Most highly exposed seronegative men lack HIV-1-specific, IFN-gamma-secreting T cells

HIV-1 protective epitope-specific CD8+ T cells in HIV-1-exposed seronegative individuals

Although previous studies have reported HIV-1-specific T cell responses in HIV-1-exposed seronegative (HESN) individuals, there has been no detailed analysis of these T cells against HIV-1 infection. We investigated HIV-1-specific CD8+ T cell responses in 200 Japanese HESN men who have sex with men (MSM). T cell responses to 143 well-characterized HIV-1 epitope peptides were analyzed by intracellular cytokine staining assay consisting of 3-week cultures of PBMCs stimulated with peptides. HLA-B∗51:01-restricted Pol TI8-specific and HLA-A∗02:06-restricted Pol SV9-specific CD8+ T cells were identified in two and one individuals, respectively, whereas CD8+ T cells specific for other HLA-A∗02:06-restricted or HLA-B∗51:01 epitopes were not present in these individuals. These epitope-specific T cells recognized HIV-1-infected cells. Because these two epitopes were previously reported to be protective in HIV-1-infected individuals, these protective epitope-specific T cells might suppress HIV-1 replication in HESN-MSM individuals. The present study suggests the contribution of protective epitope-specific T cells to protection against HIV-1 infection.

Preexisting memory CD4+ T cells contribute to the primary response in an HIV-1 vaccine trial

Naive and memory CD4+ T cells reactive with human immunodeficiency virus type 1 (HIV-1) are detectable in unexposed, unimmunized individuals. The contribution of preexisting CD4+ T cells to a primary immune response was investigated in 20 HIV-1-seronegative volunteers vaccinated with an HIV-1 envelope (Env) plasmid DNA prime and recombinant modified vaccinia virus Ankara (MVA) boost in the HVTN 106 vaccine trial (clinicaltrials.gov NCT02296541). Prevaccination naive or memory CD4+ T cell responses directed against peptide epitopes in Env were identified in 14 individuals. After priming with DNA, 40% (8/20) of the elicited responses matched epitopes detected in the corresponding preimmunization memory repertoires, and clonotypes were shared before and after vaccination in 2 representative volunteers. In contrast, there were no shared epitope specificities between the preimmunization memory compartment and responses detected after boosting with recombinant MVA expressing a heterologous Env. Preexisting memory CD4+ T cells therefore shape the early immune response to vaccination with a previously unencountered HIV-1 antigen.

Role of Different Subpopulations of CD8+ T Cells during HIV Exposure and Infection

During HIV infection, specific responses exhibited by CD8⁺ T cells are crucial to establish an early, effective, and sustained viral control, preventing severe immune alterations and organ dysfunction. Several CD8⁺ T cells subsets have been identified, exhibiting differences in terms of activation, functional profile, and ability to limit HIV replication. Some of the most important CD8⁺ T cells subsets associated with viral control, production of potent antiviral molecules, and strong polyfunctional responses include Th1-like cytokine pattern and Tc17 cells. In addition, the expression of specific activation markers has been also associated with a more effective response of CD8⁺ T cells, as evidenced in HLA-DR⁺ CD38⁻ cells. CD8⁺ T cells in both, peripheral blood and gut mucosa, are particularly important in individuals with a resistant phenotype, including HIV-exposed seronegative individuals (HESNs), long-term non-progressors (LTNPs) and HIV-controllers. Although the role of CD8⁺ T cells has been extensively explored in the context of an established HIV-1 infection, the presence of HIV-specific cells with effector abilities and a defined functional profile in HESNs, remain poorly understood. Here, we reviewed studies carried out on different subpopulations of CD8⁺ T cells in relation with natural resistance to HIV infection and progression.

CCR5 expression, haplotype and immune activation in protection from infection in HIV-exposed uninfected individuals in HIV-serodiscordant relationships

Several host factors have been implicated in resistance to HIV infection in individuals who remain HIV-seronegative despite exposure. In a cohort of HIV-serodiscordant heterosexual couples, we investigated interactions between systemic inflammation and T-cell activation in resistance to HIV infection. Males and females in stable long-term relationships with either HIV-infected or uninfected partners were recruited, blood T-cell activation (CD38, HLA-DR, CCR5 and Ki67) and plasma cytokine concentrations were evaluated. The HIV-negative exposed individuals had significantly lower frequencies of CCR5⁺ CD4⁺ and CD8⁺ T cells than unexposed individuals. Mean fluorescence intensity of CCR5 expression on CD4⁺ T cells was significantly lower in HIV-negative exposed than unexposed individuals. Protective CCR5 haplotypes (HHA/HHF*2, HHF*2/HHF*2, HHC/HHF*2, HHA/HHA, HHA/HHC and HHA/HHD) tended to be over-represented in exposed compared with unexposed individuals (38% versus 28%, P = 0·58) whereas deleterious genotypes (HHC/HHD, HHC/HHE, HHD/HHE, HHD/HHD and HHE/HHE) were under-represented (26% versus 44%; P = 0·16). Plasma concentrations of interleukin-2 (P = 0·02), interferon-γ (P = 0·05) and granulocyte-macrophage colony-stimulating factor (P = 0·006) were lower in exposed compared with unexposed individuals. Activation marker expression and systemic cytokine concentrations were not influenced by gender. We conclude that the dominant signature of resistance to HIV infection in this cohort of exposed but uninfected individuals was lower T-cell CCR5 expression and plasma cytokine concentrations.

Detection of HIV-1-specific T-cell immune responses in highly HIV-exposed uninfected individuals by in-vitro dendritic cell co-culture

BACKGROUND

Although virus-specific responses are rarely detected by conventional approaches, we report here the detection of T-cell responses in HIV-exposed seronegative (HESN) patients by two distinct assays.

