Possession of HLA class II DRB1*1303 associates with reduced viral loads in chronic HIV-1 clade C and B infection

Deciphering the host genetic factors conferring susceptibility to severe COVID-19 using exome sequencing

The COVID-19 pandemic remains a significant public health concern despite the new vaccines and therapeutics. The clinical course of acute SARS-CoV-2 infection is highly variable and influenced by several factors related to the virus and the host. Numerous genetic studies, including candidate gene, exome, and genome sequencing studies, genome-wide association studies, and other omics efforts, have proposed various Mendelian and non-Mendelian associations with COVID-19 course. In this study, we conducted whole-exome sequencing on 90 unvaccinated patients from Turkey with no known comorbidities associated with severe COVID-19. Of these patients, 30 had severe, 30 had moderate, and 30 had mild/asymptomatic disease. We identified rare variants in genes associated with SARS-CoV-2 susceptibility and pathogenesis, with an emphasis on genes related to the regulation of inflammation, and discussed these in the context of the clinical course of the patients. In addition, we compared the frequencies of common variants between each group. Even though no variant remained statistically significant after correction for multiple testing, we observed that certain previously associated genes and variants showed significant associations before correction. Our study contributes to the existing literature regarding the genetic susceptibility to SARS-CoV-2. Future studies would be beneficial characterizing the host genetic properties in different populations.

A high-resolution HLA reference panel capturing global population diversity enables multi-ancestry fine-mapping in HIV host response

Fine-mapping to plausible causal variation may be more effective in multi-ancestry cohorts, particularly in the MHC, which has population-specific structure. To enable such studies, we constructed a large (n = 21,546) HLA reference panel spanning five global populations based on whole-genome sequences. Despite population-specific long-range haplotypes, we demonstrated accurate imputation at G-group resolution (94.2%, 93.7%, 97.8% and 93.7% in admixed African (AA), East Asian (EAS), European (EUR) and Latino (LAT) populations). Applying HLA imputation to genome-wide association study data for HIV-1 viral load in three populations (EUR, AA and LAT), we obviated effects of previously reported associations from population-specific HIV studies and discovered a novel association at position 156 in HLA-B. We pinpointed the MHC association to three amino acid positions (97, 67 and 156) marking three consecutive pockets (C, B and D) within the HLA-B peptide-binding groove, explaining 12.9% of trait variance.

Genetic and epigenetic factors associated with increased severity of Covid-19

Since December 2019, a new form of severe acute respiratory syndrome (SARS) from a novel strain of coronavirus (SARS coronavirus 2 [SARS-CoV-2]) has been spreading worldwide. The disease caused by SARS-CoV-2 was named Covid-19 and declared as a pandemic by the World Health Organization in March 2020. Clinical symptoms of Covid-19 range from common cold to more severe disease defined as pneumonia, hypoxia, and severe respiratory distress. In the next stage, disease can become more critical with respiratory failure, sepsis, septic shock, and/or multiorgan failure. Outcomes of Covid-19 indicate large gaps between the male-female and the young-elder groups. Several theories have been proposed to explain variations, such as gender, age, comorbidity, and genetic factors. It is likely that mixture of genetic and nongenetic factors interplays between virus and host genetics and determines the severity of disease outcome. In this review, we aimed to summarize current literature in terms of potential host genetic and epigenetic factors that associated with increased severity of Covid-19. Several studies indicated that the genetic variants of the SARS-CoV-2 entry mechanism-related (angiotensin-converting enzymes, transmembrane serine protease-2, furin) and host innate immune response-related genes (interferons [IFNs], interleukins, toll-like receptors), and human leukocyte antigen, ABO, 3p21.31, and 9q34.2 loci are critical host determinants related to Covid-19 severity. Epigenetic mechanisms also affect Covid-19 outcomes by regulating IFN signaling, angiotensin-converting enzyme-2, and immunity-related genes that particularly escape from X chromosome inactivation. Enhanced understanding of host genetic and epigenetic factors and viral interactions of SARS-CoV-2 is critical for improved prognostic tools and innovative therapeutics.

Golub E, Aouizerat BE, Kuniholm MH, Millstein J. Association of HLA Genotype With T-Cell Activation in Human Immunodeficiency Virus (HIV) and HIV/Hepatitis C Virus-Coinfected Women

BACKGROUND

Global immune activation and HLA alleles are each associated with the pathogenesis of human immunodeficiency virus (HIV) and hepatitis C virus .

METHODS

We evaluated the relationship between 44 HLA class I and 28 class II alleles and percentages of activated CD8 (CD8+CD38+DR+) and CD4 (CD4+CD38+DR+) T cells in 586 women who were naive to highly active antiretroviral therapy. We used linear generalized estimating equation regression models, adjusting for race/ethnicity, age, HIV load, and hepatitis C virus infection and controlling for multiplicity using a false discovery rate threshold of 0.10.

