT-803 transiently elevated the total CD8⁺ effector and central memory T cell and NK cell populations in peripheral blood, while viral loads transiently decreased by ∼2 logs in all animals. Virus suppression was not sustained as T cells became less responsive to ALT-803 and waned in numbers. No effect on viral loads was observed in the second cycle of ALT-803, concurrent with downregulation of the IL-2/15 common γC and β chain receptors on both CD8⁺ T cells and NK cells. Furthermore, populations of immunosuppressive T cells increased during the second cycle of ALT-803 treatment. During the third treatment cycle, responsiveness to ALT-803 was restored. CD8⁺ T cells and NK cells increased again 3- to 5-fold, and viral loads transiently decreased again by 1 to 2 logs.IMPORTANCE Overall, our data show that ALT-803 has the potential to be used as an immunomodulatory agent to elicit effective immune control of HIV/SIV replication. We identify mechanisms to explain why virus control is transient, so that this model can be used to define a clinically appropriate treatment regimen.

Cloning, sequencing, and polymorphism analysis of novel classical MHC class I alleles in northern pig-tailed macaques (Macaca leonina)

The northern pig-tailed macaque (Macaca leonina) has been confirmed to be an independent species from the pig-tailed macaque group of Old World monkey. We have previously reported that the northern pig-tailed macaques were also susceptible to HIV-1. Here, to make this animal a potential HIV/AIDS model and to discover the mechanism of virus control, we attempted to assess the role of major histocompatibility complex (MHC) class I-restricted immune responses to HIV-1 infection, which was associated with viral replication and disease progression. As an initial step, we first cloned and characterized the classical MHC class I gene of northern pig-tailed macaques. In this study, we identified 39 MHC class I alleles including 17 MHC-A and 22 MHC-B alleles. Out of these identified alleles, 30 were novel and 9 were identical to alleles previously reported from other macaque species. The MHC-A and MHC-B loci were both duplicates as rhesus macaques and southern pig-tailed macaques. In addition, we also detected the patterns of positive selection in northern pig-tailed macaques and revealed the existence of balance selection with 20 positive selection sites in the peptide binding region. The analysis of B and F peptide binding pockets in northern and southern pig-tailed macaques and rhesus macaques suggested that they were likely to share a few common peptides to present. Thus, this study provides important MHC immunogenetics information and adds values to northern pig-tailed macaques as a promising HIV/AIDS model.

CD8 T cell response maturation defined by anentropic specificity and repertoire depth correlates with SIVΔnef-induced protection

The live attenuated simian immunodeficiency virus (LASIV) vaccine SIVΔnef is one of the most effective vaccines in inducing protection against wild-type lentiviral challenge, yet little is known about the mechanisms underlying its remarkable protective efficacy. Here, we exploit deep sequencing technology and comprehensive CD8 T cell epitope mapping to deconstruct the CD8 T cell response, to identify the regions of immune pressure and viral escape, and to delineate the effect of epitope escape on the evolution of the CD8 T cell response in SIVΔnef-vaccinated animals. We demonstrate that the initial CD8 T cell response in the acute phase of SIVΔnef infection is mounted predominantly against more variable epitopes, followed by widespread sequence evolution and viral escape. Furthermore, we show that epitope escape expands the CD8 T cell repertoire that targets highly conserved epitopes, defined as anentropic specificity, and generates de novo responses to the escaped epitope variants during the vaccination period. These results correlate SIVΔnef-induced protection with expanded anentropic specificity and increased response depth. Importantly, these findings render SIVΔnef, long the gold standard in HIV/SIV vaccine research, as a proof-of-concept vaccine that highlights the significance of the twin principles of anentropic specificity and repertoire depth in successful vaccine design.

Development of a luciferase based viral inhibition assay to evaluate vaccine induced CD8 T-cell responses

Emergence of SIV and HIV specific CD8 T cells has been shown to correlate with control of in vivo replication. Poor correlation between IFN-γ ELISPOT responses and in vivo control of the virus has triggered the development of more relevant assays to assess functional HIV-1 specific CD8 T-cell responses for the evaluation and prioritization of new HIV-1 vaccine candidates. We previously established a viral inhibition assay (VIA) that measures the ability of vaccine-induced CD8 T-cell responses to inhibit viral replication in autologous CD4 T cells. In this assay, viral replication is determined by measuring p24 in the culture supernatant. Here we describe the development of a novel VIA, referred to as IMC LucR VIA that exploits replication-competent HIV-1 infectious molecular clones (IMCs) in which the complete proviral genome is strain-specific and which express the Renilla luciferase (LucR) gene to determine viral growth and inhibition. The introduction of the luciferase readout does provide significant improvement of the read out time. In addition to switching to the LucR read out, changes made to the overall protocol resulted in the miniaturization of the assay from a 48 to a 96-well plate format, which preserved sample and allowed for the introduction of replicates. The overall assay time was reduced from 13 to 8 days. The assay has a high degree of specificity, and the previously observed non-specific background inhibition in cells from HIV-1 negative volunteers has been reduced dramatically. Importantly, we observed an increase in positive responses, indicating an improvement in sensitivity compared to the original VIA. Currently, only a limited number of "whole-genome" IMC-LucR viruses are available and our efforts will focus on expanding the panel to better evaluate anti-viral breadth. Overall, we believe the IMC LucR VIA provides a platform to assess functional CD8 T-cell responses in large-scale clinical trial testing, which will enhance the ability to select the most promising HIV-1 vaccine candidates capable of controlling HIV-1 replication in vivo.

Influence of intragenic CCL3 haplotypes and CCL3L copy number in HIV-1 infection in a sub-Saharan African population

Two CCL3 haplotypes (HapA1 and Hap-A3) and two polymorphic positions shared by the haplotypes (Hap-2SNP) were investigated together with CCL3L copy number (CN), for their role in HIV-1 disease. Hap-A1 was associated with protection from in utero HIV-1 infection: exposed-uninfected infants had higher representation of WT/Hap-A1 than infected infants (excluding intrapartum-infected infants), which maintained significance post maternal Nevirapine (mNVP) and viral load (MVL) correction (P=0.04; OR=0.33). Mother-infant pair analyses showed the protective effect of Hap-A1 is dependent on its presence in the infant. Hap-A3 was associated with increased intrapartum transmission: WT/Hap-A3 was increased in intrapartum vs. non-transmitting mothers, and remained significant post mNVP and MVL correction (P=0.02; OR=3.50). This deleterious effect of Hap-A3 seemed dependent on its presence in the mother. Hap-2SNP was associated with lower CD4 count in the non-transmitting mothers (P=0.03). CCL3 Hap-A1 was associated with high CCL3L CN in total (P=0.001) and exposed-uninfected infants (P=0.006); the effect was not additive, however having either Hap-A1 or high CCL3L CN was more significantly (P=0.0008) associated with protection from in utero infection than Hap-A1 (P=0.028) or high CCL3L CN (P=0.002) alone. Linkage disequilibrium between Hap-A1 and high CCL3L CN appears unlikely given that a Nigerian population showed an opposite relationship.

Lessons in nonhuman primate models for AIDS vaccine research: from minefields to milestones

Nonhuman primate (NHP) disease models for AIDS have made important contributions to the search for effective vaccines for AIDS. Viral diversity, persistence, capacity for immune evasion, and safety considerations have limited development of conventional approaches using killed or attenuated vaccines, necessitating the development of novel approaches. Here we highlight the knowledge gained and lessons learned in testing vaccine concepts in different virus/NHP host combinations.