METHODS

HIV-specific T-cell responses were analyzed by enzyme-linked immunospot in peripheral blood mononuclear cells from HESN patients after a 48-h co-culture with boosted dendritic cells. Additionally, a boosted flow cytometry approach was used to capture antiviral T-cell responses. Host genetic factors and T-cell activation were also analyzed to assess their implication on HIV exposure.

RESULTS

Of the 45 HESN individuals tested, up to 11 (24.4%) showed at least one response to peptide pools covering HIV Gag and Nef. A positive correlation was observed between the intensity (P = 0.0022) and magnitude (P = 0.0174) of the response detected in the HESN, and the viral load of the HIV-positive partner. Moreover, the result from the boosted flow and cytomix analyses showed a dominant Th1-like response pattern against HIV antigens, especially in CD8 T-cell populations.

CONCLUSIONS

The combined use of our boosted dendritic cell technique with a boosted flow cytometric approach allows us both to detect specific HIV-positive responses in a higher percentage of HESN patients and to define specific effector function profiles. This study contributes to a better understanding of resistance to HIV infection.

Cellular immune correlates analysis of an HIV-1 preexposure prophylaxis trial

HIV-1-specific T-cell responses in exposed seronegative subjects suggest that a viral breach of the exposure site is more common than current transmission rates would suggest and that host immunity can extinguish subsequent infection foci. The Preexposure Prophylaxis Initiative (iPrEx) chemoprophylaxis trial provided an opportunity to rigorously investigate these responses in a case-control immunology study; 84 preinfection peripheral blood mononuclear cell samples from individuals enrolled in the iPrEx trial who later seroconverted were matched with 480 samples from enrolled subjects who remained seronegative from both the placebo and active treatment arms. T-cell responses to HIV-1 Gag, Protease, Integrase, Reverse Transcriptase, Vif, and Nef antigens were quantified for all subjects in an IFN-γ enzyme-linked immunospot (ELISpot) assay. IFN-γ responses varied in magnitude and frequency across subjects. A positive response was more prevalent in those who remained persistently HIV-1-negative for Gag (P = 0.007), Integrase (P < 0.001), Vif (P < 0.001), and Nef (P < 0.001). When correlated with outcomes in the iPrEx trial, Vif- and Integrase-specific T-cell responses were associated with reduced HIV-1 infection risk [hazard ratio (HR) = 0.36, 95% confidence interval (95% CI) = 0.19-0.66 and HR = 0.52, 95% CI = 0.28-0.96, respectively]. Antigen-specific responses were independent of emtricitabine/tenofovir disoproxil fumarate use. IFN-γ secretion in the ELISpot was confirmed using multiparametric flow cytometry and largely attributed to effector memory CD4+ or CD8+ T cells. Our results show that HIV-1-specific T-cell immunity can be detected in exposed but uninfected individuals and that these T-cell responses can differentiate individuals according to infection outcomes.

Testing for risk and protective trends in genetic analyses of HIV acquisition

Host genetics studies of HIV-1 acquisition are critically important for the identification of new targets for drug and vaccine development. Analyses of such studies typically focus on pairwise comparisons of three different groups: HIV-1 positive individuals, HIV-1 high-risk seronegative individuals, and population controls. Because there is a clear expectation of how gene frequencies of risk or protective alleles would be ordered in the three groups, we are able to construct a statistical framework that offers a consistent increase in power over a wide-range of the magnitude of risk/protective effects. In this paper, we develop tests that constrain the alternative hypothesis to appropriately reflect risk or protective trends jointly across the three groups and show that they lead to a substantial increase in power over the naive pairwise approach. We develop both likelihood-ratio and score statistics that test for genetic effects across the three groups while constraining the alternative hypothesis to reflect biologically motivated trends of risk or protection. The asymptotic distribution of both statistics (likelihood ratio and score) is derived. We investigate the performance of our approach via extensive simulation studies using a biologically motivated model of HIV-1 acquisition, and find that our proposed approach leads to an increase in power of roughly 10-28%. We illustrate our approach with an analysis of the effect of the CCR5Δ32 mutation on HIV acquisition.

Alternative effector-function profiling identifies broad HIV-specific T-cell responses in highly HIV-exposed individuals who remain uninfected

The characterization of host immune responses to human immunodeficiency virus (HIV) in HIV controllers and individuals with high exposure but seronegativity to HIV (HESN) is needed to guide the development of effective preventive and therapeutic vaccine candidates. However, several technical hurdles severely limit the definition of an effective virus-specific T-cell response. By using a toggle-peptide approach, which takes HIV sequence diversity into account, and a novel, boosted cytokine staining/flow cytometry strategy, we here describe new patterns of T-cell responses to HIV that would be missed by standard assays. Importantly, this approach also allows detection of broad and strong virus-specific T-cell responses in HESN individuals that are characterized by a T-helper type 1 cytokine-like effector profile and produce cytokines that have been associated with potential control of HIV infection, including interleukin 10, interleukin 13, and interleukin 22. These results establish a novel approach to improve the current understanding of HIV-specific T-cell immunity and identify cellular immune responses and individual cytokines as potential markers of relative HIV resistance. As such, the findings also help develop similar strategies for more-comprehensive assessments of host immune responses to other human infections and immune-mediated disorders.

HIV-1 specific IgA detected in vaginal secretions of HIV uninfected women participating in a microbicide trial in Southern Africa are primarily directed toward gp120 and gp140 specificities

Background

Many participants in microbicide trials remain uninfected despite ongoing exposure to HIV-1. Determining the emergence and nature of mucosal HIV-specific immune responses in such women is important, since these responses may contribute to protection and could provide insight for the rational design of HIV-1 vaccines.

