[Show abstract][Hide abstract] ABSTRACT: Recombinant soluble, cleaved HIV-1 envelope glycoprotein SOSIP.664 gp140 trimers based on the subtype A BG505 sequence are being studied structurally and tested as immunogens in animals. For these trimers to become a vaccine candidate for human trials, they would need to be made in appropriate amounts at an acceptable quality. Accomplishing such tasks by transient transfection is likely to be challenging. The traditional way to express recombinant proteins in large amounts is via a permanent cell line, usually of mammalian origin. Making cell lines that produce BG505 SOSIP.664 trimers requires the co-expression of the Furin protease to ensure that the cleavage site between the gp120 and gp41 subunits is fully utilized.
We designed a vector capable of expressing Env and Furin, and used it to create Stable 293 T and CHO Flp-InTMcell lines through site-specific recombination. Both lines produce high quality, cleaved trimers at yields of up to 12-15 mg per 1 x 109 cells. Trimer expression at such levels was maintained for up to 30 days (10 passages) after initial seeding and was consistently superior to what could be achieved by transient transfection. Electron microscopy studies confirm that the purified trimers have the same native-like appearance as those derived by transient transfection and used to generate high-resolution structures. They also have appropriate antigenic properties, including the presentation of the quaternary epitope for the broadly neutralizing antibody PGT145.
The BG505 SOSIP.664 trimer-expressing cell lines yield proteins of an appropriate quality for structural studies and animal immunogenicity experiments. The methodology is suitable for making similar lines under Good Manufacturing Practice conditions, to produce trimers for human clinical trials. Moreover, any env gene can be incorporated into this vector system, allowing the manufacture of SOSIP trimers from multiple genotypes, either by transient transfection or from stable cell lines.
[Show abstract][Hide abstract] ABSTRACT: We describe methods to improve the properties of soluble, cleaved gp140 trimers of the human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins (Env) for use in structural studies and as immunogens. In the absence of nonionic detergents, gp140 of the KNH1144 genotype, terminating at residue 681 in gp41 (SOSIP.681), has a tendency to form higher-order complexes or aggregates, which is particularly undesirable for structure-based research. We found that this aggregation in the absence of detergent does not involve the V1, V2 or V3 variable regions of gp120. Moreover, we observed that detergent forms micelles around the membrane-proximal external region (MPER) of the SOSIP.681 gp140 trimers, whereas deleting most of the MPER residues by terminating the gp140 at residue 664 (SOSIP.664) prevented the aggregation that otherwise occurs in SOSIP.681 in the absence of detergent. Although the MPER can contribute to trimer formation, truncating most of it only modestly reduced trimerization and lacked global adverse effects on antigenicity. Thus, the MPER deletion minimally influenced the kinetics of the binding of soluble CD4 and a CD4-binding-site antibody to immobilized trimers, as detected by surface plasmon resonance. Furthermore, the MPER deletion did not alter the overall three-dimensional structure of the trimers, as viewed by negative stain electron microscopy. Homogeneous and aggregate-free MPER-truncated SOSIP Env trimers are therefore useful for immunogenicity and structural studies.
Full-text · Article · Jul 2013 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: A substantial proportion of the broadly neutralizing antibodies (bnAbs) identified in certain HIV-infected donors recognize glycan-dependent epitopes on HIV-1 gp120. Here we elucidate how the bnAb PGT 135 binds its Asn332 glycan-dependent epitope from its 3.1-Å crystal structure with gp120, CD4 and Fab 17b. PGT 135 interacts with glycans at Asn332, Asn392 and Asn386, using long CDR loops H1 and H3 to penetrate the glycan shield and access the gp120 protein surface. EM reveals that PGT 135 can accommodate the conformational and chemical diversity of gp120 glycans by altering its angle of engagement. Combined structural studies of PGT 135, PGT 128 and 2G12 show that this Asn332-dependent antigenic region is highly accessible and much more extensive than initially appreciated, which allows for multiple binding modes and varied angles of approach; thereby it represents a supersite of vulnerability for antibody neutralization.
