Development of a pseudo-typed virus particle based method to determine the efficacy of virucidal agents

The ongoing Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pandemic has highlighted the threat that viral outbreaks pose to global health. A key tool in the arsenal to prevent and control viral disease outbreaks is disinfection of equipment and surfaces with formulations that contain virucidal agents (VA). However, assessment of the efficacy of virus inactivation often requires live virus assays or surrogate viruses such as Modified Vaccinia Virus Ankara (MVA), which can be expensive, time consuming and technically challenging. Therefore, we have developed a pseudo-typed virus (PV) based approach to assess the inactivation of enveloped viruses with a fast and quantitative output that can be adapted to emerging viruses. Additionally, we have developed a method to completely remove the cytotoxicity of virucidal agents while retaining the required sensitivity to measure PV infectivity. Our results indicated that the removal of cytotoxicity was an essential step to accurately measure virus inactivation. Further, we demonstrated that there was no difference in susceptibility to virus inactivation between PVs that express the envelopes of HIV-1, SARS-CoV-2, and Influenza A/Indonesia. Therefore, we have developed an effective and safe alternative to live virus assays that enables the rapid assessment of virucidal activity for the development and optimization of virucidal reagents.

Quantifying neutralising antibody responses against SARS-CoV-2 in dried blood spots (DBS) and paired sera

The ongoing SARS-CoV-2 pandemic was initially managed by non-pharmaceutical interventions such as diagnostic testing, isolation of positive cases, physical distancing and lockdowns. The advent of vaccines has provided crucial protection against SARS-CoV-2. Neutralising antibody (nAb) responses are a key correlate of protection, and therefore measuring nAb responses is essential for monitoring vaccine efficacy. Fingerstick dried blood spots (DBS) are ideal for use in large-scale sero-surveillance because they are inexpensive, offer the option of self-collection and can be transported and stored at ambient temperatures. Such advantages also make DBS appealing to use in resource-limited settings and in potential future pandemics. In this study, nAb responses in sera, venous blood and fingerstick blood stored on filter paper were measured. Samples were collected from SARS-CoV-2 acutely infected individuals, SARS-CoV-2 convalescent individuals and SARS-CoV-2 vaccinated individuals. Good agreement was observed between the nAb responses measured in eluted DBS and paired sera. Stability of nAb responses was also observed in sera stored on filter paper at room temperature for 28 days. Overall, this study provides support for the use of filter paper as a viable sample collection method to study nAb responses.

Glycan dependent phenotype differences of HIV-1 generated from macrophage versus CD4+ T helper cell populations

Human immunodeficiency virus type 1 (HIV-1) is able to infect a variety of cell types with differences in entry efficiency and replication kinetics determined by the host cell type or the viral phenotype. The phenotype of the virus produced from these various cell types, including infectivity, co-receptor usage and neutralisation sensitivity, may also be affected by the characteristics of the producing cell. This can be due to incorporation of variant cell-specific molecules or differences in post-translational modifications of the gp41/120 envelope. In this study we produced genetically identical virus strains from macrophages, CD4-enriched lymphocytes as well as Th1 and Th2 CD4+ cell lines and compared each different virus stock for their infectivity in various cell types and sensitivity to neutralisation. In order to study the effect of the producer host cell on the virus phenotype, virus stocks were normalised on infectivity and were sequenced to confirm env gene homogeneity. Virus production by Th1 or Th2 cells did not compromise infectivity of the variant cell types tested. We observed no difference in sensitivity to co-receptor blocking agents upon viral passage through Th1 and Th2 CD4+ cell lineages nor did this affect DC-SIGN-mediated viral capture as measured in a transfer assay to CD4+ lymphocytes. Virus produced by macrophages was comparably sensitive to CC-chemokine inhibition as was virus generated from the array of CD4+ lymphocytes. We identified that virus produced from macrophages was fourteen times more resistant to 2G12 neutralisation than virus produced from CD4+ lymphocytes. Macrophage-produced dual-tropic (R5/X4) virus was six times more efficiently transmitted to CD4+ cells than lymphocyte-derived HIV-1 (p<0.0001) after DCSIGN capture. These results provide further insights to what extent the host cell influences viral phenotype and thereby various aspects of HIV-1 pathogenesis but suggest that viruses generated from Th1 versus Th2 cells are consistent in phenotype.

The Ecology of Viruses in Urban Rodents with a Focus on SARS-CoV-2

Wild animals are naturally infected with a range of viruses, some of which may be zoonotic for humans. During the human COVID pandemic there was also the possibility of rodents acquiring SARS-CoV-2 from people, so-called reverse zoonoses. To investigate this we sampled rats (Rattus norvegicus) and mice (Apodemus sylvaticus) from urban environments in 2020 during the human COVID-19 pandemic. We metagenomically sequenced lung and gut tissue and faeces for viruses, PCR screened for SARS-CoV-2, and serologically surveyed for anti-SARS-CoV-2 Spike antibodies. We describe the range of viruses that we found in these two rodent species. We found no molecular evidence of SARS-CoV-2 infection, though in rats we found lung antibody responses and evidence of neutralisation ability, that are consistent with rats being exposed to SARS-CoV-2 and / or exposed to other viruses that result in cross-reactive antibodies.

SARS-CoV-2 antibody responses associate with sex, age and disease severity in previously uninfected people admitted to hospital with COVID-19: An ISARIC4C prospective study

The SARS-CoV-2 pandemic enables the analysis of immune responses induced against a novel coronavirus infecting immunologically naïve individuals. This provides an opportunity for analysis of immune responses and associations with age, sex and disease severity. Here we measured an array of solid-phase binding antibody and viral neutralising Ab (nAb) responses in participants (n=337) of the ISARIC4C cohort and characterised their correlation with peak disease severity during acute infection and early convalescence. Overall, the responses in a Double Antigen Binding Assay (DABA) for antibody to the receptor binding domain (anti-RBD) correlated well with IgM as well as IgG responses against viral spike, S1 and nucleocapsid protein (NP) antigens. DABA reactivity also correlated with nAb. As we and others reported previously, there is greater risk of severe disease and death in older men, whilst the sex ratio was found to be equal within each severity grouping in younger people. In older males with severe disease (mean age 68 years), peak antibody levels were found to be delayed by one to two weeks compared with women, and nAb responses were delayed further. Additionally, we demonstrated that solid-phase binding antibody responses reached higher levels in males as measured via DABA and IgM binding against Spike, NP and S1 antigens. In contrast, this was not observed for nAb responses. When measuring SARS-CoV-2 RNA transcripts (as a surrogate for viral shedding) in nasal swabs at recruitment, we saw no significant differences by sex or disease severity status. However, we have shown higher antibody levels associated with low nasal viral RNA indicating a role of antibody responses in controlling viral replication and shedding in the upper airway. In this study, we have shown discernible differences in the humoral immune responses between males and females and these differences associate with age as well as with resultant disease severity.

