Serotonin reduction in post-acute sequelae of viral infection.

Post-acute sequelae of COVID-19 (PASC, "Long COVID") pose a significant global health challenge. The pathophysiology is unknown, and no effective treatments have been found to date. Several hypotheses have been formulated to explain the etiology of PASC, including viral persistence, chronic inflammation, hypercoagulability, and autonomic dysfunction. Here, we propose a mechanism that links all four hypotheses in a single pathway and provides actionable insights for therapeutic interventions. We find that PASC are associated with serotonin reduction. Viral infection and type I interferon-driven inflammation reduce serotonin through three mechanisms: diminished intestinal absorption of the serotonin precursor tryptophan; platelet hyperactivation and thrombocytopenia, which impacts serotonin storage; and enhanced MAO-mediated serotonin turnover. Peripheral serotonin reduction, in turn, impedes the activity of the vagus nerve and thereby impairs hippocampal responses and memory. These findings provide a possible explanation for neurocognitive symptoms associated with viral persistence in Long COVID, which may extend to other post-viral syndromes.

Systems analysis of innate and adaptive immunity in Long COVID.

Since the onset of the COVID-19 pandemic, significant progress has been made in developing effective preventive and therapeutic strategies against severe acute SARS-CoV-2 infection. However, the management of Long COVID (LC), an infection-associated chronic condition that has been estimated to affect 5-20% of individuals following SARS-CoV-2 infection, remains challenging due to our limited understanding of its mechanisms. Although LC is a heterogeneous disease that is likely to have several subtypes, immune system disturbances appear common across many cases. The extent to which these immune perturbations contribute to LC symptoms, however, is not entirely clear. Recent advancements in multi-omics technologies, capable of detailed, cell-level analysis, have provided valuable insights into the immune perturbations associated with LC. Although these studies are largely descriptive in nature, they are the crucial first step towards a deeper understanding of the condition and the immune system's role in its development, progression, and resolution. In this review, we summarize the current understanding of immune perturbations in LC, covering both innate and adaptive immune responses, and the cytokines and analytes involved. We explore whether these findings support or challenge the primary hypotheses about LC's underlying mechanisms. We also discuss the crosstalk between various immune system components and how it can be disrupted in LC. Finally, we emphasize the need for more tissue- and subtype-focused analyses of LC, and for enhanced collaborative efforts to analyze common specimens from large cohorts, including those undergoing therapeutic interventions. These collective efforts are vital to unravel the fundaments of this new disease, and could also shed light on the prevention and treatment of the larger family of chronic illnesses linked to other microbial infections.

HIV rebound in HIV controllers is associated with a specific fecal microbiome profile.

HIV infection is associated with gut dysbiosis, and microbiome variability may affect HIV control when antiretroviral therapy (ART) is stopped. The TLR7 agonist, vesatolimod, was previously associated with a modest delay in viral rebound following analytical treatment interruption in HIV controllers (HCs). Using a retrospective analysis of fecal samples from HCs treated with vesatolimod or placebo (NCT03060447), people with chronic HIV (CH; NCT02858401) or without HIV (PWOH), we examined fecal microbiome profile in HCs before/after treatment, and in CH and PWOH. Microbiome diversity and abundance were compared between groups to investigate the association between specific phyla/species, immune biomarkers, and viral outcomes during treatment interruption. Although there were no significant differences in gut microbiome diversity between people with and without HIV, HCs, and CH shared common features that distinguished them from PWOH. there was a trend toward greater microbiome diversity among HCs. Treatment with vesatolimod reduced dysbiosis in HCs. Firmicutes positively correlated with T-cell activation, while Bacteroidetes and Euryarchaeota inversely correlated with TLR7-mediated immune activation. Specific types of fecal microbiome abundance (e.g. Alistipes putredinis) positively correlated with HIV rebound. In conclusion, variability in the composition of the fecal microbiome is associated with markers of immune activation following vesatolimod treatment and ART interruption.

Pre-pandemic Metabolic Correlates of COVID-19 Severity and Long COVID Incidence in People Living with HIV.

