Differences in chemokine coreceptor usage between genetic subtypes of HIV-1

Faster HIV-1 disease progression among Brazilian individuals recently infected with CXCR4-utilizing strains

Introduction

Primary HIV infection is usually caused by R5 viruses, and there is an association between the emergence of CCXR4-utilizing strains and faster disease progression. We characterized HIV-1 from a cohort of recently infected individuals in Brazil, predicted the virus's co-receptor use based on the env genotype and attempted to correlate virus profiles with disease progression.

Methods

A total of 72 recently infected HIV patients were recruited based on the Serologic Testing Algorithm for Recent HIV Seroconversion and were followed every three to four months for up to 78 weeks. The HIV-1 V3 region was characterized by sequencing nine to twelve weeks after enrollment. Disease progression was characterized by CD4+ T-cell count decline to levels consistently below 350 cells/µL.

Results

Twelve out of 72 individuals (17%) were predicted to harbor CXCR4-utilizing strains; a baseline CD4<350 was more frequent among these individuals (p = 0.03). Fifty-seven individuals that were predicted to have CCR5-utilizing viruses and 10 individuals having CXCR4-utilizing strains presented with baseline CD4>350; after 78 weeks, 33 individuals with CCR5 strains and one individual with CXCR4 strains had CD4>350 (p = 0.001). There was no association between CD4 decline and demographic characteristics or HIV-1 subtype.

Conclusions

Our findings confirm the presence of strains with higher in vitro pathogenicity during early HIV infection, suggesting that even among recently infected individuals, rapid progression may be a consequence of the early emergence of CXCR4-utilizing strains. Characterizing the HIV-1 V3 region by sequencing may be useful in predicting disease progression and guiding treatment initiation decisions.

HIV-1 subtypes D and F are prevalent in Guinea Conakry

BACKGROUND

Limited data is available upon the distribution of different HIV-1/2 genotypes in the blood donor population from Guinea Conakry.

OBJECTIVES

To investigate the prevalence of HIV-1/2 subtypes in asymptomatic blood donors in Guinea Conakry, in order to update knowledge of HIV-1/2 epidemiology within this country.

STUDY DESIGN

Samples from 104 blood donors seropositive for HIV-1/2 were tested for HIV-1 by real-time RT-PCR. Those negative for HIV-1 were tested with HIV-2 nested RT-PCR. Positive samples were further amplified in the HIV-1 gag and pol regions and sequenced. Subtypes were determined by phylogenetic analysis on amplicon sequences.

RESULTS

61 samples were positive by HIV-1 real-time RT-PCR. Of the 43 negative, 2 (4.6%) were positive for HIV-2. 52/61 (85.3%) samples were positive by nested RT-PCR. Of the 52, 43 (70.5%) and 31(59.6%) sequences were obtained in the gag and pol regions, respectively; 23 for both regions. HIV-1 subtype distribution was 1 B (2.1%), 8 F (17%), 8 D (17%) and 28 CRF02_AG (59.6%) with 2 unclassified recombinants (4.3%). Unique clusters for subtype D and F distinguished Guinea from HIV-1 subtype distribution in neighboring countries.

CONCLUSIONS

Subtype F and subtype D strains, uncommon in West Africa, are a substantial part of HIV-1 epidemiology in Guinea.

Molecular epidemiology of HIV in two highly endemic areas of northeastern South Africa

There is paucity of data on the genetic landscape of HIV-1 viruses circulating in the Limpopo Province of northeastern South Africa. Here, we examine the genetic diversity of viruses from Bela-Bela and Musina, two towns with high HIV prevalence. Between June 2007 and March 2008, blood samples were collected from antiretroviral-drug-naïve individuals. Viruses were analyzed for genetic subtypes and drug resistance mutations. All of the viruses in these samples were shown by phylogenetic analysis based on gag p17, gag p24, reverse transcriptase, protease and envelope C2-C3 gene regions to belong to HIV-1 subtype C. Two of 44 reverse transcriptase sequences (4.5%) contained N rather than the consensus K at position 103. The K103N mutation is normally associated with resistance to NNRTIs. No major mutations were observed in the protease gene. However, several polymorphisms and amino acid changes normally considered to be minor drug resistance mutations were observed in the protease sequences. These results suggest that HIV-1 subtype C remains the predominant variant responsible for the epidemic in northeastern South Africa and that the prevalence of drug-resistant viruses among the naïve population is low.

Drug resistance and viral tropism in HIV-1 subtype C-infected patients in KwaZulu-Natal, South Africa: implications for future treatment options

BACKGROUND

Drug resistance poses a significant challenge for the successful application of highly active antiretroviral therapy (HAART) globally. Furthermore, emergence of HIV-1 isolates that preferentially use CXCR4 as a coreceptor for cell entry, either as a consequence of natural viral evolution or HAART use, may compromise the efficacy of CCR5 antagonists as alternative antiviral therapy.

METHODS

We sequenced the pol gene of viruses from 45 individuals failing at least 6 months of HAART in Durban, South Africa, to determine the prevalence and patterns of drug-resistance mutations. Coreceptor use profiles of these viruses and those from 45 HAART-naive individuals were analyzed using phenotypic and genotypic approaches.

RESULTS

Ninety-five percent of HAART-failing patients had at least one drug-resistant mutation. Thymidine analog mutations (TAMs) were present in 55% of patients with 9% of individuals possessing mutations indicative of the TAM1 pathway, 44% had TAM2, whereas 7% had mutations common to both pathways. Sixty percent of HAART-failing subjects had X4/dual//mixed-tropic viruses compared with 30% of HAART-naïve subjects (P < 0.02). Genetic coreceptor use prediction algorithms correlated with phenotypic results with 60% of samples from HAART-failing subjects predicted to possess CXCR4-using (X4/dual/mixed viruses) versus 15% of HAART-naïve patients.

CONCLUSIONS

The high proportion of TAMs and X4/dual/mixed HIV-1 viruses among patients failing therapy highlight the need for intensified monitoring of patients taking HAART and the problem of diminished drug options (including CCR5 antagonists) for patients failing therapy in resource-poor settings.

Human immunodeficiency virus type 1 biological variation and coreceptor use: from concept to clinical significance

There is ample evidence for intra-patient evolution of the human immunodeficiency virus type 1 (HIV-1) biological phenotype during the pathogenic process. Evolution often involves switch of coreceptor use from CCR5 to CXCR4, but change to more flexible use of CCR5 occurs over time even in patients with maintained CCR5 use. The increasing use of entry inhibitors in the clinic, often specific for one or the other HIV-1 coreceptor or with different binding properties to CCR5, calls for virus testing in patients prior to treatment initiation. Cell lines expressing CCR5/CXCR4 chimeric receptors are tools for testing viruses for mode of CCR5 use. It is conceivable that small-molecule entry inhibitors that differentially bind to CCR5 can be matched for best effect against HIV-1 with different modes of CCR5 use, thereby allowing an individualized drug choice specifically tailored for each patient.

Construction and phenotypic characterization of HIV type 1 functional envelope clones of subtypes G and F

Subtype G has been estimated to represent the fourth most prevalent clade in the HIV-1 pandemic and subtype F is widely circulating in parts of South America (frequently within BF recombinant forms) and in Romania. However, functional envelope clones of these subtypes are lacking, which are needed for studies on antibody-mediated neutralization, coreceptor usage, and efficiency of viral entry inhibitor drugs. Here we report the construction, neutralization properties, and coreceptor usage of HIV-1 functional envelope clones of subtypes G (n = 15) and F (n = 7). These clones were obtained through RT-PCR amplification of HIV-1 gp160 from plasma RNA, and were used for pseudovirus production. All 15 subtype G-enveloped pseudoviruses were resistant to neutralization by gp120-targeted broadly neutralizing monoclonal antibodies (MAbs) b12 and 2G12, while a majority were neutralized by gp41-targeted MAbs 2F5 and 4E10. With regard to the subtype F envelopes, all seven pseudoviruses were resistant to 2F5 and b12, six were resistant to G12, and six were neutralized by 4E10. Coreceptor usage testing revealed that 21 of 22 envelopes were CCR5-tropic, including all 15 subtype G envelopes, seven of which were from patients with CD4(+) T cell counts <200/ml. These results confirm the broadly neutralizing activity of 4E10 on envelope clones across all tested group M clades, including subtypes G and F, reveal the resistance of most subtype F-enveloped pseudoviruses to broadly neutralizing MAbs b12, 2G12, and 2F5, and suggest that, similarly to subtype C, CXCR4 tropism is uncommon in subtype G, even at advanced stages of infection.

