HIV receptors and the pathogenesis of AIDS

Hematopoietic Stem/Progenitor Cells and the Pathogenesis of HIV/AIDS

The interaction between human immunodeficiency virus (HIV) and hematopoietic stem/progenitor cells (HSPCs) has been of great interest. However, it remains unclear whether HSPCs can act as viral reservoirs. Many studies have reported the presence of latently infected HSPCs in the bone marrow of HIV-infected patients, whereas many other investigators have reported negative results. Hence, further evidence is required to elucidate this controversy. The other arm of HSPC investigations of HIV infection involves dynamics analysis in the early and late stages of infection to understand the impact on the pathogenesis of acquired immunodeficiency syndrome. Several recent studies have suggested reduced amounts and/or functional impairment of multipotent, myeloid, and lymphoid progenitors in HIV infection that may contribute to hematological manifestations, including anemia, pancytopenia, and T-cell depletion. In addition, ongoing and future studies on the senescence of HSPCs are expected to further the understanding of HIV pathogenesis. This mini review summarizes reports describing the basic aspects of hematopoiesis in response to HIV infection and offers insights into the association of HIV infection/exposure of the host HSPCs and hematopoietic potential.

HIV Impacts CD34+ Progenitors Involved in T-Cell Differentiation During Coculture With Mouse Stromal OP9-DL1 Cells

HIV-1 causes the loss of CD4⁺ T cells via depletion or impairment of their production. The latter involves infection of thymocytes, but the involvement of hematopoietic CD34⁺ cells remains unclear even though HIV-positive patients frequently manifest myelosuppression. In order to have a closer look at the impact of HIV-1 on T-lineage differentiation, this study utilized the OP9-DL1 coculture system, which supports in vitro T-lineage differentiation of human hematopoietic stem/progenitor cells. In the newly developed in vitro OP9-DL1/HIV-1 model, cord-derived CD34⁺ cells were infected with CXCR4-tropic HIV-1_NL4−3 and cocultured. The HIV-infected cocultures exhibited reduced CD4⁺ T-cell growth at weeks 3–5 post infection compared to autologous uninfected cocultures. Further assays and analyses revealed that CD34⁺CD7⁺CXCR4⁺ cells can be quickly depleted as early as 1 week after infection of the subset, and this was accompanied by the emergence of rare CD34⁺CD7⁺CD4⁺ cells. A subsequent theoretical model analysis suggested potential influence of HIV-1 on the differentiation rate or death rate of lymphoid progenitor cells. These results indicate that CXCR4-tropic HIV-1 strains may impact the dynamics of CD34⁺CD7⁺ lymphoid progenitor cell pools, presumably leading to impaired T-cell production potential.

The use of RetroNectin in studies requiring in vitro HIV-1 infection of human hematopoietic stem/progenitor cells

Human immunodeficiency virus (HIV) causes damage, directly or indirectly, to the whole hematopoietic system, including CD34+ hematopoietic stem/progenitor cells (HSPCs). CXCR4-tropic strains of HIV-1 may affect the function of CD34+CXCR4+ progenitor cells either by infecting the cells or modifying the dynamics of more differentiated hematopoietic cells. However, CD34+ cells are known for their resistance to HIV-1 infection in vitro, which restricts any detailed analysis of the impact of HIV on HSPCs. We report the use of RetroNectin, a recombinant fibronectin fragment used for gene transfer with lentiviral vectors, to overcome the limitation associated with CD34+ cell resistance to HIV-1 infection. RetroNectin coating of plates improved in vitro HIV-1 infectivity on human CD34+ cells by 10 fold. This resulted in stable HIV-1 infection for 5 weeks in an OP9-DL1 coculture. These results suggest that RetroNectin may be a useful tool for long-term monitoring of in vitro HIV-infected CD34+ cells.

A brief history of the global effort to develop a preventive HIV vaccine

Soon after HIV was discovered as the cause of AIDS in 1983-1984, there was an expectation that a preventive vaccine would be rapidly developed. In trying to achieve that goal, three successive scientific paradigms have been explored: induction of neutralizing antibodies, induction of cell mediated immunity, and exploration of combination approaches and novel concepts. Although major progress has been made in understanding the scientific basis for HIV vaccine development, efficacy trials have been critical in moving the field forward. In 2009, the field was reinvigorated with the modest results obtained from the RV144 trial conducted in Thailand. Here, we review those vaccine development efforts, with an emphasis on events that occurred during the earlier years. The goal is to provide younger generations of scientists with information and inspiration to continue the search for an HIV vaccine.

