Influence of HLA supertypes on susceptibility and resistance to human immunodeficiency virus type 1 infection

CTL response to HIV type 1 subtype C is poorly predicted by known epitope motifs

Cytotoxic T lymphocyte (CTL) responses are thought to be essential for the control of HIV-1 replication in vivo and immunogens that elicit CTL responses are currently a major focus of HIV vaccine research. Here we investigated two aspects of the CTL response to HIV-1 subtype C that are important for vaccine design and efficacy monitoring. First, we assessed the relationship between the CTL response and sequence diversity, using a robust statistical method. While peptides that were most frequently recognized by the CTL response in Nef and p24 tended to be conserved, this was not the case for p17 where epitope recognition coincided with highly variable regions. Second, we investigated the relationship between observed and predicted CTL responses, given the HLA genotype of infected individuals. Only 52% of the Nef peptides and 64% of the Gag peptides that elicited a CTL response contained sequence motifs thought to be required for binding by the HLA-A or -B alleles found in the corresponding patient. In a comparable subtype B dataset a much higher proportion of the peptides that elicited a CTL response were consistent with the patient HLA genotype (96% and 83% for Nef and Gag, respectively). We demonstrate that this difference between subtypes C and B is likely to result from a combination of a tendency for HLA alleles common in Southern African populations to be poorly characterized, as well as a tendency for sequence motifs associated with HLA recognition to be overspecified for sequence variation found in the B clade. Our results suggest that knowledge of HLA binding motifs is likely to be biased toward certain populations and subtypes. This can have important implications for understanding immune escape and predicting vaccine efficacy in the context of populations primarily infected with non-B subtype HIV-1.

Mucosal challenge with cell-associated or cell-free feline immunodeficiency virus induces rapid and distinctly different patterns of phenotypic change in the mucosal and systemic immune systems

The majority of human immunodeficiency virus type 1 (HIV-1) infections occur via mucosal transmission through contact with genital secretions containing cell-associated and cell-free virus. However, few studies have assessed whether exposure to cells, HIV-1 infected or uninfected, plays a role in the sexual transmission of HIV-1. This study examined phenotypic changes in mucosal and systemic lymphoid tissue 24 hr after vaginal exposure to in vitro equilibrated infectious doses of cell-associated or cell-free feline immunodeficiency virus, uninfected heterologous cells, or medium alone. We found that even at this early time-point, mucosal exposure to virus induced substantial alterations in the phenotype and distribution of leucocytes, particularly in the tissues of the mucosal immune system. Second, we found that the type of virus inoculum directly influenced the phenotypic changes seen. Vaginal exposure to cell-free virus tended to induce more generalized phenotypic changes, typically in the peripheral immune system (blood and systemic lymph nodes). In contrast, exposure to cell-associated virus was primarily associated with phenotypic shifts in the mucosal immune system (gut and mucosal/draining lymph nodes). In addition, we found that exposure to uninfected heterologous cells also induced alterations in the mucosal immune system. These data suggest that significant immune changes occur within the first 24 hr of virus exposure, well before substantial replication would be anticipated. As the mucosal immune system, and particularly the gut, is an early and persistent target for lentiviral replication, these findings have substantial implications for HIV-1 pathogenesis and vaccine development.

Polymorphisms in IRF-1 associated with resistance to HIV-1 infection in highly exposed uninfected Kenyan sex workers

OBJECTIVE

To determine the correlation between polymorphisms in the IL-4 gene cluster and resistance to HIV-1 infection.

DESIGN

: A cross-sectional genetic analysis of polymorphisms within the IL-4 gene cluster was conducted in a well-described female sex worker cohort from Nairobi, Kenya, known to exhibit differential susceptibility to HIV-1 infection.

METHODS

Microsatellite genotyping was used to screen six microsatellite markers in the IL-4 gene cluster for associations with HIV-1 resistance. Further analysis of the interferon regulatory factor 1 (IRF-1) gene was conducted by genomic sequencing. Associations between IRF-1 gene polymorphisms and the HIV-1 resistance phenotype were determined using the chi-square test and Kaplan-Meier survival analysis. The functional consequence of IRF-1 polymorphism was conducted by quantitative Western blot.

RESULTS

Three polymorphisms in IRF-1, located at 619, the microsatellite region and 6516 of the gene, showed associations with resistance to HIV-1 infection. The 619A, 179 at IRF-1 microsatellite and 6516G alleles were associated with the HIV-1-resistant phenotype and a reduced likelihood of seroconversion. Peripheral blood mononuclear cells from patients with protective IRF-1 genotypes exhibited significantly lower basal IRF-1 expression and reduced responsiveness to exogenous IFN-gamma stimulation.

CONCLUSION

Polymorphisms in the IRF-1 gene are associated with resistance to infection by HIV-1 and a lowered level of IRF-1 protein expression. This study adds IRF-1, a transcriptional immunoregulatory gene, to the list of genetic correlates of altered susceptibility to HIV-1. This is the first report suggesting that a viral transcriptional regulator might contribute to resistance to HIV-1. Further functional analysis on the role of IRF-1 polymorphisms and HIV-1 resistance is underway.

Spontaneous and antigen-induced chemokine production in exposed but uninfected partners of HIV type 1-infected individuals in North India

Exposure to human immunodeficiency virus (HIV)-1 does not inevitably result in infection and resistance to HIV-1 infection is observed in different categories of at-risk individuals. In this study, the role of beta-chemokines and alpha-chemokine in providing resistance to HIV-1 infection was evaluated in a group of 25 HIV-exposed but uninfected (EU) partners of HIV-1-infected individuals. We studied the levels of regulated on activation, normal T expressed and secreted (RANTES), macrophage inflammatory protein (MIP)-1 alpha, MIP-1 beta , and stromal cell-derived factor (SDF)-1alpha in culture supernatants of peripheral blood mononuclear cells (PBMCs) after stimulation with HIV gag p24 antigen and phytohemagglutinin (PHA). Higher gag-specific beta-chemokine responses were seen in EU individuals and HIV-positive controls when compared with healthy controls (HC). No significant difference was observed in PHA-specific beta-chemokine production between these three groups. Moreover, a spontaneous production of all the three beta-chemokines by unstimulated PBMCs was observed in EU individuals and HIV-positive controls. No significant difference was observed in alpha-chemokine (SDF-1) levels between the three groups after p24 and PHA stimulation. We conclude that in our cohort of EU individuals, beta-chemokines-mediated resistance against HIV might be present. Since beta-chemokines are produced mainly by activated T cells, our results suggest that enhanced chemokine production might be due to exposure to HIV in these individuals.

