Purpose of review
Effective treatment exists for TB and for HIV but treating both diseases simultaneously presents several challenges. This review assessed the evidence for timing of antiretroviral therapy (ART) initiation in patents co-infected with TB.
Published evidence clearly demonstrates that TB HIV integration is essential for improved survival, but the question of when to start ART during TB treatment is more complex. Five randomised controlled trials assessed this question; four trials showed no difference in incidence rates of AIDS or death between TB patients initiating ART within 2 months compared to later during TB therapy, while one trial showed a significant survival gain with ART initiation within 2 weeks of TB therapy start. All five studies found improved AIDS-free survival with earlier ART initiation in TB patients with low CD4+ T-cell counts, except among patients with TB meningitis. The survival benefit was however, accompanied by increased immune reconstitution inflammatory syndrome events.
The trial data support the World Health Organisation recommendations on when to start ART in TB-HIV co-infected patients including earlier ART initiation in severely immune-compromised patients. However, several challenges remain in integrating TB and HIV treatment in public health care services. Additional research on timing of ART is needed for patients with drug-resistant and extra-pulmonary TB, notably TB meningitis.
HIV; tuberculosis; antiretroviral therapy; immune reconstitution inflammatory syndrome (IRIS)
The mucosal environment may impact the risk for human immunodeficiency virus type 1 (HIV-1) acquisition. Immune mediators were measured in vaginal fluid collected from HPTN 035 participants who acquired HIV-1 and from those who remained HIV-1 negative (controls). Mediator concentrations were similar in samples obtained before as compared to after HIV-1 acquisition in the 8 seroconverters. Compared with controls, seroconverters were more likely to have detectable levels of HβD-2 (odds ratio [OR], 2.39; P = .005) and greater Escherichia coli bactericidal activity (OR, 1.22; P = .01) prior to seroconversion. E. coli bactericidal activity remained significant in a multivariable analysis (P = .02) and may be a biomarker for HIV-1 acquisition.
Broadly cross-neutralizing (BCN) antibodies are likely to be critical for an effective HIV vaccine. However, the ontogeny of such antibodies and their relationship with autologous viral evolution is unclear. Here, we characterized viral evolution in CAP256, a subtype C-infected individual who developed potent BCN antibodies targeting positions R166 and K169 in the V2 region. CAP256 was superinfected at 3 months postinfection with a virus that was highly sensitive to BCN V2-dependent monoclonal antibodies. The autologous neutralizing response in CAP256 was directed at V1V2, reaching extremely high titers (>1:40,000) against the superinfecting virus at 42 weeks, just 11 weeks prior to the development of the BCN response targeting the same region. Recombination between the primary and superinfecting viruses, especially in V2 and gp41, resulted in two distinct lineages by 4 years postinfection. Although neutralization of some CAP256 clones by plasma from as much as 2 years earlier suggested incomplete viral escape, nonetheless titers against later clones were reduced at least 40-fold to less than 1:1,000. Escape mutations were identified in each lineage, either at R166 or at K169, suggesting that strain-specific and BCN antibodies targeted overlapping epitopes. Furthermore, the early dependence of CAP256 neutralizing antibodies on the N160 glycan decreased with the onset of neutralization breadth, indicating a change in specificity. These data suggest rapid maturation, within 11 weeks, of CAP256 strain-specific antibodies to acquire breadth, with implications for the vaccine elicitation of BCN V2-dependent antibodies. Overall these studies demonstrate that ongoing viral escape is possible, even from BCN antibodies.