Host metabolic dysregulation, especially in tryptophan metabolism, is intricately linked to COVID-19 severity and its post-acute sequelae (Long COVID). People living with HIV (PLWH) experience similar metabolic dysregulation and face an increased risk of developing Long COVID. However, whether pre-existing HIV-associated metabolic dysregulations contribute in predisposing PLWH to severe COVID-19 outcomes remains underexplored. Analyzing pre-pandemic samples from PLWH with documented post-infection outcomes, we found specific metabolic alterations, including increased tryptophan catabolism, predicting an elevated risk of severe COVID-19 and the incidence of Long COVID. These alterations warrant further investigation for their potential prognostic and mechanistic significance in determining COVID-19 complications.

Multi-omics approach to socioeconomic disparity in metabolic syndrome reveals roles of diet and microbiome.

The epidemy of metabolic syndrome (MetS) is typically preceded by adoption of a "risky" lifestyle (e.g., dietary habit) among populations. Evidence shows that those with low socioeconomic status (SES) are at an increased risk for MetS. To investigate this, we recruited 123 obese subjects (body mass index [BMI] ≥ 30) from Chicago. Multi-omic data were collected to interrogate fecal microbiota, systemic markers of inflammation and immune activation, plasma metabolites, and plasma glycans. Intestinal permeability was measured using the sugar permeability testing. Our results suggest a heterogenous metabolic dysregulation among obese populations who are at risk of MetS. Systemic inflammation, linked to poor diet, intestinal microbiome dysbiosis, and gut barrier dysfunction may explain the development of MetS in these individuals. Our analysis revealed 37 key features associated with increased numbers of MetS features. These features were used to construct a composite metabolic-inflammatory (MI) score that was able to predict progression of MetS among at-risk individuals. The MI score was correlated with several markers of poor diet quality as well as lower levels of gut microbial diversity and abnormalities in several species of bacteria. This study reveals novel targets to reduce the burden of MetS and suggests access to healthy food options as a practical intervention.

Siglec-9 defines and restrains a natural killer subpopulation highly cytotoxic to HIV-infected cells.

Siglec-9 is an MHC-independent inhibitory receptor expressed on a subset of natural killer (NK) cells. Siglec-9 restrains NK cytotoxicity by binding to sialoglycans (sialic acid-containing glycans) on target cells. Despite the importance of Siglec-9 interactions in tumor immune evasion, their role as an immune evasion mechanism during HIV infection has not been investigated. Using in vivo phenotypic analyses, we found that Siglec-9+ CD56dim NK cells, during HIV infection, exhibit an activated phenotype with higher expression of activating receptors and markers (NKp30, CD38, CD16, DNAM-1, perforin) and lower expression of the inhibitory receptor NKG2A, compared to Siglec-9- CD56dim NK cells. We also found that levels of Siglec-9+ CD56dim NK cells inversely correlate with viral load during viremic infection and CD4+ T cell-associated HIV DNA during suppressed infection. Using in vitro cytotoxicity assays, we confirmed that Siglec-9+ NK cells exhibit higher cytotoxicity towards HIV-infected cells compared to Siglec-9- NK cells. These data are consistent with the notion that Siglec-9+ NK cells are highly cytotoxic against HIV-infected cells. However, blocking Siglec-9 enhanced NK cells' ability to lyse HIV-infected cells, consistent with the known inhibitory function of the Siglec-9 molecule. Together, these data support a model in which the Siglec-9+ CD56dim NK subpopulation is highly cytotoxic against HIV-infected cells even whilst being restrained by the inhibitory effects of Siglec-9. To harness the cytotoxic capacity of the Siglec-9+ NK subpopulation, which is dampened by Siglec-9, we developed a proof-of-concept approach to selectively disrupt Siglec/sialoglycan interactions between NK and HIV-infected cells. We achieved this goal by conjugating Sialidase to several HIV broadly neutralizing antibodies. These conjugates selectively desialylated HIV-infected cells and enhanced NK cells' capacity to kill them. In summary, we identified a novel, glycan-based interaction that may contribute to HIV-infected cells' ability to evade NK immunosurveillance and developed an approach to break this interaction.

Relationship between CD4 T cell turnover, cellular differentiation and HIV persistence during ART.

