HIV transmission biology: translation for HIV prevention

Host cell glycosylation selects for infection with CCR5- versus CXCR4-tropic HIV-1

Human immunodeficiency virus type 1 (HIV-1) infection involves a selection bottleneck that leads to transmission of one or a few variants. C-C motif chemokine receptor 5 (CCR5) or C-X-C motif chemokine receptor 4 (CXCR4) can act as coreceptors for HIV-1 viral entry. However, initial infection mostly occurs via CCR5, despite abundant expression of CXCR4 on target cells. The host factors that influence HIV-1 susceptibility and selection during transmission are unclear. Here we conduct CRISPR-Cas9 screens and identify SLC35A2 (a transporter of UDP-galactose expressed in target cells in blood and mucosa) as a potent and specific CXCR4-tropic restriction factor in primary target CD4+ T cells. SLC35A2 inactivation, which resulted in truncated glycans, not only increased CXCR4-tropic infection levels but also decreased those of CCR5-tropic strains consistently. Single-cycle infections demonstrated that the effect is cell-intrinsic. These data support a role for a host protein that influences glycan structure in regulating HIV-1 infection. Host cell glycosylation may, therefore, affect HIV-1 selection during transmission in vivo.

Knowledge about HIV and Stigmatizing Attitudes of Medical Students in Saudi Arabia Towards Patients with HIV/AIDS: A Cross-Sectional Nationwide Study

BACKGROUND

The Human Immunodeficiency Virus (HIV) and the social stigma directed toward patients with HIV are serious public health issues. We aimed to evaluate the HIV knowledge base and stigmatizing attitudes toward patients with HIV among students enrolled in medical schools in Saudi Arabia.

METHODS

This cross-sectional study included students at medical colleges in Saudi Arabia and was conducted between February and March 2023. We used non-random convenience sampling with an online chain referral via a validated Arabic questionnaire composed of 35 questions. Data were analyzed using descriptive and comparative statistics.

RESULTS

A total of 1,213 medical students (women: 56.6%) participated in the study. Students in clinical years had a higher level of HIV knowledge than their pre-clinical colleagues. Logistic regression analysis revealed that participants who gave incorrect answers to questions related to mother-to-child and casual contact HIV transmission had a higher likelihood of harboring a negative attitude towards patients with HIV. Conversely, those who correctly answered queries on prevention and treatment were less likely to have stigmatizing attitudes. A significant proportion of this cohort harbored negative attitudes toward patients with HIV, with the sex and geographic location of participants being significant predictors of negative attitudes.

CONCLUSION

Our data have revealed a significant percentage of medical students in Saudi Arabia to have misconceptions about HIV transmission and prevention, and stigmatizing attitudes toward patients with HIV, indicating a need for targeted interventions to enhance the HIV knowledge base in this population of future caregivers.

Host cell glycosylation selects for infection with CCR5- versus CXCR4-tropic HIV-1

HIV-1 infection involves a selection bottleneck that leads to transmission of one or a few HIV variants, which nearly always use CCR5 as the coreceptor (R5 viruses) for viral entry as opposed to CXCR4 (X4 viruses). The host properties that drive this selection are not well understood and may hold keys to factors that govern HIV susceptibility. In this report, we identified SLC35A2, a transporter of UDP-galactose, as a candidate X4-specific restriction factor in CRISPR-knockout screens in primary target CD4+ T cells. SLC35A2 inactivation in CD4+ T cells, which resulted in truncation of glycans due to the absence of galactose, not only increased X4 infection levels, but also consistently decreased infection levels of R5 HIV strains. Single cycle infections demonstrated that the effect is host cell dependent. SLC35A2 is expressed in CD4+ T cells at different tissue sites, with high levels in the genital tract - the site of most HIV infections. These data support a role for a host cell protein that regulates glycan structure on HIV infection, with enhanced R5 infection but reduced X4 infection associated with SLC35A2-mediated glycosylation. Host cell glycosylation may therefore contribute to R5 selection and host susceptibility during HIV transmission.

