Polymorphisms in HLA class I genes associated with both favorable prognosis of human immunodeficiency virus (HIV) type 1 infection and positive cytotoxic T-lymphocyte responses to ALVAC-HIV recombinant canarypox vaccines

Exceptional, naturally occurring HIV-1 control: Insight into a functional cure

Exceptional elite controllers represent an extremely rare group of people with HIV-1 (PWH) who exhibit spontaneous, high-level control of viral replication below the limits of detection in sensitive clinical monitoring assays and without disease progression in the absence of antiretroviral therapy for prolonged periods, frequently exceeding 25 years. Here, we discuss the different cases that have been reported in the scientific literature, their unique genetic, virological, and immunological characteristics, and their relevance as the best model for the functional cure of HIV-1.

HLA A*32 is associated to HIV acquisition while B*44 and B*53 are associated with protection against HIV acquisition in perinatally exposed infants

BACKGROUND

Human leukocyte antigen (HLA) molecules play a key role in the cellular immune system. They may be determinants of mother-to-child transmission which is the driving force in pediatric HIV infection. We intended to look at the impact of the distribution of these polymorphic HLA genes in the mother-to-child transmission (MTCT) of HIV in Cameroon.

METHODS

A total of 156 mother-baby pairs were enrolled in three hospitals of Yaounde, capital of Cameroon. After the extraction of the DNA from blood samples using the Qiagen Kit as per manufacturer' instructions, the polymorphism of the HLA class 1 ABC was determined using the PCR- sequence specific primers assay.

RESULTS

The distribution of HLA class 1 revealed that none of the allele studied was associated with transmitters or non-transmitters, so was not implicated in transmission. The regression analysis showed that HLA A*32 [OR 0.062 (CI; 0.0075 to 0.51)] is associated with HIV acquisition while HLA B*44 [OR 0.47 (CI; 0.21 to 1.14)] and HLA B*53 [OR; 0.14 (CI; 0.018 to 1.22)] were implicated in reducing the acquisition of HIV by infants. The homozygosity of locus C [OR 6.99 (CI; 1.81 to 26.88), p = 0.0027] was found as a risk factor for the acquisition, while the A*32-B*44 haplotype [OR 10.1 (CI 1.17 to 87.87), p = 0.03] was a risk factor for the transmission.

CONCLUSION

This study has found that HLA A*32, B*44 and B*53 have an impact in MTCT outcomes. The homozygosity of locus C and the A*32-B*44 haplotype were risk factors for acquisition and transmission respectively.

Association of Diverse Genotypes and Phenotypes of Immune Cells and Immunoglobulins With the Course of HIV-1 Infection

Disease progression among HIV-1-infected individuals varies widely, but the mechanisms underlying this variability remains unknown. Distinct disease outcomes are the consequences of many factors working in concert, including innate and adaptive immune responses, cell-mediated and humoral immunity, and both genetic and phenotypic factors. Current data suggest that these multifaceted aspects in infected individuals should be considered as a whole, rather than as separate unique elements, and that analyses must be performed in greater detail in order to meet the requirements of personalized medicine and guide optimal vaccine design. However, the wide adoption of antiretroviral therapy (ART) influences the implementation of systematic analyses of the HIV-1-infected population. Consequently, fewer data will be available for acquisition in the future, preventing the comprehensive investigations required to elucidate the underpinnings of variability in disease outcome. This review seeks to recapitulate the distinct genotypic and phenotypic features of the immune system, focusing in particular on comparing the surface proteins of immune cells among individuals with different HIV infection outcomes.

Safety and Immunogenicity of a Randomized Phase 1 Prime-Boost Trial With ALVAC-HIV (vCP205) and Oligomeric Glycoprotein 160 From HIV-1 Strains MN and LAI-2 Adjuvanted in Alum or Polyphosphazene

BACKGROUND

Prime-boost regimens comprising ALVAC-HIV (prime) and human immunodeficiency virus type 1 (HIV) Env (boost) induce HIV-specific neutralizing antibody and cell-mediated immune responses, but the impact of boost schedule and adjuvant requires further definition.

METHODS

A phase 1 trial was conducted. In part A (open label), 19 volunteers received oligomeric glycoprotein 160 from HIV strains MN and LAI-2 (ogp160 MN/LAI-2) with dose escalation (25, 50, 100 μg) and either polyphosphazene (pP) or alum adjuvant. In part B, 72 volunteers received either placebo (n=12) or recombinant canarypox virus expressing HIV antigens (ALVAC-HIV [vCP205]) with different doses and schedules of ogp160 MN/LAI-2 in pP or alum (n = 60).

RESULTS

The vaccines were safe and well tolerated, with no vaccine-related serious adverse events. Anti-gp70 V1V2 antibody responses were detected in 17 of 19 part A volunteers (89%) and 10%-100% of part B volunteers. Use of a peripheral blood mononuclear cell-based assay revealed that US-1 primary isolate neutralization was induced in 2 of 19 recipients of ogp160 protein alone (10.5%) and 5 of 49 prime-boost volunteers (10.2%). Among ogp160 recipients, those who received pP were more likely than those who received alum to have serum that neutralized tier 2 viruses (12% vs 0%; P = .015).

CONCLUSIONS

Administration of ogp160 with pP induces primary isolate tier 2 neutralizing antibody responses in a small percentage of volunteers, demonstrating proof of concept and underscoring the importance of further optimization of prime-boost strategies for HIV infection prevention.

CLINICAL TRIALS REGISTRATION

NCT00004579.

Comparative Analysis of the Endogenous Peptidomes Displayed by HLA-B*27 and Mamu-B*08: Two MHC Class I Alleles Associated with Elite Control of HIV/SIV Infection

Indian rhesus macaques are arguably the most reliable animal models in AIDS research. In this species the MHC class I allele Mamu-B*08, among others, is associated with elite control of SIV replication. A similar scenario is observed in humans where the expression of HLA-B*27 or HLA-B*57 has been linked to slow or no progression to AIDS after HIV infection. Despite having large differences in their primary structure, it has been reported that HLA-B*27 and Mamu-B*08 display peptides with sequence similarity. To fine-map the Mamu-B*08 binding motif and assess its similarities with that of HLA-B*27, we affinity purified the peptidomes bound to these MHC class I molecules and analyzed them by LC-MS, identifying several thousands of endogenous ligands. Sequence analysis of both sets of peptides revealed a degree of similarity in their binding motifs, especially at peptide position 2 (P2), where arginine was present in the vast majority of ligands of both allotypes. In addition, several differences emerged from this analysis: (i) ligands displayed by Mamu-B*08 tended to be shorter and to have lower molecular weight, (ii) Mamu-B*08 showed a higher preference for glutamine at P2 as a suboptimal binding motif, and (iii) the second major anchor position, found at PΩ, was much more restrictive in Mamu-B*08. In this regard, HLA-B*27 bound efficiently peptides with aliphatic, aromatic (including tyrosine), and basic C-terminal residues while Mamu-B*08 preferred peptides with leucine and phenylalanine in this position. Finally, in silico estimations of binding efficiency and competitive binding assays to Mamu-B*08 of several selected peptides revealed a good correlation between the characterized anchor motif and binding affinity. These results deepen our understanding of the molecular basis of the presentation of peptides by Mamu-B*08 and can contribute to the detection of novel SIV epitopes restricted by this allotype.