Human Leukocyte Antigen Class I and Class II Allele Frequencies and HIV-1 Infection Associations in a Chinese Cohort

China has one of the most rapidly spreading HIV-1 epidemics. To develop a vaccine targeted to specific human leukocyte antigen (HLA) epitopes in this population, allele distribution analysis is needed. We performed low-resolution class I and II HLA typing of a cohort of 393 subjects from mainland China using a polymerase chain reaction with sequence-specific primers (PCR-SSPs). We found 10 class I alleles present in more than 10% of the population: HLA-A*02, HLA-A*11, HLA-A*24, HLA-B*13, HLA-B*15, HLA-B*40, HLA-Cw*03, HLA-Cw*07, HLA-Cw*01, and HLA-Cw*06. Several class II alleles were found at high frequency (>or=10%): HLA-DRB3, HLA-DRB4, HLA-DRB5, HLA-DRB1*0701, HLA-DRB1*1501, HLA-DRB1*0401, HLA-DRB1*0901, HLA-DRB1*1201, HLA-DQB1*0601, HLA-DQB1*0301, HLA-DQB1*0201, HLA-DQB1*0501, and HLA-DQB*0303. We also estimated 2- and 3-locus haplotype frequencies. Because this cohort contained 280 HIV-1-seropositive and 113 HIV-1-seronegative individuals, we compared allele and haplotype frequencies between the infected and control groups to explore correlations between HLA antigens and susceptibility/resistance to HIV infection. The HLA-B*14 allele was only found in the HIV-1-seropositive group, and many 2-locus haplotypes were significantly overrepresented in this group: HLA-B*14/Cw*08, HLA-B*51/Cw*14, HLA-A*02/B*13, HLA-A*31/Cw*14, HLA-A*02/Cw*06, and the class II haplotype HLA-DRB1*1301/DQB1*0601. Alleles significantly increased in the HIV-1-seronegative controls were HLA-B*44, HLA-Cw*04, and HLA-DRB1*1402. Overrepresented 2-locus haplotypes in the control group were HLA-B*44/Cw*04, HLA-A*31/Cw*03, HLA-A*03/Cw*07, HLA-A*11/B*13, HLA-A*11/B*38, HLA-A*24/B*52, and HLA-A*11/Cw*01. The 3-locus haplotypes HLA-A*24/Cw*03/B*40 and HLA-A*02/B*15/DRB1*1201 were found to be increased significantly in the control group. These data contribute to the database of allele frequencies and associations with HIV infection in the Chinese population.

Cutting edge: resistance to HIV-1 infection among African female sex workers is associated with inhibitory KIR in the absence of their HLA ligands

NK cells are regulated in part by killer Ig-like receptors (KIR) that interact with HLA molecules on potential target cells. KIR and HLA loci are highly polymorphic and certain KIR/HLA combinations were found to protect against HIV disease progression. We show in this study that KIR/HLA interactions also influence resistance to HIV transmission. HIV-exposed but seronegative female sex workers in Abidjan, Côte d'Ivoire, frequently possessed inhibitory KIR genes in the absence of their cognate HLA genes: KIR2DL2/KIR2DL3 heterozygosity in the absence of HLA-C1 and KIR3DL1 homozygosity in the absence of HLA-Bw4. HIV-seropositive female sex workers were characterized by corresponding inhibitory KIR/HLA pairings: KIR2DL3 homozygosity together with HLA-C1 and a trend toward KIR3DL1/HLA-Bw4 homozygosity. Absence of ligands for inhibitory KIR could lower the threshold for NK cell activation. In addition, exposed seronegatives more frequently possessed AB KIR genotypes, which contain more activating KIR. The data support an important role for NK cells and KIR/HLA interactions in antiviral immunity.

Characterization of CD8 T-cell responses in HIV-1-exposed seronegative commercial sex workers from Nairobi, Kenya

CD8+ T-lymphocyte responses are crucial to the control of HIV-1; therefore, studying the CD8+ immune response in a naturally resistant population could provide valuable insights into an effective anti-HIV response in healthy uninfected individuals. Approximately 5-10% of the women in the Pumwani Commercial Sex Worker cohort in Nairobi, Kenya, have been highly exposed to HIV-1 yet remain HIV-IgG-seronegative and HIV-PCR negative (HIV(ES)). As IFN-gamma production correlates to cytotoxic function, the CD8+ T-lymphocyte IFN-gamma response to HIV p24 peptides was compared in HIV(ES) and HIV-infected (HIV+) individuals. Almost 40% of the HIV(ES) had a CD8+ IFN-gamma+ response that was five times lower in magnitude than that of the HIV+ group. The breadth of the response in HIV(ES) was very narrow and focused primarily on one peptide that is similar to the protective KK10 peptide. In the HIV+ group, low peripheral CD4+ counts negatively influenced the number of CD8+ cells producing IFN-gamma, which may undermine the ability to control HIV. Overall, many of the HIV(ES) women possess a HIV-1 p24-specific CD8+ IFN-gamma response, providing evidence to the specificity needed for an effective HIV vaccine.

The Impact on Coronary Artery Disease of Common Polymorphisms Known to Modulate Responses to Pathogens

There are two distinct models to explain how genetic variants contributing to cardiovascular disease may have arisen. Firstly, variants may result from random, initially neutral, mutations whose effects are largely revealed in post-reproductive individuals in industrialized societies. Alternatively, the introduced variants may confer an adaptive advantage in certain circumstances. Resistance to pathogens is one of the strongest selection pressures on human proteins. To determine whether this evolutionary pressure has made a large contribution to heart disease we tested whether seventeen polymorphisms in fourteen innate-immunity genes, with documented evidence of modulating response to pathogens, had an impact on heart disease. Genotyping was performed in 1,598 CAD subjects (ACS or stable angina) and 332 controls. The TLR4 399Ile allele had the greatest impact on ACS risk (uncorrected p = 0.006); however there was no evidence overall that the resistance alleles cumulatively influenced the risk of ACS compared to controls or stable angina patients (p = 0.12, and p = 0.40, respectively). We did note a significant interaction between age at onset of disease and combined resistance allele carriership when the ACS and non-thrombotic, stable angina groups were compared (p = 0.04, 16 d.f.). This suggests that innate immunity factors could have a greater impact on thrombus formation among younger CAD patients.

Human susceptibility to viral infection: the search for HIV-protective alleles among Africans by means of genome-wide studies

Human immunodeficiency virus (HIV) infection represents a major global health problem, with HIV now recognized as the fourth leading cause of death on a worldwide basis. One approach to developing effective anti- HIV interventions is to identify and understand the molecular mechanisms by which natural genetic variations provide protection from infection or disease progression. This approach can be used to identify human gene alleles that confer resistance or increased susceptibility to HIV infection. To date, however, this approach has been underutilized in the African population and all HIV-resistance alleles that have been described have been identified by evaluating candidate genes. This limited approach is based upon a researcher's assumption that those genes that will provide the host with a benefit can be predicted, a priori, but it does not provide for a large scale systematic screen of all possible candidate genes. Nonetheless, this method has met with some success in identifying HIV-resistance genes, mostly among the white population. The lack of a comprehensive genetic approach, both in terms of the populations studied and the percentage of the genome investigated, likely explains why all of the HIV-restriction alleles identified to date fall within two gene families, and why no resistance genes have been identified among black Africans. It is likely, as with any complex trait, that most protective alleles will provide only partial HIV resistance. Thus, HIV resistance in most persons likely arises through a QTL (quantitative trait loci) mechanism meaning that protection is a polygenic trait. This feature coupled with interpopulation genetic heterogeneity makes the candidate gene mapping approach a daunting task. A comprehensive genome-wide case-control allelic association study in the African population will maximize our chances of identifying new targets for the development of new therapeutics that have the promise of benefiting all persons infected with HIV.