[Show abstract][Hide abstract] ABSTRACT: New broad and potent neutralizing HIV-1 antibodies have recently been described that are largely dependent on the gp120 N332 glycan for Env recognition. Members of the PGT121 family of antibodies, isolated from an African donor, neutralize ∼70% of circulating isolates with a median IC50 less than 0.05 µg ml(-1). Here, we show that three family members, PGT121, PGT122 and PGT123, have very similar crystal structures. A long 24-residue HCDR3 divides the antibody binding site into two functional surfaces, consisting of an open face, formed by the heavy chain CDRs, and an elongated face, formed by LCDR1, LCDR3 and the tip of the HCDR3. Alanine scanning mutagenesis of the antibody paratope reveals a crucial role in neutralization for residues on the elongated face, whereas the open face, which accommodates a complex biantennary glycan in the PGT121 structure, appears to play a more secondary role. Negative-stain EM reconstructions of an engineered recombinant Env gp140 trimer (SOSIP.664) reveal that PGT122 interacts with the gp120 outer domain at a more vertical angle with respect to the top surface of the spike than the previously characterized antibody PGT128, which is also dependent on the N332 glycan. We then used ITC and FACS to demonstrate that the PGT121 antibodies inhibit CD4 binding to gp120 despite the epitope being distal from the CD4 binding site. Together, these structural, functional and biophysical results suggest that the PGT121 antibodies may interfere with Env receptor engagement by an allosteric mechanism in which key structural elements, such as the V3 base, the N332 oligomannose glycan and surrounding glycans, including a putative V1/V2 complex biantennary glycan, are conformationally constrained.
[Show abstract][Hide abstract] ABSTRACT: Small molecule CCR5 antagonists, such as maraviroc (MVC), likely block HIV-1 through an allosteric, noncompetitive inhibition mechanism whereas inhibition by agonists such as PSC-RANTES is less defined and may involve receptor removal by cell surface downregulation, competitive inhibition by occluding the HIV-1 envelope binding, and/or allosteric effects by altering CCR5 conformation. We explored the inhibitory mechanisms of maraviroc and PSC-RANTES by employing pairs of virus clones with differential sensitivities to these inhibitors. Intrinsic PSC-RANTES-resistant virus (YA vs RT) or those selected in PSC-RANTES treated macaques (M584 vs. P3-4) only displayed resistance in multiple-cycle assays or with a CCR5 mutant that cannot be down-regulated. In single-cycle assays, these HIV-1 clones displayed equal sensitivity to PSC-RANTES inhibition suggesting effective receptor downregulation. Prolonged PSC-RANTES exposure resulted in desensitization of the receptor to internalization such that increasing virus concentration (substrate) could saturate the receptors and overcome PSC-RANTES inhibition. In contrast, resistance to MVC was observed with the MVC-resistant HIV-1 (R3 vs. S2) in both multiple- and single-cycle assays and with altered virus concentrations which is indicative of allosteric inhibition. MVC could also mediate inhibition and possibly resistance through competitive mechanisms.
Full-text · Article · Mar 2013 · Antimicrobial Agents and Chemotherapy
[Show abstract][Hide abstract] ABSTRACT: PG9 is the founder member of an expanding family of glycan-dependent human antibodies that preferentially bind the HIV (HIV-1) envelope (Env) glycoprotein (gp) trimer and broadly neutralize the virus. Here, we show that a soluble SOSIP.664 gp140 trimer constructed from the Clade A BG505 sequence binds PG9 with high affinity (∼11 nM), enabling structural and biophysical characterizations of the PG9:Env trimer complex. The BG505 SOSIP.664 gp140 trimer is remarkably stable as assessed by electron microscopy (EM) and differential scanning calorimetry. EM, small angle X-ray scattering, size exclusion chromatography with inline multiangle light scattering and isothermal titration calorimetry all indicate that only a single PG9 fragment antigen-binding (Fab) binds to the Env trimer. An ∼18 Å EM reconstruction demonstrates that PG9 recognizes the trimer asymmetrically at its apex via contact with two of the three gp120 protomers, possibly contributing to its reported preference for a quaternary epitope. Molecular modeling and isothermal titration calorimetry binding experiments with an engineered PG9 mutant suggest that, in addition to the N156 and N160 glycan interactions observed in crystal structures of PG9 with a scaffolded V1/V2 domain, PG9 makes secondary interactions with an N160 glycan from an adjacent gp120 protomer in the antibody-trimer complex. Together, these structural and biophysical findings should facilitate the design of HIV-1 immunogens that possess all elements of the quaternary PG9 epitope required to induce broadly neutralizing antibodies against this region.