Methods and Findings

We first conducted a pilot study to compare three sampling devices (Dacron swabs, flocked nylon swabs and Merocel sponges) for detection of HIV-1-specific IgG and IgA antibodies in vaginal secretions. IgG antibodies from HIV-1-positive women reacted broadly across the full panel of eight HIV-1 envelope (Env) antigens tested, whereas IgA antibodies only reacted to the gp41 subunit. No Env-reactive antibodies were detected in the HIV-negative women. The three sampling devices yielded equal HIV-1-specific antibody titers, as well as total IgG and IgA concentrations. We then tested vaginal Dacron swabs archived from 57 HIV seronegative women who participated in a microbicide efficacy trial in Southern Africa (HPTN 035). We detected vaginal IgA antibodies directed at HIV-1 Env gp120/gp140 in six of these women, and at gp41 in another three women, but did not detect Env-specific IgG antibodies in any women.

Conclusion

Vaginal secretions of HIV-1 infected women contained IgG reactivity to a broad range of Env antigens and IgA reactivity to gp41. In contrast, Env-binding antibodies in the vaginal secretions of HIV-1 uninfected women participating in the microbicide trial were restricted to the IgA subtype and were mostly directed at HIV-1 gp120/gp140.

Quantitative and qualitative differences in the T cell response to HIV in uninfected Ugandans exposed or unexposed to HIV-infected partners

HIV-exposed and yet persistently uninfected individuals have been an intriguing, repeated observation in multiple studies, but uncertainty persists on the significance and implications of this in devising protective strategies against HIV. We carried out a cross-sectional analysis of exposed uninfected partners in a Ugandan cohort of heterosexual serodiscordant couples (37.5% antiretroviral therapy naive) comparing their T cell responses to HIV peptides with those of unexposed uninfected individuals. We used an objective definition of exposure and inclusion criteria, blinded ex vivo and cultured gamma interferon (IFN-γ) enzyme-linked immunospot assays, and multiparameter flow cytometry and intracellular cytokine staining to investigate the features of the HIV-specific response in exposed versus unexposed uninfected individuals. A response rate to HIV was detectable in unexposed uninfected (5.7%, 95% confidence interval [CI] = 3.3 to 8.1%) and, at a significantly higher level (12.5%, 95% CI = 9.7 to 15.4%, P = 0.0004), in exposed uninfected individuals. The response rate to Gag was significantly higher in exposed uninfected (10/50 [20.%]) compared to unexposed uninfected (1/35 [2.9%]) individuals (P = 0.0004). The magnitude of responses was also greater in exposed uninfected individuals but not statistically significant. The average number of peptide pools recognized was significantly higher in exposed uninfected subjects than in unexposed uninfected subjects (1.21 versus 0.47; P = 0.0106). The proportion of multifunctional responses was different in the two groups, with a higher proportion of single cytokine responses, mostly IFN-γ, in unexposed uninfected individuals compared to exposed uninfected individuals. Our findings demonstrate both quantitative and qualitative differences in T cell reactivity to HIV between HESN (HIV exposed seronegative) and HUSN (HIV unexposed seronegative) subject groups but do not discriminate as to whether they represent markers of exposure or of protection against HIV infection.

The high frequency of HIV type 1-specific cellular immune responses in seronegative individuals with parenteral and/or heterosexual HIV type 1 exposure

Some individuals remain HIV seronegative despite repeated unprotected exposure to the virus. Recent observations led to a concept that acquired immunity plays a role in protection or at least in altered susceptibility to HIV-1 infection in highly exposed seronegative (ESN) individuals. Our aim was to study HIV-specific cellular immune responses induced in parenterally and/or heterosexually ESN individuals. Nine seronegative injection drug users (IDUs), 10 seronegative individuals, and nine of their HIV-positive sexual and/or IDU partners from the cohort of IDUs were included in the study. The discordant couples had unprotected sex, and some of seronegative partners also had parenteral exposure. Cell-mediated responses were measured in peripheral blood mononuclear cells (PBMCs) by ex vivo interferon (IFN)-γ-ELISpot and ICS combining IFN-γ, tumor necrosis factor (TNF)-α, and interleukin (IL)-2 after stimulation with four consensus peptide pools (Nef, Gag, RT, Env, subtype A-EE). Thirteen out of 19 (68%) seronegative study subjects had strong Nef peptide pool-specific ELISpot responses, three (16%) subjects responded against the Gag peptide pool, and one subject had an RT peptide pool response. Nef peptide pool responses in ESN were as high as in seropositive subjects. The multiple HIV-specific cytokine production in both CD4(+) and CD8(+) T cells was shown for several ESN subjects. The functional profiles of the immune responses were different between seronegative and HIV-positive study groups. Whether the observed cellular responses have any protective role against HIV needs to be further investigated.

Chemokines at mucosal barriers and their impact on HIV infection

Aside from representing a physical barrier and providing an unfavorable chemical milieu to viral and bacterial infections, mucosae of gut and female genital tract also contain organized lymphoid structures that support the initiation of anti-microbial immune responses, and more diffuse lymphoid tissues that represent immune effector mucosal sites. Local expression of specific chemokines orchestrates lymphoid cell trafficking and positioning in the mucosa-associated lymphoid tissues, leading to their efficient priming during antigenic stimulations as well as their specific homing back where they were primed. This review examines productions and roles of mucosae-specific chemokines in healthy and pathological conditions, as well as their possible positive and deleterious effects during mucosal HIV infection.

A distinct cytokine and chemokine profile at the genital mucosa is associated with HIV-1 protection among HIV-exposed seronegative commercial sex workers

The predominance of HIV-1 sexual transmission requires a greater understanding of the interaction between HIV-1 and the mucosal immune system. The study of HIV-1-exposed seronegative (HESN) individuals serves as a model to identify the correlates of protection and to aid in microbicide development. A total of 22 cytokines/chemokines were analyzed at the systemic and mucosal compartments in 57 HESN, 51 HIV-1-negative, and 67 HIV-1-infected commercial sex workers from Nairobi, Kenya. HESN individuals had significantly lower expression of monokine induced by interferon-γ (MIG), interferon-γ-induced protein 10 (IP-10), and interleukin-1α (IL-1α) in their genital mucosa compared with controls. HESN cytokine expression also distinctly correlates with mucosal antiproteases, suggesting that HESN individuals have a unique pattern of mucosal chemokine/cytokine expression, which may result in reduced trafficking at the mucosa. These data support the immune quiescence model of protection, whereby lower T-cell activation/recruitment at the mucosal compartment reduces HIV-1 target cell numbers and is an important component of natural protection from HIV-1.