Vaginal ring adherence in sub-Saharan Africa: expulsion, removal, and perfect use

In sub-Saharan Africa, HIV incidence and prevalence remain disproportionately high among women. Vaginal rings (VRs) have been formulated for the delivery of antiretroviral-based microbicides, and their favorable safety and tolerability profiles reported in clinical studies. Although the concept of drug release through a VR has existed since 1970, and VRs have been marketed since 1992 for contraceptive or hormone replacement purposes, VR use as a microbicide delivery system is a novel application. This is the first study to evaluate VR adherence among African women in the context of its potential use as an HIV prevention method, to examine predictors of adherence, and to describe clinical or contextual reasons for VR removals or nonadherence. This was a randomized trial of the safety and acceptability of a placebo VR worn for 12 weeks in 170 HIV-negative, African women aged 18-35 in four clinic sites in South Africa and Tanzania. The findings suggest that adherence to VR use in the context of HIV prevention trials in these communities should be high, thereby enabling more accurate assessment of an active microbicide safety and efficacy.

Vaginal microbicides to prevent human immunodeficiency virus infection in women: perspectives on the female genital tract, sexual maturity and mucosal inflammation

Topically applied vaginal microbicides to protect against human immunodeficiency (HIV) virus infection offer an important female-controlled prevention strategy. Microbicides have been in development for more than 2 decades, and have included various agents that disrupt cellular and microbial membranes (surfactants), restore the natural acidic protective pH of the vagina (acid buffers), and those that interfere with interactions between HIV envelope proteins and cellular receptors (anionic polymers). Although none of these candidate microbicides have shown significant protection against HIV in clinical trials, a topical gel, including the antiretroviral drug tenofovir (TFV) 1% was the first microbicide to be tested to show some protection against HIV infection. This review explores the effect of female genital tract biology and anatomy, mucosal inflammation, and age on the effectiveness of microbicides to prevent HIV infection.

Functional analysis of naturally occurring mutations in the open reading frame of CCR5 in HIV-infected Chinese patients and healthy controls

We studied polymorphism of the HIV coreceptor CC chemokine receptor (CCR) 5 in 1099 Chinese adults residing in Hong Kong, including 785 HIV-negative healthy donors and 314 HIV-positive patients. Ten mutants in the CCR5 open reading frame were identified, 7 of which were nonsynonymous. The frequencies of these alleles did not show a significant difference between HIV patients and healthy controls. G106R, Delta32, R223Q, 299(FS), and S336I were cloned from prevalent mutant genes, and their effects on HIV infection were analyzed by a series of in vitro experiments to determine their transcription levels, expression levels, conformational changes, and HIV coreceptor function. R223Q is the most prevalent CCR5 mutant in ethnic Chinese, with a frequency of 0.046, which does not affect HIV infection in vitro, however. The S336I mutant also does not affect its transcription, expression, or HIV coreceptor function. Similar to 299(FS), the mutant G106R located in the third transmembrane domain results in diminished HIV coreceptor function in vitro through conformation changes in ECL2.

Neuroimmune and neurovirological aspects of human immunodeficiency virus infection

Like most lentiviruses, HIV-1 causes both immune suppression and neurological disease. Neurological disease may occur at any stage of HIV infection but is most apparent with severe immune suppression. Cognitive impairment, reflected strikingly by HIV-associated dementia, has attracted intense interest since the outset of the HIV epidemic, and understanding of its pathogenesis has been spurred on by the emergence of several hypotheses outlining potential pathogenic mechanisms. The release of inflammatory molecules by HIV-infected microglia and macrophages and the concurrent neuronal damage play central roles in the conceptualization of HIV neuropathogenesis. Many inflammatory molecules appear to contribute to the pathogenic cascade and their individual roles remain undefined. At the same time, the abundance of virus in the brain and the type or strain of virus found in the brain may also be important codeterminants of neurological disease, as shown for other neurotropic viruses. Coreceptor use by HIV found in the brain appears to closely mirror what has been reported in systemic macrophages. The impact of HAART on viral genotype and phenotype found in the brain, and its relationship to clinical disease, remain uncertain. Several interesting animal models have been developed, using other lentiviruses, transgenic animals, and HIV-infected SCID mice, that may prove useful in future pathogenesis and therapeutic studies. Despite the progress in the understanding of HIV neuropathogenesis, many questions remain unanswered.