Full-text · Article · Feb 2013 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Antibiotic disruption of the intestinal microbiota may cause susceptibility to pathogens that is resolved by progressive bacterial outgrowth and colonization. Succession is central to ecological theory but not widely documented in studies of the vertebrate microbiome. Here, we study succession in the hamster gut after treatment with antibiotics and exposure to Clostridium difficile. C. difficile infection is typically lethal in hamsters, but protection can be conferred with neutralizing antibodies against the A and B toxins. We compare treatment with neutralizing monoclonal antibodies (mAb) to treatment with vancomycin, which prolongs the lives of animals but ultimately fails to protect them from death. We carried out longitudinal deep sequencing analysis and found distinctive waves of succession associated with each form of treatment. Clindamycin sensitization prior to infection was associated with the temporary suppression of the previously dominant Bacteroidales and the fungus Saccinobaculus in favor of Proteobacteria. In mAb-treated animals, C. difficile proliferated before joining Proteobacteria in giving way to re-expanding Bacteroidales and the fungus Wickerhamomyces. However, the Bacteroidales lineages returning by day 7 were different from those that were present initially, and they persisted for the duration of the experiment. Animals treated with vancomycin showed a different set of late-stage lineages that were dominated by Proteobacteria as well as increased disparity between the tissue-associated and luminal cecal communities. The control animals showed no change in their gut microbiota. These data thus suggest different patterns of ecological succession following antibiotic treatment and C. difficile infection.
[Show abstract][Hide abstract] ABSTRACT: The spore-forming bacterium Clostridium difficile represents the principal cause of hospital-acquired diarrhea and pseudomembranous colitis worldwide. C. difficile infection (CDI) is mediated by 2 bacterial toxins, A and B; neutralizing these toxins with monoclonal antibodies (mAbs) provides
a potential nonantibiotic strategy for combating the rising prevalence, severity, and recurrence of CDI. Novel antitoxin mAbs
were generated in mice and were humanized. The humanized antitoxin A mAb PA-50 and antitoxin B mAb PA-41 have picomolar potencies
in vitro and bind to novel regions of the respective toxins. In a hamster model for CDI, 95% of animals treated with a combination
of humanized PA-50 and PA-41 showed long-term survival relative to 0% survival of animals treated with standard antibiotics
or comparator mAbs. These humanized mAbs provide insight into C. difficile intoxication and hold promise as potential nonantibiotic agents for improving clinical management of CDI.
Full-text · Article · Jun 2012 · The Journal of Infectious Diseases
[Show abstract][Hide abstract] ABSTRACT: The trimeric envelope glycoprotein complex (Env) is the focus of vaccine development programs aimed at generating protective humoral responses to human immunodeficiency virus type 1 (HIV-1). N-Linked glycans, which constitute almost half of the molecular mass of the external Env domains, produce considerable structural heterogeneity and are a major impediment to crystallization studies. Moreover, by shielding the peptide backbone, glycans can block attempts to generate neutralizing antibodies against a substantial subset of potential epitopes when Env proteins are used as immunogens. Here, we describe the partial deglycosylation of soluble, cleaved recombinant Env trimers by inhibition of the synthesis of complex N-glycans during Env production, followed by treatment with glycosidases under conditions that preserve Env trimer integrity. The partially deglycosylated trimers are stable, and neither abnormally sensitive to proteolytic digestion nor prone to aggregation. Moreover, the deglycosylated trimers retain or increase their ability to bind CD4 and antibodies that are directed to conformational epitopes, including the CD4-binding site and the V3 region. However, as expected, they do not react with glycan-dependent antibodies 2G12 and PGT123, or the C-type lectin receptor DC-SIGN. Electron microscopic analysis shows that partially deglycosylated trimers have a structure similar to fully glycosylated trimers, indicating that removal of glycans does not substantially perturb the structural integrity of the trimer. The glycan-depleted Env trimers should be useful for structural and immunogenicity studies.