RESULTS

Ten HLA alleles were associated with CD8 and/or CD4 T-cell activation. Lower percentages of activated CD8 and/or CD4 T cells were associated with protective alleles B*57:03 (CD8 T cells, -6.6% [P = .002]; CD4 T cells, -2.7% [P = .007]), C*18:01 (CD8 T cells, -6.6%; P < .0008) and DRB1*13:01 (CD4 T cells, -2.7%; P < .0004), and higher percentages were found with B*18:01 (CD8 T cells, 6.2%; P < .0003), a detrimental allele. Other alleles/allele groups associated with activation included C*12:03, group DQA1*01:00, DQB1*03:01, DQB1*03:02, DQB1*06:02, and DQB1*06:03.

CONCLUSION

These findings suggest that a person's HLA type may play a role in modulating T-cell activation independent of viral load and sheds light on the relationship between HLA, T-cell activation, immune control, and HIV pathogenesis.

Immune correlates of the Thai RV144 HIV vaccine regimen in South Africa

One of the most successful HIV vaccines to date, the RV144 vaccine tested in Thailand, demonstrated correlates of protection including cross-clade V1V2 immunoglobulin G (IgG) breadth, Env-specific CD4+ T cell polyfunctionality, and antibody-dependent cellular cytotoxicity (ADCC) in vaccinees with low IgA binding. The HIV Vaccine Trials Network (HVTN) 097 trial evaluated this vaccine regimen in South Africa, where clade C HIV-1 predominates. We compared cellular and humoral responses at peak and durability immunogenicity time points in HVTN 097 and RV144 vaccinee samples, and evaluated vaccine-matched and cross-clade immune responses. At peak immunogenicity, HVTN 097 vaccinees exhibited significantly higher cellular and humoral immune responses than RV144 vaccinees. CD4+ T cell responses were more frequent in HVTN 097 irrespective of age and sex, and CD4+ T cell Env-specific functionality scores were higher in HVTN 097. Env-specific CD40L+ CD4+ T cells were more common in HVTN 097, with individuals having this pattern of expression demonstrating higher median antibody responses to HIV-1 Env. IgG and IgG3 binding antibody rates and response magnitude to gp120 vaccine- and V1V2 vaccine-matched antigens were higher or comparable in HVTN 097 than in RV144 ADCC, and ADCP functional antibody responses were elicited in HVTN 097. Env-specific IgG and CD4+ Env responses declined significantly over time in both trials. Overall, cross-clade immune responses associated with protection were better than expected in South Africa, suggesting wider applicability of this regimen.

HIV long-term non-progressors elite controllers: an interplay between host, immune and viral factors

There is a rare group of HIV-1-infected individuals who show permanent control of clinical progression for over 10 years, maintain CD4+ cells >500 μl and have undetectable viral loads; they are designated long-term non-progressors elite controllers (LTNPs ECs). Multiple studies have demonstrated the necessary contribution of at least two of host, immune and viral factors to the LTNP phenotype. This group of individuals is not homogenous because of the different involvement of these factors. We will review the role of each of these and their combinations to the LTNP EC phenotype. LTNP EC individuals offer an opportunity for the investigation into the mechanisms for the spontaneous control of HIV infection.

Possible clearance of transfusion-acquired nef/LTR-deleted attenuated HIV-1 infection by an elite controller with CCR5 Δ32 heterozygous and HLA-B57 genotype

BACKGROUND

Subject C135 is one of the members of the Sydney Blood Bank Cohort, infected in 1981 through transfusion with attenuated nef/3' long terminal repeat (LTR)-deleted HIV-1, and has maintained undetectable plasma viral load and steady CD4 cell count, in the absence of therapy. Uniquely, C135 combines five factors separately associated with control of viraemia: nef/LTR-deleted HIV-1, HLA-B57, HLA-DR13, heterozygous CCR5 Δ32 genotype and vigorous p24-stimulated peripheral blood mononuclear cell (PBMC) proliferation. Therefore, we studied in detail viral burden and immunological responses in this individual.

METHODS

PBMC and gut and lymph node biopsy samples were analysed for proviral HIV-1 DNA by real-time and nested PCRs, and nef/LTR alleles by nested PCR. HIV-specific antibodies were studied by Western blotting, and CD4+ and CD8+ T lymphocyte responses were measured by proliferation and cytokine production in vitro.

RESULTS

PBMC samples from 1996, but not since, showed amplification of nef alleles with gross deletions. Infectious HIV-1 was never recovered. Proviral HIV-1 DNA was not detected in recent PBMC or gut or lymph node biopsy samples. C135 has a consistently weak antibody response and a substantial CD4+ T cell proliferative response to a previously described HLA-DR13-restricted epitope of HIV-1 p24 in vitro, which augmented a CD8+ T cell response to an immunodominant HLA-B57-restricted epitope of p24, while his T cells show reduced levels of CCR5.

CONCLUSIONS

Subject C135's early PCR and weak antibody results are consistent with limited infection with a poorly replicating nef/LTR-deleted strain of HIV-1. With his HLA-B57-restricted gag-specific CD8 and helper HLA-DR13-restricted CD4 T cell proliferative responses, C135 appears to have cleared his HIV-1 infection 37 years after transfusion.