Disparate associations of HLA class I markers with HIV-1 acquisition and control of viremia in an African population

BACKGROUND

Acquisition of human immunodeficiency virus type 1 (HIV-1) infection is mediated by a combination of characteristics of the infectious and the susceptible member of a transmission pair, including human behavioral and genetic factors, as well as viral fitness and tropism. Here we report on the impact of established and potential new HLA class I determinants of heterosexual HIV-1 acquisition in the HIV-1-exposed seronegative (HESN) partners of serodiscordant Zambian couples.

METHODOLOGY/PRINCIPAL FINDINGS

We assessed the relationships of behavioral and clinically documented risk factors, index partner viral load, and host genetic markers to HIV-1 transmission among 568 cohabiting couples followed for at least nine months. We genotyped subjects for three classical HLA class I genes known to influence immune control of HIV-1 infection. From 1995 to December 2006, 240 HESNs seroconverted and 328 remained seronegative. In Cox proportional hazards models, HLA-A*68:02 and the B*42-C*17 haplotype in HESN partners were significantly and independently associated with faster HIV-1 acquisition (relative hazards = 1.57 and 1.55; p = 0.007 and 0.013, respectively) after controlling for other previously established contributing factors in the index partner (viral load and specific class I alleles), in the HESN partner (age, gender), or in the couple (behavioral and clinical risk score). Few if any previously implicated class I markers were associated here with the rate of acquiring infection.

CONCLUSIONS/SIGNIFICANCE

A few HLA class I markers showed modest effects on acquisition of HIV-1 subtype C infection in HESN partners of discordant Zambian couples. However, the striking disparity between those few markers and the more numerous, different markers found to determine HIV-1 disease course makes it highly unlikely that, whatever the influence of class I variation on the rate of infection, the mechanism mediating that phenomenon is identical to that involved in disease control.

[Factors involved in resistance to human immunodeficiency virus infection]

Repeated exposure to human immunodeficiency virus (HIV) is not always associated with infection and a subset of individuals remains persistently as HIV-seronegative despite multiple episodes of HIV exposure. These individuals are called HIV-exposed seronegatives (ESN). Several genetic and immunological factors have been involved in this resistance to HIV acquisition. Genetic factors have been linked to genes encoding chemokine receptors and their natural ligands as well as genes of the major histocompatibility complex. Immunological factors include both innate and adaptive immunity. The study of ESN provides a unique opportunity to unveil the mechanisms of natural protection against viral infection. Their better understanding may lead to novel preventive and immune-therapeutic approaches, including vaccines.

Differences in HIV-specific T cell responses between HIV-exposed and -unexposed HIV-seronegative individuals

HIV-1-specific T lymphocyte responses in individuals exposed to HIV-1 but who remain persistently seronegative (HESNs) have been reported in some but not all previous studies. This study was designed to resolve unequivocally the question of whether HESNs make HIV-1-specific T cell responses. We performed a blind investigation to measure HIV-1-specific T cell responses in both HIV-1-serodiscordant couples and HIV-1-unexposed seronegative controls (HUSNs). We found low-frequency HIV-1-specific T cells in both HESNs and HUSNs but show that the response rates were higher over time in the former (P = 0.01). Furthermore, the magnitudes of the HIV-1-specific T cell responses were significantly higher among responding HESNs than among HUSNs over time (P = 0.002). In both groups, responses were mediated by CD4 T cells. The responses were mapped to single peptides, which often corresponded to epitopes restricted by multiple HLA-DR types that have previously been detected in HIV-1-infected patients. HIV-1-specific T cell responses in HUSNs and some HESNs likely represent cross-reactivity to self or foreign non-HIV-1 antigens. The significantly greater T cell responses in HESNs, including in two who were homozygous for CCR5Δ32, demonstrates that HIV-1-specific T cell responses can be induced or augmented by exposure to HIV-1 without infection.

Epigenetic control of IRF1 responses in HIV-exposed seronegative versus HIV-susceptible individuals

Not all individuals exposed to HIV become infected. Understanding why these HIV-exposed seronegative individuals remain uninfected will help inform the development of preventative measures against HIV infection. Interferon regulatory factor-1 (IRF1) plays a critical role both in host antiviral immunity and in HIV-1 replication. This study examined IRF1 expression regulation in the ex vivo peripheral blood mononuclear cells of HIV-exposed seronegative commercial sex workers who can be epidemiologically defined as relatively resistant to HIV infection (HIV-R), versus HIV-uninfected, susceptible controls (HIV-S). Whereas HIV-susceptible individuals demonstrated a biphasic, prolonged increase in IRF1 expression after interferon-γ stimulation, HIV-R individuals demonstrated a robust, but transient response. We also found that the IRF1 promoter in HIV-R was primed by increased basal histone deacetylase-2 binding, independently of transcription regulators, STAT1 and nuclear factor-κB/p65, implicating an epigenetic silencing mechanism. Interestingly, the transitory IRF1 response in HIV-R was sufficient in comparable regulation of interleukin-12 and interleukin-4 expression compared with the HIV-susceptible controls. This is the first study characterizing IRF1 responsiveness in individuals who demonstrate altered susceptibility to HIV infection. These data suggest that transitory IRF1 responsiveness in HIV-R may be one of the key contributors to the altered susceptibility to HIV infection during the early stages of primary HIV infection.

