Immunization with HIV-1 trimeric SOSIP.664 BG505 or founder virus C (FVCEnv) covalently complexed to two-domain CD4S60C elicits cross-clade neutralizing antibodies in New Zealand white rabbits.

Background: An ongoing challenge in HIV-1 vaccine research is finding a novel HIV-1 envelope glycoprotein (Env)-based immunogen that elicits broadly cross-neutralizing antibodies (bnAbs) without requiring complex sequential immunization regimens to drive the required antibody affinity maturation. Previous vaccination studies have shown monomeric Env and Env trimers which contain the GCN4 leucine zipper trimerization domain and are covalently bound to the first two domains of CD4 (2dCD4S60C) generate potent bnAbs in small animals. Since SOSIP.664 trimers are considered the most accurate, conformationally intact representation of HIV-1 Env generated to date, this study further evaluated the immunogenicity of SOSIP.664 HIV Env trimers (the well characterized BG505 and FVCEnv) covalently complexed to 2dCD4S60C. Methods: Recombinant BG505 SOSIP.664 and FVCEnv SOSIP.664 were expressed in mammalian cells, purified, covalently coupled to 2dCD4S60C and antigenically characterized for their interaction with HIV-1 bnAbs. The immunogenicity of BG505 SOSIP.664-2dCD4S60C and FVCEnv SOSIP.664-2dCD4S60C was investigated in New Zealand white rabbits and compared to unliganded FVCEnv and 2dCD4S60C. Rabbit sera were tested for the presence of neutralizing antibodies against a panel of 17 pseudoviruses. Results: Both BG505 SOSIP.664-2dCD4S60C and FVCEnv SOSIP.664-2dCD4S60C elicited a potent, HIV-specific response in rabbits with antibodies having considerable potency and breadth (70.5% and 76%, respectively) when tested against a global panel of 17 pseudoviruses mainly composed of harder-to-neutralize multiple clade tier-2 pseudoviruses. Conclusion: BG505 SOSIP.664-2dCD4S60C and FVCEnvSOSIP.664-2dCD4S60C are highly immunogenic and elicit potent, broadly neutralizing antibodies, the extent of which has never been reported previously for SOSIP.664 trimers. Adding to our previous results, the ability to consistently elicit these types of potent, cross-neutralizing antibody responses is dependent on novel epitopes exposed following the covalent binding of Env (independent of sequence and conformation) to 2dCD4S60C. These findings justify further investment into research exploring modified open, CD4-bound Env conformations as novel vaccine immunogens.

Covalent binding of human two-domain CD4 to an HIV-1 subtype C SOSIP.664 trimer modulates its structural dynamics.

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) mediates host cell infection by binding to the cellular receptor CD4. Recombinant Env bound to CD4 has been explored for its potential as an HIV vaccine immunogen as receptor binding exposes otherwise shielded, conserved functional sites. Previous preclinical studies showed an interchain disulphide linkage facilitated between Env and 2dCD4S60C generates an immunogenic complex that elicits potent, broadly neutralizing antibodies (bNAbs) against clinically relevant HIV-1. This study investigated conformational dynamics of 2dCD4WT and 2dCD4S60C bound to an HIV-1C SOSIP.664 Env trimer using hydrogen-deuterium exchange mass spectrometry. The Env:2dCD4S60C complex maintains key contact residues required for MHCII and Env/gp120 binding and the residues encompassing Ibalizumab's epitope. Important residues remaining anchored, with an increased flexibility in surrounding regions, evidenced by the higher exchange seen in flanking residues compared to Env:2dCD4WT. While changes in Env:2dCD4S60C dynamics in domain 1 were moderate, domain 2 exhibited greater variation. Lack of stability-inducing H-bonds in these allosteric sites suggest the improved immunogenicity of Env:2dCD4S60C result from exposed CD4 residues providing diverse/novel antigenic targets for the development of potent, broadly neutralizing Ibalizumab-like antibodies.