Flow cytometry based identification of simian immunodeficiency virus Env-specific B lymphocytes

SIV infection of macaques is the most widely employed model for preclinical AIDS vaccine and pathogenesis research. In macaques, high-titer virus-specific antibodies are induced by infection, and antibody responses can drive evolution of viral escape variants. However, neutralizing antibodies (Nabs) induced in response to SIVmac239 and SIVmac251 infection or immunization are generally undetectable or of low titer, and the identification and cloning of potent Nabs from SIVmac-infected macaques remains elusive. Based on recent advances in labeling HIV-specific B lymphocytes [1-3], we have generated recombinant, secreted, soluble SIVmac envelope (Env) proteins (gp120 and gp140) for detection and quantification of SIVmac Env-specific B lymphocytes. In contrast to HIV-1, we found that soluble SIVmac239 gp140 retains the ability to form stable oligomers without the necessity for introducing additional, stabilizing modifications. Soluble oligomeric gp140 reacted with rhesus anti-SIV Env-specific monoclonal antibodies (MAbs), and was used to deplete Env-specific antibodies with SIV neutralization capability from plasma taken from a rhesus macaque immunized with live attenuated SIVmac239∆nef. Soluble gp120 and gp140 bound to SIV-specific immortalized B cells, and to SIV Env-specific B lymphocytes in peripheral blood of immunized animals. These reagents will be useful for analyzing development of Env-specific B cell responses in preclinical studies using SIV-infected or vaccinated rhesus macaques.

Broadening of CD8+ cell responses in vaccine-based simian immunodeficiency virus controllers

OBJECTIVE

In our prior study on a prophylactic T-cell-based vaccine, some vaccinated macaques controlled a simian immunodeficiency virus (SIV) challenge. These animals allowed viremia in the acute phase but showed persistent viral control after the setpoint. Here, we examined the breadth of postchallenge virus-specific cellular immune responses in these SIV controllers.

DESIGN

We previously reported that in a group of Burmese rhesus macaques possessing the MHC haplotype 90-120-Ia, immunization with a Gag-expressing vaccine results in nonsterile control of a challenge with SIVmac239 but not a mutant SIV carrying multiple cytotoxic T lymphocyte (CTL) escape gag mutations. In the present study, we investigated whether broader cellular immune responses effective against the mutant SIV replication are induced after challenge in those vaccinees that maintained wild-type SIVmac239 control.

METHODS

We analyzed cellular immune responses in these SIV controllers (n = 8).

RESULTS

These controllers elicited CTL responses directed against SIV non-Gag antigens as well as Gag in the chronic phase. Postvaccinated, prechallenge CD8(+) cells obtained from these animals suppressed wild-type SIV replication in vitro, but mostly had no suppressive effect on the mutant SIV replication, whereas CD8(+) cells in the chronic phase after challenge showed efficient antimutant SIV efficacy. The levels of in-vitro antimutant SIV efficacy of CD8(+) cells correlated with Vif-specific CD8(+) T-cell frequencies. Plasma viremia was kept undetectable even after the mutant SIV superchallenge in the chronic phase.

CONCLUSION

These results suggest that vaccine-based wild-type SIV controllers can acquire CD8(+) cells with the potential to suppress replication of SIV variants carrying CTL escape mutations.

Emergence of simian immunodeficiency virus-specific cytotoxic CD4+ T cells and increased humoral responses correlate with control of rebounding viremia in CD8-depleted macaques infected with Rev-independent live-attenuated simian immunodeficiency virus

Indian rhesus macaques infected with the Rev-independent live-attenuated SIVmac239 strains control viremia to undetectable levels, have persistent but low cellular and humoral anti-SIV responses, and show no signs of immune deficiency. To analyze the immune mechanisms responsible for viral control, five macaques infected at day 1 after birth were subjected to CD8(+) cell depletion at 6.7 y postinfection. This resulted in viremia increases to 3.7-5.5 log(10) RNA copies, supporting a role of CD8-mediated responses in the control of viral replication. The rebounding viremia was rapidly controlled to levels below the threshold of detection, and occurred in the absence of SIV-specific CD8(+) T cells and significant CD8(+) T cell recovery in four of the five animals, suggesting that other mechanisms are involved in the immunological control of viremia. Monitoring immune responses at the time of viral control demonstrated a burst of circulating SIV-specific CD4(+) T cells characterized as CD45RA(-)CD28(+)CD95(+)CCR7(-) and also granzyme B(+), suggesting cytotoxic ability. Control of viremia was also concomitant with increases in humoral responses to Gag and Env, including a transient increase in neutralizing Abs against the neutralization-resistant SIVmac239 in four of five animals. These data demonstrate that a combination of cellular responses mediated by CD4(+) T cells and humoral responses was associated with the rapid control of the rebounding viremia in macaques infected by the Rev-independent live-attenuated SIV, even in the absence of measurable SIV-specific CD8(+) T cells in the blood, emphasizing the importance of different components of the immune response for full control of SIV infection.

Simian immunodeficiency virus infection alters chemokine networks in lung tissues of cynomolgus macaques: association with Pneumocystis carinii infection

Infection by HIV-1 frequently leads to pulmonary complications, including alterations to local immune environments. To better understand these alterations, we have examined in detail the patterns and levels of expression of chemokine, cytokine, and chemokine receptor mRNAs in lung tissues from 16 uninfected or simian immunodeficiency virus (SIV)/DeltaB670 infected cynomolgus macaques at different stages of infection. Among the most up-regulated immune genes were interferon (IFN)-gamma, IFN-gamma-inducible CXCR3 ligands, and CCR5 ligands, as well as the cognate chemokine receptors. These changes were greatest in animals with clear Pneumocystis carinii coinfection. Immunohistochemistry and in situ hybridization revealed monocytes/macrophages to be the predominant type of cell infiltrating into lung tissues and serving as the major cellular source of chemokines. To explore the causes of chemokine alterations, we treated macaque lung cells with IFN-gamma, lipopolysaccharide, Poly(I:C), and P. carinii in vitro, and results revealed that these stimuli can induce the expression of CXCR3 ligand and/or CCR5 ligand mRNAs. Taken together, these studies provide a comprehensive definition of the chemokine networks available to modulate cellular recruitment to lung tissues during SIV infection and implicate both cytokines (IFN-gamma) and pathogens (SIV and P. carinii) as contributors to increased expression of pro-inflammatory chemokines.

Extralymphoid CD8+ T cells resident in tissue from simian immunodeficiency virus SIVmac239{Delta}nef-vaccinated macaques suppress SIVmac239 replication ex vivo

Live-attenuated vaccination with simian immunodeficiency virus (SIV) SIVmac239Deltanef is the most successful vaccine product tested to date in macaques. However, the mechanisms that explain the efficacy of this vaccine remain largely unknown. We utilized an ex vivo viral suppression assay to assess the quality of the immune response in SIVmac239Deltanef-immunized animals. Using major histocompatibility complex-matched Mauritian cynomolgus macaques, we did not detect SIV-specific functional immune responses in the blood by gamma interferon (IFN-gamma) enzyme-linked immunospot assay at select time points; however, we found that lung CD8(+) T cells, unlike blood CD8(+) T cells, effectively suppress virus replication by up to 80%. These results suggest that SIVmac239Deltanef may be an effective vaccine because it elicits functional immunity at mucosal sites. Moreover, these results underscore the limitations of relying on immunological measurements from peripheral blood lymphocytes in studies of protective immunity to HIV/SIV.

Polyfunctional CD4+ T-cell induction in neutralizing antibody-triggered control of simian immunodeficiency virus infection

Rapid depletion of memory CD4(+) T cells and delayed induction of neutralizing antibody (NAb) responses are characteristics of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections. Although it was speculated that postinfection NAb induction could have only a limited suppressive effect on primary HIV replication, a recent study has shown that a single passive NAb immunization of rhesus macaques 1 week after SIV challenge can result in reduction of viral loads at the set point, indicating a possible contribution of postinfection NAb responses to virus control. However, the mechanism accounting for this NAb-triggered SIV control has remained unclear. Here, we report rapid induction of virus-specific polyfunctional T-cell responses after the passive NAb immunization postinfection. Analysis of SIV Gag-specific responses of gamma interferon, tumor necrosis factor alpha, interleukin-2, macrophage inflammatory protein 1beta, and CD107a revealed that the polyfunctionality of Gag-specific CD4(+) T cells, as defined by the multiplicity of these responses, was markedly elevated in the acute phase in NAb-immunized animals. In the chronic phase, despite the absence of detectable NAbs, virus control was maintained, accompanied by polyfunctional Gag-specific T-cell responses. These results implicate virus-specific polyfunctional CD4(+) T-cell responses in this NAb-triggered virus control, suggesting possible synergism between NAbs and T cells for control of HIV/SIV replication.

