Langerhans cell tropism of human immunodeficiency virus type 1 subtype A through F isolates derived from different transmission groups

The Differential Anti-HIV Effect of a New Humic Substance-Derived Preparation in Diverse Cells of the Immune System

The anti-HIV activity of a new humic substance-derived preparation has been studied in individual pools of immune cells (CD4+ T lymphocytes, macrophages, dendritic cells). Near-complete inhibition of the HIV infection (by more than 90%) was achieved by treating each of the abovementioned cell types with non-toxic concentrations of the preparation. The inhibitory effect demonstrates the possibility of preventing the depletion of a significant portion of functionally important immune cells. A comparative study of infection inhibition in individual cell pools has allowed us to reveal the differences in the preparation's effectiveness in each of the cell populations. A R5-tropic HIV-1 infection in macrophages exhibited maximum sensitivity to the preparation: 90% and 50% inhibition of the infection were observed in the presence of concentrations as low as 1.4 and 0.35 μg/ml, respectively. A 15- and 19-fold higher concentration was required to achieve the same extent of inhibition in dendritic cells infected with the same strain. The effectiveness of the drug in CD4 + T lymphocytes is quite comparable to its effectiveness in macrophages. The drug is universally effective for both the T- and M-tropic variants of HIV-1.

Current Trends of HIV Recombination Worldwide

One of the major characteristics of HIV-1 is its high genetic variability and extensive heterogeneity. This characteristic is due to its molecular traits, which in turn allows it to vary, recombine, and diversify at a high frequency. As such, it generates complex molecular forms, termed recombinants, which evade the human immune system and so survive. There is no sequence constraint to the recombination pattern as it appears to occur at inter-group (between groups M and O), as well as interand intra-subtype within group M. Rapid emergence and active global transmission of HIV-1 recombinants, known as circulating recombinant forms (CRFs) and unique recombinant forms (URFs), requires urgent attention. To date, 55 CRFs have been reported around the world. The first CRF01_AE originated from Central Africa but spread widely in Asia. The most recent CRF; CRF55_01B is a recombinant form of CRF01_AE and subtype B, although its origin is yet to be publicly disclosed. HIV-1 recombination is an ongoing event and plays an indispensable role in HIV epidemics in different regions. Africa, Asia and South America are identified as recombination hot-spots. They are affected by continual emergence and cocirculation of newly emerging CRFs and URFs, which are now responsible for almost 20% of HIV-1 infections worldwide. Better understanding of recombinants is necessary to determine their biological and molecular attributes.

HIV-1 Trans Infection of CD4(+) T Cells by Professional Antigen Presenting Cells

Since the 1990s we have known of the fascinating ability of a complex set of professional antigen presenting cells (APCs; dendritic cells, monocytes/macrophages, and B lymphocytes) to mediate HIV-1 trans infection of CD4(+) T cells. This results in a burst of virus replication in the T cells that is much greater than that resulting from direct, cis infection of either APC or T cells, or trans infection between T cells. Such APC-to-T cell trans infection first involves a complex set of virus subtype, attachment, entry, and replication patterns that have many similarities among APC, as well as distinct differences related to virus receptors, intracellular trafficking, and productive and nonproductive replication pathways. The end result is that HIV-1 can sequester within the APC for several days and be transmitted via membrane extensions intracellularly and extracellularly to T cells across the virologic synapse. Virus replication requires activated T cells that can develop concurrently with the events of virus transmission. Further research is essential to fill the many gaps in our understanding of these trans infection processes and their role in natural HIV-1 infection.

CCR5- and CXCR4-tropic subtype C human immunodeficiency virus type 1 isolates have a lower level of pathogenic fitness than other dominant group M subtypes: implications for the epidemic

Human immunodeficiency virus type 1 (HIV-1) subtype C is the dominant subtype globally, due largely to the incidence of subtype C infections in sub-Saharan Africa and east Asia. We compared the relative replicative fitness (ex vivo) of the major (M) group of HIV-1 subtypes A, B, C, D, and CRF01_AE and group O isolates. To estimate pathogenic fitness, pairwise competitions were performed between CCR5-tropic (R5) or CXCR4-tropic (X4) virus isolates in peripheral blood mononuclear cells (PBMC). A general fitness order was observed among 33 HIV-1 isolates; subtype B and D HIV-1 isolates were slightly more fit than the subtype A and dramatically more fit than the 12 subtype C isolates. All group M isolates were more fit (ex vivo) than the group O isolates. To estimate ex vivo transmission fitness, a subset of primary HIV-1 isolates were examined in primary human explants from penile, cervical, and rectal tissues. Only R5 isolates and no X4 HIV-1 isolates could replicate in these tissues, whereas the spread to PM1 cells was dependent on active replication and passive virus transfer. In tissue competition experiments, subtype C isolates could compete with and, in some cases, even win over subtype A and D isolates. However, when the migratory cells from infected tissues were mixed with a susceptible cell line, the subtype C isolates were outcompeted by other subtypes, as observed in experiments with PBMC. These findings suggest that subtype C HIV-1 isolates might have equal transmission fitness but reduced pathogenic fitness relative to other group M HIV-1 isolates.

Setting the stage: host invasion by HIV

For more than two decades, HIV has infected millions of people worldwide each year through mucosal transmission. Our knowledge of how HIV secures a foothold at both the molecular and cellular levels has been expanded by recent investigations that have applied new technologies and used improved techniques to isolate ex vivo human tissue and generate in vitro cellular models, as well as more relevant in vivo animal challenge systems. Here, we review the current concepts of the immediate events that follow viral exposure at genital mucosal sites where most documented transmissions occur. Furthermore, we discuss the gaps in our knowledge that are relevant to future studies, which will shape strategies for effective HIV prevention.

Clinical significance of human immunodeficiency virus type 1 replication fitness

The relative fitness of a variant, according to population genetics theory, is that variant's relative contribution to successive generations. Most drug-resistant human immunodeficiency virus type 1 (HIV-1) variants have reduced replication fitness, but at least some of these deficits can be compensated for by the accumulation of second-site mutations. HIV-1 replication fitness also appears to influence the likelihood of a drug-resistant mutant emerging during treatment failure and is postulated to influence clinical outcomes. A variety of assays are available to measure HIV-1 replication fitness in cell culture; however, there is no agreement regarding which assays best correlate with clinical outcomes. A major limitation is that there is no high-throughput assay that incorporates an internal reference strain as a control and utilizes intact virus isolates. Some retrospective studies have demonstrated statistically significant correlations between HIV-1 replication fitness and clinical outcomes in some patient populations. However, different studies disagree as to which clinical outcomes are most closely associated with fitness. This may be in part due to assay design, sample size limitations, and differences in patient populations. In addition, the strength of the correlations between fitness and clinical outcomes is modest, suggesting that, at present, it would be difficult to utilize these assays for clinical management.

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.

Is HIV-1 evolving to a less virulent form in humans?

During the rapid spread of HIV-1 in humans, the main (M) group of HIV-1 has evolved into ten distinct subtypes, undergone countless recombination events and diversified extensively. The impact of this extreme genetic diversity on the phenotype of HIV-1 has only recently become a research focus, but early findings indicate that the dominance of HIV-1 subtype C in the current epidemic might be related to the lower virulence of this subtype compared with other subtypes. Here, we explore whether HIV-1 has reached peak virulence or has already started the slow path to attenuation.