Broadly Neutralizing Antibody Responses in a Large Longitudinal Sub-Saharan HIV Primary Infection Cohort

Broadly neutralizing antibodies (bnAbs) are thought to be a critical component of a protective HIV vaccine. However, designing vaccines immunogens able to elicit bnAbs has proven unsuccessful to date. Understanding the correlates and immunological mechanisms leading to the development of bnAb responses during natural HIV infection is thus critical to the design of a protective vaccine. The IAVI Protocol C program investigates a large longitudinal cohort of primary HIV-1 infection in Eastern and South Africa. Development of neutralization was evaluated in 439 donors using a 6 cross-clade pseudo-virus panel predictive of neutralization breadth on larger panels. About 15% of individuals developed bnAb responses, essentially between year 2 and year 4 of infection. Statistical analyses revealed no influence of gender, age or geographical origin on the development of neutralization breadth. However, cross-clade neutralization strongly correlated with high viral load as well as with low CD4 T cell counts, subtype-C infection and HLA-A*03(-) genotype. A correlation with high overall plasma IgG levels and anti-Env IgG binding titers was also found. The latter appeared not associated with higher affinity, suggesting a greater diversity of the anti-Env responses in broad neutralizers. Broadly neutralizing activity targeting glycan-dependent epitopes, largely the N332-glycan epitope region, was detected in nearly half of the broad neutralizers while CD4bs and gp41-MPER bnAb responses were only detected in very few individuals. Together the findings suggest that both viral and host factors are critical for the development of bnAbs and that the HIV Env N332-glycan supersite may be a favorable target for vaccine design.

Cytokine production associated with smallpox vaccine responses

Smallpox was eradicated 34 years ago due to the success of the smallpox vaccine; yet, the vaccine continues to be studied because of its importance in responding to potential biological warfare and the adverse events associated with current smallpox vaccines. Interindividual variations in vaccine response are observed and are, in part, due to genetic variation. In some cases, these varying responses lead to adverse events, which occur at a relatively high rate for the smallpox vaccine compared with other vaccines. Here, we aim to summarize the cytokine responses associated with smallpox vaccine response to date. Along with a description of each of these cytokines, we describe the genetic and adverse event data associated with cytokine responses to smallpox vaccination.

Success and failure of the cellular immune response against HIV-1

The cellular immune response to HIV-1 has now been studied in extraordinary detail. A very large body of data provides the most likely reasons that the HIV-specific cellular immune response succeeds in a small number of people but fails in most. Understanding the success and failure of the HIV-specific cellular immune response has implications that extend not only to immunotherapies and vaccines for HIV-1 but also to the cellular immune response in other disease states. This Review focuses on the mechanisms that are most likely responsible for durable and potent immunologic control of HIV-1. Although we now have a detailed picture of the cellular immune responses to HIV-1, important questions remain regarding the nature of these responses and how they arise.

Immune activation and HIV persistence: implications for curative approaches to HIV infection

Despite complete or near-complete suppression of human immunodeficiency virus (HIV) replication with combination antiretroviral therapy, both HIV and chronic inflammation/immune dysfunction persist indefinitely. Untangling the association between the virus and the host immune environment during therapy might lead to novel interventions aimed at either curing the infection or preventing the development of inflammation-associated end-organ disease. Chronic inflammation and immune dysfunction might lead to HIV persistence by causing virus production, generating new target cells, enabling infecting of activated and resting target cells, altering the migration patterns of susceptible target cells, increasing the proliferation of infected cells, and preventing normal HIV-specific clearance mechanisms from function. Chronic HIV production or replication might contribute to persistent inflammation and immune dysfunction. The rapidly evolving data on these issues strongly suggest that a vicious cycle might exist in which HIV persistence causes inflammation that in turn contributes to HIV persistence.

Potential elucidation of a novel CTL epitope in HIV-1 protease by the protease inhibitor resistance mutation L90M

The combination of host immune responses and use of antiretrovirals facilitate partial control of human immunodeficiency virus type 1 (HIV-1) infection and result in delayed progression to Acquired Immunodeficiency Syndrome (AIDS). Both treatment and host immunity impose selection pressures on the highly mutable HIV-1 genome resulting in antiretroviral resistance and immune escape. Researchers have shown that antiretroviral resistance mutations can shape cytotoxic T-lymphocyte immunity by altering the epitope repertoire of HIV infected cells. Here it was discovered that an important antiretroviral resistance mutation, L90M in HIV protease, occurs at lower frequencies in hosts that harbor the B*15, B*48 or A*32 human leukocyte antigen subtypes. A likely reason is the elucidation of novel epitopes by L90M. NetMHCPan predictions reveal increased affinity of the peptide spanning the HIV protease region, PR 89–97 and PR 90–99 to HLA-B*15/B*48 and HLA-A*32 respectively due to the L90M substitution. The higher affinity could increase the chance of the epitope being presented and recognized by Cytotoxic T-lymphocytes and perhaps provide additional immunological pressures in the presence of antiretroviral attenuating mutations. This evidence supports the notion that knowledge of HLA allotypes in HIV infected individuals could augment antiretroviral treatment by the elucidation of epitopes due to antiretroviral resistance mutations in HIV protease.

Vaccinomics, adversomics, and the immune response network theory: individualized vaccinology in the 21st century

Vaccines, like drugs and medical procedures, are increasingly amenable to individualization or personalization, often based on novel data resulting from high throughput "omics" technologies. As a result of these technologies, 21st century vaccinology will increasingly see the abandonment of a "one size fits all" approach to vaccine dosing and delivery, as well as the abandonment of the empiric "isolate-inactivate-inject" paradigm for vaccine development. In this review, we discuss the immune response network theory and its application to the new field of vaccinomics and adversomics, and illustrate how vaccinomics can lead to new vaccine candidates, new understandings of how vaccines stimulate immune responses, new biomarkers for vaccine response, and facilitate the understanding of what genetic and other factors might be responsible for rare side effects due to vaccines. Perhaps most exciting will be the ability, at a systems biology level, to integrate increasingly complex high throughput data into descriptive and predictive equations for immune responses to vaccines. Herein, we discuss the above with a view toward the future of vaccinology.

Human leucocyte antigen-Bw4 and Gag-specific T cell responses are associated with slow disease progression in HIV-1B-infected anti-retroviral therapy-naive Chinese

In China, the majority of human immunodeficiency virus (HIV) infections are predominately subtype B. It is important to characterize the HIV-1 subtype B-specific and its T cell response within the Chinese population, with the aim of identifying protective correlates of immunity to control HIV-1 infections. In this study, we performed a comprehensive analysis looking into the magnitude/strength of T cell responses directed at the Gag protein of the HIV-1 subtype B, one of the most conserved HIV-1 proteins. The study group consisted of anti-retroviral native and chronic HIV-1 subtype B-infected individuals. We used enzyme-linked immunospot (ELISPOT) assay to quantify the total T cell responses to HIV-1 Gag at the single peptide level. Twenty-eight (38%) peptides were recognized in 24 (82·8%) individuals. The p24 was identified as the most frequently recognized subunit protein with the greatest T cell response in the test, which correlated positively with CD4(+) T cell count and inversely with viral load (VL). At the level of the human leucocyte antigen (HLA) supertypes, we detected the highest levels and a significant correlation with both the CD4(+) T cell count and the VL with Gag T cell responses in Bw4/Bw4. These findings demonstrate that (i) the HIV-1B Gag p24-specific immune responses play an important role in controlling viral replication and slowing clinical progression; and (ii) HLA-Bw4/Bw4 allele has stronger T cell responses, which is associated with slow clinical progression in Chinese HIV patients.