A Quantitative Method for the Study of HIV-1 and Mycobacterium tuberculosis Coinfection

Mycobacterium tuberculosis and human immunodeficiency virus-1 (HIV-1) syndemic interactions are a major global health concern. Despite the clinical significance of coinfection, our understanding of the cellular pathophysiology and the therapeutic pharmacodynamic impact of coinfection is limited. Here, we use single-round infectious HIV-1 pseudotyped viral particles expressing green fluorescent protein alongside M. tuberculosis expressing mCherry to study pathogenesis and treatment. We report that HIV-1 infection inhibited intracellular replication of M. tuberculosis and demonstrate the therapeutic activity of antiviral treatment (efavirenz) and antimicrobial treatment (rifampicin). The described method could be applied for detailed mechanistic studies to inform the development of novel treatment strategies.

The HCV Envelope Glycoprotein Down-Modulates NF-κB Signalling and Associates With Stimulation of the Host Endoplasmic Reticulum Stress Pathway

Following acute HCV infection, the virus establishes a chronic disease in the majority of patients whilst few individuals clear the infection spontaneously. The precise mechanisms that determine chronic HCV infection or spontaneous clearance are not completely understood but are proposed to be driven by host and viral genetic factors as well as HCV encoded immunomodulatory proteins. Using the HIV-1 LTR as a tool to measure NF-κB activity, we identified that the HCV E1E2 glycoproteins and more so the E2 protein down-modulates HIV-1 LTR activation in 293T, TZM-bl and the more physiologically relevant Huh7 liver derived cell line. We demonstrate this effect is specifically mediated through inhibiting NF-κB binding to the LTR and show that this effect was conserved for all HCV genotypes tested. Transcriptomic analysis of 293T cells expressing the HCV glycoproteins identified E1E2 mediated stimulation of the endoplasmic reticulum (ER) stress response pathway and upregulation of stress response genes such as ATF3. Through shRNA mediated inhibition of ATF3, one of the components, we observed that E1E2 mediated inhibitory effects on HIV-1 LTR activity was alleviated. Our in vitro studies demonstrate that HCV Env glycoprotein activates host ER Stress Pathways known to inhibit NF-κB activity. This has potential implications for understanding HCV induced immune activation as well as oncogenesis.

Measuring Proviral HIV-1 DNA: Hurdles and Improvements to an Assay Monitoring Integration Events Utilising Human Alu Repeat Sequences

Integrated HIV-1 DNA persists despite antiretroviral therapy and can fuel viral rebound following treatment interruption. Hence, methods to specifically measure the integrated HIV-1 DNA portion only are important to monitor the reservoir in eradication trials. Here, we provide an up-to-date overview of the literature on the different approaches used to measure integrated HIV-1 DNA. Further, we propose an implemented standard-curve free assay to quantify integrated HIV-1 DNA, so-called Alu-5LTR PCR, which utilises novel primer combinations. We tested the Alu-5LTR PCR in 20 individuals on suppressive ART for a median of nine years; the results were compared to those produced with the standard-free Alu-gag assay. The numbers of median integrated HIV-1 DNA copies were 5 (range: 1–12) and 14 (5–26) with the Alu-gag and Alu-5LTR, respectively. The ratios between Alu-gag vs Alu-5LTR results were distributed within the cohort as follows: most patients (12/20, 60%) provided ratios between 2–5, with 3/20 (15%) and 5/20 (25%) being below or above this range, respectively. Alu-5LTR assay sensitivity was also determined using an “integrated standard”; the data confirmed the increased sensitivity of the assay, i.e., equal to 0.25 proviruses in 10,000 genomes. This work represents an improvement in the field of measuring proviral HIV-1 DNA that could be employed in future HIV-1 persistence and eradication studies.

Generation of Liposomes to Study the Effect of Mycobacterium Tuberculosis Lipids on HIV-1 cis- and trans-Infections

Tuberculosis (TB) is the leading cause of death among HIV-1-infected individuals and Mycobacterium tuberculosis (Mtb) co-infection is an early precipitate to AIDS. We aimed to determine whether Mtb strains differentially modulate cellular susceptibility to HIV-1 infection (cis- and trans-infection), via surface receptor interaction by their cell envelope lipids. Total lipids from pathogenic (lineage 4 Mtb H37Rv, CDC1551 and lineage 2 Mtb HN878, EU127) and non-pathogenic (Mycobacterium bovis BCG and Mycobacterium smegmatis) Mycobacterium strains were integrated into liposomes mimicking the lipid distribution and antigen accessibility of the mycobacterial cell wall. The resulting liposomes were tested for modulating in vitro HIV-1 cis- and trans-infection of TZM-bl cells using single-cycle infectious virus particles. Mtb glycolipids did not affect HIV-1 direct infection however, trans-infection of both R5 and X4 tropic HIV-1 strains were impaired in the presence of glycolipids from M. bovis, Mtb H37Rv and Mtb EU127 strains when using Raji-DC-SIGN cells or immature and mature dendritic cells (DCs) to capture virus. SL1, PDIM and TDM lipids were identified to be involved in DC-SIGN recognition and impairment of HIV-1 trans-infection. These findings indicate that variant strains of Mtb have differential effect on HIV-1 trans-infection with the potential to influence HIV-1 disease course in co-infected individuals.

Variation around the dominant viral genome sequence contributes to viral load and outcome in patients with Ebola virus disease

BACKGROUND

Viral load is a major contributor to outcome in patients with Ebola virus disease (EVD), with high values leading to a fatal outcome. Evidence from the 2013-2016 Ebola virus (EBOV) outbreak indicated that different genotypes of the virus can have different phenotypes in patients. Additionally, due to the error-prone nature of viral RNA synthesis in an individual patient, the EBOV genome exists around a dominant viral genome sequence. The minor variants within a patient may contribute to the overall phenotype in terms of viral protein function. To investigate the effects of these minor variants, blood samples from patients with acute EVD were deeply sequenced.

RESULTS

We examine the minor variant frequency between patients with acute EVD who survived infection with those who died. Non-synonymous differences in viral proteins were identified that have implications for viral protein function. The greatest frequency of substitution was identified at three codon sites in the L gene-which encodes the viral RNA-dependent RNA polymerase (RdRp). Recapitulating this in an assay for virus replication, these substitutions result in aberrant viral RNA synthesis and correlate with patient outcome.