Dynamics of HIV infection: a cellular automata approach

We use a cellular automata model to study the evolution of human immunodeficiency virus (HIV) infection and the onset of acquired immunodeficiency syndrome (AIDS). The model takes into account the global features of the immune response to any pathogen, the fast mutation rate of the HIV, and a fair amount of spatial localization, which may occur in the lymph nodes. Our results reproduce the three-phase pattern observed in T cell and virus counts of infected patients, namely, the primary response, the clinical latency period, and the onset of AIDS. The dynamics of real experimental data is related to the transient behavior of our model and not to its steady state. We have also found that the infected cells organize themselves into spatial structures, which are responsible for the decrease on the concentration of uninfected cells, leading to AIDS.

The Biology and Evolution of HIV

▪ Abstract  This review examines the current state of knowledge about HIV/AIDS in terms of its origins, pathogenesis, genetic variation, and evolutionary biology. The HIV virus damages the host's immune system, resulting in AIDS, which is characterized by immunodeficiency, opportunistic infections, neoplasms, and neurological problems. HIV is a complex retrovirus with a high mutation rate. This mutation rate allows the virus to evade host immune responses, and evidence indicates that selection favors more virulent strains with rapid replication. While a number of controversial theories attempt to explain the origin of HIV/AIDS, phylogenetic evidence suggests a zoonotic transmission of HIV to humans and implicates the chimpanzee (Pan troglodytes troglodytes) as the source of HIV-1 infection and the sooty mangabey as the source of HIV-2 infection in human populations. New therapies provide hope for increased longevity among people living with AIDS, but the biology of HIV presents significant obstacles to finding a cure and/or vaccine. HIV continues to be a threat to the global population because of its fast mutation rate, recombinogenic effect, and its use of human defenses to replicate itself.

Anomalous behavior of the contact process with aging

The effect of power-law aging on a contact process is studied by simulation and using a mean-field approach. The introduced type of aging accounts for, e.g., the growth of the virus fitness (HIV infection). We find that the system may approach its stationary state in a nontrivial, nonmonotonous way. For the particular value of the aging exponent alpha=1 we observe a rich set of behaviors: depending on the process parameters, the relaxation to the stationary state proceeds as 1/ln t or via a power law with a nonuniversal exponent. Simulation results suggest that for 0<alpha<1, the absorbing-state phase transition is in the universality class of directed percolation.

Getting to know HIV

Since the Human Immunodeficiency Virus was first isolated in 1983, we have come to know it in exquisite detail. Yet we still do not understand sufficiently how it causes disease. Neither do we know why chimpanzees and some African monkeys, which are the natural reservoir of the precursors of HIV-1 and HIV-2, can harbour similar levels of virus without becoming ill. Our knowledge of the replication cycle of HIV as a retrovirus has been pivotal in the development of antiviral drugs. Our knowledge of the cellular tropism and cell surface receptors exploited by the virus help to explain the pattern of immune deficiency, wasting and dementia that make up the clinical dimensions of AIDS. The extraordinary rate of genetic and phenotypic evolution of the virus - both within the infected individual and across the worldwide pandemic - partially explains why no vaccine constructs to date have been successful. HIV comprises just 9 genes but represents one of humanity's most formidable foes.