Separate developmental programs for HLA-A and -B cell surface expression during differentiation from embryonic stem cells to lymphocytes, adipocytes and osteoblasts

A major problem of allogeneic stem cell therapy is immunologically mediated graft rejection. HLA class I A, B, and Cw antigens are crucial factors, but little is known of their respective expression on stem cells and their progenies. We have recently shown that locus-specific expression (HLA-A, but not -B) is seen on some multipotent stem cells, and this raises the question how this is in other stem cells and how it changes during differentiation. In this study, we have used flow cytometry to investigate the cell surface expression of HLA-A and -B on human embryonic stem cells (hESC), human hematopoietic stem cells (hHSC), human mesenchymal stem cells (hMSC) and their fully-differentiated progenies such as lymphocytes, adipocytes and osteoblasts. hESC showed extremely low levels of HLA-A and no -B. In contrast, multipotent hMSC and hHSC generally expressed higher levels of HLA-A and clearly HLA-B though at lower levels. IFNγ induced HLA-A to very high levels on both hESC and hMSC and HLA-B on hMSC. Even on hESC, a low expression of HLA-B was achieved. Differentiation of hMSC to osteoblasts downregulated HLA-A expression (P = 0.017). Interestingly HLA class I on T lymphocytes differed between different compartments. Mature bone marrow CD4(+) and CD8(+) T cells expressed similar HLA-A and -B levels as hHSC, while in the peripheral blood they expressed significantly more HLA-B7 (P = 0.0007 and P = 0.004 for CD4(+) and CD8(+) T cells, respectively). Thus different HLA loci are differentially regulated during differentiation of stem cells.

Consistency of HLA associations between two independent measles vaccine cohorts: a replication study

Associations between HLA genotypes and measles vaccine humoral and cellular immune responses were examined to better understand immunogenetic drivers of vaccine response. Two independent study cohorts of healthy schoolchildren were examined: cohort one, 346 children between 12 and 18 years of age; and cohort two, 388 children between 11 and 19 years of age. All received two age-appropriate doses of measles-containing vaccine. The purpose of this study was to identify and replicate associations between HLA genes and immune responses following measles vaccination found in our first cohort. Associations of comparable magnitudes and with similar p-values were observed between B*3503 (1st cohort p=0.01; 2nd cohort p=0.07), DQA1*0201 (1st cohort p=0.03; 2nd cohort p=0.03), DQB1*0303 (1st cohort p=0.10; 2 cohort p=0.02), DQB1*0602 (1st cohort p=0.07; 2nd cohort p=0.10), and DRB1*0701 (1st cohort p=0.03; 2nd cohort p=0.07) alleles and measles-specific antibody levels. Suggestive, yet consistent, associations were observed between the B7 (1st cohort p=0.01; 2nd cohort p=0.08) supertype and higher measles antibody levels in both cohorts. Also, in both cohorts, the B*0801 and DRB1*0301 alleles, C*0802 and DPA1*0202 alleles, and DRB1*1303 alleles displayed consistent associations with variations in IFN-γ, IL-2 and IL-10 secretion, respectively. This study emphasizes the importance of replicating HLA associations with measles vaccine-induced humoral and cellular immune responses and increases confidence in the results. These data will inform strategies for functional studies and novel vaccine development, including epitope-based measles vaccines. This is the first HLA association replication study with measles vaccine-specific immune responses to date.

Vaccine-induced HIV-specific CD8+ T cells utilize preferential HLA alleles and target-specific regions of HIV-1

Most T cell-based HIV-1 vaccine candidates induce responses of limited breadth for reasons that are unclear. We evaluated vaccine-induced T-cell responses in individuals receiving an HIV-1 recombinant adenoviral vaccine. Certain HLA alleles (B27, B57, B35, and B14) are preferentially utilized to mount HIV-specific responses, whereas other alleles (A02 and B07) are rarely utilized (P < 0.001). This preference seems due to 4 following factors individually or in combination: higher affinity of specific peptides to specific HLA alleles; higher avidity of T-cell receptor; HLA and peptide interaction; and/or higher surface expression of certain HLA. Thus, HLA immunodominance plays a substantial role in vaccine-induced T-cell responses.

ALVAC-HIV as a prophylactic and therapeutic vaccine: highlights from over a decade of clinical trials

ALVAC-HIV vaccines (vCP125, vCP205, vCP300, vCP1433, vCP1452 and vCP1521) are preparations of a modified recombinant canarypox virus designed to induce or augment CD8+ immune responses. As the focus of several Phase I–III trials, they have been the most extensively studied live vector-based HIV vaccines. Overall, ALVAC-HIV induces modest CD8+ T-cell responses in approximately 20–50% of recipients. The addition of IL-2, recombinant glycoprotein 120 or 160, Remune or LIPO-6T to ALVAC-HIV does not appear to enhance overall CD8+ T-cell immune responses. The ability of ALVAC-HIV to induce interclade immunity and immunogenicity in newborns with perinatal exposure to HIV has important implications for the control of HIV worldwide. Experience from clinical trials in over 10,000 HIV-infected and noninfected individuals has shown that ALVAC constructs are safe, with reactogenicity profiles similar to those reported for currently licensed vaccines. Despite seemingly modest immunogenicity at the present time, studies to date have set the stage for further exploration of the potential of ALVAC-HIV vaccines. This report highlights findings from clinical trials using ALVAC-HIV, alone and in combination with other agents, as both a prophylactic and a therapeutic vaccine.

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

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

Human leukocyte antigen variants B*44 and B*57 are consistently favorable during two distinct phases of primary HIV-1 infection in sub-Saharan Africans with several viral subtypes

As part of an ongoing study of early human immunodeficiency virus type 1 (HIV-1) infection in sub-Saharan African countries, we have identified 134 seroconverters (SCs) with distinct acute-phase (peak) and early chronic-phase (set-point) viremias. SCs with class I human leukocyte antigen (HLA) variants B*44 and B*57 had much lower peak viral loads (VLs) than SCs without these variants (adjusted linear regression beta values of -1.08 ± 0.26 log(10) [mean ± standard error] and -0.83 ± 0.27 log(10), respectively; P < 0.005 for both), after accounting for several nongenetic factors, including gender, age at estimated date of infection, duration of infection, and country of origin. These findings were confirmed by alternative models in which major viral subtypes (A1, C, and others) in the same SCs replaced country of origin as a covariate (P ≤ 0.03). Both B*44 and B*57 were also highly favorable (P ≤ 0.03) in analyses of set-point VLs. Moreover, B*44 was associated with relatively high CD4(+) T-cell counts during early chronic infection (P = 0.02). Thus, at least two common HLA-B variants showed strong influences on acute-phase as well as early chronic-phase VL, regardless of the infecting viral subtype. If confirmed, the identification of B*44 as another favorable marker in primary HIV-1 infection should help dissect mechanisms of early immune protection against HIV-1 infection.

