Humoral and Innate Antiviral Immunity as Tools to Clear Persistent HIV Infection

HIV-1 latency reversal agent boosting is not limited by opioid use

Opioid use may affect the HIV-1 reservoir and its reversal from latency. We studied 47 virally suppressed people with HIV (PWH) and observed that lower concentration of HIV-1 latency reversal agents (LRAs), used with small molecules that did not reverse latency, synergistically increased the magnitude of HIV-1 reactivation ex vivo, regardless of opioid use. This LRA boosting, which combined a second mitochondria-derived activator of caspases mimetic or low-dose PKC agonist with histone deacetylase inhibitors, generated more unspliced HIV-1 transcription than PMA with ionomycin (PMAi), the maximal known HIV-1 reactivator. LRA boosting associated with greater histone acetylation, modulated surface activation-induced markers, and altered T cell production of TNF-α, IL-2, and IFN-γ. HIV-1 reservoirs in PWH contained unspliced and polyadenylated virus mRNA, the ratios of which were greater in resting than total CD4+ T cells and corrected to 1:1 with PMAi exposure. We characterized treated suppressed HIV-1 infection as a period of inefficient, not absent, virus transcription. Multiply spliced HIV-1 transcripts and virion production did not consistently increase with LRA boosting, suggesting the presence of a persistent posttranscriptional block. LRA boosting can be leveraged to probe mechanisms of an effective cellular HIV-1 latency reversal program.

HIV-1 latency reversal agent boosting is not limited by opioid use

The opioid epidemic may impact the HIV-1 reservoir and its reversal from latency in virally suppressed people with HIV (PWH). We studied forty-seven PWH and observed that lowering the concentration of HIV-1 latency reversal agents (LRA), used in combination with small molecules that do not reverse latency, synergistically increases the magnitude of HIV-1 re-activation ex vivo, regardless of opioid use. This LRA boosting, which combines a Smac mimetic or low-dose protein kinase C agonist with histone deacetylase inhibitors, can generate significantly more unspliced HIV-1 transcription than phorbol 12-myristate 13-acetate (PMA) with ionomycin (PMAi), the maximal known HIV-1 reactivator. LRA boosting associated with greater histone acetylation in CD4+ T cells and modulated T cell activation-induced markers and intracellular cytokine production; Smac mimetic-based boosting was less likely to induce immune activation. We found that HIV-1 reservoirs in PWH contain unspliced and polyadenylated (polyA) virus mRNA, the ratios of which are greater in resting than total CD4+ T cells and can correct to 1:1 with PMAi exposure. Latency reversal results in greater fold-change increases to HIV-1 poly(A) mRNA than unspliced message. Multiply spliced HIV-1 transcripts and virion production did not consistently increase with LRA boosting, suggesting the presence of a persistent post-transcriptional block. LRA boosting can be leveraged to probe the mechanisms of an effective cellular HIV-1 latency reversal program.

HIV reservoir: antiviral immune responses and immune interventions for curing HIV infection

ABSTRACT

Antiretroviral therapy against human immunodeficiency virus (HIV) is effective in controlling viral replication but cannot completely eliminate HIV due to the persistence of the HIV reservoir. Innate and adaptive immune responses have been proposed to contribute to preventing HIV acquisition, controlling HIV replication and eliminating HIV-infected cells. However, the immune responses naturally induced in HIV-infected individuals rarely eradicate HIV infection, which may be caused by immune escape, an inadequate magnitude and breadth of immune responses, and immune exhaustion. Optimizing these immune responses may solve the problems of epitope escape and insufficient sustained memory responses. Moreover, immune interventions aimed at improving host immune response can reduce HIV reservoirs, which have become one focus in the development of innovative strategies to eliminate HIV reservoirs. In this review, we focus on the immune response against HIV and how antiviral immune responses affect HIV reservoirs. We also discuss the development of innovative strategies aiming to eliminate HIV reservoirs and promoting functional cure of HIV infection.