Protective immunity against hepatitis C virus infection

There is increasing evidence that a small percentage of individuals exposed to the hepatitis C virus have the capacity to generate a strong cellular immune response against the virus and avoid persistent infection, and perhaps do so repeatedly after re-exposure. This article reviews the evidence that the responses identified in this unique group of individuals represent the protective immunity that will need to be elicited by hepatitis C virus vaccines.

Reduced CD4 T cell activation and in vitro susceptibility to HIV-1 infection in exposed uninfected Central Africans

BACKGROUND

Environmentally driven immune activation was suggested to contribute to high rates of HIV-1 infection in Africa. We report here a study of immune activation markers and susceptibility to HIV-1 infection in vitro of forty-five highly exposed uninfected partners (EUs) of HIV-1 infected individuals in Central African Republic, in comparison with forty-four low-risk blood donors (UCs).

RESULTS

Analysis of T lymphocyte subsets and activation markers in whole blood showed that the absolute values and the percentage of HLA-DR+CD4 T cells and of CCR5+CD4 T cells were lower in the EUs than in the UCs (p = 0.0001). Mutations in the CCR5 coding region were not found in either group. Susceptibility to in vitro infection of unstimulated peripheral blood mononuclear cells, prior of PHA activation, was decreased in EUs compared to UCs, either using a CXCR4-tropic or a CCR5-tropic HIV-1 strain (p = 0.02 and p = 0.05, respectively). Levels of MIP-1beta, but not of MIP-1alpha or RANTES, in the supernatants of PHA-activated PBMC, were higher in the EUs than in the UCs (p = 0.007).

CONCLUSION

We found low levels of CD4 T cell activation and reduced PBMC susceptibility to HIV-1 infection in Central African EUs, indicating that both may contribute to the resistance to HIV-1 infection.

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.

Suppressed cellular alloimmune responses in HIV-exposed seronegative female sex workers

Particular human leucocyte antigen (HLA) polymorphisms have been associated with a reduced risk of HIV transmission. However, protective alloimmune responses expected to result from such a genetic predisposition have not been demonstrated. To this end, we analysed and compared cellular and humoral alloimmune responses in a cohort of female sex workers who remained human immunodeficiency virus (HIV)-seronegative despite more than 3 years of high-risk sexual activity (ESN FSWs) with those of low-risk HIV-seronegative female blood donors in Abidjan, Côte d'Ivoire. ESN FSWs showed significantly lower allostimulated CD69 expression and secretion of interferon-gamma, macrophage inflammatory protein (MIP)-1beta and RANTES (regulated upon activation, normal T-cell expressed and secreted) by lymphocytes than controls. In contrast, ESN FSWs showed significantly higher mitogen-stimulated CD69 expression and secretion of tumour necrosis factor-alpha and MIP-1beta than controls. Suppression of cellular alloimmune responses among ESN FSWs was associated with a higher self-reported frequency of unprotected sex. Levels of anti-HLA class I alloantibodies in plasma were not significantly different between ESN FSWs and controls. These findings indicate that frequent sexual exposure to multiple partners results in suppression rather than activation of cellular alloimmune responses. Our data support the hypothesis that suppressed cellular alloimmune responses may play a role in protection against HIV infection.

nef gene sequence variation among HIV-1-infected African children*

BACKGROUND

There are few data on African children infected with nonclade B HIV-1 in endemic settings, which limits generalizations about pathogenesis and progression. Genotypic and phenotypic variations in host immunogenetics and HIV-1 negative factor (nef) accessory protein may influence disease progression and have frequently been characterized in subjects infected with clade B HIV-1.

METHODS

In this descriptive study, we report nef gene sequence variation and host genetic polymorphisms in 32 Kenyan children, including 12 slow progressors.

RESULTS

Phylogenetic analysis identified HIV-1 clades A, C and D and a recombinant A/D subtype. Grossly defective nef genes or significant changes from relevant clade reference sequences were not identified in children with delayed disease progression.

CONCLUSIONS

nef sequence variations may not be common in perinatally infected African children. Further studies are warranted in HIV-1-infected subjects in settings where infection is endemic.

HLA class II disease associations in southern Africa

Southern Africa harbors several population groups representing a diversity of gene pool origins. This provides a unique opportunity to study genetic disease predisposition in these populations against a common environmental background. Human leukocyte antigen (HLA) association studies of these populations could improve knowledge on inter-population variation and HLA-related disease susceptibility. The aim of this paper is to review HLA class II disease associations reported for southern African population groups, compare them with findings in other populations and identify those unique to southern Africa. A number of HLA class II disease associations appear to be unique to southern African populations. These include DRB1*14011 association with insulin-dependent diabetes mellitus susceptibility in the Xhosa and DRB1*10 and DQB1*0302 with rheumatoid arthritis susceptibility in the South African (SA) Indian and SA Coloreds, respectively. A noteworthy similarity in class II disease association was observed among southern African Caucasoid and their European parental populations. Unique HLA class II disease associations observed in southern Africa are consistent with the notion that unique environmental and natural selective factors have resulted in certain ethnic-specific HLA class II disease associations, while common HLA class II disease associations found across different populations support the notion that common diseases are caused by common, ancient alleles present in indigenous African populations.

Prospective study of one million deaths in India: rationale, design, and validation results

BACKGROUND

Over 75% of the annual estimated 9.5 million deaths in India occur in the home, and the large majority of these do not have a certified cause. India and other developing countries urgently need reliable quantification of the causes of death. They also need better epidemiological evidence about the relevance of physical (such as blood pressure and obesity), behavioral (such as smoking, alcohol, HIV-1 risk taking, and immunization history), and biological (such as blood lipids and gene polymorphisms) measurements to the development of disease in individuals or disease rates in populations. We report here on the rationale, design, and implementation of the world's largest prospective study of the causes and correlates of mortality.