Immune activation correlates with and predicts CXCR4 co-receptor tropism switch in HIV-1 infection.

HIV-1 cell entry is mediated by binding to the CD4-receptor and chemokine co-receptors CCR5 (R5) or CXCR4 (X4). R5-tropic viruses are predominantly detected during early infection. A switch to X4-tropism often occurs during the course of infection. X4-tropism switching is strongly associated with accelerated disease progression and jeopardizes CCR5-based HIV-1 cure strategies. It is unclear whether host immunological factors play a causative role in tropism switching. We investigated the relationship between immunological factors and X4-tropism in a cross-sectional study in HIV-1 subtype C (HIV-1C)-infected patients and in a longitudinal HIV-1 subtype B (HIV-1B) seroconverter cohort. Principal component analysis identified a cluster of immunological markers (%HLA-DR+ CD4+ T-cells, %CD38+HLA-DR+ CD4+ T-cells, %CD38+HLA-DR+ CD8+ T-cells, %CD70+ CD4+ T-cells, %CD169+ monocytes, and absolute CD4+ T-cell count) in HIV-1C patients that was independently associated with X4-tropism (aOR 1.044, 95% CI 1.003-1.087, p = 0.0392). Analysis of individual cluster contributors revealed strong correlations of two markers of T-cell activation (%HLA-DR+ CD4+ T-cells, %HLA-DR+CD38+ CD4+ T-cells) with X4-tropism, both in HIV-1C patients (p = 0.01;p = 0.03) and HIV-1B patients (p = 0.0003;p = 0.0001). Follow-up data from HIV-1B patients subsequently revealed that T-cell activation precedes and independently predicts X4-tropism switching (aHR 1.186, 95% CI 1.065-1.321, p = 0.002), providing novel insights into HIV-1 pathogenesis and CCR5-based curative strategies.

HIV Drug Resistance in Adults Receiving Early vs. Delayed Antiretroviral Therapy: HPTN 052.

INTRODUCTION: We evaluated HIV drug resistance in adults who received early vs. delayed antiretroviral therapy (ART) in a multinational trial [HIV Prevention Trials Network (HPTN) 052, enrollment 2005-2010]. In HPTN 052, 1763 index participants were randomized to start ART at a CD4 cell count of 350-550 cells/mm (early ART arm) or <250 cells/mm (delayed ART arm). In May 2011, interim study results showed benefit of early ART, and all participants were offered ART regardless of CD4 cell count; the study ended in 2015. METHODS: Virologic failure was defined as 2 consecutive viral loads >1000 copies/mL >24 weeks after ART initiation. Drug resistance testing was performed for pretreatment (baseline) and failure samples from participants with virologic failure. RESULTS: HIV genotyping results were obtained for 211/249 participants (128 early ART arm and 83 delayed ART arm) with virologic failure. Drug resistance was detected in 4.7% of participants at baseline; 35.5% had new resistance at failure. In univariate analysis, the frequency of new resistance at failure was lower among participants in the early ART arm (compared with delayed ART arm, P = 0.06; compared with delayed ART arm with ART initiation before May 2011, P = 0.032). In multivariate analysis, higher baseline viral load (P = 0.0008) and ART regimen (efavirenz/lamivudine/zidovudine compared with other regimens, P = 0.024) were independently associated with higher risk of new resistance at failure. CONCLUSIONS: In HPTN 052, the frequency of new drug resistance at virologic failure was lower in adults with early ART initiation. The main factor associated with reduced drug resistance with early ART was lower baseline viral load.

Molecular characterisation of rifampicin-resistant Mycobacterium tuberculosis strains from Malawi.