Host genetic variation and HIV disease: from mapping to mechanism

This review aims to provide a summary of current knowledge of host genetic effects on human immunodeficiency virus (HIV) disease. Mapping of simple single nucleotide polymorphisms (SNP) has been largely successful in HIV, but more complex genetic associations involving haplotypic or epigenetic variation, for example, remain elusive. Mechanistic insights explaining SNP associations are incomplete, but continue to be forthcoming. The number of robust immunogenetic correlates of HIV is modest and their discovery mostly predates the genome-wide era. Nevertheless, genome-wide evaluations have nicely validated the impact of HLA and CCR5 variants on HIV disease, and importantly, made clear the many false positive associations that were previously suggested by studies using the candidate gene approach. We describe how multiple HIV outcome measures such as acquisition, viral control, and immune decline have been studied in adults and in children, but that collectively these identify only the two replicable loci responsible for modifying HIV disease, CCR5, and HLA. Recent heritability estimates in this disease corroborate the modest impact of genetic determinants and their oligogenic nature. While the mechanism of protection afforded by genetic variants that diminish CCR5 expression is clear, new aspects of HLA class I-mediated protection continue to be uncovered. We describe how these genetic findings have enhanced insights into immunobiology, been clinically translated into CCR5 antagonists, allowed prioritization of antigens for vaccination efforts, and identified targets for genome-editing interventions. Finally, we describe how studies of genetically complex parts of the genome using new tools may begin revealing additional correlates.

Human Leukocyte Antigen (HLA) and Immune Regulation: How Do Classical and Non-Classical HLA Alleles Modulate Immune Response to Human Immunodeficiency Virus and Hepatitis C Virus Infections?

The genetic factors associated with susceptibility or resistance to viral infections are likely to involve a sophisticated array of immune response. These genetic elements may modulate other biological factors that account for significant influence on the gene expression and/or protein function in the host. Among them, the role of the major histocompatibility complex in viral pathogenesis in particular human immunodeficiency virus (HIV) and hepatitis C virus (HCV), is very well documented. We, recently, added a novel insight into the field by identifying the molecular mechanism associated with the protective role of human leukocyte antigen (HLA)-B27/B57 CD8⁺ T cells in the context of HIV-1 infection and why these alleles act as a double-edged sword protecting against viral infections but predisposing the host to autoimmune diseases. The focus of this review will be reexamining the role of classical and non-classical HLA alleles, including class Ia (HLA-A, -B, -C), class Ib (HLA-E, -F, -G, -H), and class II (HLA-DR, -DQ, -DM, and -DP) in immune regulation and viral pathogenesis (e.g., HIV and HCV). To our knowledge, this is the very first review of its kind to comprehensively analyze the role of these molecules in immune regulation associated with chronic viral infections.

Impact of HLA-DRB1 allele polymorphisms on control of HIV infection in a Peruvian MSM cohort

Associations between HLA class II polymorphisms and HIV control were assessed in a Peruvian MSM cohort. Among 233 treatment naïve HIV+ individuals, DRB1*13:02 was linked to elevated viral loads (P = .044) while DRB1*12:01 showed significantly lower viral set points (P = .015) and restricted a dominant T cell response to HIV Gag p24 (P = .038). The present work contributes to a better knowledge of the Peruvian immunogenetics and supports the important role of HLA class II restricted T cells in HIV control.

Increased HIV-1 superinfection risk in carriers of specific human leukocyte antigen alleles

OBJECTIVE

The aim of this study was to characterize the demographic, behavioural, clinical and immunogenetic determinants of HIV-1 superinfection in a high-risk cohort of MSM.

DESIGN

A retrospective cohort study of prospectively followed MSM.

METHODS

Ninety-eight MSM with acute or early HIV-1 monoinfection were followed for a median of 15.6 months. Demographic and human leukocyte antigen (HLA) genotype data were collected at enrolment. Sexual behaviour, clinical and the infection status (monoinfection or superinfection) data were recorded at each visit (at enrolment and thereafter at a median of 4.2-month intervals). HIV-1 superinfection risk was determined by Cox regression and Kaplan-Meier survival analysis.

RESULTS

Ten individuals (10.2%) had superinfection during follow-up. Cox regression did not show significantly increased superinfection risk for individuals with an increased amount of condomless anal intercourse, lower CD4 T-cell count or higher viral load, but higher number of sexual contacts demonstrated a trend towards significance [hazard ratio, 4.74; 95% confidence interval (95% CI), 0.87-25.97; P = 0.073]. HLA-A*29 (hazard ratio, 4.10; 95% CI, 0.88-14.76; P = 0.069), HLA-B*35 (hazard ratio, 4.64; 95% CI, 1.33-18.17; P = 0.017), HLA-C*04 (hazard ratio, 5.30; 95% CI, 1.51-20.77; P = 0.010), HLA-C*16 (hazard ratio, 4.05; 95% CI, 0.87-14.62; P = 0.071), HLA-DRB1*07 (hazard ratio, 3.29; 95% CI, 0.94-12.90; P = 0.062) and HLA-DRB1*08 (hazard ratio, 15.37; 95% CI, 2.11-79.80; P = 0.011) were associated with an increased risk of superinfection at α = 0.10, whereas HLA-DRB1*11 was associated with decreased superinfection risk (hazard ratio, 0.13; 95% CI, 0.00-1.03; P = 0.054).

