Polymorphic human gene(s) determines differential susceptibility of CD4 lymphocytes to infection by certain HIV-1 isolates

Resistance to human immunodeficiency virus infection: a rare but neglected state

The natural history of human immunodeficiency virus (HIV) infection is well understood. In most individuals sexually exposed to HIV, the risk of becoming infected depends on the viral load and on sexual practices and gender. However, a low percentage of individuals who practice frequent unprotected sexual intercourse with HIV-infected partners remain uninfected. Although the systematic study of these individuals has made it possible to identify HIV resistance factors including protective genetic patterns, such epidemiological situations remain paradoxical and not fully understood. In vitro experiments have demonstrated that peripheral blood mononuclear cells (PBMCs) from HIV-free, unexposed blood donors are not equally susceptible to HIV infection; in addition, PBMCs from highly exposed seronegative individuals are generally resistant to infection by primary HIV clinical isolates. We review the literature on permissiveness of PBMCs from healthy blood donors and uninfected hyperexposed individuals to sustained infection and replication of HIV-1 in vitro. In addition, we focus on recent evidence indicating that the gut microbiota may either contribute to natural resistance to or delay replication of HIV infected individuals.

Improved assays to measure and characterize the inducible HIV reservoir

BACKGROUND

Improved assays are critical to better characterize the HIV reservoir and to reliably evaluate candidate intervention strategies. Here we describe different methods to quantify the HIV reservoir.

METHODS

We developed an optimized quantitative viral outgrowth assay (QVOA) to quantify the frequency of cells harboring replication-competent HIV, which is simpler and more sensitive than classical QVOAs. We also developed new inducible RNA assays that concomitantly measure the frequency of cell-associated [ca-] (gag and tat-rev) and cell-free [cf-] HIV RNA after three days of anti-CD3/CD28 stimulation.

FINDINGS

The median frequency of the infected cells measured after induction was 94 IQR[60-132], 16 IQR [9-29] and 2.9 IQR[1.9-6.8] cells/10⁶ CD4⁺ T-cells for ca-RNA gag and tat-rev, and cf-RNA, respectively. There are a large proportion of transcription-competent proviruses (ca-RNA) that seemed unable to form complete virions (cf-RNA), suggesting post-transcriptional blocks or defective proviruses. Importantly, the median frequency of infected CD4⁺ T-cells as estimated by 3-day inducible cf-RNA assay was not statistically different from the frequency measured by the QVOA (median of 3.3 [1.9-6.2] IUPM). The latently infected cells detected by the inducible cf-RNA assay correlated highly with the QVOA ( r= 0.67, p < .001), and both assays were equivalent in 60% of the samples tested, suggesting that most cells induced to produce virions are generating replication-competent virus.

INTERPRETATION

These inducible RNA assays provide more sensitivity and a greater dynamic range for the monitoring of reduction of the reservoir by eradication strategies. Such assays may serve as robust and useful tools for clinical investigations of the HIV reservoir.

Development of a contemporary globally diverse HIV viral panel by the EQAPOL program

The significant diversity among HIV-1 variants poses serious challenges for vaccine development and for developing sensitive assays for screening, surveillance, diagnosis, and clinical management. Recognizing a need to develop a panel of HIV representing the current genetic and geographic diversity NIH/NIAID contracted the External Quality Assurance Program Oversight Laboratory (EQAPOL) to isolate, characterize and establish panels of HIV-1 strains representing global diverse subtypes and circulating recombinant forms (CRFs), and to make them available to the research community. HIV-positive plasma specimens and previously established isolates were collected through a variety of collaborations with a preference for samples from acutely/recently infected persons. Source specimens were cultured to high-titer/high-volume using well-characterized cryopreserved PBMCs from National y donors. Panel samples were stored as neat culture supernatant or diluted into defibrinated plasma. Characterization for the final expanded virus stocks included viral load, p24 antigen, infectivity (TCID), sterility, coreceptor usage, and near full-length genome sequencing. Viruses are made available to approved, interested laboratories using an online ordering application. The current EQAPOL Viral Diversity panel includes 100 viral specimens representing 6 subtypes (A, B, C, D, F, and G), 2 sub-subtypes (F1 and F2), 7 CRFs (01, 02, 04, 14, 22, 24, and 47), 19 URFs and 3 group O viruses from 22 countries. The EQAPOL Viral Diversity panel is an invaluable collection of well-characterized reagents that are available to the scientific community, including researchers, epidemiologists, and commercial manufacturers of diagnostics and pharmaceuticals to support HIV research, as well as diagnostic and vaccine development.

Host polymorphism in steps of the HIV-1 lifecycle after entry and other genetic variants influencing HIV-1 pathogenesis

PURPOSE OF REVIEW

Dominant host factors modifying the susceptibility to HIV-1 include diversity in the major histocompatibility complex class I, and alleles of chemokine and chemokine receptor genes. Additional host factors, particularly those determining cell permissiveness to viral replication, are expected to play a significant role in HIV-1 pathogenesis.

RECENT FINDINGS

A growing number of publications (n = 32) propose new variants (n = 27) modifying HIV-1 susceptibility in genes (n = 17) needed for the viral lifecycle, in antiviral innate defense, and in a number of soluble and membrane proteins.

SUMMARY

Although there are multiple publications describing putative associations of host genetic variants and susceptibility to HIV-1, most reports are yet to be confirmed by subsequent publications, or have led to conflicting data among laboratories.

Generation of transmitted/founder HIV-1 infectious molecular clones and characterization of their replication capacity in CD4 T lymphocytes and monocyte-derived macrophages

Genome sequences of transmitted/founder (T/F) HIV-1 have been inferred by analyzing single genome amplicons of acute infection plasma viral RNA in the context of a mathematical model of random virus evolution; however, few of these T/F sequences have been molecularly cloned and biologically characterized. Here, we describe the derivation and biological analysis of ten infectious molecular clones, each representing a T/F genome responsible for productive HIV-1 clade B clinical infection. Each of the T/F viruses primarily utilized the CCR5 coreceptor for entry and replicated efficiently in primary human CD4(+) T lymphocytes. This result supports the conclusion that single genome amplification-derived sequences from acute infection allow for the inference of T/F viral genomes that are consistently replication competent. Studies with monocyte-derived macrophages (MDM) demonstrated various levels of replication among the T/F viruses. Although all T/F viruses replicated in MDM, the overall replication efficiency was significantly lower compared to prototypic "highly macrophage-tropic" virus strains. This phenotype was transferable by expressing the env genes in an isogenic proviral DNA backbone, indicating that T/F virus macrophage tropism mapped to Env. Furthermore, significantly higher concentrations of soluble CD4 were required to inhibit T/F virus infection compared to prototypic macrophage-tropic virus strains. Our findings suggest that the acquisition of clinical HIV-1 subtype B infection occurs by mucosal exposure to virus that is not highly macrophage tropic and that the generation and initial biological characterization of 10 clade B T/F infectious molecular clones provides new opportunities to probe virus-host interactions involved in HIV-1 transmission.