Identifying the targets of broadly neutralizing antibodies to HIV-1 and understanding how these antibodies develop remain important goals in the quest to rationally develop an HIV-1 vaccine. We previously identified a participant in the CAPRISA Acute Infection Cohort (CAP257) whose plasma neutralized 84% of heterologous viruses. In this study we showed that breadth in CAP257 was largely due to the sequential, transient appearance of three distinct broadly neutralizing antibody specificities spanning the first 4.5 years of infection. The first specificity targeted an epitope in the V2 region of gp120 that was also recognized by strain-specific antibodies 7 weeks earlier. Specificity for the autologous virus was determined largely by a rare N167 antigenic variant of V2, with viral escape to the more common D167 immunotype coinciding with the development of the first wave of broadly neutralizing antibodies. Escape from these broadly neutralizing V2 antibodies through deletion of the glycan at N160 was associated with exposure of an epitope in the CD4 binding site that became the target for a second wave of broadly neutralizing antibodies. Neutralization by these CD4 binding site antibodies was almost entirely dependent on the glycan at position N276. Early viral escape mutations in the CD4 binding site drove an increase in wave two neutralization breadth, as this second wave of heterologous neutralization matured to recognize multiple immunotypes within this site. The third wave targeted a quaternary epitope that did not overlap any of the four known sites of vulnerability on the HIV-1 envelope and remains undefined. Altogether this study showed that the human immune system is capable of generating multiple broadly neutralizing antibodies in response to a constantly evolving viral population that exposes new targets as a consequence of escape from earlier neutralizing antibodies.
Four sites of vulnerability for broadly neutralizing antibodies to HIV-1 have been identified thus far. How these broadly reactive antibodies arise, and the host-pathogen interactions that drive the affinity maturation necessary for neutralization breadth are poorly understood. This study details the sequential development of three distinct broadly neutralizing antibody responses within a single HIV-1 infected individual over 4.5 years of infection. We show how escape from the first wave of antibodies targeting V2 exposed a second site that was the stimulus for a new wave of glycan dependent broadly neutralizing antibodies against the CD4 binding site. These data highlight how antibody evolution in response to viral escape mutations served to broaden the host immune response to these two epitopes. Finally, we document a third wave of neutralization that targets an undefined epitope that did not appear to overlap with the four known sites of vulnerability on the HIV-1 envelope. These data support the design of templates for sequential immunization strategies aimed at increasing neutralization breadth through the recognition of multiple epitopes and their immunotypes.
The antiretroviral agent, tenofovir, formulated as a vaginal microbicide gel, reduces human immunodeficiency virus (HIV) acquisition by 39% in women. This study assessed the role of preexisting immune activation in HIV acquisition in women from the CAPRISA 004 trial, to identify potential strategies to increase the effectiveness of tenofovir gel. Systemic cytokine and cellular immune mediators (platelets and natural killer [NK] cells) were assessed in women at high risk for HIV assigned to either tenofovir or placebo gel in the CAPRISA 004 trial. Notwithstanding tenofovir gel use, women who acquired HIV had significantly higher systemic innate immune activation prior to infection than women who remained uninfected. Activation of both soluble (cytokine) and cellular (NK cells) immune mediators were associated with HIV acquisition, individually or in combination. Hence, an innate immune activation suppressant could be added to tenofovir gel as a potential combination gel strategy in developing the next generation of higher efficacy antiretroviral microbicides.
Background. Eight decades ago, the ratio of monocytes to lymphocytes (hereafter, the “ML ratio”) was noted to affect outcomes of mycobacterial infection in rabbits. Recent transcriptomic studies support a role for relative proportions of myeloid and lymphoid transcripts in tuberculosis outcomes. The ML ratio in peripheral blood is known to be governed by hematopoietic stem cells with distinct biases.
Methods. The predictive value of the baseline ML ratio was modeled in 2 prospective cohorts of HIV-infected adults starting cART in South Africa (primary cohort, 1862 participants; replication cohort, 345 participants). Incident tuberculosis was diagnosed with clinical, radiographic, and microbiologic methods per contemporary guidelines. Kaplan-Meier survival analyses and Cox proportional hazards modeling were conducted.
Results. The incidence rate of tuberculosis differed significantly by baseline ML ratio: 32.61 (95% confidence interval [CI], 15.38–61.54), 16.36 (95% CI, 12.39–21.23), and 51.80 (95% CI, 23.10–101.71) per 1000 patient-years for ML ratios of less than the 5th percentile, between the 5th and 95th percentiles, and greater than the 95th percentile, respectively (P = .007). Neither monocyte counts nor lymphocyte counts alone were associated with tuberculosis. After adjustment for sex, World Health Organization human immunodeficiency virus disease stage, CD4+ T-cell counts, and previous history of tuberculosis, hazards of disease were significantly higher for patients with ML ratios of less than the 5th percentile or greater than the 95th percentile (adjusted hazard ratio, 2.47; 95% CI, 1.39–4.40; P = .002).