CONCLUSIONS

Together, these findings support the notion that in patients who survived EVD, in some cases, the genetic variability of the virus resulted in deleterious mutations that affected viral protein function, leading to reduced viral load. Such mutations may also lead to persistent strains of the virus and be associated with recrudescent infections.

Measuring the Success of HIV-1 Cure Strategies

HIV-1 eradication strategies aim to achieve viral remission in the absence of antiretroviral therapy (ART). The development of an HIV-1 cure remains challenging due to the latent reservoir (LR): long-lived CD4 T cells that harbor transcriptionally silent HIV-1 provirus. The LR is stable despite years of suppressive ART and is the source of rebound viremia following therapy interruption. Cure strategies such as "shock and kill" aim to eliminate or reduce the LR by reversing latency, exposing the infected cells to clearance via the immune response or the viral cytopathic effect. Alternative strategies include therapeutic vaccination, which aims to prime the immune response to facilitate control of the virus in the absence of ART. Despite promising advances, these strategies have been unable to significantly reduce the LR or increase the time to viral rebound but have provided invaluable insight in the field of HIV-1 eradication. The development and assessment of an HIV-1 cure requires robust assays that can measure the LR with sufficient sensitivity to detect changes that may occur following treatment. The viral outgrowth assay (VOA) is considered the gold standard method for LR quantification due to its ability to distinguish intact and defective provirus. However, the VOA is time consuming and resource intensive, therefore several alternative assays have been developed to bridge the gap between practicality and accuracy. Whilst a cure for HIV-1 infection remains elusive, recent advances in our understanding of the LR and methods for its eradication have offered renewed hope regarding achieving ART free viral remission.

Bile-salt stimulated lipase polymorphisms do not associate with HCV susceptibility

Bile-salt stimulate lipase (BSSL) is a glycoprotein found in human milk and blood that can potently bind DC-SIGN. The BSSL gene is highly polymorphic with a variant number of O-linked glycosylated 11 amino acid repeats at the C-terminus of the protein, encoded in exon 11 of the gene. It has been shown that certain BSSL genotypes associate with decreased HIV-1 transmission in vitro and decreased HIV-1 disease progression. The protein forms dimers and individuals possessing one high (typically 14-21) and one low (typically 7-11) number of repeat domains has been shown to have stronger binding of BSSL to DC-SIGN and HIV-1 inhibitory activity in vitro. Since we previously demonstrated that SNPs within the DC-SIGN gene can associate with risk of HCV sexual transmission and which can be linked to diminished DC-SIGN gene expression we aimed to identify whether BSSL polymorphisms associated similarly through differential binding to DC-SIGN. DNA was isolated from the HIV-1 infected MSM cohort (MOSAIC) composed of HCV multiple exposed uninfected (MEU) (N = 30) and multiple exposed HCV infected (MEI) (N = 32) individuals and from the Amsterdam cohort studies (ACS) intravenous drug using (IDU) cohort (22 MEI and 40 MEU). The numbers of repeats in exon 11 were determined by PCR with repeat distributions compared between MEI and MEU. No statistical significant difference in the copy number of exon 11 repeats, or combinations of, in the BSSL gene was observed when comparing HCV infected MEI with MEU, thus the exon 11 repeat copy number in the BSSL gene does not affect HCV susceptibility.

Schistosoma mansoni soluble egg antigen (SEA) and recombinant Omega-1 modulate induced CD4+ T-lymphocyte responses and HIV-1 infection in vitro

Parasitic helminths evade, skew and dampen human immune responses through numerous mechanisms. Such effects will likely have consequences for HIV-1 transmission and disease progression. Here we analyzed the effects that soluble egg antigen (SEA) from Schistosoma mansoni had on modulating HIV-1 infection and cytokine/chemokine production in vitro. We determined that SEA, specifically through kappa-5, can potently bind to DC-SIGN and thereby blocks DC-SIGN mediated HIV-1 trans-infection (p<0.05) whilst not interfering with cis-infection. DCs exposed to SEA whilst maturing under Th2 promoting conditions, will upon co-culture with naïve T-cells induce a T-cell population that was less susceptible to HIV-1 R5 infection (p<0.05) compared to DCs unexposed to SEA, whereas HIV-1 X4 virus infection was unaffected. This was not observed for DCs exposed to SEA while maturing under Th1 or Th1/Th2 (T_mix) promoting conditions. All T-cell populations induced by SEA exposed DCs demonstrate a reduced capacity to produce IFN-γ and MIP-1β. The infection profile of T-cells infected with HIV-1 R5 was not associated with down-modulation of CCR5 cell surface expression. We further show that DCs maturing under T_mix conditions exposed to plant recombinant omega-1 protein (rω-1), which demonstrates similar functions to natural ω-1, induced T-cell populations that were less sensitive for HIV-1 R5 infection (p<0.05), but not for X4 virus infection. This inhibition associated again with a reduction in IFN-γ and MIP-1β expression, but additionally correlated with reduced CCR5 expression. We have shown that SEA parasite antigens and more specifically rω-1 can modulate HIV-1 infectivity with the potential to influence disease course in co-infected individuals.

Parasitic helminths have developed a number of strategies to evade, skew and dampen human immune responses. Such effects will likely have consequences for HIV-1 transmission and disease progression. Here we analyzed the effect that soluble egg antigen (SEA) from Schistosoma mansoni had on HIV-1 infection in vitro. We determined that SEA, through kappa-5, can potently block DC-SIGN mediated HIV-1 trans-infection of CD4⁺ T-lymphocytes, but not block cis-infection. Dendritic cells (DC) exposed to SEA during maturation under Th2 skewing conditions, induce T-cell populations that are less susceptible to HIV-1 R5 infection compared to cells induced by unexposed DCs. HIV-1 X4 infection was unaffected. This restricted infection profile was not associated with down-modulation of CCR5 surface expression or observed differences in cytokine/chemokine production. Using recombinant omega-1, an abundant component of SEA, HIV-1 R5 infection was similarly inhibited with no effect on HIV-1 X4 infection levels. Hence SEA possesses antigens, namely omega-1, that can modulate HIV-1 infection and potentially influence disease course in co-infected individuals.

