Patterns of Changes in Human Immunodeficiency Virus Type 1 V3 Sequence Populations Late in Infection

Self Cite

The initiation of drug therapy or the addition of a new drug to preexisting therapy can have a significant impact on human immunodeficiency virus type 1 (HIV-1) populations within a person. Drug therapy directed at reverse transcriptase and protease can result in dramatic decreases in virus load, causing a contraction in the virus population that represents a potential genetic bottleneck as a subset of virus with genomes carrying resistance mutations repopulate the host. While this bottleneck exerts an effect directly on the region that is being targeted by the drugs, it also affects other regions of the viral genome. We have applied heteroduplex tracking assays (HTA) specific to variable regions 1 and 2 (V1/V2) and variable region 3 (V3) of the HIV-1 env gene to analyze the effect of a genetic bottleneck created by the selection of resistance to ritonavir, a protease inhibitor. Subjects were classified into groups on the basis of the extent of the initial drop in virus load and the duration of virus load reduction. Subjects with a strong initial drop in virus load exhibited a loss of heterogeneity in the env region at virus load rebound; in contrast, subjects with a weak initial drop in virus load exhibited little to no loss of heterogeneity at virus load rebound in either region of env examined. The duration of virus load reduction also affected env populations. Subjects that had prolonged reductions exhibited slower population diversification and the appearance of new V1/V2 species after rebound. The longer reduction of virus load in these subjects may have allowed for improved immune system function, which in turn could have selected for new escape mutants. Subjects with rapid rebound quickly reequilibrated the entry env variants back into the resistant population. When the pro gene developed further resistance mutations subsequent to virus load rebound, no changes were observed in V1/V2 or V3 populations, suggesting that the high virus loads allowed the env populations to reequilibrate rapidly. The rapid equilibration of env variants during pro gene sequence transitions at high virus load suggests that recombination is active in defining the HIV-1 sequence population. Conversely, part of the success of suppressive antiviral therapy may be to limit the potential for evolution through recombination, which requires dually infected cells.

Section: Characterization Of Virus Populations At Trial Entrysupporting

confidence: 67%

Effect of a Protease Inhibitor-Induced Genetic Bottleneck on Human Immunodeficiency Virus Type 1 env Gene Populations

Kitrinos

Nelson

Resch

et al. 2005

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“…For determination of whether the CD4-independent viruses from different patients were preexistent in the viral isolates from the ARRP and for examination of the relative abundance of the CD4-independent variants, heteroduplex tracking assays (HTA) were performed as previously described (18,25). Briefly, viral RNA was isolated from culture supernatants and used in RT-PCR to generate 400-bp V1/V2 or 144-bp V3 products.…”

Section: Methodsmentioning

confidence: 99%

“…Some products were cloned into the pT7Blue-3 vector by use of the Perfectly Blunt cloning kit (Novagen). Clones were screened by HTA and sequenced as described previously (25).…”

Section: Methodsmentioning

confidence: 99%

Isolation of CD4-Independent Primary Human Immunodeficiency Virus Type 1 Isolates That Are Syncytium Inducing and Acutely Cytopathic for CD8⁺Lymphocytes

Zerhouni

Nelson

Saha

2004

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Previous studies have established the existence of CD4-independent simian immunodeficiency virus, human immunodeficiency virus type 2 (HIV-2), and laboratory strains of HIV-1. However, whether CD4-independent viruses may also exist in HIV-1-infected patients has remained unclear. We have recently reported the isolation of viruses from an AIDS patient that were able to infect CD8 ؉ cells independent of CD4, using CD8 as a receptor. Using a similar approach, here we examined viruses from 12 randomly selected patients (obtained from the AIDS Research and Reference Program, National Institutes of Health) for the presence of CD4-independent HIV-1. CD4-independent variants were isolated from infected CD8؉ cells from the viral quasispecies of 7 of 12 patients. The CD4-independent isolates were able to infect primary CD8 ؉ cells as well as a CD4؊ CD8 ؉ T-cell line. Soluble CD4 and blocking anti-CD4 or -CD8 antibody had no effect on infection of CD8 ؉ cells. Remarkably, two of the seven CD4-independent isolates, but not their parental bulk viruses, induced syncytia and caused acute death of infected CD8؉ cells. Some of the CD4-independent variants were also able to infect U87 cells that were negative for CD4, CD8, and common HIV coreceptors, suggesting a novel entry mechanism for these isolates. The CD4-independent isolates were derived from adults and children infected with subtypes A, B, and D. Although no common motif for CD4 independence was found, novel sequence changes were observed in critical areas of the envelopes of the CD4-independent viruses. These results demonstrate that HIV-1-infected patients can frequently harbor viruses that are able to mediate CD4-independent infection of CD8 ؉ cells. In addition, this study also provides evidence of primary HIV-1 variants that are syncytium inducing and acutely cytopathic for CD8 ؉ lymphocytes.