Conclusions. The ML ratio may be a useful, readily available tool to stratify the risk of tuberculosis and suggests involvement of hematopoietic stem cell bias in tuberculosis pathogenesis.
tuberculosis; HIV; combination antiretroviral therapy; monocytes; lymphocytes; ML ratio
Human immunodeficiency virus (HIV) prevention tools that women can use and control are urgently needed. Microbicides are chemical products applied to the vagina or rectum to prevent the sexual transmission of HIV. Four classes of candidate microbicides have been tested to date: those that (1) enhance the natural defences in the vagina to inactivate HIV; (2) inactivate HIV in the vagina; (3) prevent HIV from attaching to, and fusing with, the host cells; and (4) prevent HIV from replicating in genital tract host cells. Despite numerous disappointing efficacy trial results over the past 20 years, substantial progress is now being made in microbicide development after the release of the CAPRISA 004 trial, which provided proof-of-concept that topical antiretroviral microbicides can prevent sexual transmission of HIV and herpes simplex type-2 infection. Microbicides, which fill an important gap for women-controlled prevention methods, have the potential to alter the course of the HIV pandemic.
HIV; women; microbicide prevention
Background. Diagnosis and treatment of sexually transmitted infections (STIs) is a public health priority, particularly in regions where the incidence of human immunodeficiency virus (HIV) infection is high. In most developing countries, STIs are managed syndromically. We assessed the adequacy of syndromic diagnosis of STIs, compared with laboratory diagnosis of STIs, and evaluated the association between STI diagnosis and the risk of HIV acquisition in a cohort of high-risk women.
Methods. HIV-uninfected high-risk women (n = 242) were followed for 24 months. Symptoms of STIs were recorded, and laboratory diagnosis of common STI pathogens was conducted every 6 months. Forty-two cytokines were measured by Luminex in cervicovaginal lavage specimens at enrollment. Human immunodeficiency virus type 1 (HIV-1) infection was evaluated monthly.
Results. Only 12.3% of women (25 of 204) who had a laboratory-diagnosed, discharge-causing STI had clinically evident discharge. Vaginal discharge was thus a poor predictor of laboratory-diagnosed STIs (sensitivity, 12.3%; specificity, 93.8%). Cervicovaginal cytokine concentrations did not differ between women with asymptomatic STIs and those with symptomatic STIs and were elevated in women with asymptomatic STIs, compared with women with no STIs or bacterial vaginosis. Although laboratory-diagnosed STIs were associated with increased risk of HIV infection (hazard ratio, 3.3 [95% confidence interval, 1.5–7.2)], clinical symptoms were not.
Conclusions. Syndromic STI diagnosis dependent on vaginal discharge was poorly predictive of laboratory-diagnosed STI. Laboratory-diagnosed STIs were associated with increased susceptibility to HIV acquisition, while vaginal discharge was not.
Background. The biggest challenge in human immunodeficiency virus type 1 (HIV-1) prevention in Africa is the high HIV-1 burden in young women. In macaques, proinflammatory cytokine production in the genital tract is necessary for target cell recruitment and establishment of simian immunodeficiency virus (SIV) infection following vaginal inoculation. The purpose of this study was to assess if genital inflammation during early HIV-1 infection predisposes women to rapid disease progression.
Methods. Inflammatory cytokine concentrations were measured in cervicovaginal lavage (CVL) from 49 women 6, 17, 30, and 55 weeks after HIV-1 infection and from 22 of these women before infection. Associations between genital inflammation and viral load set point and blood CD4 cell counts 12 months after infection were investigated.
Results. Elevated genital cytokine concentrations 6 and 17 weeks after HIV-1 infection were associated with higher viral load set points and, to a lesser extent, with CD4 depletion. CVL cytokine concentrations during early infection did not differ relative to preinfection but were elevated in women who had vaginal discharge, detectable HIV-1 RNA in their genital tracts, and lower blood CD4 counts.