BACKGROUND: Availability and access to the detection of resistance to anti-tuberculosis drugs remains a significant challenge in Malawi due to limited diagnostic services. The Xpert® MTB/RIF can detect Mycobacterium tuberculosis and resistance to rifampicin in a single, rapid assay. Rifampicin-resistant M. tuberculosis has not been well studied in Malawi. OBJECTIVES: We aimed to determine mutations in the rifampicin resistance determining region (RRDR) of the rpoB gene of M. tuberculosis strains which were defined as resistant to rifampicin by the Xpert MTB/RIF assay. METHODS: Rifampicin-resistant isolates from 43 adult patients (≥ 18 years) from various districts of Malawi were characterised for mutations in the RRDR (codons 507-533) of the rpoB gene by DNA sequencing. RESULTS: Mutations were found in 37/43 (86%) of the resistant isolates in codons 511, 512, 513, 516, 522, 526 and 531. The most common mutations were in codons 526 (38%), 531 (29.7%) and 516 (16.2%). Mutations were not found in 6/43 (14%) of the resistant isolates. No novel rpoB mutations other than those previously described were found among the rifampicin-resistant M. tuberculosis complex strains. CONCLUSION: This study is the first to characterise rifampicin resistance in Malawi. The chain-termination DNA sequencing employed in this study is a standard method for the determination of nucleotide sequences and can be used to confirm rifampicin resistance obtained using other assays, including the Xpert MTB/RIF. Further molecular cluster analysis, such as spoligotyping and DNA finger printing, is still required to determine transmission dynamics and the epidemiological link of the mutated strains.

Moderate Levels of Pre-Treatment HIV-1 Antiretroviral Drug Resistance Detected in the First South African National Survey.

BACKGROUND: In order to assess the level of transmitted and/or pre-treatment antiretroviral drug resistance to HIV-1, the World Health Organization (WHO) recommends that regular surveys are conducted. This study's objective was to assess the frequency of HIV-1 antiretroviral drug resistance in patients initiating antiretroviral treatment (ART) in the public sector throughout South Africa. METHODS: A prospective cross-sectional survey was conducted using probability proportional to size sampling. This method ensured that samples from each province were proportionally collected, based on the number of patients receiving ART in each region. Samples were collected between March 2013 and October 2014. Pol sequences were obtained using RT-PCR and Sanger sequencing and submitted to the Stanford Calibrated Population Resistance tool v6.0. RESULTS: A total of 277 sequences were available for analysis. Most participants were female (58.8%) and the median age was 34 years (IQR: 29-42). The median baseline CD4-count was 149 cells/mm3 (IQR: 62-249) and, based on self-reporting, participants had been diagnosed as HIV-positive approximately 44 days prior to sample collection (IQR: 23-179). Subtyping revealed that 98.2% were infected with HIV-1 subtype C. Overall, 25 out of 277 patients presented with ≥1 surveillance drug resistance mutation (SDRM, 9.0%, 95% CI: 6.1-13.0%). Non-nucleoside reverse transcriptase inhibitor (NNRTI) mutations were the most numerous mutations detected (n = 23). Only two patients presented with a protease inhibitor (PI) mutation. In four patients ≥4 SDRMs were detected, which might indicate that these patients were not truly ART-naïve or were infected with a multi-resistant virus. CONCLUSIONS: These results show that the level of antiretroviral drug resistance in ART-naïve South Africans has reached moderate levels, as per the WHO classification. Therefore, regular surveys of pre-treatment drug resistance levels in all regions of South Africa is highly recommended to monitor the changing levels of pre-treatment antiretroviral drug resistance.

Design, Synthesis, and Biological Evaluation of 1,2-Dihydroisoquinolines as HIV-1 Integrase Inhibitors.

6-Endo-dig-cyclization is an efficient method for the synthesis of 1,2-dihydroisoquinolines. We have synthesized few 1,2-dihydroisoquinolines having different functionality at the C-1, C-3, C-7, and N-2 positions for evaluation against HIV-1 integrase (HIV1-IN) inhibitory activity. A direct nitro-Mannich condensation of o-alkynylaldimines and dual activation of o-alkynyl aldehydes by inexpensive cobalt chloride yielded desired compounds. Out of 24 compounds, 4m and 6c came out as potent integrase inhibitors in in vitro strand transfer (ST) assay, with IC50 value of 0.7 and 0.8 µM, respectively. Molecular docking of these compounds in integrase revealed strong interaction between metal and ligands, which stabilizes the enzyme-inhibitor complex. The ten most active compounds were subjected to antiviral assay. Out of those, 6c reduced the level of p24 viral antigen by 91%, which is comparable to RAL in antiviral assay. Interestingly, these compounds showed similar ST inhibitory activity in G140S mutant, suggesting they can act against resistant strains.