CONCLUSION

HLA genes may, in part, elucidate the genetic basis of differential superinfection risk, and provide important information for the development of efficient prevention and treatment strategies of HIV-1 superinfection.

HIV Controllers Exhibit Enhanced Frequencies of Major Histocompatibility Complex Class II Tetramer+ Gag-Specific CD4+ T Cells in Chronic Clade C HIV-1 Infection

Immune control of viral infections is heavily dependent on helper CD4+ T cell function. However, the understanding of the contribution of HIV-specific CD4+ T cell responses to immune protection against HIV-1, particularly in clade C infection, remains incomplete. Recently, major histocompatibility complex (MHC) class II tetramers have emerged as a powerful tool for interrogating antigen-specific CD4+ T cells without relying on effector functions. Here, we defined the MHC class II alleles for immunodominant Gag CD4+ T cell epitopes in clade C virus infection, constructed MHC class II tetramers, and then used these to define the magnitude, function, and relation to the viral load of HIV-specific CD4+ T cell responses in a cohort of untreated HIV clade C-infected persons. We observed significantly higher frequencies of MHC class II tetramer-positive CD4+ T cells in HIV controllers than progressors (P = 0.0001), and these expanded Gag-specific CD4+ T cells in HIV controllers showed higher levels of expression of the cytolytic proteins granzymes A and B. Importantly, targeting of the immunodominant Gag41 peptide in the context of HLA class II DRB1*1101 was associated with HIV control (r = -0.5, P = 0.02). These data identify an association between HIV-specific CD4+ T cell targeting of immunodominant Gag epitopes and immune control, particularly the contribution of a single class II MHC-peptide complex to the immune response against HIV-1 infection. Furthermore, these results highlight the advantage of the use of class II tetramers in evaluating HIV-specific CD4+ T cell responses in natural infections.IMPORTANCE Increasing evidence suggests that virus-specific CD4+ T cells contribute to the immune-mediated control of clade B HIV-1 infection, yet there remains a relative paucity of data regarding the role of HIV-specific CD4+ T cells in shaping adaptive immune responses in individuals infected with clade C, which is responsible for the majority of HIV infections worldwide. Understanding the contribution of HIV-specific CD4+ T cell responses in clade C infection is particularly important for developing vaccines that would be efficacious in sub-Saharan Africa, where clade C infection is dominant. Here, we employed MHC class II tetramers designed to immunodominant Gag epitopes and used them to characterize CD4+ T cell responses in HIV-1 clade C infection. Our results demonstrate an association between the frequency of HIV-specific CD4+ T cell responses targeting an immunodominant DRB1*11-Gag41 complex and HIV control, highlighting the important contribution of a single class II MHC-peptide complex to the immune response against HIV-1 infections.

HLA class II genes modulate vaccine-induced antibody responses to affect HIV-1 acquisition

In the RV144 vaccine trial, two antibody responses were found to correlate with HIV-1 acquisition. Because human leukocyte antigen (HLA) class II-restricted CD4(+) T cells are involved in antibody production, we tested whether HLA class II genotypes affected HIV-1-specific antibody levels and HIV-1 acquisition in 760 individuals. Indeed, antibody responses correlated with acquisition only in the presence of single host HLA alleles. Envelope (Env)-specific immunoglobulin A (IgA) antibodies were associated with increased risk of acquisition specifically in individuals with DQB1*06. IgG antibody responses to Env amino acid positions 120 to 204 were higher and were associated with decreased risk of acquisition and increased vaccine efficacy only in the presence of DPB1*13. Screening IgG responses to overlapping peptides spanning Env 120-204 and viral sequence analysis of infected individuals defined differences in vaccine response that were associated with the presence of DPB1*13 and could be responsible for the protection observed. Overall, the underlying genetic findings indicate that HLA class II modulated the quantity, quality, and efficacy of antibody responses in the RV144 trial.

Genetic Markers of the Host in Persons Living with HTLV-1, HIV and HCV Infections

Human T-cell leukemia virus type 1 (HTLV-1), hepatitis C virus (HCV) and human immunodeficiency virus type 1 (HIV-1) are prevalent worldwide, and share similar means of transmission. These infections may influence each other in evolution and outcome, including cancer or immunodeficiency. Many studies have reported the influence of genetic markers on the host immune response against different persistent viral infections, such as HTLV-1 infection, pointing to the importance of the individual genetic background on their outcomes. However, despite recent advances on the knowledge of the pathogenesis of HTLV-1 infection, gaps in the understanding of the role of the individual genetic background on the progress to disease clinically manifested still remain. In this scenario, much less is known regarding the influence of genetic factors in the context of dual or triple infections or their influence on the underlying mechanisms that lead to outcomes that differ from those observed in monoinfection. This review describes the main factors involved in the virus–host balance, especially for some particular human leukocyte antigen (HLA) haplotypes, and other important genetic markers in the development of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and other persistent viruses, such as HIV and HCV.