SIV Evolutionary Dynamics in Cynomolgus Macaques during SIV-Mycobacterium tuberculosis Co-Infection

Co-infection with Mycobacterium tuberculosis (Mtb) and human immunodeficiency virus (HIV) is a worldwide public health concern, leading to worse clinical outcomes caused by both pathogens. We used a non-human primate model of simian immunodeficiency virus (SIV)-Mtb co-infection, in which latent Mtb infection was established prior to SIV_mac251 infection. The evolutionary dynamics of SIV env was evaluated from samples in plasma, lymph nodes, and lungs (including granulomas) of SIV-Mtb co-infected and SIV only control animals. While the diversity of the challenge virus was low and overall viral diversity remained relatively low over 6–9 weeks, changes in viral diversity and divergence were observed, including evidence for tissue compartmentalization. Overall, viral diversity was highest in SIV-Mtb animals that did not develop clinical Mtb reactivation compared to animals with Mtb reactivation. Among lung granulomas, viral diversity was positively correlated with the frequency of CD4+ T cells and negatively correlated with the frequency of CD8+ T cells. SIV diversity was highest in the thoracic lymph nodes compared to other sites, suggesting that lymphatic drainage from the lungs in co-infected animals provides an advantageous environment for SIV replication. This is the first assessment of SIV diversity across tissue compartments during SIV-Mtb co-infection after established Mtb latency.

Sex Hormone Therapy and Tenofovir Diphosphate Concentration in Dried Blood Spots: Primary Results of the Interactions Between Antiretrovirals And Transgender Hormones Study

BACKGROUND

Sex hormone and preexposure prophylaxis (PrEP) drug interactions among transgender women (TGW), transgender men (TGM), and cisgender men (CGM) are not fully understood.

METHODS

TGM and TGW on at least 6 months of stable sex hormone therapy containing testosterone or estradiol (respectively) were enrolled in a 4-week study of directly observed dosing of daily oral coformulated emtricitabine and tenofovir disoproxil fumarate (FTC/TDF). TFV-DP in dried blood spots and sex hormones in serum were measured at weekly intervals. TFV-DP was compared with 2- and 4-week samples from Directly Observed Therapy Dried Blood Spots (DOT-DBS) Study (NCT02022657).

RESULTS

From May 2017 to June 2018, 24 TGM and 24 TGW were enrolled. Testosterone (total and free) and estradiol concentrations were comparable before and after 4 weeks of PrEP use in TGM and TGW, respectively. Historical controls included 17 cisgender women (CGW) and 15 CGM. TFV-DP concentrations at week 4 were comparable between TGW and TGM (mean difference, -6%; 95% confidence interval [CI], -21% to 12%; P = .47), comparable between TGW and CGM (mean difference, -12%; 95% CI, -27% to 7%; P = .21) and were lower among TGM compared with CGW (mean difference, -23%; 95% CI, -36% to -7%; P = .007). All persons in all groups were projected to reach the TFV-DP threshold that has been associated with high protection from human immunodeficiency virus.

CONCLUSIONS

CGM, TGM, and TGW had comparable TFV-DP concentrations in dried blood spots after 4 weeks of directly observed daily FTC/TDF PrEP use. Serum hormone concentrations were not affected by FTC/TDF PrEP use.

CLINICAL TRIALS REGISTRATION

NCT04050371.

HIV and Messenger RNA (mRNA) Vaccine

Human immunodeficiency virus (HIV) is a part of the lentivirus genus of the retroviridae family that incorporates its genome into the host DNA via a series of complex steps. HIV can be classified into two types, HIV-type 1 (HIV-1) and HIV-type 2 (HIV-2), with HIV-1 being the most common type worldwide. Seventy-six million people have been infected since the start of the pandemic, with a mortality rate of 33 million. Even after 40 years, no cure has been developed for this pandemic. The development of the mRNA vaccine has led to further research for the utilization of mRNA vaccine in HIV, in attempts to create a prophylactic and therapeutic treatment. Although messenger RNA (mRNA) vaccine has been around for many years, it has recently drawn attention due to its role and response in the unforeseen coronavirus pandemic. mRNA vaccine has faced its fair-share of challenges, but it also offers many advantages compared to conventional vaccines such as safety, efficacy, rapid preparation, and versatility. mRNA vaccine has shown promising results and has great potential. In this review, we discuss the types of mRNA vaccine, along with development, delivery, advantages, challenges, and how we are working to overcome these challenges.