Env-2dCD4 S60C complexes act as super immunogens and elicit potent, broadly neutralizing antibodies against clinically relevant human immunodeficiency virus type 1 (HIV-1).

The ability to induce a broadly neutralizing antibody (bNAb) response following vaccination is regarded as a crucial aspect in developing an effective vaccine against human immunodeficiency virus type 1 (HIV-1). The bNAbs target the HIV-1 envelope glycoprotein (Env) which is exposed on the virus surface, thereby preventing cell entry. To date, conventional vaccine approaches such as the use of Env-based immunogens have been unsuccessful. We expressed, purified, characterized and evaluated the immunogenicity of several unique HIV-1 subtype C Env immunogens in small animals. Here we report that vaccine immunogens based on Env liganded to a two domain CD4 variant, 2dCD4(S60C) are capable of consistently eliciting potent, broadly neutralizing antibody responses in New Zealand white rabbits against a panel of clinically relevant HIV-1 pseudoviruses. This was irrespective of the Env protein subtype and context. Importantly, depletion of the anti-CD4 antibodies appeared to abrogate the neutralization activity in the rabbit sera. Taken together, this data suggests that the Env-2dCD4(S60C) complexes described here are "super" immunogens, and potentially immunofocus antibody responses to a unique epitope spanning the 2dCD4(60C). Recent data from the two available anti-CD4 monoclonal antibodies, Ibalizumab and CD4-Ig (and bispecific variants thereof) have highlighted that the use of these broad and potent entry inhibitors could circumvent the need for a conventional vaccine targeting HIV-1. Overall, the ability of the unique Env-2dCD4(S60C) complexes to elicit potent bNAb responses has not been described previously, reinforcing that further investigation for their utility in preventing and controlling HIV-1/SIV infection is warranted.

Functional roles of HIV-1 Vpu and CD74: Details and implications of the Vpu-CD74 interaction.

HIV-1 Vpu has a variety of functions, including CD4 degradation and the downregulation of MHCII. Downregulation of the MHCII occurs through Vpu binding to the cytoplasmic domain of CD74, the chaperone for antigen presentation. The CD74 cytoplasmic domain also plays a vital role in cell signaling through the activation of an NF-κB signal cascade for the maturation, proliferation and survival of B cells as well as by binding the macrophage inhibitory factor. In view of these functions, it follows that the Vpu-CD74 interaction has multiple downstream consequences for the immune system as it not only impairs foreign antigen presentation but may also have an effect on signal transduction cascades. It is thought that Vpu specifically targets intracellular CD74 while other HIV-1 proteins cannot. Therefore, this protein-protein interaction would be a potential drug target in order to reduce viral persistence. We review the functional importance and specific binding site of Vpu and CD74.

High prevalence of the K65R mutation in HIV-1 subtype C infected patients failing tenofovir-based first-line regimens in South Africa.