Dendritic cell-mediated viral transmission: a potential drug target?

Dendritic cells (DCs) are important in the sexual transmission of HIV-1, the most common route of acquiring HIV-1. HIV-1 subverts the biological function of DCs to facilitate its transport from site of entry at mucosal tissues to lymphoid tissues to infect T cells. Recent data have furthered our understanding of how DCs mediate viral transmission to T cells. DCs capture HIV-1 through specific attachment receptors, such as DC-SIGN, which not only facilitate HIV-1 transmission, but also infection of DCs. Therefore, these receptors are very promising targets for the design of inhibitors or vaccination strategies to prevent mucosal HIV-1 transmission. It is becoming evident that other viruses also use DCs for their transmission. This review will discuss the mechanism of HIV-1 transmission and potential intervention strategies.

Genetic characterization of diverse HIV-1 strains in an immigrant population living in New York City

New York City (NYC) is one of the original foci of the HIV-1 epidemic and has a greater number of AIDS cases than any other city in the United States. NYC also hosts the highest number of immigrants among the nation's cities: more than 2 million among a total population of 8 million. Such a high rate of immigration could act as a potential source for introducing and disseminating novel HIV-1 strains into the United States. Our current study focuses on the genetic characterization of HIV-1 strains circulating in an immigrant population in NYC. Of the 505 HIV-1-positive specimens obtained, 196 were available for viral sequencing from the C2 to V3 region of env. Phylogenetic analysis using maximum-likelihood and neighbor-joining methods demonstrated that non-B subtypes and circulating recombinant forms (CRFs) accounted for 43.4% (85 of 196 cases), whereas the remaining 56.6% (111 of 196) cases had viral variants similar to the typical North American subtype B virus. Of those non-B subtypes and CRFs, subtype A and CRF02 dominated (63.5% combined); other subtypes, including C, D, F1, G, CRF01_AE, and CRF06_cpx, were also detected. Two HIV-1 sequences do not cluster with any known subtypes or CRFs. Furthermore, the distribution of non-B subtypes and CRFs was consistent with the countries of origin, suggesting that many of the study subjects were likely infected in their home country before they entered the United States. Subtype B viruses identified in the immigrant population showed no significant differences from the typical North American B subtype, however, indicating that a significant proportion of the immigrants must have been infected after they came to the United States. Public health officials and physicians should be aware of the growing genetic diversity of HIV-1 in this country, particularly in areas with sizable immigrant populations.

A diversidade do HIV-1: uma ferramenta para o estudo da pandemia

Uma das características mais marcantes do HIV-1 é a imensa diversidade observada entre as cepas que compõem a pandemia de HIV/AIDS. Na última década, a classificação das variantes do vírus em grupos, subtipos e formas recombinantes circulantes (CRF) e a observação de padrões específicos de mutação têm provado serem ferramentas poderosas para os estudos da dinâmica molecular do vírus. O acompanhamento da distribuição mundial da diversidade do HIV-1 tem sido empregado, por exemplo, em programas de vigilância epidemiológica, bem como na reconstrução da história de epidemias regionais. Além disto, a observação de padrões específicos de distribuição espacial do vírus sugere a existência de diferenças na patogenia e transmissibilidade entre os diversos subtipos. A análise molecular das seqüências do vírus também permite a estimativa do tempo de divergência entre as variantes e das forças dinâmicas que modelam as árvores filogenéticas.

Cell reservoirs in lymph nodes infected with HIV-1 subtype E differ from subtype B: identification by combined in situ polymerase chain reaction and immunohistochemistry

In Thailand, the predominant HIV subtype is E, rather than subtype B as in North America and Europe. Subtype E has the ability to replicate in vitro in Langerhans cells. We hypothesized that this cell type might constitute a reservoir for the HIV virus in infected lymph nodes. We examined lymph nodes from 25 HIV-1 subtype E-infected patients to determine the immunophenotype of HIV-1-infected cells, their numbers and their distribution. The presence of HIV was detected either by in situ reverse transcriptase-polymerase chain reaction or immunoperoxidase. Cell identity was determined by double labelling using alkaline phosphatase-based immunohistochemistry. The majority of HIV-infected cells in the lymph nodes were Langerhans cells (CD1a+S100+) and Langerhans-related dendritic cells (p55+S100+). These cells were located in the paracortical areas of lymph nodes, with a few cells scattered at the edges of germinal centers, but were absent from germinal centers themselves, in contrast to the reported distribution of subtype B virus. In addition, multinucleated giant cells were significantly more common in HIV-infected nodes (64%) compared to controls (4%) (P=0.00002). In conclusion, Langerhans histiocytes and related cells are reservoirs for HIV subtype E in lymph nodes. Disrupting the pathway of infection of Langerhans cells and related cells may be a viable strategy to interfere with transmission of HIV subtype E.

The replicative fitness of primary human immunodeficiency virus type 1 (HIV-1) group M, HIV-1 group O, and HIV-2 isolates

The main (M) group of human immunodeficiency virus type 1 (HIV-1) is responsible for the global AIDS epidemic while HIV-1 group O (outlier) and HIV type 2 are endemic only in west and central Africa. The failure of HIV-2 and especially HIV-1 group O to spread following the initial zoonotic jumps is not well understood. This study was designed to examine the relative replicative capacities between these human lentiviruses. A pairwise competition experiment was performed with peripheral blood mononuclear cells with eight HIV-2 isolates, 6 group O viruses, and 15 group M viruses of subtype A (2 viruses), B (5 viruses), C (4 viruses), D (2 viruses) and CRF01_AE (2 viruses). HIV-1 group M isolates of any subtype were typically 100-fold-more fit than group O or HIV-2 strains when competed in peripheral blood mononuclear cells from various humans. This order in replicative fitness was also observed when virus pairs were added to human dendritic cells and then cocultured with primary, quiescent T cells, which is the model for HIV-1 transmission. These results suggest that reduced replicative and transmission fitness may be contributing to the low prevalence and limited geographical spread of HIV-2 and group O HIV-1 in the human population.

A pathophysiological approach to antiretroviral therapy

A discussion of the pathophysiology of HIV infection is important not only to understand both routine and novel therapeutic approaches, but also to appreciate the challenges of long-term control and viral eradication. This article will first briefly review certain pathophysiologic principles of HIV infection that have particular therapeutic implications, and then discuss general tenets of antiretroviral therapy, followed by new developments in the field.

The evolution of HIV and its consequences

Since the beginning of the AIDS epidemic in 1981, HIV-1 has demonstrated an amazing ability to mutate. HIV-1 was introduced into the human population in the early to mid twentieth century in central Africa. During ensuing decades, this extraordinary mutational capacity has resulted in the circulation of HIV-1 strains that are quite different from one another, yet still remarkably pathogenic. The potential impact of this viral diversity on treatment, monitoring,and vaccine development is discussed.

HIV-1 fitness and macrophages

HIV-1 comprises a collection of closely related, but not identical, viruses or quasispecies. Fitness represents a selective advantage for propagation among populations of organisms competing in a particular environment and is an important characteristic of viruses because of a link between fitness and pathogenesis. Environmental differences based on the type of cell that is targeted for infection or the cell type that produces virus, impact fitness. CD4-expressing cells of lymphocyte or macrophage lineage are the principal host cells for HIV-1, although the milieu in lymphocytes is distinct from the macrophage environment from the perspective of cell half-life and activation, signal transduction and expression of coreceptors, and bioavailability of antiretroviral drugs. Multiple viral determinants, including entry via envelope glycoproteins, replication by reverse transcriptase, and virion maturation by protease activity, contribute to fitness in different cells and provide targets for current antiretroviral therapies. This review focuses on fitness of HIV-1 in macrophages and examines the impact of protease inhibitors on fitness of quasispecies and an unexplained discordance between fitness and pathogenesis.