The reservoir of latent HIV

The persistence of latent reservoir of the human immunodeficiency virus (HIV) is currently the major challenge in curing HIV infection. After HIV infects the human body, the latent HIV is unable to be recognized by the body’s immune system. Currently, the widely adopted antiretroviral therapy (ART) is also unble to eliminate it, thus hindering the progress of HIV treatment. This review discusses the existence of latent HIV vault for HIV treatment, its formation and factors affecting its formation, cell, and tissue localization, methods for detection and removing latent reservoir, to provide a comprehensive understanding of latent HIV vault, in order to assist in the future research and play a potential role in achieving HIV treatment.

Broadly binding and functional antibodies and persisting memory B cells elicited by HIV vaccine PDPHV

Since publishing our original reports on the safety and immunogenicity of a polyvalent DNA prime-protein boost HIV vaccine (PDPHV) which elicited high titer antibody responses with broad specificity, neutralizing activities to multiple HIV-1 subtypes, as well as poly-functional T cell responses, accumulated findings from other HIV vaccine studies indicated the important roles of Ig isotype distribution, Fc medicated functions and the persistence of memory immune responses which were not studied in previous PDPHV related reports. The current report provides further detailed characterization of these parameters in human volunteers receiving the PDPHV regimen. Antibody responses were assessed using IgG isotype and gp70-V1V2-binding ELISAs, peptide arrays, and antibody-dependent cellular cytotoxicity (ADCC) assays. B cell ELISPOT was used to detect gp120-specific memory B cells. Our results showed that the gp120-specific antibodies were primarily of the IgG1 isotype. HIV-1 envelope protein variable regions V1 and V2 were actively targeted by the antibodies as determined by specific binding to both peptide and V1V2-carrying scaffolds. The antibodies showed potent and broad ADCC responses. Finally, the B cell ELISPOT analysis demonstrated persistence of gp120-specific memory B cells for at least 6 months after the last dose. These data indicate that broadly reactive binding Abs and ADCC responses as well as durable gp120-specific memory B cells were elicited by the polyvalent heterologous prime-boost vaccination regimens and showed great promise as a candidate HIV vaccine.

The Importance of Cellular Immune Response to HIV: Implications for Antibody Production and Vaccine Design

Despite many years from the discovery of human immunodeficiency virus (HIV), a prophylactic vaccine against HIV is still needed. The failure of most of the vaccine clinical trials in the field has different causes, mainly due by the difficulties to identify the correct antigen able to prime the optimal B cell lineage and then make the series of somatic mutations necessary to generate broadly neutralizing antibodies (bNAbs). B cells are responsible for the bNAbs production; however, their function is strongly influenced by the presence of a population of CD4+ T lymphocytes, mainly present in the lymphoid organs, the T follicular helper cells (Tfh). In this review, the importance of the contribution of Tfh cells in HIV response is highlighted and future therapy perspectives based on these observations are described. The advanced technology available nowadays and the wide knowledge built over the past years for HIV may eventually create the best scenario for the generation of an effective vaccine.

Bispecific antibodies: a novel approach for targeting prominent biomarkers

Many types of cancers are prevalent in India and worldwide. Monoclonal antibodies (MAbs) are one of the major types of cancer therapeutics, which have included MAbs of hybridoma, chimeric, humanized, or human origin. MAbs are mostly generated currently by direct cloning from B cells. Bispecific antibodies (BAbs), as the name suggests, have two different antigen-binding domains in a single molecule and thus have dual functionality/specificity combined in a single antibody. In addition to the detection of two different antigenic molecules, the dual functionality of BAbs can be utilized to mount T-cell-mediated killing of tumor cells wherein one Fv binds to the tumor-specific antigen and the another recruits T cells to the site of action. Breast cancer and prostate cancer are among the most prevalent cancers in women and men, respectively. Biomarkers such as HER2 and ER/PR are expressed in breast cancer, while overexpression of hepsin and prostate-specific membrane antigen is observed in prostate cancer. Developing BAbs against these biomarkers may be a potent therapeutic option to target breast and prostate cancer, respectively. Therefore, an efficient method using recombinant DNA technology and mammalian cell culture platform is required to generate BAbs against specific diseases as biomarkers as well as for the generation of antibody-based therapeutics.