Rectal and seminal HIV-1 RNA decay towards virological suppression in infected MSM initiating dolutegravir/abacavir/lamivudine

BACKGROUND

The time at which the protective effect of starting ART is achieved in male rectal and genital reservoirs is not clearly established.

OBJECTIVES

To quantify HIV-1 RNA decay towards virological suppression in rectal mucosa and semen in MSM starting dolutegravir/abacavir/lamivudine (DTG/ABC/3TC).

METHODS

A longitudinal cohort study of ART-naive HIV-positive MSM was performed. HIV-1 RNA was quantified in rectal mucosa and seminal plasma samples at day 1 of ART initiation (baseline) and every 4 weeks until week 20 (w20; all participants) and week 64 (w64; 6 of 12 participants).

RESULTS

Twelve MSM, with median (IQR) age 36 (33-40) years and baseline CD4+ count 449 (411-503) cells/mm3, were included. At baseline, HIV-1 RNA was detectable in all plasma and seminal samples and 10/12 rectal samples. All participants achieved plasma virological suppression by w20, whereas HIV-1 RNA was detectable in 42% and 50% of seminal and rectal samples, respectively. At w64, HIV-1 RNA was detectable in 1/6 seminal and 1/6 rectal samples. A relationship of baseline seminal and rectal HIV-1 RNA levels with viral shedding in reservoirs (HIV-1 RNA >200 copies/mL or copies/swab) was found. In addition, a significant association of baseline plasma viral load with time to rectal HIV-1 RNA <200 copies/swab was found (P=0.025).

CONCLUSIONS

Viral decay after initiating DTG/ABC/3TC is slower in rectal mucosa and semen than in plasma. Approximately half of patients achieved undetectable HIV-1 RNA levels in rectal and genital secretions at w20 and in some patients viral shedding persisted for up to 1 year. Initial plasma viral load influences time to rectal suppression.

Communication Chaos from Discrepancies in Personal Protective Equipment and Preoperative Guidelines

OBJECTIVES/HYPOTHESIS

To compare personal protective equipment (PPE) guidelines, specifically respirator use, among international public health agencies, academic hospitals, and otolaryngology-head and neck surgery (OHNS) departments in the United States for the care of coronavirus-19 (COVID-19) patients.

STUDY DESIGN

Cross sectional survey.

METHODS

Review of publicly available public health and academic hospitals guidelines along with review of communication among otolaryngology departments.

RESULTS

Among 114 academic institutions affiliated with OHNS residencies, 20 (17.5%) institutions provided public access to some form of guidance on PPE and 73 (64%) provided information on screening or diagnostic testing. PPE guidelines were uniquely described based on several variables: location of care, COVID-19 status, involvement of aerosol generating or high-risk procedures, and physical distance from the patient. Six hospital guidelines were highlighted. Across these six institutions, there was agreement that N95 respirators were needed for high-risk patients undergoing high-risk procedures. Variations existed among institutions for scenarios with low-risk patients. Definitions of the low-risk patient and high-risk procedures were inconsistent among institutions. Three of the highlighted institutions had OHNS departments recommending higher level of airway protection than the institution.

CONCLUSIONS

OHNS departments typically had more stringent PPE guidance than their institution. Discrepancies in communicating PPE use were frequent and provide inconsistent information on how healthcare workers should protect themselves in the COVID-19 pandemic. Identification of these inconsistencies serves as an opportunity to standardize communication and develop evidence-based guidelines.

LEVEL OF EVIDENCE

V Laryngoscope, 131:E746-E754, 2021.

Transmission routes of human immunodeficiency virus and affecting factors

Acquired immunodeficiency syndrome (AIDS) was first reported more than 30 years ago among homosexuals in the United States. The epidemiology of this disease indicates that there are three modes of transmission: Blood, mother-to-child, and sexual contact transmission. The pathogen of AIDS is human immunodeficiency virus (HIV), primarily HIV-1. HIV-1 could not break through the structurally and functionally integral skin, and primarily invades the human body through the mucosa irrespective of their integrity. Therefore, the mucosae are the natural transmission routes for HIV-1. The mucosae involved in HIV-1 transmission include the mucosae of the gastrointestinal tract and the urogenital tract. The risks of HIV-1 transmission vary significantly between mucosal sites and individuals, and are associated with mucosal integrity, abundance of target cells, immune status of the host, commensal microbes, and host genetic background. Many factors are closely related to the barrier function of the mucosa, and studies on their roles in HIV-1 invasion could promote the prevention and control of mucosal transmission of HIV-1.