IgA Fc receptors

The IgA receptor family comprises a number of surface receptors including the polymeric Ig receptor involved in epithelial transport of IgA/IgM, the myeloid specific IgA Fc receptor (FcalphaRI or CD89), the Fcalpha/muR, and at least two alternative IgA receptors. These are the asialoglycoprotein receptor and the transferrin receptor, which have been implicated in IgA catabolism, and tissue IgA deposition. In this review we focus on the biology of FcalphaRI (CD89). FcalphaRI is expressed on neutrophils, eosinophils, monocytes/macrophages, dendritic cells, and Kupffer cells. This receptor represents a heterogeneously glycosylated transmembrane protein that binds both IgA subclasses with low affinity. A single gene encoding FcalphaRI has been isolated, which is located within the leukocyte receptor cluster on chromosome 19. The FcalphaRI alpha chain lacks canonical signal transduction domains but can associate with the FcR gamma-chain that bears an activation motif (ITAM) in the cytoplasmic domain, allowing activatory functions. FcalphaRI expressed alone mediates endocytosis and recyling of IgA. No FcalphaRI homologue has been defined in the mouse, and progress in defining the in vivo role of FcalphaRI has been made using human FcalphaRI transgenic (Tg) mice. FcalphaRI-Tg mice demonstrated FcalphaRI expression on Kupffer cells and so defined a key role for the receptor in mucosal defense. The receptor functions as a second line of antibacterial defense involving serum IgA rather than secretory IgA. Studies in FcalphaRI-Tg mice, furthermore, defined an essential role for soluble FcalphaRI in the development of IgA nephropathy by formation of circulating IgA-FcalphaRI complexes. Finally, recent work points out a role for human IgA in treatment of infectious and neoplastic diseases.

Depletion of Langerhans cells in human papillomavirus type 16-infected skin is associated with E6-mediated down regulation of E-cadherin

Human papillomavirus type 16 (HPV16) is an oncogenic virus that causes persistent infections in cervical epithelium. The chronic nature of HPV16 infections suggests that this virus actively evades the host immune response. Intraepithelial Langerhans cells (LC) are antigen-presenting cells that are critical in T-cell priming in response to viral infections of the skin. Here we show that HPV16 infection is directly associated with a reduction in the numbers of LC in infected epidermis. Adhesion between keratinocytes (KC) and LC, mediated by E-cadherin, is important in the retention of LC in the skin. Cell surface E-cadherin is reduced on HPV16-infected basal KC, and this is directly associated with the reduction in numbers of LC in infected epidermis. Expression of a single viral early protein, HPV16 E6, in KC reduces levels of cell surface E-cadherin thereby interfering with E-cadherin-mediated adhesion. Through this pathway, E6 expression in HPV16-infected KC may limit presentation of viral antigens by LC to the immune system, thus preventing the initiation of a cell-mediated immune response and promoting survival of the virus.

The interaction of immunodeficiency viruses with dendritic cells

Dendritic cells (DCs) can influence HIV-1 and SIV pathogenesis and protective mechanisms at several levels. First, HIV-1 productively infects select populations of DCs in culture, particularly immature DCs derived from blood monocytes and skin (Langerhans cells). However, there exist only a few instances in which HIV-1- or SIV-infected DCs have been identified in vivo in tissue sections. Second, different types of DCs reliably sequester and transmit infectious HIV-1 and SIV in culture, setting up a productive infection in T cells interacting with the DCs. This stimulation of infection in T cells may explain the observation that CD4+ T lymphocytes are the principal cell type observed to be infected with HIV-1 in lymphoid tissues in vivo. DCs express a C-type lectin, DC-SIGN/CD209, that functions to bind HIV-1 (and other infectious agents) and transmit virus to T cells. When transfected into the THP-1 cell line, the cytosolic domain of DC-SIGN is needed for HIV-1 sequestration and transmission. However, DCs lacking DC-SIGN (Langerhans cells) or expressing very low levels of DC-SIGN (rhesus macaque monocyte-derived DCs) may use additional molecules to bind and transmit immunodeficiency viruses to T cells. Third, DCs are efficient antigen-presenting cells for HIV-1 and SIV antigens. Infection with several recombinant viral vectors as well as attenuated virus is followed by antigen presentation to CD4+ and CD8+ T cells. An intriguing pathway that is well developed in DCs is the exogenous pathway for nonreplicating viral antigens to be presented on class I MHC products. This should allow DCs to stimulate CD8+ T cells after uptake of antibody-coated HIV-1 and dying infected T cells. It has been proposed that DCs, in addition to expanding effector helper and killer T cells, induce tolerance through T cell deletion and suppressor T cell formation, but this must be evaluated directly. Fourth, DCs are likely to be valuable in improving vaccine design. Increasing DC uptake of a vaccine, as well as increasing their numbers and maturation, should enhance efficacy. However, DCs can also capture antigens from other cells that are initially transduced with a DNA vaccine or a recombinant viral vector. The interaction of HIV-1 and SIV with DCs is therefore intricate but pertinent to understanding how these viruses disrupt immune function and elicit immune responses.

Human Leydig cells are productively infected by some HIV-2 and SIV strains but not by HIV-1

OBJECTIVES

With the use of highly active antiretroviral therapy, the identification of HIV reservoirs within the body has become an important issue. However, the testis has been largely ignored despite representing a pharmacologic sanctuary which could act as a viral reservoir.

DESIGN

Because alterations in testosterone production have frequently been reported in HIV-infected individuals, we investigated whether the testosterone-producing Leydig cells could become directly infected by HIV-1, HIV-2 or SIV.

METHODS

Purified Leydig cells were infected with a panel of HIV-1, HIV-2 and SIV strains and examined for expression of HIV/SIV receptors. Additionally, the impact of CD4 transduction on Leydig cell infection was determined.

RESULTS

Leydig cells were unable to support productive infection of the seven HIV-1 isolates tested. No CD4, CXCR4 or CCR5 expression was evident on the surface of Leydig cells and transduction with a CD4 expressing adenovirus did not induce HIV-1 infection. In contrast, some primary and laboratory adapted CD4-independent HIV-2 and SIV strains were able to enter and replicate productively in Leydig cells.

CONCLUSIONS

Our results suggest that Leydig cells do not represent a target for HIV-1 infection within the testis. In contrast, Leydig cells support HIV-2 and SIV infection and thus represent a potential target for infection. Receptor use and significance of HIV-2/SIV infection of Leydig cells remain to be determined.