METHODS AND FINDINGS

We will monitor nearly 14 million people in 2.4 million nationally representative Indian households (6.3 million people in 1.1 million households in the 1998-2003 sample frame and 7.6 million people in 1.3 million households in the 2004-2014 sample frame) for vital status and, if dead, the causes of death through a well-validated verbal autopsy (VA) instrument. About 300,000 deaths from 1998-2003 and some 700,000 deaths from 2004-2014 are expected; of these about 850,000 will be coded by two physicians to provide causes of death by gender, age, socioeconomic status, and geographical region. Pilot studies will evaluate the addition of physical and biological measurements, specifically dried blood spots. Preliminary results from over 35,000 deaths suggest that VA can ascertain the leading causes of death, reduce the misclassification of causes, and derive the probable underlying cause of death when it has not been reported. VA yields broad classification of the underlying causes in about 90% of deaths before age 70. In old age, however, the proportion of classifiable deaths is lower. By tracking underlying demographic denominators, the study permits quantification of absolute mortality rates. Household case-control, proportional mortality, and nested case-control methods permit quantification of risk factors.

CONCLUSIONS

This study will reliably document not only the underlying cause of child and adult deaths but also key risk factors (behavioral, physical, environmental, and eventually, genetic). It offers a globally replicable model for reliably estimating cause-specific mortality using VA and strengthens India's flagship mortality monitoring system. Despite the misclassification that is still expected, the new cause-of-death data will be substantially better than that available previously.

Genetic influences on HIV infection: implications for vaccine development

Human HIV infection is characterised by great variability in outcome. Much of this variability is due either to viral variation or host genetic factors, particularly major histocompatibility complex differences within genetically diverse populations. The study of non-human primates infected with well characterised simian immunodeficiency virus strains has recently allowed further dissection of the critical role of genetic influences on both susceptibility to infection and progression to AIDS. This review summarises the important role of many host genetic factors on HIV infection and highlights important variables that will need to be taken into account in evaluating effective HIV vaccines.

Resistance to HIV infection

The biological correlates of an effective immune response that could contain or prevent HIV infection remain elusive despite substantial scientific accomplishments in understanding the interactions among the virus, the individual and the community. The observation that some individuals appear to possess resistance to HIV infection or its consequences has generated a host of epidemiologic investigations to identify biological or behavioral characteristics of these individuals. These data might hold the keys to developing appropriate strategies for mimicking the effective responses of those who appear immune. In this paper we review genetic mechanisms including the role of chemokines and their receptors, cytokines, host genetic immune response to HIV infection, local immune response correlating with behavioral variables, co-infection and immune based mechanisms that have been elucidated so far. We offer suggestions for how to use these observations as platforms for future research to further understand natural resistance to HIV infection through cohort studies, population genotype sampling, mathematical modeling of virus-host interactions and behavioral analyses.

Basics of the virology of HIV-1 and its replication

Human immunodeficiency virus is undoubtedly the causative agent of AIDS. The understanding of HIV-1 pathogenesis is essential to develop and maintain antiretroviral treatment and vaccination. Since the first isolation of HIV-1 in cell culture, thousands of publications dealing with HIV and/or AIDS per year were released. In this review we give a basic overview of the virology of HIV-1 including the functions of the different HIV-1 proteins required for effective viral replication. Moreover, we summarize the interactive processes between HIV-1 and its target cells. Finally, the HIV-1 specific immune response and the current status of antiretroviral therapy are briefly described in this review.

Lack of associations between HLA class II alleles and resistance to HIV-1 infection among white, non-Hispanic homosexual men

HLA class II alleles were molecularly typed for 100 high-risk seronegative men and 184 low-risk seroconverters from the Multicenter AIDS Cohort Study (MACS). Seven resistant individuals homozygous for CCR5 Delta32 deletions were excluded from analysis. In the univariate analysis, no significant HLA class II associations with resistance/susceptibility to HIV type 1 infection were identified. However, the transporter associated with antigen presentation 2 (TAP2) Ala 665 variant associated with resistance in earlier analyses in the MACS was in linkage disequilibrium with some HLA class II alleles. After adjusting for the established associations with HLA-A*0205 subgroup and TAP2 Ala 665 variant, no HLA class II alleles were independently associated with resistance/susceptibility to HIV-1 infection. Other genetic factors in the HLA class II-TAP region of the major histocompatibility complex might be involved.

Global human genetics of HIV-1 infection and China

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

Major histocompatibility complex class II (HLA-DRB and -DQB) allele frequencies in Botswana: association with human immunodeficiency virus type 1 infection

Southern Africa is facing an unprecedented public health crisis due to the high prevalence of human immunodeficiency virus type 1 (HIV-1). Vaccine development and testing efforts, mainly based on elicitation of HIV-specific T cells, are under way. To understand the role of human leukocyte antigen (HLA) class II alleles in HIV pathogenesis and to facilitate HLA-based HIV-1 vaccine design, we analyzed the frequencies of HLA class II alleles within the southern African country of Botswana. Common HLA class II alleles were identified within the Botswana population through the molecular genotyping of DRB and DQB1 loci. The DRB1 allele groups DRB1*01, DRB1*02/15, DRB1*03, DRB1*11, and DRB1*13 were encountered at frequencies above 20%. Within the DQB1 locus, DQB1*06 (47.7%) was the most common allele group, followed by DQB1*03 (39.2%) and DQB1*04 (25.8%). We found that DRB1*01 was more common in HIV-negative than in HIV-positive individuals and that those who expressed DRB1*08 had lower median viral loads. We demonstrate that the frequencies of certain HLA class II alleles in this Botswana population differ substantially from those in North American populations, including African-Americans. Common allele groups within Botswana cover large percentages of other African populations and could be targeted in regional vaccine designs.

Human immunodeficiency virus mutations during the first month of infection are preferentially found in known cytotoxic T-lymphocyte epitopes

The full protein coding region of human immunodeficiency virus (HIV) genomes were sequenced using plasma collected from nine African-Americans prior to seroconversion and 7 to 28 days later. HIV mutations emerged in seven of these subjects at a genomewide rate of 2% per year. The location of nonsynonymous (NS) HIV mutations within these subjects was compared to their potential HLA-A and B types restricted CTL epitopes reported in the Los Alamos National Laboratory HIV immunology database. A statistically significant (P < 0.005) number of the early NS mutations (13.5%) were found within previously reported CTL epitopes. A virus sequencing and reported CTL epitopes database analysis therefore support a model where a significant proportion of very early nonsynonymous HIV mutations are selected by CTL.