Longitudinal study of primary HIV-1 isolates in drug-naïve individuals reveals the emergence of variants sensitive to anti-HIV-1 monoclonal antibodies

To study how virus evolution affects neutralization sensitivity and to determine changes that occur in and around epitopes, we tested the ability of 13 anti-HIV-1 gp120 (anti-V2, anti-V3, anti-CD4bd and anti-carbohydrate) human monoclonal antibodies (mAbs) to neutralize sequential viruses obtained from five HIV-1 chronically infected drug naïve individuals. Overall, primary viruses collected from patients at first visit were resistant to neutralization by all anti-HIV-1 mAbs with the exception of one virus sensitive to IgG1b12. Four of the five patients' viruses evolved increased sensitivity to neutralization by anti-V3 mAbs. Virus collected from a patient obtained 31 months later, evolved increased sensitivity to anti-V2, anti-V3, and anti-CD4bd mAbs. Furthermore, the anti-V2 and anti-CD4bd mAbs also exhibited increased neutralization capacities against virus collected from a patient 29 months later. Of the seven anti-V3 mAbs, five showed increased potency to neutralize the evolved virus from a patient collected after 11 months, and three exhibited increased potency against viruses from two patients collected 29 and 36 months later. Anti-V3 mAbs exhibited the most breadth and potency in neutralizing the evolving viruses. Sequence analysis of the envelope regions revealed amino acid conservation within the V3 loop, while most of the changes identified occurred outside the core epitopes and in particular within the C3 region; these may account for increased neutralization sensitivity. These studies demonstrate that in vivo, HIV-1 can evolve increased neutralization sensitivity to mAbs and that the spectrum of neutralization capacities by mAbs can be broader when studied in longitudinal analysis.

Impaired viral entry cannot explain reduced CD4+ T cell susceptibility to HIV type 1 in certain highly exposed individuals

Rare individuals report repeated unprotected HIV-1 sexual exposures, yet remain seronegative for years. We investigated the possibility that reduced in vitro CD4(+) T cell susceptibility to HIV-1 infection protects such highly exposed seronegative (ES) individuals. Susceptibility to three R5-tropic HIV-1 isolates, regardless of inoculating dose, was remarkably similar between 81 ES and 33 low-risk controls. In 94% (99/105) of donors, we observed a 1.36 log-unit range in HIV-1(JR-CSF) production, with similar results for HIV-1(1192). The median frequency of intracellular Gag(+) T cells after single-round infection was similar in ES (5.2%) and controls (7.2%), p = 0.456. However, in repeated testing, CD4(+) T cells from two controls (6.1%) and four ES (4.9%) exhibited a 10- to 2500-fold reduction in HIV-1 production and required 5- to 12-fold greater HIV-1(1192) and HIV-1(JR-CSF) inocula to establish infection (TCID(50)). Reduced viral entry cannot explain the low producer phenotype; no differences in CCR5 receptor density or beta-chemokine production were observed. In conclusion, we have identified a remarkably narrow range of HIV-1 susceptibility in seronegative donors regardless of risk activity, which can be applied as a benchmark to assess vaccine-induced antiviral effector activities. However, CD4(+) T cells from a subset of individuals demonstrated reduced HIV-1 susceptibility unexplained by impaired entry, lending support to the possibility that cellular restriction of HIV-1 may account for continued seronegativity in some of those having repeated sexual exposure. Identifying the host-virus interactions responsible for diminished in vitro susceptibility may contribute to the development of novel therapeutic strategies.

Donor variability in HIV binding to peripheral blood mononuclear cells

BACKGROUND

HIV infection of cells varies greatly between individuals, with multiple steps in the replication cycle potentially contributing to the variability. Although entry and post-entry variability of HIV infection levels in cells has been demonstrated, variability in HIV binding has not been examined. In this study, we examined variability of HIV binding to peripheral blood mononuclear cells (PBMC) from different donors.

RESULTS

HIV binding to PBMC varied up to 3.9-fold between individuals and was independent of CD4. Replication of HIV in donor PBMC required CD4 and paralleled virus binding trends of donor PBMC. To assess the stability of virus binding phenotypes over time, HIV was bound to donors with low- and high-binding phenotypes. The binding phenotypes were maintained when tested weekly over a 4-week period for 3 of 4 donors, while one high-binding donor decreased to lower binding on the 4th week. The low- and high-binding phenotypes were also preserved across different HIV strains. Experiments performed to determine if there was an association between HIV binding levels and specific cell subset levels within PBMC showed no correlation, suggesting that HIV binds to multiple cell subsets.

CONCLUSION

These results show that differences exist in HIV binding to donor PBMC. Our data also show that HIV binding to donor PBMC is CD4-independent and can change over time, suggesting that virus binding variability is due to differences in the expression of changeable cell-surface host factors. Taken together, this study highlights the impact of cell-surface factors in HIV binding to, and infection of, PBMC which likely represents an important step in HIV infection in vivo.

Primary isolates of human immunodeficiency virus type 1 are usually dominated by the major variants found in blood

The isolation of primary strains of human immunodeficiency virus (HIV) is an invaluable tool for assessing properties of viruses replicating in HIV-infected subjects. A common method for obtaining a primary isolate is coculture of peripheral blood mononuclear cells (PBMCs) from HIV-infected subjects with PBMCs from uninfected donors. However, such in vitro expansion may disturb the composition (identities and relative proportions of constituting viral species) of the original viral population. We developed a GeneScan assay to monitor HIV populations by detecting variants that differ in the length of the V1/V2 coding region of the envelope gene. This assay was used to compare proviral DNAs from the PBMCs of eight subjects to the corresponding primary isolates. Major variants found in uncultured PBMCs usually persisted during culturing, while the minor variants frequently disappeared, resulting in a reduction in viral diversity. The outgrowth of the initial (2 to 4 days) viral population appeared to be determined by random events. However, subsequent changes in the population were deterministic, and as a result, the compositions of primary isolates from parallel cultures were often very similar. For two of three subjects studied, the source of HIV-negative PBMCs had little effect on the composition of primary isolates, while for the third subject donor-dependent effects were observed. Overall, our results show that most primary isolates accurately represent the major viruses found in a subject's blood and that rapid population-based genotyping methods are useful for detecting isolates with perturbed viral populations.

Role of common human TRIM5alpha variants in HIV-1 disease progression

Background

The retroviral restriction factor tripartite motif protein (TRIM)5α, is characterized by marked amino acid diversity among primates, including specific clusters of residues under positive selection. The identification of multiple non-synonymous changes in humans suggests that TRIM5α variants might be relevant to retroviral pathogenesis. Previous studies have shown that such variants are unlikely to modify susceptibility to HIV-1 infection, or the course of early infection. However, the longterm effect of carrying Trim5α variants on disease progression in individuals infected with HIV-1 has not previously been investigated.

Methods

In a cohort of 979 untreated individuals infected with HIV-1 with median follow up 3.2 years and 9,828 CD4 T cell measurements, we analysed common amino acid variations: H43Y, V112F, R136Q, G249D, and H419Y. The rate of CD4 T cell decline before treatment was used as the phenotype. In addition, we extended previous work on the in vitro susceptibility of purified donor CD4 T cells (n = 125) to HIV-1 infection, and on the susceptibility of HeLa cells that were stably transduced with the different TRIM5 variants. Haplotypes were analysed according to the most parsimonious evolutionary structure, where two main human TRIM5α groups can be defined according to the residue at amino acid 136. Humans present both Q136 and R136 at similar frequency, and additional TRIM5α amino acid variants are almost exclusively derived from R136-carrying haplotypes.