DC-SIGN Polymorphisms Associate with Risk of Hepatitis C Virus Infection Among Men who Have Sex with Men but not Among Injecting Drug Users

We aimed to identify whether genetic polymorphisms within L-SIGN or DC-SIGN correlate with hepatitis C virus (HCV) susceptibility. A men who have sex with men (MSM) and an injecting drug users (IDU) cohort of HCV cases and multiple-exposed uninfected controls were genotyped for numerous L-SIGN and DC-SIGN polymorphisms. DC-SIGN single nucleotide polymorphisms (SNPs) -139, -871, and -939 correlated with HCV acquisition in the MSM cohort only. When the same SNPs were introduced into a transcription activity assay they demonstrated a reduction in expression with predicted alteration in binding of transcription factors. DC-SIGN promoter SNPs correlated with risk of HCV acquisition via sexual but not IDU exposure, likely through modulation of mRNA expression levels.

SNP rs688 within the low-density lipoprotein receptor (LDL-R) gene associates with HCV susceptibility

BACKGROUND & AIMS

Despite high-risk behaviour, 10%-20% of HCV multiple exposed individuals remain uninfected (MEU), whilst the remainder become infected (MEI). We hypothesize that host factors play a role in HCV susceptibility. We aimed to identify polymorphisms in host genes that encode for proteins involved in viral entry: CD81, Scavenger receptor 1 (SR-1), Low-density lipoprotein receptor (LDL-R), Claudin-1 (CLDN1), Occludin (OCLN) and Niemann-Pick C1-like 1 (NPC1L1).

METHODS

Multiple exposed infected and MEU from two observational cohorts were selected. From the MSM study of acute infection with HCV (MOSAIC), HIV-1 infected MEU cases (n = 30) and HIV-1 infected MEI controls (n = 32) were selected based on reported high-risk behaviour. From the Amsterdam Cohorts Studies (ACS) injecting drug users (IDU) cohort, MEU cases (n = 40) and MEI controls (n = 22) were selected who injected drugs for ≥2 years, in the nineties, when HCV incidence was high. Selected single nucleotide polymorphisms (SNPs) were determined by sequencing or SNP assays.

RESULTS

No associations were found for SNPs within genes coding for CD81, SR-1, Claudin-1 or Occludin between the MEU and MEI individuals from either cohort. We did observe a significant association for rs688 within the LDL-R gene with HCV infection (OR: 0.41 P = 0.001), however, LDL cholesterol levels did not vary between individuals carrying the differential SNPs. Additionally, a marginal significant effect was found for rs217434 and rs2072183 (OR: 2.07 P = 0.032 and OR: 1.76 P = 0.039, respectively) within NPC1L1.

CONCLUSIONS

Our results demonstrate that the rs688 SNP within the LDL-R gene associates with HCV susceptibility through mucosal as well as intravenous exposure.

Comparative analysis and generation of a robust HIV-1 DNA quantification assay

HIV-1 infection cannot be cured due to the presence of the latent reservoir (LR). Novel cure or treatment strategies, such as "shock and kill" or therapeutic vaccination, aim to reduce or eradicate the LR. Cure strategies utilise robust DNA quantification assays to measure the change in the LR in low copy scenarios. No standard assay exists, which impedes the reliable comparison of results from different therapy and vaccine trials and HIV-1 total DNA quantification methods have not been previously compared. The HIV-1 long terminal repeat (LTR) has been shown to be the best target for DNA quantification. We have analysed two HIV-1 quantification assays, both able to differentiate between the variant HIV-1 DNA forms via the use of pre-amplification and primers targeting LTR. We identify a strong correlation (r=0.9759, P<0.0001) between assays which is conserved in low copy samples (r=0.8220, P<0.0001) indicating that these assays may be used interchangeably. The RvS assay performed significantly (P=0.0021) better than the CV assay when quantifying HIV-1 total DNA in patient CD4+ T lymphocytes. Sequence analysis demonstrated that viral diversity can limit DNA quantification, however in silico analysis of the primers indicated that within the target region nucleotide miss-matches appear infrequently. Further in silico analysis using up to-date sequence information led to the improvement of primers and enabled us to establish a more broadly specific assay with significantly higher HIV-1 DNA quantification capacity in patient samples (p=0.0057, n=17).

Detection, characterization, and enrollment of donors of Ebola convalescent plasma in Sierra Leone

BACKGROUND

Passive therapy with convalescent plasma provides an early opportunity to intervene in Ebola virus disease (EVD). Methods for field screening and selection of potential donors and quantifying plasma antibody are needed.

STUDY DESIGN AND METHODS

Recombinant Ebola virus glycoprotein (EBOV GP) was formatted into immunoglobulin G‐capture, competitive, and double‐antigen bridging enzyme immunoassays (EIAs). EVD survivors in Freetown, Sierra Leone, were recruited as potential plasma donors and assessed locally using sera alone and/or paired sera and oral fluids (ORFs). Uninfected controls comprised unexposed Gambians and communities in Western Area, Sierra Leone. Antibody neutralization in selected sera was measured retrospectively in a pseudotype virus assay.

RESULTS

A total of 115 potential donors were considered for enrollment: 110 plasma samples were concordantly reactive in the three EIAs; three were concordantly unreactive and two were reactive in two of three EIAs (98.2% agreement; 95% confidence interval [CI], 93.9%‐99.8%). In 88 donors with paired ORF and plasma, G‐capture EIA reactivity correlated well in the two analytes (R² = 0.795). Plasma and ORF from 44 Gambians were unreactive. ORF samples from 338 of 339 unexposed Western Area community controls were unreactive (specificity, 99.7%; 95% CI, 98.4%‐99.7%); ORF samples from 113 of 116 Kerry Town EVD survivors were reactive (sensitivity, 97.4%; 95% CI, 92.5%‐99.5%). Strong reactivity in G‐capture and/or competitive EIAs identified donors with high plasma EBOV GP antibody levels in the double‐antigen bridging assay, correlating with high levels of neutralizing antibody.

CONCLUSIONS

In‐field testing can qualify convalescent donors for providing high‐titer antibody.