Lack of detectable HIV-1-specific CD8(+) T cell responses in Zambian HIV-1-exposed seronegative partners of HIV-1-positive individuals

Human immunodeficiency virus type 1 (HIV-1)–specific T cell responses were characterized in a blinded study involving infected individuals and their seronegative exposed uninfected (EU) partners from Lusaka, Zambia. HIV-1–specific T cell responses were detected ex vivo in all infected individuals and amplified, on average, 27-fold following in vitro expansion. In contrast, no HIV-1–specific T cell responses were detected in any of the EU partners ex vivo or following in vitro expansion. These data demonstrate that the detection of HIV-1–specific T cell immunity in EU individuals is not universal and that alternative mechanisms may account for protection in these individuals.

Low-level exposure to HIV induces virus-specific T cell responses and immune activation in exposed HIV-seronegative individuals

HIV-specific T cells response and T cell activation are frequently seen in exposed seronegative individuals (ESN). In this study, we report HIV-specific response and level of T cell activation in ESN partners of HIV-infected patients presenting low or undetectable levels of HIV-RNA. We evaluated 24 HIV-serodiscordant couples. ESN were classified into three categories of exposure to HIV (very low, low, and moderate-high), considering levels of HIV-RNA in their infected partner and frequency of sexual high-risk practices within the last 12 mo. HIV-specific T cell responses and activation levels in T cell subsets were evaluated by flow cytometry. We reported that 54% of ESN had detectable HIV-specific T cells response, being the highest prevalence seen in the low exposure group (64%). Several T cell subsets were significantly increased in ESN when compared with controls: CD4(+)CD38(+) (p = 0.006), CD4(+)HLA-DR(-)CD38(+) (p = 0.02), CD4(+)CD45RA(+)CD27(+)HLA-DR(-)CD38(+) (p = 0.002), CD8(+)CD45RA(+)CD27(+)CD38(-)HLA-DR(+) (p = 0.02), and CD8(+)CD45RA(+)CD27(-)CD38(+)HLA-DR(+) (p = 0.03). Activation of CD8(+) T cells was increased in ESN with detectable HIV T cell responses compared with ESN lacking these responses (p = 0.04). Taken together, these results suggest that persistent but low sexual HIV exposure is able to induce virus-specific T cells response and immune activation in a high proportion of ESN, suggesting that virus exposure may occur even in conditions of maximal viral suppression in the HIV-infected partner.

Acute mucosal pathogenesis of feline immunodeficiency virus is independent of viral dose in vaginally infected cats

BACKGROUND

The mucosal pathogenesis of HIV has been shown to be an important feature of infection and disease progression. HIV-1 infection causes depletion of intestinal lamina propria CD4+ T cells (LPL), therefore, intestinal CD4+ T cell preservation may be a useful correlate of protection in evaluating vaccine candidates. Vaccine studies employing the cat/FIV and macaque/SIV models frequently use high doses of parenterally administered challenge virus to ensure high plasma viremia in control animals. However, it is unclear if loss of mucosal T cells would occur regardless of initial viral inoculum dose. The objective of this study was to determine the acute effect of viral dose on mucosal leukocytes and associated innate and adaptive immune responses.

RESULTS

Cats were vaginally inoculated with a high, middle or low dose of cell-associated and cell-free FIV. PBMC, serum and plasma were assessed every two weeks with tissues assessed eight weeks following infection. We found that irrespective of mucosally administered viral dose, FIV infection was induced in all cats. However, viremia was present in only half of the cats, and viral dose was unrelated to the development of viremia. Importantly, regardless of viral dose, all cats experienced significant losses of intestinal CD4+ LPL and CD8+ intraepithelial lymphocytes (IEL). Innate immune responses by CD56+CD3- NK cells correlated with aviremia and apparent occult infection but did not protect mucosal T cells. CD4+ and CD8+ T cells in viremic cats were more likely to produce cytokines in response to Gag stimulation, whereas aviremic cats T cells tended to produce cytokines in response to Env stimulation. However, while cell-mediated immune responses in aviremic cats may have helped reduce viral replication, they could not be correlated to the levels of viremia. Robust production of anti-FIV antibodies was positively correlated with the magnitude of viremia.

CONCLUSIONS

Our results indicate that mucosal immune pathogenesis could be used as a rapid indicator of vaccine success or failure when combined with a physiologically relevant low dose mucosal challenge. We also show that innate immune responses may play an important role in controlling viral replication following acute mucosal infection, which has not been previously identified.

Repeated rectal SHIVSF162P3 exposures do not consistently induce sustained T cell responses prior to systemic infection in the repeat-low dose preclinical macaque model

The macaque model of repeated SHIV exposures is increasingly used as a preclinical tool to evaluate biomedical HIV intervention strategies. It is unclear whether multiple virus exposures induce immune responses in macaques, as documented in uninfected individuals repeatedly exposed to HIV. We here address whether repeated, rectal SHIV(SF162P3) exposures lead to systemic T cell activation in 12 rhesus macaques, and whether this is associated with increased infection resistance. Eight macaques became systemically infected after 2-7 exposures, three macaques were less susceptible (infection after 10-12 exposures), and one macaque remained uninfected after 14 exposures. PBMCs were retrospectively monitored for increases in T cell activation by analyzing the proportion of CD8(+) T cells, recently activated or proliferated T cells (markers CD38, Ki67), a marker for cytotoxicity (granzyme B), or T cell-produced plasma cytokines (IFN-gamma, RANTES, IL-2). Repeated virus exposures did not induce sustained, potent, or diverse T cell responses prior to systemic infection. Some changes occurred in the analyzed parameters during repeated virus exposures, but similar T cell activities were also observed in five SHIV-unexposed control macaques. Thus, we found no evidence that delayed infection or resistance to infection was associated with systemic, long-lasting, protective T cell responses to repeated rectal virus exposures. Our results provide further insights into the repeat exposure macaque model. We find that this model can be used for testing biomedical prevention strategies without concern of eliciting a systemic vaccination effect.