Comparing the ex vivo fitness of CCR5-tropic human immunodeficiency virus type 1 isolates of subtypes B and C

Continual human immunodeficiency virus type 1 (HIV-1) evolution and expansion within the human population have led to unequal distribution of HIV-1 group M subtypes. In particular, recent outgrowth of subtype C in southern Africa, India, and China has fueled speculation that subtype C isolates may be more fit in vivo. In this study, nine subtype B and six subtype C HIV-1 isolates were added to peripheral blood mononuclear cell cultures for a complete pairwise competition experiment. All subtype C HIV-1 isolates were less fit than subtype B isolates (P < 0.0001), but intrasubtype variations in HIV-1 fitness were not significant. Increased fitness of subtype B over subtype C was also observed in primary CD4(+) T cells and macrophages from different human donors but not in skin-derived human Langerhans cells. Detailed analysis of the retroviral life cycle during several B and C virus competitions indicated that the efficiency of host cell entry may have a significant impact on relative fitness. Furthermore, phyletic analyses of fitness differences suggested that, for a recombined subtype B/C HIV-1 isolate, higher fitness mapped to the subtype B env gene rather than the subtype C gag and pol genes. These results suggest that subtype B and C HIV-1 may be transmitted with equal efficiency (Langerhans cell data) but that subtype C isolates may be less fit following initial infection (T-cell and macrophage data) and may lead to slower disease progression.

The sequential introduction of HIV-1 subtype B and CRF01AE in Singapore by sexual transmission: accelerated V3 region evolution in a subpopulation of Asian CRF01 viruses

The rapid spread of the human immunodeficiency virus type 1 (HIV-1) circulating recombinant form (CRF) 01AE throughout Asia demonstrates the dynamic nature of emerging epidemics. To further characterize the dissemination of these strains regionally, we sequenced 58 strains from Singapore and found that subtype B and CRF01 were introduced separately, by homosexual and heterosexual transmission, respectively. Protein similarity scores of the Singapore CRF01, as well as all Asian strains, demonstrated a complex distribution of scores in the V3 loop--some strains had very similar V3 loop sequences, while others were highly divergent. Furthermore, we found a strong correlation between the loss of a V3 glycosylation site and the divergent strains. This suggests that loss of this glycosylation site may make the V3 loop more susceptible to immune surveillance. The identification of a rapidly evolving population of CRF01AE variants should be considered when designing new candidate vaccines and when evaluating breakthrough strains from current vaccine trials.

Analysis of partial pol and env sequences indicates a high prevalence of HIV type 1 recombinant strains circulating in Gabon

Forty-one HIV-1 strains from Gabonese patients were studied according to the following strategy: nested polymerase chain reaction were performed to obtain an approximately 1,100-bp fragment containing the protease gene and the 5' half of the reverse transcriptase gene. Additional amplifications were carried out to obtain an approximately 700-bp fragment encompassing the C2V3 env gene. Fragments of 600 to 1,200 bp in the gag gene overlapping the pol sequences were used for the study of recombination patterns. Phylogenetic analyses of the different fragments were used to investigate HIV-1 diversity in Gabon. Thirty-one strains were sequenced in the env and pol genes and phylogenetic analyses classified them as subtype A (n = 2), D (n = 4), G (n = 1), H (n = 1), CRF02 (n = 8), and CRF MAL-like (n = 6); in addition, there were 6 unique recombinant forms and 1 unclassified strain, and in 2 cases pol/env sequences classified strains as subtype D whereas gag phylogeny classified them as subtype A. In 10 cases only 1 fragment was available: 4 env (2 subtype D, 1 subtype H, and 1 subtype U) and 6 pol (1 subtype A, 1 subtype C, 2 subtype G, and 2 subtype U). Minor mutations associated with viral resistance to antiretroviral drugs were observed in more than 80% of analyzed strains. Our study confirms the extensive HIV-1 diversity found in Central Africa, with more than 70% of strains from Gabon exhibiting discordant clustering in pol and env genomic regions and less than 60% concordance between sequencing and heteroduplex mobility assay genotyping. These findings highlight the fact that Central Africa represents the epicenter for the origin of HIV-1. The strategy of sequencing pol in association with env has proved to be useful for analysis of the recombinant strains. The main advantage of this approach is that it also allows for evaluation of genotypic susceptibility to antiretroviral drugs without the need for supplementary analyses.

Rapid detection of human immunodeficiency virus type 1 subtype e infection by PCR

The CRF01_AE (subtype E) strain of human immunodeficiency virus type 1 (HIV-1), originally reported in Thailand, spread rapidly to and showed prevalence in several countries in Southeast Asia, including Taiwan. This strain was also found in other regions of the world. Based on sequence analysis of the vpu gene, a nested PCR assay including an outer primer pair and a subtype E-specific inner primer pair was developed in this study for rapid detection of subtype E viruses. It was tested with 397 HIV-1-positive samples of known subtypes. For these samples, the sensitivity of detection of subtype E viruses was 100% (127 of 127), and the specificity was 97.8% (264 of 270). Although six samples of either subtype A or G showed a positive PCR, most of the cross-reactivity could be reduced by raising the annealing temperature from 54 degrees C to 63 degrees C. When tested with 195 HIV-positive samples of unknown subtypes, the assay had a sensitivity of 98.0% and a specificity of 98.6%. This is a simple, convenient, and sensitive method for rapid detection of subtype E viruses, especially in regions in which viruses of subtypes B and E are predominant.

Selection following isolation of human immunodeficiency virus type 1 in peripheral blood mononuclear cells and herpesvirus saimiri-transformed T cells is comparable

In attempts to improve isolation rates and virus yields for human immunodeficiency virus (HIV), the use of herpesvirus saimiri-immortalized T cells (HVS T cells) has been investigated as an alternative to/improvement over peripheral blood mononuclear cells (PBMCs). Here we characterize isolates rescued, in the two cell types, from two asymptomatic, long-term non-progressing HIV-1-infected individuals. All rescued viruses replicated in PBMCs and HVS T cells only, displaying a non-syncytium inducing (NSI) phenotype, and using CCR5 as co-receptor. Furthermore, PBMC/HVS T cell virus pairs displayed similar neutralization profiles. Full-length, expression-competent env genes were rescued from all virus isolates and directly from the patient samples using proviral DNA and viral RNA as templates. Compared with the sequences retrieved directly from the patient samples, both cell types showed similar selection characteristics. Whilst the selections were distinct for individual patient samples, they shared a common characteristic in selecting for viruses with increased negative charge across the V2 domain of the viral glycoproteins. The latter was observed at the env gene sequencing level for three other patients whose HIV strains were isolated in PBMCs only. This further supports a common selection for viral sequences that display a macrophage-tropic/NSI phenotype and shows that HVS T cells are a viable alternative to PBMCs for HIV-1 isolation.

Maintenance of glycoprotein-determined phenotype in an HIV type 1 (pNL43) env gene-cassetting system

Here we report the construction and use of a full-length env gene-cassetting system, C2, based on the HIV-1 infectious molecular clone NL43. C2 produces virus with the same phenotype as NL43 but with 2-fold lower growth kinetics. The latter probably relates to alteration in the vpu and/or nef genes. C2-env chimeras of macrophage-tropic and T cell-tropic laboratory strains and primary HIV-1 isolates retain the glycoprotein-determined phenotypes of their parent viruses. The cassette will assist studies of HIV-1 pathogenesis.

Comparative loss and maturation of peripheral blood dendritic cell subpopulations in African and non-African HIV-1-infected patients

OBJECTIVES

To quantify the percentage of the two major subpopulations of blood dendritic cells (DC) in HIV-1-seropositive Ugandan individuals infected with non-clade B viruses and compare this with that seen in clade B HIV-1 infected non-African individuals. DC maturation/activation status was also investigated via the expression of CD86.

