Sustained virologic control in SIV+ macaques after antiretroviral and α4β7 antibody therapy

Antiretroviral drug therapy (ART) effectively suppresses replication of both the immunodeficiency viruses, human (HIV) and simian (SIV); however, virus rebounds soon after ART is withdrawn. SIV-infected monkeys were treated with a 90-day course of ART initiated at 5 weeks post infection followed at 9 weeks post infection by infusions of a primatized monoclonal antibody against the α4β7 integrin administered every 3 weeks until week 32. These animals subsequently maintained low to undetectable viral loads and normal CD4+ T cell counts in plasma and gastrointestinal tissues for more than 9 months, even after all treatment was withdrawn. This combination therapy allows macaques to effectively control viremia and reconstitute their immune systems without a need for further therapy.

A Randomized, Controlled Trial of ZMapp for Ebola Virus Infection

BACKGROUND

Data from studies in nonhuman primates suggest that the triple monoclonal antibody cocktail ZMapp is a promising immune-based treatment for Ebola virus disease (EVD).

METHODS

Beginning in March 2015, we conducted a randomized, controlled trial of ZMapp plus the current standard of care as compared with the current standard of care alone in patients with EVD that was diagnosed in West Africa by polymerase-chain-reaction (PCR) assay. Eligible patients of any age were randomly assigned in a 1:1 ratio to receive either the current standard of care or the current standard of care plus three intravenous infusions of ZMapp (50 mg per kilogram of body weight, administered every third day). Patients were stratified according to baseline PCR cycle-threshold value for the virus (≤22 vs. >22) and country of enrollment. Oral favipiravir was part of the current standard of care in Guinea. The primary end point was mortality at 28 days.

RESULTS

A total of 72 patients were enrolled at sites in Liberia, Sierra Leone, Guinea, and the United States. Of the 71 patients who could be evaluated, 21 died, representing an overall case fatality rate of 30%. Death occurred in 13 of 35 patients (37%) who received the current standard of care alone and in 8 of 36 patients (22%) who received the current standard of care plus ZMapp. The observed posterior probability that ZMapp plus the current standard of care was superior to the current standard of care alone was 91.2%, falling short of the prespecified threshold of 97.5%. Frequentist analyses yielded similar results (absolute difference in mortality with ZMapp, -15 percentage points; 95% confidence interval, -36 to 7). Baseline viral load was strongly predictive of both mortality and duration of hospitalization in all age groups.

CONCLUSIONS

In this randomized, controlled trial of a putative therapeutic agent for EVD, although the estimated effect of ZMapp appeared to be beneficial, the result did not meet the prespecified statistical threshold for efficacy. (Funded by the National Institute of Allergy and Infectious Diseases and others; PREVAIL II ClinicalTrials.gov number, NCT02363322 .).

HIV-1 gp120: A Target for Therapeutics and Vaccine Design

Although extraordinary progress has been made in the treatment and prevention of HIV infection, the AIDS pandemic continues to rage globally with 2.1 million infections and 1.6 million AIDS-related deaths reported in 2013. Until an effective vaccine is developed, new strategies for treatment and prevention are needed. Regarding the prevention of HIV infection, a major focus of prevention research in general and vaccine research in particular involves the interaction of the HIV-1 envelope protein gp120 with cell-surface receptors, with the hope that a greater understanding of these interactions will lead to the development of novel strategies aimed at preventing and even treating HIV-1 infection. Particular attention has been directed toward gaining a more precise understanding of the early events in transmission focusing on that critical window of time when HIV first establishes infection in the host. Here we describe some of the recent findings involving HIV-1 envelope interactions with cell surface receptors that are relevant to transmission and which may represent new opportunities to develop strategies to prevent HIV infection.

Antimicrobial Resistance

IMPORTANCE

The development of antibiotics is considered among the most important advances of modern science. Antibiotics have saved millions of lives. However, antimicrobial resistance (AMR) threatens this progress and presents significant risks to human health.

OBJECTIVE

To identify factors associated with AMR, the current epidemiology of important resistant organisms, and possible solutions to the AMR problem.

DATA SOURCES, STUDY SELECTION, AND DATA SYNTHESIS

PubMed (2000-2016), NIH REPORTER, and ClinicalTrials.gov databases were searched for articles and entries related to AMR, focusing on epidemiology, clinical effects of AMR, discovery of novel agents to treat AMR bacterial infections, and nonpharmacological strategies to eliminate or modify AMR bacteria. In addition to articles and entries found in these databases, selected health policy reports and public health guidance documents were reviewed. Of 217 articles, databases, and reports identified, 103 were selected for review.