The precise role of CD4 T cell turnover in maintaining HIV persistence during antiretroviral therapy (ART) has not yet been well characterized. In resting CD4 T cell subpopulations from 24 HIV-infected ART-suppressed and 6 HIV-uninfected individuals, we directly measured cellular turnover by heavy water labeling, HIV reservoir size by integrated HIV-DNA (intDNA) and cell-associated HIV-RNA (caRNA), and HIV reservoir clonality by proviral integration site sequencing. Compared to HIV-negatives, ART-suppressed individuals had similar fractional replacement rates in all subpopulations, but lower absolute proliferation rates of all subpopulations other than effector memory (TEM) cells, and lower plasma IL-7 levels (p = 0.0004). Median CD4 T cell half-lives decreased with cell differentiation from naïve to TEM cells (3 years to 3 months, p<0.001). TEM had the fastest replacement rates, were most highly enriched for intDNA and caRNA, and contained the most clonal proviral expansion. Clonal proviruses detected in less mature subpopulations were more expanded in TEM, suggesting that they were maintained through cell differentiation. Earlier ART initiation was associated with lower levels of intDNA, caRNA and fractional replacement rates. In conclusion, circulating integrated HIV proviruses appear to be maintained both by slow turnover of immature CD4 subpopulations, and by clonal expansion as well as cell differentiation into effector cells with faster replacement rates.

Viral and Host Biomarkers of HIV Remission Post Treatment Interruption.

PURPOSE OF REVIEW: HIV rebound/remission after antiretroviral therapy (ART) interruption is likely influenced by (a) the size of the inducible replication-competent HIV reservoir and (b) factors in the host environment that influence immunological pressures on this reservoir. Identifying viral and/or host biomarkers of HIV rebound after ART cessation may improve the safety of treatment interruptions and our understanding of how the viral-host interplay results in post-treatment control. Here we review the predictive and functional significance of recently suggested viral and host biomarkers of time to viral rebound and post-treatment control following ART interruption. RECENT FINDINGS: There are currently no validated viral or host biomarkers of viral rebound; however, several biomarkers have been recently suggested. A combination of viral and host factors will likely be needed to predict viral rebound and to better understand the mechanisms contributing to post-treatment control of HIV, critical steps to developing a cure for HIV infection.

The African natural product knipholone anthrone and its analogue anthralin (dithranol) enhance HIV-1 latency reversal.

A sterilizing or functional cure for HIV is currently precluded by resting CD4+ T cells that harbor latent but replication-competent provirus. The "shock-and-kill" pharmacological ap-proach aims to reactivate provirus expression in the presence of antiretroviral therapy and target virus-expressing cells for elimination. However, no latency reversal agent (LRA) to date effectively clears viral reservoirs in humans, suggesting a need for new LRAs and LRA combinations. Here, we screened 216 compounds from the pan-African Natural Product Library and identified knipholone anthrone (KA) and its basic building block anthralin (dithranol) as novel LRAs that reverse viral latency at low micromolar concentrations in multiple cell lines. Neither agent's activity depends on protein kinase C; nor do they inhibit class I/II histone deacetylases. However, they are differentially modulated by oxidative stress and metal ions and induce distinct patterns of global gene expression from established LRAs. When applied in combination, both KA and anthralin synergize with LRAs representing multiple functional classes. Finally, KA induces both HIV RNA and protein in primary cells from HIV-infected donors. Taken together, we describe two novel LRAs that enhance the activities of multiple "shock-and-kill" agents, which in turn may inform ongoing LRA combination therapy efforts.

Intact Human Immunodeficiency Virus (HIV) Reservoir Estimated by the Intact Proviral DNA Assay Correlates With Levels of Total and Integrated DNA in the Blood During Suppressive Antiretroviral Therapy.

Accurate characterization of the human immunodeficiency virus (HIV) reservoir is imperative to develop an effective cure. HIV was measured in antiretroviral therapy-suppressed individuals using the intact proviral DNA assay (IPDA), along with assays for total or integrated HIV DNA, and inducible HIV RNA or p24. Intact provirus correlated with total and integrated HIV.