METHODS

The percentage of blood DC was quantified by using flow cytometry. DC were identified as the lineage (CD3, CD14, CD16, CD19, CD20, CD56)-negative, HLA-DR-positive population and the two major subpopulations were differentiated by CD11c expression.

RESULTS

The percentage of blood DC was reduced significantly in HIV-1-seropositive African individuals when compared with controls (0.21 and 0.39% respectively). A similar reduction was also seen in non-African patients residing in the UK (0.19% compared with 0.36% for controls). However, there was no selective loss in either CD11c-positive or CD11c-negative subpopulations. The percentage of blood DC expressing CD86 was significantly greater in HIV-1-seropositive individuals when compared with controls and the increased expression was largely confined to CD11c-negative DC.

CONCLUSIONS

Africans infected with non-clade B HIV-1 showed similar reductions in the percentage of blood DC to non-Africans infected with clade B viruses. There was no selective loss of either DC subpopulation, suggesting that the ability of DC to acquire and present antigens or to produce interferon-alpha may both be impaired in HIV-1 infection.

Phylogenetic analysis of multiple heterosexual transmission events involving subtype b of HIV type 1

Between 1996 and 1999 thirteen cases of HIV infection were detected in Doncaster, a small town in the north of England (population approximately 250,000). A complex network of shared sexual histories involving local nightclubs linked these cases, with the only known risk factor being heterosexual intercourse. A series of frozen blood samples was collected in 1998-1999 and amplified by PCR to generate full-length gp120 clones. Sequencing demonstrated that all the transmission events in this heterosexual group involved the B subtype of HIV-1. When relationships between the samples were assessed it became clear that these 13 cases represented at least three separate strains of HIV-1, indicating that HIV is well established in this community. Eleven of the 13 cases were related, forming two distinct groups. Further investigation revealed that one group contained five patients whose general health was good and who were not receiving HAART. In contrast, the second group of six patients, including the putative index case, were symptomatic, receiving HAART, and may have been infected with a CXCR-4-utilizing virus. Several of the cases that were linked by genetic criteria were not linked by contact tracing, implying that further undiagnosed cases may exist in this community. To our knowledge, this is the largest outbreak of HIV studied within the heterosexual community in the United Kingdom to date, suggesting that this route of infection is becoming more common within the United Kingdom.

Viral load differences in early infection with two HIV-1 subtypes

OBJECTIVES

Information on early HIV-1 infection has come primarily from studies of persons infected with subtype B in North America and Europe; much less is known about other subtypes. The purpose of the present study was to compare the virologic and immunologic parameters following seroconversion among recently-infected persons infected with either of two different HIV-1 subtypes.

METHOD

A prospective cohort study was carried out at methadone treatment clinics administered by the Bangkok Metropolitan Administration, Thailand. A total of 130 HIV-1-infected seroconverters (103 with HIV-1 subtype E and 27 with subtype B) were included in the study. The main outcome measures were serial HIV-1 RNA viral load, natural killer cell percentage, CD4 and CD8 lymphocyte counts since seroconversion.

RESULTS

The demographic and behavioral characteristics of persons with either subtype were similar. Median RNA viral levels at the earliest time within 3 months of seroconversion were more than three times higher for persons infected with subtype E than subtype B (63 100 versus 18 050 copies/ml, P = 0.001). However, this difference decreased over time such that viral loads were similar at 12, 18, and 24 months following seroconversion. The CD4 and CD8 lymphocyte counts were similar in infections with either subtype during the entire period up to 24 months post-seroconversion.

CONCLUSIONS

Higher viral loads associated with subtype E may result from inter-subtype biological differences; however, the epidemiological dynamics of transmission in Bangkok may have also contributed to this phenomenon.

Significance of HIV-1 genetic subtypes

HIV is the most significant new pathogen that emerged during the twentieth century. Since the recognition of AIDS in 1981, HIV has caused a worldwide epidemic. HIV-1 mutates extensively and shows high genetic diversity and thereby poses significant challenges for effective surveillance and disease control. At the beginning of the 1990s phylogenetic analyses of HIV-1 sequences from different sources of the world epidemic revealed that HIV-1 can be divided into different clades or subtypes. However, most of the knowledge from that time was based on information from western countries, where subtype B predominated. Important questions were raised about the possibility that genetic and phenotypic differences in HIV-1 may affect transmissibility, infectivity and pathogenicity, in addition to responses to therapy and vaccines. On this basis this study was initiated in 1994, and presented as a thesis in 1999. This paper gives an overview of the results from this thesis (based on 6 original papers) and the conclusions drawn. In summary, determination of the genetic subtype of HIV-1 probably has little value for routine clinical care of individual patients, but provides a powerful tool for monitoring changes in local and global transmission patterns.

The maturation of dendritic cells results in postintegration inhibition of HIV-1 replication

Maturation of dendritic cells (DC) is known to result in decreased capacity to produce HIV due to postentry block of its replicative cycle. In this study, we compared the early phases of this cycle in immature DC (iDC) and mature DC (mDC) generated from monocytes cultured with GM-CSF and IL-4, trimeric CD40 ligand (DC(CD40LT)), or monocyte-conditioned medium (DC(MCM)) being added or not from day 5. Culture day 8 cells exposed to X4 HIV-1(LAI) or R5 HIV-1(Ba-L) were analyzed by semiquantitative R-U5 PCR, which detects total HIV DNA. CXC chemokine receptor 4(low) (CXCR4(low)) CCR5(+) iDC harbored similar viral DNA amounts when exposed to either strain. HIV-1(LAI) entered more efficiently into DC(CD40LT) or DC(MCM) with up-regulated CXCR4. CCR5(low) DC(CD40LT) still allowed entry of HIV-1(Ba-L), whereas CCR5(-) DC(MCM) displayed reduced permissivity to this virus. Comparing amounts of late (long terminal repeat (LTR)-gag PCR) and total (R-U5 PCR) viral DNA products showed that HIV-1(Ba-L) reverse transcription was more efficient than that of HIV-1(LAI), but was not affected by DC maturation. Southern blot detection of linear, circular, and integrated HIV DNA showed that maturation affected neither HIV-1 nuclear import nor integration. When assessing virus transcription by exposing iDC to pNL4-3.GFP or pNL4-3.Luc viruses pseudotyped with the G protein of vesicular stomatitis virus (VSV-G), followed by culture with or without CD40LT or MCM, GFP and luciferase activities decreased by 60-75% in mDC vs iDC. Thus, reduced HIV replication in mDC is primarily due to a postintegration block occurring mainly at the transcriptional level. We could not relate this block to altered expression and nuclear localization of NF-kappa B proteins and SP1 and SP3 transcription factors.

The pathogenesis of HIV-1 infection

Epidemiologists have long established beyond all reasonable doubt that infection by the human immunodeficiency virus type 1 (HIV-1) leads to the acquired immune deficiency syndrome (AIDS). Natural history cohorts have demonstrated that the median time from infection to development of AIDS is approximately 12 years, and that this long duration is broadly similar in all populations infected by HIV-1, in all risk groups, in all ethnic groups and in all geographical areas. These epidemiological observations suggest that HIV-1 causes AIDS largely independently of human major histocompatibility complex (MHC) and HIV-1 sequence polymorphisms, as great diversity of both these factors exist world-wide. This is not to say that HLA and HIV diversity do not affect the natural history of HIV disease, but these observations support a common mechanism of HIV-1 pathogenesis which is largely independent of human and viral diversity.