Conclusion. Genital inflammation during early HIV-1 infection was associated with higher viral load set point and CD4 depletion, which are markers of rapid disease progression. Strategies aimed at reducing genital inflammation during early HIV-1 infection may slow disease progression.
Broadly neutralizing antibodies to the CD4 binding site (CD4bs) of gp120 are generated by some HIV-1-infected individuals, but little is known about the prevalence and evolution of this antibody response during the course of HIV-1 infection. We analyzed the sera of 113 HIV-1 seroconverters from three cohorts for binding to a panel of gp120 core proteins and their corresponding CD4bs knockout mutants. Among sera collected between 99 and 258 weeks post-HIV-1 infection, 88% contained antibodies to the CD4bs and 47% contained antibodies to resurfaced stabilized core (RSC) probes that react preferentially with broadly neutralizing CD4bs antibodies (BNCD4), such as monoclonal antibodies (MAbs) VRC01 and VRC-CH31. Analysis of longitudinal serum samples from a subset of 18 subjects revealed that CD4bs antibodies to gp120 arose within the first 4 to 16 weeks of infection, while the development of RSC-reactive antibodies was more varied, occurring between 10 and 152 weeks post-HIV-1 infection. Despite the presence of these antibodies, serum neutralization mediated by RSC-reactive antibodies was detected in sera from only a few donors infected for more than 3 years. Thus, CD4bs antibodies that bind a VRC01-like epitope are often induced during HIV-1 infection, but the level and potency required to mediate serum neutralization may take years to develop. An improved understanding of the immunological factors associated with the development and maturation of neutralizing CD4bs antibodies during HIV-1 infection may provide insights into the requirements for eliciting this response by vaccination.
We previously reported that integrating antiretroviral therapy (ART) with tuberculosis treatment reduces mortality. However, optimal time to initiate ART during tuberculosis treatment remains contentious.
To address this, we conducted a 3-arm, open-label randomized controlled trial in South Africa in acid-fast bacilli smear positive patients (n=642) with HIV and CD4+ counts <500 cells/mm3. Findings on the early therapy group (ART initiated within 4 weeks of tuberculosis treatment initiation, n=214) and late therapy group (ART initiated within the first 4 weeks of the continuation phase of tuberculosis treatment, n=215) are presented here.
Median CD4+ count and viral load at baseline was 150 cells/mm3 and 161000 copies/ml, being similar in both groups. Incidence rate of AIDS or death was 6.9 (18/259.4) and 7.8 (19/244.2) per 100 person-years in the early and late therapy groups respectively (Incidence Rate Ratio (IRR)=0.89; 95%Confidence Interval (95%CI): 0.44,1.79; P=0.73). However, in patients with CD4+ counts <50 cells/mm3, the incidence rates of AIDS or death were 8.5 (early) and 26.3 (late) per 100 person-years (IRR=0.32; 95%CI: 0.07,1.13; P=0.06). Immune reconstitution inflammatory syndrome (IRIS) incidence rates were 20.2 (early) and 7.7 (late) per 100 person-years (IRR=2.62; 95%CI: 1.48,4.82; P<0.001). Adverse events requiring antiretroviral drug switches occurred in 10 (early) and 1 (late) patients (P=0.006).
The benefits of AIDS-free survival balanced against the risks of IRIS and ART-related adverse events, support early ART initiation in patients with CD4+ counts <50 cells/mm3 and deferred ART initiation to the continuation phase of tuberculosis treatment when CD4+ counts are higher.
Tenofovir gel, an antiretroviral-based vaginal microbicide, reduced HIV acquisition by 39% in women in a recent randomised controlled clinical trial in South Africa.
To inform policy we used a dynamical model of HIV transmission, calibrated to the epidemic in South Africa, to determine the population-level impact of this microbicide on HIV incidence, prevalence and deaths and to evaluate its cost-effectiveness.