Human leukocyte antigen genotypes in the genetic control of adaptive immune responses to smallpox vaccine

BACKGROUND

The role of human leukocyte antigen (HLA) genes in mediating adaptive immune responses to smallpox vaccine remains unknown.

METHODS

We determined genotypes for a group of individuals (n = 1071) who received a single dose of smallpox vaccine (Dryvax, Wyeth Laboratories) and examined associations between HLA alleles and 15 immune outcomes to smallpox vaccine on a per-locus and a per-allele level.

RESULTS

We found significant associations between the HLA-B and HLA - DQB1 loci and vaccinia-induced antibodies (P = .04 for each locus), with the HLA-B*1302 (P = .036), B*3802 (P = .011), DQB1*0302 (P = .015), and DQB1*0604 (P = .017) alleles being associated with higher levels. Significant global associations were identified between vaccinia-specific interferon (IFN)-γ and DQA1 (P = .003), interleukin (IL)-1β and HLA-B (P = .004), tumor necrosis factor (TNF)-α and HLA-B (P = .006), and IL-6 and HLA-B locus (P = .016) for secreted cytokines, as well as between CD8α(+) IFN-γ Elispot responses and DQB1 (P = .027). Subjects carrying B*3906 (P = .006) and B*5701 (P < .001) secreted higher levels of IL-1β than did subjects who did not carry these alleles. Subjects carrying the B*5301 (P = .047) and B*5601 (P = .008) alleles secreted less IL-1β, compared with subjects who did not carry these alleles. The B*3502 (P = .009), B*5601 (P = .004), and B*5701 (P < .001) alleles were significantly associated with variations in TNF-α secretion.

CONCLUSIONS

These data suggest that variations in antibody and cellular IFN-γ, IL-1β, TNF-α, and IL-6 immune responses after receipt of smallpox vaccine are genetically controlled by HLA genes or genes in close linkage disequilibrium to these alleles.

Qualitative features of the HIV-specific CD8+ T-cell response associated with immunologic control

PURPOSE OF REVIEW

Over the past 2 years, a clearer picture has emerged regarding the properties of HIV-specific CD8+ T cells associated with immunologic control of HIV replication. These properties represent a potential mechanism by which rare patients might control HIV replication in the absence of antiretroviral therapy. This review addresses the background and recent findings that have lead to our current understanding of these mechanism(s).

RECENT FINDINGS

Patients with immunologic control of HIV are not distinguished by targeted specificities, or greater numbers or breadth of their HIV-specific CD8+ T-cell response. For this reason, recent work has focused greater attention on qualitative features of this response. The qualitative features most closely associated with immunologic control of HIV are related to the granule-exocytosis-mediated elimination of HIV-infected CD4 T cells. The ability of HIV-specific CD8+ T cells to increase their contents of proteins known to mediate cytotoxicity, such as granzyme B and perforin, appears to be a critical means by which HIV-specific cytotoxic capacity is regulated.

SUMMARY

Investigation from multiple groups has now focused upon HIV-specific CD8+ T-cell granule-exocytosis-mediated cytotoxicity as a correlate of immunologic control of HIV. In the near future, a more detailed understanding of the qualities associated with immunologic control may provide critical insights regarding the necessary features of a response that should be stimulated by immunotherapies or T-cell-based vaccines.

An Ad5-vectored HIV-1 vaccine elicits cell-mediated immunity but does not affect disease progression in HIV-1-infected male subjects: results from a randomized placebo-controlled trial (the Step study)

BACKGROUND

The Step study was a randomized trial to determine whether an adenovirus type 5 (Ad5) vector vaccine, which elicits T cell immunity, can lead to control of human immunodeficiency virus (HIV) replication in participants who became HIV-infected after vaccination.

METHODS

We evaluated the effect of the vaccine on trends in HIV viral load, CD4+ T cell counts, time to initiation of antiretroviral therapy (ART), and AIDS-free survival in 87 male participants who became infected with HIV during the Step study and who had a median of 24 months of post-infection follow-up.

RESULTS

There was no overall effect of vaccine on mean log(10) viral load (estimated difference between groups, -0.11; P = .47). In a subset of subjects with protective HLA types (B27, B57, B58), mean HIV-1 RNA level over time was lower among vaccine recipients. There was no significant difference in CD4+ T cell counts, time to ART initiation, or in AIDS-free survival between HIV-1-infected subjects who received vaccine versus those who received placebo.

CONCLUSIONS

HIV RNA levels, CD4+ T cell counts, time to initiation of ART, and AIDS-free survival were similar in vaccine and placebo recipients. There may have been a favorable effect of vaccine on HIV-1 RNA levels in participants with HLA types associated with better control of HIV-1.

Trivalent adenovirus type 5 HIV recombinant vaccine primes for modest cytotoxic capacity that is greatest in humans with protective HLA class I alleles

If future HIV vaccine design strategies are to succeed, improved understanding of the mechanisms underlying protection from infection or immune control over HIV replication remains essential. Increased cytotoxic capacity of HIV-specific CD8+ T-cells associated with efficient elimination of HIV-infected CD4+ T-cell targets has been shown to distinguish long-term nonprogressors (LTNP), patients with durable control over HIV replication, from those experiencing progressive disease. Here, measurements of granzyme B target cell activity and HIV-1-infected CD4+ T-cell elimination were applied for the first time to identify antiviral activities in recipients of a replication incompetent adenovirus serotype 5 (Ad5) HIV-1 recombinant vaccine and were compared with HIV-negative individuals and chronically infected patients, including a group of LTNP. We observed readily detectable HIV-specific CD8+ T-cell recall cytotoxic responses in vaccinees at a median of 331 days following the last immunization. The magnitude of these responses was not related to the number of vaccinations, nor did it correlate with the percentages of cytokine-secreting T-cells determined by ICS assays. Although the recall cytotoxic capacity of the CD8+ T-cells of the vaccinee group was significantly less than that of LTNP and overlapped with that of progressors, we observed significantly higher cytotoxic responses in vaccine recipients carrying the HLA class I alleles B*27, B*57 or B*58, which have been associated with immune control over HIV replication in chronic infection. These findings suggest protective HLA class I alleles might lead to better outcomes in both chronic infection and following immunization due to more efficient priming of HIV-specific CD8+ T-cell cytotoxic responses.

Host genetic determinants of T cell responses to the MRKAd5 HIV-1 gag/pol/nef vaccine in the step trial

Understanding how human genetic variation impacts individual response to immunogens is fundamental for rational vaccine development. To explore host mechanisms involved in cellular immune responses to the MRKAd5 human immunodeficiency virus type 1 (HIV-1) gag/pol/nef vaccine tested in the Step trial, we performed a genome-wide association study of determinants of HIV-specific T cell responses, measured by interferon γ enzyme-linked immunospot assays. No human genetic variant reached genome-wide significance, but polymorphisms located in the major histocompatibility complex (MHC) region showed the strongest association with response to the HIV-1 Gag protein: HLA-B alleles known to be associated with differences in HIV-1 control were responsible for these associations. The implication of the same HLA alleles in vaccine-induced cellular immunity and in natural immune control is of relevance for vaccine design. Furthermore, our results demonstrate the importance of considering the host immunogenetic background in the analysis of immune responses to T cell vaccines.