Human alpha defensin in HIV-exposed but uninfected individuals

Human alpha defensins 1, 2, and 3 are produced by CD8 T cells of HIV-infected long-term nonprogressors and have an antiviral activity. alpha Defensins were examined in peripheral blood mononuclear cells (PBMCs), cervical-vaginal mononuclear cells (CVMCs), and cervical biopsies of 9 HIV-1-exposed but uninfected women (ESNs), 10 HIV-infected patients (HIV), and 13 low-risk healthy controls (HCs). Results showed that, whereas alpha defensin production and alpha defensin-expressing CD8 lymphocytes were comparable in ESNs and HIV patients, constitutive alpha defensin production by peripheral CD8 and CVMCs was augmented in ESNs compared with HCs (P = 0.001 and P = 0.058, respectively); alpha defensin mRNA was increased in PBMCs of ESNs; unstimulated, alpha defensin-expressing peripheral and mucosal CD8 lymphocytes were 10-fold higher in ESNs compared with HCs (P = 0.003 and P = 0.01, respectively); and alpha defensin mRNA and alpha defensin-expressing cells were augmented in cervical biopsies of ESN compared with HCs (mRNA:P = 0.03). The differences were reduced upon in vitro mitogen stimulation. A robust constitutive production of alpha defensin is seen in HIV-exposed uninfected individuals; these peptides could have a role in the potentially protective immune response that characterizes ESNs.

From the Old World to the New World: an ecologic study of population susceptibility to HIV infection

It remains unclear why the global distribution of human immunodeficiency virus (HIV), between and within continents, is so heterogeneous. This ecologic study of 34 populations of the Americas explored the hypothesis that populations differ in their intrinsic, biological susceptibility to HIV which, together with exposure, might determine the ultimate 'mature' prevalence. If true, national HIV prevalence in populations of the Americas should be predictable from each country's ethnic mosaic, inter-racial admixture and HIV prevalence in regions of Africa, Europe and Asia from where their ancestors migrated. For each country, the adult population (15-49 years) was multiplied by the proportion corresponding to each ethnic group by HIV prevalence in the country/region of origin of each group, yielding the predicted prevalences, which were then compared with observed prevalences documented by UNAIDS for 2001. Predicted and observed HIV prevalences were highly correlated (r = 0.70, P < 0.001). In North America, predicted prevalences were within 0.5% of the observed values, except for African-Americans and African-Canadians. In Central and South America, differences between predicted and observed prevalences were <1.0% except in Honduras and Guyana. Some Caribbean countries had a predicted prevalence identical to the observed one, but there were outliers. Overall, predicted prevalence was 0.93% and observed prevalence 0.64%; two-thirds of this difference was attributed to Brazil. Although it was not possible to adjust to the confounding effects of sexual behaviour and cofactors of transmission (such as sexually transmitted infections) because of the lack of nationally representative data for each and every country, a number of arguments reviewed in the paper suggest that confounders cannot explain all this association and that differential susceptibility might be an important determinant of steady-state HIV prevalence.

Human immunodeficiency virus (HIV)-2-specific T lymphocyte proliferative responses in HIV-2-infected and in HIV-2-exposed but uninfected individuals in Guinea-Bissau

Human immunodeficiency virus (HIV)-2-specific T lymphocyte proliferative responses were determined in cultures of peripheral blood mononuclear cells from HIV-2-exposed uninfected individuals, HIV-2-infected individuals and HIV-negative controls in Guinea-Bissau. Increased HIV-2-specific T lymphocyte proliferative responses were detected in both groups compared to HIV-negative controls (healthy HIV-uninfected individuals without known exposure to an HIV-infected person); five out of 29 of the HIV-2-exposed uninfected and half (16 of 32) of the HIV-2-infected individuals had stimulation indexes >2, compared to one out of 49 of the HIV-negative controls (P = 0.003 and P < 0.0001, respectively). The exposed uninfected individuals had reactivity to a HIV-2 V3-peptide corresponding to amino acids 311-326 of the envelope glycoprotein, while the HIV-2-infected people reacted mainly to HIV-2 whole viral lysate. Thus, this study demonstrates a high degree of HIV-2-specific T helper cell activity, as measured by lymphocyte proliferation, in HIV-2-exposed uninfected individuals as well as in HIV-2-infected subjects. These immune responses could be important for resistance to the infection and for the control of established infection and, thus, play a role in the lower transmission and progression of HIV-2 compared to HIV-1.

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.

An independent role of protective HLA class II alleles in rheumatoid arthritis severity and susceptibility

OBJECTIVE

To prospectively investigate the effect of the DERAA-encoding HLA alleles on disease susceptibility and severity in a large cohort of patients with rheumatoid arthritis (RA), and to differentiate protective effects from non-predisposition by comparing subgroups of patients with an equal amount of predisposition alleles.

METHODS

HLA class II alleles were determined in 440 patients with early RA and in 423 healthy controls. In order to study the effect of HLA on disease severity, radiographic joint destruction was evaluated, using the modified Sharp/van der Heijde method, during 4 years of followup.

RESULTS

The presence of DERAA-encoding HLA-DRB1 alleles conferred a lower risk of developing RA for both the presence and absence of SE alleles (odds ratio 0.6). At all time points, radiographic destruction was significantly less severe in DERAA-positive patients with 1 SE allele compared with DERAA-negative patients with 1 SE allele. Additionally, a protective effect of DERAA was detected in the groups of patients who were prone to having more severe disease because of the presence of anti-cyclic citrullinated peptide antibodies or because of smoking.

CONCLUSION

DERAA-encoding HLA-DRB1 alleles independently protect against RA and are associated with less severe disease.

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

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

Laboratory-based risk factors for cytomegalovirus retinitis

BACKGROUND

Very few studies have investigated risk factors for cytomegalovirus (CMV) retinitis. Identifying these risk factors will have many benefits, including helping establish screening regimens, examination frequency regimens, and targeted prophylaxis with oral therapy with valganciclovir or other anti-CMV agents. The purpose of this study was to determine the laboratory-based risk factors for CMV retinitis in patients with AIDS.

METHODS

We conducted a case-control study involving 120 patients in whom CMV retinitis had been diagnosed in 1990-99 and 159 patients without CMV retinitis from the same period. The sampling was from a primary study base in eastern Ontario and western Quebec of patients with AIDS and CD4 counts less than 50 cells/microL at the time of diagnosis of retinitis in the case subjects or an analogous date for the control subjects. There were two components to the study. In the first component (n = 279) we examined standard-of-care laboratory tests (hematologic and nutrition variables) done during the study period. In the second component (n = 57), which was a subset of the first, we examined laboratory tests (HLA type, qualitative and quantitative CMV polymerase chain reaction [PCR] and HIV load) on stored blood samples from the eastern Ontario site. Multivariate logistic regression was used to model the data and control for confounding. We developed a systematic model-building strategy, from assumption testing to model building to model checking.

RESULTS

A low hemoglobin concentration was a statistically significant predictor of CMV retinitis (odds ratio [OR] 0.96, 95% confidence interval [CI] 0.94-0.98). Both qualitative CMV PCR (OR 21.71, 95% CI 1.80-261.67) and quantitative CMV PCR (OR 33.03,95% CI 2.32-469.39) were strong predictors of CMV retinitis. Among the 80 HLA types tested, HLA-Bw4 (OR 11.68, 95% CI 1.29-105.82) and HLA-DRB115 (OR 9.34, 95% CI 1.14-76.41) were significant predictors of CMV retinitis, whereas HLA-Cw7 was protective against CMV retinitis (OR 0.09, 95% CI 0.01-0.67).