The importance of semen leukocytes in HIV-1 transmission and the development of prevention strategies

HIV-1 sexual transmission occurs mostly through contaminated semen, which is a complex mixture of soluble factors with immunoregulatory functions and cells. It is well established that semen cells from HIV-1-infected men are able to produce the virus and that are harnessed to efficiently interact with mucosal barriers exposed during sexual intercourse. Several cofactors contribute to semen infectivity and may enhance the risk of HIV-1 transmission to a partner by increasing local HIV-1 replication in the male genital tract, thereby increasing the number of HIV-1-infected cells and the local HIV-1 shedding in semen. The introduction of combination antiretroviral therapy has improved the life expectancy of HIV-1 infected individuals; however, there is evidence that systemic viral suppression does not always reflect full viral suppression in the seminal compartment. This review focus on the role semen leukocytes play in HIV-1 transmission and discusses implications of the increased resistance of cell-mediated transmission to immune-based prevention strategies.

Broadly neutralizing antibodies potently inhibit cell-to-cell transmission of semen leukocyte-derived SHIV162P3

BACKGROUND

HIV-1 sexual transmission occurs mostly through infected semen, which contains both free virions and infected leukocytes. Transmission initiated by infected cells has been shown by several in vitro and in vivo studies and a reduced capacity of broadly neutralizing antibodies (bNAbs) to inhibit cell-to-cell transmission has also been reported. However, due to limitations of available experimental models, there is yet no clarity to which extend bNAbs can prevent transmission mediated by semen leukocytes.

METHODS

We developed a novel in vitro assay to measure cell-cell transmission that makes use of splenocytes or CD45+ semen leukocytes collected from acutely SHIV162P3-infected cynomolgus macaques. A panel of 11 bNAbs was used either alone or in combination to assess their inhibitory potential against both cell-free and cell-cell infection.

FINDINGS

Splenocytes and semen leucocytes displayed a similar proportion of CD4+T-cell subsets. Either cell type transferred infection in vitro to target TZM-bl cells and PBMCs. Moreover, infection of macaques was achieved following intravaginal challenge with splenocytes. The anti-N-glycans/V3 loop bNAb 10-1074 was highly efficient against cell-associated transmission mediated by infected spleen cells and its potency was maintained when transmission was mediated by CD45+ semen leukocytes.

INTERPRETATION

These results support the use of bNAbs in preventative or therapeutic studies aiming to block transmission events mediated not only by free viral particles but also by infected cells. Our experimental system could be used to predict in vivo efficacy of bNAbs.

FUNDING

This work was funded by the ANRS and the European Commission.

Systematic Review and Meta-Analysis of Global Prevalence of HBsAg and HIV and HCV Antibodies among People Who Inject Drugs and Female Sex Workers

The main objective of this study was to evaluate the prevalence of human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), hepatitis C virus (HCV) and hepatitis B virus (HBV) and their co-infections among people who inject drugs (PWID) and female sex workers (FSWs). Data sources were searched from January 2008 to October 2018 in different databases. Data were analyzed in Stata 16 software using the Metaprop command. The results showed that the prevalence of HIV, HCV and HBV among PWID was 15%, 60% and 6%, respectively. The prevalence of HIV, HCV and HBV among FSWs was 5%, 1% and 3%, respectively. The prevalence of HIV/HCV, HIV/HBV, HCV/HBV and HIV/HCV/HBV co-infections among PWID was 13%, 2%, 3% and 2%, respectively. The prevalence of HIV/HCV and HIV/HBV co-infections among FSWs was 3% and 1%, respectively. The results show that the prevalence of HCV and HIV infections in PWID and the prevalence of HIV in FSWs is higher than their prevalence in the general population. Interventions for the prevention of HIV and HCV in PWID appear to be poor, and may not be sufficient to effectively prevent HIV and HCV transmission.