Cofactors that may influence vaccine responses

PURPOSE OF REVIEW

This review summarizes recent developments related to cofactors that may influence response to vaccination.

RECENT FINDINGS

The unexpected increased HIV acquisition among vaccinees in the Step trial with prior exposure to adenovirus type 5 (Ad5) led to several studies trying to understand whether an underlying biological risk factor may have been responsible for this observation. Demographic factors and genetic background of the human populations in HIV vaccine trials remain a source of potential variation in responses observed in vaccine trials, yet empirical data remain limited on the impact of those factors. Coinfections, particularly those that may modulate the immune response, are a further concern for HIV vaccine trialists, with recent data providing further insight into effects of coinfections on innate and adaptive immunity and vaccine responses.

SUMMARY

Individuals and human populations display variation in response to vaccination. Key explanatory variables for this variation include host factors, such as host genetics, and environmental factors, such as prior exposure to the vaccine vector, coinfection with other pathogens, and demographic factors. This review will outline some of the recent developments investigating the role of various cofactors on vaccine responses, with a particular emphasis on studies of HIV vaccines.

The influence of human leukocyte antigen class I alleles and their population frequencies on human immunodeficiency virus type 1 control among African Americans

Populations of African ancestry continue to account for a disproportionate burden of the human immunodeficiency virus type 1 (HIV-1) epidemic in the United States. We investigated the effects of human leukocyte antigen (HLA) class I markers in association with virologic and immunologic control of HIV-1 infection among 338 HIV-1 subtype B-infected African Americans in 2 cohorts: Reaching for Excellence in Adolescent Care and Health (REACH) and HIV Epidemiology Research Study (HERS). One-year treatment-free interval measurements of HIV-1 RNA viral loads and CD4(+) T cells were examined both separately and combined to represent 3 categories of HIV-1 disease control (76 controllers, 169 intermediates, and 93 noncontrollers). Certain previously or newly implicated HLA class I alleles (A*32, A*36, A*74, B*14, B*1510, B*3501, B*45, B*53, B*57, Cw*04, Cw*08, Cw*12, and Cw*18) were associated with 1 or more of the endpoints in univariate analyses. After multivariable adjustments for other genetic and nongenetic risk factors of HIV-1 progression, the subset of alleles more strongly or consistently associated with HIV-1 disease control included A*32, A*74, B*14, B*45, B*53, B*57, and Cw*08. Carriage of infrequent HLA-B but not HLA-A alleles was associated with more favorable disease outcomes. Certain HLA class I associations with control of HIV-1 infection cross the boundaries of race and viral subtype, whereas others appear confined within one or the other of those boundaries.

Prime-boost immunization with poxvirus or adenovirus vectors as a strategy to develop a protective vaccine for HIV-1

Challenges in the development of an effective HIV-1 vaccine are myriad with significant hurdles posed by viral diversity, the lack of a human correlate of protection and difficulty in creating immunogens capable of eliciting broadly neutralizing antibodies. The implicit requirement for novel approaches to these problems has resulted in vaccine candidates designed to elicit cellular and/or humoral immune responses, to include recombinant DNA, viral and bacterial vectors, and subunit proteins. Here, we review data from clinical studies primarily of poxvirus and adenovirus vector vaccines, used in a heterologous prime-boost combination strategy. Currently, this strategy appears to hold the most promise for an effective vaccine based on results from immunogenicity testing and nonhuman primate challenge models, as well as the modest efficacy recently observed in the Thai prime-boost trial.

Highly avid, oligoclonal, early-differentiated antigen-specific CD8+ T cells in chronic HIV-2 infection

HIV-1-specific CD8(+) T cells are present in most HIV-1-infected people and play an important role in controlling viral replication, but the characteristics of an effective HIV-specific T-cell response are largely unknown. The majority of HIV-2-infected people behave as long-term non-progressors while those who progress to AIDS do so in a manner indistinguishable from HIV-1. A detailed study of HIV-2 infection may identify protective immune responses. Robust gag p26-specific T-cell responses are elicited during HIV-2 infection and correlate with control of viremia. In this study, we analyzed features of an HLA-B 3501-restricted T-cell response to HIV-2 p26 that may contribute to virus control. In contrast to HIV-1, HIV-2-specific T cells are at an early stage of differentiation (CD27(+)CD28(+)), a finding that relates directly to CD4(+) T-cell levels and inversely to immune activation. The cells demonstrate IFN-gamma secretion, oligoclonal T-cell receptor Vbeta gene segment usage, exceptional avidity and secretion of pro-inflammatory cytokines. Despite the potentially strong selection pressure imposed on the virus by these cells, there was no evidence of HIV-2 sequence evolution. We propose that in chronic HIV-2 infection, the maintenance of early-differentiated, highly avid CD8(+) T cells could account for the non-progressive course of disease. Such responses may be desirable from an HIV vaccine.

Application of pharmacogenomics to vaccines

The field of pharmacogenomics and pharmacogenetics provides a promising science base for vaccine research and development. A broad range of phenotype/genotype data combined with high-throughput genetic sequencing and bioinformatics are increasingly being integrated into this emerging field of vaccinomics. This paper discusses the hypothesis of the 'immune response gene network' and genetic (and bioinformatic) strategies to study associations between immune response gene polymorphisms and variations in humoral and cellular immune responses to prophylactic viral vaccines, such as measles-mumps-rubella, influenza, HIV, hepatitis B and smallpox. Immunogenetic studies reveal promising new vaccine targets by providing a better understanding of the mechanisms by which gene polymorphisms may influence innate and adaptive immune responses to vaccines, including vaccine failure and vaccine-associated adverse events. Additional benefits from vaccinomic studies include the development of personalized vaccines, the development of novel vaccines and the development of novel vaccine adjuvants.

Two MHC class I molecules associated with elite control of immunodeficiency virus replication, Mamu-B*08 and HLA-B*2705, bind peptides with sequence similarity

HLA-B27- and -B57-positive HIV-infected humans have long been associated with control of HIV replication, implying that CD8(+) T cell responses contribute to control of viral replication. In a similar fashion, 50% of Mamu-B*08-positive Indian rhesus macaques control SIVmac239 replication and become elite controllers with chronic-phase viremia <1000 viral RNA copies/ml. Interestingly, Mamu-B*08-restricted SIV-derived epitopes appeared to match the peptide binding profile for HLA-B*2705 in humans. We therefore defined a detailed peptide-binding motif for Mamu-B*08 and investigated binding similarities between the macaque and human MHC class I molecules. Analysis of a panel of approximately 900 peptides revealed that despite substantial sequence differences between Mamu-B*08 and HLA-B*2705, the peptide-binding repertoires of these two MHC class I molecules share a remarkable degree of overlap. Detailed knowledge of the Mamu-B*08 peptide-binding motif enabled us to identify six additional novel Mamu-B*08-restricted SIV-specific CD8(+) T cell immune responses directed against epitopes in Gag, Vpr, and Env. All 13 Mamu-B*08-restricted epitopes contain an R at the position 2 primary anchor and 10 also possess either R or K at the N terminus. Such dibasic peptides are less prone to cellular degradation. This work highlights the relevance of the Mamu-B*08-positive SIV-infected Indian rhesus macaque as a model to examine elite control of immunodeficiency virus replication. The remarkable similarity of the peptide-binding motifs and repertoires for Mamu-B*08 and HLA-B*2705 suggests that the nature of the peptide bound by the MHC class I molecule may play an important role in control of immunodeficiency virus replication.