Immunity and protection by live attenuated HIV/SIV vaccines

Live attenuated virus vaccines have shown the greatest potential to protect against simian immunodeficiency virus (SIV) infection, a model for human immunodeficiency virus (HIV). Immunity against the vaccine virus is thought to mediate protection. However, it is shown computationally that the opposite might be true. According to the model, the initial growth of the challenge strain, its peak load, and its potential to be pathogenic is higher if immunity against the vaccine virus is stronger. This is because the initial growth of the challenge strain is mainly determined by virus competition rather than immune suppression. The stronger the immunity against the vaccine strain, the weaker its competitive ability relative to the challenge strain, and the lower the level of protection. If the vaccine virus does protect the host against a challenge, it is because the competitive interactions between the viruses inhibit the initial growth of the challenge strain. According to these arguments, an inverse correlation between the level of attenuation and the level of protection is expected, and this has indeed been observed in experimental data.

Efficient inhibition of SIV replication in rhesus CD4+ T-cell clones by autologous immortalized SIV-specific CD8+ T-cell clones

CD8(+) cytotoxic T lymphocyte (CTL) responses play an important role in controlling the replication of primate lentiviruses. Induction of these responses is a key objective for most current AIDS vaccine approaches. Despite a variety of approaches for measuring properties and activities of CTL, the functions responsible for controlling viral replication in vivo have not been clearly identified. Assays measuring CTL-mediated suppression of viral replication in vitro are beginning to be used as possible correlates of in vivo virus suppressive activity, but the utility and interpretive value of these assays are typically limited by properties of the cells that have been used. We investigated the capacity of SIV-specific CTL clones (effectors), immortalized by transduction with human telomerase reverse transcriptase (hTERT), to suppress SIV replication in autologous hTERT immortalized CD4(+) T-cell clones (targets). Immortalized and non-immortalized SIV-specific effector cells showed IFN-gamma production and degranulation in response to viral antigen specific stimulation and significantly inhibited SIV(mac)239 replication (2 to 4 log decrease in viral RNA or cell-associated proviral DNA) (p<0.0005). Our in vitro assays of inhibition of viral replication, using T-cell clones as effectors and targets, provide a well-defined approach for evaluating possible mechanisms of CTL-mediated control of viral production which may involve direct killing of infected target cells and/or release of proinflammatory cytokines such as IFN-gamma and TNF-alpha. The use of hTERT immortalized effector and target cells for such assays preserves relevant functional properties while providing a convenient, reproducible means of conducting studies over time.

Induction of CD8+ cells able to suppress CCR5-tropic simian immunodeficiency virus SIVmac239 replication by controlled infection of CXCR4-tropic simian-human immunodeficiency virus in vaccinated rhesus macaques

Recent recombinant viral vector-based AIDS vaccine trials inducing cellular immune responses have shown control of CXCR4-tropic simian-human immunodeficiency virus (SHIV) replication but difficulty in containment of pathogenic CCR5-tropic simian immunodeficiency virus (SIV) in rhesus macaques. In contrast, controlled infection of live attenuated SIV/SHIV can confer the ability to contain SIV superchallenge in macaques. The specific immune responses responsible for this control may be induced by live virus infection but not consistently by viral vector vaccination, although those responses have not been determined. Here, we have examined in vitro anti-SIV efficacy of CD8+ cells in rhesus macaques that showed prophylactic viral vector vaccine-based control of CXCR4-tropic SHIV89.6PD replication. Analysis of the effect of CD8+ cells obtained at several time points from these macaques on CCR5-tropic SIVmac239 replication in vitro revealed that CD8+ cells in the chronic phase after SHIV challenge suppressed SIV replication more efficiently than those before challenge. SIVmac239 superchallenge of two of these macaques at 3 or 4 years post-SHIV challenge was contained, and the following anti-CD8 antibody administration resulted in transient CD8+ T-cell depletion and appearance of plasma SIVmac239 viremia in both of them. Our results indicate that CD8+ cells acquired the ability to efficiently suppress SIV replication by controlled SHIV infection, suggesting the contribution of CD8+ cell responses induced by controlled live virus infection to containment of HIV/SIV superinfection.

A decline in CCL3-5 chemokine gene expression during primary simian-human immunodeficiency virus infection

BACKGROUND

The CC-chemokines CCL3, CCL4 and CCL5 have been found to block the entry of CCR5-tropic HIV into host cells and to suppress the viral replication in vitro, but the in vivo role of endogenous CC-chemokines in HIV-1 infection is still incompletely understood.

METHODOLOGY/PRINCIPLE FINDINGS

In this study, the primate host CCL3, CCL4 and CCL5 gene expression was evaluated in response to simian-human immunodeficiency virus (SHIV) infection in rhesus macaque model. Five rhesus macaques were inoculated with CCR5-tropic SHIV(SF162P4). The mRNA levels of CCL3, CCL4 and CCL5 were measured by real-time PCR at post inoculation day (PID) 0, 7, 14, 21, 35, 56 and 180 in peripheral blood. In addition, a selected subset of samples from CXCR4-tropic SHIV(Ku1)-infected macaques was included with objective to compare the differences in CC-chemokine down-regulation caused by the two SHIVs. Gut-associated lymphoid tissues (GALT) collected from SHIV(SF162P4)-infected animals were also tested by flow cytometry and confocal microscopy to corroborate the gene expression results. Predictably, higher viral loads and CD4+ T cell losses were observed at PID 14 in macaques infected with SHIV(Ku1) than with SHIV(SF162P4). A decline in CC-chemokine gene expression was also found during primary (PID 7-21), but not chronic (PID 180) stage of infection.

CONCLUSIONS

It was determined that A) SHIV(SF162P4) down-regulated the CC-chemokine gene expression during acute stage of infection to a greater extent (p<0.05) than SHIV(Ku1), and B) such down-regulation was not paralleled with the CD4+ T cell depletion. Evaluation of CC-chemokine enhancing immunomodulators such as synthetic CpG-oligonucleotides could be explored in future HIV vaccine studies.

Changes in soluble factor-mediated CD8+ cell-derived antiviral activity in cynomolgus macaques infected with simian immunodeficiency virus SIVmac251: relationship to biological markers of progression

Cross-sectional studies have shown that the capacity of CD8+ cells from human immunodeficiency virus (HIV)-infected patients and simian immunodeficiency virus (SIV) SIVmac-infected macaques to suppress the replication of human and simian immunodeficiency viruses in vitro depends on the clinical stage of disease, but little is known about changes in this antiviral activity over time in individual HIV-infected patients or SIV-infected macaques. We assessed changes in the soluble factor-mediated noncytolytic antiviral activity of CD8+ cells over time in eight cynomolgus macaques infected with SIVmac251 to determine the pathophysiological role of this activity. CD8+ cell-associated antiviral activity increased rapidly in the first week after viral inoculation and remained detectable during the early phase of infection. The net increase in antiviral activity of CD8+ cells was correlated with plasma viral load throughout the 15 months of follow-up. CD8+ cells gradually lost their antiviral activity over time and acquired virus replication-enhancing capacity. Levels of antiviral activity correlated with CD4+ T-cell counts after viral set point. Concentrations of beta-chemokines and interleukin-16 in CD8+ cell supernatants were not correlated with this antiviral activity, and alpha-defensins were not detected. The soluble factor-mediated antiviral activity of CD8+ cells was neither cytolytic nor restricted to major histocompatibility complex. This longitudinal study strongly suggests that the increase in noncytolytic antiviral activity from baseline and the maintenance of this increase over time in cynomolgus macaques depend on both viral replication and CD4+ T cells.