RESULTS

The increase in AMR has been driven by a diverse set of factors, including inappropriate antibiotic prescribing and sales, use of antibiotics outside of the health care sector, and genetic factors intrinsic to bacteria. The problem has been exacerbated by inadequate economic incentives for pharmaceutical development of new antimicrobial agents. A range of specific AMR concerns, including carbapenem- and colistin-resistant gram-negative organisms, pose a clinical challenge. Alternative approaches to address the AMR threat include new methods of antibacterial drug identification and strategies that neutralize virulence factors.

CONCLUSIONS AND RELEVANCE

Antimicrobial resistance poses significant challenges for current clinical care. Modified use of antimicrobial agents and public health interventions, coupled with novel antimicrobial strategies, may help mitigate the effect of multidrug-resistant organisms in the future.

Defective HIV-1 proviruses produce novel protein-coding RNA species in HIV-infected patients on combination antiretroviral therapy

Despite years of plasma HIV-RNA levels <40 copies per milliliter during combination antiretroviral therapy (cART), the majority of HIV-infected patients exhibit persistent seropositivity to HIV-1 and evidence of immune activation. These patients also show persistence of proviruses of HIV-1 in circulating peripheral blood mononuclear cells. Many of these proviruses have been characterized as defective and thus thought to contribute little to HIV-1 pathogenesis. By combining 5'LTR-to-3'LTR single-genome amplification and direct amplicon sequencing, we have identified the presence of "defective" proviruses capable of transcribing novel unspliced HIV-RNA (usHIV-RNA) species in patients at all stages of HIV-1 infection. Although these novel usHIV-RNA transcripts had exon structures that were different from those of the known spliced HIV-RNA variants, they maintained translationally competent ORFs, involving elements of gag, pol, env, rev, and nef to encode a series of novel HIV-1 chimeric proteins. These novel usHIV-RNAs were detected in five of five patients, including four of four patients with prolonged viral suppression of HIV-RNA levels <40 copies per milliliter for more than 6 y. Our findings suggest that the persistent defective proviruses of HIV-1 are not "silent," but rather may contribute to HIV-1 pathogenesis by stimulating host-defense pathways that target foreign nucleic acids and proteins.

Anti-α4β7 mAb prevents MAdCAM-1-mediated activation and HIV replication in CD4+ T cells

HIV-1 preferentially infects α4β7+ CD4+ T cells, causing irreversible depletion of these cells in gut-associated lymphoid tissue (GALT) during the acute phase of infection. α4β7 mediates homing of CD4+ T cells to GALT through an interaction with mucosal addressin cell adhesion molecule-1 (MAdCAM-1), expressed on gut endothelial venules. In a rhesus macaque model of HIV transmission, administration of an anti-α4β7 mAb protected GALT from SIV infection. The mechanism(s) underlying this protection are poorly understood. We hypothesized that the anti-α4β7 mAb prevents MAdCAM mediated co-stimulation in a manner that could contribute to the protection that we observed. We determined that costimulation of CD4+ T cells through MAdCAM could support both proliferation of CD4+ T cells and viral replication in a manner that was inhibited by the anti-α4β7 mAb. In addition, MAdCAM costimulation induced the up-regulation of Ki-67, CD38 and CXCR5. Interestingly, we found that MAdCAM could induce the expression of CD45RO on naïve CD4+ T cells in the absence of proliferation, suggesting that this mode of costimulation is unique. These results indicate that costimulation of CD4+ T cells via MAdCAM provides a signal that promotes replication of HIV. Moreover, an anti-α4β7 mAb that interferes with the binding of MAdCAM to α4β7 inhibits both proliferation and viral replication, providing a potential mechanism for the capacity of this mAb to protect rhesus macaques from infection by SIV.