Results

We observed modest differences in disease progression for evolutionary branches carrying R136-derived haplotypes, and with the non-synonymous polymorphisms G249D and H419Y. In vitro analysis of susceptibility of donor CD4 T cells, and of the various transduced HeLa cell lines supported the absence of significant differential restriction of HIV-1 infection by the various huTRIM5α alleles.

Conclusion

Common human variants of TRIM5α have no effect or modest effect on HIV-1 disease progression. These variants occur at sites conserved throughout evolution, and are remote from clusters of positive selection in the primate lineage. The evolutionary value of the substitutions remains unclear.

Host genetics of HIV-1 susceptibility

Susceptibility to HIV-1 and the rate of disease progression reflect the influence of the genetic diversity of the virus as well as the variation in host factors. The virus will co-evolve with the host, escaping and adapting to host-determined influences. Dominant host factors currently identified include diversity in the major histocompatibility complex class I, and alleles of chemokine, chemokine receptor and cytokine genes. Recent work proposes new variants in life cycle genes and in antiviral innate defense, which modify HIV-1 susceptibility. Comparative genomics generates information on host cell barriers that may explain the current distribution of these viruses among human and nonhuman primates. A greater understanding of the genetic basis of human susceptibility to HIV-1 contributes to an understanding of the pathogenesis of the disease, helps identify new targets for prophylaxis and vaccine development and will lead to predictive tools to identify those at risk of rapid disease progression.

Use of a combined ex vivo/in vivo population approach for screening of human genes involved in the human immunodeficiency virus type 1 life cycle for variants influencing disease progression

Humans differ substantially with respect to susceptibility to human immunodeficiency virus type 1 (HIV-1). We evaluated variants of nine host genes participating in the viral life cycle for their role in modulating HIV-1 infection. Alleles were assessed ex vivo for their impact on viral replication in purified CD4 T cells from healthy blood donors (n = 128). Thereafter, candidate alleles were assessed in vivo in a cohort of HIV-1-infected individuals (n = 851) not receiving potent antiretroviral therapy. As a benchmark test, we tested 12 previously reported host genetic variants influencing HIV-1 infection as well as single nucleotide polymorphisms in the nine candidate genes. This led to the proposition of three alleles of PML, TSG101, and PPIA as potentially associated with differences in progression of HIV-1 disease. In a model considering the combined effects of new and previously reported gene variants, we estimated that their effect might be responsible for lengthening or shortening by up to 2.8 years the period from 500 CD4 T cells/mul to <200 CD4 T cells/mul.

Entry and transcription as key determinants of differences in CD4 T-cell permissiveness to human immunodeficiency virus type 1 infection

Isolated primary human cells from different donors vary in their permissiveness-the ability of cells to be infected and sustain the replication of human immunodeficiency virus type 1 (HIV-1). We used replicating HIV-1 and single-cycle lentivirus vectors in a population approach to identify polymorphic steps during viral replication. We found that phytohemagglutinin-stimulated CD4(+) CD45RO(+) CD57(-) T cells from healthy blood donors (n = 128) exhibited a 5.2-log-unit range in virus production. For 20 selected donors representing the spectrum of CD4 T-cell permissiveness, we could attribute up to 42% of the total variance in virus production to entry factors and 48% to postentry steps. Efficacy at key intracellular steps of the replicative cycle (reverse transcription, integration, transcription and splicing, translation, and budding and release) varied from 0.71 to 1.45 log units among donors. However, interindividual differences in transcription efficiency alone accounted for 64 to 83% of the total variance in virus production that was attributable to postentry factors. While vesicular stomatitis virus G protein-mediated fusion was more efficacious than CCR5/CD4 entry, the latter resulted in greater transcriptional activity per proviral copy. The phenotype of provirus transcription was stable over time, indicating that it represents a genetic trait.

Restriction of multiple divergent retroviruses by Lv1 and Ref1

The mouse gene Fv1 encodes a saturable restriction factor that selectively blocks infection by N-tropic or B-tropic murine leukemia virus (MLV) strains. Despite the absence of an Fv1 gene, a similar activity is present in humans that blocks N-MLV infection (Ref1). Moreover, some non-human primate cell lines express a potentially related inhibitor of HIV-1 and/or SIVmac infection (Lv1). Here, we examine the spectrum of retrovirus-restricting activities expressed by human and African green monkey cell lines. Human cells restrict N-MLV and equine infectious anemia virus (EIAV), but not HIV-1, HIV-2, SIVmac or SIVagm, whilst AGM cells restrict N-MLV, EIAV, HIV-1, HIV-2 and SIVmac. Remarkably, in each example examined, restriction of infection by a given retrovirus can be abrogated at least partially by saturation with another retrovirus, provided that it is also restricted but regardless of whether it is closely related. These data suggest that restriction factors in human and non-human primate cells are able to recognize and block infection by multiple, widely divergent retroviruses and that the factors themselves may be related.

Cellular inhibitors with Fv1-like activity restrict human and simian immunodeficiency virus tropism

Many nonhuman primate cells are unable to support the replication of HIV-1, whereas others are nonpermissive for infection by simian immunodeficiency virus from macaques (SIVmac). Here, we show that restricted HIV-1 and SIVmac infection of primate cell lines shares some salient features with Fv1 and Ref1-mediated restriction of murine retrovirus infection. In particular, the nonpermissive phenotype is most evident at low multiplicities of infection, results in reduced accumulation of reverse transcription products, and is dominant in heterokaryons generated by fusion of permissive and nonpermissive target cells. Moreover, in nonpermissive primate cells, HIV-1 and SIVmac infection is cooperative, and enveloped HIV-1 virus-like particles, minimally containing Gag and protease, abrogate restriction. In African green monkey cells, HIV-1 virus-like particles ablate restrictions to HIV-1 and SIVmac, suggesting that both are restricted by the same factor. Finally, a virus that contains an HIV-1 capsid-p2 domain in an SIVmac background exhibits a tropism for primate cells that is HIV-1-like rather than SIVmac-like. These data indicate the existence of one or more saturable inhibitors that are polymorphic in primates and prevent HIV and SIV infection by targeting the capsid of the incoming lentivirus particle.

Herpesvirus saimiri-immortalized human lymphocytes: novel hosts for analyzing HIV type 1 in vitro neutralization

Herpesvirus saimiri-immortalized CD4(+) T lymphocytes (HVS T cells) are activated memory cells that support efficient replication of primary R5 strains of HIV-1, which predominate in virus transmission. Being continuous, they are phenotypically more stable and technically less demanding than peripheral blood mononuclear cells (PBMCs). Here we present the first report using HVS T cells to assay HIV-1 neutralization in vitro. Neutralization sensitivities of paired viruses isolated from individuals in both HVS T cells (CN-2 cells) and PBMCs were similar, with homologous and heterologous plasma/sera in both CN-2- and PBMC-based assays. Analysis of V3 loop and CD4-binding site (CD4-BS) sequences showed that changes present in CN-2 isolates were neither more numerous nor more significant than those selected in their PBMC counterparts. Neutralization profiles of CN-2/PBMC virus pairs were similar again when V3- and CD4-binding site (BS)-specific monoclonal antibodies, whose mapped epitopes were conserved or of similar sequence in the virus pairs, were tested. Unlike other T cell line isolates, CN-2 isolates were not more sensitive to neutralization than their PBMC counterparts. We also show that HVS T cells do not appear to exert significant biological selection pressures on primary isolates. Paired viruses have a similar phenotype with respect to syncytium formation, cell tropism, and coreceptor usage. Thus CN-2 cells are suitable hosts for assaying neutralization and could be useful in standardizing neutralization assays performed in different laboratories.