BACKGROUND: Tenofovir (TDF) has replaced stavudine (d4T) as the preferred nucleoside reverse transcriptase inhibitor (NRTI) in first-line regimens in South Africa, but limited information is available on the resistance patterns that develop after the introduction of TDF. This study investigated the antiretroviral drug resistance patterns in South African HIV-1 subtype C-infected patients failing stavudine- (d4T) and tenofovir- (TDF) based first-line regimens and assess the suitability of TDF as the preferred first-line nucleotide reverse transcriptase inhibitor (NRTI). METHODS: Resistance patterns of HIV-1 from 160 adult patients virologically failing TDF- (n = 80) and d4T- (n = 80) based first-line regimens were retrospectively analyzed. The pol gene was sequenced using an in-house protocol and mutations were analysed using the IAS-USA 2014 Drug Resistance Mutation list. RESULTS: Compared to d4T-exposed patients (n = 7), patients failing on a TDF-containing regimen (n = 43) were almost 5 times more likely to present with a K65R mutation (aRR 4.86 95% CI 2.29 - 10.34). Y115F was absent in the d4T group, and detected in 13.8% (n = 11) of TDF-exposed patients, p = 0.0007. Virus from 9 of the 11 patients (82.0%) who developed the Y115F mutation also developed K65R. Intermediate or high-level resistance to most NRTIs was common in the TDF-treatment group, but these patients twice more likely to remain susceptible to AZT as compared to those exposed to d4T (aRR 2.09 95% CI 1.13 - 3.90). CONCLUSION: The frequency of the TDF induced K65R mutation was higher in our setting compared to non-subtype C dominated countries. However, despite the higher frequency of cross-resistance to NRTIs, most patients remained susceptible to AZT, which is reflected in the South African treatment guidelines that recommend AZT as an essential component of second-line regimens.

The evaluation of statins as potential inhibitors of the LEDGF/p75-HIV-1 integrase interaction.

Lovastatin was identified through virtual screening as a potential inhibitor of the LEDGF/p75-HIV-1 integrase interaction. In an AlphaScreen assay, lovastatin inhibited the purified recombinant protein-protein interaction (IC50 = 1.97 ± 0.45 µm) more effectively than seven other tested statins. None of the eight statins, however, yielded antiviral activity in vitro, while only pravastatin lactone yielded detectable inhibition of HIV-1 integrase strand transfer activity (31.65% at 100 µm). A correlation between lipophilicity and increased cellular toxicity of the statins was observed.

Generation and characterization of an HIV-1 subtype C transmitted and early founder virus consensus sequence.

The tight bottleneck during HIV-1 transmission generally results in only a single virus variant being transmitted. Investigation of the HIV-1 envelope glycoprotein (Env) can identify vulnerabilities of transmitting viruses that can be targeted by vaccines designed to elicit protection against global HIV-1. This study generated an HIV-1 subtype C consensus transmitted and early founder virus Env (EnvFVC) after detailed sequence analysis of 1,894 env genes obtained from 80 acutely infected individuals from South Africa, Malawi, and Zambia. The inferred EnvFVC sequence incorporates characteristics of transmitted and early founder viruses and results in the expression of a functional and conformationally intact Env. Overall, the "subtype-based" or "region-based" EnvFVC described here can be used in the development of a useful immunogen for novel vaccine design.

High-level cross-resistance to didanosine observed in South African children failing an abacavir- or stavudine-based 1st-line regimen.

BACKGROUND: The knowledge-base of emerging drug resistance profiles in children exposed to abacavir-based antiretroviral regimens in South Africa is very limited. This study investigated the suitability of didanosine-based 2nd-line regimens for children in the context of antiretroviral drug resistance patterns emerging after 1st-line virologic failure. METHODS: A retrospective dataset of 354 antiretroviral drug resistant genotypes from children failing either abacavir (n = 81) or stavudine (n = 273) based 1st-line regimens, was analysed. Samples were sent to the HIV genotyping laboratory at Charlotte Maxeke Johannesburg Academic Hospital, for routine testing. Pol sequences were submitted to the Stanford HIV drug resistance database for genotypic predictions. RESULTS: Children were exposed to abacavir or stavudine-based 1st-line regimens for an average of 21 and 36 months, respectively. The frequency of reduced susceptibility to didanosine was substantial in the abacavir-exposed group (69.1%).This reduced susceptibility was commonly attributed to L74V/I (n = 44) and to a lesser extent K65R (n = 10) mutations. Didanosine resistance was observed in 43.2% of patients exposed to stavudine-based regimens. In contrast, most children remained susceptible to stavudine regardless of exposure to abacavir (77.8%) or stavudine (74.7%). At least 80% of children remained susceptible to zidovudine irrespective of stavudine or abacavir-exposure. The presence of the K65R mutation was more common after abacavir pressure (12.3% vs 1.8%). CONCLUSION: Analysis revealed that didanosine-based 2nd-line regimens have limitations for South African children, given the high frequency of mutations that confer cross-resistance to didanosine; especially after abacavir-exposure. This data has influenced South African paediatric treatment guidelines, which now recommend zidovudine-based 2nd-line regimens.