Blood CXCR3+ CD4 T Cells Are Enriched in Inducible Replication Competent HIV in Aviremic Antiretroviral Therapy-Treated Individuals

We recently demonstrated that lymph nodes (LNs) PD-1⁺/T follicular helper (Tfh) cells from antiretroviral therapy (ART)-treated HIV-infected individuals were enriched in cells containing replication competent virus. However, the distribution of cells containing inducible replication competent virus has been only partially elucidated in blood memory CD4 T-cell populations including the Tfh cell counterpart circulating in blood (cTfh). In this context, we have investigated the distribution of (1) total HIV-infected cells and (2) cells containing replication competent and infectious virus within various blood and LN memory CD4 T-cell populations of conventional antiretroviral therapy (cART)-treated HIV-infected individuals. In the present study, we show that blood CXCR3-expressing memory CD4 T cells are enriched in cells containing inducible replication competent virus and contributed the most to the total pool of cells containing replication competent and infectious virus in blood. Interestingly, subsequent proviral sequence analysis did not indicate virus compartmentalization between blood and LN CD4 T-cell populations, suggesting dynamic interchanges between the two compartments. We then investigated whether the composition of blood HIV reservoir may reflect the polarization of LN CD4 T cells at the time of reservoir seeding and showed that LN PD-1⁺ CD4 T cells of viremic untreated HIV-infected individuals expressed significantly higher levels of CXCR3 as compared to CCR4 and/or CCR6, suggesting that blood CXCR3-expressing CD4 T cells may originate from LN PD-1⁺ CD4 T cells. Taken together, these results indicate that blood CXCR3-expressing CD4 T cells represent the major blood compartment containing inducible replication competent virus in treated aviremic HIV-infected individuals.

Utility of integrated HIV-1 DNA quantification in cure studies

Numerous HIV-1 curative strategies have been proposed to eradicate the virus reservoir pool that remains integrated within target cells, despite successful antiretroviral therapy. To test the impact of such interventions on this reservoir, a universal marker of persistence is needed. Quantifying integrated HIV-1 DNA load has been proposed as a strong virological marker. In this paper, we provide a detailed description of the most commonly used assays to quantify integrated HIV-1 DNA and applications in relevant clinical studies produced over the last 20 years with a major focus on the recent literature. We discuss the potential for using this marker of virological persistence and the technical limitations that need to be addressed.

The search for a T cell line for testing novel antiviral strategies against HIV-1 isolates of diverse receptor tropism and subtype origin

The world-wide HIV epidemic is characterized by increasing genetic diversity with multiple viral subtypes, circulating recombinant forms (CRFs) and unique recombinant forms (URFs). Antiretroviral drug design and basic virology studies have largely focused on HIV-1 subtype B. There have been few direct comparisons by subtype, perhaps due to the lack of uniform and standardized culture systems for the in vitro propagation of diverse HIV-1 subtypes. Although peripheral blood mononuclear cells (PBMCs) are major targets and reservoirs of HIV, PBMCs culturing is relatively difficult and not always reproducible. In addition, long-term experiments cannot be performed because PBMCs are short-lived cells. We faced these problems during the in vitro testing of an experimental RNA interference (RNAi) based gene therapy. Therefore, many T cell lines that support HIV-1 infection were tested and compared for replication of HIV-1 isolates, including viruses that use different receptors and diverse subtypes. The PM1 T cell line was comparable to PBMCs for culturing of any of the HIV-1 strains and subtypes. The advantage of PM1 cells in long-term cultures for testing the safety and efficacy of an RNAi-based gene therapy was demonstrated. PM1 may thus provide a valuable research tool for studying new anti-HIV therapies.

Increased HIV-1 activity in anal high-grade squamous intraepithelial lesions compared with unaffected anal mucosa in men who have sex with men

We studied 3 patients with focal intra-anal tissue high-grade squamous intraepithelial lesions (HSILs). All had increased human immunodeficiency virus type 1 (HIV-1) RNA and DNA in lesions compared with that in healthy mucosa. HIV-1 RNA and HIV-1 episomal DNA were indicative of ongoing viral replication, more so in anal HSILs.

Quantitation of HIV-1 DNA with a sensitive TaqMan assay that has broad subtype specificity

The increasing diversity of HIV-1 isolates makes virus quantitation challenging, especially when diverse isolates co-circulate in a geographical area. Measuring the HIV-1 DNA levels in cells has become a valuable practical tool for fundamental and clinical research. A quantitative HIV-1 DNA assay was developed based on TaqMan(®) technology. Primers that target the highly conserved LTR region were designed to detect a broad array of HIV-1 variants, including viral isolates from many subtypes, with high sensitivity. Introduction of a pre-amplification step prior to the TaqMan(®) reaction allowed the specific amplification of fully reverse transcribed viral DNA. Execution of the pre-amplification step with a second primer set enables for the exclusive quantitation of the 2-LTR circular HIV-1 DNA form.

Human immunodeficiency virus type 1 gp120 envelope characteristics associated with disease progression differ in family members infected with genetically similar viruses

The human immunodeficiency virus type 1 (HIV-1) envelope protein provides the primary contact between the virus and host, and is the main target of the adaptive humoral immune response. The length of gp120 variable loops and the number of N-linked glycosylation events are key determinants for virus infectivity and immune escape, while the V3 loop overall positive charge is known to affect co-receptor tropism. We selected two families in which both parents and two children had been infected with HIV-1 for nearly 10 years, but who demonstrated variable parameters of disease progression. We analysed the gp120 envelope sequence and compared individuals that progressed to those that did not in order to decipher evolutionary alterations that are associated with disease progression when individuals are infected with genetically related virus strains. The analysis of the V3-positive charge demonstrated an association between higher V3-positive charges with disease progression. The ratio between the amino acid length and the number of potential N-linked glycosylation sites was also shown to be associated with disease progression with the healthier family members having a lower ratio. In conclusion in individuals initially infected with genetically linked virus strains the V3-positive charges and N-linked glycosylation are associated with HIV-1 disease progression and follow varied evolutionary paths for individuals with varied disease progression.

HIV type 1 mother-to-child transmission facilitated by distinctive glycosylation sites in the gp120 envelope glycoprotein

The human immunodeficiency virus type 1 (HIV-1) characteristics associated with mother-to-child transmission (MTCT) are still poorly understood. We studied a cohort of 30 mothers from Rwanda infected with HIV-1 subtype A or C viruses of whom seven infected their children either during gestation or soon after birth. CD4 counts and viral load did not significantly differ between nontransmitting mother (NTM) versus transmitting mother (TM) groups. In contrast to earlier studies we not only analyzed and compared the genotypic characteristics of the V1-V5 region of the gp120 envelope of viruses found in TM and their infected children, but also included data from the NTM. No differences were found with respect to length and number of potential N-glycosylation sites (PNGS) in the V1-V2 and the V1-V5 region. We identified that viruses with a PNGS on positions AA234 and AA339 were preferably transmitted and that viruses with PNGS-N295 showed a disadvantage in transmission. We also showed that the frequency of PNGS-N339 in the viruses of TM and infected children was significantly higher than the frequency in NTM in our cohort and in viruses undergoing sexual transmission while the frequency of PNGS-N295 in children was significantly lower than the frequency in TM and acute horizontal infections. Collectively, our results provide evidence that the presence of the PNGS-N339 site and absence of the PNGS-N295 site in the gp120 envelope confers an advantage to HIV-1 when considering MTCT.