Selective transmission of R5 HIV-1 variants: where is the gatekeeper?

To enter target cells HIV-1 uses CD4 and a coreceptor. In vivo the coreceptor function is provided either by CCR5 (for R5) or CXCR4 (for X4 HIV-1). Although both R5 and X4 HIV-1 variants are present in body fluids (semen, blood, cervicovaginal and rectal secretions), R5 HIV-1 appears to transmit infection and dominates early stages of HIV disease. Moreover, recent sequence analysis of virus in acute infection shows that, in the majority of cases of transmission, infection is initiated by a single virus. Therefore, the existence of a "gatekeeper" that selects R5 over X4 HIV-1 and that operates among R5 HIV-1 variants has been suggested. In the present review we consider various routes of HIV-transmission and discuss potential gatekeeping mechanisms associated with each of these routes. Although many mechanisms have been identified none of them explains the almost perfect selection of R5 over X4 in HIV-1 transmission. We suggest that instead of one strong gatekeeper there are multiple functional gatekeepers and that their superimposition is sufficient to protect against X4 HIV-1 infection and potentially select among R5 HIV-1 variants. In conclusion, we propose that the principle of multiple barriers is more general and not restricted to protection against X4 HIV-1 but rather can be applied to other phenomena when one factor has a selective advantage over the other(s). In the case of gatekeepers for HIV-1 transmission, the task is to identify them and to decipher their molecular mechanisms. Knowledge of the gatekeepers' localization and function may enable us to enhance existing barriers against R5 transmission and to erect the new ones against all HIV-1 variants.

Clinical use of CCR5 inhibitors in HIV and beyond

Since the discovery of CCR5 as a coreceptor for HIV entry, there has been interest in blockade of the receptor for treatment and prevention of HIV infection. Although several CCR5 antagonists have been evaluated in clinical trials, only maraviroc has been approved for clinical use in the treatment of HIV-infected patients. The efficacy, safety and resistance profile of CCR5 antagonists with a focus on maraviroc are reviewed here along with their usage in special and emerging clinical situations. Despite being approved for use since 2007, the optimal use of maraviroc has yet to be well-defined in HIV and potentially in other diseases. Maraviroc and other CCR5 antagonists have the potential for use in a variety of other clinical situations such as the prevention of HIV transmission, intensification of HIV treatment and prevention of rejection in organ transplantation. The use of CCR5 antagonists may be potentiated by other agents such as rapamycin which downregulate CCR5 receptors thus decreasing CCR5 density. There may even be a role for their use in combination with other entry inhibitors. However, clinical use of CCR5 antagonists may have negative consequences in diseases such as West Nile and Tick-borne encephalitis virus infections. In summary, CCR5 antagonists have great therapeutic potential in the treatment and prevention of HIV as well as future use in novel situations such as organ transplantation. Their optimal use either alone or in combination with other agents will be defined by further investigation.

Clinical significance of HIV-1 coreceptor usage

The identification of phenotypically distinct HIV-1 variants with different prevalence during the progression of the disease has been one of the earliest discoveries in HIV-1 biology, but its relevance to AIDS pathogenesis remains only partially understood. The physiological basis for the phenotypic variability of HIV-1 was elucidated with the discovery of distinct coreceptors employed by the virus to infect susceptible cells. The role of the viral phenotype in the variable clinical course and treatment outcome of HIV-1 infection has been extensively investigated over the past two decades. In this review, we summarize the major findings on the clinical significance of the HIV-1 coreceptor usage.

Viral sequence analysis from HIV-infected mothers and infants: molecular evolution, diversity, and risk factors for mother-to-child transmission

Great progress has been made in understanding the pathogenesis, treatment, and transmission of HIV and the factors influencing the risk of mother-to-child transmission (MTCT). Many questions regarding the molecular evolution and genetic diversity of HIV in the context of MTCT remain unanswered. Further research to identify the selective factors governing which variants are transmitted, how the compartmentalization of HIV in different cells and tissues contributes to transmission, and the influence of host immunity, viral diversity, and recombination on MTCT may provide insight into new prevention strategies and the development of an effective HIV vaccine.

Epidemiology of HIV-1 subtypes in an urban area of northern Italy

The distribution of the different subtypes of HIV varies from one region of the world to another. Subtype B is predominant in Europe and the USA, but there has been a gradual increase in non-B subtypes as a result of migration from regions where they are endemic, and this may have important implications for the control of HIV-1. The aim of this study was to assess the prevalence of HIV-1 subtypes in an urban area of northern Italy in the period 1997-2008. Forty-nine (12.2%; 95% CI, 9.00-15.40) of 401 patients investigated carried a non-B subtype, the prevalence of which was 7.7% (95% CI, 4.96-10.44) among native Italians and 55.3% (95% CI, 39.49-71.11) among non-Italians, 1.6% (95% CI, 0.00-3.81) among ex-intravenous drug addicts, 7.6% (95% CI, 1.21-13.99) among homosexual/bisexual men and 20.5% (95% CI, 14.83-26.17) among heterosexuals, 6.8% (95% CI, 3.37-10.23) among Italians infected as a result of sexual contacts in Italy, and 55.0% (95% CI, 33.20-76.80) among Italians infected abroad or by foreign partners. Overall prevalence increased from 2.9% (95% CI, 0.00-6.11) before 1993 to 23.0% (95% CI, 16.31-29.69) in the period 2001-2008. The results demonstrate that there has been an increase in non-B subtypes (especially sexually transmitted infections), particularly among patients infected abroad or by foreign partners.

HIV-1 subtype C envelope characteristics associated with divergent rates of chronic disease progression

Background

HIV-1 envelope diversity remains a significant challenge for the development of an efficacious vaccine. The evolutionary forces that shape the diversity of envelope are incompletely understood. HIV-1 subtype C envelope in particular shows significant differences and unique characteristics compared to its subtype B counterpart. Here we applied the single genome sequencing strategy of plasma derived virus from a cohort of therapy naïve chronically infected individuals in order to study diversity, divergence patterns and envelope characteristics across the entire HIV-1 subtype C gp160 in 4 slow progressors and 4 progressors over an average of 19.5 months.

Results

Sequence analysis indicated that intra-patient nucleotide diversity within the entire envelope was higher in slow progressors, but did not reach statistical significance (p = 0.07). However, intra-patient nucleotide diversity was significantly higher in slow progressors compared to progressors in the C2 (p = 0.0006), V3 (p = 0.01) and C3 (p = 0.005) regions. Increased amino acid length and fewer potential N-linked glycosylation sites (PNGs) were observed in the V1-V4 in slow progressors compared to progressors (p = 0.009 and p = 0.02 respectively). Similarly, gp41 in the progressors was significantly longer and had fewer PNGs compared to slow progressors (p = 0.02 and p = 0.02 respectively). Positive selection hotspots mapped mainly to V1, C3, V4, C4 and gp41 in slow progressors, whereas hotspots mapped mainly to gp41 in progressors. Signature consensus sequence differences between the groups occurred mainly in gp41.

Conclusions

These data suggest that separate regions of envelope are under differential selective forces, and that envelope evolution differs based on disease course. Differences between slow progressors and progressors may reflect differences in immunological pressure and immune evasion mechanisms. These data also indicate that the pattern of envelope evolution is an important correlate of disease progression in chronic HIV-1 subtype C infection.

HIV-1 subtype distribution in the Gambia and the significant presence of CRF49_cpx, a novel circulating recombinant form

Background

Detailed local HIV-1 sequence data are essential for monitoring the HIV epidemic, for maintaining sensitive sequence-based diagnostics, and to aid in designing vaccines.

Results

Reported here are full envelope sequences derived from 38 randomly selected HIV-1 infections identified at a Gambian clinic between 1991 and 2009. Special care was taken to generate sequences from circulating viral RNA as uncloned products, either by limiting dilution or single genome amplification polymerase chain reaction (PCR). Within these 38 isolates, eight were subtyped as A and 18 as CRF02_AG. A small number of subtype B, C, D viruses were identified. Surprising, however, was the identification of six isolates with subtype J-like envelopes, a subtype found normally in Central Africa and the Democratic Republic of the Congo (DRC), with gag p24 regions that clustered with subtype A sequences. Near full-length sequence from three of these isolates confirmed that these represent a novel circulating recombinant form of HIV-1, now named CRF49_cpx.