If women use Tenofovir-gel in 80% or more of sexual encounters (high coverage), it could avert 2.33 (0.12 to 4.63) million new infections and save 1.30 (0.07 to 2.42) million lives and if used in 25% of sexual encounters (low coverage), it could avert 0.50 (0.04 to 0.77) million new infections and save 0.29 (0.02 to 0.44) million deaths, over the next 20 years. At US$0.50 per application, the cost per infection averted at low coverage is US$2,392 (US$562 to US$4,222) and the cost per disability-adjusted life year saved is US$104 (US$27 to US$181); at high coverage the costs are about 30% less.
Over twenty years the use of Tenofovir gel in South Africa could avert up to 2 million new infections and 1 million AIDS deaths. Even with low rates of gel use it is highly cost-effective and compares favourably with other control methods. This female controlled prevention method could have a significant impact on the epidemic of HIV in South Africa. Programmes should aim to achieve gel use in more than 25% of sexual encounters to significantly alter the course of the epidemic.
HIV prevention; microbicide gel; Tenofovir; South Africa; cost effectiveness
Background In mature generalized human immunodeficiency virus (HIV) epidemics, as survival from accessing antiretroviral treatment (ART) increases, HIV prevalence data may be suboptimal and difficult to interpret without HIV incidence rates.
Objective To determine the HIV incidence rate among rural and urban women in KwaZulu-Natal, South Africa.
Methods We conducted a prospective cohort study from March 2004 to May 2007. Volunteers were recruited from a rural family-planning clinic and an urban clinic for sexually transmitted infections. Consenting, HIV-uninfected women aged 14–30 years were enrolled. Demographic, clinical, sexual and behavioural data were collected using standardized questionnaires with HIV risk reduction counselling and HIV testing. Pelvic examinations were completed at quarterly visits.
Results The HIV prevalence at screening was 35.7% [95% confidence interval (CI) 32.7–38.8] amongst rural women and 59.3% (95% CI 56.5–62.0) amongst urban women. A total of 594/2240 (26.5%) enrolled women contributed to 602 person-years (PYs) of follow-up. The median age was 22 years [inter-quartile range 18–23 years]. HIV incidence rate was 6.5/100 PY (95% CI 4.4–9.2) amongst rural women and 6.4/100 PY (95% CI 2.6–13.2) amongst urban women. HIV incidence rate of 17.2/100 PY (95% CI 2.1–62.2) was highest amongst urban women <20 years of age and 10.2/100 PY (95% CI 4.1–20.9) amongst rural women ≥25 years of age.
Conclusion HIV incidence rates are devastatingly high in young women in rural and urban KwaZulu-Natal, despite reports of stabilized HIV prevalence observed in current surveillance data. The diffuse nature of the HIV epidemic underscores the urgent need to enhance HIV prevention and treatment modalities.
HIV incidence; HIV prevalence; young women; South Africa
Griffithsin (GRFT), Cyanovirin-N (CV-N) and Scytovirin (SVN) are lectins that inhibit HIV-1 infection by binding to multiple mannose-rich glycans on the HIV-1 envelope glycoproteins (Env). Here we show that these lectins neutralize subtype C primary virus isolates in addition to Env-pseudotyped viruses obtained from plasma and cervical vaginal lavages. Among 15 subtype C pseudoviruses, the median IC50 values were 0.4, 1.8 and 20.1 nM for GRFT, CV-N and SVN, respectively, similar to what was found for subtype B and A. Analysis of Env sequences suggested that concomitant lack of glycans at positions 234 and 295 resulted in natural resistance to these compounds, which was confirmed by site-directed mutagenesis. Furthermore, the binding sites for these lectins overlapped that of the 2G12 monoclonal antibody epitope, which is generally absent on subtype C Env. This data support further research on these lectins as potential microbicides in the context of HIV-1 subtype C infection.
Griffithsin; Cyanovirin-N; Scytovirin; lectins; HIV-1 subtype C; microbicides; 2G12 monoclonal antibody
The Duffy-null trait and ethnic neutropenia are highly prevalent in Africa. The authors found that the trait of Duffy-null–associated low neutrophil counts associated with increased HIV-1 susceptibility. The possible contribution of this trait to the high prevalence of HIV-1 in Africa requires further investigation
Background. The Duffy-null trait and ethnic netropenia are both highly prevalent in Africa. The influence of pre-seroconversion levels of peripheral blood cell counts (PBCs) on the risk of acquiring human immunodeficiency virus (HIV)–1 infection among Africans is unknown.