“…K03455] in standard reference HXB2) very frequently distinguish primary X4 from R5 viruses (9,15,16,21,42,66), with positions 24 and 27 implicated in some cases (10,37). However, while evolutionary studies of the R5-X4 transition have been undertaken (30,38,61,62), the actual mutational pathway or pathways by which R5 viruses that establish infections in vivo evolve into X4 viruses (i.e., the specific evolutionary sequence of mutations required) has been largely unexplored. It is not clear whether the appearance of basic amino acids at sites 11 and 25 is sufficient or even necessary in most cases in vivo to lead to the outgrowth of X4 virus or whether, instead, a more gradual process of mutation accumulation takes place.…”

mentioning

confidence: 99%

“…If mutant accumulation does occur in a more gradual process, this may provide an opportunity for both early detection and arrest of X4 development. Viruses that can use both coreceptors (R5X4 viruses) are known to arise around the time of R5-to-X4 transition (2,8,38,61), but their evolutionary role in that transition is not certain. The answers to questions of in vivo evolution cannot be approached by phenotypic assays alone, and analyses based on the appearance of positively charged mutations at V3 sites 11 and 25 have led to incomplete and sometimes ambiguous conclusions regarding the transition process (35).…”

mentioning

confidence: 99%

Improved Coreceptor Usage Prediction and GenotypicMonitoring of R5-to-X4 Transition by Motif Analysis of HumanImmunodeficiency Virus Type 1 env V3 LoopSequences

Jensen

Wout

et al. 2003

389

423

Early in infection, human immunodeficiency virus type 1 (HIV-1) generally uses the CCR5 chemokine receptor (along with CD4) for cellular entry. In many HIV-1-infected individuals, viral genotypic changes arise that allow the virus to use CXCR4 (either in addition to CCR5 or alone) as an entry coreceptor. This switch has been associated with an acceleration of both CD3؉ T-cell decline and progression to AIDS. While it is well known that the V3 loop of gp120 largely determines coreceptor usage and that positively charged residues in V3 play an important role, the process of genetic change in V3 leading to altered coreceptor usage is not well understood. Further, the methods for biological phenotyping of virus for research or clinical purposes are laborious, depend on sample availability, and present biosafety concerns, so reliable methods for sequencebased "virtual phenotyping" are desirable. We introduce a simple bioinformatic method of scoring V3 amino acid sequences that reliably predicts CXCR4 usage (sensitivity, 84%; specificity, 96%). This score (as determined on the basis of position-specific scoring matrices [PSSM]) can be interpreted as revealing a propensity to use CXCR4 as follows: known R5 viruses had low scores, R5X4 viruses had intermediate scores, and X4 viruses had high scores. Application of the PSSM scoring method to reconstructed virus phylogenies of 11 longitudinally sampled individuals revealed that the development of X4 viruses was generally gradual and involved the accumulation of multiple amino acid changes in V3. We found that X4 viruses were lost in two ways: by the dying off of an established X4 lineage or by mutation back to low-scoring V3 loops.Early studies of the biological properties of human immunodeficiency virus type 1 (HIV-1) found that virus isolates could be placed into as few as two phenotypic categories (defined in vitro as either non-syncytium-inducing [NSI] or syncytium-inducing [SI]) in certain CD4 ϩ T-cell lines. These phenotypes were often found to be associated with differences in growth properties and cytopathicity on peripheral blood mononuclear cells (PBMC) (1,14,46) and in cellular host range (3,48). Ultimately, the difference between the NSI and SI phenotypes was shown to be due largely to the differential use of chemokine receptors as coreceptors for viral entry: NSI viruses predominantly use CCR5, while SI viruses can use CCR5 and CXCR4 or CXCR4 exclusively (2, 29, 31, 52, 54). Results determined on the basis of SI phenotype and/or coreceptor usage typing showed that although HIV-1 present at primary infections used the CCR5 coreceptor (R5 virus) ϳ90% of the time (63, 67, 68), a substantial proportion of individuals eventually developed virus that used the CXCR4 coreceptor (X4 virus). These X4/SI viruses are associated with accelerated CD4 decline and more rapid progression of HIV-1 disease (8,28,33,43,47). Little is known about the mechanisms by which these viruses come to predominate among the HIV-1 strains present in an infected person. For example, it is no...