Viral tropism and antiretroviral drug resistance in HIV-1 subtype C-infected patients failing highly active antiretroviral therapy in Johannesburg, South Africa.

Reports show that up to 30% of antiretroviral drug-naive patients in Johannesburg have CXCR4-utilizing HIV-1 subtype C. We assessed whether HIV-1 subtype C-infected individuals failing highly active antiretroviral therapy (HAART) have a higher proportion of CXCR4-utilizing viruses compared to antiretroviral drug-naive patients. The V3 loop was sequenced from plasma from 100 randomly selected HAART-failing patients, and tropism was established using predictive algorithms. All patients harbored HIV-1 subtype C with at least one antiretroviral drug resistance mutation. Viral tropism prediction in individuals failing HAART revealed similar proportions (29%) of X4-utilizing viruses compared to antiretroviral drug-naive patients (30%). Findings are in contrast to reports from Durban in which 60% of HAART-failing subjects harbored X4/dual/mixed-tropic viruses. Despite differences in proportions of X4-tropism within South Africa, the high proportion of thymidine analogue mutations (TAMs) and CXCR4-utilizing HIV-1 highlights the need for intensified monitoring of HAART patients and the predicament of diminishing drug options, including CCR5 antagonists, for patients failing therapy.

HIV-1 phenotypic reverse transcriptase inhibitor drug resistance test interpretation is not dependent on the subtype of the virus backbone.

To date, the majority of HIV-1 phenotypic resistance testing has been performed with subtype B virus backbones (e.g. HXB2). However, the relevance of using this backbone to determine resistance in non-subtype B HIV-1 viruses still needs to be assessed. From 114 HIV-1 subtype C clinical samples (36 ARV-naïve, 78 ARV-exposed), pol amplicons were produced and analyzed for phenotypic resistance using both a subtype B- and C-backbone in which the pol fragment was deleted. Phenotypic resistance was assessed in resulting recombinant virus stocks (RVS) for a series of antiretroviral drugs (ARV's) and expressed as fold change (FC), yielding 1660 FC comparisons. These Antivirogram® derived FC values were categorized as having resistant or sensitive susceptibility based on biological cut-off values (BCOs). The concordance between resistance calls obtained for the same clinical sample but derived from two different backbones (i.e. B and C) accounted for 86.1% (1429/1660) of the FC comparisons. However, when taking the assay variability into account, 95.8% (1590/1660) of the phenotypic data could be considered as being concordant with respect to their resistance call. No difference in the capacity to detect resistance associated with M184V, K103N and V106M mutations was noted between the two backbones. The following was concluded: (i) A high level of concordance was shown between the two backbone phenotypic resistance profiles; (ii) Assay variability is largely responsible for discordant results (i.e. for FC values close to BCO); (iii) Confidence intervals should be given around the BCO's, when assessing resistance in HIV-1 subtype C; (iv) No systematic resistance under- or overcalling of subtype C amplicons in the B-backbone was observed; (v) Virus backbone subtype sequence variability outside the pol region does not contribute to phenotypic FC values. In conclusion the HXB2 virus backbone remains an acceptable vector for phenotyping HIV-1 subtype C pol amplicons.

Natural killer cells that respond to human immunodeficiency virus type 1 (HIV­1) peptides are associated with control of HIV­1 infection.