No preview · Article · May 2012 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: The HIV envelope (Env) protein gp120 is protected from antibody recognition by a dense glycan shield. However, several of the recently identified PGT broadly neutralizing antibodies appear to interact directly with the HIV glycan coat. Crystal structures of antigen-binding fragments (Fabs) PGT 127 and 128 with Man(9) at 1.65 and 1.29 angstrom resolution, respectively, and glycan binding data delineate a specific high mannose-binding site. Fab PGT 128 complexed with a fully glycosylated gp120 outer domain at 3.25 angstroms reveals that the antibody penetrates the glycan shield and recognizes two conserved glycans as well as a short β-strand segment of the gp120 V3 loop, accounting for its high binding affinity and broad specificity. Furthermore, our data suggest that the high neutralization potency of PGT 127 and 128 immunoglobulin Gs may be mediated by cross-linking Env trimers on the viral surface.
[Show abstract][Hide abstract] ABSTRACT: The initial step in HIV-1 infection occurs with the binding of cell surface CD4 to trimeric HIV-1 envelope glycoproteins (Env), a heterodimer of a transmembrane glycoprotein (gp41) and a surface glycoprotein (gp120). The design of soluble versions of trimeric Env that display structural and functional properties similar to those observed on intact viruses is highly desirable from the viewpoint of designing immunogens that could be effective as vaccines against HIV/AIDS. Using cryoelectron tomography combined with subvolume averaging, we have analyzed the structure of SOSIP gp140 trimers, which are cleaved, solubilized versions of the ectodomain of trimeric HIV-1 Env. We show that unliganded gp140 trimers adopt a quaternary arrangement similar to that displayed by native unliganded trimers on the surface of intact HIV-1 virions. When complexed with soluble CD4, Fab 17b, which binds to gp120 at its chemokine coreceptor binding site, or both soluble CD4 and 17b Fab, gp140 trimers display an open conformation in which there is an outward rotation and displacement of each gp120 protomer. We demonstrate that the molecular arrangements of gp120 trimers in the closed and open conformations of the soluble trimer are the same as those observed for the closed and open states, respectively, of trimeric gp120 on intact HIV-1 BaL virions, establishing that soluble gp140 trimers can be designed to mimic the quaternary structural transitions displayed by native trimeric Env.
Full-text · Article · Jun 2011 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: The anti-CCR5 antibody PRO 140 has shown potent and prolonged antiretroviral activity in subjects infected with CCR5-tropic
(R5) HIV-1. Prior studies have examined single intravenous doses ranging up to 5 mg/kg of body weight or up to three subcutaneous
doses ranging up to 324 mg. Here we report the results of a randomized, double-blind, placebo-controlled trial that examined
the antiviral activity, tolerability, and pharmacokinetics of single 5-mg/kg and 10-mg/kg intravenous infusions of PRO 140
in 31 treated subjects. Eligibility criteria included HIV-1 RNA levels of >5,000 copies/ml, CD4+ cell counts of >300/μl, no antiretroviral therapy for ≥12 weeks, and detection of only R5 HIV-1 in the original Trofile assay.
Following poststudy testing with an enhanced-sensitivity Trofile assay, one subject treated with 10 mg/kg was reclassified
as having dual/mixed-tropic virus at screening, and the data for that subject were censored from efficacy analyses. The mean
maximum reduction of the HIV-1 RNA level from the baseline level was 1.8 log10 units for both the 5-mg/kg and 10-mg/kg doses (P < 0.0001 relative to placebo). Viral loads reached their nadir at day 12 posttreatment and remained significantly (P < 0.01) reduced through day 29 for both PRO 140 dose groups. Treatment was generally well tolerated, with no dose-limiting
toxicity being observed. Peak serum concentrations and overall exposures increased proportionally with dose. In summary, single
5-mg/kg and 10-mg/kg doses of PRO 140 exhibited potent, long-lived antiviral activity and were generally well tolerated. The
findings further delineate the safety and antiviral properties of this novel, long-acting antiretroviral agent.