Multiple Approaches for Increasing the Immunogenicity of an Epitope-Based Anti-HIV Vaccine

The development of a highly effective vaccine against the human immunodeficiency virus (HIV) will likely be based on rational vaccine design, since traditional vaccine approaches have failed so far. In recent years, an understanding of what type of immune response is protective against infection and/or disease facilitated vaccine design. T cell-based vaccines against HIV have the goal of limiting both transmission and disease progression by inducing broad and functionally relevant T cell responses. In this context, CD4(+) T cells play a direct cytotoxic role and are also important for the generation and maintenance of functional CD8(+) T and B cell responses. The use of MHC-binding algorithms has allowed the identification of novel CD4(+) T cell epitopes that could be used in vaccine design, the so-called epitope-driven vaccine design. Epitope-based vaccines have the ability to focus the immune response on highly antigenic, conserved epitopes that are fully recognized by the target population. We have recently mapped a set of conserved multiple HLA-DR-binding HIV-1 CD4 epitopes and observed interferon (IFN)-γ-producing CD4(+) T cells when we tested these peptides in peripheral blood mononuclear cells (PBMCs) from HIV-infected individuals. We then designed multiepitopic DNA vaccines that induced broad and polyfunctional T cell responses in immunized mice. In this review we will focus on alternative strategies to increase the immunogenicity of an epitope-based vaccine against HIV infection.

Innate and Adaptive Immune Regulation During Chronic Viral Infections

Chronic viral infections represent a unique challenge to the infected host. Persistently replicating viruses outcompete or subvert the initial antiviral response, allowing the establishment of chronic infections that result in continuous stimulation of both the innate and adaptive immune compartments. This causes a profound reprogramming of the host immune system, including attenuation and persistent low levels of type I interferons, progressive loss (or exhaustion) of CD8(+) T cell functions, and specialization of CD4(+) T cells to produce interleukin-21 and promote antibody-mediated immunity and immune regulation. Epigenetic, transcriptional, posttranscriptional, and metabolic changes underlie this adaptation or recalibration of immune cells to the emerging new environment in order to strike an often imperfect balance between the host and the infectious pathogen. In this review we discuss the common immunological hallmarks observed across a range of different persistently replicating viruses and host species, the underlying molecular mechanisms, and the biological and clinical implications.

Development of a Sendai virus vector-based AIDS vaccine inducing T cell responses

Virus-specific CD8(+) T-cell responses play a major role in the control of HIV replication, and induction of HIV-specific T-cell responses is an important strategy for AIDS vaccine development. Optimization of the delivery system and immunogen would be the key for the development of an effective T cell-based AIDS vaccine. Heterologous prime-boost vaccine regimens using multiple viral vectors are a promising protocol for efficient induction of HIV-specific T-cell responses, and the development of a variety of potent viral vectors have been attempted. This review describes the current progress of the development of T cell-based AIDS vaccines using viral vectors, focusing on Sendai virus vectors, whose phase I clinical trials have been performed.

Associations of host genetic variants on CD4⁺ lymphocyte count and plasma HIV-1 RNA in antiretroviral naïve children

BACKGROUND

CD4 T-lymphocyte (CD4) counts and HIV plasma RNA concentration (RNA) are 2 key HIV disease markers. The complex interplay between virus and host genetics may contribute to differences in viral set point and CD4 status. Determining the effects of host genetic variation on HIV disease markers is often complicated by the use of antiretroviral therapy. In this study, the association between genetic variants and baseline HIV RNA and CD4 counts was examined in a large cohort of antiretroviral naïve children.

METHODS

Specimens from 1053 HIV-infected children were screened for single nucleotide polymorphisms in 78 regions from 17 genes. Linear regression with a robust variance estimator was used to test the association between genetic markers with HIV RNA and CD4 count, controlling for age, race/ethnicity and study. False discovery rate (FDR) controlling was used to adjust for multiple testing.

RESULTS

The study population was 60% black, 26% Hispanic and 13% white; median age 2.35 years; 55% female. Baseline median CD4 count was 780/mm; median log10 HIV RNA was 5.17 copies/mL. For analyses of the associations of genetic makers with baseline CD4 count, 6 HLA and 4 additional markers exhibited P < 0.05, but none met the criteria for statistical significance with FDR controlled at 0.05. For baseline HIV RNA, HLA DRB1*15, DRB1*10, B-27/57, B-14, Cw-8, B-57 were statistically significant with FDR controlled at 0.05.