Simian-human immunodeficiency virus containing a human immunodeficiency virus type 1 subtype-E envelope gene: persistent infection, CD4(+) T-cell depletion, and mucosal membrane transmission in macaques

The envelope (env) glycoprotein of human immunodeficiency virus type 1 (HIV-1) determines several viral properties (e.g., coreceptor usage, cell tropism, and cytopathicity) and is a major target of antiviral immune responses. Most investigations on env have been conducted on subtype-B viral strains, prevalent in North America and Europe. Our study aimed to analyze env genes of subtype-E viral strains, prevalent in Asia and Africa, with a nonhuman primate model for lentivirus infection and AIDS. To this end, we constructed a simian immunodeficiency virus/HIV-1 subtype-E (SHIV) recombinant clone by replacing the env ectodomain of the SHIV-33 clone with the env ectodomain from the subtype-E strain HIV-1(CAR402), which was isolated from an individual in the Central African Republic. Virus from this recombinant clone, designated SHIV-E-CAR, replicated efficiently in macaque peripheral blood mononuclear cells. Accordingly, juvenile macaques were inoculated with cell-free SHIV-E-CAR by the intravenous or intravaginal route; virus replicated in these animals but did not produce hematological abnormalities. In an attempt to elicit the pathogenic potential of the recombinant clone, we serially passaged this viral clone via transfusion of blood and bone marrow through juvenile macaques to produce SHIV-E-P4 (fourth-passage virus). The serially passaged virus established productive infection and CD4(+) T-cell depletion in juvenile macaques inoculated by either the intravenous or the intravaginal route. Determination of the coreceptor usage of SHIV-E-CAR and serially passaged SHIV-E-P4 indicated that both of these viruses utilized CXCR4 as a coreceptor. In summary, the serially passaged SHIV subtype-E chimeric virus will be important for studies aimed at developing a nonhuman primate model for analyzing the functions of subtype-E env genes in viral transmission and pathogenesis and for vaccine challenge experiments with macaques immunized with HIV-1 env antigens.

Genetic heterogeneity of HIV-1 in Greece

The aim of this study was to detect and determine the genetic variation of HIV-1 in Greece and to analyze the phylogenetic relationships and transmission dynamics of identified variants. Eighty-six blood samples from HIV-1 seroconverted patients of different risk groups were collected from the AIDS clinic, AHEPA Hospital, Thessaloniki, Greece. Retroviral DNA was extracted from uncultured peripheral blood mononuclear cells. HIV-1 DNA sequences encoding a 500-bp fragment of the gp120 C2-C3 region were amplified from each study subject, and they were genetically subtyped by heteroduplex mobility assay and DNA sequencing. Genetic distances and phylogenetic relationships of DNA sequences were estimated using PHYLIP software. Our results revealed that 82 out of 86 (95.3%) subjects carried subtype B sequences, while four (4.7%) carried subtype A sequences. Subtype A in Greek individuals not having traveled abroad was documented. An average of intrasubtype B genetic divergence of 15% was noted. Our findings demonstrate the presence of at least two genetic subtypes of HIV-1 in northern Greece--subtype B and subtype A. The predominant subtype is subtype B, which was transmitted into Greece by multiple sources. Our observations lend support to the argument that the distribution of HIV-1 subtypes is determined by founder effects or other processes rather than any tropism for particular cell types or mode of transmission.

Functional differences between the long terminal repeat transcriptional promoters of human immunodeficiency virus type 1 subtypes A through G

The current human immunodeficiency virus type 1 (HIV-1) shows an increasing number of distinct viral subtypes, as well as viruses that are recombinants of at least two subtypes. Although no biological differences have been described so far for viruses that belong to different subtypes, there is considerable sequence variation between the different HIV-1 subtypes. The HIV-1 long terminal repeat (LTR) encodes the transcriptional promoter, and the LTR of subtypes A through G was cloned and analyzed to test if there are subtype-specific differences in gene expression. Sequence analysis demonstrated a unique LTR enhancer-promoter configuration for each subtype. Transcription assays with luciferase reporter constructs showed that all subtype LTRs are functional promoters with a low basal transcriptional activity and a high activity in the presence of the viral Tat transcriptional activator protein. All subtype LTRs responded equally well to the Tat trans activator protein of subtype B. This result suggests that there are no major differences in the mechanism of Tat-mediated trans activation among the subtypes. Nevertheless, subtype-specific differences in the activity of the basal LTR promoter were measured in different cell types. Furthermore, we measured a differential response to tumor necrosis factor alpha treatment, and the induction level correlated with the number of NF-kappaB sites in the respective LTRs, which varies from one (subtype E) to three (subtype C). In general, subtype E was found to encode the most potent LTR, and we therefore inserted the core promoter elements of subtype E in the infectious molecular clone of the LAI isolate (subtype B). This recombinant LAI-E virus exhibited a profound replication advantage compared with the original LAI virus in the SupT1 T-cell line, indicating that subtle differences in LTR promoter activity can have a significant impact on viral replication kinetics. These results suggest that there may be considerable biological differences among the HIV-1 subtypes.

High frequency of non-B subtypes in newly diagnosed HIV-1 infections in Switzerland

HIV-1 subtypes were determined in newly diagnosed residents of Switzerland. Blood was anonymously collected from patients with a first confirmed positive HIV-1 test result. Viral DNA from the env V3-V5 region was amplified by nested polymerase chain reaction (PCR) and screened for subtype B by heteroduplex mobility assay. All amplicons not identified as B were sequenced. From November 1996 to February 1998, 206 samples were analyzed. Main transmission risks were unprotected heterosexual (55.7%) or homosexual (27.1%) sexual contact or intravenous drug use (12.9%). Subtype B dominated in patients of Swiss, other European, American, or Asian citizenship; particularly high frequencies were found in homosexuals (97%) and drug users (94%). Non-B subtypes including A, C, D, E, F, G, H, a possible B/F recombinant, and a sequence related to J were present in 28.2% (95% confidence interval [CI], 22.9%-35.0%). Non-B were frequent in African citizens (95%), heterosexually infected individuals (44%), and women (43%). Heterosexually infected Swiss males harbored non-B strains in 18% and females in 33%. The results document a change in the epidemiology of newly diagnosed HIV-1 infections in Switzerland: predominance of heterosexual transmission and a high frequency of non-B subtypes.

Monocyte-derived dendritic cells as a model for the study of HIV-1 infection: productive infection and phenotypic changes during culture in human serum

Dendritic cells (DC) have been implicated in the initial selection for macrophage-tropic HIV-1 during transmission and in the generation of high-level virus replication during interactions with CD4 T cells. The role of DC as viral reservoirs and the extent of productive infection is unclear, but the ability to generate large numbers of DC from blood monocytes has produced a tractable model for study of DC-HIV-1 interactions. When cultured in granulocyte-macrophage colony stimulating factor and IL-4, sorted CD14+ monocytes rapidly lost phagocytic function for both 93 nm and 977 nm latex particles and developed the surface markers and function of DC. After 7 days, when returned to medium containing human serum without cytokines, some monocyte-derived dendritic cells (MDDC) became adherent, but retained the costimulatory markers CD80 and CD86 and continued to express CD83 and CD40. The MDDC stimulated allogeneic CD4 T cells, did not express new macrophage markers and remained non-phagocytic. With or without TNF-alpha, MDDC generated in cytokines were infected by macrophage and T cell-tropic virus and produced higher reverse transcriptase levels than did the autologous monocyte-derived macrophages (MDM). When added to T cells, the infected MDDC were able to infect T cells with a wider range of viral isolates than were MDM.