Preinfection human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes failed to prevent HIV type 1 infection from strains genetically unrelated to viruses in long-term exposed partners

Understanding the mechanisms underlying potential altered susceptibility to human immunodeficiency virus type 1 (HIV-1) infection in highly exposed seronegative (ES) individuals and the later clinical consequences of breakthrough infection can provide insight into strategies to control HIV-1 with an effective vaccine. From our Seattle ES cohort, we identified one individual (LSC63) who seroconverted after over 2 years of repeated unprotected sexual contact with his HIV-1-infected partner (P63) and other sexual partners of unknown HIV-1 serostatus. The HIV-1 variants infecting LSC63 were genetically unrelated to those sequenced from P63. This may not be surprising, since viral load measurements in P63 were repeatedly below 50 copies/ml, making him an unlikely transmitter. However, broad HIV-1-specific cytotoxic T-lymphocyte (CTL) responses were detected in LSC63 before seroconversion. Compared to those detected after seroconversion, these responses were of lower magnitude and half of them targeted different regions of the viral proteome. Strong HLA-B27-restricted CTLs, which have been associated with disease control, were detected in LSC63 after but not before seroconversion. Furthermore, for the majority of the protein-coding regions of the HIV-1 variants in LSC63 (except gp41, nef, and the 3' half of pol), the genetic distances between the infecting viruses and the viruses to which he was exposed through P63 (termed the exposed virus) were comparable to the distances between random subtype B HIV-1 sequences and the exposed viruses. These results suggest that broad preinfection immune responses were not able to prevent the acquisition of HIV-1 infection in LSC63, even though the infecting viruses were not particularly distant from the viruses that may have elicited these responses.

Identification of a WT1 protein-derived peptide, WT1, as a HLA-A 0206-restricted, WT1-specific CTL epitope

The Wilms' tumor gene WT1 is overexpressed in various kinds of hematopoietic malignancies as well as solid cancers, and this protein has been demonstrated to be an attractive target antigen for cancer immunotherapy. WT1-specific CTL epitopes with a restriction of HLA-A 2402 or HLA-A 0201 have been already identified. In the present study it has been demonstrated that a 9-mer WT1-derived WT1(187) peptide, which had already been shown to elicit a WT1-specific CTL response with a restriction of HLA-A 0201, can also elicit a CTL response with a restriction of HLA-A 0206. In all three different HLA-A 0206(+) healthy donors examined, WT1(187) peptide-specific CTL could be generated from peripheral blood mononuclear cells, and the CTL showed cytotoxic activity that depended on dual expression of WT1 and HLA-A 0206 molecules. The present study describes the first identification of a HLA-A 0206-restricted, WT1-specific CTL epitope. The present results should help to broaden the application of WT1 peptide-based immunotherapy from only HLA-A 0201-positive to HLA-A 0206-positive cancer patients as well.

Impaired viral entry cannot explain reduced CD4+ T cell susceptibility to HIV type 1 in certain highly exposed individuals

Rare individuals report repeated unprotected HIV-1 sexual exposures, yet remain seronegative for years. We investigated the possibility that reduced in vitro CD4(+) T cell susceptibility to HIV-1 infection protects such highly exposed seronegative (ES) individuals. Susceptibility to three R5-tropic HIV-1 isolates, regardless of inoculating dose, was remarkably similar between 81 ES and 33 low-risk controls. In 94% (99/105) of donors, we observed a 1.36 log-unit range in HIV-1(JR-CSF) production, with similar results for HIV-1(1192). The median frequency of intracellular Gag(+) T cells after single-round infection was similar in ES (5.2%) and controls (7.2%), p = 0.456. However, in repeated testing, CD4(+) T cells from two controls (6.1%) and four ES (4.9%) exhibited a 10- to 2500-fold reduction in HIV-1 production and required 5- to 12-fold greater HIV-1(1192) and HIV-1(JR-CSF) inocula to establish infection (TCID(50)). Reduced viral entry cannot explain the low producer phenotype; no differences in CCR5 receptor density or beta-chemokine production were observed. In conclusion, we have identified a remarkably narrow range of HIV-1 susceptibility in seronegative donors regardless of risk activity, which can be applied as a benchmark to assess vaccine-induced antiviral effector activities. However, CD4(+) T cells from a subset of individuals demonstrated reduced HIV-1 susceptibility unexplained by impaired entry, lending support to the possibility that cellular restriction of HIV-1 may account for continued seronegativity in some of those having repeated sexual exposure. Identifying the host-virus interactions responsible for diminished in vitro susceptibility may contribute to the development of novel therapeutic strategies.

Potentially exposed but uninfected individuals produce cytotoxic and polyfunctional human immunodeficiency virus type 1-specific CD8(+) T-cell responses which can be defined to the epitope level

We measured CD8(+) T-cell responses in 12 potentially exposed but uninfected men who have sex with men by using cytokine flow cytometry. Four of the individuals screened exhibited polyfunctional immune responses to human immunodeficiency virus type 1 Gag or Vif. The minimum cytotoxic T lymphocyte epitope was mapped in one Gag responder.

Not just sheer luck! Immune correlates of protection against HIV-1 infection

Susceptibility to HIV infection is widely different among individuals, and it is known that individuals can be identified who are repeatedly exposed to HIV but in whom neither infection nor disease are seen. The possibility that sheer luck is not the only determinant of this phenomenon begun to be considered in 1989 when it was reported that T cell responses to HIV proteins could be detected in antibody-negative sexual partners of known HIV-positive men. In this review, we will summarize the body of knowledge that stemmed from that first observation.