CONCLUSIONS

These results provide strong evidence that HLA DRB1*15, DRB1*10, B-27/57, B-14, Cw-8, B-57 are associated with HIV RNA and play a role in HIV pathogenesis in infected children.

Association of HLA-DRB1-restricted CD4⁺ T cell responses with HIV immune control

The contribution of HLA class II-restricted CD4(+) T cell responses to HIV immune control is poorly defined. Here, we delineated previously uncharacterized peptide-DRB1 restrictions in functional assays and analyzed the host genetic effects of HLA-DRB1 alleles on HIV viremia in a large cohort of HIV controllers and progressors. We found distinct stratifications in the effect of HLA-DRB1 alleles on HIV viremia, with HLA-DRB1*15:02 significantly associated with low viremia and HLA-DRB1*03:01 significantly associated with high viremia. Notably, a subgroup of HLA-DRB1 variants linked with low viremia showed the ability to promiscuously present a larger breadth of peptides with lower functional avidity when compared to HLA-DRB1 variants linked with high viremia. Our data provide systematic evidence that HLA-DRB1 variant expression has a considerable impact on the control of HIV replication, an effect that seems to be mediated primarily by the protein specificity of CD4(+) T cell responses to HIV Gag and Nef.

Immunogenetics of HIV disease

Host genetic factors are a major contributing factor to the inter-individual variation observed in response to human immunodeficiency virus (HIV) infection and are linked to resistance to HIV infection among exposed individuals, as well as rate of disease progression and the likelihood of viral transmission. Of the genetic variants that have been shown to affect the natural history of HIV infection, the human leukocyte antigen (HLA) class I genes exhibit the strongest and most consistent association, underscoring a central role for CD8(+) T cells in resistance to the virus. HLA proteins play important roles in T-cell-mediated adaptive immunity by presenting immunodominant HIV epitopes to cytotoxic T lymphocytes (CTLs) and CD4(+) T cells. Genetic and functional data also indicate a function for HLA in natural killer cell-mediated innate immunity against HIV by interacting with killer cell immunoglobulin-like receptors (KIR). We review the HLA and KIR associations with HIV disease and discuss the mechanisms underlying these associations.

Hierarchy of CD4 T cell epitopes of the ANRS Lipo5 synthetic vaccine relies on the frequencies of pre-existing peptide-specific T cells in healthy donors

The Agence National de Recherche sur le SIDA et les hepatitis Lipo5 vaccine is composed by five long fragments of HIV proteins and was recently shown to induce in seronegative volunteers a CD4 T cell response largely dominated by the G2 fragment. To understand this response profile, we submitted the five HIV fragments to HLA-DR-binding assays and evaluated the frequency of naive Lipo5-specific CD4 T lymphocytes in the blood of 22 healthy individuals. We enumerated the Lipo5-specific T cell lines induced in vitro by weekly rounds of specific stimulation. Four peptides and hence not only G2 exhibited a broad specificity for HLA-DR molecules. In contrast, most of the T cell lines specific for Lipo5 reacted with G2, revealing a G2-specific T cell repertoire superior to 2 cells per million, whereas it is close to 0.4 for the other peptides. We also found good cross-reactivity of all the peptides with clade B and C variants and that G2 and P1 are able to recruit T cells that recognize HIV-infected cells. We therefore mainly observed very good concordance between the frequency to individual Lipo5 peptides among vaccinees in a large-scale vaccine trial and the distribution of peptide specificity of the in vitro induced T cell lines. These findings underline the role of the size of the epitope-specific naive repertoire in shaping the CD4 T cell response after vaccination and highlight the value of evaluating the naive repertoire to predict vaccine immunogenicity.

Innate and Adaptive Immunity in Long-Term Non-Progression in HIV Disease

Long-term non-progressors (LTNP) were identified after 10-15 years of the epidemic, and have been the subject of intense investigation ever since. In a small minority of cases, infection with nef/3'LTR deleted attenuated viral strains allowed control over viral replication. A common feature of LTNP is the readily detected proliferation of CD4 T-cells in vitro, in response to p24. In some cases, the responding CD4 T-cells have cytotoxic effector function and may target conserved p24 epitopes, similar to the CD8 T-cells described below. LTNP may also carry much lower HIV DNA burden in key CD4 subsets, presumably resulting from lower viral replication during primary infection. Some studies, but not others, suggest that LTNP have CD4 T-cells that are relatively resistant to HIV infection in vitro. One possible mechanism may involve up-regulation of the cell cycle regulator p21/waf in CD4 T-cells from LTNP. Delayed progression in Caucasian LTNP is also partly associated with heterozygosity of the Δ32 CCR5 allele, probably through decreased expression of CCR5 co-receptor on CD4 T-cells. However, in approximately half of Caucasian LTNP, two host genotypes, namely HLA-B57 and HLA-B27, are associated with viral control. Immunodominant CD8 T-cells from these individuals target epitopes in p24 that are highly conserved, and escape mutations have significant fitness costs to the virus. Furthermore, recent studies have suggested that these CD8 T-cells from LTNP, but not from HLA-B27 or HLA-B57 progressors, can cross-react with intermediate escape mutations, preventing full escape via compensatory mutations. Humoral immunity appears to play little part in LTNP subjects, since broadly neutralizing antibodies are rare, even amongst slow progressors. Recent genome-wide comparisons between LTNP and progressors have confirmed the HLA-B57, HLA-B27, and delta32 CCR5 allelic associations, plus indicated a role for HLA-C/KIR interactions, but have not revealed any new genotypes so far. Nevertheless, it is hoped that studying the mechanisms of intracellular restriction factors, such as the recently identified SAMHD1, will lead to a better understanding of non-progression.