INTERPRETATION

We have identified laboratory variables that elevate (or decrease) the risk of CMV retinitis. These findings may be useful to clinicians and health policy experts in developing rational guidelines for screening, examination frequency and targeted prophylaxis for patients with AIDS.

Novel interferon regulatory factor-1 polymorphisms in a Kenyan population revealed by complete gene sequencing

Variation in susceptibility to HIV-1 infection depends on numerous factors, and host genetic variation has been well-described as an important component. As a transcriptional regulator, interferon regulatory factor 1 (IRF-1) plays a key role in both innate and adaptive immunity against viral infection. IRF-1 has also been shown to directly interact with HIV-1 5' LTR and efficiently initiate or amplify HIV-1 replication. By complete gene sequencing, we investigated genetic polymorphism of the IRF-1 gene in an HIV-1-endemic Kenyan population. This population displayed extensive genetic diversity at the IRF-1 locus. Fifty-three single nucleotide polymorphisms (SNPs) were identified in this population, including 26 novel SNPs. Two insertion and one deletion polymorphisms in IRF-1 were also identified. Linkage disequilibrium (LD) among these genetic variations was shown to be common in IRF-1. The functional consequences of these mutations in the context of HIV-1/AIDS remain to be determined. We also identified 35 consistent discrepancies between IRF-1 GenBank sequences and our population based sequencing data, suggesting that the previously submitted GenBank data were not representative of the majority of human IRF-1 sequences.

Structures of HLA-A*1101 complexed with immunodominant nonamer and decamer HIV-1 epitopes clearly reveal the presence of a middle, secondary anchor residue

HLA-A*1101 is one of the most common human class I alleles worldwide. An increased frequency of HLA-A*1101 has been observed in cohorts of female sex workers from Northern Thailand who are highly exposed to HIV-1 and yet have remained persistently seronegative. In view of this apparent association of HLA-A*1101 with resistance to acquisition of HIV-1 infection, and given the importance of eliciting strong CTL responses to control and eliminate HIV-1, we have determined the crystal structure of HLA-A*1101 complexed with two immunodominant HIV-1 CTL epitopes: the nonamer reverse transcriptase(313-321) (AIFQSSMTK) and decamer Nef(73-82) (QVPLRPMTYK) peptides. The structures confirm the presence of primary anchor residues P2-Ile/-Val and P9-/P10-Lys, and also clearly reveal the presence of secondary anchor residues P6-Ser for reverse transcriptase and P7-Met for Nef. The overall backbone conformation of both peptides is defined as two bulges that are separated by a more buried middle residue. In this study, we discuss how this topology may offer functional advantages in the selection and presentation of HIV-1 CTL epitopes by HLA-A*1101. Overall, this structural analysis permits a more accurate definition of the peptide-binding motif of HLA-A*1101, the characterization of its antigenic surface, and the correlation of molecular determinants with resistance to HIV-1 infection. These studies are relevant for the rational design of HLA-A*1101-restricted CTL epitopes with improved binding and immunological properties for the development of HIV-1 vaccines.

Variation in vaccine response in normal populations

Genetic polymorphisms of the human leukocyte antigen (HLA) system significantly influence the variation in immune responses to viral vaccines. Considerable data on the genetic determinants of immune responses to the measles vaccine support the importance of HLA genes in determining the variation in vaccine response. HLA class I and class II, TAP, and HLA-DM allele associations with measles-specific antibody levels following measles vaccination have revealed, in part, the immunologic basis for mechanisms of measles immunity variation. Associations between HLA genotype and immune responses have also been reported for other vaccines and infectious diseases, such as hepatitis B and C, human papillomaviruses, and influenza. Vaccine pharmacogenomics may provide important insights for the design and development of new peptide-based vaccines against measles and other pathogens.

Persistence of low levels of simian immunodeficiency virus in macaques that were transiently viremic by conventional testing

Transient SIV viremia after experimental SIV challenge has been documented. Whether SIV persists in these transiently viremic macaques remains unclear. In the present study, we applied a sensitive PCR and found persistent low levels of SIVmne infection (LLSI) (range: 0.1-5.3 SIV DNA copies/10(6) PBMC) in seven macaques that were transiently positive by conventional assays, which was 10(2)- to 10(6)-fold less than those of SIVmne infected monkeys with typical disease progression. SIV envelope V1 sequences remained homogeneous in these macaques for the 6-year study period, with a mean evolution rate of 0.005% per site per year, which was not different from zero (P = 0.612) and significantly lower than that (0.56-1.18%) in macaques with progressive infection of SIVmne. LLSI macaques have remained free from SIV-associated illness, and are still alive 10 years after virus inoculation. Understanding the mechanisms underlying this outcome may provide valuable insight into therapy and vaccine development.

Human leukocyte antigen (HLA) B*18 and protection against mother-to-child HIV type 1 transmission

Human leukocyte antigen (HLA) molecules regulate the cellular immune system and may be determinants of infant susceptibility to human immunodeficiency virus type 1 (HIV-1) infection. Molecular HLA typing for class I alleles was performed on infants followed in a Kenyan perinatal cohort. Early HIV-1 infection status was defined as infection occurring at birth or month 1, while late infection via breast milk was defined as first detection of HIV-1 after 1 month of age. Likelihood ratio tests based on a proportional hazards model adjusting for maternal CD4 T cell count and HIV-1 viral load at 32 weeks of gestation were used to test associations between infant allelic variation and incident HIV-1 infection. Among 433 infants, 76 (18%) were HIV-1 infected during 12 months of follow-up. HLA B*18 was associated with a significantly lower risk of early HIV-1 transmission [relative risk (RR) = 0.26; 95% confidence interval (CI) 0.04-0.82], and none of the 24 breastfeeding infants expressing HLA B*18 who were uninfected at month 1 acquired HIV-1 late via breast milk. We observed a trend toward increased early HIV-1 acquisition for infants presenting HLA A*29 (RR = 2.0; 95% CI 1.0-3.8) and increased late HIV-1 acquisition via breast milk for both Cw*07 and Cw*08 (RR = 4.0; 95% CI 1.0-17.8 and RR = 7.2; 95% CI 1.2-37.3, respectively). HLA B*18 may protect breast-feeding infants against both early and late HIV-1 acquisition, a finding that could have implications for the design and monitoring of HIV-1 vaccines targeting cellular immune responses against HIV-1.