The antiviral efficacy of simian immunodeficiency virus-specific CD8+ T cells is unrelated to epitope specificity and is abrogated by viral escape

CD8(+) T lymphocytes appear to play a role in controlling human immunodeficiency virus (HIV) replication, yet routine immunological assays do not measure the antiviral efficacy of these cells. Furthermore, it has been suggested that CD8+ T cells that recognize epitopes derived from proteins expressed early in the viral replication cycle can be highly efficient. We used a functional in vitro assay to assess the abilities of different epitope-specific CD8+ T-cell lines to control simian immunodeficiency virus (SIV) replication. We compared the antiviral efficacies of 26 epitope-specific CD8+ T-cell lines directed against seven SIV epitopes in Tat, Nef, Gag, Env, and Vif that were restricted by either Mamu-A*01 or Mamu-A*02. Suppression of SIV replication varied depending on the epitope specificities of the CD8+ T cells and was unrelated to whether the targeted epitope was derived from an early or late viral protein. Tat(28-35)SL8- and Gag(181-189)CM9-specific CD8+ T-cell lines were consistently superior at suppressing viral replication compared to the other five SIV-specific CD8+ T-cell lines. We also investigated the impact of viral escape on antiviral efficacy by determining if Tat(28-35)SL8- and Gag(181-189)CM9-specific CD8+ T-cell lines could suppress the replication of an escaped virus. Viral escape abrogated the abilities of Tat(28-35)SL8- and Gag(181-189)CM9-specific CD8+ T cells to control viral replication. However, gamma interferon (IFN-gamma) enzyme-linked immunospot and IFN-gamma/tumor necrosis factor alpha intracellular-cytokine-staining assays detected cross-reactive immune responses against the Gag escape variant. Understanding antiviral efficacy and epitope variability, therefore, will be important in selecting candidate epitopes for an HIV vaccine.

Not all cytokine-producing CD8+ T cells suppress simian immunodeficiency virus replication

Current assays of CD8+ T-lymphocyte function measure cytokine production rather than the ability of these lymphocytes to suppress viral replication. Here we show that CD8+ T-cell clones recognizing the same epitope vary enormously in the ability to suppress simian immunodeficiency virus SIVmac239 replication in an in vitro suppression assay. However, all Nef(165-173)IW9- and Vif(66-73)HW8-specific clones from elite controllers effectively suppressed SIV replication. Interestingly, in vitro suppression efficacy was not always associated with the ability to produce gamma interferon, tumor necrosis factor alpha, or interleukin-2.

Induction of a virus-specific effector-memory CD4+ T cell response by attenuated SIV infection

We investigated simian immunodeficiency virus (SIV)-specific CD4⁺ T cell responses in rhesus macaques chronically infected with attenuated or pathogenic SIV strains. Analysis of SIVΔnef-infected animals revealed a relatively high frequency of SIV-specific CD4⁺ T cells representing 4–10% of all CD4⁺ T lymphocytes directed against multiple SIV proteins. Gag-specific CD4⁺ T cells in wild-type SIV-infected animals were 5–10-fold lower in frequency and inversely correlated with the level of plasma viremia. SIV-specific CD4⁺ cells from SIVΔnef animals were predominantly CD27⁻CD28⁻CD45RA^lowCCR7⁻CCR5⁻, consistent with an effector–memory subset, and included a fully differentiated CD45RA⁺CCR7⁻ subpopulation. In contrast, SIV-specific CD4⁺ T cells from SIV-infected animals were mostly CD27⁺CD28⁺CD45RA⁻CCR7⁺CCR5⁺, consistent with an early central memory phenotype. The CD45RA⁺CCR7⁻CD4⁺ subset from SIVΔnef animals was highly enriched for effector CD4⁺ T cells, as indicated by the perforin expression and up-regulation of the lysosomal membrane protein CD107a after SIV Gag stimulation. SIV-specific CD4⁺ T cells in attenuated SIV-infected animals were increased in frequency in bronchioalveolar lavage and decreased in lymph nodes, consistent with an effector–memory T cell population. The ability of SIVΔnef to induce a high frequency virus-specific CD4⁺ T cell response with direct effector function may play a key role in protective immunity produced by vaccination with attenuated SIV strains.

The Toll-like receptor 7 (TLR7) agonist, imiquimod, and the TLR9 agonist, CpG ODN, induce antiviral cytokines and chemokines but do not prevent vaginal transmission of simian immunodeficiency virus when applied intravaginally to rhesus macaques

The initial host response to viral infection occurs after Toll-like receptors (TLRs) on dendritic cells (DC) are stimulated by viral nucleic acids (double-stranded RNA, single-stranded RNA) and alpha interferon (IFN-alpha) and IFN-beta are produced. We hypothesized that pharmacologic induction of innate antiviral responses in the cervicovaginal mucosa by topical application of TLR agonists prior to viral exposure could prevent or blunt vaginal transmission of simian immunodeficiency virus (SIV). To test this hypothesis, we treated rhesus monkeys intravaginally with either the TLR9 agonist, CpG oligodeoxynucleotides (ODN), or the TLR7 agonist, imiquimod. Both immune modifiers rapidly induced IFN-alpha and other antiviral effector molecules in the cervicovaginal mucosa of treated animals. However, both CpG ODN and imiquimod also induced proinflammatory cytokine expression in the cervicovaginal mucosa. In the vaginal mucosa of imiquimod-treated monkeys, we documented a massive mononuclear cell infiltrate consisting of activated CD4(+) T cells, DC, and beta-chemokine-secreting cells. After vaginal SIV inoculation, all TLR agonist-treated animals became infected and had plasma vRNA levels that were higher than those of control monkeys. We conclude that induction of mucosal innate immunity including an IFN-alpha response is not sufficient to prevent sexual transmission of human immunodeficiency virus.

Tat(28-35)SL8-specific CD8+ T lymphocytes are more effective than Gag(181-189)CM9-specific CD8+ T lymphocytes at suppressing simian immunodeficiency virus replication in a functional in vitro assay

Epitope-specific CD8+ T lymphocytes may play an important role in controlling human immunodeficiency virus (HIV)/simian immunodeficiency virus replication. Unfortunately, standard cellular assays do not measure the antiviral efficacy (the ability to suppress virus replication) of CD8+ T lymphocytes. Certain epitope-specific CD8+ T lymphocytes may be better than others at suppressing viral replication. We compared the antiviral efficacy of two immunodominant CD8+ T lymphocyte responses--Tat(28-35)SL8 and Gag(181-189)CM9--by using a functional in vitro assay. Viral suppression by Tat-specific CD8+ T lymphocytes was consistently greater than that of Gag-specific CD8+ T lymphocytes. Such differences in antigen-specific CD8+-T-lymphocyte efficacy may be important for selecting CD8+ T lymphocyte epitopes for inclusion in future HIV vaccines.

Cloning, expression, and functional characterization of cynomolgus monkey (Macaca fascicularis) CC chemokine receptor 1

The CC chemokine receptor 1 (CCR1) has emerged as a relevant factor contributing to inflammatory diseases such as allergic asthma. Commonly used animal models of allergic airway inflammation, especially murine models, have certain limitations. The elaborate, nonhuman, primate models of asthma display the highest comparability with the situation in humans. These models play an important role in the understanding of the pathogenesis of asthma. To improve the understanding in cynomolgus monkey models, we identified and characterized CCR1 in this nonhuman primate. Initially, we cloned the cynomolgus monkey CCR1 (cCCR1) gene, and the sequence analysis revealed high homology at the nucleotide (92%) and amino acid (88.4%) levels with its human counterpart. Human embryonic kidney 293 cells were stably transfected with cCCR1 and used in functional assays. Among those CCR1 ligands tested, CCL14(9-74) was most potent in the induction of intracellular Ca2+ fluxes as observed for human CCR1 (hCCR1). Complete cross-desensitization could be achieved between CCL14(9-74) and CCL15. However, CCL3 could not fully abrogate the response to the potent ligand CCL14(9-74). Competition-binding studies with radiolabeled CCL3 concordantly showed that CCL14(9-74) has a higher affinity to cCCR1 than hCCL3. Moreover, differential tissue-specific expression of cCCR1 was investigated by real-time quantitative polymerase chain reaction, displaying the highest levels in spleen. This study adds basic information needed for the evaluation of the role of CCR1 in the pathophysiology of asthma using the highly relevant cynomolgus monkey model and in addition, aids in the preclinical evaluation of potential novel drugs targeting CCR1.