HLA and in vitro susceptibility to HIV infection

Since the beginning of the epidemic of acquired immunodeficiency syndrome (AIDS), evidence has accumulated that genetic factors are involved in the pathogenesis of the disease. Among the candidate molecules suspected to control susceptibility to human immunodeficiency virus (HIV) infection and fast or slow progression of AIDS are the human leukocyte antigens (HLA). Investigating HLA-HIV correlation was mainly performed by investigating cohorts of patients with HIV/AIDS for a period of time and then statistically correlating certain features of AIDS with particular HLA alleles. This type of in vivo investigations resulted in the generation of an immense literature on the subject with so many HLA alleles being found to correlate with certain features of AIDS. Because of the complexity of AIDS pathogenesis and the involvement of many factors in the disease process, the different investigators failed to agree on the involvement of certain HLA molecules in AIDS pathogenesis. Some reports deny, or fail to confirm the existence of association between HLA and HIV progression to AIDS. This is probably due to the different ethnic backgrounds of the populations studied, the complexity of the HLA system, and to the ways these studies were conducted. This article briefly addresses our current knowledge on the HLA-HIV correlation in vivo and discusses alternative in vitro studies.

Contribution of immune activation to the pathogenesis and transmission of human immunodeficiency virus type 1 infection

The life cycle of human immunodeficiency virus type 1 (HIV-1) is intricately related to the activation state of the host cells supporting viral replication. Although cellular activation is essential to mount an effective host immune response to invading pathogens, paradoxically the marked systemic immune activation that accompanies HIV-1 infection in vivo may play an important role in sustaining phenomenal rates of HIV-1 replication in infected persons. Moreover, by inducing CD4+ cell loss by apoptosis, immune activation may further be central to the increased rate of CD4+ cell turnover and eventual development of CD4+ lymphocytopenia. In addition to HIV-1-induced immune activation, exogenous immune stimuli such as opportunistic infections may further impact the rate of HIV-1 replication systemically or at localized anatomical sites. Such stimuli may also lead to genotypic and phenotypic changes in the virus pool. Together, these various immunological effects on the biology of HIV-1 may potentially enhance disease progression in HIV-infected persons and may ultimately outweigh the beneficial aspects of antiviral immune responses. This may be particularly important for those living in developing countries, where there is little or no access to antiretroviral drugs and where frequent exposure to pathogenic organisms sustains a chronically heightened state of immune activation. Moreover, immune activation associated with sexually transmitted diseases, chorioamnionitis, and mastitis may have important local effects on HIV-1 replication that may increase the risk of sexual or mother-to-child transmission of HIV-1. The aim of this paper is to provide a broad review of the interrelationship between immune activation and the immunopathogenesis, transmission, progression, and treatment of HIV-1 infection in vivo.

Analysis of cellular factors influencing the replication of human immunodeficiency virus type I in human macrophages derived from blood of different healthy donors

We analyzed parameters influencing HIV-1 infectibility of cells of the monocyte/macrophage lineage (MO/MAC) isolated from different healthy donors. The proportion of in vitro-infected cells and replication kinetics in different donor MAC ranged from 0.03 to 99% p24 antigen-positive MAC and from undetectable RT activity up to 5 x 10(6) cpm/ml/90 min, respectively. As a quantitative measurement for HIV-1 susceptibility of donor MO/MAC, we determined TCID(50) values of defined virus stocks which varied up to 3000-fold depending on the donor MAC used for titration. As host factors which may influence the viral infection we determined the expression of virus receptors CD4, CCR5, CXCR4, and CCR3 as well as the secretion of the natural ligands of CCR5, which altogether showed no correlation with HIV-1 infectibility of the cells. Moreover, other MO-derived secretory factors which might affect viral infection of these cells could be excluded. Furthermore, expression of maturation-related antigens CD14, CD16, HLA-DR, and MAX.1/CPM was determined. Analysis of the reverse transcription process revealed that restricted HIV-1 infection was reflected by highly reduced or even undetectable full-length HIV-1 DNA formation, although early and intermediate transcripts appeared, suggesting that viral replication is blocked after entry at the level of early reverse transcription.

A conserved mechanism of retrovirus restriction in mammals

The murine Fv1 gene restricts infection by N- or B-tropic murine leukemia viruses at a postentry, preintegration stage. The Fv1-sensitive viruses previously used for the study of Fv1 encode an ecotropic envelope gene and thus only infect rodent cells. Consequently, the study of Fv1 restriction has been carried out solely in mice and murine cell lines. By infection with retroviral vectors containing N- or B-tropic core and pantropic vesicular stomatitis virus-G envelope protein, we now demonstrate that cell lines derived from various mammalian species, including humans, have an Fv1-like retrovirus restriction function, preventing N-tropic vector infection. Like Fv1, restriction is directed at amino acid 110 of the viral capsid protein. In contrast to Fv1, the novel restriction is characterized by the absence of reverse-transcribed viral DNA. We speculate that these activities have been selected for by retroviral epidemics in the distant past.

The replicative capacity of rhesus macaque peripheral blood mononuclear cells for simian immunodeficiency virus in vitro is predictive of the rate of progression to AIDS in vivo

Survival of rhesus macaques (Macaca mulatta) experimentally infected with simian immunodeficiency virus (SIV) varies significantly from animal to animal. Some animals die within 2 months while others survive for more than 5 years, even when identical inocula are used. This diversity in survival creates a significant problem in the design of therapeutic and vaccine trials using the SIV-macaque model because the use of small numbers of animals may provide results that are misleading. Identifying an in vitro assay that could determine the survival of monkeys prior to infection would prove extremely useful for stratifying experimental groups. Analysis of the survival of a cohort of 59 control animals obtained from over a decade of vaccine and therapeutic trials has demonstrated that the ability of peripheral blood mononuclear cells (PBMC) from a naïve animal to produce virus in vitro was highly predictive of disease progression in vivo following experimental inoculation. Animals classified in vitro as high producers of virus progressed to disease significantly more rapidly than animals classified as either low (P=0.002) or intermediate (P=0.013) producers of virus. The hierarchy of high and low virus production was maintained in purified CD4(+) T cell cultures, indicating that this phenotype is an intrinsic property of the CD4(+) T cell itself. These findings should significantly aid in the design of vaccine and therapeutic trials using the SIV-macaque model. Furthermore, since these studies suggest that the rate of virus replication is controlled by innate characteristics of the individual, they provide new insight into the pathogenesis of AIDS.