Neuropathogenicity and sensitivity to antibody neutralization of lactate dehydrogenase-elevating virus are determined by polylactosaminoglycan chains on the primary envelope glycoprotein

Common strains of lactate dehydrogenase-elevating virus (LDV, an arterivirus), such as LDV-P and LDV-vx, are highly resistant to antibody neutralization and invariably establish a viremic, persistent, yet asymptomatic, infection in mice. Other LDV strains, LDV-C and LDV-v, have been identified that, in contrast, are highly susceptible to antibody neutralization and are incapable of a high viremic persistent infection, but at the same time have gained the ability to cause paralytic disease in immunosuppressed C58 and AKR mice. Our present results further indicate that these phenotypic differences represent linked properties that correlate with the number of N-glycosylation sites associated with the single neutralization epitope on the short ectodomain of the primary envelope glycoprotein, VP-3P. The VP-3P ectodomains of LDV-P/vx possess three N-glycosylation sites, whereas those of LDV-C/v lack the two N-terminal sites. We have now isolated four independent neutralization escape variants of neuropathogenic LDV-C and LDV-v on the basis of their ability to establish a high viremic persistent infection in mice. The VP-3P ectodomains of all four variants had specifically regained two N-glycosylation sites concomitant with decreased immunogenicity of the neutralization eptitope and decreased sensitivity to antibody neutralization as well as loss of neuropathogenicity.

Enhanced inhibition of human immunodeficiency virus type 1 by Met-stromal-derived factor 1beta correlates with down-modulation of CXCR4

CXCR4 is a chemokine receptor used by some strains of HIV-1 as an entry coreceptor in association with cell surface CD4 on human cells. In human immunodeficiency virus type 1 (HIV-1)-infected individuals, the appearance of viral isolates with a tropism for CXCR4 (T tropic) has been correlated with late disease progression. The presumed natural ligands for CXCR4 are SDF-1alpha and SDF-1beta, which are proposed to play a role in blocking T-tropic HIV-1 cell entry. Here, we demonstrate that addition of an N-terminal methionine residue to SDF-1beta (Met-SDF-1beta) results in a dramatically enhanced functional activity compared to that of native SDF-1beta. Equivalent concentrations of Met-SDF-1beta are markedly more inhibitory for T-tropic HIV-1 replication than SDF-1beta. A comparison of the biological activities of these two forms of SDF-1beta reveals that Met-SDF-1beta induces a more pronounced intracellular calcium flux yet binds with slightly lower affinity to CXCR4 than SDF-1beta. Down-modulation of CXCR4 is similar after exposure of cells to either chemokine form for 2 h. However, after a 48-h incubation, the surface expression of CXCR4 is much lower for cells treated with Met-SDF-1beta. The enhanced blocking of T-tropic HIV-1 by Met-SDF-1beta appears to be related to prolonged CXCR4 down-modulation.

V3 recombinants indicate a central role for CCR5 as a coreceptor in tissue infection by human immunodeficiency virus type 1

Binding of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120 to both CD4 and one of several chemokine receptors (coreceptors) permits entry of virus into target cells. Infection of tissues may establish latent viral reservoirs as well as cause direct pathologic effects that manifest as clinical disease such as HIV-associated dementia. We sought to identify the critical coreceptors recognized by HIV-1 tissue-derived strains as well as to correlate these coreceptor preferences with site of infection and dementia diagnosis. To reconstitute coreceptor use, we cloned HIV-1 envelope V3 sequences encoding the primary determinants of coreceptor specificity from 13 brain-derived and 6 colon-derived viruses into an isogenic (NL4-3) viral background. All V3 recombinants utilized the chemokine receptor CCR5 uniformly and efficiently as a coreceptor but not CXCR4, BOB/GPR15, or Bonzo/STRL33. Other receptors such as CCR3, CCR8, and US28 were inefficiently and variably used as coreceptors by various envelopes. CCR5 without CD4 present did not allow for detectable infection by any of the tested recombinants. In contrast to the pathogenic switch in coreceptor specificity frequently observed in comparisons of blood-derived viruses early after HIV-1 seroconversion and after onset of AIDS, the characteristics of these V3 recombinants suggest that CCR5 is a primary coreceptor for brain- and colon-derived viruses regardless of tissue source or diagnosis of dementia. Therefore, tissue infection may not depend significantly on viral envelope quasispeciation to broaden coreceptor range but rather selects for CCR5 use throughout disease progression.