Methods. The triangular relationship among pre-seroconversion PBC counts, host genotypes, and risk of HIV acquisition was determined in a prospective cohort of black South African high-risk female sex workers. Twenty-seven women had seroconversion during follow-up, and 115 remained HIV negative for 2 years, despite engaging in high-risk activity.
Results. Pre-seroconversion neutrophil counts in women who subsequently had seroconversion were significantly lower, whereas platelet counts were higher, compared with those who remained HIV negative. Comprising 27% of the cohort, subjects with pre-seroconversion neutrophil counts of <2500 cells/mm3 had a ∼3-fold greater risk of acquiring HIV infection. In a genome-wide association analyses, an African-specific polymorphism (rs2814778) in the promoter of Duffy Antigen Receptor for Chemokines (DARC −46T > C) was significantly associated with neutrophil counts (P = 7.9 × 10−11). DARC −46C/C results in loss of DARC expression on erthyrocytes (Duffy-null) and resistance to Plasmodium vivax malaria, and in our cohort, only subjects with this genotype had pre-seroconversion neutrophil counts of <2500 cells/mm3. The risk of acquiring HIV infection was ∼3-fold greater in those with the trait of Duffy-null–associated low neutrophil counts, compared with all other study participants.
Conclusions. Pre-seroconversion neutrophil and platelet counts influence risk of HIV infection. The trait of Duffy-null–associated low neutrophil counts influences HIV susceptibility. Because of the high prevalence of this trait among persons of African ancestry, it may contribute to the dynamics of the HIV epidemic in Africa.
A small proportion of HIV-infected individuals generate a neutralizing antibody (NAb) response of exceptional magnitude and breadth. A detailed analysis of the critical epitopes targeted by broadly neutralizing antibodies should help to define optimal targets for vaccine design. HIV-1-infected subjects with potent cross-reactive serum neutralizing antibodies were identified by assaying sera from 308 subjects against a multiclade panel of 12 “tier 2” viruses (4 each of subtypes A, B, and C). Various neutralizing epitope specificities were determined for the top 9 neutralizers, including clade A-, clade B-, clade C-, and clade A/C-infected donors, by using a comprehensive set of assays. In some subjects, neutralization breadth was mediated by two or more antibody specificities. Although antibodies to the gp41 membrane-proximal external region (MPER) were identified in some subjects, the subjects with the greatest neutralization breadth targeted gp120 epitopes, including the CD4 binding site, a glycan-containing quaternary epitope formed by the V2 and V3 loops, or an outer domain epitope containing a glycan at residue N332. The broadly reactive HIV-1 neutralization observed in some subjects is mediated by antibodies targeting several conserved regions on the HIV-1 envelope glycoprotein.
Young girls in sub Saharan Africa are reported to have higher rates of human immunodeficiency virus (HIV) infection compared to boys in the same age group. Knowledge of HIV status amongst high schools learners provides an important gateway to prevention and treatment services. This study aimed at determining the HIV prevalence and explored the feasibility of HIV testing among high school learners.
Between September 2010 and February 2011, a linked, anonymous cross-sectional survey was conducted in two public sector high schools in the rural KwaZulu-Natal midlands. Following written informed consent, dried blood spot samples (DBS) were collected and tested for HIV. The overall and age-specific HIV prevalence were compared with select demographic variables.
The HIV prevalence in learners aged 12 to 25 in school A was 4.7% (95% CI 2.8-6.5) compared to 2.5% (95% CI 1.6-3.5) in school B, (p = 0.04). Whilst the HIV prevalence was similar for boys at 1.3% (95% CI 0-2.8) in school A and 1.7% (95% CI 0.5-2.8) in school B, the prevalence in girls was consistently higher and was 7.7% (95% CI 4.5-10.9) in school A and 3.2% (95% CI 1.8-4.6) in school B. The age-specific HIV prevalence in girls increased 1.5 to 2 fold for each two year age category, while for boys the prevalence was stable across all age groups.