Characterization of the Transmitted Virus in an Ongoing HIV-1 Epidemic Driven by Injecting Drug Use

Understanding features of the HIV-1 transmission process has the potential to inform biological interventions for prevention. We have examined the transmitted virus in a cohort of people who inject drugs and who are at risk of HIV-1 infection through blood contamination when injecting in a group. This study focused on seven newly infected participants in St. Petersburg, Russia, who were in acute or early infection. We used end-point dilution polymerase chain reaction to amplify single viral genomes to assess the complexity of the transmitted virus. We also used deep sequencing to further assess the complexity of the virus. We interpret the results as indicating that a single viral variant was transmitted in each case, consistent with a model where the exposure to virus during transmission was limited. We also looked at phenotypic properties of the viral Env protein in isolates from acute and chronic infection. Although differences were noted, there was no consistent pattern that distinguished the transmitted variants. Similarly, despite the reduced genetic heterogeneity of the more recent subtype A HIV-1 epidemic in St. Petersburg, we did not see reduced variance in the neutralization properties compared to isolates from the more mature subtype C HIV-1 epidemic. Finally, in looking at members of injecting groups related to the acute HIV-1 infection/early subjects, we found examples of sequence linkage consistent with ongoing and rapid spread of HIV-1 in these groups. These studies emphasize the dynamic nature of this epidemic and reinforce the idea that improved prevention methods are needed.

Neutralizing Antibody-Based Prevention of Cell-Associated HIV-1 Infection

Improved vaccine-mediated protection against HIV-1 requires a thorough understanding of the mode of HIV-1 transmission and how various immune responses control transmission. Cell-associated HIV-1 is infectious and contributes to HIV-1 transmission in humans. Non-human primate models of cell-associated SIV infection demonstrate that cell-associated SIV is more infectious than cell-free SIV. In a recently described chimeric simian–human immunodeficiency virus (SHIV) macaque model, it was demonstrated that an occult infection with cell-associated SHIV can be established that evades passive protection with a broadly neutralizing antibody (bnAb). Indeed, considerable in vitro data shows that bnAbs have less efficacy against cell-associated HIV-1 than cell-free HIV-1. Optimizing the protective capacity of immune responses such as bnAbs against cell-associated infections may be needed to maximize their protective efficacy.

Gp120 V5 Is Targeted by the First Wave of Sequential Neutralizing Antibodies in SHIVSF162P3N-Infected Rhesus Macaques

Simian-human immunodeficiency virus (SHIV) infection provides a relevant animal model to study HIV-1 neutralization breadth. With previously identified SHIV_SF162P3N infected rhesus macaques that did or did not develop neutralization breadth, we characterized the transmitted/founder viruses and initial autologous/homologous neutralizing antibodies in these animals. The plasma viral load and blood CD4 count did not distinguish macaques with and without breadth, and only one tested homologous envelope clone revealed a trend for macaques with breadth to favor an early homologous response. In two macaques with breadth, GB40 and FF69, infected with uncloned SHIV_SF162P3N, multiple viral variants were transmitted, and the transmitted variants were not equal in neutralization sensitivity. The targets of initial autologous neutralizing antibodies, arising between 10 and 20 weeks post infection, were mapped to N462 glycan and G460a in gp120 V5 in GB40 and FF69, respectively. Although it is unclear whether these targets are related to later neutralization breadth development, the G460a target but not N462 glycan appeared more common in macaques with breadth than those without. Longitudinal plasmas revealed 2⁻3 sequential waves of neutralizing antibodies in macaques with breadth, implicating that 3 sequential envelope variants, if not more, may be required for the broadening of HIV-1 neutralizing antibodies.

High-grade anal intraepithelial neoplasia is associated with HIV-1 RNA rectal shedding in virologically suppressed MSM

OBJECTIVE

The protective effect of ART has not yet been definitively established in MSM. We aimed to characterize the factors associated with persistent HIV-1 RNA rectal shedding.

METHODS

Prospective study including virologically suppressed MSM from an HIV cohort. High-resolution anoscopy (HRA) was performed for screening of anal dysplasia, and rectal sampling for HIV-1 RNA quantification and sexually transmitted infections (STIs) investigation through multiplex PCR. Both generalized linear mixed (GLM) and zero-altered negative binomial (ZANB) models were performed.