Chemokine receptor polymorphism and autologous neutralizing antibody response in long-term HIV-1 infection

We have previously reported that slowly progressing HIV infection (SPI) was associated with the presence of contemporaneous autologous neutralizing antibodies. In contrast, a group of individuals with more rapidly progressing infection (RPI) generally lacked these antibodies. To understand the importance of autologous neutralizing antibodies in SPI more fully, we have now conducted a prospective study taking consecutive blood samples from the individuals with SPI (8 patients) and RPI (10 patients). Blood sampling in the group with SPI was done 110 and 123 months after the estimated seroconversion and at similar time points in the group with RPI. Virus isolation was attempted at both time points in both groups of individuals; crossed neutralization assays were set up with autologous virus. These confirmed our previous finding of significant autologous neutralizing titers in the group with SPI (geometric mean titer [GMT] 8.7 versus 1.6 in SPI and RPI, respectively; p = 0.0048). However, not all individuals with SPI possessed autologous neutralizing antibodies, indicating that other factors may be decisive for SPI. Furthermore, neutralizing antibody titers did not increase from early to late serum samples. Finally, late virus isolates from individuals with SPI generally remained sensitive to neutralization by early serum samples. Virus phenotype (SI/NSI) and CCR5 genotype was determined for all individuals. Neither showed significant correlation with SPI. However, all SPI individuals who were heterozygous for the CCR5 deletion were infected with virus of NSI phenotype. In contrast, all RPI individuals who were heterozygous for the CCR5 deletion were infected with virus of SI phenotype (p = .028). Thus, a beneficial effect of having a partly nonfunctional CCR5 coreceptor may depend on the viral SI/NSI phenotype.

A broad range of chemokine receptors are used by primary isolates of human immunodeficiency virus type 2 as coreceptors with CD4

Like human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV), HIV-2 requires a coreceptor in addition to CD4 for entry into cells. HIV and SIV coreceptor molecules belong to a family of seven-transmembrane-domain G-protein-coupled receptors. Here we show that primary HIV-2 isolates can use a broad range of coreceptor molecules, including CCR1, CCR2b, CCR3, CCR4, CCR5, and CXCR4. Despite broad coreceptor use, the chemokine ligand SDF-1 substantially blocked HIV-2 infectivity of peripheral blood mononuclear cells, indicating that its receptor, CXCR4, was the predominant coreceptor for infection of these cells. However, expression of CXCR4 together with CD4 on some cell types did not confer susceptibility to infection by all CXCR4-using virus isolates. These data therefore indicate that another factor(s) influences the ability of HIV-2 to replicate in human cell types that express the appropriate receptors for virus entry.

Effects of [D-Ala1] peptide T-NH2 and HIV envelope glycoprotein gp120 on cyclic AMP dependent protein kinases in normal and psoriatic human fibroblasts

In addition to acquired immunodeficiency syndrome (AIDS), persons infected with human immunodeficiency virus often develop cutaneous manifestations, including severe psoriasis. In previous studies, we have established that psoriatic fibroblasts and erythrocytes obtained from psoriatic patients exhibit decreased levels of cyclic adenosine monophosphate (cAMP) dependent protein kinase (PKA) activity and of 8-azido-[32P]cAMP binding to the RI and RII regulatory subunits of PKA. Because treatment of patients with peptide T (an octapeptide sequence found in the human immunodeficiency virus envelope glycoprotein gp120) has been observed to result in an improvement in the psoriatic condition, studies were initiated to determine if peptide T and gp120 protein treatment of normal and psoriatic human fibroblasts resulted in any changes in PKA. Exposure of psoriatic fibroblasts to peptide T resulted in a time (4 h to 6 d) and dose [10(-14)-10(-8) M] dependent increase in the levels of 8-azido-[32P]cAMP binding to the RI and RII regulatory subunits of PKA, along with a corresponding increase in PKA activity. Peptide T exhibited a biphasic dose dependent response, with maximal effects on PKA noted at 10(-12)M peptide T. Treatment of normal human fibroblasts with peptide T did not result in any change in PKA levels. Conversely, treatment of normal human fibroblasts for 18 h with gp120 protein [10(-13) M] resulted in a significant decrease in the levels of 8-azido-[32P]cAMP binding to RI and RII and in PKA activity. The presence of peptide T blocked this effect of the gp120 protein. These results indicate that peptide T and gp120 protein may inversely alter the intracellular levels of 8-azido-[32P]cAMP binding to RI and RII, and of PKA activity in susceptible cells. These observed changes in the cyclic AMP-PKA signaling pathway, a biochemical marker for psoriasis, may offer some mechanistic insight into the noted beneficial effects of peptide T treatment, including an improvement in psoriatic lesions.