HIV-specific antibodies but not t-cell responses are associated with protection in seronegative partners of HIV-1-infected individuals in Cambodia

To study biological factors related to protection against HIV-1 infection in Cambodia, we recruited 48 partners of HIV-1-infected patients who remained uninfected (exposed uninfected individuals, EUs) despite unprotected sexual intercourse for more than 1 year and 49 unexposed controls (UCs). HIV-1-specific antibodies (IgA anti-gp41 and IgG anti-CD4-gp120 complex), T-cell responses, and cellular factors that may be involved in protection (peripheral blood mononuclear cell [PBMC] resistance to HIV-1 infection and beta-chemokine production) were evaluated. Anti-HIV-1 antibodies were higher in EUs than those in UCs (P = 0.01 and P = 0.04 for anti-gp41 and anti-CD4-gp120, respectively). We observed a decreased susceptibility to a primary Cambodian isolate, HIV-1KH019, in EU PBMCs as compared with UC PBMCs (P = 0.03). A weak T-cell response to one pool of HIV-1 Gag peptides was found by ELISpot in 1 of 19 EUs. Whereas T-cell specific immunity was not associated to protection, our results suggest that HIV-specific humoral immunity and reduced cell susceptibility to infection may contribute to protection against HIV-1 infection in Cambodian EUs.

HIV vaccines

A prophylactic vaccine for HIV-1 is badly needed. Despite 20 years of effort, it is still a long way off. However, considerable progress has been made in understanding the problem. The virus envelope has evolved to evade neutralizing antibodies in an extraordinary way, yet a vaccine that can stimulate such antibodies remains the best hope. Anti-HIV-1 T cell responses are evaded by continuous mutation of the virus. Vaccine strategies that concentrate on stimulating T cell immunity will at best generate broadly reactive and persisting T cell responses that can suppress virus without preventing infection, limiting or preventing the damage the virus causes. The SIV macaque models give encouragement that this is possible, but they need further understanding. Therapeutic vaccination should also be considered.

Understanding the "lucky few": the conundrum of HIV-exposed, seronegative individuals

It has been known for many years that not all individuals who are repeatedly exposed to HIV-1 show evidence of viral replication, seroconvert, and eventually develop disease. Quite apart from those who seroconvert but progress slowly to AIDS (ie, slow progressors, long-term nonprogressors, elite controllers), these rare, exposed seronegatives either resist infection or harbor extremely low levels of virus that may be detected only using ultrasensitive methods (occult infection). The correlates of protection that confer this unique status to a tiny minority of HIV-exposed individuals remain a subject of intense interest, investigation, and controversy, as no single genetic or immunologic parameter has yet been able to fully explain this phenomenon. However, there is general consensus that studying these individuals may provide invaluable information to aid in the design of vaccines and therapeutic approaches. This review describes the major findings on this important topic, with a focus on immunologic studies.

Interactive association of proviral load and IFN-gamma-secreting T cell responses in HIV-1C infection

We investigated the interactive relationship between proviral DNA load and virus-specific IFN-gamma-secreting T cell responses in HIV-1C infection. The presence or absence of correlation, and inverse or direct type of correlation, if any, were dependent on targeted viral gene product. Responses to Gag p24 or to Pol were associated with lower proviral DNA load. Associations between proviral DNA load and T cell responses did not necessarily mirror relationships between plasma RNA load and T cell responses. An interaction analysis showed a synergy in that lower proviral DNA and lower plasma RNA load were associated with high Gag p24-specific IFN-gamma-secreting T cell response (interaction test P = 0.0003). Our findings support the idea that HIV proteins have differential value for vaccine design, and suggest that, for HIV-1C, Gag p24 may be one of the most attractive regions to include in vaccine designs to control both plasma RNA load and cell-associated proviral DNA load.

Global human genetics of HIV-1 infection and China

Genetic polymorphisms in human genes can influence the risk for HIV-1 infection and disease progression, although the reported effects of these alleles have been inconsistent. This review highlights the recent discoveries on global and Chinese genetic polymorphisms and their association with HIV-1 transmission and disease progression.

[Mechanisms of resistance to sexual transmission of HIV-1]

Sexual transmission is the most common pathway for HIV-1; nevertheless some individuals remain seronegative despite repeated high risk sexual exposure. These were grouped in cohorts of "highly exposed but persistently seronegative" individuals, mostly prostitutes and flailing couples. Three lines of defence were observed in these cohorts. The first one is the mucosal barrier, the determining factors of which are the type of epithelium (monolayer or multilayer), epithelial integrity, and the pre-existing microflora. The second one is linked to innate immunity directly related to the genetic and/or immune predispositions of the individual: mutations affecting the CCR5 chemokine receptor, secretion of protective soluble factors, and particular HLA alleles. The third one is acquired immunity via the mechanisms of humoral and/or specific cellular immunity. These studies suggest anti HIV-1 vaccinal strategies aiming at a local immunization combining the different types of responses observed in these individuals.

Combined effect of CCR5-Delta32 heterozygosity and the CCR5 promoter polymorphism -2459 A/G on CCR5 expression and resistance to human immunodeficiency virus type 1 transmission

Exposed seronegative individuals (ES) with persistent high-risk sexual behavior may be less susceptible to human immunodeficiency virus type 1 (HIV-1) infection because they carry the chemokine receptor (CR) gene alleles CCR5 open reading frame (ORF) Delta32, CCR5 promoter -2459G, or CCR2 ORF 64I (CCR2-64I), all of which have been found to diminish HIV-1 infectivity and/or disease progression. To investigate this, we determined the haplotypes for these three genetic loci in 93 ES and 247 low-risk control individuals. To test if protective haplotypes exert their effect by modulating CR expression, we measured the protein expression of CCR5 and CXCR4 on circulating CD4+ T cells and CD14+ monocytes in 71 ES and 92 controls. To avoid investigator bias, the analysis was performed without knowledge of each subject's risk and genotype. The CCR5 -2459G allele was significantly enriched in ES Caucasian men, who constituted the majority (84%) of the ES cohort, compared to the control Caucasian men (P = 0.02). This increase was mostly attributable to a higher frequency of the -2459 A/G versus the -2459 A/A genotype in individuals heterozygous for the delta32 allele (P = 0.012). No protective influence of the CCR2-64I allele was observed. The haplotypes CCR5 ORF delta32/CCR5 -2459A (in complete linkage disequilibrium) and CCR5 ORF wt/CCR5 -2459G had a cumulative negative effect on the expression of CCR5, since we measured significantly reduced CCR5 densities on both T-helper cells and monocytes only when both haplotypes were present. Densities of CCR5 on lymphocytes and monocytes were correlated (r = 0.59; P < 0.0001), indicating concordance of CCR5 expression patterns across different cell types. We conclude that the CCR5 ORF delta32/wt-CCR5 -2459 A/G genotype combination offers an advantage in resisting sexual HIV-1 transmission and that this effect is mediated by a relative paucity of CCR5 on potential target cells of HIV-1.