RESULTS

One hundred and fifty-five rectal swab samples from 132 virologically suppressed MSM were included. HIV-1 RNA was detectable in 61 (39.3%) samples, with median (IQR) rectal viral load (rVL) of 295.8 (158.8-522) copies/swab. Multivariable GLM showed that the presence of high-grade anal intraepithelial neoplasia (HG-AIN; OR 2.85 [95% CI 1.10-7.38]) and a protease inhibitor-based regimen (OR 2.49 [0.98-6.34]) resulted in increased risk for rectal HIV-1 shedding, whereas higher nadir CD4+/CD8+ T-cell ratio (OR 0.18 [0.04-0.93]) was negatively associated with rectal shedding. ZANB analyses showed that the best predictors of having detectable rVL were lower nadir CD4+/CD8+ T-cell ratio (OR 0.98 [0.96-0.99]) and PI-based regimens (OR 4.85 [1.29-18.24]); the presence of HG-AIN (RR 2.50 [1.41-4.45]), and a higher burden of STIs (RR 1.39 [1.03-1.85]) were predictors of rectal HIV-1 shedding intensity.

CONCLUSION

The prevalence of HIV-1 RNA rectal shedding is high in virologically suppressed MSM. In addition to ART and the immune system integrity, local factors, including the co-existence of HG-AIN and the burden of STIs, may account for the persistence of HIV-1 RNA shedding in rectal mucosa.

Mapping mutational effects along the evolutionary landscape of HIV envelope

The immediate evolutionary space accessible to HIV is largely determined by how single amino acid mutations affect fitness. These mutational effects can shift as the virus evolves. However, the prevalence of such shifts in mutational effects remains unclear. Here, we quantify the effects on viral growth of all amino acid mutations to two HIV envelope (Env) proteins that differ at >100 residues. Most mutations similarly affect both Envs, but the amino acid preferences of a minority of sites have clearly shifted. These shifted sites usually prefer a specific amino acid in one Env, but tolerate many amino acids in the other. Surprisingly, shifts are only slightly enriched at sites that have substituted between the Envs—and many occur at residues that do not even contact substitutions. Therefore, long-range epistasis can unpredictably shift Env’s mutational tolerance during HIV evolution, although the amino acid preferences of most sites are conserved between moderately diverged viral strains.

The virus that causes AIDS, or HIV, has a protein called Env on its surface, which is essential for the virus to infect cells. Env can also be recognized by the immune system, which then targets the virus for destruction or blocks it from infecting cells. Unfortunately, Env evolves very quickly, which means that HIV can evade our defenses. However, there are limits to how much this protein can change, since it still needs to perform its essential role in helping viruses enter cells.

In the century since HIV first appeared in human populations, the virus has evolved considerably. There are now many HIV strains that infect people, and they bear Env proteins with substantially different sequences. However, it is not clear if these changes in sequence have resulted in Envs from distinct strains being able to tolerate different mutations.

To examine this question, Haddox et al. compared how the Envs from two strains of HIV react to modifications in their sequences. They created all possible individual mutations in the proteins, and the resulting collections of mutated viruses were then tested for their ability to infect cells in the laboratory.

Most mutations had similar effects in both Env proteins. This allowed Haddox et al. to identify portions of the protein that easily accommodate changes, and portions that must remain unchanged for viruses to remain infectious—at least in the laboratory. Some of these mutations are under different types of pressures when the virus faces the immune system, and those were identified using computational approaches.

However, some mutations were tolerated differently by the two Env proteins. Therefore, viral strains differ in how their Env proteins can evolve. The parts of Env that showed differences in mutational tolerance between the strains were not necessarily the parts that differ in sequence. This shows that changes in sequence in one part of the protein can modify how other portions evolve.

It remains to be determined whether changes in tolerance to mutations translate into differences in how the virus can escape immunity. This is an important question given that the rapid evolution of Env is a major obstacle to creating a vaccine for HIV.

HIV-1 strains belonging to large phylogenetic clusters show accelerated escape from integrase inhibitors in cell culture compared with viral isolates from singleton/small clusters

Objectives: Viral phylogenetics revealed two patterns of HIV-1 spread among MSM in Quebec. While most HIV-1 strains (n = 2011) were associated with singleton/small clusters (cluster size 1–4), 30 viral lineages formed large networks (cluster size 20–140), contributing to 42% of diagnoses between 2011 and 2015. Herein, tissue culture selections ascertained if large cluster lineages possessed higher replicative fitness than singleton/small cluster isolates, allowing for viral escape from integrase inhibitors.