Evaluation of a newly developed assay designed to assess the interaction between α4β7 and MAdCAM

HIV infection is characterized by high-level replication in gut-associated lymphoid tissues (GALT). This occurs in part because α4β7 +/CD4+ T cells are a preferred target of HIV infection. α4β7 functions as a gut homing receptor. Homing is mediated through a specific interaction with MAdCAM that is expressed on the surface of the high-endothelial venules that line the gut. In addition, α4β7 binds to the V2 domain of HIV gp120. In an SIV model of HIV mucosal transmission, an antibody specific for α4β7 +was found to prevent infection, but the underlying mechanism for this protection is not fully understood. We have proposed that signaling through α4β7 + facilitates HIV transmission, and that the protection from infection that we observed may reflect the capacity of the anti-α4β7 mAb we employed to interfere with this signaling. In order to investigate the role of α4β7+ signaling in mucosal transmission, we have employed a newly developed adhesion assay (Peachman and Rao) that measures the interaction between either the V2 domain of HIV gp120 or MAdCAM with cells expressing α4β7. We have used this assay to evaluate small molecules and antibody antagonists of these interactions. We have found that small molecule antagonists that bind to the active site in α4β7 abrogate binding of cells to both MAdCAM and the V2 domain of HIV gp120. In addition, we determined that retinoic acid increases the adhesion of MAdCAM and V2 to α4β7 expressing cells. This assay should aid in the development of novel strategies designed to interfere with the trafficking of α4β7 +cells to GALT and to mucosal transmission of HIV.

MAdCAM signaling through integrin α4β7 modulates surface expression of CCR5 and markers of CD4+ T cell activation

Integrin α4β7 mediates homing of lymphocytes, including CD4+ T cells, to gut-associated lymphoid tissue (GALT) through an interaction with Mucosal Addressin Cell Adhesion Molecule (MAdCAM), expressed on gut endothelial venules. MAdCAM facilitates rolling adhesion of CD4+ T lymphocytes along the gut endothelium prior to extravasation. Previous work also indicates that MAdCAM interactions with α4β7 provide a co-stimulatory signal to T cells. α4β7+/CD4+ T cells are a preferred target of HIV during the acute phase of infection. We hypothesized that signaling through α4β7 via MAdCAM renders cells susceptible to HIV infection and replication. In this study we characterized the response of α4β7+/CD4+ T cells to costimulation via MAdCAM in order to better understand whether the induced phenotype would support an enhanced degree of viral replication. We found that CD4+ T cells upregulated CCR5, an HIV coreceptor, in response to MAdCAM costimulation. We also observed the rapid induction of CD69, a known marker of activation. This induction was restricted to α4β7+ cells, including both the CD45RO+ α4β7+ memory subset and CD45ROneg/α4β7+ naive cell subset. We also observed decreased surface expression of two MAdCAM ligands; integrin β7+ was down-regulated within four hours post MAdCAM costimulation and L-selectin was shed with similar kinetics. This shedding occurred primarily in the CD45ROneg subset. Overall these results indicate that MAdCAM-mediated costimulation through α4β7 activates CD4+ T cells in a unique manner that is likely conducive to viral replication. Of note we found that CCR5, the principal HIV coreceptor, was upregulated. Interestingly, the surface expression of two MAdCAM ligands, L-selectin and α4β7, were both reduced.

Maintenance of HIV-Specific Memory B-Cell Responses in Elite Controllers Despite Low Viral Burdens

Human immunodeficiency virus (HIV)-specific B-cell responses in infected individuals are maintained by active HIV replication. Suppression of viremia by antiretroviral therapy (ART) leads to quantitative and qualitative changes that remain unclear. Accordingly, B-cell responses were investigated in elite controllers (ECs), who maintain undetectable HIV levels without ART, and in individuals whose viremia was suppressed by ART. Despite a higher HIV burden in the ART group, compared with the EC group, frequencies of HIV-specific B cells were higher in the EC group, compared with those in the ART group. However, the initiation of ART in several ECs was associated with reduced frequencies of HIV-specific B cells, suggesting that responses are at least in part sustained by HIV replication. Furthermore, B-cell responses to tetanus toxin but not influenza hemagglutinin in the ART group were lower than those in the EC group. Thus, the superior HIV-specific humoral response in ECs versus ART-treated individuals is likely due to a more intact humoral immune response in ECs and/or distinct responses to residual HIV replication.