Human immunodeficiency virus (HIV)-specific natural killer (CD3- cells), CD4, and CD8 T cellular responses were determined in 79 HIV­1-infected women in response to HIV­1 peptide pools (Gag, Pol, Nef, Reg, and Env) with use of a whole­blood intracellular cytokine staining assay that measures interferon-γ and/or interleukin-2. HIV­specific CD3- cell responses to any region (Env and Reg predominantly targeted) were associated with lower viral load (P = .031) and higher CD4 T cell count (P = .015). Env­specific CD3- cell responses were stronger in women who had both Gag CD4 and CD8 T cell responses and, in turn, was associated with lower viral load (P = .005). CD3- cell responders had significantly higher representation of CD4 T cell responses to Env and Reg (P = .012 and P = .015, respectively) and higher magnitudes of CD4 T cell responses (P = .017 and P = .037, respectively) than did nonresponders. Peptide­specific natural killer cells are associated with markers of less severe disease progression among HIV­1-infected women (lower viral load and higher CD4 T cell count) and with stronger HIV­specific T cell responses.

Stabilization of HIV-1 gp120-CD4 receptor complex through targeted interchain disulfide exchange.

HIV-1 enters cells via interaction between the trimeric envelope (Env) glycoprotein gp120/gp41 and the host cell surface receptor molecule CD4. The requirement of CD4 for viral entry has rationalized the development of recombinant CD4-based proteins as competitive viral attachment inhibitors and immunotherapeutic agents. In this study, we describe a novel recombinant CD4 protein designed to bind gp120 through a targeted disulfide-exchange mechanism. According to structural models of the gp120-CD4 receptor complex, substitution of Ser(60) on the CD4 domain 1 alpha-helix with Cys positions a thiol in proximity of the gp120 V1/V2 loop disulfide (Cys(126)-Cys(196)), satisfying the stereochemical and geometric conditions for redox exchange between CD4 Cys(60) and gp120 Cys(126), and the consequent formation of an interchain disulfide bond. In this study, we provide experimental evidence for this effect by describing the expression, purification, refolding, receptor binding and antiviral activity analysis of a recombinant two-domain CD4 variant containing the S60C mutation (2dCD4-S60C). We show that 2dCD4-S60C binds HIV-1 gp120 with a significantly higher affinity than wild-type protein under conditions that facilitate disulfide exchange and that this translates into a corresponding increase in the efficacy of CD4-mediated viral entry inhibition. We propose that targeted redox exchange between conserved gp120 disulfides and nucleophilic moieties positioned strategically on CD4 (or CD4-like scaffolds) conceptualizes a new strategy in the development of high affinity HIV-1 Env ligands, with important implications for therapy and vaccine development. More generally, this chalcogen substitution approach provides a general means of stabilizing receptor-ligand complexes where the structural and biophysical conditions for disulfide exchange are satisfied.

Characterization of HIV type 1 genetic diversity among South African participants enrolled in the AIDS Vaccine Integrated Project (AVIP) study.

The genetic diversity of HIV-1 strains circulating among HIV-1-infected South Africans was investigated in a cohort of 420 individuals enrolled as part of the AIDS Vaccine Integrated Project (AVIP) study. Representative samples (10%) were randomly selected from treatment-naive participants. Viral RNA was extracted for reverse transcriptase-initiated amplification and population-based sequencing of partial pol (encompassing protease and reverse transcriptase) and full-length integrase. Overall, HIV-1 sequences confirmed that 97.1% and 96.9% were HIV-1 subtype C in pol and integrase, respectively. Two participants were infected with unique A1/C and C/A1 recombinants in pol/integrase. Further pol sequence analysis identified mutation patterns associated with high level resistance to NNRTIs in two participants, whereas no primary mutations conferring resistance to integrase inhibitors were detected. The predominance of HIV-1 subtype C in South African populations is therefore confirmed in the AVIP cohort finalized for testing preventive or therapeutic vaccines against HIV-1 infection.