Conclusions

This study expands the HIV-1 sequence database from the Gambia and will provide important data for HIV diagnostics, patient care, and vaccine development.

Structural and functional studies of CCAAT/enhancer binding sites within the human immunodeficiency virus type 1 subtype C LTR

Human immunodeficiency virus type 1 (HIV-1) subtype C, which is most predominant in sub-Saharan Africa as well as in Asia and India, is the most prevalent subtype worldwide. A large number of transcription factor families have been shown to be involved in regulating HIV-1 gene expression in T lymphocytes and cells of the monocyte-macrophage lineage. Among these, proteins of the CCAAT/enhancer binding protein (C/EBP) family are of particular importance in regulating HIV-1 gene expression within cells of the monocytic lineage during the course of hematologic development and cellular activation. Few studies have examined the role of C/EBPs in long terminal repeat (LTR)-directed viral gene expression of HIV-1 subtypes other than subtype B. Within subtype B viruses, two functional C/EBP sites located upstream of the TATA box are required for efficient viral replication in cells of the monocyte-macrophage lineage. We report the identification of three putative subtype C C/EBP sites, upstream site 1 and 2 (C-US1 and C-US2) and downstream site 1 (C-DS1). C-US1 and C-DS1 were shown to form specific DNA-protein complexes with members of the C/EBP family (C/EBPα, β, and δ). Functionally, within the U-937 monocytic cell line, subtype B and C LTRs were shown to be equally responsive to C/EBPβ-2, although the basal activity of subtype C LTRs appeared to be higher. Furthermore, the synergistic interaction between C/EBPβ-2 and Tat with the subtype C LTR was also observed in U-937 cells as previously demonstrated with the subtype B LTR.

NeuroAIDS in Africa

In July 2009, the Center for Mental Health Research on AIDS at the National Institute of Mental Health organized and supported the meeting "NeuroAIDS in Africa." This meeting was held in Cape Town, South Africa, and was affiliated with the 5th IAS Conference on HIV Pathogenesis, Treatment and Prevention. Presentations began with an overview of the epidemiology of HIV in sub-Saharan Africa, the molecular epidemiology of HIV, HIV-associated neurocognitive disorders (HANDs), and HAND treatment. These introductory talks were followed by presentations on HAND research and clinical care in Botswana, Cameroon, Ethiopia, The Gambia, Kenya, Malawi, Nigeria, Senegal, South Africa, Uganda, and Zambia. Topics discussed included best practices for assessing neurocognitive disorders, patterns of central nervous system (CNS) involvement in the region, subtype-associated risk for HAND, pediatric HIV assessments and neurodevelopment, HIV-associated CNS opportunistic infections and immune reconstitution syndrome, the evolving changes in treatment implementation, and various opportunities and strategies for NeuroAIDS research and capacity building in the region.

Low frequency of CXCR4-using viruses in patients at the time of primary non-subtype-B HIV-1 infection

We used genotypic and phenotypic assays to estimate the frequency of X4/DM viruses in 131 patients infected with non-subtype-B viruses at the time of primary HIV-1 infection (PHI). All patients were enrolled in the French PRIMO Cohort from 1996 to 2007. Most strains belonged to CRF02_AG (51.1%) and subtype A (14.5%). Sixteen viruses (12.2%) were classified as CXCR4 tropic ("X4 strains") by the combined criteria of amino acids 11 and 25 of the V3 loop (11/25) and net charge rules and/or the SVMgeno2pheno(10%) algorithm: 6 strains by the combined genotypic rule, 7 by the SVMgeno2pheno(10%) algorithm, and 3, clustering in subtype D, by both algorithms. However, only one strain (0.8%), belonging to subtype A, was defined as a dual-tropic (DM) virus by the phenotypic assay. The 67 CRF02_AG strains included 2 classified as X4 strains by the combined genotypic rule (3%) and 2 others classified as X4 strains by SVMgeno2pheno(10%) (3%), but none of these 4 strains was an X4 or DM strain according to the phenotypic assay. These results suggest that the cellular virus reservoir was established with X4 strains in very few non-subtype-B-infected patients at the time of PHI. Genotypic predictions can overestimate the proportion of non-subtype-B X4 viruses at PHI.

HIV-1 viral subtype differences in the rate of CD4+ T-cell decline among HIV seroincident antiretroviral naive persons in Rakai district, Uganda

BACKGROUND

Data on the effect of HIV-1 viral subtype on CD4 T-cell decline are limited.

METHODS

We assessed the rate of CD4 T-cell decline per year among 312 HIV seroincident persons infected with different HIV-1 subtypes. Rates of CD4 decline by HIV-1 subtype were determined by linear mixed effects models, using an unstructured convariance structure.

RESULTS

A total of 59.6% had D, 15.7% A, 18.9% recombinant viruses (R), and 5.8% multiple subtypes (M). For all subtypes combined, the overall rate of CD4 T-cell decline was -34.5 [95% confidence interval (CI), -47.1, -22.0] cells/ microL per yr, adjusted for age, sex, baseline CD4 counts, and viral load. Compared with subtype A, the adjusted rate of CD4 cell loss was -73.7/microL/yr (95% CI, -113.5, -33.8, P < 0.001) for subtype D, -43.2/microL/yr (95% CI, -90.2, 3.8, P = 0.072) for recombinants, and -63.9/microL/yr (95% CI, -132.3, 4.4, P = 0.067) for infection with multiple HIV subtypes. Square-root transformation of CD4 cell counts did not change the results.

CONCLUSIONS

Infection with subtype D is associated with significantly faster rates of CD4 T-cell loss than subtype A. This may explain the more rapid disease progression for subtype D compared with subtype A.

Conserved determinants of enhanced CCR5 binding in the human immunodeficiency virus subtype D envelope third variable loop

Human immunodeficiency virus 1 subtype D (HIV-1D) contributes to a significant portion of the HIV-1 disease burden in eastern and central Africa, and is associated with more rapid disease progression. Its viral envelope sequences, particularly in the third variable region (V3), are highly divergent from other major subtypes yet have rarely been studied to date. We evaluated the V3 and select bridging sheet residues of the HIV-1D 94UG114 envelope by alanine-scanning mutagenesis to determine the residues involved in CCR5 usage conservation in the face of sequence variability. We found most single alanine mutations capable of abolishing CCR5 binding, suggesting binding contacts that are highly sensitive to mutation. Despite drastic binding defects across the board, most mutants mediated fusion at or near wild-type levels, demonstrating an ability to accommodate changes in CCR5 affinity while maintaining the ability to complete entry. Three of the alanine mutations did not abolish CCR5 binding but rather resulted in enhanced CCR5 binding. The positions of these residues were found to be conserved between strains of two subtypes, revealing similar V3 elements that suggest a conservation of constraints in V3 loop conformation.

Frequent CXCR4 tropism of HIV-1 subtype A and CRF02_AG during late-stage disease--indication of an evolving epidemic in West Africa

BACKGROUND

HIV-1 is one of the fastest evolving pathogens, and is distinguished by geographic and genetic variants that have been classified into different subtypes and circulating recombinant forms (CRFs). Early in infection the primary coreceptor is CCR5, but during disease course CXCR4-using HIV-1 populations may emerge. This has been correlated with accelerated disease progression in HIV-1 subtype B. Basic knowledge of HIV-1 coreceptor tropism is important due to the recent introduction of coreceptor antagonists in antiretroviral therapy, and subtype-specific differences regarding how frequently HIV-1 CXCR4-using populations appear in late-stage disease need to be further investigated. To study how frequently CXCR4-using populations appear in late-stage disease among HIV-1 subtype A and CRF02_AG, we evaluated the accuracy of a recombinant virus phenotypic assay for these subtypes, and used it to determine the HIV-1 coreceptor tropism of plasma samples collected during late-stage disease in Guinea-Bissau. We also performed a genotypic analysis and investigated subtype-specific differences in the appearance of CXCR4 tropism late in disease.