Methods: Primary HIV-1 isolates from large 20+ cluster (n = 11) or singleton/small cluster (n = 6) networks were passagedin vitro in escalating concentrations of dolutegravir, elvitegravir and lamivudine for 24–36 weeks. Sanger and deep sequencing assessed genotypic changes under selective drug pressure.

Results: Large cluster HIV-1 isolates selected for resistance to dolutegravir, elvitegravir and lamivudine faster than HIV-1 strains forming small clusters. With dolutegravir, large cluster HIV-1 variants acquired solitary R263K (n = 7), S153Y (n = 1) or H51Y (n = 1) mutations as the dominant quasi-species within 8–12 weeks as compared with small cluster lineages where R263K (n = 1/6), S153Y (1/6) or WT species (4/6) were observed after 24 weeks. Interestingly, dolutegravir-associated mutations compromised viral replicative fitness, precluding escalations in concentrations beyond 5–10 nM. With elvitegravir, large cluster variants more rapidly acquired first mutations (T66I, A92G, N155H or S147G) by week 8 followed by sequential accumulation of multiple mutations leading to viral escape (>10 μM) by week 24.

Conclusions: Further studies are needed to understand virological features of large cluster viruses that may favour their transmissibility, replicative competence and potential to escape selective antiretroviral drug pressure.

The Role of Immune Responses in HIV Mother-to-Child Transmission

HIV mother-to-child transmission (MTCT) represents a success story in the HIV/AIDS field given the significant reduction in number of transmission events with the scale-up of antiretroviral treatment and other prevention methods. Nevertheless, MTCT still occurs and better understanding of the basic biology and immunology of transmission will aid in future prevention and treatment efforts. MTCT is a unique setting given that the transmission pair is known and the infant receives passively transferred HIV-specific antibodies from the mother while in utero. Thus, infant exposure to HIV occurs in the face of HIV-specific antibodies, especially during delivery and breastfeeding. This review highlights the immune correlates of protection in HIV MTCT including humoral (neutralizing antibodies, antibody-dependent cellular cytotoxicity, and binding epitopes), cellular, and innate immune factors. We further discuss the future implications of this research as it pertains to opportunities for passive and active vaccination with the ultimate goal of eliminating HIV MTCT.

Owl monkey CCR5 reveals synergism between CD4 and CCR5 in HIV-1 entry

Studying HIV-1 replication in the presence of functionally related proteins from different species has helped define host determinants of HIV-1 infection. Humans and owl monkeys, but not macaques, encode a CD4 receptor that permits entry of transmissible HIV-1 variants due to a single residue difference. However, little is known about whether divergent CCR5 receptor proteins act as determinants of host-range. Here we show that both owl monkey (Aotus vociferans) CD4 and CCR5 receptors are functional for the entry of transmitted HIV-1 when paired with human versions of the other receptor. By contrast, the owl monkey CD4/CCR5 pair is generally a suboptimal receptor combination, although there is virus-specific variation in infection with owl monkey receptors. Introduction of the human residues 15Y and 16T within a sulfation motif into owl monkey CCR5 resulted in a gain of function. These findings suggest there is cross-talk between CD4 and CCR5 involving the sulfation motif.

Genetic bottlenecks in intraspecies virus transmission

Ultimately, viral evolution is a consequence of mutations that arise within and spread between infected hosts. The transmission bottleneck determines how much of the viral diversity generated in one host passes to another during transmission. It therefore plays a vital role in linking within-host processes to larger evolutionary trends. Although many studies suggest that transmission severely restricts the amount of genetic diversity that passes between individuals, there are important exceptions to this rule. In many cases, the factors that determine the size of the transmission bottleneck are only beginning to be understood. Here, we review how transmission bottlenecks are measured, how they arise, and their consequences for viral evolution.