The high HIV prevalence in female learners underscores the importance of sexual reproductive health and schools-based HIV testing programs as an important gateway to prevention and treatment services.
Young girls; HIV prevalence; surveillance
The C3-V4 region is a major target of autologous neutralizing antibodies in HIV-1 subtype C infection. We previously identified a Center for AIDS Program of Research in South Africa (CAPRISA) participant, CAP88, who developed a potent neutralizing-antibody response within 3 months of infection that targeted an epitope in the C3 region of the HIV-1 envelope (P. L. Moore et al., PLoS Pathog. 5:e1000598, 2009). Here we showed that these type-specific antibodies could be adsorbed using recombinant gp120 from the transmitted/founder virus from CAP88 but not by gp120 made from other isolates. Furthermore, this activity could be depleted using a chimeric gp120 protein that contained only the C3 region from the CAP88 viral envelope engrafted onto the unrelated CAP63 viral envelope (called 63-88C3). On the basis of this, a differential sorting of memory B cells was performed using gp120s made from 63-88C3 and CAP63 labeled with different fluorochromes as positive and negative probes, respectively. This strategy resulted in the isolation of a highly specific monoclonal antibody (MAb), called CAP88-CH06, that neutralized the CAP88 transmitted/founder virus and viruses from acute infection but was unable to neutralize CAP88 viruses isolated at 6 and 12 months postinfection. The latter viruses contained 2 amino acid changes in the alpha-2 helix of C3 that mediated escape from this MAb. One of these changes involved the introduction of an N-linked glycan at position 339 that occluded the epitope, while the other mutation (either E343K or E350K) was a charge change. Our data validate the use of differential sorting to isolate a MAb targeting a specific epitope in the envelope glycoprotein and provided insights into the mechanisms of autologous neutralization escape.
An understanding of how broadly neutralizing activity develops in HIV-1-infected individuals is needed to guide vaccine design and immunization strategies. Here we used a large panel of 44 HIV-1 envelope variants (subtypes A, B, and C) to evaluate the presence of broadly neutralizing antibodies in serum samples obtained 3 years after seroconversion from 40 women enrolled in the CAPRISA 002 acute infection cohort. Seven of 40 participants had serum antibodies that neutralized more than 40% of viruses tested and were considered to have neutralization breadth. Among the samples with breadth, CAP257 serum neutralized 82% (36/44 variants) of the panel, while CAP256 serum neutralized 77% (33/43 variants) of the panel. Analysis of longitudinal samples showed that breadth developed gradually starting from year 2, with the number of viruses neutralized as well as the antibody titer increasing over time. Interestingly, neutralization breadth peaked at 4 years postinfection, with no increase thereafter. The extent of cross-neutralizing activity correlated with CD4+ T cell decline, viral load, and CD4+ T cell count at 6 months postinfection but not at later time points, suggesting that early events set the stage for the development of breadth. However, in a multivariate analysis, CD4 decline was the major driver of this association, as viral load was not an independent predictor of breadth. Mapping of the epitopes targeted by cross-neutralizing antibodies revealed that in one individual these antibodies recognized the membrane-proximal external region (MPER), while in two other individuals, cross-neutralizing activity was adsorbed by monomeric gp120 and targeted epitopes that involved the N-linked glycan at position 332 in the C3 region. Serum antibodies from the other four participants targeted quaternary epitopes, at least 2 of which were PG9/16-like and depended on the N160 and/or L165 residue in the V2 region. These data indicate that fewer than 20% of HIV-1 subtype C-infected individuals develop antibodies with cross-neutralizing activity after 3 years of infection and that these antibodies target different regions of the HIV-1 envelope, including as yet uncharacterized epitopes.