HIV heterosexual transmission: a hypothesis about an additional potential determinant

Transmission rates of human immunodeficiency virus (HIV) during heterosexual intercourse vary dramatically around the world. In Asia and South America, they are extraordinarily high, whereas in the United States and Europe, rates are much lower even after a large number of unprotected contacts. The transmission rates in Africa also probably are high, but the available studies unfortunately are weak. In Thailand, female-to-male transmission rates per contact were estimated at.056 (l in 18) compared to.0002 to.0015 (1/5000-1. 5/1000) for male-to-female transmission in the United States and Europe. Male-to-female transmission in Thailand appears to show, as expected, even greater transmission likelihood compared to female-to-male rates. In general, in the United States and Europe, transmission rates within heterosexual couples range from less than 10% to 22%, whereas in Thailand and Brazil, the rates exceed 40%. The much lower transmission rate per contact in the United States and Europe is based on an assumption that HIV transmitters are a homogeneous group. Wiley and colleagues argue that transmitters are likely to be a heterogeneous group with a large percentage of very low frequency transmitters and a small percentage of high frequency transmitters. That hypothesis is given some support by a cluster of cases in rural New York State in which one man appeared to infect 31% of his many contacts.

Definition of the stage of host cell genetic restriction of replication of human immunodeficiency virus type 1 in monocytes and monocyte-derived macrophages by using twins

Using identical (ID) twins, we have previously demonstrated that host cell genes exert a significant impact on productive human immunodeficiency virus (HIV) infection of monocytes and macrophages (J. Chang et al., J. Virol. 70:7792-7803, 1996). Therefore, the stage in the replication cycle at which these host genetic influences act was investigated in a study using 8 pairs of ID twins and 10 pairs of sex- and age-matched unrelated donors (URDs). In the first phase of the study, blood monocytes and monocyte-derived macrophages (MDM) of ID twins and URDs were infected with 15 HIV type 1 strains. Four well-characterized primary isolates and HIV-BaL were then examined in more detail. The host cell genetic effect in MDM was exerted predominantly prior to complete reverse transcription, as the HIV DNA level and p24 antigen levels were concordant (r = 0.91, P = 0.0001) and similar between the pairs of ID twin pairs (r = 0.96, P = 0.0001) but discordant between URD pairs (r = 0.11, P = 0.3) in both phases of the study. To further examine genetic influence on viral entry, we examined the proportion of CCR5 membrane expression on MDM. As expected, there was wide variability in proportion of MDM expressing CCR5 among URDs (r = 0. 58, P = 0.2); however, this variability was significantly reduced between ID twin pairs (r = 0.81, P = 0.01). Differences in viral entry did not necessarily correlate with CCR5 expression, and only very low levels of CCR5 expression restricted HIV entry and production. In summary, the host cell genetic effect on HIV replication in macrophages appears to be exerted predominantly pre-reverse transcription. Although CCR5 was necessary for infection, other unidentified host genes are likely to limit productive infection.

Enhanced replication of M-tropic HIV-1 strains in Herpesvirus saimiri immortalised T-cells which express CCR5

A better characterisation of mononuclear cell-tropic (M-tropic) HIV-1 is central to disease control as these viruses predominate in disease transmission. M-tropic viruses do not replicate in conventional T-cell lines, and virus titres obtained in peripheral blood mononuclear cells (PBMC) are low. Human T-lymphocytes which have been immortalised by Herpesvirus saimiri strain C488 (HVS T-cells) are highly permissive to the replication of T-cell tropic strains of HIV. This study aimed to determine if HVS T-cells support replication of M-tropic HIV isolates that have not been adapted to conventional T-cell lines. A panel of PBMC low passage/primary field isolates and their molecular clones was used. Results show that infection in HVS T-cells was longer lived than in PBMC. In terms of peak virus titre and duration of productive infection, the two HVS T-cell lines studied were superior to PBMC, and one supported enhanced replication of all M-tropic isolates. This is important for generating M-tropic virus pools of sufficient titre for further biological studies such as virus neutralisation, co receptor usage and testing of antivirals. Phenotypic analysis showed that HVS T-cells are CD4+-activated memory cells expressing both CXCR-4 and CCR5 co receptors. Thus, HVS immortalisation appears to select for the T-cell subset targeted by HIV-1 in vivo.

Host genes and infectious diseases. HIV, other pathogens, and a public health perspective

INTRODUCTION

The global impact of infectious diseases is tremendous. In 1996, the 17 million deaths from infectious diseases accounted for one third of all deaths worldwide, while the acute and chronic morbidity from infectious diseases adds an additional great burden on global health. Multiple factors, host and nonhost, influence the susceptibility of individuals and populations to infectious diseases, as well as the severity of the illness once infected.

METHODS

We review the influence of host genes on the susceptibility to and severity of viral, bacterial, parasitic and fungal infectious diseases, on vaccine responsiveness and on treatments for infections. HIV/AIDS is discussed in detail because it is an example of an infectious disease influenced by multiple host genes and because of its impact. Although the HIV/AIDS pandemic dates only since the late 1970s, it has claimed the lives of 11 million people worldwide and, today, more than 30 million people are estimated to be HIV infected.

CONCLUSION

Our greater understanding of the genetic factors that influence morbidity and mortality of infectious disease leads to new avenues of prevention and treatment that can improve the health of individuals and populations.

A Novel Mechanism of CD4 Lymphocyte Depletion Involves Effects of HIV on Resting Lymphocytes: Induction of Lymph Node Homing and Apoptosis Upon Secondary Signaling Through Homing Receptors

Recently, we reported that abortive HIV infection of resting human T lymphocytes up-regulated expression of CD62L, the receptor for homing to lymph nodes (LNs), and enhanced homing of these cells from the blood into the LNs (Wang et al., 1997, Virology 228:141). This suggested that HIV-induced homing of resting lymphocytes (which comprise &gt;98% of all lymphocytes) may be a major mechanism for the reduction of CD4+ lymphocytes in the blood of infected individuals. This mechanism also could be partially responsible for the lymphadenopathy that often develops at the same time that CD4+ lymphocytes are disappearing from the blood. In this study, we show that secondary signaling through the homing receptors (CD62L, CD44, CD11a) of abortively infected resting CD4+ T lymphocytes induced apoptosis. These signals would occur as the cells home into the LNs. Apoptosis did not occur after secondary signaling through some other receptors (CD26, CD4, CD45, and HLA class I) or in HIV-exposed resting CD8+ lymphocytes signaled through the homing receptors. These findings indicate that HIV-induced homing of resting CD4+ lymphocytes to LNs results in death of many of these cells. This was confirmed in the LNs of SCID mice that were i.v. injected with HIV-exposed resting human lymphocytes. Thus, these effects of HIV upon binding to resting CD4+ T lymphocytes, which are not permissive for HIV replication, may significantly contribute to their depletion in vivo. These findings also offer an explanation for the bystander effect observed in the LNs of AIDS patients, whereby cells not making virus are dying.

Differences in HIV replication in CD4+ lymphocytes are not related to beta-chemokine production

CD4+ T lymphocytes from different donors vary in their ability to replicate different isolates of HIV. Beta-chemokines have been shown to reduce the rate of HIV replication in cultured cells. We now demonstrate, using CD4+ cells from 19 different donors, that the variations in viral replication observed in CD4+ lymphocytes are not due to endogenous production of beta-chemokines by the cells. Instead of finding a correlation of high-level beta-chemokine production with low-level replication of virus, we found either no consistent relationship between these two parameters or a correlation between high-level beta-chemokine production and high-level virus replication. This observation was made with both chemokine-sensitive and chemokine-resistant HIV isolates. Thus, other mechanisms appear to be involved in the variability in HIV replication in cultured CD4+ cells.