RESULTS

We found that the recombinant virus phenotypic assay accurately predicted HIV-1 coreceptor tropism of subtype A and CRF02_AG. Over the study period (1997-2007), we found an increasing and generally high frequency of CXCR4 tropism (86%) in CRF02_AG. By sequence analysis of the V3 region of our samples we developed a novel genotypic rule for predicting CXCR4 tropism in CRF02_AG, based on the combined criteria of the total number of charged amino acids and net charge. This rule had higher sensitivity than previously described genotypic rules and may be useful for development of future genotypic tools for this CRF. Finally, we conducted a literature analysis, combining data of 498 individuals in late-stage disease, and found high amounts of CXCR4 tropism for all major HIV-1 subtypes (60-77%), except for subtype C (15%).

CONCLUSIONS

The increase in CXCR4 tropism over time suggests an evolving epidemic of CRF02_AG. The results of the literature analysis demonstrate the need for further studies investigating subtype-specific emergence for CXCR4-tropism; this may be particularly important due to the introduction of CCR5-antagonists in HIV treatment regimens.

Viral tropism, fitness and pathogenicity of HIV-1 subtype C

The majority of studies on HIV-1 pathogenesis have been conducted on subtype B HIV-1 (B-HIV) strains. However, B-HIV strains constitute the minority of HIV-1 cases worldwide, and are not common in regions that stand to benefit the most from advances in HIV-1 research such as southern Africa and Asia, where the HIV-1 pandemic is at its worst. The majority of individuals with HIV-1 are infected with subtype C HIV-1 (C-HIV) and reside in Southern Africa and Central Asia. Relatively little is known about C-HIV, but current evidence suggests the pathogenesis of C-HIV is distinct from B-HIV and other HIV-1 subtypes. This article summarizes what is currently known about the viral tropism, fitness and pathogenicity of C-HIV, and compares and contrasts these features to B-HIV. A thorough understanding of the molecular pathogenesis of C-HIV is important for a targeted approach to developing vaccines and novel drugs optimized for effectiveness in populations that are most in need.

Donor and recipient envs from heterosexual human immunodeficiency virus subtype C transmission pairs require high receptor levels for entry

Compact, glycan-restricted envelope (Env) glycoproteins are selected during heterosexual transmission of subtype C HIV-1. Donor and recipient glycoproteins (Envs) from six transmission pairs were evaluated for entry into HeLa cells expressing different levels of CD4 and CCR5. Donor and recipient Envs demonstrated efficient entry into cells expressing high levels of CD4 and CCR5, and entry declined as CCR5 levels decreased. Infectivity for all Envs was severely impaired in cells expressing low levels of CD4, even at the highest CCR5 levels. In 5/6 pairs, there was no significant difference in efficiency of receptor utilization between the donor and recipient Envs in these HeLa-derived cell lines. Thus, HIV-1 transmission does not appear to select for viruses that can preferentially utilize low levels of entry receptors.

Impact of HIV-1 viral subtype on disease progression and response to antiretroviral therapy

BACKGROUND

Our intention was to compare the rate of immunological progression prior to antiretroviral therapy (ART) and the virological response to ART in patients infected with subtype B and four non-B HIV-1 subtypes (A, C, D and the circulating recombinant form, CRF02-AG) in an ethnically diverse population of HIV-1-infected patients in south London.

METHODS

A random sample of 861 HIV-1-infected patients attending HIV clinics at King's and St Thomas' hospitals' were subtyped using an in-house enzyme-linked immunoassay and env sequencing. Subtypes were compared on the rate of CD4 cell decline using a multi-level random effects model. Virological response to ART was compared using the time to virological suppression (< 400 copies/ml) and rate of virological rebound (> 400 copies/ml) following initial suppression.

RESULTS

Complete subtype and epidemiological data were available for 679 patients, of whom 357 (52.6%) were white and 230 (33.9%) were black African. Subtype B (n = 394) accounted for the majority of infections, followed by subtypes C (n = 125), A (n = 84), D (n = 51) and CRF02-AG (n = 25). There were no significant differences in rate of CD4 cell decline, initial response to highly active antiretroviral therapy and subsequent rate of virological rebound for subtypes B, A, C and CRF02-AG. However, a statistically significant four-fold faster rate of CD4 decline (after adjustment for gender, ethnicity and baseline CD4 count) was observed for subtype D. In addition, subtype D infections showed a higher rate of virological rebound at six months (70%) compared with subtypes B (45%, p = 0.02), A (35%, p = 0.004) and C (34%, p = 0.01)

CONCLUSIONS

This is the first study from an industrialized country to show a faster CD4 cell decline and higher rate of subsequent virological failure with subtype D infection. Further studies are needed to identify the molecular mechanisms responsible for the greater virulence of subtype D.

Glycosylation site-specific analysis of clade C HIV-1 envelope proteins

The extensive glycosylation of HIV-1 envelope proteins (Envs), gp120/gp41, is known to play an important role in evasion of host immune response by masking key neutralization epitopes and presenting the Env glycosylation as "self" to the host immune system. The Env glycosylation is mostly conserved but continues to evolve to modulate viral infectivity. Thus, profiling Env glycosylation and distinguishing interclade and intraclade glycosylation variations are necessary components in unraveling the effects of glycosylation on Env's immunogenicity. Here, we describe a mass spectrometry-based approach to characterize the glycosylation profiles of two rVV-expressed clade C Envs by identifying the glycan motifs on each glycosylation site and determining the degree of glycosylation site occupancy. One Env is a wild-type Env, while the other is a synthetic "consensus" Env (C.CON). The observed differences in the glycosylation profiles between the two clade C Envs show that C.CON has more unutilized sites and high levels of high mannose glycans; these features mimic the glycosylation profile of a Group M consensus immunogen, CON-S. Our results also reveal a clade-specific glycosylation pattern. Discerning interclade and intraclade glycosylation variations could provide valuable information in understanding the molecular differences among the different HIV-1 clades and in designing new Env-based immunogens.

HIV-1 subtypes and differences in heterosexual HIV transmission among HIV-discordant couples in Rakai, Uganda

OBJECTIVE

To determine whether heterosexual transmission of HIV differs according to HIV-1 subtype.

DESIGN

A retrospective observational cohort.

METHODS

HIV-1 subtype effects on heterosexual HIV-1 transmission were determined among 268 HIV-discordant couples retrospectively identified from a population cohort in Rakai, Uganda. HIV-1 subtype (gag and gp41 sequencing and multiregion hybridization assay) and viral loads (reverse transcriptase PCR) were determined. Adjusted incidence rate ratios (adj IRR) of HIV transmission by subtype were estimated by multivariable Poisson regression adjusting for characteristics of index HIV-positive and HIV-negative partners.

RESULTS

Adjusting for index HIV-positive partners' age, viral load, stage of disease, genital ulcer disease, and HIV-negative partners' genital ulcer disease and nonuse of condoms, subtype A viruses were associated with a higher rate of transmission than subtype D [adj.IRR 1.98, 95% confidence interval (CI) 1.17-3.34], but no differences in transmission were observed between recombinant viruses and subtype D (aIRR 1.53, P = 0.25). Index-positive partners' age less than 30 years (adj.IRR 3.44, 95% CI 1.75-6.78) and viral load (adj.IRR 2.37, 95% CI 1.75-3.21), and index-negative partners' genital ulcer disease (adj.IRR 1.71, 95% CI 1.08-2.70) and nonuse of condoms (adj.IRR 1.94, 95% CI 1.15-3.28) were significant determinants of HIV transmission.

CONCLUSION

In Rakai, Uganda, subtype A viruses have a significantly higher rate of heterosexual transmission than subtype D viruses. Differential subtype transmission efficiency may be important for HIV vaccine evaluation and could contribute to subtype-specific HIV epidemics in sub-Saharan Africa.

Functional and genetic analysis of coreceptor usage by dualtropic HIV-1 subtype C isolates

It is widely documented that a complete switch from the predominant CCR5 (R5) to CXCR4 (X4) phenotype is less common for HIV-1 subtype C (HIV-1C) compared to other major subtypes. We investigated whether dualtropic HIV-1C isolates represented dualtropic, mixed R5 and X4 clones or both. Thirty of 35 functional HIV-1 env clones generated by bulk PCR amplification from peripheral blood mononuclear cells (PBMCs) infected with seven dualtropic HIV-1C isolates utilized CXCR4 exclusively. Five of 35 clones displayed dualtropism. Endpoint dilution of one isolate did not yield a substantial proportion of R5-monotropic env clones. Sequence-based predictive algorithms showed that env sequences from PBMCs, CXCR4 or CCR5-expressing cell lines were indistinguishable and all possessed X4/dualtropic characteristics. We describe HIV-1C CXCR4-tropic env sequence features. Our results suggest a dramatic loss of CCR5 monotropism as dualtropism emerges in HIV-1C which has important implications for the use of coreceptor antagonists in therapeutic strategies for this subtype.