HIV-1 disease progression is associated with bile-salt stimulated lipase (BSSL) gene polymorphism

Background

DC-SIGN expressed by dendritic cells captures HIV-1 resulting in trans-infection of CD4⁺ T-lymphocytes. However, BSSL (bile-salt stimulated lipase) binding to DC-SIGN interferes with HIV-1 capture. DC-SIGN binding properties of BSSL associate with the polymorphic repeated motif of BSSL exon 11. Furthermore, BSSL binds to HIV-1 co-receptor CXCR4. We hypothesized that BSSL modulates HIV-1 disease progression and emergence of CXCR4 using HIV-1 (X4) variants.

Results

The relation between BSSL genotype and HIV-1 disease progression and emergence of X4 variants was studied using Kaplan Meier and multivariate Cox proportional hazard analysis in a cohort of HIV-1 infected men having sex with men (n = 334, with n = 130 seroconverters). We analyzed the association of BSSL genotype with set-point viral load and CD4 cell count, both pre-infection and post-infection at viral set-point. The number of repeats in BSSL exon 11 were highly variable ranging from 10 to 18 in seropositive individuals and from 5–17 in HRSN with 16 repeats being dominant (>80% carry at least one allele with 16 repeats). We defined 16 to 18 repeats as high (H) and less than 16 repeats as low (L) repeat numbers. Homozygosity for the high (H) repeat number BSSL genotype (HH) correlated with high CD4 cell numbers prior to infection (p = 0.007). In HIV-1 patients, delayed disease progression was linked to the HH BSSL genotype (RH = 0.462 CI = 0.282–0.757, p = 0.002) as was delayed emergence of X4 variants (RH = 0.525, 95% CI = 0.290–0.953, p = 0.034). The LH BSSL genotype, previously found to be associated with enhanced DC-SIGN binding of human milk, was identified to correlate with accelerated disease progression in our cohort of HIV-1 infected MSM (RH = 0.517, 95% CI = 0.328–0.818, p = 0.005).

Conclusion

We identify BSSL as a marker for HIV-1 disease progression and emergence of X4 variants. Additionally, we identified a relation between BSSL genotype and CD4 cell counts prior to infection.

Transmission of two distinct HIV type 1 strains to an individual that were harbored for many years by another

The concept of transmission bottlenecks in HIV-1 infection is well established. Coinfections and superinfections have been increasingly documented and provide a founding cause for the expansion of viral diversity through recombination. It is still relatively unclear how HIV-1 will propagate and evolve in individuals infected with more than one viral strain. Here we report on the parallel transmission of genetically distant viral strains cocirculating in one individual over many years to a single recipient.

Binding of human milk to pathogen receptor DC-SIGN varies with bile salt-stimulated lipase (BSSL) gene polymorphism

Objective

Dendritic cells bind an array of antigens and DC-SIGN has been postulated to act as a receptor for mucosal pathogen transmission. Bile salt-stimulated lipase (BSSL) from human milk potently binds DC-SIGN and blocks DC-SIGN mediated trans-infection of CD4⁺ T-lymphocytes with HIV-1. Objective was to study variation in DC-SIGN binding properties and the relation between DC-SIGN binding capacity of milk and BSSL gene polymorphisms.

Study Design

ELISA and PCR were used to study DC-SIGN binding properties and BSSL exon 11 size variation for human milk derived from 269 different mothers distributed over 4 geographical regions.

Results

DC-SIGN binding properties were highly variable for milks derived from different mothers and between samplings from different geographical regions. Differences in DC-SIGN binding were correlated with a genetic polymorphism in BSSL which is related to the number of 11 amino acid repeats at the C-terminus of the protein.

Conclusion

The observed variation in DC-SIGN binding properties among milk samples may have implications for the risk of mucosal transmission of pathogens during breastfeeding.

Altered dynamics and differential infection profiles of lymphoid and myeloid cell subsets during acute and chronic HIV-1 infection

The dynamics of immune cell populations during acute HIV-1 infection are not fully deciphered, especially for non-T cells. In this study, we tested whether specific cellular subsets of the innate arm of the immune response are affected early after HIV-1 infection. Using a cohort of HIV-1-infected individuals, we have monitored the relative frequency of blood T lymphocytes, monocytes, and DCs at various infection stages and measured their respective intracellular HIV-1 DNA loads. The HIV-1 DNA load in naive CD4(+) T lymphocytes, which are lost very early during acute infection, was ten- to 100-fold lower than in CD57(-) and CD57(+) memory CD4(+) T lymphocytes. We observed that despite rapid, persistent loss after HIV-1 infection, pDCs represented a non-negligible HIV-1 DNA reservoir. CD16(+) proinflammatory cDCs and monocytes accumulated gradually, and HIV-infected CD16(+) monocytes contained higher HIV-1 DNA loads than their CD16(-) counterpart during acute infection. During chronic infection, CD16(+) cDCs exhibited higher HIV-1 DNA loads than the CD16(-) population. Overall, our results demonstrate that non-T cell compartments are a major HIV-1 DNA reservoir, and CD16(+) monocytes and CD16(+) cDCs potentially play an important role in HIV-1 dissemination.

Preferential infection and depletion of Mycobacterium tuberculosis-specific CD4 T cells after HIV-1 infection

HIV-1 preferentially infects M. tuberculosis-specific CD4+ T cells due to their increased production of IL-2.

HIV-1 infection results in the progressive loss of CD4 T cells. In this study, we address how different pathogen-specific CD4 T cells are affected by HIV infection and the cellular parameters involved. We found striking differences in the depletion rates between CD4 T cells to two common opportunistic pathogens, cytomegalovirus (CMV) and Mycobacterium tuberculosis (MTB). CMV-specific CD4 T cells persisted after HIV infection, whereas MTB-specific CD4 T cells were depleted rapidly. CMV-specific CD4 T cells expressed a mature phenotype and produced very little IL-2, but large amounts of MIP-1β. In contrast, MTB-specific CD4 T cells were less mature, and most produced IL-2 but not MIP-1β. Staphylococcal enterotoxin B–stimulated IL-2–producing cells were more susceptible to HIV infection in vitro than MIP-1β–producing cells. Moreover, IL-2 production was associated with expression of CD25, and neutralization of IL-2 completely abrogated productive HIV infection in vitro. HIV DNA was found to be most abundant in IL-2–producing cells, and least abundant in MIP-1β–producing MTB-specific CD4 T cells from HIV-infected subjects with active tuberculosis. These data support the hypothesis that differences in function affect the susceptibility of pathogen-specific CD4 T cells to HIV infection and depletion in vivo, providing a potential mechanism to explain the rapid loss of MTB-specific CD4 T cells after HIV infection.