Full-text · Article · Oct 2010 · Antimicrobial Agents and Chemotherapy
[Show abstract][Hide abstract] ABSTRACT: PRO 140 is a humanized CCR5 monoclonal antibody that has demonstrated potent antiviral activity when it is administered intravenously to adults infected with CCR5-tropic (R5) human immunodeficiency virus type 1 (HIV-1). This study is the first to evaluate subcutaneous administration.
A randomized, double-blind, placebo-controlled study was conducted among 44 subjects with HIV-1 RNA levels of >5000 copies/mL, CD4(+) cell counts of >300 cells/microL, no receipt of antiretroviral therapy for >or=12 weeks, and only R5 HIV-1 detectable. Subjects received placebo, 162 mg of PRO 140, or 324 mg of PRO 140 weekly for 3 weeks or 324 mg of PRO 140 every other week for 2 doses by means of subcutaneous infusion. Subjects were monitored for 58 days for safety, antiviral effects, and PRO 140 serum concentrations.
Subcutaneous PRO 140 demonstrated potent and prolonged antiretroviral activity. Mean log(10) reductions in HIV-1 RNA level were 0.23, 0.99 (P=.009), 1.37 (P<.001), and 1.65 (P<.001) for the placebo, 162 mg weekly, 324 mg biweekly, and 324 mg weekly dose groups, respectively. Viral loads remained suppressed between successive doses. Treatment was generally well tolerated.
This trial demonstrates proof of concept for a monoclonal antibody administered subcutaneously in HIV-1 infected individuals. Subcutaneous PRO 140 offers the potential for significant dose-dependent HIV-1 RNA suppression and infrequent patient self-administration.
ClinicalTrials.gov identifier: NCT00642707 .
Preview · Article · Apr 2010 · The Journal of Infectious Diseases
[Show abstract][Hide abstract] ABSTRACT: Natural polymorphisms in the heterogeneous human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein may have an impact on both sensitivity to entry inhibitors and viral replicative fitness. Of significant interest is variation in the V3 crown due to its involvement in direct engagement with the coreceptor. Two positions in the crown (318 and 319) appear to be important in determining intrinsic susceptibility to multiple entry inhibitors. Thus, we evaluated a series of natural polymorphisms at positions 318 and 319 in three distinct CCR5-tropic envelope genetic backgrounds to address their role in replicative fitness and sensitivity to entry inhibitors. Change at position 319 to each of the three major consensus amino acids (A, T, and R) resulted in variation in sensitivity to entry inhibitors and altered replicative fitness, but the effects of any one amino acid depended on the envelope context. Change of the nearly invariant tyrosine at position 318 to a rare arginine resulted in increased sensitivity to entry inhibitors and decreased replicative fitness independent of envelope context. Polymorphisms in the V3 crown that showed increased susceptibility to entry inhibitors also exhibited decreased entry efficiency, replicative fitness in primary peripheral blood mononuclear cells, and ability to replicate in primary macrophages. These findings suggest that differences in coreceptor affinity and/or avidity may underlie these phenotypic characteristics.