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.

Effect of CD8+ lymphocyte depletion on virus containment after simian immunodeficiency virus SIVmac251 challenge of live attenuated SIVmac239delta3-vaccinated rhesus macaques

Although live attenuated vaccines can provide potent protection against simian immunodeficiency virus (SIV) and simian-human immunodeficiency virus challenges, the specific immune responses that confer this protection have not been determined. To test whether cellular immune responses mediated by CD8+ lymphocytes contribute to this vaccine-induced protection, we depleted rhesus macaques vaccinated with the live attenuated virus SIVmac239Delta3 of CD8+ lymphocytes and then challenged them with SIVmac251 by the intravenous route. While vaccination did not prevent infection with the pathogenic challenge virus, the postchallenge levels of virus in the plasmas of vaccinated control animals were significantly lower than those for unvaccinated animals. The depletion of CD8+ lymphocytes at the time of challenge resulted in virus levels in the plasma that were intermediate between those of the vaccinated and unvaccinated controls, suggesting that CD8+ cell-mediated immune responses contributed to protection. Interestingly, at the time of challenge, animals expressing the Mamu-A*01 major histocompatibility complex class I allele showed significantly higher frequencies of SIV-specific CD8+ T-cell responses and lower neutralizing antibody titers than those in Mamu-A*01- animals. Consistent with these findings, the depletion of CD8+ lymphocytes abrogated vaccine-induced protection, as judged by the peak postchallenge viremia, to a greater extent in Mamu-A*01+ than in Mamu-A*01- animals. The partial control of postchallenge viremia after CD8+ lymphocyte depletion suggests that both humoral and cellular immune responses induced by live attenuated SIV vaccines can contribute to protection against a pathogenic challenge and that the relative contribution of each of these responses to protection may be genetically determined.

Kinetics of expansion of SIV Gag-specific CD8+ T lymphocytes following challenge of vaccinated macaques

The ability of memory T cells to mount a recall response plays a key role in the ability of vaccinated animals to contain viral challenge. In this study, we intensively monitored the expansion of SIV Gag-specific CD8+ T cells in peripheral blood and tissues of rhesus macaques vaccinated with the attenuated strain SIVmac239Delta3 and challenged with the pathogenic viruses SIVmac239 or SIVsmE660. Although all vaccinated animals were infected with challenge virus, peak levels of plasma viremia in vaccinees were decreased by 1.5 to 2 logs as compared with naive controls. Decreased levels of plasma viremia in vaccinated animals were evident as early as 7 days post-challenge, well before the expansion of SIV-specific CD8+ T cells. Expansion of SIV-specific CD8+ T cells was not observed in peripheral blood or tissues until at least 14 days after infection and did not occur in most animals until after the initial peak of viral replication. The observation that expansion of SIV-specific CD8+ T cells is delayed until 7 days or more after initial detection of viremia highlights fundamental limitations in the ability of lentivirus-specific CD8+ T cells to mediate protection against challenge.

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.

High beta-chemokine expression levels in lymphoid tissues of simian/human immunodeficiency virus 89.6-vaccinated rhesus macaques are associated with uncontrolled replication of simian immunodeficiency virus challenge inoculum

Viral suppression by noncytolytic CD8+ T cells, in addition to that by classic antiviral CD8+ cytotoxic T lymphocytes, has been described for human immunodeficiency virus and simian immunodeficiency virus (SIV) infections. However, the role of soluble effector molecules, especially beta-chemokines, in antiviral immunity is still controversial. In an attenuated vaccine model, approximately 60% of animals immunized with simian/human immunodeficiency virus (SHIV) 89.6 and then challenged intravaginally with SIVmac239 controlled viral replication (viral RNA level in plasma, <10(4) copies/ml) and were considered protected (K. Abel, L. Compton, T. Rourke, D. Montefiori, D. Lu, K. Rothaeusler, L. Fritts, K. Bost, and C. J. Miller, J. Virol. 77:3099-3118, 2003). To determine the in vivo importance of beta-chemokine secretion and CD8+-T-cell proliferation in the control of viral replication in this vaccine model, we examined the relationship between viral RNA levels in the axillary and genital lymph nodes of vaccinated, protected (n = 20) and vaccinated, unprotected (n = 11) monkeys by measuring beta-chemokine mRNA levels and protein expression, the frequency of CD8+ T cells expressing beta-chemokines, and the extent of CD8+-T-cell proliferation. Tissues from uninfected (n = 3) and unvaccinated, SIVmac239-infected (n = 9) monkeys served as controls. Axillary and genital lymph nodes from unvaccinated and vaccinated, unprotected monkeys had significantly higher beta-chemokine mRNA expression levels and increased numbers of beta-chemokine-positive cells than did vaccinated, protected animals. Furthermore, the lymph nodes of vaccinated, unprotected monkeys had significantly higher numbers of beta-chemokine(+) CD8+ T cells than did vaccinated, protected monkeys. Lymph nodes from vaccinated, unprotected animals also had significantly more CD8+-T-cell proliferation and marked lymph node hyperplasia than the lymph nodes of vaccinated, protected monkeys. Thus, higher levels of virus replication were associated with increased beta-chemokine secretion and there is no evidence that beta-chemokines contributed to the SHIV89.6-mediated control of viral replication after intravaginal challenge with SIVmac239.

Human and simian immunodeficiency virus-infected chimpanzees do not have increased intracellular levels of beta-chemokines in contrast to infected humans

This study was undertaken to explain why chimpanzees infected with HIV-1 (human immunodeficiency virus type 1) or SIV(cpz) (simian immunodeficiency virus of chimpanzee) are relatively resistant to AIDS (acquired immunodeficiency syndrome). The numbers of beta-chemokine-positive cells were compared between uninfected and infected humans and chimpanzees using three-color cytofluorometry. In humans, the percentage of beta-chemokine-positive cells was significantly higher in CD8(+) T and natural killer (NK) cells than in CD4(+) T cells in both uninfected and HIV-1-infected individuals. In the presence of HIV-1 infection, however, both CD8(+) and CD4(+) T cell subsets contained significantly more beta-chemokine-positive cells than in the absence of infection. Interestingly, in chimpanzees two important differences were noted. First, their percentage of beta-chemokine-positive CD8(+) T and NK cells was significantly higher than in uninfected humans. Second, in contrast to humans, infection with either HIV-1 or with SIV(cpz) was not associated with increased numbers of beta-chemokine-positive cells. These results indicate that: constitutive high levels of intracellular beta-chemokines in chimpanzees' CD8 lymphocytes and NK cells do not necessarily correspond to lower levels of virus replication during the chronic phase of infection; and increased percentages of beta-chemokine-positive cells in HIV-infection are not a correlate of disease resistance. The data suggest that neither pre-nor post-exposure levels of intracellular beta-chemokines are correlated with the subsequent control of disease progression.