The targets of broadly cross-neutralizing (BCN) antibodies are of great interest in the HIV vaccine field. We have identified a subtype C HIV-1-superinfected individual, CAP256, with high-level BCN activity, and characterized the antibody specificity mediating breadth. CAP256 developed potent BCN activity peaking at 3 years postinfection, neutralizing 32 (76%) of 42 heterologous viruses, with titers of antibodies against some viruses exceeding 1:10,000. CAP256 showed a subtype bias, preferentially neutralizing subtype C and A viruses over subtype B viruses. CAP256 BCN serum targeted a quaternary epitope which included the V1V2 region. Further mapping identified residues F159, N160, L165, R166, D167, K169, and K171 (forming the FN/LRD-K-K motif) in the V2 region as crucial to the CAP256 epitope. However, the fine specificity of the BCN response varied over time and, while consistently dependent on R166 and K169, became gradually less dependent on D167 and K171, possibly contributing to the incremental increase in breadth over 4 years. The presence of an intact FN/LRD-K-K motif in heterologous viruses was associated with sensitivity, although the length of the adjacent V1 loop modulated the degree of sensitivity, with a shorter V1 region significantly associated with higher titers. Repair of the FN/LRD-K-K motif in resistant heterologous viruses conferred sensitivity, with titers sometimes exceeding 1:10,000. Comparison of the CAP256 epitope with that of the PG9/PG16 monoclonal antibodies suggested that these epitopes overlapped, adding to the mounting evidence that this may represent a common neutralization target that should be further investigated as a potential vaccine candidate.
The CAPRISA 004 trial assessed effectiveness and safety of a 1% vaginal gel formulation of tenofovir, a nucleotide reverse transcriptase inhibitor, for the prevention of HIV acquisition in women. A double-blind, randomized controlled trial was conducted comparing tenofovir gel (n=445) with placebo gel (n=444) in sexually active, HIV-uninfected 18-40 year-old women in urban and rural KwaZulu-Natal, South Africa HIV serostatus, safety, sexual behavior and gel and condom use were assessed at monthly follow-up visits for 30 months. HIV incidence in the tenofovir gel arm was 5.6 per 100 women-years (wy), i.e. person time of study observation, (38/680.6wy) compared to 9.1 per 100 wy (60/660.7wy) in the placebo gel arm (Incidence Rate Ratio (IRR)=0.61; p=0.017).In high adherers (gel adherence >80%), HIV incidence was 54% lower (p=0.025) in the tenofovir gel arm. In intermediate adherers (gel adherence 50-80%) and low adherers (gel adherence < 50%) the HIV incidence reduction was 38% and 28% respectively. Tenofovir gel reduced HIV acquisition by an estimated 39% overall, and by 54% in women with high gel adherence. No increase in the overall adverse event rates was observed. There were no changes in viral load and no tenofovir resistance in HIV seroconvertors. Tenofovir gel could potentially fill an important HIV prevention gap, especially for women unable to successfully negotiate mutual monogamy or condom use.
Deciphering immune events during early stages of human immunodeficiency virus type 1 (HIV-1) infection is critical for understanding the course of disease. We characterized the hierarchy of HIV-1-specific T-cell gamma interferon (IFN-γ) enzyme-linked immunospot (ELISPOT) assay responses during acute subtype C infection in 53 individuals and associated temporal patterns of responses with disease progression in the first 12 months. There was a diverse pattern of T-cell recognition across the proteome, with the recognition of Nef being immunodominant as early as 3 weeks postinfection. Over the first 6 months, we found that there was a 23% chance of an increased response to Nef for every week postinfection (P = 0.0024), followed by a nonsignificant increase to Pol (4.6%) and Gag (3.2%). Responses to Env and regulatory proteins appeared to remain stable. Three temporal patterns of HIV-specific T-cell responses could be distinguished: persistent, lost, or new. The proportion of persistent T-cell responses was significantly lower (P = 0.0037) in individuals defined as rapid progressors than in those progressing slowly and who controlled viremia. Almost 90% of lost T-cell responses were coincidental with autologous viral epitope escape. Regression analysis between the time to fixed viral escape and lost T-cell responses (r = 0.61; P = 0.019) showed a mean delay of 14 weeks after viral escape. Collectively, T-cell epitope recognition is not a static event, and temporal patterns of IFN-γ-based responses exist. This is due partly to viral sequence variation but also to the recognition of invariant viral epitopes that leads to waves of persistent T-cell immunity, which appears to associate with slower disease progression in the first year of infection.