Human Immunodeficiency Virus

In this chapter we will discuss the diagnosis and monitoring of individuals with HIV infection. The application and interpretation of these tests does not change dramatically when used in the immunocompromised host. The principal approach to the diagnosis of HIV infection involves serologic testing, although nucleic acid amplification tests play an important role in the diagnosis of acute HIV infection. The algorithm for diagnosis of HIV continues to evolve with newer assays that are able to detect infection within an earlier timeframe after HIV transmission. Viral load testing for HIV-1 is the cornerstone for monitoring patients on antiretroviral therapy. Genotypic and phenotypic resistance tests are employed when antiretroviral resistance is suspected and results help guide therapy. The tropism assay must be performed to determine the efficacy of CCR5 chemokine receptor antagonists. Next-generation sequencing methods are an innovative approach to assessing archived antiretroviral resistance in patients with virologic suppression. The success of antiretroviral therapy with improved long-term outcomes has made transplantation in HIV-infected patients a reality.

Factors determining human-to-human transmissibility of zoonotic pathogens via contact

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There are several modes of contact transmission of pathogens amongst humans.

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Factors promoting contact transmission act at the pathogen, host or environmental levels.

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Common pathogen factors are immune evasion, high viral load and low infectious dose.

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Common host factors are crowding, promiscuity and the presence of co-infections.

The pandemic potential of zoonotic pathogens lies in their ability to become efficiently transmissible amongst humans. Here, we focus on contact-transmitted pathogens and discuss the factors, at the pathogen, host and environmental levels that promote or hinder their human-to-human transmissibility via the following modes of contact transmission: skin contact, sexual contact, respiratory contact and multiple route contact. Factors common to several modes of transmission were immune evasion, high viral load, low infectious dose, crowding, promiscuity, and co-infections; other factors were specific for a pathogen or mode of contact transmission. The identification of such factors will lead to a better understanding of the requirements for human-to-human spread of pathogens, as well as improving risk assessment of newly emerging pathogens.

The first 24 h: targeting the window of opportunity for antibody-mediated protection against HIV-1 transmission

PURPOSE OF REVIEW

I will review evidence that antibodies protect against HIV-1 transmission in a short window of opportunity, involving neutralization, Fc-mediated effector function, or both.

RECENT FINDINGS

The last decade witnessed a dramatic progress in the understanding of antibody-mediated protection against HIV-1, including active and passive immunization studies in nonhuman primates; association between reduced infection risk and the specificities and function of antibodies in the RV144 clinical trial; identification of potent, broadly neutralizing antibodies; high-resolution structural studies of the HIV-1 envelope trimer; and an increasing appreciation that Fc-mediated effector function is critical to protection against transmission for neutralizing and nonneutralizing antibodies. Less information is known about how antibodies protect in situ, except that they must do in the first 24 h after exposure. New evidence suggests that antibodies protect in an acute innate immune environment involving the NXLRX1 inflammasome and transforming growth factor beta (TGF-β) that favors infection and rapid dissemination of CCR6RORγ Th17 cells.

SUMMARY

These recent findings set the stage for understanding how antibodies can prevent the transmission of HIV-1. In this context, antibodies must prevent infection in an innate immune environment that strongly favors transmission. This information is key for the development of a vaccine against HIV-1.

ART influences HIV persistence in the female reproductive tract and cervicovaginal secretions

The recently completed HIV prevention trials network study 052 is a landmark collaboration demonstrating that HIV transmission in discordant couples can be dramatically reduced by treating the infected individual with antiretroviral therapy (ART). However, the cellular and virological events that occur in the female reproductive tract (FRT) during ART that result in such a drastic decrease in transmission were not studied and remain unknown. Here, we implemented an in vivo model of ART in BM/liver/thymus (BLT) humanized mice in order to better understand the ability of ART to prevent secondary HIV transmission. We demonstrated that the entire FRT of BLT mice is reconstituted with human CD4+ cells that are shed into cervicovaginal secretions (CVS). A high percentage of the CD4+ T cells in the FRT and CVS expressed CCR5 and therefore are potential HIV target cells. Infection with HIV increased the numbers of CD4+ and CD8+ T cells in CVS of BLT mice. Furthermore, HIV was present in CVS during infection. Finally, we evaluated the effect of ART on HIV levels in the FRT and CVS and demonstrated that ART can efficiently suppress cell-free HIV-RNA in CVS, despite residual levels of HIV-RNA+ cells in both the FRT and CVS.