Comparisons of CD8+ T cells specific for human immunodeficiency virus, hepatitis C virus, and cytomegalovirus reveal differences in frequency, immunodominance, phenotype, and interleukin-2 responsiveness

To better understand the components of an effective immune response to human immunodeficiency virus (HIV), the CD8(+) T-cell responses to HIV, hepatitis C virus (HCV), and cytomegalovirus (CMV) were compared with regard to frequency, immunodominance, phenotype, and interleukin-2 (IL-2) responsiveness. Responses were examined in rare patients exhibiting durable immune-mediated control over HIV, termed long-term nonprogressors (LTNP) or elite controllers, and patients with progressive HIV infection (progressors). The magnitude of the virus-specific CD8(+) T-cell response targeting HIV, CMV, and HCV was not significantly different between LTNP and progressors, even though their capacity to proliferate to HIV antigens was preserved only in LTNP. In contrast to HIV-specific CD8(+) T-cell responses of LTNP, HLA B5701-restricted responses within CMV pp65 were rare and did not dominate the total CMV-specific response. Virus-specific CD8(+) T cells were predominantly CD27(+)45RO(+) for HIV and CD27(-)45RA(+) for CMV; however, these phenotypes were highly variable and heavily influenced by the degree of viremia. Although IL-2 induced significant expansions of CMV-specific CD8(+) T cells in LTNP and progressors by increasing both the numbers of cells entering the proliferating pool and the number of divisions, the proliferative capacity of a significant proportion of HIV-specific CD8(+) T cells was not restored with exogenous IL-2. These results suggest that immunodominance by HLA B5701-restricted cells is specific to HIV infection in LTNP and is not a feature of responses to other chronic viral infections. They also suggest that poor responsiveness to IL-2 is a property of HIV-specific CD8(+) T cells of progressors that is not shared with responses to other viruses over which immunologic control is maintained.

The specificity and polymorphism of the MHC class I prevents the global adaptation of HIV-1 to the monomorphic proteasome and TAP

The large diversity in MHC class I molecules in a population lowers the chance that a virus infects a host to which it is pre-adapted to escape the MHC binding of CTL epitopes. However, viruses can also lose CTL epitopes by escaping the monomorphic antigen processing components of the pathway (proteasome and TAP) that create the epitope precursors. If viruses were to accumulate escape mutations affecting these monomorphic components, they would become pre-adapted to all hosts regardless of the MHC polymorphism. To assess whether viruses exploit this apparent vulnerability, we study the evolution of HIV-1 with bioinformatic tools that allow us to predict CTL epitopes, and quantify the frequency and accumulation of antigen processing escapes. We found that within hosts, proteasome and TAP escape mutations occur frequently. However, on the population level these escapes do not accumulate: the total number of predicted epitopes and epitope precursors in HIV-1 clade B has remained relatively constant over the last 30 years. We argue that this lack of adaptation can be explained by the combined effect of the MHC polymorphism and the high specificity of individual MHC molecules. Because of these two properties, only a subset of the epitope precursors in a host are potential epitopes, and that subset differs between hosts. We estimate that upon transmission of a virus to a new host 39%–66% of the mutations that caused epitope precursor escapes are released from immune selection pressure.

Greater viral rebound and reduced time to resume antiretroviral therapy after therapeutic immunization with the ALVAC-HIV vaccine (vCP1452)

OBJECTIVE

Evaluate immunogenicity and clinical efficacy of two immunization strategies with the ALVAC-HIV-recombinant canarypox vaccine (vCP1452) in treated HIV-infected patients.

DESIGN

Randomized, double-blind, placebo-controlled, phase II study of vCP1452 immunization in chronically HIV-infected patients on therapy with CD4 T-cell count more than 350 cells/microl, CD4 nadir less than 400 cells/microl and pHIV-RNA less than 400 copies/ml. Patients were equally randomized to four injections at weeks 0, 4, 8, 20; three injections at weeks 4, 8, 20; and placebo. The primary endpoint was vaccine immunogenicity at week 24 measured by enzyme-linked immunospot-interferon-gamma against the HIV-gag-reverse transcriptase-nef vaccine sequences. Secondary endpoints included time to treatment resumption and viral quantitation following treatment interruption at week 24. Criteria to resume therapy included CD4 T-cell count decline less than 250 cells/microl or 50% decrease from baseline or pHIV-RNA more than 50,000 copies/ml.

RESULTS

Sixty-five patients enrolled. Changes from baseline in HIV-specific T cells in the four injection arms (+480 spot-forming cells/M-peripheral blood mononuclear cell) were significant compared to placebo (+8; P = 0.014), but not in the three injection arms (+322). The week 36 pHIV-RNA (log10 copies/ml) after treatment interruption was higher in the four (4.71; P = 0.023) and three (4.82; P = 0.009) injection arms compared to placebo (4.40). Percentages of patients reaching treatment resumption criteria by week 48 were 74, 55 and 23% in the three respective arms (P = 0.013). Two independent factors influenced time to therapy resumption: immunization (hazards ratio = 2.7, P = 0.048 for three injections; hazards ratio = 4.1, P = 0.003 for four injections) and CD4 nadir (hazards ratio = 0.4, P = 0.002).

CONCLUSIONS

Significant immunogenicity was induced by vCP1452; however, this strategy was independently associated with a shorter time to resume therapy and higher viral rebound.

Crippling HIV one mutation at a time

Accumulating data suggest that not all human immunodeficiency virus (HIV)-1–specific immune responses are equally effective at controlling HIV-1 replication. A new study now demonstrates that multiple immune-driven sequence polymorphisms in the highly conserved HIV-1 Gag region of transmitted viruses are associated with reduced viral replication in newly infected humans. These data suggest that targeting these and other conserved viral regions may be the key to developing an effective HIV-1 vaccine.

Targeting of a CD8 T cell env epitope presented by HLA-B*5802 is associated with markers of HIV disease progression and lack of selection pressure

In HIV-infected persons, certain HLA class I alleles are associated with effective control of viremia, while others are associated with rapid disease progression. Among the most divergent clinical outcomes are the relatively good prognosis in HLA-B*5801 expressing persons and poor prognosis with HLA-B*5802. These two alleles differ by only three amino acids in regions involved in HLA-peptide recognition. This study evaluated a cohort of over 1000 persons with chronic HIV clade C virus infection to determine whether clinical outcome differences associated with B*5801 (n = 93) and B*5802 ( n = 259) expression are associated with differences in HIV-1-specific CD8 (+) T cell responses. The overall breadth and magnitude of HIV-1-specific CD8(+) T cell responses were lower in persons expressing B*5802, and epitope presentation by B*5802 contributed significantly less to the overall response as compared to B*5801-restricted CD8 (+) T cells. Moreover, viral load in B*5802-positive persons was higher and CD4 cell counts lower when this allele contributed to the overall CD8 (+) T cell response, which was detected exclusively through a single epitope in Env. In addition, persons heterozygous for B*5802 compared to persons homozygous for other HLA-B alleles had significantly higher viral loads. Viral sequencing revealed strong selection pressure mediated through B*5801-restricted responses but not through B*5802. These data indicate that minor differences in HLA sequence can have a major impact on epitope recognition, and that selective targeting of Env through HLA-B*5802 is at least ineffectual if not actively adverse in the containment of viremia. These results provide experimental evidence that not all epitope-specific responses contribute to immune containment, a better understanding of which is essential to shed light on mechanisms involved in HIV disease progression.