Generation of HIV-1 primary isolates representative of plasma variants using the U87.CD4 cell line

In order to obtain HIV-1 primary isolates in settings with limited access to donor PBMCs, a culture method was developed where patient PBMCs infected with HIV-1 were cultured together with U87.CD4 cells. Using this non-laborious method, it is possible to harvest virus solely on the basis of syncytia formation and circumventing monitoring of viral replication by CA-p24 ELISA. Primary isolates from 23 out of 33 patients (70%) were isolated successfully. From PCR amplification and sequencing of the V1V5 region of the viral gp120 envelope gene, primary isolates were compared with variants obtained from plasma and PBMCs of 13 patients. The primary isolates of seven patients (54%) resembled closely the plasma viral quasispecies, whereas different variants were isolated from the other patients (46%). Three patients harboured a dual infection, while this remained unnoticed from sequencing the plasma or PBMC compartment. The primary isolates were highly infectious for TZM-bl cells and could infect CD4-enriched lymphocytes. This study demonstrates that it is possible to grow viral isolates using a non-laborious and simple method. These isolates may be used in the field for studies on antiretroviral therapy or for vaccine trials.

Differences in HIV type 1 RNA plasma load profile of closely related cocirculating Ethiopian subtype C strains: C and C'

Two HIV-1 subtype C subclusters have been identified in Ethiopia (C and C') with little knowledge regarding their biological or clinical differences. We longitudinally monitored HIV-1 viral loads and CD4(+) T cell counts for 130 subtype C-infected individuals from Ethiopia over 5 years. The genetic subclusters C and C' were determined and comparisons were made between the groups. None of the study individuals received antiretroviral therapy. Subcluster C' was found to be the more prevalent (72.3%) genotype circulating. Individuals infected with subcluster C' harbored higher viral loads in comparison to subcluster C-infected individuals when the CD4(+) T cell counts were high (500-900 cells/mm(3)), whereas at low CD4(+) T cell counts (0-150 cells/mm(3)) individuals infected with subcluster C viruses showed higher viral loads. We identified a greater number of deaths among individuals infected with subcluster C viruses in comparison to C'. Our results indicate that infection with subcluster C viruses leads to a more rapid onset of disease, despite the initial lower HIV-1 RNA plasma loads. Additionally, the higher viral loads seen for HIV-1 subcluster C' infections at higher CD4(+) T cell counts can help explain the higher prevalence of this subtype in Ethiopia.

Lack of in vivo compartmentalization among HIV-1 infected naïve and memory CD4+ T cell subsets

Viral compartmentalization between naïve and memory CD4(+) T cell subsets has been described, but only for individuals who were receiving antiretroviral therapy (ART). We present here an extensive analysis of the viral quasispecies residing in the naïve, central and effector memory CD4(+) T cell subsets in a number of therapy naïve individuals and representing an array of HIV-1 subtypes. We longitudinally analyzed subset-specific infection and evolution in a subtype B infected individual who switches from CCR5 to dual CCR5/CXCR4 coreceptor usage. We show that the central memory subset, the predominantly infected subset, harbors a more diverse viral population compared to the others. Through sequence analysis of the env C2V3 region we demonstrate a lack of viral compartmentalization among all subsets. Upon coreceptor switch we observe a pronounced increase in the infection level of the naïve population. Our findings emphasize the importance of all CD4(+) T cell subsets to viral evolution.

Mucin 6 in seminal plasma binds DC-SIGN and potently blocks dendritic cell mediated transfer of HIV-1 to CD4(+) T-lymphocytes

Many viruses transmitted via the genital or oral mucosa have the potential to interact with dendritic cell-specific intercellular adhesion molecule-3 grabbing non integrin (DC-SIGN) expressed on immature dendritic cells (iDCs) that lie below the mucosal surface. These cells have been postulated to capture and disseminate human immunodeficiency virus type-1 (HIV-1) to CD4(+) lymphocytes, potentially through breaches in the mucosal lining. We have previously described that BSSL (bile salt-stimulated lipase) in human milk can bind DC-SIGN and block transfer. Here we demonstrate that seminal plasma has similar DC-SIGN blocking properties as BSSL in human milk. Using comparative SDS-PAGE and Western blotting combined with mass spectrometry we identified mucin 6 as the DC-SIGN binding component in seminal plasma. Additionally, we demonstrate that purified mucin 6 binds DC-SIGN and successfully inhibits viral transfer. Mucin 6 in seminal plasma may therefore interfere with the sexual transmission of HIV-1 and other DC-SIGN co-opting viruses.

RNA Detection and Subtype C Assessment of HIV-1 in Infants with Diarrhea in Ethiopia

In the absence of chemoprophylaxis, HIV-1 transmission occurs in 13-42% of infants born to HIV-1 positive mothers. All exposed infants acquire maternal HIV-1 antibodies that persist for up to 15 months, thereby hampering diagnosis. In resource limited settings, clinical symptoms are the indices of established infection against validated laboratorybased markers. Here we enrolled 1200 children hospitalized for diarrheal and other illnesses. 20-25% of those tested, aged 15 months or younger, were found to be HIV-1-seropositive. Where sufficient plasma was available, HIV-1 RNA detection was performed using a subtype-insensitive assay, with 71.1% of seropositive infants presenting with diarrhea showing positive. From sub-typing analysis, we identified that viruses of the C’ sub-cluster were predominated amongst infants. Although this study may overestimate the HIV-1 frequency through testing symptomatic infants, diarrhea can be seen as a useful marker indicating HIV-1 infection in infants less than 15 months old.

Only five of 10 strictly conserved disulfide bonds are essential for folding and eight for function of the HIV-1 envelope glycoprotein

Protein folding in the endoplasmic reticulum goes hand in hand with disulfide bond formation, and disulfide bonds are considered key structural elements for a protein's folding and function. We used the HIV-1 Envelope glycoprotein to examine in detail the importance of its 10 completely conserved disulfide bonds. We systematically mutated the cysteines in its ectodomain, assayed the mutants for oxidative folding, transport, and incorporation into the virus, and tested fitness of mutant viruses. We found that the protein was remarkably tolerant toward manipulation of its disulfide-bonded structure. Five of 10 disulfide bonds were dispensable for folding. Two of these were even expendable for viral replication in cell culture, indicating that the relevance of these disulfide bonds becomes manifest only during natural infection. Our findings refine old paradigms on the importance of disulfide bonds for proteins.