Recent advances in research of HIV infection: implications of viral and host genetics on treatment and prevention

The genetic diversity among human immunodeficiency virus (HIV) subtypes as well as the variability of viral sequences found in HIV-infected individuals presents a number of difficult obstacles for the development of universally effective HIV treatment and prevention methods. Here, we present a brief summary of recent developments in the analysis of viral genetics and human genomics to provide insight into future methods for HIV treatment and prevention. Recent studies have mined viral sequences found in newly infected individuals to identify common features of all transmitted viruses that could provide potential targets for HIV vaccine development. Analysis of human immunogenetics has identified specific alleles associated with reduced virus loads in HIV-infected individuals providing valuable information that may influence individual responses to treatment and prevention methods. Increased sensitivity of antiretroviral drug resistance testing has improved the detection of hidden drug resistant virus but also highlighted the potential for drug resistant viruses to reduce the effectiveness of clinical treatment regimens. The rapidly expanding amount of data generated by studies of viral genetics and human immunogenetics will provide valuable information to guide the design of new strategies to improve clinical treatment and enhance HIV vaccine development.

CD8+ and CD4+ cytotoxic T cell escape mutations precede breakthrough SIVmac239 viremia in an elite controller

Background

Virus-specific T cells are critical components in the containment of immunodeficiency virus infections. While the protective role of CD8+ T cells is well established by studies of CD8+ T cell-mediated viral escape, it remains unknown if CD4+ T cells can also impose sufficient selective pressure on replicating virus to drive the emergence of high-frequency escape variants. Identifying a high frequency CD4+ T cell driven escape mutation would provide compelling evidence of direct immunological pressure mediated by these cells.

Results

Here, we studied a SIVmac239-infected elite controller rhesus macaque with a 1,000-fold spontaneous increase in plasma viral load that preceded disease progression and death from AIDS-related complications. We sequenced the viral genome pre- and post-breakthrough and demonstrate that CD8+ T cells drove the majority of the amino acid substitutions outside of Env. However, within a region of Gag p27^CA targeted only by CD4+ T cells, we identified a unique post-breakthrough mutation, Gag D205E, which abrogated CD4+ T cell recognition. Further, we demonstrate that the Gag p27^CA-specific CD4+ T cells exhibited cytolytic activity and that SIV bearing the Gag D205E mutation escapes this CD4+ T cell effector function ex vivo.

Conclusions

Cumulatively, these results confirm the importance of virus specific CD8+ T cells and demonstrate that CD4+ T cells can also exert significant selective pressure on immunodeficiency viruses in vivo during low-level viral replication. These results also suggest that further studies of CD4+ T cell escape should focus on cases of elite control with spontaneous viral breakthrough.

The T-cell response to HIV

HIV is a disease in which the original clinical observations of severe opportunistic infections gave the first clues regarding the underlying pathology, namely that HIV is essentially an infection of the immune system. HIV infects and deletes CD4(+) T cells that normally coordinate the adaptive T- and B-cell response to defend against intracellular pathogens. The immune defect is immediate and profound: At the time of acute infection with an AIDS virus, typically more than half of the gut-associated CD4(+) T cells are depleted, leaving a damaged immune system to contend with a life-long infection.

HIV-1 dynamics: a reappraisal of host and viral factors, as well as methodological issues

The dynamics of HIV-1 viremia is a complex and evolving landscape with clinical and epidemiological (public health) implications. Most studies have relied on the use of set-point viral load (VL) as a readily available proxy of viral dynamics to assess host and viral correlates. This review highlights recent findings from population-based studies of set-point VL, focusing primarily on robust data related to host genetics. A comprehensive understanding of viral dynamics will clearly need to consider both host and viral characteristics, with close attention to (i) the timing of VL measurements, (ii) the biology of viral evolution, (iii) compartments of active viral replication, (iv) the transmission source partner as the immediate past microenvironment, and (v) proper application of statistical models.