Engineering antibody-based molecules for HIV treatment and cure

PURPOSE OF REVIEW

Immunotherapy strategies alternative to current antiretroviral therapies will need to address viral diversity while increasing the immune system's ability to efficiently target the latent virus reservoir. Antibody-based molecules can be designed based on broadly neutralizing and non-neutralizing antibodies that target free virions and infected cells. These multispecific molecules, either by IgG-like or non-IgG-like in structure, aim to target several independent HIV-1 epitopes and/or engage effector cells to eliminate the replicating virus and infected cells. This detailed review is intended to stimulate discussion on future requirements for novel immunotherapeutic molecules.

RECENT FINDINGS

Bispecific and trispecific antibodies are engineered as a single molecules to target two or more independent epitopes on the HIV-1 envelope (Env). These antibody-based molecules have increased avidity for Env, leading to improved neutralization potency and breadth compared with single parental antibodies. Furthermore, bispecific and trispecific antibodies that engage cellular receptors with one arm of the molecule help concentrate inhibitory molecules to the sites of potential infection and facilitate engagement of immune effector cells and Env-expressing target cells for their elimination.

SUMMARY

Recently engineered antibody-based molecules of different sizes and structures show promise in vitro or in vivo and are encouraging candidates for HIV treatment.

A Role of Intracellular Toll-Like Receptors (3, 7, and 9) in Response to Mycobacterium tuberculosis and Co-Infection with HIV

Mycobacterium tuberculosis (Mtb) is a highly infectious acid-fast bacillus and is known to cause tuberculosis (TB) in humans. It is a leading cause of death from a sole infectious agent, with an estimated 1.5 million deaths yearly worldwide, and up to one third of the world's population has been infected with TB. The virulence and susceptibility of Mtb are further amplified in the presence of Human Immunodeficiency Virus (HIV). Coinfection with Mtb and HIV forms a lethal combination. Previous studies had demonstrated the synergistic effects of Mtb and HIV, with one disease accelerating the disease progression of the other through multiple mechanisms, including the modulation of the immune response to these two pathogens. The response of the endosomal pattern recognition receptors to these two pathogens, specifically toll-like receptors (TLR)-3, -7, and -9, has not been elucidated, with some studies producing mixed results. This article seeks to review the roles of TLR-3, -7, and -9 in response to Mtb infection, as well as Mtb-HIV-coinfection via Toll-interleukin 1 receptor (TIR) domain-containing adaptor inducing INF-β (TRIF)-dependent and myeloid differentiation factor 88 (MyD88)-dependent pathways.

Redirection of Cord Blood T Cells and Natural Killer Cells for Elimination of Autologous HIV-1-Infected Target Cells Using Bispecific DART® Molecules

Mother-to-child transmission of HIV-1 remains a major global health challenge. Currently, HIV-1-infected infants require strict lifelong adherence to antiretroviral therapy to prevent replication of virus from reservoirs of infected cells, and to halt progression of disease. There is a critical need for immune interventions that can be deployed shortly after infection to eliminate HIV-1-infected cells in order to promote long-term remission of viremia, or to potentially cure pediatric HIV-1-infection. Bispecific HIV × CD3 DART® molecules able to co-engage the HIV-1 envelope protein on the surface of infected cells and CD3 on cytolytic T cells have been previously shown to eliminate HIV-1 infected cells in vitro and are candidates for passive immunotherapy to reduce the virus reservoir. However, their potential utility as therapy for infant HIV-1 infection is unclear as the ability of these novel antibody-based molecules to work in concert with cells of the infant immune system had not been assessed. Here, we use human umbilical cord blood as a model of the naïve neonatal immune system to evaluate the ability of HIV x CD3 DART molecules to recruit and redirect neonatal effector cells for elimination of autologous CD4⁺ T cells infected with HIV-1 encoding an envelope gene sequenced from a mother-to-child transmission event. We found that HIV × CD3 DART molecules can redirect T cells present in cord blood for elimination of HIV-infected CD4⁺ T cells. However, we observed reduced killing by T cells isolated from cord blood when compared to cells isolated from adult peripheral blood-likely due to the absence of the memory and effector CD8⁺ T cells that are most cytolytic when redirected by bispecific DART molecules. We also found that newly developed HIV × CD16 DART molecules were able to recruit CD16-expressing natural killer cells from cord blood to eliminate HIV-infected cells, and the activity of cord blood natural killer cells could be substantially increased by priming with IL-15. Our results support continued development of HIV-specific DART molecules using relevant preclinical animal models to optimize strategies for effective use of this immune therapy to reduce HIV-1 infection in pediatric populations.