Simian-human immunodeficiency virus SHIV89.6-induced protection against intravaginal challenge with pathogenic SIVmac239 is independent of the route of immunization and is associated with a combination of cytotoxic T-lymphocyte and alpha interferon responses

Attenuated primate lentivirus vaccines provide the most consistent protection against challenge with pathogenic simian immunodeficiency virus (SIV). Thus, they provide an excellent model to examine the influence of the route of immunization on challenge outcome and to study vaccine-induced protective anti-SIV immune responses. In the present study, rhesus macaques were immunized with live nonpathogenic simian-human immunodeficiency virus (SHIV) 89.6 either intravenously or mucosally (intranasally or intravaginally) and then challenged intravaginally with pathogenic SIVmac239. The route of immunization did not affect mucosal challenge outcome after a prolonged period of systemic infection with the nonpathogenic vaccine virus. Further, protection from the SIV challenge was associated with the induction of multiple host immune effector mechanisms. A comparison of immune responses in vaccinated-protected and vaccinated-unprotected animals revealed that vaccinated-protected animals had higher frequencies of SIV Gag-specific cytotoxic T lymphocytes and gamma interferon (IFN-gamma)-secreting cells during the acute phase postchallenge. Vaccinated-protected animals also had a more pronounced increase in peripheral blood mononuclear cell IFN-alpha mRNA levels than did the vaccinated-unprotected animals in the first few weeks after challenge. Thus, innate as well as cellular anti-SIV immune responses appeared to contribute to the SHIV89.6-induced protection against intravaginal challenge with pathogenic SIVmac239.

Replication, immunogenicity, and protective properties of live-attenuated simian immunodeficiency viruses expressing interleukin-4 or interferon-gamma

Nef deletion mutants of SIV-expressing interleukin-4 (SIV-IL4) or interferon-gamma (SIV-IFN) were constructed to study the effect of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) on viral load, immunogenicity, and protective properties. Four rhesus monkeys were infected with SIV-IL4 and four were infected with SIV-IFN. During the acute phase of infection, the cell-associated viral load, but not the plasma viral RNA load, was approximately 10-fold lower in SIV-IFN-infected macaques than in SIV-IL4-infected rhesus monkeys. The viral load declined to hardly detectable levels 4 months postinfection in all animals. SIV antibody titers and the affinity of these antibodies were higher in SIV-IL4-infected macaques than in SIV-IFN-infected animals, consistent with a stimulation of T helper cell type 2 immune responses by IL-4. At peak viremia, there was a trend to higher interleukin-12 and perforin mRNA levels of the lymph nodes in the SIV-IFN-infected macaques than in the SIV-IL4-infected monkeys. Deletion of the viral IFN gene, but not the viral IL-4 gene, after the development of antiviral immune responses suggests a repressive effect of IFN, but not IL-4, on virus spread in vivo. A trend to higher set point viral RNA levels in SIV-IL4-infected monkeys in comparison to monkeys infected with the parental nef deletion mutant and similar viral RNA levels during the acute phase of infection suggest that IL-4 expression leads to a slight reduction in the control of virus replication by host immune responses. However, SIV-IL4 and SIV-IFN induced protection against a homologous challenge virus. Subsequent challenge with an SIV-HIV-1 hybrid virus (SHIV) also revealed protection in the absence of neutralizing antibodies.

[Present situation regarding development of an HIV vaccine]

The AIDS epidemic continues to advance, and the development of a preventive HIV vaccine has become a major objective for scientific research. An effective vaccine against this virus is not available and complete protection still has not been achieved in animal models. In this review the major challenges related to the development of a vaccine against HIV are analyzed, particularly the mechanisms involved in viral escape from the immune response, and the results obtained with the various therapeutic and preventive vaccine prototypes are summarized. Finally, the social, economic and health aspects related to research on HIV vaccines and the current controversy around the performance of clinical trials with these agents is discussed.

Live, attenuated simian immunodeficiency virus SIVmac-M4, with point mutations in the Env transmembrane protein intracytoplasmic domain, provides partial protection from mucosal challenge with pathogenic SIVmac251

Attenuated molecular clones of simian immunodeficiency virus (SIVmac) are important tools for studying the correlates of protective immunity to lentivirus infection in nonhuman primates. The most highly attenuated SIVmac mutants fail to induce disease but also fail to induce immune responses capable of protecting macaques from challenge with pathogenic virus. We recently described a novel attenuated virus, SIVmac-M4, containing multiple mutations in the transmembrane protein (TM) intracytoplasmic domain. This domain has been implicated in viral assembly, infectivity, and cytopathogenicity. Whereas parental SIVmac239-Nef(+) induced persistent viremia and simian AIDS in rhesus macaques, SIVmac-M4 induced transient viremia in juvenile and neonatal macaques, with no disease for at least 1 year postinfection. In this vaccine study, 8 macaques that were infected as juveniles (n = 4) or neonates (n = 4) with SIVmac-M4 were challenged with pathogenic SIVmac251 administered through oral mucosa. At 1 year postchallenge, six of the eight macaques had low to undetectable plasma viremia levels. Assays of cell-mediated immune responses to SIVmac Gag, Pol, Env, and Nef revealed that all animals developed strong CD8(+) T-cell responses to Gag after challenge but not before. Unvaccinated control animals challenged with SIVmac251 developed persistent viremia, had significantly weaker SIV-specific T-cell responses, and developed AIDS-related symptoms. These findings demonstrate that SIVmac-M4, which contains a full-length Nef coding region and multiple point mutations in the TM, can provide substantial protection from mucosal challenge with pathogenic SIVmac251.

A comparative investigation of CC chemokines and SIV suppressor factors generated by CD8+ and CD4+ T cells and CD14+ monocytes

The capacity of CD8+ and CD4+ T cells and CD14+ monocytes to generate the CC chemokines, RANTES, MIP-1alpha and MIP-1beta, and SIV suppressor factors were studied using cells separated from PBMC of macaques immunized with the 70-kDa heat shock protein (HSP70). Unimmunized macaques showed low levels of the three CC chemokines and SIV-SF, and they showed little variation between PBMC and the two subsets of T cells stimulated with PHA. Immunization with HSP70 elicited an increase in the in vitro concentration of each of the three CC chemokines and SF. This was found with PBMC, CD4+ and CD8+ T cells and to a lesser extent with monocytes, when conventionally separated enriched cell subsets were examined from the same PBMC. However, the concentrations of the three CC chemokines derived from highly purified cell-sorted populations (>95%) were greatly increased, as compared with the enriched cell subsets. The concentration of each of the three chemokines was highest for CD8+ T cells, decreased with CD4+ T cells and was lowest with the CD14+ monocytes, but the latter were not stimulated. Neutralization assays with antibodies to the three CC chemokines showed that the antiviral activity generated by the four populations of cells could be largely accounted for by the three CC chemokines. The results of this comparative study suggests that CD8+ as well as CD4+ T cells and CD14+ monocytes generate the three CC chemokines and SIV-SF when stimulated with a mitogen, and that the baseline innate level can be upregulated by adaptive immune responses to a specific antigen.

Mechanisms of protection against simian immunodeficiency virus infection

One of the obstacles to the development of an effective AIDS vaccine has been the limited information on the mechanisms of protective immunity to HIV. In macaques, immunization with attenuated simian immunodeficiency viruses (SIV) has proved to be one of the most effective strategies to induce protection against infection or disease with pathogenic lentiviruses. Infection with attenuated SIV strains induces a broad range of SIV-specific immune responses, including relatively potent cytotoxic T lymphocyte (CTL) and antibody responses. Several studies of macaques vaccinated with attenuated SIV have demonstrated correlations between CTL responses or antibody responses and protection but more detailed studies are needed to document the relative importance of these responses in protective immunity.

In vitro replication of SIVcpz is suppressed by beta-chemokines and CD8+ T cells but not by natural killer cells of infected chimpanzees

Unlike humans, chimpanzees are relatively resistant to AIDS after infection with HIV-1 or simian immunodeficiency virus of chimpanzee (SIVcpz). We hypothesized that resistance to disease progression is associated with efficient suppression of virus replication possibly by beta-chemokines secreted by CD8+ lymphocytes and especially natural killer (NK) cells. In vitro suppression of virus replication can be easily studied in SIVcpz-infected chimpanzees because they produce high infectious virus titers in their peripheral blood. A study was undertaken to assess the sensitivity of SIVcpz to beta-chemokines in vitro and to investigate the role of endogenous beta-chemokines in relation to the in vitro capacity of CD8+ lymphocytes and NK cells of chimpanzees to suppress SIVcpz replication. Our results show that SIVcpz uses CCR5 as a coreceptor to gain cell entry and is sensitive to recombinant beta-chemokines in vitro. Here we report that despite their potent capacity to produce RANTES, NK cells of infected chimpanzees do not suppress SIVcpz replication in vitro, in contrast to CD8+ lymphocytes. We also show that endogenous beta-chemokines are not the predominant factors mediating in vitro suppression.