The carbohydrate at asparagine 386 on HIV-1 gp120 is not essential for protein folding and function but is involved in immune evasion

BACKGROUND

The HIV-1 envelope glycoprotein gp120, which mediates viral attachment to target cells, consists for approximately 50% of sugar, but the role of the individual sugar chains in various aspects of gp120 folding and function is poorly understood. Here we studied the role of the carbohydrate at position 386. We identified a virus variant that had lost the 386 glycan in an evolution study of a mutant virus lacking the disulfide bond at the base of the V4 domain.

RESULTS

The 386 carbohydrate was not essential for folding of wt gp120. However, its removal improved folding of a gp120 variant lacking the 385-418 disulfide bond, suggesting that it plays an auxiliary role in protein folding in the presence of this disulfide bond. The 386 carbohydrate was not critical for gp120 binding to dendritic cells (DC) and DC-mediated HIV-1 transmission to T cells. In accordance with previous reports, we found that N386 was involved in binding of the mannose-dependent neutralizing antibody 2G12. Interestingly, in the presence of specific substitutions elsewhere in gp120, removal of N386 did not result in abrogation of 2G12 binding, implying that the contribution of N386 is context dependent. Neutralization by soluble CD4 and the neutralizing CD4 binding site (CD4BS) antibody b12 was significantly enhanced in the absence of the 386 sugar, indicating that this glycan protects the CD4BS against antibodies.

CONCLUSION

The carbohydrate at position 386 is not essential for protein folding and function, but is involved in the protection of the CD4BS from antibodies. Removal of this sugar in the context of trimeric Env immunogens may therefore improve the elicitation of neutralizing CD4BS antibodies.

Statins disrupt CCR5 and RANTES expression levels in CD4(+) T lymphocytes in vitro and preferentially decrease infection of R5 versus X4 HIV-1

BACKGROUND

Statins have previously been shown to reduce the in vitro infection of human immunodeficiency virus type 1 (HIV-1) through modulation of Rho GTPase activity and lipid raft formation at the cell surface, as well as by disrupting LFA-1 incorporation into viral particles.

PRINCIPLE FINDINGS

Here we demonstrate that treatment of an enriched CD4(+) lymphocyte population with lovastatin (Lov), mevastatin (Mev) and simvastatin (activated and non-activated, Sim(A) and Sim(N), respectively) can reduce the cell surface expression of the CC-chemokine receptor CCR5 (P<0.01 for Sim(A) and Lov). The lowered CCR5 expression was associated with down-regulation of CCR5 mRNA expression. The CC-chemokine RANTES protein and mRNA expression levels were slightly increased in CD4(+) enriched lymphocytes treated with statins. Both R5 and X4 HIV-1 were reduced for their infection of statin-treated cells; however, in cultures where statins were removed and where a decrease in CCR5 expression was observed, there was a preferential inhibition of infection with an R5 versus X4 virus.

CONCLUSIONS

The results indicate that the modulation of CC-chemokine receptor (CCR5) and CC-chemokine (RANTES) expression levels should be considered as contributing to the anti-viral effects of statins, preferentially inhibiting R5 viruses. This observation, in combination with the immunomodulatory activity exerted by statins, suggests they may possess more potent anti-HIV-1 activity when applied during the early stages of infection or in lowering viral transmission. Alternatively, statin treatment could be considered as a way to modulate immune induction such as during vaccination protocols.

Characterization of an HIV-1 group M variant that is distinct from the known subtypes

We identified an HIV-1 variant that belongs to the M group, with limited similarity of short genetic regions (100-200 nt) to subtype K, but the remainder of the genome is unrelated to any established HIV-1 subtype. The isolate was obtained from an HIV-1-positive male, living in the Netherlands, who encountered the virus before 1989, most probably via heterosexual contact in Africa. We describe the full-length genome sequence of four biological clones that were obtained from two samples collected 5 years apart. At both time points all open reading frames were intact. Within the 5-year interval, the person received antiretroviral therapy with zalcitabine and zidovudine for almost 4 years. Evolution of drug-resistant variants is likely given the increase in viral RNA load to +/-10,000 copies/ml during the last year of treatment. Surprisingly, the only regular RT mutation acquired during this period was K70R, which suggests that the genetic background of this variant is perhaps not suitable for the generation of the standard 41L, 67N, and 215Y/F mutations that typically arise during prolonged, nonsuccessful, zidovudine treatment. Awaiting the discovery of at least two additional, epidemiologically unrelated patients with a phylogenetically related HIV-1 variant, we can designate this variant a new HIV-1 subtype, or a distinct branch of subtype K.

Efficient Capture of Antibody Neutralized HIV-1 by Cells Expressing DC-SIGN and Transfer to CD4+T Lymphocytes

Infection of CD4+ T lymphocytes is enhanced by the capture and subsequent transfer of HIV-1 by dendritic cells (DCs) via the interaction with C-type lectins such as the DC-specific ICAM-grabbing nonintegrin (DC-SIGN). Numerous HIV-1 envelope-directed neutralizing Abs have been shown to successfully block the infection of CD4(+) T lymphocytes. In this study, we find that HIV-1-neutralized with the mAb 2F5 is more efficiently captured by immature monocyte-derived DCs (iMDDCs) and DC-SIGN-expressing Raji cells (Raji-DC-SIGN). Furthermore, a 2F5-neutralized virus captured by these cells was able to subsequently infect CD4+ T lymphocytes upon the release of HIV-1 from iMDDCs, thereby enhancing infection. We show that upon transfer via DC-SIGN-expressing cells, HIV-1 is released from immune-complexes with the Abs 2F5 and 4E10 (gp41-directed) and 2G12, 4.8D, and 1.7b (gp120-directed). The nonneutralizing V3-21 (V3 region of the gp120-directed) Ab enhanced HIV-1 infection upon capture and transfer via Raji-DC-SIGN cells, whereas no infection was observed with the neutralizing b12 Ab (gp120-directed), indicating that different Abs have variant effects on inhibiting HIV-1 transfer to CD4+ T lymphocytes. The increased capture of the 2F5-neutralized virus by iMDDCs was negated upon blocking the Fc receptors. Blocking DC-SIGN on iMDDCs resulted in a 70-75% inhibition of HIV-1 capture at 37 degrees C, whereas at 4 degrees C a full block was observed, showing that the observed transfer is mediated via DC-SIGN. Taken together, we propose that DC-SIGN-mediated capture of neutralized HIV-1 by iMDDCs has the potential to induce immune evasion from the neutralization effects of HIV-1 Abs, with implications for HIV-1 pathogenesis and vaccine development.