SLAM Family Receptor Signaling in Viral Infections: HIV and Beyond

The signaling lymphocytic activation molecule (SLAM) family of receptors are expressed on the majority of immune cells. These receptors often serve as self-ligands, and play important roles in cellular communication and adhesion, thus modulating immune responses. SLAM family receptor signaling is differentially regulated in various immune cell types, with responses generally being determined by the presence or absence of two SLAM family adaptor proteins-Ewing's sarcoma-associated transcript 2 (EAT-2) and SLAM-associated adaptor protein (SAP). In addition to serving as direct regulators of the immune system, certain SLAM family members have also been identified as direct targets for specific microbes and viruses. Here, we will discuss the known roles for these receptors in the setting of viral infection, with special emphasis placed on HIV infection. Because HIV causes such complex dysregulation of the immune system, studies of the roles for SLAM family receptors in this context are particularly exciting.

Microglial Cells: The Main HIV-1 Reservoir in the Brain

Despite efficient combination of the antiretroviral therapy (cART), which significantly decreased mortality and morbidity of HIV-1 infection, a definitive HIV cure has not been achieved. Hidden HIV-1 in cellular and anatomic reservoirs is the major hurdle toward a functional cure. Microglial cells, the Central Nervous system (CNS) resident macrophages, are one of the major cellular reservoirs of latent HIV-1. These cells are believed to be involved in the emergence of drugs resistance and reseeding peripheral tissues. Moreover, these long-life reservoirs are also involved in the development of HIV-1-associated neurocognitive diseases (HAND). Clearing these infected cells from the brain is therefore crucial to achieve a cure. However, many characteristics of microglial cells and the CNS hinder the eradication of these brain reservoirs. Better understandings of the specific molecular mechanisms of HIV-1 latency in microglial cells should help to design new molecules and new strategies preventing HAND and achieving HIV cure. Moreover, new strategies are needed to circumvent the limitations associated to anatomical sanctuaries with barriers such as the blood brain barrier (BBB) that reduce the access of drugs.

Strategies to eradicate HIV from infected patients: elimination of latent provirus reservoirs

35 years since identification of HIV as the causative agent of AIDS, and 35 million deaths associated with this disease, significant effort is now directed towards the development of potential cures. Current anti-retroviral (ART) therapies for HIV/AIDS can suppress virus replication to undetectable levels, and infected individuals can live symptom free so long as treatment is maintained. However, removal of therapy allows rapid re-emergence of virus from a highly stable reservoir of latently infected cells that exist as a barrier to elimination of the infection with current ART. Prospects of a cure for HIV infection are significantly encouraged by two serendipitous cases where individuals have entered remission following stem cell transplantation from compatible HIV-resistant donors. However, development of a routine cure that could become available to millions of infected individuals will require a means of specifically purging cells harboring latent HIV, preventing replication of latent provirus, or destruction of provirus genomes by gene editing. Elimination of latently infected cells will require a means of exposing this population, which may involve identification of a natural specific biomarker or therapeutic intervention to force their exposure by reactivation of virus expression. Accordingly, the proposed "Shock and Kill" strategy involves treatment with latency-reversing agents (LRA) to induce HIV provirus expression thus exposing these cells to killing by cellular immunity or apoptosis. Current efforts to enable this strategy are directed at developing improved combinations of LRA to produce broad and robust induction of HIV provirus and enhancing the elimination of cells where replication has been reactivated by targeted immune modulation. Alternative strategies may involve preventing re-emergence virus from latently infected cells by "Lock and Block" intervention, where transcription of provirus is inhibited to prevent virus spread or disruption of the HIV provirus genome by genome editing.