Apoptotic killing of CD4+ T lymphocytes in HIV-1-infected PHA-stimulated PBL cultures is mediated by CD8+ LAK cells

In vitro infection of PHA-stimulated, normal CD4+ human peripheral blood T lymphocytes (PBLs) with several HIV-1 isolates did not result in cytopathology, despite high levels of virus replication and the fact that some of these isolates were cytopathic in certain cell lines. In contrast, infection of unfractionated PBLs (containing CD8+ as well as CD4+ lymphocytes) with these isolates always resulted in death of the infected CD4+ T lymphocytes. It has been well documented that PHA stimulation and culture of PBLs in medium containing IL-2 generates lymphokine-activated killer (LAK) cell activity which can destroy many transformed cells and virus-infected normal cells. When CD8+ T lymphocytes from PHA-stimulated PBLs were added to HIV-1-infected purified CD4+ T lymphocytes, significant lysis occurred. This cytotoxicity was not MHC class I-restricted, and depletion of CD8+ T lymphocytes from unfractionated PBL cultures shortly after HIV infection largely abolished the killing of the infected CD4+ T lymphocytes. These results demonstrated that CD8+ LAK cells were killing the CD4+ T lymphocytes in unfractionated PBL cultures infected with these noncytopathic HIV-1 strains. Care is thus warranted when studying HIV cytopathology in unfractionated PBL cultures. Morphological and DNA gel electrophoretic analyses of HIV-infected CD4+ T lymphocytes being killed by CD8+ LAK cells demonstrated that apoptosis was the predominant mechanism of LAK cell-mediated killing. In contrast, necrosis was the major mechanism involved in killing of purified CD4+ T lymphocytes by HIV-1 strains which were directly cytopathic. These findings may explain some of the discrepancies in the literature concerning reports of either apoptotic or necrotic killing of cells by HIV in vitro. Moreover, these data strongly suggest that direct killing by replicating HIV-1 in vivo should reveal necrotic cells and immune effector cell killing should reveal apoptotic cells. Since the latter are much more frequently observed in vivo, perhaps immune effector-mediated depletion of CD4+ T lymphocytes is more important as a pathogenic mechanism.

The extent of early viral replication is a critical determinant of the natural history of simian immunodeficiency virus infection

Different patterns of viral replication correlate with the natural history of disease progression in humans and macaques infected with human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV), respectively. However, the viral and host factors influencing these patterns of viral replication in vivo are poorly understood. We intensively studied viral replication in macaques receiving identical inocula of SIV. Marked differences in viral replication patterns were apparent within the first week following inoculation, a time prior to the development of measurable specific immune effector responses to viral antigens. Plasma viral RNA levels measured on day 7 postinoculation correlated with levels measured in the postacute phase of infection. Differences in the susceptibility of host cells from different animals to in vitro SIV infection correlated with the permissiveness of the animals for early in vivo viral replication and hence with the postacute set point level of plasma viremia. These results suggest that host factors that exert their effects prior to full development of specific immune responses are critical in establishing the in vivo viral replication pattern and associated clinical course in subjects infected with SIV and, by extension, with HIV-1.

Neutralization titres of HIV-1-specific monoclonal antibodies vary according to the batch of primary human peripheral blood lymphocytes, but do not vary coordinately

Human peripheral blood lymphocytes (PBL) were collected from five healthy adults under standard conditions and on a number of different occasions, and used in neutralization assays of human immunodeficiency virus type 1 (HIV-1) strain IIIB with three monoclonal antibodies (mAbs). Variations in neutralization titre were observed with different batches of PBLs with, for example, titres of ICR39.3b ranging from 1/10 to over 1/40000. However titres were as high, or higher, in PBLs than in C8166 cells (a human CD4+ T lymphoblastoid cell line) in 82% (28/34) of tests made. Most surprising was that neutralization by the three mAbs did not vary coordinately. In one batch of PBLs the neutralization titre of one of the mAbs might be increased while that of another mAb did not increase, or decrease. Thus PBLs could not be described as giving high or low levels of neutralization without reference to a specific mAb. This was not an assay problem as infectivity titres were relatively constant (varying by 1 to 1.4 fold with respect to C8166 cells), and neutralization titres were reproducible with the same batch of frozen PBLs over a three month period. Only one donor gave consistently low neutralization titres (defined here as 1/200; 2/2 batches tested) with all three mAbs, but all other donors gave similarly low titres with one of their batches of PBLs. The non-coordinate variation in neutralization titre indicates the advisability of using antibodies of several different specificities in any kind of preventive or therapeutic immunity.

Endogenous retroviruses and the evolution of resistance to retroviral infection

The current AIDS epidemic has rekindled interest in the evolution of retroviruses and the development of resistance to infection. Retroviruses and their vertebrate hosts have coexisted for millions of years, during which time a variety of host defence mechanisms has evolved. One repeated strategy is to use endogenous retroviruses to combat infection by their exogenous relatives.

Characterization of proviral DNA from an individual with long-term, nonprogressive infection with HIV-1 and nonrecoverable virus

A small proportion of individuals infected with HIV-1 known as long-term nonprogressors (LTNPs) remain healthy and immunologically normal, with stable numbers of CD4+ lymphocytes, for prolonged periods without the administration of antiretroviral agents. The long terminal repeat (LTR) of HTV-1 proviral DNA of an LTNP from whom virus was consistently not recoverable has now been isolated by a nested polymerase chain reaction (PCR) method and shown to contain a total of 38 point mutations, only four of which affect promoter and enhancer elements, compared with the IIIB strain of HIV-1. Almost the entire HIV-1 proviral DNA was then isolated from the proband by a long PCR approach. Restriction enzyme digestion of the proviral DNA revealed no large deletions in the gag, pol, or env genes, although the loss of an Nco I site was apparent. Amplification of the env gene by long PCR also yielded a product apparently identical in size to that obtained with HIV-1 strain IIIB. Analysis by long PCR of HIV-1 proviral DNA from LTNPs with nonrecoverable virus may clarify the mechanism of long-term nonprogression and contribute to the development of HIV-1 vaccines.

Activity of human immunodeficiency virus type 1 promoter/TAR regions and tat1 genes derived from individuals with different rates of disease progression

Different rates of disease progression may be associated with different human immunodeficiency virus type 1 (HIV-1) promoter and/or transactivator activities. We therefore analyzed the sequences and activities of the first exon of Tat, tat1, and the promoter/trans-acting responsive (TAR) regions amplified directly from peripheral blood mononuclear cells obtained from five long-term nonprogressors and eight progressing HIV-1-infected individuals. The majority of tat1 alleles and promoter/TAR regions from all patients were intact and showed comparable activities in transient reporter assays. A substantial number of point mutations and some length variations were observed in the promoter/TAR region. In a single nonprogressor, the Sp1 binding site 3 was consistently altered and the transcriptional activity in the presence of Tat was diminished. Some LTR clones from a rapid progressor contained a fourth Sp1 binding site, which was associated with an elevated basal promoter activity. These data suggest that defects in the promoter/TAR region or tat1 are rare and that different promoter/transactivator activities are not commonly associated with different progression rates.