Potent neutralizing serum immunoglobulin A (IgA) in human immunodeficiency virus type 2-exposed IgG-seronegative individuals

The mechanisms behind the resistance to human immunodeficiency virus type 2 (HIV-2) infection are still not fully understood. In the present study, we explored the HIV-2-specific humoral serum immunoglobulin A (IgA) immune response in HIV-2-exposed IgG-seronegative (EGSN) individuals. Serum samples from heterosexual EGSN individuals and their known HIV-2-infected partners, as well as controls originating from Guinea-Bissau in Africa, were studied. Antibody reactivity to native and recombinant envelope glycoproteins was investigated, and the capacity of purified serum IgA to neutralize HIV-2(SBL6669) was tested. Our results showed that 16 of 25 EGSN samples exhibited reactivity against whole HIV-2 antigen, 6 of 25 samples reacted with recombinant gp36 (rgp36), and 3 of 25 samples were positive against HIV-2 rgp105; no reactivity to native HIV-2 gp125 was detected. Purified serum IgA antibodies from both EGSN and HIV-2-positive individuals, but not that from the negative controls, exhibited neutralization of HIV-2(SBL6669). The most potent neutralization activity was exhibited by IgA purified from EGSN compared to infected individuals' IgA. The antigenic pattern of the HIV-2-positive partners showed that all serum IgA samples were reactive to whole HIV-2 antigen, and 14 of 15 reacted with rgp36. For rgp105 and gp125, 5 of 15 and 4 of 15 samples exhibited binding, respectively. The serum of the EGSN group had a higher mean IgA concentration than that of the negative controls (P < 0.05). Thus, we describe HIV-2-specific serum IgA antigen reactivity and show a more potent serum IgA-mediated HIV-2-neutralizing activity in EGSN individuals than in HIV-2-infected patients.

Transmission of HIV-1 and HLA-B allele-sharing within serodiscordant heterosexual Zambian couples

Factors that might increase risk of HIV-1 transmission include age, sex, and amount of HIV-1 RNA in plasma, but findings for HLA allele-sharing are not in agreement. We tested the hypothesis that allele sharing at HLA loci is associated with increased risk of transmission of HIV-1 infection in cohabiting heterosexual Zambian couples. We studied 125 initially serodiscordant partners with sequence-confirmed interpartner HIV-1 transmission and 104 couples who were persistently serodiscordant, and we analysed relations with molecularly typed HLA-A, B, and C alleles by survival techniques. After adjustment for other genetic and non-genetic risk factors seen with heterosexual transmission of HIV-1 in this cohort, sharing of HLA-B alleles was independently associated with accelerated intracouple transmission (relative hazard 2.23, 95% CI 1.52-3.26, p<0.0001). Selective pressure by HLA-B alleles on transmitted viruses accords with current understanding of the effect of B locus polymorphism in HIV-1 and perhaps other infections.

Risk associated HIV-1 cross-clade resistance of whole peripheral blood mononuclear cells from exposed uninfected individuals with wild-type CCR5

Highly HIV exposed, persistently uninfected individuals (EUs) may hold clues to the generation of effective vaccine induced acquired immunity against HIV, and considerable effort has been devoted to detecting and characterizing HIV specific immune responses in EU cohorts. When searching for such clues, it is important to exclude individuals with genetically determined absence of receptors, as this protective mechanism could not be induced by HIV specific vaccines. Homozygosity for the DeltaC32 mutation of CCR5 prevents R5 HIV infection, independent of any virus-specific immune responses that may be acquired by exposure, while heterozygosity influences susceptibility to low level exposure. Reports on the in vitro susceptibility of EU cells compared to controls have been conflicting. Therefore, we studied 14 EUs with homozygous wild type CCR5, using a newly developed in vitro challenge assay (IVCA) to measure the magnitude and breadth of resistance to infection among EUs. CD8+ cells were relatively increased compared to controls, and were largely responsible for resistance to challenge, which depended on dose of virus inoculum, and extended across clades. Consistent with some EU cohort studies, resistance waned among individuals who reduced their high-risk behavior.

Human immunodeficiency virus type 1 fitness is a determining factor in viral rebound and set point in chronic infection

Human immunodeficiency virus type 1 (HIV-1) isolates from 20 chronically infected patients who participated in a structured treatment interruption (STI) trial were studied to determine whether viral fitness influences reestablishment of viremia. Viruses derived from individuals who spontaneously controlled viremia had significantly lower in vitro replication capacities than viruses derived from individuals that did not control viremia after interruption of antiretroviral therapy (ART), and replication capacities correlated with pre-ART and post-STI viral set points. Of note, no clinically relevant improvement of viral loads upon STI occurred. Virus isolates from controlling and noncontrolling patients were indistinguishable in terms of coreceptor usage, genetic subtype, and sensitivity to neutralizing antibodies. In contrast, viruses from controlling patients exhibited increased sensitivity to inhibition by chemokines. Sensitivity to inhibition by RANTES correlated strongly with slower replication kinetics of the virus isolates, suggesting a marked dependency of these virus isolates on high coreceptor densities on the target cells. In summary, our data indicate that viral fitness is a driving factor in determining the magnitude of viral rebound and viral set point in chronic HIV-1 infection, and thus fitness should be considered as a parameter influencing the outcome of therapeutic intervention in chronic infection.

CD4 cell and CD8 cell-mediated resistance to HIV-1 infection in exposed uninfected intravascular drug users in Vietnam

OBJECTIVE

To identify mechanisms of resistance to HIV-1 infection in exposed uninfected individuals.

DESIGN

We examined in-vitro cell susceptibility to HIV-1 infection in highly exposed Vietnamese intravascular drug users (IDU) who, despite a history of more than 10 years of drug use and a high prevalence of other blood-borne viral infections, remain apparently HIV uninfected.

METHODS

Forty-five exposed uninfected IDU and 50 blood donors were included in the study. Peripheral blood mononuclear cells (PBMC) or CD4 cell susceptibilities to HIV infection were evaluated using three HIV-1 isolates with different tropisms. Polymerase chain reaction analysis of HIV-1-DNA replication intermediates was used to characterize the restriction of HIV-1 replication in CD4 cells. Homologous CD8 cells were mixed with infected CD4 cells to evaluate their role in virus suppression.

RESULTS

We observed a relative resistance to PBMC infection with HIV-1 in 21 out of 45 exposed uninfected IDU, but only in five out of 50 unexposed controls (P < 0.001). PBMC resistance was related either to an inhibition of HIV-1 replication in CD4 cells or to CD8 cell-mediated viral suppression. HIV-1 replication in CD4 cells was restricted at the early stages of the viral cycle.

CONCLUSION

Reduced PBMC susceptibility to HIV-1 infection was associated with resistance to infection in exposed uninfected IDU. Distinct mechanisms are involved in in-vitro resistance and may contribute to the apparent protection from HIV-1 transmission in this systemically exposed population.