HIV subtype D is associated with dementia, compared with subtype A, in immunosuppressed individuals at risk of cognitive impairment in Kampala, Uganda

BACKGROUND

In the United States, clade B is the predominant human immunodeficiency virus (HIV) subtype, whereas in sub-Saharan Africa, clades A, C, and D are the predominant subtypes. HIV subtype may have an impact on HIV disease progression. The effect of HIV subtype on the risk of dementia has, to our knowledge, not been examined. The objective of this study was to examine the relationship between HIV subtype and the severity of HIV-associated cognitive impairment among individuals initiating antiretroviral therapy in Uganda.

METHODS

Sixty antiretroviral-naive HIV-infected individuals with advanced immunosuppression who were at risk of HIV-associated cognitive impairment underwent neurological, neuropsychological, and functional assessments, and gag and gp41 regions were subtyped. Subtype assignments were generated by sequence analysis using a portion of the gag and gp41 regions.

RESULTS

Thirty-three HIV-infected individuals were infected with subtype A, 2 with subtype C, 9 with subtype D, and 16 with A/D recombinants. Eight (89%) of 9 HIV-infected individuals with subtype D had dementia, compared with 7 (24%) of 33 HIV-infected individuals with subtype A (P = .004).

CONCLUSIONS

These results suggest that, in untreated HIV-infected individuals with advanced immunosuppression who are at risk of developing HIV-associated cognitive impairment, HIV dementia may be more common among patients infected with subtype D virus than among those infected with subtype A virus. These findings provide the first evidence, to our knowledge, to demonstrate that HIV subtypes may have a pathogenetic factor with respect to their capacity to cause cognitive impairment. Additional studies are needed to confirm this observation and to define the mechanism by which subtype D leads to an increased risk of neuropathogenesis.

Virus entry via the alternative coreceptors CCR3 and FPRL1 differs by human immunodeficiency virus type 1 subtype

Human immunodeficiency virus type 1 (HIV-1) infects target cells by binding to CD4 and a chemokine receptor, most commonly CCR5. CXCR4 is a frequent alternative coreceptor (CoR) in subtype B and D HIV-1 infection, but the importance of many other alternative CoRs remains elusive. We have analyzed HIV-1 envelope (Env) proteins from 66 individuals infected with the major subtypes of HIV-1 to determine if virus entry into highly permissive NP-2 cell lines expressing most known alternative CoRs differed by HIV-1 subtype. We also performed linear regression analysis to determine if virus entry via the major CoR CCR5 correlated with use of any alternative CoR and if this correlation differed by subtype. Virus pseudotyped with subtype B Env showed robust entry via CCR3 that was highly correlated with CCR5 entry efficiency. By contrast, viruses pseudotyped with subtype A and C Env proteins were able to use the recently described alternative CoR FPRL1 more efficiently than CCR3, and use of FPRL1 was correlated with CCR5 entry. Subtype D Env was unable to use either CCR3 or FPRL1 efficiently, a unique pattern of alternative CoR use. These results suggest that each subtype of circulating HIV-1 may be subject to somewhat different selective pressures for Env-mediated entry into target cells and suggest that CCR3 may be used as a surrogate CoR by subtype B while FPRL1 may be used as a surrogate CoR by subtypes A and C. These data may provide insight into development of resistance to CCR5-targeted entry inhibitors and alternative entry pathways for each HIV-1 subtype.

Appreciating HIV type 1 diversity: subtype differences in Env

Human immunodeficiency virus type 1 (HIV-1) group M is responsible for the current AIDS pandemic and exhibits exceedingly high levels of viral genetic diversity around the world, necessitating categorization of viruses into distinct lineages, or subtypes. These subtypes can differ by around 35% in the envelope (Env) glycoproteins of the virus, which are displayed on the surface of the virion and are targets for both neutralizing antibody and cell-mediated immune responses. This diversity reflects the remarkable ability of the virus to adapt to selective pressures, the bulk of which is applied by the host immune response, and represents a serious obstacle for developing an effective vaccine with broad coverage. Thus, it is important to understand the underlying biological consequences of intersubtype diversity. Recent studies have revealed that some of the HIV-1 subtypes exhibit phenotypic differences stemming from subtle changes in Env structure, particularly within the highly immunogenic V3 domain, which participates directly in viral entry. This review will therefore explore current research that describes subtype differences in Env at the genetic and phenotypic level, focusing in particular on V3, and highlighting recent discoveries about the unique features of subtype C Env, which is the most globally prevalent subtype.

Predicted co-receptor tropism and sequence characteristics of China HIV-1 V3 loops: implications for the future usage of CCR5 antagonists and AIDS vaccine development

BACKGROUND

The co-receptor tropism of any given HIV-1 isolate is closely associated with the progression of AIDS. Understanding the co-receptor tropism and genetic diversity of circulating HIV-1 strains is critical for AIDS treatment and vaccine development.

METHODS

All available China HIV-1 V3 sequences with known subtypes/circulating recombinant forms (CRFs) and transmission routes were retrieved from the Los Alamos HIV Sequence Database. HIV-1 co-receptor tropism was predicted using online tool HIV-1 PhenoPred.

RESULTS

All C/CRF07_BC/CRF08_BC strains appeared to use CCR5 for cell entry (R5 strains), while 61.1% of subtype B and 38.7% of CRF01_AE were also R5, indicating a higher prevalence of R5 (76.9%) than X4. The prevalence of R5 remained relatively stable over the different sample years regardless of C/CRF07_BC/CRF08_BC, B, or CRF01_AE subtypes. The co-receptor usage of HIV-1 appeared to be associated with the different subtypes, rather than transmission route. Furthermore, the V3 sequences of C/CRF07_BC/CRF08_BC were more genetically homogeneous relative to both subtypes B and CRF01_AE.

CONCLUSIONS

The higher prevalence of R5 and higher level of homogeneity of V3 sequences in C/CRF07_BC/CRF08_BC suggest that CCR5 antagonists will be promising drugs for future AIDS treatment in China, and that circulating R5 strains are valuable candidates for AIDS vaccine development.

High-affinity binding of southern African HIV type 1 subtype C envelope protein, gp120, to the CCR5 coreceptor

HIV-1 subtype C is the fastest spreading subtype worldwide and predominantly uses the CCR5 coreceptor, showing minimal transition to the X4 phenotype. This raises the possibility that envelope proteins of HIV-1 subtype C have structural features that favor interaction with CCR5. Preference for CCR5 could arise from enhanced affinity of HIV-1 subtype C for CCR5. To test this, we have characterized the interaction of gp120 envelope proteins from HIV-1 subtype C clones with CD4 and CCR5. Recombinant gp120 proteins from isolates of HIV-1 subtypes B and C were expressed, purified, and assessed in a CD4 binding assay and a CCR5 chemokine competition binding assay. All gp120 proteins bound to CD4-expressing cells, except one, 97ZA347ts, which had Arg substituted for the Cys239 in the conserved C2 loop. Reconstitution of Cys239, using site-directed mutagenesis, restored CD4 binding, while introducing Arg or Ser into position 239 of the functional Du151 gp120 protein abrogated CD4 binding. This shows that the Cys228-Cys239 disulfide bond of gp120 is required for high-affinity binding to CD4. Recombinant gp120 proteins from two HIV-1 subtype B clones bound CCR5 in the presence of CD4, while gp120 from the X4-tropic, HxB2, clone did not bind CCR5. gp120 from two functional HIV-1 subtype C clones, Du151 and MOLE1, bound CCR5 with high affinity in the presence of CD4 and Du151 showed significant CCR5 binding in the absence of CD4. A gp120 from a nonfunctional subtype C clone had lower affinity for CCR5. These results indicate that HIV-1 subtype C proteins have high affinity for CCR5 with variable dependence on CD4.