Genetic characterization of vif, vpr, and vpu sequences from long-term survivors of human immunodeficiency virus type 1 infection

The identification of HIV-1-infected individuals who remain asymptomatic despite prolonged infection presents a unique opportunity to understand virologic and host factors involved in the pathogenesis of AIDS. We have previously identified 10 long-term survivors (LTS) who are clinically healthy and immunologically normal despite 13 to 15 years of HIV-1 infection. In this study, we examined three accessory genes of HIV-1, vif, vpr, and vpu, in these LTS. A total of 52 vif, 54 vpr, and 55 vpu nucleotide sequences were obtained from the peripheral blood mononuclear cells of these patients. Analysis of these sequences revealed no gross deletions or insertions. Most of the clones were full-length with an intact open reading frame. Phylogenetic analyses of the vif, vpr, and vpu sequences from the LTS suggested that the HIV-1 strains found in the study subjects are not significantly different from those found in patients with AIDS and that the viruses in the LTS are unlikely to share a common genetic origin. Furthermore, a similar degree of overall genetic diversity between viruses from the LTS and AIDS patients suggests that there is unlikely a significant correlation between the degree of genetic diversity and the rate of disease development. Factors other than genetic divergence, such as viral load and phenotype, are likely to impact more on disease status.

HIV induces homing of resting T lymphocytes to lymph nodes

In vivo infection with human immunodeficiency virus type 1 (HIV-1) leads to gradual depletion of CD4+ T lymphocytes from the peripheral blood and later from the lymphoid organs. The mechanism of CD4 cell depletion is not known. HIV can only replicate in dividing lymphocytes, but greater than 98% of the lymphocytes in vivo at any given time are resting and are not permissive for productive infection. We found that exposure of resting CD4+ T lymphocytes to HIV-1 transiently upregulated expression of cell surface CD62L (L-selectin), the receptor for homing to lymph nodes, with concomitant enhanced ability of these cells to bind to lymph node high endothelial venules in an ex vivo homing assay (increased approximately 12-fold, P < 0.001) and to home from the blood into lymph nodes following intravenous injection into SCID mice. This suggested the possibility that decreases in numbers of CD4+ T lymphocytes in the blood of HIV-1-infected subjects may reflect enhanced homing of abortively infected, resting lymphocytes into lymph nodes rather than direct virus replication in and killing of these cells, and may explain development of lymphadenopathy at a time when numbers of CD4+ T lymphocytes in the blood fall.

Interactions between Exogenous and Endogenous Retroviruses

Retroviruses are distinguished from other viruses by several features. Notably, some retroviruses are present as normal elements in the genomes of virtually all vertebrates (endogenous proviruses). Others are exogenous, i.e. horizontally transmitted agents, many of which cause fatal diseases. The endogenous retroviruses are genetically transmitted and to a large extent their significance is uncertain. However, there is evidence suggesting that they contribute to the development of diseases in several animal species. Most importantly, some endogenous retroviruses are capable of interacting with exogenous counterparts through a variety of different mechanisms with serious consequences to the host. Conversely, others are advantageous in that they protect against exogenous retroviruses. In this review various types of interactions between endogenous and exogenous retroviruses are discussed, including receptor interference, recombination, phenotypic mixing, immunological interactions and heterologous trans-activation. Copyright 1997 S. Karger AG, Basel

Neutralization of primary human immunodeficiency virus type 1 isolates: a study of parameters implicated in neutralization in vitro

Various studies have reported that primary human immunodeficiency viruses seem to be more refractory to neutralization by HIV-positive sera than T cell line-adapted strains. In this study we also show that adaptation of the HIV-1SF-2 strain, produced in PBMCs, to the cell line CEM-SS renders this isolate sensitive to neutralization by almost all the sera tested. Further neutralization studies should thus focus on the development of an assay involving primary isolates in order to detect antibodies having a neutralizing activity in vivo. Neutralization protocols currently use either an antibody end-point dilution assay, which combines a fixed inoculum of virus with serial dilutions of antibody, or an infectivity reduction assay, which uses serial dilutions of virus with a single dilution of antibody. We have developed an assay designed for studying the neutralization of primary isolates that combines these two approaches. Performing the assay on PBMCs allows all primary isolates to be analyzed, not just those multiplying in T cell lines. The neutralizing titer measured on PBMCs for human HIV-positive sera is low, but reproducible and independent of the virus titer in a given experiment. It can be increased about five-fold by changing the temperature and duration of virus-serum interaction (overnight at 4 degrees C instead of 1 hr at 37 degrees C). These results emphasize the need for a relevant neutralization assay involving primary isolates and primary cells for a better understanding of the role of humoral response in HIV infection.

Virologic and serologic markers of rapid progression to AIDS after HIV-1 seroconversion

The association between early virologic and immunologic events after human immunodeficiency virus type 1 (HIV-1) infection and progression of HIV-1 infection to acquired immunodeficiency syndrome (AIDS) was studied among 59 homosexual men with documented time of seroconversion. Epidemiologic factors, such as number of lifetime sexual partners, history of sexually transmitted diseases, and other factors, also were studied. All 17 seroconverters in the cohort who developed AIDS within 3 years (rapid progressors = RPs) were compared with 42 men without AIDS for at least 6 years seroconversion (nonrapid progressors = non-RPs). Plasma levels of HIV-1 RNA, p24 antigen, antibodies to HIV-1 structural genes, beta-2 microglobulin, neopterin, and interferon-alpha were measured at four time points: (a) the last seronegative visit, (b) the first seropositive visit, (c) the visit closest to AIDS (or the corresponding visit for the non-RPs) and (d) 6 years after seroconversion (for non-RPs). Up to seroconversion, the RPs had a significantly higher number of lifetime sexual partners than non-RPs (503 versus 171, respectively). At the first seropositive visit, RPs had significantly higher concentrations of plasma HIV-1 RNA (p < 0.01) and prevalence of p24 antigenemia (p < 0.001) and significantly lower levels of antibodies to the HIV-1 gag proteins p17 and p24 (p < 0.01-0.001) compared with non-RPs. These differences increased during follow-up visits. Antibodies to p66 and gp120 were significantly different only at the visit closet to AIDS (p < 0.001), as were beta-2 microglobulin and interferon alpha. These findings suggest that early virologic-immunologic events after HIV-1 infection may determine the rate of progression to AIDS. Anti-gag immune response may prevent rapid progression of HIV-1 disease and should be considered for future vaccine studies.