Maturational characteristics of HIV-specific antibodies in viremic individuals

Despite the rare appearance of potent HIV-neutralizing mAbs in infected individuals requiring prolonged affinity maturation, little is known regarding this process in the majority of viremic individuals. HIV-infected individuals with chronic HIV viremia have elevated numbers of nonconventional tissue-like memory (TLM) B cells that predominate in blood over conventional resting memory (RM) B cells. Accordingly, we investigated affinity maturation in these 2 memory B cell populations. Analysis of IgG-expressing TLM B cells revealed a higher number of cell divisions compared with RM B cells; however, TLM B cells paradoxically displayed significantly lower frequencies of somatic hypermutation (SHM). To assess Ab reactivity in TLM and RM B cells, single-cell cloning was performed on HIV envelope CD4-binding site-sorted (CD4bs-sorted) B cells from 3 individuals with chronic HIV viremia. Several clonal families were present among the 127 cloned recombinant mAbs, with evidence of crosstalk between TLM and RM B cell populations that was largely restricted to non-VH4 families. Despite evidence of common origins, SHM frequencies were significantly decreased in TLM-derived mAbs compared with SHM frequencies in RM-derived mAbs. However, both cell populations had lower frequencies of SHMs than did broadly neutralizing CD4bs-specific mAbs. There was a significant correlation between SHM frequencies and the HIV-neutralizing capacities of the mAbs. Furthermore, HIV neutralization was significantly higher in the RM-derived mAbs compared with that seen in the TLM-derived mAbs, and both SHM frequencies and neutralizing capacity were lowest in TLM-derived mAbs with high polyreactivity. Thus, deficiencies in memory B cells that arise during chronic HIV viremia provide insight into the inadequacy of the Ab response in viremic individuals.

The Role of the Virtuous Investigator in Protecting Human Research Subjects

In his famous 1966 New England Journal of Medicine article, Henry Beecher concluded that a critical safeguard for protecting human participants, more reliable than informed consent, was the "presence of an intelligent, informed, conscientious, compassionate, responsible investigator." This article examines Beecher's appeal to reliance on the "virtuous" investigator in light of the critical role that investigators play in research ethics and the systems of research protections that have been developed since Beecher's writing. It addresses the extent to which research ethics rely on virtuous investigators; the meaning of virtuous, as distinct from compliance with the rules and regulations that guide ethical research; the particular virtues that it might be important for investigators to have; and the impact of the existing system of human subjects protections on the virtuous investigator. The virtuous investigator who is motivated to take ethical responsibilities seriously is an essential safeguard for the protection of human research participants and an important complement to the system of oversight protections. However, since the current human subjects protection system does not promote virtue or ethical resourcefulness by investigators, attention to enhancing a culture of professional responsibility might serve to forge a synergy between the protections afforded by the current oversight system and those provided by the virtuous investigator.

Immune correlates of vaccine protection against HIV-1 acquisition

The partial efficacy reported in the RV144 HIV vaccine trial in 2009 has driven the HIV vaccine field to define correlates of risk associated with HIV-1 acquisition and connect these functionally to preventing HIV infection. Immunological correlates, mainly including CD4(+) T cell responses to the HIV envelope and Fc-mediated antibody effector function, have been connected to reduced acquisition. These immunological correlates place immunological and genetic pressure on the virus. Indeed, antibodies directed at conserved regions of the V1V2 loop and antibodies that mediate antibody-dependent cellular cytotoxicity to HIV envelope in the absence of inhibiting serum immunoglobulin A antibodies correlated with decreased HIV risk. More recently, researchers have expanded their search with nonhuman primate studies using vaccine regimens that differ from that used in RV144; these studies indicate that non-neutralizing antibodies are associated with protection from experimental lentivirus challenge as well. These immunological correlates have provided the basis for the design of a next generation of vaccine regimens to improve upon the qualitative and quantitative degree of magnitude of these immune responses on HIV acquisition.

A Paradoxical Treatment for a Paradoxical Condition: Infliximab Use in Three Cases of Mycobacterial IRIS

The management of corticosteroid refractory immune reconstitution inflammatory syndrome (IRIS) is currently unclear. Infliximab administration was associated with clinical improvement without significant adverse events in 3 patients with mycobacterial IRIS. Immunologic and virologic responses to antiretroviral therapy were unaffected. Tumor necrosis factor blockade may be beneficial for IRIS and warrants further study in clinical trials.

HIV reservoirs as obstacles and opportunities for an HIV cure

The persistence of HIV reservoirs remains a formidable obstacle to achieving sustained virologic remission in HIV-infected individuals after antiretroviral therapy (ART) is discontinued, even if plasma viremia has been successfully suppressed for prolonged periods of time. Numerous approaches aimed at eradicating the virus, as well as maintaining its prolonged suppression in the absence of ART, have had little success. A better understanding of the pathophysiologic nature of HIV reservoirs and the impact of various interventions on their persistence is essential for the development of successful therapeutic strategies against HIV or the long-term control of infection. Here, we discuss the persistent HIV reservoir as a barrier to cure as well as the current therapeutic strategies aimed at eliminating or controlling the virus in the absence of ART.