Insights into the role of host genetic and T-cell factors in resistance to HIV transmission from studies of highly HIV-exposed Thais

Studies of resistance to HIV-1 transmission are likely to be valuable for the design of vaccines and other efforts to prevent HIV. Here, we review the T-cell and genetic factors associated with resistance to HIV-1 transmission in studies of highly exposed but persistently seronegative (HEPS) women from northern Thailand. Women were enrolled in two sex-worker studies and in a discordant couple study. We performed Cr51 cytotoxic T lymphocyte (CTL), interferon-gamma (IFN-gamma) ELISPOT, and proliferation assays as well as genetic studies, including HLA-class I typing. CTL and ELISPOT studies showed a skewing of T-cell responses to conserved HIV-1 proteins in HEPS, but not in HIV-1-seropositive women. T-cell responses were extremely long-lived in some HEPS women. In the two sex-worker studies, HLA-A11 was associated with resistance to HIV-1 transmission. These data provide promise for the ability of CTL to control HIV and emphasize the importance of developing HIV vaccines that stimulate strong, long-lasting Tcell responses.

HIV-1 Env-specific cytotoxic T-lymphocyte responses in exposed, uninfected Kenyan sex workers: a prospective analysis

The prospective significance of HIV-specific cytotoxic T lymphocyte (CTL) responses in highly exposed, persistently seronegative populations is unknown. In 1996-1997 we screened for CTL responses against HIV clade B Env in 39 recently enrolled Kenyan female sex workers, and followed these women prospectively. Annual HIV incidence was 5.8%. CTL were independently associated with age and recent HIV-1 exposure,but were not prospectively associated with protection in a multivariable model that included HIV-1 exposure and duration of sex work.

Peptide mapping of feline immunodeficiency virus by IFN-gamma ELISPOT

Interferon-gamma (IFN-gamma) enzyme-linked immunospot (ELISPOT) has become an important tool in studying antigen-specific T lymphocyte responses. Soluble peptides can be used to map T-cell epitopes, providing information that is useful in the design and evaluation of vaccines as well as studies of immunopathogenesis. To date, this assay has not been widely utilized in feline immunodeficiency virus (FIV) research. We have developed a feline IFN-gamma ELISPOT assay and used it to determine FIV-specific T-cell epitopes recognized by infected cats. A panel of 331 peptides, 15 amino acids in length and overlapping by 10 residues was synthesized. The peptide library spanned the FIV structural (Gag), envelope (Env), reverse transcriptase (RT), and open-reading-frame A (OrfA) proteins. Initially, 34 pools, containing 7-10 peptides each were screened by IFN-gamma ELISPOT against peripheral blood mononuclear cells (PBMC) from eight cats chronically infected with the NCSU(1) molecular clone of FIV and four uninfected control cats. Individual peptides from pools recognized by FIV+ cats were then evaluated and optimal peptides were combined into pools representing Gag, Env, RT, and OrfA. A higher percentage of FIV infected cats were identified as responders against the peptide pools when using fresh PBMC as compared to cryopreserved PBMC. In vitro restimulation of cryopreserved PBMC with the peptide pools improved the sensitivity of the assay to similar levels as observed from fresh samples. Individual peptides used in the pools were generally found to stimulate CD8+ T-cells more efficiently than CD4+ T-cells. Comparison of the peptide sequences to representative FIV sequences from clades A-D showed conservation was high among Gag and RT peptides, variable among Env peptides and low for OrfA peptides. The IFN-gamma ELISPOT assay and FIV-specific peptide pools we describe here will be useful in assessing cell-mediated responses to experimental FIV vaccines.

Correlates of resistance to HIV-1 infection in homosexual men with high-risk sexual behaviour

OBJECTIVE

To investigate possible correlates of HIV resistance in participants from the Amsterdam Cohort of Homosexual men who have remained HIV seronegative despite high-risk sexual behaviour.

DESIGN/METHODS

We studied in vitro HIV-1 susceptibility and adaptive and innate immunity in 29 high-risk seronegative (HRSN) and 15 HIV-negative pre-seroconversion (pre-SC) homosexual men from the same Amsterdam Cohort Study (ACS) who seroconverted to HIV-1 positive during active follow-up. Host genetics were compared between HRSN and HIV-positive ACS participants.

RESULTS

We found lower in vitro susceptibility for a CCR5-using (R5) HIV-1 variant, higher RANTES production levels, but no difference in coreceptor expression in HRSN as compared with pre-SC controls. Reduced R5 in vitro susceptibility of two HRSN tested was restored to normal levels by addition of antibodies against beta-chemokines. A higher proportion of HRSN carried the SDF-1 3'A variant and HLA-A*11, A*31 and Cw*15 alleles. ELIspot analysis with HIV-1 peptide stimulation revealed low frequencies of HIV-1-specific CD8 interferon-gamma producing cytotoxic T cells in both HRSN and pre-SC controls.

CONCLUSIONS

Low in vitro R5 susceptibility of cells from the HRSN men was due to beta-chemokine mediated inhibition of virus replication. The presence of HIV-1 specific cytotoxic T cells in both HRSN and pre-SC participants may signify exposure to the virus rather than protection from infection. Host genetic characteristics and other factors affecting innate immunity may contribute to differential resistance to HIV-1 infection among exposed seronegative individuals.