The dendritic cell-T cell milieu of the lymphoid tissue of the tonsil provides a locale in which SIV can reside and propagate at chronic stages of infection

Previous studies described the presence of numerous human immunodeficiency virus (HIV)-positive cells within and just beneath the mucosal surfaces of the tonsillar tissue of HIV-1-infected individuals. The virus-positive cells were most abundant in the dendritic cell (DC)-T cell rich areas of the lymphoepithelia lining the crypts, and consisted of multinucleated syncytia that contained DCs. This suggested that such cells within the tonsillar tissue might represent a site for chronic virus replication in infected individuals. Using the simian immunodeficiency virus (SIV)-macaque system, we chose to study further the viral distribution within the tonsillar tissue of animals infected via the vaginal route 8-10 months earlier. Our initial studies demonstrated that in situ hybridization (ISH)-positive DCs and T cells could be identified within the genital mucosa and draining lymph nodes of these infected animals even at this chronic stage of infection. Here we specifically examined the distal mucosa-associated lymphoid tissues of the tonsil. ISH-positive cells were mostly restricted to the DC-rich T cell areas of the underlying lymphoid tissue. However, T cells were the most commonly infected cell type and virus-positive cells were rarely found within the epithelia. In isolated cell suspensions, ISH-positive lymphocytes were often tightly associated with ISH-negative DCs, although few ISH-positive lymphocytes were often tightly associated with ISH-negative DCs, although few ISH-positive DCs could be identified within these clusters. Therefore, the naturally occurring DC-T cell milieu of the lymphoid tissue of the tonsil provides a locale in which SIV can reside and propagate on a chronic basis, even many months after the animals were infected by virus crossing the genital mucosa.

Long terminal repeat promoter/enhancer activity of different subtypes of HIV type 1

Transcription of the HIV-1 provirus genome is regulated by a complex interplay between viral regulatory proteins and cellular transcription factors that interact with the viral long terminal repeat (LTR) region of HIV-1. However, several cellular transcription factors have been identified that can interact with the HIV-1 LTR; the significance of all of these factors is not clearly understood. In this study we have characterized the LTR region of different subtypes of HIV-1 with regard to nucleotide sequence and promoter activity. The LTR regions of HIV-1 from peripheral blood mononuclear cells of 29 infected individuals originating from 10 different geographical regions were sequenced and further analyzed for promoter/enhancer activity in transient transfection of HeLa cells, in the context of a reporter gene and in the context of the complete virus genome. We found several subtype-specific LTR sequences of the various HIV-1 strains, such as an insertion that created a potential third NF-kappaB site in the LTR of the subtype C strains. The USF-binding site in the NRE also contained subtype-specific sequences. Interestingly, the promoter/enhancer activities of the subtype C LTRs were higher than the activities of the other subtypes analyzed here (subtypes A, B, D, E, and G), suggesting that the potential third NF-kappaB site may confer higher LTR activity or that the subtype C NRE may be less potent. Thus, our data suggest that genetic diversity of the LTR may result in HIV-1 subtypes with different replicative properties.

Expanded tropism of primary human immunodeficiency virus type 1 R5 strains to CD4(+) T-cell lines determined by the capacity to exploit low concentrations of CCR5

Human immunodeficiency virus type 1 (HIV-1) non-syncytium-inducing (NSI) strains predominantly use the chemokine receptor CCR5, while syncytium-inducing (SI) strains use CXCR4. In vitro, SI isolates infect and replicate in a range of CD4(+) CXCR4(+) T-cell lines, whereas NSI isolates usually do not. Here we describe three NSI strains that are able to infect two CD4(+) T-cell lines, Molt4 and SupT1. For one strain, a variant of JRCSF selected in vitro, replication on Molt4 was previously shown to be conferred by a single amino-acid change in the V1 loop (M.T. Boyd et al., J. Virol. 67:3649-3652, 1993). On CD4(+) cell lines expressing different coreceptors, these strains use CCR5 predominantly and do not replicate in CCR5-negative peripheral blood mononuclear cells derived from individuals homozygous for Delta32 CCR5. Furthermore, infection of Molt4 and SupT1 by each of these three strains is potently inhibited by ligands for CCR5, including 2D7, a monoclonal antibody specific for CCR5. CCR5 mRNA was present in both Molt4 and SupT1 by reverse transcription-PCR, although CCR5 protein could not be detected either on the cell surface or in intracellular vesicles. The expanded tropism of the three strains shown here is therefore not due to adaptation to a new coreceptor but due to the capacity to exploit extremely low levels of CCR5 on Molt4 and SupT1 cells. This novel tropism observed for a subset of primary HIV-1 isolates may represent an extended tropism to new CD4(+) cell types in vivo.

Primary human immunodeficiency virus type 2 (HIV-2) isolates infect CD4-negative cells via CCR5 and CXCR4: comparison with HIV-1 and simian immunodeficiency virus and relevance to cell tropism in vivo

Cell surface receptors exploited by human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) for infection are major determinants of tropism. HIV-1 usually requires two receptors to infect cells. Gp120 on HIV-1 virions binds CD4 on the cell surface, triggering conformational rearrangements that create or expose a binding site for a seven-transmembrane (7TM) coreceptor. Although HIV-2 and SIV strains also use CD4, several laboratory-adapted HIV-2 strains infect cells without CD4, via an interaction with the coreceptor CXCR4. Moreover, the envelope glycoproteins of SIV of macaques (SIV(MAC)) can bind to and initiate infection of CD4(-) cells via CCR5. Here, we show that most primary HIV-2 isolates can infect either CCR5(+) or CXCR4(+) cells without CD4. The efficiency of CD4-independent infection by HIV-2 was comparable to that of SIV, but markedly higher than that of HIV-1. CD4-independent HIV-2 strains that could use both CCR5 and CXCR4 to infect CD4(+) cells were only able to use one of these receptors in the absence of CD4. Our observations therefore indicate (i) that HIV-2 and SIV envelope glycoproteins form a distinct conformation that enables contact with a 7TM receptor without CD4, and (ii) the use of CD4 enables a wider range of 7TM receptors to be exploited for infection and may assist adaptation or switching to new coreceptors in vivo. Primary CD4(-) fetal astrocyte cultures expressed CXCR4 and supported replication by the T-cell-line-adapted ROD/B strain. Productive infection by primary X4 strains was only triggered upon treatment of virus with soluble CD4. Thus, many primary HIV-2 strains infect CCR5(+) or CXCR4(+) cell lines without CD4 in vitro. CD4(-) cells that express these coreceptors in vivo, however, may still resist HIV-2 entry due to insufficient coreceptor concentration on the cell surface to trigger fusion or their expression in a conformation nonfunctional as a coreceptor. Our study, however, emphasizes that primary HIV-2 strains carry the potential to infect CD4(-) cells expressing CCR5 or CXCR4 in vivo.