Simian immunodeficiency viruses with defective nef genes show increased susceptibility to the noncytotoxic antiviral activity of CD8+ lymphocytes

The noncytotoxic soluble factor produced by CD8+ T cells inhibits replication of HIV and SIV in vitro and is thought to play a crucial role in combatting infection in vivo. We determined the effect of human CD8+ lymphocytes on the in vitro replication potential of both wild-type and nef-defective mutants of the simian immunodeficiency virus SIVmac251. Although replication of wild-type SIVmac251 in unstimulated human PBMC supplemented with IL-2 was unaffected by the presence of CD8+ T cells, the nef mutants were susceptible to the inhibitory effects. The effect of exogenous IL-2 depended upon the culture conditions: (i) in nonstimulated human PBMC depleted of CD8+ T cells, addition of IL-2 had a positive effect on the growth of the nef-defective viruses; (ii) in total human PBMC, IL-2 appeared to reinforce the CD8+ T-cell-dependent inhibition of the same mutant viruses. This strongly suggests that IL-2 stimulates the noncytotoxic anti-HIV/SIV response of CD8+ cells present in PBMC cultures. PHA stimulation of unfractionated human PBMC overrode the suppression of viral replication by CD8+ T cells. Depletion of activated T cells expressing the IL-2 receptor alpha-chain (CD25+ T cells), present in small amounts in these primary T cell cultures, dramatically reduced viral replication, indicating that the depleted cell population harbors the target cells permissive for viral replication. Furthermore, using neutralizing antibodies we could show that inhibition by the beta-chemokines MIP-1alpha, MIP-1beta, and RANTES and the inhibitory effect of CD8+ lymphocytes on nef mutant SIVmac viruses are harbored on different levels.

Vaccination with DNA containing tat coding sequences and unmethylated CpG motifs protects cynomolgus monkeys upon infection with simian/human immunodeficiency virus (SHIV89.6P)

Recent evidence suggests that a CD8-mediated cytotoxic T cell response against the Tat protein of human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) controls primary infection after pathogenic virus challenge, and correlates with the status of long-term nonprogressor in humans. Due to the presence of unmethylated CpG sequences, DNA vaccination can boost the innate immunity driving more potent T cell-mediated immune responses. Therefore, cynomolgus monkeys were vaccinated with a tat-expressing vector containing defined unmethylated CpG sequences (pCV-tat). Here it is shown that the intramuscular inoculation of the pCV-tat contained primary infection with the highly pathogenic SHIV89.6P virus preventing the CD4(+) T cell decline in all the vaccinated monkeys. Undetectable virus replication and negative virus isolation correlated in all cases with the presence of anti-Tat CTLs. However, a CD8-mediated non cytolytic antiviral activity was also present in all protected animals. Of note, this activity was absent in the controls but was present in the monkey inoculated with the CpG-rich vector alone that was partially protected against viral challenge (i.e. no virus replication but positive virus isolation). These results suggest that a CTL response against Tat protects against primary infection by blocking virus replication at its early stage, in the absence of sterilizing immunity. Nevertheless, the boost of the innate immunity by CpG sequences can contribute to this protection both by driving more potent CTL responses and by inducing other CD8-mediated antiviral activities. Thus, the CpG-rich tat DNA vaccine may represent a promising candidate for preventive and therapeutic vaccination against AIDS.

Role of CD8+ cell-produced anti-viral factors in protective immunity in HIV-2-exposed but seronegative macaques resistant to intrarectal SIVsm challenge

The cell-mediated immune response is likely to be important in controlling HIV/SIV infection. There is evidence that beta-chemokines and other, as yet unknown, anti-viral factors play a role in host defence against HIV infection. We reported previously that HIV-2 exposed but seronegative cynomolgus macaques developed SIV-specific cytotoxic T lymphocytes and were resistant to mucosal SIV challenge. The aim of this study was to examine CD8+ cell-dependent production of beta-chemokines and other anti-viral factors in these macaques. The animals, selected from among 17 monkeys enrolled in two separate experiments, were either treated with an anti-viral drug or immunized passively with HIV-2 antibody-positive serum. Three of these monkeys were protected against repeated HIV-2 challenge and were also able to control SIV infection 3 years later. Control samples were obtained from four macaques that became SIV infected and from 39 naïve animals. The three resistant monkeys showed significantly higher production of RANTES and MIP-1alpha than the 39 naïve animals. In addition, SIV infection was suppressed by CD8+ cell culture supernatants of these monkeys. However, antibodies to chemokines only partially neutralized CD8+ cell-mediated SIV suppression indicating that the anti-viral activity observed in these monkeys was the result of combined action of several inhibitory factors.

DNA vaccination of macaques with several different Nef sequences induces multispecific T cell responses

CD8(+) T lymphocytes play a key role in controlling viremia during primary human immunodeficiency virus-1 and in maintaining disease-free infection. It has recently been shown that DNA immunization of rhesus monkeys can elicit strong, long-lived antigen-specific cytotoxic T lymphocyte (CTL) responses. In previous work, it was shown that macaque CTL responses to lipopeptide vaccination were directed against a limited number of epitopes. In the present study, we used the DNA immunization approach to enlarge T cell responses to several epitopes and to multiple isolates. We immunized macaques with a mixture of six plasmids reflecting the variability of Nef epitopic regions in the simian immunodeficiency virus (SIV) mac251 primary isolate. The Nef genes from viruses included in the SIVmac251 primary isolate were sequenced and the six selected sequences were individually subcloned into the pCI vector, under cytomegalovirus enhancer/promoter control, and injected into macaques. We show that DNA immunization with Nef sequences induced interferon-gamma (IFN-gamma) secreting cell responses directed against several regions of Nef. Reacting T cell lines were expanded in vitro and multispecific CTL responses mapping the 96-138 Nef region were analyzed. Several peptides recognized by CTL were identified and studies using peptides reflecting the variability of Nef indicated that all of the Nef variants were recognized in the 96-138 region. Moreover, CTL responses were directed against an immunodominant epitope located in a functional region within the Nef protein that is essential for viral replication. This work shows that our approach of DNA immunization with several sequences induced multispecific T cell responses recognizing variants included in the SIVmac251 primary isolate.

Chemokines and viruses: the dearest enemies

The relation between viruses and the chemokine system is characterized by a complex blend of enmity and attraction. Chemokines are key regulators of innate and adaptive immune responses against invading microorganisms, including viruses. They act not only as immune system "traffic officers," controlling leukocyte migration under both physiological and pathological conditions, but also as fine orchestrators that modulate the induction, amplification, and cytokine-secretion pattern of antiviral responses. However, viruses have succeeded in turning the chemokine system into an ally. During the course of a long parallel evolution, viruses have captured from their hosts the genetic information for encoding chemokines and chemokine receptors and have reprogrammed it for evading the control of the immune system. Moreover, selected viral agents, most notably primate immunodeficiency retroviruses, have adopted chemokine receptors as essential gateways for entry into their target cells. The endogenous secretion of chemokines is thus emerging as an important in vivo mechanism of viral control, which is potentially inducible by effective vaccines. The deepening knowledge of the interactions between viruses and chemokines may lead to novel therapeutic and preventive strategies for the control of viral and inflammatory diseases.