NK and CD4+ T cell cooperative immune responses correlate with control of disease in a macaque simian immunodeficiency virus infection model

Control of infectious disease may be accomplished by successful vaccination or by complex immunologic and genetic factors favoring Ag-specific multicellular immune responses. Using a rhesus macaque model, we evaluated Ag-specific T cell-dependent NK cell immune responses in SIV-infected macaques, designated "controlling" or "noncontrolling" based on long-term chronic viremia levels, to determine whether NK cell effector functions contribute to control of SIV infection. We observed that Gag stimulation of macaque PBMCs induced subset-specific NK cell responses in SIV-controlling but not SIV-noncontrolling animals, as well as that circulatory NK cell responses were dependent on Ag-specific IL-2 production by CD4(+) central memory T cells. NK cell activation was blocked by anti-IL-2-neutralizing Ab and by CD4(+) T cell depletion, which abrogated the Gag-specific responses. Among tissue-resident cells, splenic and circulatory NK cells displayed similar activation profiles, whereas liver and mucosal NK cells displayed a decreased activation profile, similar in SIV-controlling and -noncontrolling macaques. Lack of T cell-dependent NK cell function was rescued in SIV-noncontrolling macaques through drug-mediated control of viremia. Our results indicate that control of disease progression in SIV-controlling macaques is associated with cooperation between Ag-specific CD4(+) T cells and NK cell effector function, which highlight the importance of such cell-to-cell cooperativity in adaptive immunity and suggest that this interaction should be further investigated in HIV vaccine development and other prophylactic vaccine approaches.

Transcriptional network predicts viral set point during acute HIV-1 infection

BACKGROUND

HIV-1-infected individuals with higher viral set points progress to AIDS more rapidly than those with lower set points. Predicting viral set point early following infection can contribute to our understanding of early control of HIV-1 replication, to predicting long-term clinical outcomes, and to the choice of optimal therapeutic regimens.

METHODS

In a longitudinal study of 10 untreated HIV-1-infected patients, we used gene expression profiling of peripheral blood mononuclear cells to identify transcriptional networks for viral set point prediction. At each sampling time, a statistical analysis inferred the optimal transcriptional network that best predicted viral set point. We then assessed the accuracy of this transcriptional model by predicting viral set point in an independent cohort of 10 untreated HIV-1-infected patients from Malawi.

RESULTS

The gene network inferred at time of enrollment predicted viral set point 24 weeks later in the independent Malawian cohort with an accuracy of 87.5%. As expected, the predictive accuracy of the networks inferred at later time points was even greater, exceeding 90% after week 4. The composition of the inferred networks was largely conserved between time points. The 12 genes comprising this dynamic signature of viral set point implicated the involvement of two major canonical pathways: interferon signaling (p<0.0003) and membrane fraction (p<0.02). A silico knockout study showed that HLA-DRB1 and C4BPA may contribute to restricting HIV-1 replication.

CONCLUSIONS

Longitudinal gene expression profiling of peripheral blood mononuclear cells from patients with acute HIV-1 infection can be used to create transcriptional network models to early predict viral set point with a high degree of accuracy.

Interplay between HIV-1 and Host Genetic Variation: A Snapshot into Its Impact on AIDS and Therapy Response

As of February 2012, 50 circulating recombinant forms (CRFs) have been reported for HIV-1 while one CRF for HIV-2. Also according to HIV sequence compendium 2011, the HIV sequence database is replete with 414,398 sequences. The fact that there are CRFs, which are an amalgamation of sequences derived from six or more subtypes (CRF27_cpx (cpx refers to complex) is a mosaic with sequences from 6 different subtypes besides an unclassified fragment), serves as a testimony to the continual divergent evolution of the virus with its approximate 1% per year rate of evolution, and this phenomena per se poses tremendous challenge for vaccine development against HIV/AIDS, a devastating disease that has killed 1.8 million patients in 2010. Here, we explore the interaction between HIV-1 and host genetic variation in the context of HIV/AIDS and antiretroviral therapy response.

Lack of association between HLA class II alleles and in vitro replication capacities of recombinant viruses encoding HIV-1 subtype C Gag-protease from chronically infected individuals

It is unknown whether favorable HLA class II alleles may attenuate HIV-1 through selection pressure in a manner similar to that of protective HLA class I alleles. We investigated the relationship between HLA class II alleles and in vitro replication capacities of recombinant viruses encoding HIV-1 subtype C Gag-protease from chronically infected individuals. No associations were found between individual alleles and lower replication capacity, suggesting no significant HIV-1 attenuation by HLA class II-restricted Gag-specific CD4(+) T cell immune pressure.

HIV controllers: a multifactorial phenotype of spontaneous viral suppression

A small minority of HIV-infected individuals, known as HIV controllers, is able to exert long-term control over HIV replication in the absence of treatment. Increasing evidence suggests that the adaptive immune system plays a critical role in this control but also that a combination of several host and/or viral factors, rather than a single cause, leads to this rare phenotype. Here, we review recent advances in the study of these remarkable individuals. We summarize the epidemiology and clinical characteristics of HIV controllers, and subsequently describe contributing roles of host genetic factors, innate and adaptive immune responses, and viral factors to this phenotype. We emphasize distinctive characteristics of HIV-specific CD4 T cell responses and of CD4 T cell subpopulations that are frequently found in HIV controllers. We discuss major controversies in the field and the relevance of the study of HIV controllers for the development of novel therapeutic strategies and vaccines.