Full-text · Article · Sep 2007 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Fitness is a parameter used to quantify how well an organism adapts to its environment; in the present study, fitness is a measure of how well strains of human immunodeficiency virus type 1 (HIV-1) replicate in tissue culture. When HIV-1 develops resistance in vitro or in vivo to antiretroviral drugs such as reverse transcriptase or protease inhibitors, its fitness is often impaired. Here, we have investigated whether the development of resistance in vitro to a small molecule CCR5 inhibitor, AD101, has an associated fitness cost. To do this, we developed a growth-competition assay involving dual infections with molecularly cloned viruses that are essentially isogenic outside the env genes under study. Real-time TaqMan quantitative PCR (QPCR) was used to quantify each competing virus individually via probes specific to different, phenotypically silent target sequences engineered within their vif genes. Head-to-head competition assays of env clones derived from the AD101 escape mutant isolate, the inhibitor-sensitive parental virus, and a passage control virus showed that AD101 resistance was not associated with a fitness loss. This observation is consistent with the retention of the resistant phenotype when the escape mutant was cultured for a total of 20 passages in the absence of the selecting compound. Amino acid substitutions in the V3 region of gp120 that confer complete AD101 resistance cause a fitness loss when introduced into an AD101-sensitive, parental clone; however, in the resistant isolate, changes elsewhere in env that occurred prior to the substitutions within V3 appear to compensate for the adverse effect of the V3 changes on replicative capacity. These in vitro studies may have implications for the development and management of resistance to other CCR5 inhibitors that are being evaluated clinically for the treatment of HIV-1 infection.
[Show abstract][Hide abstract] ABSTRACT: Human immunodeficiency virus type 1 (HIV-1) infection can be inhibited by small molecules that target the CCR5 coreceptor. Here, we describe some properties of clonal viruses resistant to one such inhibitor, SCH-D, using both chimeric, infectious molecular clones and Env-pseudotypes. Studies using combinations of CCR5 ligands, including small molecule inhibitors, monoclonal antibodies (MAbs) and chemokine derivatives such as PSC-RANTES, show that the fully SCH-D-resistant viruses enter target cells by using the SCH-D-bound form of CCR5. However, the way resistance to SCH-D and other small molecule CCR5 inhibitors is manifested depends on the target cell and the nature of the assay (single- vs. multi-cycle). In multi-cycle assays using primary lymphocytes, SCH-D does not inhibit resistant molecular clones, and it can even enhance their infectivity modestly. In contrast, the same viruses (as Env-pseudotypes) are significantly inhibited by SCH-D in single-cycle entry assays using U87-CD4/CCR5 cells, resistance being manifested by incomplete inhibition at high SCH-D concentrations. When a single-cycle, Env-pseudotype entry assay was performed using either U87-CD4/CCR5 cells or PBMC under comparable conditions, entry was inhibited by up to 88% in the former cells but by only 28% in the PBMC. Hence, there are both cell- and assay-dependent influences on how resistance is manifested. We also take this opportunity to correct our previous report that SCH-D-resistant isolates are also substantially cross-resistant to PSC-RANTES [Marozsan, A.J., Kuhmann, S.E., Morgan, T., Herrera, C., Rivera-Troche, E., Xu, S., Baroudy, B.M., Strizki, J., Moore, J.P., 2005. Generation and properties of a human immunodeficiency virus type 1 isolate resistant to the small molecule CCR5 inhibitor, SCH-417690 (SCH-D). Virology 338 (1), 182-199]. A substantial element of this resistance was attributable to the unappreciated carry-over of SCH-D from the selection cultures into analytical assays.
[Show abstract][Hide abstract] ABSTRACT: We describe the generation of two genetically related human immunodeficiency virus type 1 (HIV-1) isolates highly (>20,000-fold) resistant to the small molecule CCR5 inhibitor, SCH-417690 (formerly SCH-D). Both viruses were cross-resistant to other small molecules targeting entry via CCR5, but they were inhibited by some MAbs against the same coreceptor on primary CD4+ T-cells. The resistant isolates remained sensitive to inhibitors of other stages of virus entry, and to replication inhibitors acting post-entry. Neither escape mutant could replicate detectably in peripheral blood mononuclear cells (PBMC) from two donors homozygous for the CCR5-Delta32 allele and both were insensitive to the CXCR4-specific inhibitor, AMD3100. Hence, the SCH-D escape mutants retained the R5 phenotype. One of the resistant isolates was, however, capable of replication in U87.CD4.CXCR4 cells and, after expansion in those cells, was sensitive to AMD3100 in primary CD4+ T-cells. Hence, some X4 variants may be present in this escape mutant swarm. A notable observation was that the SCH-D escape mutants were also cross-resistant to PSC-RANTES and AOP-RANTES, chemokine derivatives that are reported to down-regulate cell surface CCR5 almost completely. However, the extent to which CCR5 is down-regulated was dependent upon the detection MAb. Hence, the escape mutants may be using a CCR5 configuration that is only detected by some anti-CCR5 MAbs. Finally, two SCH-D-resistant clonal viruses revealed no amino acid changes in the gp120 V3 region relative to the parental viruses, in marked contrast to clones resistant to the AD101 small molecule CCR5 inhibitor that possess 4 such sequence changes. Several sequence changes elsewhere in gp120 (V2, C3 and V4) were present in the SCH-D-resistant clones. Their influence on the resistant phenotype remains to be determined.