Specific nature of cellular immune responses elicited by chimpanzees against HIV-1

Recent epidemiologic and phylogenetic analyses suggest that in the human population human immunodeficiency virus (HIV-1) is a relatively new pathogen that arose by zoonotic transmission from chimpanzees. In humans the morbidity and mortality figures due to HIV infection are extremely high. In a very small percentage of the human population, however, individuals have been identified who were infected for more than 20 years and have no evidence of disease progression. In contrast to most infected humans, almost all chimpanzees appear to be resistant to the pathologic effects caused by lentiviruses such as HIV-1. Here we review the characteristics of the HIV-1-specific cell-mediated immune responses mounted by chimpanzees, and we postulate the mechanisms that have evolved that facilitate their resistance to acquired immunodeficiency syndrome.

The influence of HLA genotype on AIDS

Genetic resistance to infectious diseases is likely to involve a complex array of immune-response and other genes with variants that impose subtle but significant consequences on gene expression or protein function. We have gained considerable insight into the genetic determinants of HIV-1 disease, and the HLA class I genes appear to be highly influential in this regard. Numerous reports have identified a role for HLA genotype in AIDS outcomes, implicating many HLA alleles in various aspects of HIV disease. Here we review the HLA associations with progression to AIDS that have been consistently affirmed and discuss the underlying mechanisms behind some of these associations based on functional studies of immune cell recognition.

Persistence of extraordinarily low levels of genetically homogeneous human immunodeficiency virus type 1 in exposed seronegative individuals

Some individuals remain inexplicably seronegative and lack evidence for human immunodeficiency virus type 1 (HIV-1) infection by conventional serologic or virologic testing despite repeated high-risk virus exposures. Here, we examined 10 exposed seronegative (ES) individuals exhibiting HIV-1-specific cytotoxicity for the presence of HIV-1. We discovered HIV-1 DNA in resting CD4(+) T cells (mean, 0.05 +/- 0.01 copies per million cells) at multiple visits spanning 69 to 130 weeks in two ES individuals at levels that were on average 10(4)- to 10(6)-fold lower than those of other HIV-1-infected populations reported. Sequences of HIV-1 envelope and gag genes remained markedly homogeneous, indicating little to undetectable virus replication. These results provide the evidence for HIV-1 infection in ES individuals below the detection limit of standard assays, suggesting that extraordinary control of infection can occur. The two HIV-infected ES individuals remained healthy and were not superinfected with other HIV-1 strains despite continued high-risk sexual exposures to multiple HIV-infected partners. Understanding the mechanisms that confer diminished replicative capacity of HIV-1 in these hosts is paramount to developing strategies for protection against and control of HIV-1 infection.

Innate and adaptive mucosal immunity in protection against HIV infection

Control of the HIV pandemic requires an effective vaccine. The difficulties in developing a preventive vaccine are generally believed to be due to the rapid rate of mutation of HIV that escapes cytotoxic lymphocytes (CTL) and the problems in induction of neutralising antibodies to wild strains of HIV. These difficulties should re-orientate vaccine strategy into four somewhat neglected areas of immunisation. Innate immunity, with its rapid protective response to infection that is independent of memory and relies on an optimal mucosal adjuvant. Targeting the genital and rectal mucosa, with the associated lymph nodes, as an immune response has to be elicited directly on encountering HIV during sexual intercourse. Stimulating a broadly based adaptive immune response that enhances the memory CD4(+) and CD8(+) T cells and B cells, induces maturation of dendritic cells and results in Th1 polarised immunity. Taking advantage of "experiments of nature", by utilising host antigens, as manifested by protection against HIV infection in homozygous Delta32 CCR5 individuals and in allo-immunity.

Effects of MHC class I on HIV/SIV disease in primates

Data indicate that resistance to HIV-1 disease involves an array of contrasting HLA genotypic effects that are subtle, but significant, particularly when these genetic effects are considered as a whole. Numerous reports attributing a role for HLA genotype in AIDS outcomes have been reported, and a few of these have been affirmed in multiple studies. Functional studies of immune cell recognition have provided clues to the underlying mechanisms behind some of the strongest HLA associations, suggesting the means by which relative resistance or susceptibility to the virus may occur. SIV infection in non-human primates has served as an invaluable model for understanding AIDS pathogenesis (in rhesus monkeys) and viral resistance (in chimpanzee). The effect of rhesus MHC class I molecules on the evolution of SIV has been convincingly described [19], and a recent study in humans has suggested that selection pressure conferred by HLA molecules is responsible for specific genetic variation in HIV-1 [114]. HIV-1 may eventually have conspicuous evolutionary effects on HLA and other AIDS restriction genes, a prolonged process that could have occurred in chimpanzee [92]. To prevent such an outcome, it will be necessary to approach the disease from many perspectives, andapply comprehensively the knowledge gained to the successful control of the virus.

Association between virus-specific T-cell responses and plasma viral load in human immunodeficiency virus type 1 subtype C infection

Virus-specific T-cell immune responses are important in restraint of human immunodeficiency virus type 1 (HIV-1) replication and control of disease. Plasma viral load is a key determinant of disease progression and infectiousness in HIV infection. Although HIV-1 subtype C (HIV-1C) is the predominant virus in the AIDS epidemic worldwide, the relationship between HIV-1C-specific T-cell immune responses and plasma viral load has not been elucidated. In the present study we address (i) the association between the level of plasma viral load and virus-specific immune responses to different HIV-1C proteins and their subregions and (ii) the specifics of correlation between plasma viral load and T-cell responses within the major histocompatibility complex (MHC) class I HLA supertypes. Virus-specific immune responses in the natural course of HIV-1C infection were analyzed in the gamma interferon (IFN-gamma)-enzyme-linked immunospot assay by using synthetic overlapping peptides corresponding to the HIV-1C consensus sequence. For Gag p24, a correlation was seen between better T-cell responses and lower plasma viral load. For Nef, an opposite trend was observed where a higher T-cell response was more likely to be associated with a higher viral load. At the level of the HLA supertypes, a lower viral load was associated with higher T-cell responses to Gag p24 within the HLA A2, A24, B27, and B58 supertypes, in contrast to the absence of such a correlation within the HLA B44 supertype. The present study demonstrated differential correlations (or trends to correlation) in various HIV-1C proteins, suggesting (i) an important role of the HIV-1C Gag p24-specific immune responses in control of viremia and (ii) more rapid viral escape from immune responses to Nef with no restraint of plasma viral load. Correlations between the level of IFN-gamma-secreting T cells and viral load within the MHC class I HLA supertypes should be considered in HIV vaccine design and efficacy trials.

Balanced polymorphism selected by genetic versus infectious human disease

The polymorphisms within the human genome include several functional variants that cause debilitating inherited diseases. An elevated frequency of some of these deleterious mutations can be explained by a beneficial effect that confers a selective advantage owing to disease resistance in carriers of such mutations during an infectious disease outbreak. We here review plausible examples of balanced functional polymorphisms and their roles in the defense against pathogens. The genome organization of the chemokine receptor and HLA gene clusters and their influence on the HIV/AIDS epidemic provides compelling evidence for the interaction of infectious and genetic diseases in recent human history.