Chemokine receptors as HIV-1 coreceptors: roles in viral entry, tropism, and disease

In addition to CD4, the human immunodeficiency virus (HIV) requires a coreceptor for entry into target cells. The chemokine receptors CXCR4 and CCR5, members of the G protein-coupled receptor superfamily, have been identified as the principal coreceptors for T cell line-tropic and macrophage-tropic HIV-1 isolates, respectively. The updated coreceptor repertoire includes numerous members, mostly chemokine receptors and related orphans. These discoveries provide a new framework for understanding critical features of the basic biology of HIV-1, including the selective tropism of individual viral variants for different CD4+ target cells and the membrane fusion mechanism governing virus entry. The coreceptors also provide molecular perspectives on central puzzles of HIV-1 disease, including the selective transmission of macrophage-tropic variants, the appearance of T cell line-tropic variants in many infected persons during progression to AIDS, and differing susceptibilities of individuals to infection and disease progression. Genetic findings have yielded major insights into the in vivo roles of individual coreceptors and their ligands; of particular importance is the discovery of an inactivating mutation in the CCR5 gene which, in homozygous form, confers strong resistance to HIV-1 infection. Beyond providing new perspectives on fundamental aspects of HIV-1 transmission and pathogenesis, the coreceptors suggest new avenues for developing novel therapeutic and preventative strategies to combat the AIDS epidemic.

The Susceptibility to X4 and R5 Human Immunodeficiency Virus-1 Strains of Dendritic Cells Derived In Vitro From CD34+ Hematopoietic Progenitor Cells Is Primarily Determined by Their Maturation Stage

Dendritic cells (DC) were sorted on day 8 from cultures of CD34+ cells with stem cell factor/Flt-3 ligand/ granulocyte-macrophage colony-stimulating factor (GM-CSF)/tumor necrosis factor- (TNF-)/interleukin-4 (IL-4). Exposing immature CCR5+CXCR4lo/− DC to CCR5-dependent human immunodeficiency virus (HIV)-1Ba-L led to productive and cytopathic infection, whereas only low virus production occurred in CXCR4-dependent HIV-1LAI–exposed DC. PCR analysis of the DC 48 hours postinfection showed efficient entry of HIV-1Ba-L but not of HIV-1LAI. CD40 ligand- or monocyte-conditioned medium-induced maturation of HIV-1Ba-L–infected DC reduced virus production by about 1 Log, while cells became CCR5−. However, HIV-1Ba-L–exposed mature DC harbored 15-fold more viral DNA than their immature counterparts, ruling out inhibition of virus entry. Simultaneously, CXCR4 upregulation by mature DC coincided with highly efficient entry of HIV-1LAI which, nonetheless, replicated at the same low level in mature as in immature DC. In line with these findings, coculture of HIV-1Ba-L–infected immature DC with CD3 monoclonal antibody–activated autologous CD4+ T lymphocytes in the presence of AZT decreased virus production by the DC. Finally, whether they originated from CD1a+CD14− or CD1a−CD14+ precursors, DC did not differ as regards permissivity to HIV, although CD1a+CD14− precursor-derived immature DC could produce higher HIV-1Ba-L amounts than their CD1a−CD14+ counterparts. Thus, both DC permissivity to, and capacity to support replication of, HIV is primarily determined by their maturation stage.

The Susceptibility to X4 and R5 Human Immunodeficiency Virus-1 Strains of Dendritic Cells Derived In Vitro From CD34+ Hematopoietic Progenitor Cells Is Primarily Determined by Their Maturation Stage

Dendritic cells (DC) were sorted on day 8 from cultures of CD34+ cells with stem cell factor/Flt-3 ligand/ granulocyte-macrophage colony-stimulating factor (GM-CSF)/tumor necrosis factor- (TNF-)/interleukin-4 (IL-4). Exposing immature CCR5+CXCR4lo/− DC to CCR5-dependent human immunodeficiency virus (HIV)-1Ba-L led to productive and cytopathic infection, whereas only low virus production occurred in CXCR4-dependent HIV-1LAI–exposed DC. PCR analysis of the DC 48 hours postinfection showed efficient entry of HIV-1Ba-L but not of HIV-1LAI. CD40 ligand- or monocyte-conditioned medium-induced maturation of HIV-1Ba-L–infected DC reduced virus production by about 1 Log, while cells became CCR5−. However, HIV-1Ba-L–exposed mature DC harbored 15-fold more viral DNA than their immature counterparts, ruling out inhibition of virus entry. Simultaneously, CXCR4 upregulation by mature DC coincided with highly efficient entry of HIV-1LAI which, nonetheless, replicated at the same low level in mature as in immature DC. In line with these findings, coculture of HIV-1Ba-L–infected immature DC with CD3 monoclonal antibody–activated autologous CD4+ T lymphocytes in the presence of AZT decreased virus production by the DC. Finally, whether they originated from CD1a+CD14− or CD1a−CD14+ precursors, DC did not differ as regards permissivity to HIV, although CD1a+CD14− precursor-derived immature DC could produce higher HIV-1Ba-L amounts than their CD1a−CD14+ counterparts. Thus, both DC permissivity to, and capacity to support replication of, HIV is primarily determined by their maturation stage.

Functional complementation of the envelope hypervariable V3 loop of human immunodeficiency virus type 1 subtype B by the subtype E V3 loop

The hypervariable V3 loop within gp120 of human immunodeficiency virus type 1 (HIV-1) is the major determinant of cell tropism and the entry coreceptor usage of the virus. However, the information obtained thus far has been from only subtype B from North America and Europe, and little is known about other subtypes whose V3 amino acids differ by as much as 50% from subtype B V3. In this study, we examined the functional potential of the V3 element of the HIV-1 subtype E, the most crucial variant causing the AIDS epidemic throughout southeast Asia. A panel of HIV-1LAI recombinants was constructed by the overlap extension method, by which the LAI V3 loop was precisely replaced by that of the subtype E nonsyncytium-inducing (NSI) or syncytium-inducing (SI) variant. All of the recombinant viruses infected peripheral blood mononuclear cells, whereas only those with SI V3 infected MT2 cells, a CD4(+) T cell line. Consistently, the SI V3 recombinants used CXCR4, while the NSI V3 recombinants used CCR5 for infection of HOS-CD4(+) cells. Finally, only the NSI V3 sequence conferred CC-chemokine sensitivity on the parental virus. The data support the notion that the HIV-1 V3 loop consists of a relatively independent domain in gp120 and suggest that the subtype E V3 loop indeed contains the functional element to dictate the cell tropism, coreceptor preference, and chemokine sensitivity of the virus. These findings are of immediate importance in understanding V3 structure-function relationship and for examining phenotypic evolution of HIV-1 subtype E.

Mucosal dendritic cells and immunodeficiency viruses

Dendritic cells [DCs] have been implicated in the pathogenesis of human immunodeficiency virus type 1 (HIV-1). When skin was used as a model for mucosae, the cutaneous DC-T cell milieu allowed the growth of HIV-1 and much of the newly produced virus could be detected in multinucleated DC-T cell syncytia. Such virus replication occurs irrespective of the genetic subtype, the syncytium- and non-syncytium-inducing capacities of the viruses, and whether they are classified as T cell- or macrophage-tropic. Similar DC-syncytia have been identified within the mucosal surfaces of the tonsillar tissue of HIV-1-infected persons. More recently, it was demonstrated that DC-T cell mixtures from the skin, mucosae, and blood of healthy macaques similarly support the replication of simian immunodeficiency virus. In both the human and monkey systems, active virus replication requires the presence of both DCs and T cells. Further studies using the macaque model are underway to elucidate the role of DCs in the transmission and spread of HIV infection.