Microglial Cells: The Main HIV-1 Reservoir in the Brain

Despite efficient combination of the antiretroviral therapy (cART), which significantly decreased mortality and morbidity of HIV-1 infection, a definitive HIV cure has not been achieved. Hidden HIV-1 in cellular and anatomic reservoirs is the major hurdle toward a functional cure. Microglial cells, the Central Nervous system (CNS) resident macrophages, are one of the major cellular reservoirs of latent HIV-1. These cells are believed to be involved in the emergence of drugs resistance and reseeding peripheral tissues. Moreover, these long-life reservoirs are also involved in the development of HIV-1-associated neurocognitive diseases (HAND). Clearing these infected cells from the brain is therefore crucial to achieve a cure. However, many characteristics of microglial cells and the CNS hinder the eradication of these brain reservoirs. Better understandings of the specific molecular mechanisms of HIV-1 latency in microglial cells should help to design new molecules and new strategies preventing HAND and achieving HIV cure. Moreover, new strategies are needed to circumvent the limitations associated to anatomical sanctuaries with barriers such as the blood brain barrier (BBB) that reduce the access of drugs.

Susceptibility to Neutralization by Broadly Neutralizing Antibodies Generally Correlates with Infected Cell Binding for a Panel of Clade B HIV Reactivated from Latent Reservoirs

Efforts to cure human immunodeficiency virus (HIV) infection are obstructed by reservoirs of latently infected CD4+ T cells that can reestablish viremia. HIV-specific broadly neutralizing antibodies (bNAbs), defined by unusually wide neutralization breadths against globally diverse viruses, may contribute to the elimination of these reservoirs by binding to reactivated cells, thus targeting them for immune clearance. However, the relationship between neutralization of reservoir isolates and binding to corresponding infected primary CD4+ T cells has not been determined. Thus, the extent to which neutralization breadths and potencies can be used to infer the corresponding parameters of infected cell binding is currently unknown. We assessed the breadths and potencies of bNAbs against 36 viruses reactivated from peripheral blood CD4+ T cells from antiretroviral (ARV)-treated HIV-infected individuals by using paired neutralization and infected cell binding assays. Single-antibody breadths ranged from 0 to 64% for neutralization (80% inhibitory concentration [IC80] of ≤10 μg/ml) and from 0 to 89% for binding, with two-antibody combinations (results for antibody combinations are theoretical/predicted) reaching levels of 0 to 83% and 50 to 100%, respectively. Infected cell binding correlated with virus neutralization for 10 of 14 antibodies (e.g., for 3BNC117, r = 0.82 and P < 0.0001). Heterogeneity was observed, however, with a lack of significant correlation for 2G12, CAP256.VRC26.25, 2F5, and 4E10. Our results provide guidance on the selection of bNAbs for interventional cure studies, both by providing a direct assessment of intra- and interindividual variabilities in neutralization and infected cell binding in a novel cohort and by defining the relationships between these parameters for a panel of bNAbs.IMPORTANCE Although antiretroviral therapies have improved the lives of people who are living with HIV, they do not cure infection. Efforts are being directed towards harnessing the immune system to eliminate the virus that persists, potentially resulting in virus-free remission without medication. HIV-specific antibodies hold promise for such therapies owing to their ability to both prevent the infection of new cells (neutralization) and direct the killing of infected cells. We isolated 36 HIV strains from individuals whose virus was suppressed by medication and tested 14 different antibodies for neutralization of these viruses and for binding to cells infected with the same viruses (critical for engaging natural killer cells). For both neutralization and infected cell binding, we observed variation both between individuals and amongst different viruses within an individual. For most antibodies, neutralization activity correlated with infected cell binding. These data provide guidance on the selection of antibodies for clinical trials.