Drug resistance differences among HIV types and subtypes: a growing problem

Although HIV-1 subtype B accounts for only 10% of worldwide HIV infections, almost all knowledge regarding antiretroviral (ARV) drug development and viral resistance is based on this subtype. More recently, an increasing body of evidence suggests that distinct HIV genetic variants possess different biological properties, including susceptibility and response to ARVs. In this review, we will summarize recent in vitro and in vivo studies reporting such differences. In general terms, infections with most HIV variants respond well to ARVs, but minor differences in susceptibility, in the emergence and selection of subtype-specific drug resistance mutations and in the acquisition of similar mutations over the period of ARV exposure have been reported. Such differences impact on drugresistance interpretation algorithms, which are mostly based on inference from sequence information. Despite the differences observed, clinical response to ARV therapy among subjects infected with distinct HIV variants is effective, and the dissemination of ARV access in developing countries where non-B subtypes prevail should not be delayed.

HIV-1 diversity among inmates of Italian prisons

In Italy, the prevalence of non-B HIV-1 subtypes ranges reportedly from 5.4% to 12.6%, yet there are no data on their circulation in prisons, where the prevalence of HIV infection is high. A retrospective study was conducted to evaluate the circulation of non-B subtypes and to characterize their determinants in five Italian prisons. To this end an aliquot of samples of blood was taken in the period 2001-2006 from all 262 HIV-positive inmates in whom antiretroviral treatment had failed. Complete HIV-1 PR and RT regions were sequenced for all samples and subjected to phylogenetic analysis; 250 (95.4%) sequences clustered with subtype B. The non-B subtype was found in 4% of Italian prison inmates and 16.7% of non-Italian prison inmates; the overall percentage increased from 1.8% for inmates infected in 1982-1990 to 4.4% in 1991-1999 and 21.9% in 2000-2006. Factors significantly associated with non-B subtypes were an exposure to other than injecting drug use and a first positive HIV test in 2000-2006. Non-B subtypes were distributed within five monophyletic clades. In all cases but one, it was possible to correlate the history of HIV-exposure to the origin of the clade, with high bootstrap values. In conclusion, although the sample may not be representative of the prison inmate population in Italy, the data suggest strongly that the circulation of non-B subtypes has apparently increased. Non-B subtypes were found to have been associated with heterosexual contact and time of the first HIV-positive test. Knowledge of the different subtypes circulating in prisons may be useful for tracking the epidemiology of HIV infection and for choosing antiretroviral therapy.

HIV-1 tropism and survival in vertically infected Ugandan infants

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1) may utilize the CXCR4 coreceptor (X4 virus), the CCR5 coreceptor (R5 virus), or both (dual/mixed [DM] virus). We analyzed HIV-1 coreceptor tropism in Ugandan infants enrolled in the HIVNET (HIV Network for Prevention Trials) 012 trial.

METHODS

Plasma or serum was analyzed using a commercial coreceptor tropism assay. HIV env subtype was determined by phylogenetic methods.

RESULTS

Tropism results were obtained for 57 samples from infants collected 6-14 weeks after birth. Fifty-two infants had only R5 virus, and 5 had either X4 or DM virus. The mothers of those 5 infants also had X4 or DM virus. In infants, subtype D infection was associated with high-level infectivity in CCR5-bearing cells and also with the detection of X4 or DM strains. High-level infectivity in CCR5-bearing cells was associated with decreased infant survival, but infection with X4 or DM virus was not. HIV clones from infants with DM viral populations showed different patterns of coreceptor use. V3 loop sequence-based algorithms predicted the tropism of some, but not all, env clones.

CONCLUSIONS

Complex patterns of HIV tropism were found in HIV-infected newborn infants. Subtype D infection was associated with X4 virus and with high-level replication in CCR5-bearing cells. High-level replication of R5 virus was associated with decreased infant survival.

Effect of human immunodeficiency virus Type 1 (HIV-1) subtype on disease progression in persons from Rakai, Uganda, with incident HIV-1 infection

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1) subtypes differ in biological characteristics that may affect pathogenicity.

METHODS

We determined the HIV-1 subtype-specific rates of disease progression among 350 HIV-1 seroconverters. Subtype, viral load, and CD4(+) cell count were determined. Cox proportional hazards regression modeling was used to estimate adjusted hazard ratios (HRs) of progression to acquired immunodeficiency syndrome (AIDS) (defined as a CD4(+) cell count of < or =250 cells/mm(3)) and to AIDS-associated death.

RESULTS

A total of 59.1% of study subjects had subtype D strains, 15.1% had subtype A, 21.1% had intersubtype recombinant subtypes, 4.3% had multiple subtypes, and 0.3% had subtype C. Of the 350 subjects, 129 (37%) progressed to AIDS, and 68 (19.5%) died of AIDS. The median time to AIDS onset was shorter for persons with subtype D (6.5 years), recombinant subtypes (5.6 years), or multiple subtypes (5.8 years), compared with persons with subtype A (8.0 years; P = .022). Relative to subtype A, adjusted HRs of progression to AIDS were 2.13 [95% confidence interval {CI}, 1.10-4.11] for subtype D, 2.16 [95% CI, 1.05-4.45] for recombinant subtypes, and 4.40 [95% CI, 1.71-11.3] for multiple subtypes. The risk of progression to death was significantly higher for subtype D (adjusted HR, 5.65; 95% CI, 1.37-23.4), recombinant subtypes (adjusted HR, 6.70; 95% CI, 1.56-28.8), and multiple subtypes (adjusted HR, 7.67; 95% CI, 1.27-46.3), compared with subtype A.

CONCLUSIONS

HIV disease progression is affected by HIV-1 subtype. This finding may impact decisions on when to initiate antiretroviral therapy and may have implications for future trials of HIV-1 vaccines aimed at slowing disease progression.

Exceptional molecular and coreceptor-requirement properties of molecular clones isolated from an Human Immunodeficiency Virus Type-1 subtype C infection

BACKGROUND

The pathogenic significance of coreceptor switch in the viral infection of HIV-1 is not completely understood. This situation is more complex in subtype C infection where coreceptor switch is either absent or extremely rare. To gain insights into the mechanisms that underlie coreceptor requirement of subtype C, we screened several primary viral isolates and identified a clinical sample that demonstrated a potential to grow on standard T-cell lines with no detectable CCR5 expression. The subject was diagnosed with HIV-1 associated dementia in the absence of opportunistic infections of the brain. To isolate molecular clones from this virus, we devised a novel strategy based on anchor primers that target a sequence in the reverse transcriptase, highly conserved among diverse subtypes of HIV-1.

RESULTS

Using this strategy, we isolated 8 full-length molecular clones from the donor. Two of the eight molecular clones, 03In94_D17 and 03In94_D24, (D17 and D24) generated replication-competent viruses. Phylogenetic analysis of the full-length viral sequences revealed that both clones were non-recombinant subtype C viruses. They contain intact open reading frames in all the viral proteins. Both the viral clones are endowed with several unique molecular and biological properties. The viral promoter of the clones is characterized by the presence of four NF-kB binding elements, a feature rarely seen in the subtype C HIV-1 LTR. Interestingly, we identified the coexistence of two different forms of Rev, a truncated form common to subtype C and a full-length form less common for this subtype, in both proviral and plasma virus compartments. An exceptional property of the viruses, atypical of subtype C, is their ability to use a wide range of coreceptors including CCR5, CXCR4, and several others tested. Sequence analysis of Env of D17 and D24 clones identified differences within the variable loops providing important clues for the expanded coreceptor use. The V1, V2 and V4 loops in both of the molecular clones are longer due to the insertion of several amino acid residues that generated potential N-linked glycosylation sites.

CONCLUSION

The exceptional biological and molecular properties of these clones make them invaluable tools to understand the unique pathogenic characteristics of subtype C.