Protective immunity against feline immunodeficiency virus induced by inoculation with vif-deleted proviral DNA

To determine whether live-attenuated feline immunodeficiency virus (FIV) proviral DNA will induce protective immunity, a plasmid clone constructed with a FIV provirus containing a deletion in the viral accessory gene vif (FIV-pPPR-Deltavif) was inoculated as proviral DNA into four cats by the intramuscular route. After 43 weeks, these cats were boosted with the same proviral plasmid. Analysis of peripheral blood mononuclear cells at several time points after the primary and booster inoculations revealed no detectable virus or proviral DNA. At 6 weeks after the booster, immunized cats and additional naive control cats were challenged with a cell-free preparation of the infectious biological isolate FIV-PPR by the intraperitoneal route. Virus was detected after challenge in unvaccinated control cats but not in any of the FIV-pPPR-Deltavif-immunized cats. Both FIV Gag- and Env-specific cytotoxic T lymphocyte (CTL) activities were detected in peripheral blood cells of control cats after challenge infection, whereas only one of four cats immunized with FIV-pPPR-Deltavif DNA exhibited a measurable CTL response to Env following challenge. Although anti-Gag antibodies were not detected after both proviral DNA inoculation and challenge, anti-Env antibodies were found in FIV-pPPR-Deltavif-immunized cats after vaccination as well as after challenge. These findings indicate that inoculation with FIV-pPPR-Deltavif proviral DNA induced resistance to challenge with infectious FIV and that a vif deletion mutant may provide a relatively safe attenuated lentiviral vaccine.

Effects of in vivo CD8(+) T cell depletion on virus replication in rhesus macaques immunized with a live, attenuated simian immunodeficiency virus vaccine

The role of CD8(+) T lymphocytes in controlling replication of live, attenuated simian immunodeficiency virus (SIV) was investigated as part of a vaccine study to examine the correlates of protection in the SIV/rhesus macaque model. Rhesus macaques immunized for >2 yr with nef-deleted SIV (SIVmac239Deltanef) and protected from challenge with pathogenic SIVmac251 were treated with anti-CD8 antibody (OKT8F) to deplete CD8(+) T cells in vivo. The effects of CD8 depletion on viral load were measured using a novel quantitative assay based on real-time polymerase chain reaction using molecular beacons. This assay allows simultaneous detection of both the vaccine strain and the challenge virus in the same sample, enabling direct quantification of changes in each viral population. Our results show that CD8(+) T cells were depleted within 1 h after administration of OKT8F, and were reduced by as much as 99% in the peripheral blood. CD8(+) T cell depletion was associated with a 1-2 log increase in SIVmac239Deltanef plasma viremia. Control of SIVmac239Deltanef replication was temporally associated with the recovery of CD8(+) T cells between days 8 and 10. The challenge virus, SIVmac251, was not detectable in either the plasma or lymph nodes after depletion of CD8(+) T cells. Overall, our results indicate that CD8(+) T cells play an important role in controlling replication of live, attenuated SIV in vivo.

Generation of CD8+ T cell-generated suppressor factor and beta-chemokines by targeted iliac lymph node immunization in rhesus monkeys challenged with SHIV-89.6P by the rectal route

The targeted lymph node (TLN) immunization strategy was investigated in macaques, in order to determine the efficacy in generating secretory, systemic, and cellular immune responses, CD8+ T cell-generated suppressor factors, and beta-chemokines. TLN immunization of the rectal and genital mucosa-associated iliac lymph nodes (TILNs) was compared with axillary TLN immunization (TAxLN) using HIV-1 MN/LAI gp140env and SIV p27gag in alum. Significantly higher immune responses, as well as CD8+ T cell-generated anti-SIV factors and the beta-chemokines RANTES, MIP-1alpha, and MIP-1beta, were elicited by iliac as compared with axillary TLN immunization. The immune responses induced by TLN immunization were examined for their capacity to prevent rectal mucosal infection by the pathogenic dual-tropic SHIV-89.6P. Despite significant secretory, serum, cellular, and beta-chemokine responses, the macaques were infected by SHIV-89.6P. Whether the lack of protection was associated with the antigenic unrelatedness of SHIV-89.6P to the immunizing HIV-1 MN/LAI gp140 or to the virus utilizing CXCR4 to a much greater extent than CCR5, remains to be determined.

Multiepitopic B- and T-cell responses induced in humans by a human immunodeficiency virus type 1 lipopeptide vaccine

We have attempted to develop an anti-human immunodeficiency virus (HIV) lipopeptide vaccine with several HIV-specific long peptides modified by C-terminal addition of a single palmitoyl chain. A mixture of six lipopeptides derived from regulatory or structural HIV-1 proteins (Nef, Gag, and Env) was prepared. A phase I study was conducted to evaluate immunogenicity and tolerance in lipopeptide vaccination of HIV-1-seronegative volunteers given three injections of either 100, 250, or 500 microg of each lipopeptide, with or without immunoadjuvant (QS21). This report analyzes in detail B- and T-cell responses induced by vaccination. The lipopeptide vaccine elicited strong and multiepitopic B- and T-cell responses. Vaccinated subjects produced specific immunoglobulin G antibodies that recognized the Nef and Gag proteins. After the third injection, helper CD4(+)-T-cell responses as well as specific cytotoxic CD8(+) T cells were also obtained. These CD8(+) T cells were able to recognize naturally processed viral proteins. Finally, specific gamma interferon-secreting CD8(+) T cells were also detected ex vivo.

Simian immunodeficiency virus-specific cytotoxic T lymphocytes and protection against challenge in rhesus macaques immunized with a live attenuated simian immunodeficiency virus vaccine

In this study, we examined the role of simian immunodeficiency virus (SIV)-specific cytotoxic T lymphocytes (CTLs) in macaques immunized with an attenuated strain of simian immunodeficiency virus (SIVmac239Deltanef) in protection against pathogenic challenge with SIVmac251. Our results indicate that attenuated SIVmac239Deltanef can elicit specific CTL precursor cells (CTLp), but no correlation was observed between breadth or strength of CTLp response to structural proteins SIV-Env, -Gamg or -Pol (as measured by limiting dilution assay) and protection against infection. In one animal, we longitudinally followed the SIV-Gag-specific response to an MHC class I Mamu-A*01-restricted epitope p11C, C-M using a tetrameric MHC/peptide complex reagent. A low frequency of SIV p11C, C-M peptide-specific tetramer-reactive cells was present at the time of challenge but could be expanded in vitro. Surprisingly, the low level of Mamu-A*01/p11C, C-M-specific CTLs induced through attenuated SIVmac239Deltanef vaccination increased in the absence of detectable SIVmac251 or SIVmac239Deltanef proviral DNA. Overall, our results suggest that protection against infection in this model can be achieved through more than one mechanism, with SIV-specific CTLs being important in controlling SIVmac239Deltanef viral replication postchallenge.

Immunization with live attenuated simian immunodeficiency virus induces strong type 1 T helper responses and beta-chemokine production

Immunization with live attenuated simian immunodeficiency virus (SIV) strains has proved to be one of the most effective strategies to induce protective immunity in the SIV/macaque model. To better understand the role that CD4(+) T helper responses may play in mediating protection in this model, we characterized SIV-specific proliferative and cytokine responses in macaques immunized with live attenuated SIV strains. Macaques chronically infected with live attenuated SIV had strong proliferative responses to SIV proteins, with stimulation indices of up to 74. The magnitude of the proliferative response to SIV Gag varied inversely with the degree of attenuation; Gag-specific but not envelope-specific responses were lower in animals infected with more highly attenuated SIV strains. SIV-specific stimulation of lymphocytes from vaccinated macaques resulted in secretion of interferon-gamma, IL-2, regulated-upon-activation, normal T cells expressed and secreted (RANTES), macrophage inflammatory protein (MIP)-1alpha, and MIP-1beta but not IL-4 or IL-10. Intracellular flow cytometric analysis documented that, in macaques vaccinated with SIVmac239Deltanef, up to 2% of all CD4(+)T cells were specific for SIV p55. The ability of live attenuated SIV to induce a strong, sustained type 1 T helper response may play a role in the success of this vaccination approach to generate protection against challenge with wild-type SIV.