Identification of a HIV Gp41-Specific Human Monoclonal Antibody With Potent Antibody-Dependent Cellular Cytotoxicity

Antibody-Dependent Cellular Cytotoxicity (ADCC) is a major mechanism of protection against viral infections in vivo. Identification of HIV-1-specific monoclonal antibodies (mAbs) with potent ADCC activity may help develop an effective HIV-1 vaccine. In present study, we isolated such human mAb, designated E10, from an HIV-1-infected patient sample by single B cell sorting and single cell PCR. E10 bound to gp140 trimer and linear peptides derived from gp41 membrane proximal external region (MPER). E10 epitope (QEKNEQELLEL) overlapped with mAb 2F5 epitope. However, E10 differentiated from 2F5 in neutralization breadth and potency, as well as ADCC activity. E10 showed low neutralization activity and narrow spectrum of neutralization compared to 2F5, but it mediated higher ADCC activity than 2F5 at low antibody concentration. Fine mapping of E10 epitope may potentiate MPER-based subunit vaccine development.

Modeling the immune response to HIV infection

The interplay between immune response and HIV is intensely studied via mathematical modeling, with significant insights but few direct answers. In this short review, we highlight advances and knowledge gaps across different aspects of immunity. In particular, we identify the innate immune response and its role in priming the adaptive response as ripe for modeling. The latter have been the focus of most modeling studies, but we also synthesize key outstanding questions regarding effector mechanisms of cellular immunity and development of broadly neutralizing antibodies. Thus far, most modeling studies aimed to infer general immune mechanisms; we foresee that significant progress will be made next by detailed quantitative fitting of models to data, and prediction of immune responses.

Broad-Spectrum and Personalized Guide RNAs for CRISPR/Cas9 HIV-1 Therapeutics

The clustered regularly interspaced short palindromic repeats (CRISPR)-associated Cas9 system has been used to excise the HIV-1 proviral genome from latently infected cells, potentially offering a cure for HIV-infected patients. Recent studies have shown that most published HIV-1 guide RNAs (gRNAs) do not account for the diverse viral quasispecies within or among patients, which continue to diversify with time even in long-term antiretroviral therapy (ART)-suppressed patients. Given this observation, proviral genomes were deep sequenced from 23 HIV-1-infected patients in the Drexel Medicine CNS AIDS Research and Eradication Study cohort at two different visits. Based on the spectrum of integrated proviral DNA polymorphisms observed, three gRNA design strategies were explored: based on the patient's own HIV-1 sequences (personalized), based on consensus sequences from a large sample of patients [broad-spectrum (BS)], or a combination of both approaches. Using a bioinformatic algorithm, the personalized gRNA design was predicted to cut 46 of 48 patient samples at 90% efficiency, whereas the top 4 BS gRNAs (BS4) were predicted to excise provirus from 44 of 48 patient samples with 90% efficiency. Using a mixed design with the top three BS gRNAs plus one personalized gRNA (BS3 + PS1) resulted in predicted excision of provirus from 45 of 48 patient samples with 90% efficiency. In summary, these studies used an algorithmic design strategy to identify potential BS gRNAs to target a spectrum of HIV-1 long teriminal repeat (LTR) quasispecies for use with a small HIV-1-infected population. This approach should advance CRISPR/Cas9 excision technology taking into account the extensive molecular heterogeneity of HIV-1 that persists in situ after prolonged ART.

Broadly neutralizing antibodies: What is needed to move from a rare event in HIV-1 infection to vaccine efficacy?