Evaluation of eight different bioinformatics tools to predict viral tropism in different human immunodeficiency virus type 1 subtypes

Human immunodeficiency virus type 1 (HIV-1) tropism can be assessed using phenotypic assays, but this is quite laborious, expensive, and time-consuming and can be made only in sophisticated laboratories. More accessible albeit reliable tools for testing of HIV-1 tropism are needed in view of the prompt introduction of CCR5 antagonists in clinical practice. Bioinformatics tools based on V3 sequences might help to predict HIV-1 tropism; however, most of these methods have been designed by taking only genetic information derived from HIV-1 subtype B into consideration. The aim of this study was to evaluate the performances of several genotypic tools to predict HIV-1 tropism in non-B subtypes, as data on this issue are scarce. Plasma samples were tested using a new phenotypic tropism assay (Phenoscript-tropism; Eurofins), and results were compared with estimates of coreceptor usage using eight different genotypic predictor softwares (Support Vector Machine [SVM], C4.5, C4.5 with positions 8 to 12 only, PART, Charge Rule, geno2pheno coreceptor, Position-Specific Scoring Matrix X4R5 [PSSM(X4R5)], and PSSM(sinsi)). A total of 150 samples were tested, with 115 belonging to patients infected with non-B subtypes and 35 drawn from subtype B-infected patients, which were taken as controls. When non-B subtypes were tested, the concordances between the results obtained using the phenotypic assay and distinct genotypic tools were as follows: 78.8% for SVM, 77.5% for C4.5, 82.5% for C4.5 with positions 8 to 12 only, 82.5% for PART, 82.5% for Charge Rule, 82.5% for PSSM(X4R5), 83.8% for PSSM(sinsi), and 71.3% for geno2pheno. When clade B viruses were tested, the best concordances were seen for PSSM(X4R5) (91.4%), PSSM(sinsi) (88.6%), and geno2pheno (88.6%). The sensitivity for detecting X4 variants was lower for non-B than for B viruses, especially in the case of PSSM(sinsi) (38.4% versus 100%, respectively), SVM(wetcat) (46% versus 100%, respectively), and PART (30% versus 90%, respectively). In summary, while inferences of HIV-1 coreceptor usage using genotypic tools seem to be reliable for clade B viruses, their performances are poor for non-B subtypes, in which they particularly fail to detect X4 variants.

HIV-1 biological phenotype and predicted coreceptor usage based on V3 loop sequence in paired PBMC and plasma samples

Paired PBMCs and plasma samples from 34 HIV-infected patients were studied to verify the relationship between coreceptor use based on genotyping of V3 region of HIV-1 envelope gp120 and biological phenotype with virus isolation and subsequent correlation to clinical characteristics. The "11/25" rule, geno2pheno and PSSM were compared. All SI patients were HIV-1 subtype B (p=0.04) and had a lower CD4 count than NSI patients (p=0.01), while no differences were observed in mean HIV-RNA (log) (p=0.6). SI phenotype was not associated with AIDS-defining events (p=0.1) or with concurrent antiretroviral therapy (p=0.4). With geno2pheno, which shows the highest sensibility (83%), an X4 or X4/R5 genotype in PBMC DNA was also associated to B-subtype and lower CD4 count (p=0.01) compared to R5 isolates. Based on plasma RNA sequences, the predicted coreceptor usage agreed with PBMC DNA in 79% of cases with the "11/25" rule, 82% with geno2pheno, and 82% with PSSM. A X4 virus in plasma (but not in PBMCs) was significantly associated with HAART in all three methods (p=0.01 for "11/25" rule, p=0.01 for geno2pheno and p=0.03 for PSSM). Due to viral mixtures and/or difficulties in genotype interpretation, current V3 sequence-based methods cannot accurately predict HIV-1 coreceptor use.

Subtype-specific conformational differences within the V3 region of subtype B and subtype C human immunodeficiency virus type 1 Env proteins

The V3 region of the human immunodeficiency virus type 1 gp120 Env protein is a key domain in Env due to its role in interacting with the coreceptors CCR5 and CXCR4. We examined potential subtype-specific V3 region differences by comparing patterns of amino acid variability and probing for subtype-specific structures using 11 anti-V3 monoclonal antibodies (V3 MAbs). Differences between the subtypes in patterns of variability were most evident in the stem and turn regions of V3 (positions 9 to 24), with the two subtypes being very similar in the base region. The characteristics of the binding of V3 MAbs to Env proteins of the subtype B virus JR-FL and the subtype C virus BR025 suggested three patterns, as each group of MAbs recognized a specific conformation- or sequence-based epitope. Viruses pseudotyped with Env from JR-FL and BR025 were resistant to neutralization by the V3 MAbs, although the replacement of the Env V3 region of the SF162 virus with the JR-FL V3 created a pseudotyped virus that was hypersensitive to neutralization. A single mutation in V3 (H13R) made this chimeric Env selectively resistant to one group of V3 MAbs, consistent with the mAb binding properties. We hypothesize that there are intrinsic differences in V3 conformation between subtype B and subtype C that are localized to the stem and turn regions and that these differences have two important biological consequences: first, subtype B and subtype C V3 regions can have subtype-specific epitopes that will inherently limit antibody cross-reactivity, and second, V3 conformational differences may potentiate the frequent evolution of R5- into X4-tropic variants of subtype B but limit subtype C virus from using the same mechanism to evolve X4-tropic variants as efficiently.

Clinical impact of HIV-1 subtype: are there important differences?

The enormous genetic diversity of HIV-1 is a major challenge to vaccine development and may have important clinical consequences. HIV-1 group M predominates globally, with nine subtypes, several sub-subtypes and over 30 circulating recombinant forms that may exhibit differences with respect to transmissibility, pathogenicity and development of antiretroviral resistance. Subtype D appears to be more virulent than other subtypes, in particular subtype A. Subtype C may be less virulent and more transmissible, although the evidence for this is inconclusive. All group M non-B subtypes appear to be equally susceptible to combination antiretroviral therapy, but development of resistance mutations may vary significantly between subtypes. Further research into the clinical implications of HIV-1 diversity is crucial for effective HIV-1 prevention and treatment.

Impact of human immunodeficiency virus (HIV) subtypes on HIV-associated neurological disease

Among the many variables affecting transmission and pathogenesis of the human immunodeficiency virus type 1(HIV-1), the effects of HIV subtypes, or clades, on disease progression remain unclear. Although debated, some studies have found that the variable env and pol sequences of different subtypes of HIV-1 may endow some subtypes with greater degrees of cell tropism, virulence, and drug resistance, which may lead to differences in overall disease progression. HIV-associated dementia (HAD) appears to be associated with viral diversity and markers of immune activation. Africa has the highest prevalence of HIV, largest viral diversity, and is where clade recombination occurs most frequently. All of these factors would suggest that HAD would pose the largest threat in this region of the world. Although investigations into the effects of different subtypes on overall disease progression are well documented, few have looked into the effects of subtypes on neurological disease progression. This review highlights the need for more international research involving the neurological effects and especially the clinical presentation of dementia for the entire range of the group M HIV-1 subtypes.

Relation between chemokine receptor use, disease stage, and HIV-1 subtypes A and D: results from a rural Ugandan cohort

OBJECTIVES

To determine whether there are differences in coreceptor use in subjects infected with HIV-1 envelope subtypes A and D that could explain the differences in progression rates between these subtypes in a rural Ugandan cohort.

METHODS

HIV-1 was subtyped in env by V3 sequencing or heteroduplex mobility assay. Coreceptor use was determined by the ability of the isolates to replicate in U87 CD4 cells expressing different coreceptors. The Fisher exact test was used to examine the relation between coreceptor use and subtype, clinical stage, and V3 charge. The Kruskall-Wallis nonparametric test was used to examine the association between median CD4 cell counts, coreceptor use, and subtype. Logistic regression was used to examine predicted coreceptor use at different CD4 groupings.

RESULTS

Isolates from 66 participants were analyzed. Thirty-one were infected with subtype A, and 35 were infected with subtype D. Although this work was based on a small sample size, we found statistically significant differences. The probability of having an X4 virus was higher in subtype D infections than in subtype A infections among those with a non-AIDS clinical status (Fisher exact test, P = 0.040). Logistic regression analysis, in which we predicted X4 use by subtype and stratified by CD4 group, confirmed these findings among those with a CD4 count >200 cells/microL (likelihood ratio test, P = 0.003). R5 viruses were associated with higher median CD4 cell counts than X4 or X4/R5 (Kruskall-Wallis test, P = 0.0045). A V3 charge of +5 and greater was highly associated with X4 virus (Fisher exact test, P = 0.006).

CONCLUSIONS

These subtype differences in coreceptor use may partially explain the faster progression rates we have previously reported in individuals infected with subtype D compared with subtype A. Our observations may have implications for the future use of coreceptor inhibitors in this population.