Inhibition of HIV type 1 BaL replication by MIP-1alpha, MIP-1beta, and RANTES in macrophages

The beta-chemokines RANTES, MIP-1alpha, and MIP-1beta have been shown to inhibit the infection of T cells by macrophage-tropic HIV-1 strains by blocking env-driven HIV-1 fusion through competition for the chemokine receptors or receptor downregulation. This study was aimed at testing whether beta-chemokines also inhibit the productive infection of monocyte-derived macrophages (MDMs) by a monocytotropic HIV-1 strain, by using virus yield assays. The action of the beta-chemokines MIP-1alpha, MIP-1beta, and RANTES was captured with that of the alpha-chemokine interleukin 8 (IL-8) and of interferon alpha (IFN-alpha), which is a well-known broad-range inhibitor of viral replication. While IL-8 did not inhibit HIV-1 BaL replication in MDMs, the beta-chemokines were dose-dependently inhibitory. RANTES was the most effective, reaching at 300 ng/ml a protection similar to that obtained with IFN-alpha at 1000 IU/ml, and was even more inhibitory when added to MDMs after virus attachment. In contrast to IFN-alpha, the antiviral activity of beta-chemokines was restricted to HIV, because another virus was not inhibited. As compared with untreated MDMs, full-length proviral DNA at day 1 postinfection was inhibited in MDMs treated with RANTES either before or after the absorption phase, and even more so in IFN-treated MDMs, whereas in IL-8-treated MDMs no inhibition was observed. Our results indicate that in MDMs both RANTES and IFN affect early steps of HIV-1 BaL replication, preceding the completion of viral DNA synthesis.

Genetic restriction of AIDS pathogenesis by an SDF-1 chemokine gene variant. ALIVE Study, Hemophilia Growth and Development Study (HGDS), Multicenter AIDS Cohort Study (MACS), Multicenter Hemophilia Cohort Study (MHCS), San Francisco City Cohort (SFCC)

Stromal-derived factor (SDF-1) is the principal ligand for CXCR4, a coreceptor with CD4 for T lymphocyte cell line-tropic human immunodeficiency virus-type 1 (HIV-1). A common polymorphism, SDF1-3'A, was identified in an evolutionarily conserved segment of the 3' untranslated region of the SDF-1 structural gene transcript. In the homozygous state, SDF1-3'A/3'A delays the onset of acquired immunodeficiency syndrome (AIDS), according to a genetic association analysis of 2857 patients enrolled in five AIDS cohort studies. The recessive protective effect of SDF1-3'A was increasingly pronounced in individuals infected with HIV-1 for longer periods, was twice as strong as the dominant genetic restriction of AIDS conferred by CCR5 and CCR2 chemokine receptor variants in these populations, and was complementary with these mutations in delaying the onset of AIDS.

Immunology of HIV and pregnancy. The effects of each on the other

Infection with HIV may significantly affect the human immune response. Depletion of CD4 T cells directly or indirectly results in global immune dysfunction, including both cellular and humoral components of the immune system. Ongoing viral replication leads to progressive immune destruction despite apparent clinical latency. The end result, if left untreated, is CD4 T-cell depletion, severe immune compromise, opportunistic infection, and eventual death. Pregnancy has been purported to induce an altered immune state to protect the fetus from immune rejection that may leave the mother with impaired immunity. This theoretical risk has been overemphasized, and, in fact, only limited data suggest that certain infections may have worse presentations and outcomes during pregnancy. The mother maintains immunocompetence throughout gestation and is not overwhelmed with opportunistic infection. Women infected with HIV may experience some decline in CD4 T-cell percentages and possibly in function. It is not clear whether any of the effects will significantly affect long-term outcome. Infection with HIV may predispose pregnant women to a variety of adverse pregnancy outcomes, including preterm labor, prematurity, low-birth-weight infants, postpartum endometritis, and other infectious morbidity. Larger controlled studies are necessary to determine the frequency of these adverse outcomes and whether they will predominantly affect the severely immunocompromised HIV-infected pregnant women.