The elicitation of broadly neutralizing antibodies (bnAbs) is considered crucial for an effective, preventive HIV-1 vaccine. Led by the discovery of a new generation of potent bnAbs, the field has significantly advanced over the past decade. There is a wealth of knowledge about the development of bnAbs in natural infection, their specificity, potency, breadth and function. Yet, devising immunogens and vaccination regimens that evoke bnAb responses has not been successful. Where are the roadblocks in their development? What can we learn from natural infection, where bnAb induction is possible but rare? Herein, we will reflect on key discoveries and discuss open questions that may bear crucial insights needed to move towards creating effective bnAb vaccines.

Novel vaccines: Technology and development

The development and widespread use of vaccines, which are defined by the World Health Organization as "biological preparations that improve immunity to a particular disease," represents one of the most significant strides in medicine. Vaccination was first applied to reduce mortality and morbidity from infectious diseases. The World Health Organization estimates that vaccines prevent 2 to 3 million human deaths annually, and these numbers would increase by at least 6 million if all children received the recommended vaccination schedule. However, the origins of allergen immunotherapy share the same intellectual paradigm, and subsequent innovations in vaccine technology have been applied beyond the prevention of infection, including in the treatment of cancer and allergic diseases. This review will focus on how new and more rational approaches to vaccine development use novel biotechnology, target new mechanisms, and shape the immune system response, with an emphasis on discoveries that have direct translational relevance to the treatment of allergic diseases.

Evaluation of the Innate Immune Modulator Acitretin as a Strategy To Clear the HIV Reservoir

The persistence of HIV despite suppressive antiretroviral therapy is a major roadblock to HIV eradication. Current strategies focused on inducing the expression of latent HIV fail to clear the persistent reservoir, prompting the development of new approaches for killing HIV-positive cells. Recently, acitretin was proposed as a pharmacological enhancer of the innate cellular defense network that led to virus reactivation and preferential death of infected cells. We evaluated the capacity of acitretin to reactivate and/or to facilitate immune-mediated clearance of HIV-positive cells. Acitretin did not induce HIV reactivation in latently infected cell lines (J-Lat and ACH-2). We could observe only modest induction of HIV reactivation by acitretin in latently green fluorescent protein-HIV-infected Jurkat cells, comparable to suboptimal concentrations of vorinostat, a known latency-reversing agent (LRA). Acitretin induction was insignificant, however, compared to optimal concentrations of LRAs. Acitretin failed to reactivate HIV in a model of latently infected primary CD4+ T cells but induced retinoic acid-inducible gene I (RIG-I) and mitochondrial antiviral signaling (MAVS) expression in infected and uninfected cells, confirming the role of acitretin as an innate immune modulator. However, this effect was not associated with selective killing of HIV-positive cells. In conclusion, acitretin-mediated stimulation of the RIG-I pathway for HIV reactivation is modest and thus may not meaningfully affect the HIV reservoir. Stimulation of the RIG-I-dependent interferon (IFN) cascade by acitretin may not significantly affect the selective destruction of latently infected HIV-positive cells.

Non-neutralizing Antibodies Alter the Course of HIV-1 Infection In Vivo

Non-neutralizing antibodies (nnAbs) to HIV-1 show little measurable activity in prevention or therapy in animal models yet were the only correlate of protection in the RV144 vaccine trial. To investigate the role of nnAbs on HIV-1 infection in vivo, we devised a replication-competent HIV-1 reporter virus that expresses a heterologous HA-tag on the surface of infected cells and virions. Anti-HA antibodies bind to, but do not neutralize, the reporter virus in vitro. However, anti-HA protects against infection in humanized mice and strongly selects for nnAb-resistant viruses in an entirely Fc-dependent manner. Similar results were also obtained with tier 2 HIV-1 viruses using a human anti-gp41 nnAb, 246D. While nnAbs are demonstrably less effective than broadly neutralizing antibodies (bNAbs) against HIV-1 in vitro and in vivo, the data show that nnAbs can protect against and alter the course of HIV-1 infection in vivo. PAPERCLIP.