Immunological control of chronic HIV-1 infection: HLA-mediated immune function and viral evolution in adolescents

BACKGROUND

Differential protein targeting by HIV-specific CD8 T cells is associated with disparate plasma viral loads; however, it is unclear if the quality of these responses differs depending upon the specificity of the targeted epitopes.

METHODS

We examined HIV-specific CD8 T-cell responses in HIV-infected adolescents carrying either an HLA class I allele associated with a favorable prognosis (HLA-B*57) or an allele associated with usual disease progression (HLA-B*35 or HLA-B*53) using interferon-gamma ELISpot and ICS assays.

RESULTS

In an interferon-gamma ELISpot assay, p24 was the dominant protein targeted by B*57 carriers while responses to Nef dominated in B*35 or B*53 positive carriers. This differential protein targeting did not change during 4 years of follow-up. In these chronically infected adolescents, there were no significant differences in the quality of the immunodominant T-cell responses between the B*57 and B*35/B*53 carriers as measured by peptide avidity, degranulation, and immune memory markers. There was a trend towards higher expression of interleukin-2 from B*57-KF11 restricted CD8 T cells although this difference was not significant. Nevertheless both B*57 and B*35/53-restricted responses were relatively potent as reflected by the propensity of CD8 T cells to escape in p24 and Nef, respectively.

CONCLUSIONS

Differential protein targeting rather than the quality of T-cell responses appears to be a major distinguishing feature of HIV-specific CD8 T cells induced in B*57 carriers. These data suggest that viral fitness costs associated with CD8 T-cell pressure is an important factor determining differences in the viral load among HIV-infected patients.

Heterogeneity in vaccine immune response: the role of immunogenetics and the emerging field of vaccinomics

Recent advances in the fields of immunology, genetics, molecular biology, bioinformatics, and the Human Genome Project have allowed for the emergence of the field of vaccinomics. Vaccinomics encompasses the fields of immunogenetics and immunogenomics as applied to understanding the mechanisms of heterogeneity in immune responses to vaccines. In this study, we examine the role of HLA genes, cytokine genes, and cell surface receptor genes as examples of how genetic polymorphism leads to individual and population variations in immune responses to vaccines. In turn, this data, in concert with new high-throughput technology, inform the immune-response network theory to vaccine response. Such information can be used in the directed and rational development of new vaccines, and this new golden age of vaccinology has been termed "predictive vaccinology", which will predict the likelihood of a vaccine response or an adverse response to a vaccine, the number of doses needed and even whether a vaccine is likely to be of benefit (i.e., is the individual at risk for the outcome for which the vaccine is being administered?).

Mamu-B*08-positive macaques control simian immunodeficiency virus replication

Certain major histocompatibility complex (MHC) class I alleles are associated with the control of human immunodeficiency virus and simian immunodeficiency virus (SIV) replication. We have designed sequence-specific primers for detection of the rhesus macaque MHC class I allele Mamu-B*08 by PCR and screened a cohort of SIV-infected macaques for this allele. Analysis of 196 SIV(mac)239-infected Indian rhesus macaques revealed that Mamu-B*08 was significantly overrepresented in elite controllers; 38% of elite controllers were Mamu-B*08 positive compared to 3% of progressors (P = 0.00001). Mamu-B*08 was also associated with a 7.34-fold decrease in chronic phase viremia (P = 0.002). Mamu-B*08-positive macaques may, therefore, provide a good model to understand the correlates of MHC class I allele-associated immune protection and viral containment in human elite controllers.

HLA homozygosity does not adversely affect measles vaccine-induced cytokine responses

The association between HLA homozygosity and measles-specific Th(1) (IFN-gamma, IL-2 and IL-12p40) and Th(2) (IL-4 and IL-10) cytokine responses were assessed in a group of 339 healthy schoolchildren 12-18 years of age previously immunized with two doses of live-attenuated measles virus vaccine. No associations were observed between class I HLA homozygosity and measles-specific cytokine levels. Children who were homozygous at the class II DRB1, DQA1, DPA1 and DPB1 loci had higher median IFN-gamma secretion levels compared with children who were heterozygous for DRB1 (77.7 vs. 39.5 pg/ml, p=0.05), DQA1 (60.9 vs. 36.6 pg/ml, p=0.03), DPA1 (46.1 vs. 27.1 pg/ml, p=0.01) and DPB1 (61.5 vs. 36.0 pg/ml, p=0.01) loci, respectively. Homozygosity at increasing numbers of HLA loci ( >or=4) was associated with increased IFN-gamma secretion levels (test for trend p-value=0.01). Our results suggest that HLA homozygosity showed no disadvantage for measles-specific cytokine responses and instead was associated with increased IFN-gamma levels.

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

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

HLA Alleles Associated with Delayed Progression to AIDS Contribute Strongly to the Initial CD8(+) T Cell Response against HIV-1

BACKGROUND

Very little is known about the immunodominance patterns of HIV-1-specific T cell responses during primary HIV-1 infection and the reasons for human lymphocyte antigen (HLA) modulation of disease progression.

METHODS AND FINDINGS

In a cohort of 104 individuals with primary HIV-1 infection, we demonstrate that a subset of CD8(+) T cell epitopes within HIV-1 are consistently targeted early after infection, while other epitopes subsequently targeted through the same HLA class I alleles are rarely recognized. Certain HLA alleles consistently contributed more than others to the total virus-specific CD8(+) T cell response during primary infection, and also reduced the absolute magnitude of responses restricted by other alleles if coexpressed in the same individual, consistent with immunodomination. Furthermore, individual HLA class I alleles that have been associated with slower HIV-1 disease progression contributed strongly to the total HIV-1-specific CD8(+) T cell response during primary infection.

CONCLUSIONS

These data demonstrate consistent immunodominance patterns of HIV-1-specific CD8(+) T cell responses during primary infection and provide a mechanistic explanation for the protective effect of specific HLA class I alleles on HIV-1 disease progression.