Twin studies demonstrate a host cell genetic effect on productive human immunodeficiency virus infection of human monocytes and macrophages in vitro

Biological and genetic variability is a prominent feature of human immunodeficiency virus (HIV) strains, especially in tropism, syncytium formation, and replicative capacity. To determine whether there were variable host cell effects on HIV replication in monocytes, three different strains of low-passage-number monocytotropic blood isolates of HIV and the laboratory-adapted strain Ba-L were inoculated into panels of adherent monocytes drawn from 44 different donors, and peak extracellular HIV p24 antigen titers were compared. The clinical HIV strains showed patterns of either moderate or low-level replication in most donor monocytes (20 to 4,000 pg/ml). However, within this range there was marked variation in peak titers in most donors. HIV type 1 Ba-L replicated in all donor monocytes to much higher levels with less variability (30 to 40 ng/ml). Furthermore, replication of 21 clinical blood-derived strains of HIV in blood monocytes and monocyte-derived macrophages (MDM) from pairs of identical twins and age-matched unrelated donors (URD) of the same sex were compared. In all of the seven pairs of identical twins, the kinetics of replication (measured by extracellular HIV p24 antigen) of panels of four clinical HIV type 1 isolates in monocytes were similar within pairs. However, marked and significant differences in kinetics of HIV production occurred within 10 of the 12 unrelated donor pairs (P = 0.0007). The remaining two URD pairs showed similar kinetic patterns, but only one pair had the same HLA-DR genotype. Similar results were observed with monocytes/MDMs obtained from a second bleed of the same donor. Hence, discordant patterns of HIV replication kinetics between URD monocyte pairs contrasted with concordant patterns in identical twin monocytes. These data strongly suggest a host cell genetic effect on productive viral replication in monocytes and MDMs. So far, no consistent genetic linkage of HIV replication pattern with HLA-DR genotype has been observed.

Dynamics and modulation of human immunodeficiency virus type 1 transcripts in vitro and in vivo

The dynamics of human immunodeficiency virus type 1 (HIV-1) transcription was analyzed in vitro and in vivo by using a specific molecular approach which allows accurate quantitation of the different classes of viral mRNAs. Unspliced (US) and multiply spliced (MS) HIV-1 transcripts were assayed by competitive reverse transcription (cRT)-PCR, using a single competitor RNA bearing in tandem internally deleted sequences of both template species. Acute HIV-1 infection of primary peripheral blood mononuclear cells (PBMCs), monocytes/macrophages cells, and the A3.01 T-lymphocyte-derived cell line was studied; both classes of HIV-1 mRNAs increased exponentially (r2 > 0.98) at days 1 to 3 and 1 to 4 postinfection in HIV(IIIB)-infected A3.01 cells and PBMCs, respectively, whereas monocytes/macrophages infected with monocytotropic HIV(BaL) exhibited a linear (r2 = 0.81 to 0.94) accumulation of US and MS transcripts. Following induction of chronically infected ACH-2 cells, MS transcripts increased 2 h postinduction and peaked at 5 h (doubling time, 58 min), while at 24 h, US mRNAs increased 3,053-fold compared with basal time (doubling time, 137 min). To address the biopathological significance of HIV-1 expression pattern during infection progression, pilot cross-sectional and longitudinal analyses were carried out with samples from untreated and treated HIV-1-infected patients. In almost all untreated (recently infected, long-term nonprogressor, and progressor) patients, MS transcript levels followed the general trend of systemic HIV-1 activity. In patients under treatment with powerful antiretroviral compounds, viral MS transcripts rapidly fell to undetectable levels, indicating that in vivo, levels of MS mRNAs in PBMCs are closely associated with the number of newly infected cells and suggesting a new role for the quantitative analysis of HIV-1 transcription in infected patients.

Resistance to HIV-1 infection in caucasian individuals bearing mutant alleles of the CCR-5 chemokine receptor gene

HIV-1 and related viruses require co-receptors, in addition to CD4, to infect target cells. The chemokine receptor CCR-5 (ref.1) was recently demonstrated to be a co-receptor for macrophage-tropic (M-tropic) HIV-1 strains, and the orphan receptor LESTR (also called fusin) allows infection by strains adapted for growth in transformed T-cell lines (T-tropic strains). Here we show that a mutant allele of CCR-5 is present at a high frequency in caucasian populations (allele frequency, 0.092), but is absent in black populations from Western and Central Africa and Japanese populations. A 32-base-pair deletion within the coding region results in a frame shift, and generates a non-functional receptor that does not support membrane fusion or infection by macrophage- and dual-tropic HIV-1 strains. In a cohort of HIV-1 infected caucasian subjects, no individual homozygous for the mutation was found, and the frequency of heterozygotes was 35% lower than in the general population. White blood cells from an individual homozygous for the null allele were found to be highly resistant to infection by M-tropic HIV-1 viruses, confirming that CCR-5 is the major co-receptor for primary HIV-1 strains. The lower frequency of heterozygotes in seropositive patients may indicate partial resistance.

Recombinant human immunodeficiency virus type 1 genomes with tat unconstrained by overlapping reading frames reveal residues in Tat important for replication in tissue culture

Human immunodeficiency virus type 1 (HIV-1) Tat is essential for virus replication and is a potent trans activator of viral gene expression. Evidence suggests that Tat also influences virus infectivity and cytopathicity. Extensive structure-function studies of Tat in subgenomic settings with point mutagenesis and transient transfection readouts have been performed. These reporter assays have defined certain amino acid residues as being important for trans activation of reporter plasmids. However, they have not directly addressed functions related to virus replication. Here, we have studied Tat structure-function in the setting of replicating viruses. We characterized mutations that emerged in Tat during HIV-1 infections of T lymphocytes. To ensure that the selection pressure for change was directed toward protein function, we constructed HIV-Is in which the Tat reading frame was freed from constraints exerted by overlapping with the reading frames of vpr, rev, and env. When these recombinant viruses were passaged in T cells, 26 novel nucleotide changes in tat were observed from sequencing of 220 independently isolated clones. Recloning of these changes into a pNL4-3 molecular background allowed for the characterization of residues in Tat important for virus replication. Interestingly, many of the changes that affected replication when they were assayed in transient trans activation of plasmid reporters were found to be relatively neutral. We conclude that the structure-function of Tat in virus replication is incompletely reflected by activity measurements based only on subgenomic transient transfections.

Antibody neutralization of HIV-1

Neutralizing antibodies are a major component of host defense against viruses, and appear to be particularly important in limiting the spread of cell-free virus. Results from vaccine trials in animal models suggest that these antibodies may contribute to protection against human immunodeficiency virus (HIV) infection. Here, Pascal Poignard and colleagues discuss recent developments in this area, with particular emphasis on the measurement, specificity and mechanism of the antibody response, and its significance for vaccine production.

Quality control of HIV cultures in a clinical retrovirology laboratory

The culture of primary HIV isolates requires fresh phytohemagglutinin (PHA) stimulated peripheral blood mononuclear cells (PBMC) from seronegative donors. The variation inherent in donor cells, obtained from many different individuals, might affect the likelihood of virus isolation. We developed a quality control (QC) procedure which could determine quantitatively the susceptibility of random donor cells to HIV infection. The QC reagents consisted of cells and supernatants infected with a syncytium-inducing clinical isolate of HIV. Six 5-fold dilutions of QC cells (starting at 1000 cells) and supernatant (starting at a 1:200 dilution) were cultured in parallel with 1 x 10(6) 2-3-day-old PHA stimulated donor cells. After 7 or 14 days the resulting culture supernatant was tested for syncytia formation with MT-2 cells. A total of 127 sequential donors were tested over an 11 month period. All but one donor PBMC preparation was capable of being infected by the QC reagents (and this particular donor was permissive for several other primary isolates). The standard variation observed among all cultures was about one 5-fold dilution. The coefficient of variation ranged from 10.7 to 17.3%. These results suggest that the mononuclear cells from most, if not all, individuals are permissive for HIV to approximately the same level. Other quality control measures used in the laboratory are described.