Slower evolution of human immunodeficiency virus type 1 quasispecies during progression to AIDS

The evolution of human immunodeficiency virus type 1 (HIV-1) quasispecies at the envelope gene was studied from the time of infection in 11 men who experienced different rates of CD4+ cell count decline and 6 men with unknown dates of infection by using DNA heteroduplex mobility assays. Quasispecies were genetically homogeneous near the time of seroconversion. Subsequently, slower proviral genetic diversification and higher plasma viremia correlated with rapid CD4+ cell count decline. Except for the fastest progressors to AIDS, highly diverse quasispecies developed in all subjects within 3 to 4 years. High quasispecies diversity was then maintained for years until again becoming more homogeneous in a subset of late-stage AIDS patients. Individuals who maintained high CD4+ cell counts showed continuous genetic turnover of their complex proviral quasispecies, while more closely related sets of variants were found in longitudinal samples of severely immunocompromised patients. The limited number of variants that grew out in short-term PBMC cocultures were rare in the uncultured proviral quasispecies of healthy, long-term infected individuals but more common in vivo in patients with low CD4+ cell counts. The slower evolution of HIV-1 observed during rapid progression to AIDS and in advanced patients may reflect ineffective host-mediated selection pressures on replicating quasispecies.

Selective employment of chemokine receptors as human immunodeficiency virus type 1 coreceptors determined by individual amino acids within the envelope V3 loop

The chemokine receptor CCR5 acts as an essential cofactor for cell entry by macrophage-tropic human immunodeficiency virus type 1 (HIV-1) strains, whereas CXCR4 acts as an essential cofactor for T-cell-line-adapted strains. We demonstrated that the specific amino acids in the V3 loop of the HIV-1 envelope protein that determine cellular tropism also regulate chemokine coreceptor preference for cell entry by the virus. Further, a strong correlation was found between HIV-1 strains classified as syncytium inducing in standard assays and those using CXCR4 as a coreceptor. These data support the hypothesis that progressive adaptation to additional coreceptors is a key molecular basis for HIV-1 phenotypic evolution in vivo.

Contrasting genetic influence of CCR2 and CCR5 variants on HIV-1 infection and disease progression. Hemophilia Growth and Development Study (HGDS), Multicenter AIDS Cohort Study (MACS), Multicenter Hemophilia Cohort Study (MHCS), San Francisco City Cohort (SFCC), ALIVE Study

The critical role of chemokine receptors (CCR5 and CXCR4) in human immunodeficiency virus-type 1 (HIV-1) infection and pathogenesis prompted a search for polymorphisms in other chemokine receptor genes that mediate HIV-1 disease progression. A mutation (CCR2-64I) within the first transmembrane region of the CCR2 chemokine and HIV-1 receptor gene is described that occurred at an allele frequency of 10 to 15 percent among Caucasians and African Americans. Genetic association analysis of five acquired immunodeficiency syndrome (AIDS) cohorts (3003 patients) revealed that although CCR2-64I exerts no influence on the incidence of HIV-1 infection, HIV-1-infected individuals carrying the CCR2-64I allele progressed to AIDS 2 to 4 years later than individuals homozygous for the common allele. Because CCR2-64I occurs invariably on a CCR5-+-bearing chromosomal haplotype, the independent effects of CCR5-Delta32 (which also delays AIDS onset) and CCR2-64I were determined. An estimated 38 to 45 percent of AIDS patients whose disease progresses rapidly (less than 3 years until onset of AIDS symptoms after HIV-1 exposure) can be attributed to their CCR2-+/+ or CCR5-+/+ genotype, whereas the survival of 28 to 29 percent of long-term survivors, who avoid AIDS for 16 years or more, can be explained by a mutant genotype for CCR2 or CCR5.

Role of dendritic and follicular dendritic cells in HIV infection and pathogenesis

Dendritic cells (DCs) and follicular dendritic cells (FDCs) play important roles in HIV-mediated pathogenesis. Recent studies have defined new DC subsets and shown that DCs in lymphoid mucosa can both harbor virus and stimulate its spread into CD4(+) T cells. FDCs harbor unspliced HIV mRNA and immune complexed virus, but not actively infectious virus, yet these cells are a key regulated reservoir of virions.