Initiation of antiretroviral therapy during chronic SIV infection leads to rapid reduction in viral loads and the level of T-cell immune response

In the present era of increasing resistance of human immunodeficiency virus (HIV) to antiviral drugs, exploration of adjunct therapies directed at immune responses in combination with antiretroviral drugs may be of value for the treatment of acquired immunodeficiency syndrome. In this study, we designed a model for immune therapy using SIVmac251 infection in rhesus macaques. We explored the outcomes of primary infection on viral loads and the resulting T-cell immune responses in primates. The SIV-infected rhesus macaque model exhibited features similar to those observed in HIV-1 infection of humans. Major histocompatibility complex (MHC) segregation with viral loads were found to associate with viral containment and hence the duration of the disease-free latency period. Thus a better understanding of the relative roles of MHC class I allele in control of viral replication may provide important information for prophylactic or therapeutic vaccine designs. Mamu-A01 is significantly associated with higher immune response and control of viral replication. This allele is frequent in rhesus macaques of Indian origin (22%). Interestingly, Mamu-B01 (26% animals) was associated with lower immune responses and higher viral loads. Another allele, A08 was also predominantly present in 37% of the animals in this study. We observed higher viral replication in individual SIV-infected rhesus monkeys that did not demonstrate strong cellular immune responses. The results are important for understanding SIV disease progression in different MHC Mamu alleles and also for improving the interpretation and quality of pre-clinical studies in rhesus monkeys.

The role of human leukocyte antigen class I polymorphism in HIV/AIDS

PURPOSE OF REVIEW

Polymorphism at human leukocyte antigen class I loci accounts for a portion of the individual variability in susceptibility to, and evolution of, HIV-1 infection. Evaluation of the impact of class I polymorphism has improved, with refined techniques for genotyping, quantifying peptide binding characteristics of class I molecules, and measuring cytotoxic T lymphocyte responses.

RECENT FINDINGS

Most class I alleles that are particularly advantageous or disadvantageous in controlling HIV/AIDS are human leukocyte antigen-B locus products. Some act more uniformly than others, across racial and viral subtype boundaries, and different alleles may exert their effects at different times during the course of infection. Disease progression may be retarded by alleles of less common supertypes. The virus mutates to escape host pressure exerted by class 1 programmed cytotoxic T lymphocytes, and may or may not revert to its earlier form, depending on the toll taken on its replication capacity.

SUMMARY

Large virologically and immunologically well defined cohorts will be critical for increasingly comprehensive evaluation of the multiple small effects conferred by these highly polymorphic loci. Elucidating these effects at the population, clinical, cellular, and molecular levels poses a formidable challenge, but the reward could be vaccine constructs customized to the genetic profiles of individual populations, along with more effective individualized therapeutic intervention.

Inhibition of HIV-1-specific T-cells and increase of viral load during immunosuppressive treatment in an HIV-1 infected patient with Chlamydia trachomatis induced arthritis

BACKGROUND

Studies in HIV-1 infected long-term non-progressors could demonstrate a strong HIV-1-specific CTL response, but it is difficult to prove that this strong CTL response actually is the cause of the efficient control of HIV-1 and not the consequence of low HIV-1 replication in these patients.

OBJECTIVE

Studies of HIV-1-specific immunity and viral replication in patients undergoing immunosuppressive therapy provide important opportunities to understand the role of HIV-1-specific T-cells.

RESULTS

In this report we describe an HLA B27 positive patient with normal CD4 counts and a low viral load of 200 copies/ml without antiretroviral therapy who exhibited a very strong HIV-1-specific CTL response. He had to be treated with steroids, NSAIDS and hydroxchloroquine because of a severe inflammatory reactive arthritis triggered by an acute Chlamydia trachomatis infection. Analysis of HIV-1 specific T-cells by gamma-IFN-ELISPOT revealed a high frequency of HIV-1 gag-specific CTL both in blood and synovial fluid, whereas gag-specific CD4-cells could be detected only in the peripheral blood. Further analysis revealed that the gag-specific T-cells were predominantly targeting the HLA B27-restricted CTL epitope KRWIILGLNK (KK10). Immunosuppressive therapy by prednisone was associated with a moderate increase of HIV-1 viremia and a decrease both in the number and in the gamma-IFN production of KK10-specific CTL indicating that inhibition of CTL function contributed to the increase of viral load.

CONCLUSIONS

This study is suggesting that HIV-1 specific CTL play an important role in the control of HIV-1, at least in this patient. Inhibition of CTL function by immunosuppressive therapy with prednisone may enhance viral replication. In addition, we could demonstrate for the first time the migration of HIV-1 specific T-cells into the synovial fluid.

Influence of host genetic variation on susceptibility to HIV type 1 infection

For this review of genetic susceptibility to human immunodeficiency virus type 1 infection, far more information was available on factors involved in acquisition of the virus by an uninfected "recipient" than on propagation by the infected "donor." Genetic variation presumably alters transmission from an infected host primarily by regulating the replication of virus and the concentration of particles circulating in blood and mucosal secretions of the potential donor. Thus, the effects of host genetic variation on transmission are inextricably bound to the well-established and powerful effects on virus load at different stages of infection. Teasing apart the effects in both donors and recipients has been and will continue to be quite difficult.

Poxvirus-based vaccine candidates for HIV: two decades of experience with special emphasis on canarypox vectors

Poxvirus vectors have emerged as important vectors for licensed veterinary vaccines and candidate vaccines for humans. Vaccinia, highly-attenuated vaccinia strains and avipoxviruses have been assessed extensively in preclinical models, as well as in humans, to determine their immunogenicity and protective efficacy against HIV. The attenuated vaccinia strains and avipoxviruses have been shown to be safe and able to carry HIV genes and express their proteins to induce both antibodies and cellular immune responses. Preclinical studies show protection against HIV challenge. When using a live attenuated vector system, one must be cognizant of the potential for immune dampening because of vector-specific immunity. In this regard, avipoxviruses, such as canarypox, appear free of the inhibitory effects of vector immunity and repeated use. Unlike vaccinia-based vectors derived from classical vaccine strains, NYVAC and modified vaccinia Ankara may be less susceptible to this effect. In the coming 5 to 10 years, we will certainly know whether this class of vaccine candidates, either alone or in a prime-boost format with other vectors or proteins, will contribute to HIV disease management either from a preventive or therapeutic perspective. Additional Phase I and II studies, as well as human efficacy trials will provide new information. Furthermore, it is hoped that this body of data will contribute to a better understanding of the relevance of specific immunogenicity end points to protection and the predictive value of available animal models in HIV vaccine development.

HLA-DQ6 and ingestion of contaminated water: possible gene-environment interaction in an outbreak of Leptospirosis

Leptospirosis is a zoonosis that can cause severe multisystem disease. While host gene-environment interactions likely modify infectious disease susceptibility, including for leptopsirosis, this has not been documented. In a 1998 leptospirosis outbreak investigation among triathletes in a lake swim, swallowing lake-water was a disease risk-factor. We used genomic DNA from 85 anonymized blood-sample remainders from that investigation to examine the association of laboratory-confirmed leptospirosis with gene polymorphisms (TNF-alpha alleles and serologically defined genotypes for HLA-DRB1 and HLA-DQB1). HLA-DQ6-positive triathletes had increased risk of laboratory-confirmed leptospirosis (OR=2.8, P=0.04) compared to DQ6-negatives. DQ6-positive triathletes swallowing lake-water had greatest risk (OR 8.46, P< or =0.001). This first report of a genetic risk-factor affecting susceptibility to leptospirosis is also the first documented gene-environment interaction (DQ6 and swallowed water) affecting infectious disease susceptibility. Based on these preliminary findings, we hypothesize a role for superantigens in leptospirosis and underscore the importance of outbreak investigations for understanding infectious disease gene-environment interactions.