[Show abstract][Hide abstract] ABSTRACT: The ability of one primary human immunodeficiency virus type 1 (HIV-1) isolate to outcompete another in primary CD4+ human lymphoid cells appears to be mediated by the efficiency of host cell entry. This study was designed to test the role
of entry on fitness of wild-type HIV-1 isolates (e.g., replicative capacity) and to examine the mechanism(s) involved in differential
entry efficiency. The gp120 coding regions of two diverse HIV-1 isolates (the more-fit subtype B strain, B5-91US056, and less-fit
C strain, C5-97ZA003) were cloned into a neutral HIV-1 backbone by using a recently described yeast cloning technique. The
fitness of the primary B5 HIV-1 isolates and its env gene cloned into the NL4-3 laboratory strain had similar fitness, and both were more fit than the C5 primary isolate and
its env/NL4-3 chimeric counterpart. Increased fitness of the B5 over C5 virus was mediated by the gp120 coding region of the env gene. An increase in binding/fusion, as well as decreased sensitivity to entry inhibitors (PSC-RANTES and T-20), was observed
in cell fusion assays mediated by B5 gp120 compared to C5 gp120. Competitive binding assays using a novel whole virus-cell
system indicate that the primary or chimeric B5 had a higher avidity for CD4/CCR5 on host cells than the C5 counterpart. This
increased avidity of an HIV-1 isolate for its cell receptors may be a significant factor influencing overall replicative capacity
Full-text · Article · Jul 2005 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Protease inhibitors (PIs) block HIV-1 maturation into an infectious virus particle by inhibiting the protease processing of gag and gag-pol precursor proteins. We have used a simple anti-HIV-1 p24 Western blot to monitor the processing of p55gag precursor into the mature p24 capsid immediately following the first dosage of a PI-containing treatment regimen. Evidence of PI activity was observed in plasma virus as early as 72 hours post treatment-initiation and was predictive of plasma viral RNA decrease at 4 weeks.
Full-text · Article · May 2005 · AIDS Research and Therapy
[Show abstract][Hide abstract] ABSTRACT: Differential phenotypes or properties of HIV-1 gene products in primary virus isolates are difficult to assess due to interference by the high degree of sequence variation across the entire genome. Thus, chimeric viruses provide a powerful tool to study the function of single gene products or genetic elements in the context of a neutral viral genomic backbone. In this chapter, we describe how to produce HIV-1 chimeric viruses utilizing a yeast-based homologous recombination cloning technique to insert env sequences first into a yeast cloning vector and then into the common pNL4-3 virus backbone. This technique is not limited to the env gene, but can be used to build chimeric viruses with any HIV-1 gene or genetic element. This cloning technique involves the use of a shuttle vector that can replicate in yeast and bacterial cells. Along with acting as a shuttle vector for subsequent subcloning into pNL4-3, this construct pRec/env can also be used to express to the env gene product, gp120/gp41, on the surface of mammalian cells. The chimeric viruses produced by this cloning method are capable of undergoing multiple rounds of replication and are therefore very useful to study drug sensitivity, coreceptor usage, and viral fitness as influenced by a single gene or gene fragment of a primary HIV-1 isolate from any group M subtype.
No preview · Article · Feb 2005 · Methods in Molecular Biology