Coreceptor tropism in human immunodeficiency virus type 1 subtype D: high prevalence of CXCR4 tropism and heterogeneous composition of viral populations

In human immunodeficiency virus type 1 (HIV-1) subtype B, CXCR4 coreceptor use ranges from approximately 20% in early infection to approximately 50% in advanced disease. Coreceptor use by non-subtype B HIV is less well characterized. We studied coreceptor tropism of subtype A and D HIV-1 collected from 68 pregnant, antiretroviral drug-naive Ugandan women (HIVNET 012 trial). None of 33 subtype A or 10 A/D-recombinant viruses used the CXCR4 coreceptor. In contrast, nine (36%) of 25 subtype D viruses used both CXCR4 and CCR5 coreceptors. Clonal analyses of the nine subtype D samples with dual or mixed tropism revealed heterogeneous viral populations comprised of X4-, R5-, and dual-tropic HIV-1 variants. In five of the six samples with dual-tropic strains, V3 loop sequences of dual-tropic clones were identical to those of cocirculating R5-tropic clones, indicating the presence of CXCR4 tropism determinants outside of the V3 loop. These dual-tropic variants with R5-tropic-like V3 loops, which we designated "dual-R," use CCR5 much more efficiently than CXCR4, in contrast to dual-tropic clones with X4-tropic-like V3 loops ("dual-X"). These observations have implications for pathogenesis and treatment of subtype D-infected individuals, for the association between V3 sequence and coreceptor tropism phenotype, and for understanding potential mechanisms of evolution from exclusive CCR5 use to efficient CXCR4 use by subtype D HIV-1.

High prevalence of the CCR5Delta32 HIV-resistance mutation among Estonian HIV type 1-infected individuals

The aim of this survey was to investigate human immunodeficiency virus type 1 (HIV-1) coreceptor, chemokine receptor 5 (CCR5), polymorphism among Estonian HIV-1-infected individuals. Homozygous CCR5Delta32 genotypes have been associated with resistance to HIV-1 infection; however, inconsistent evidence exists as to whether a single copy of a mutant allele among heterozygotes confers protection from HIV-1 infection. In an Estonian population the frequency of the CCR5Delta32 allele has been found to be among the greatest observed to date. Ironically, Estonia is concomitantly characterized by a very high HIV-1 prevalence. We compared the allele frequencies in a healthy control population to the HIV-positive group. The frequency of heterozygous individuals did not differ significantly between the HIV-positive group and the control population. Allele frequencies were analyzed among different risk groups as well as groups with different HIV genetic backgrounds. We did not find a difference between CCR5Delta32 allele frequencies among intravenous drug users (IDUs) and sexually infected persons. Likewise, the distribution of CCR5Delta32 allele frequencies among patients infected with different subtypes did not differ while data from "pure" subtypes A, B, and CRF06_cpx were pooled and evaluated against unique recombinant forms.

Global and regional distribution of HIV-1 genetic subtypes and recombinants in 2004

OBJECTIVE

To estimate the global and regional distribution of HIV-1 subtypes and recombinants in 2004.

DESIGN

A study was conducted in which molecular epidemiological data on HIV-1 subtype distribution in individual countries were combined with country-specific estimates of the number of people living with HIV.

METHODS

HIV-1 subtype data were collected for 23 874 HIV-1 samples from 70 countries, which together accounted for 89% of all people living with HIV worldwide in 2004. The proportions of HIV-1 infections due to various subtypes detected in each country were combined with the number of HIV infected people in the respective countries to generate regional and global HIV-1 subtype distribution estimates.

RESULTS

Subtype C accounted for 50% of all infections worldwide in 2004. Subtypes A, B, D and G accounted for 12%, 10%, 3% and 6%, respectively. The subtypes F, H, J and K together accounted for 0.94% of infections. The circulating recombinant forms CRF01_AE and CRF02_AG each were responsible for 5% of cases, and CRF03_AB for 0.1%. Other recombinants accounted for the remaining 8% of infections. All recombinant forms taken together were responsible for 18% of infections worldwide.

CONCLUSION

Combining data on HIV-1 subtype distribution in individual countries with country-specific estimates of the number of people living with HIV provided a good method to generate estimates of the global and regional HIV-1 genetic diversity in 2004. The results could serve as an important resource for HIV scientists, public health officials and HIV vaccine developers.

Genetic and phylogenetic characterization of structural genes from non-B HIV-1 subtypes in Italy

A molecular and phylogenetic characterization on env and gag subgenomic regions has been performed in our laboratory on HIV-1 variants identified in seropositive individuals residing in Italy, infected in the 1999-2001 period, and five non-B-subtype HIV-1 isolates have been described. To confirm the phylogenetic characterization and to determine the genomic organization of three non-B HIV-1 isolates (A, G, and CRF02- AG), the complete gag, pol, and gp120 ORFs (approx. 6900 bp) have been sequenced for each of them. The phylogenetic tree analyses performed on the whole sequence or on individual genes suggested, for the A and G isolates, the identification of divergent strains that do not cluster into any of the known subsubtypes. This has been further validated by pairwise distance analysis. On the contrary, the phylogenetic classification of the CRF02-AG isolate has been confirmed and an overall typical pattern of intragenomic breakpoints has been observed by a Simplot analysis. These results confirm the constant HIV-1 molecular evolution and indicate the relevance of a continuous molecular monitoring of HIV-1 isolates for the development of appropriate vaccine candidates.

Risk of HIV-1 transmission by breastfeeding among mothers infected with recombinant and non-recombinant HIV-1 genotypes

BACKGROUND

Viral genotype and intersubtype recombination may influence the rate and/or timing of mother-to-child HIV-1 transmission.

METHODS

We determined the HIV-1 subtype of the C2-C5 env and 5'LTR regions from milk and blood samples of 61 Tanzanian mothers who transmitted the virus through breastfeeding and their HIV-1 positive non-transmitting controls. Cases and controls were matched on infant's age at sample collection. All mothers resided in Dar es Salaam, Tanzania.

RESULTS

Most infections among cases were due to recombinant viruses (41.0%), followed by HIV-1 subtype A (26.2%), subtype D (19.7%), and subtype C (13.1%). In multivariate analysis including maternal CD4+ cell counts, HIV disease stage, and proviral load in breast milk, the odds of breast milk transmission were 7.2 times higher if the mother carried an intersubtype recombinant genome in comparison to a subtype C virus (p=0.02). Viruses with recombinant LTRs were 4.9 times more likely to be transmitted through breastfeeding than viruses with non-recombinant LTRs of subtype A, C or D combined (p=0.01).

CONCLUSIONS

This suggested that intersubtype recombinant genomes, and especially recombination within the LTR, might render HIV-1 more fit for transmission via breast milk in comparison with non-recombinant subtypes A, C, and D.

A reliable phenotype predictor for human immunodeficiency virus type 1 subtype C based on envelope V3 sequences

In human immunodeficiency virus type 1 (HIV-1) subtype B infections, the emergence of viruses able to use CXCR4 as a coreceptor is well documented and associated with accelerated CD4 decline and disease progression. However, in HIV-1 subtype C infections, responsible for more than 50% of global infections, CXCR4 usage is less common, even in individuals with advanced disease. A reliable phenotype prediction method based on genetic sequence analysis could provide a rapid and less expensive approach to identify possible CXCR4 variants and thus increase our understanding of subtype C coreceptor usage. For subtype B V3 loop sequences, genotypic predictors have been developed based on position-specific scoring matrices (PSSM). In this study, we apply this methodology to a training set of 279 subtype C sequences of known phenotypes (228 non-syncytium-inducing [NSI] CCR5(+) and 51 SI CXCR4(+) sequences) to derive a C-PSSM predictor. Specificity and sensitivity distributions were estimated by combining data set bootstrapping with leave-one-out cross-validation, with random sampling of single sequences from individuals on each bootstrap iteration. The C-PSSM had an estimated specificity of 94% (confidence interval [CI], 92% to 96%) and a sensitivity of 75% (CI, 68% to 82%), which is significantly more sensitive than predictions based on other methods, including a commonly used method based on the presence of positively charged residues (sensitivity, 47.8%). A specificity of 83% and a sensitivity of 83% were achieved with a validation set of 24 SI and 47 NSI unique subtype C sequences. The C-PSSM performs as well on subtype C V3 loops as existing subtype B-specific methods do on subtype B V3 loops. We present bioinformatic evidence that particular sites may influence coreceptor usage differently, depending on the subtype.