Escape of human immunodeficiency virus from immune control

Cytotoxic T lymphocytes (CTL) play a crucial role in the attempt to control infection with human immunodeficiency virus (HIV). Variation in epitopes recognized by CTL is common and frequently offers potential escape routes for mutant virus. Proof of escape, however, requires demonstration of increased frequency of virus particles or provirus that carry the escape sequence. There are now several recorded examples of virus variants that escape from CTL and are then selected. Most dramatic are those in which the CTL response has been dominated by CTL recognizing a single epitope that has suddenly changed, resulting in escape to fixation. This has been seen both early and late in the infection, leaving no doubt that escape occurs. Such escape is likely to be favored when the antiviral CTL response is oligoclonal and focused on a small number of immunodominant epitopes. The heterogeneous CTL response seen in many HIV-infected patients may result from successive waves of virus escape followed by new CTL responses specific for subdominant epitopes. Mutant virus can escape by several different routes, including failure of the mutated peptide to bind to the presenting HLA molecule and altered interactions with T cell receptors (TCR), including antagonism.

Cytotoxic T lymphocytes and viral turnover in HIV type 1 infection

To understand the role of the immune system in limiting HIV type 1 replication, it is critical to know to what extent the rapid turnover of productively infected cells is caused by viral cytopathicity or by immune-mediated lysis. We show that uncultured peripheral blood mononuclear cells of many patients contain cytotoxic T lymphocytes (CTL) that lyse target cells-at plausible peripheral blood mononuclear cell-to-target ratios-with half-lives of less than 1 day. In 23 patients with CD4 counts ranging from 10 to 900 per microliter, the average rate of CTL-mediated lysis corresponds to a target cell half-life of 0.7 day. We develop mathematical models to calculate the turnover rate of infected cells subjected to immune-mediated lysis and viral cytopathicity and to estimate the fraction of cells that are killed by CTL as opposed to virus. The models provide new interpretations of drug treatment dynamics and explain why the observed rate of virus decline is roughly constant for different patients. We conclude that in HIV type 1 infection, CTL-mediated lysis can reduce virus load by limiting virus production, with small effects on the half-life of infected cells.

The CXC chemokine SDF-1 is the ligand for LESTR/fusin and prevents infection by T-cell-line-adapted HIV-1

A putative chemokine receptor that we previously cloned and termed LESTR has recently been shown to function as a co-receptor (termed fusin) for lymphocyte-tropic HIV-1 strains. Cells expressing CD4 became permissive to infection with T-cell-line-adapted HIV-1 strains of the syncytium-inducing phenotype after transfection with LESTR/fusin complementary DNA. We report here the indentification of a human chemokine of the CXC type, stromal cell-derived factor 1 (SDF-1), as the natural ligand for LESTR/fusin, and we propose the term CXCR-4 for this receptor, in keeping with the new chemokine-receptor nomenclature. SDF-1 activates Chinese hamster ovary (CHO) cells transfected with CXCR-4 cDNA as well as blood leukocytes and lymphocytes. In cell lines expressing CXCR-4 and CD4, and in blood lymphocytes, SDF-1 is a powerful inhibitor of infection by lymphocyte-tropic HIV-1 strains, whereas the CC chemokines RANTES, MIP-1 alpha and MIP-1 beta, which were shown previously to prevent infection with primary, monocyte-tropic viruses, are inactive. In combination with CC chemokines, which block the infection with monocyte/macrophage-tropic viruses, SDF-1 could help to decrease virus load and prevent the emergence of the syncytium-inducing viruses which are characteristic of the late stages of AIDS.

Changing the natural history of HIV disease

Our understanding of the pathogenesis of AIDS has advanced considerably since the disease was first reported 15 years ago. We now know that the primary damage inflicted by HIV-1 is mainly brought about by active virus replication. With the advent of sensitive tools for monitoring HIV replication in vivo, an individual's risk of disease progression can be assessed early in the course of the infection and the efficacy of antiviral therapies can now be determined accurately and expeditiously. When used appropriately, potent combinations of antiviral drugs seem to be able to circumvent the inherent tendency of HIV-1 to generate drug-resistant viruses, the main reason for failure of all antiviral therapies, and are significantly more effective than earlier approaches. For the first time, rational approaches to contain and perhaps eliminate HIV-1 infection can be pursued.