BCL6 Inhibitor-Mediated Downregulation of Phosphorylated SAMHD1 and T Cell Activation Are Associated with Decreased HIV Infection and Reactivation.

Clearance of HIV-infected germinal center (GC) CD4+ follicular helper T cells (Tfh) after combination antiretroviral therapy (ART) is essential to an HIV cure. Blocking B cell lymphoma 6 (BCL6; the master transcription factor for Tfh cells) represses HIV infection of tonsillar CD4+ Tfh ex vivo, reduces GC formation, and limits immune activation in vivo We assessed the anti-HIV activity of a novel BCL6 inhibitor, FX1, in Tfh/non-Tfh CD4+ T cells and its impact on T cell activation and SAMHD1 phosphorylation (Thr592). FX1 repressed HIV-1 infection of peripheral CD4+ T cells and tonsillar Tfh/non-Tfh CD4+ T cells (P < 0.05) and total elongated and multispliced HIV-1 RNA production during the first round of viral life cycle (P < 0.01). Using purified circulating CD4+ T cells from uninfected donors, we demonstrate that FX1 treatment resulted in downregulation pSAMHD1 expression (P < 0.05) and T cell activation (HLA-DR, CD25, and Ki67; P < 0.01) ex vivo corresponding with inhibition of HIV-1 and HIV-2 replication. Ex vivo HIV-1 reactivation using purified peripheral CD4+ T cells from HIV-infected ART-suppressed donors was also blocked by FX1 treatment (P < 0.01). Our results indicate that BCL6 function contributes to Tfh/non-Tfh CD4+ T cell activation and cellular susceptibility to HIV infection. BCL6 inhibition represents a novel therapeutic strategy to potentiate HIV suppression in Tfh/non-Tfh CD4+ T cells without reactivation of latent virus.IMPORTANCE The expansion and accumulation of HIV-infected BCL6+ Tfh CD4+ T cells are thought to contribute to the persistence of viral reservoirs in infected subjects undergoing ART. Two mechanisms have been raised for the preferential retention of HIV within Tfh CD4+ T cells: (i) antiretroviral drugs have limited tissue distribution, resulting in insufficient tissue concentration and lower efficacy in controlling HIV replication in lymphoid tissues, and (ii) cytotoxic CD8+ T cells within lymphoid tissues express low levels of chemokine receptor (CXCR5), thus limiting their ability to enter the GCs to control/eliminate HIV-infected Tfh cells. Our results indicate that the BCL6 inhibitor FX1 can not only repress HIV infection of tonsillar Tfh ex vivo but also suppress HIV infection and reactivation in primary, non-Tfh CD4+ T cells. Our study provides a rationale for targeting BCL6 protein to extend ART-mediated reduction of persistent HIV and/or support strategies toward HIV remission beyond ART cessation.

A20 upregulation during treated HIV disease is associated with intestinal epithelial cell recovery and function.

TRIAL REGISTRATION: ClinicalTrials.gov Clinical Trial NCT00594880.

Oncostatic treatment effect of triple negative breast cancer cell line with copper (I)-nicotinate complex.

The treatment of triple-negative breast cancer (TNBC) remains a major challenge. The present study aimed to throw more light on the role of copper (I)-nicotinate complex (CNC) as an antitumor as well as a proapoptotic agent. In this study, the HCC-1806 cell line was used as a model for TNBC. Cell cycle, apoptosis assay, and programmed cell death protein-1 were investigated by flowcytometry. Besides, the comet assay was performed using a fluorescence microscope. The enzyme-linked immunosorbent assay technique was used for the detection of phospho-Chk1 at ser 317 and caspase-3. Moreover, the gene expression of survivin was identified by real-time polymerase chain reaction. Finally, superoxide dismutase (SOD) was calorimetrically assayed. The viability of HCC-1806 cells treated with CNC was decreased in a dose-dependent manner. The tendency for apoptotic machinery was observed through the increase in the sub G0 peak, the percentage of early and late apoptotic phases, and the elevation in caspase-3 levels associated with a downregulation of the survivin gene expression. The antioxidant property of the complex, reflected by elevated SOD activity, may contribute to mediate the cell death pathways. Low concentrations of CNC were found to favor the apoptotis-mediated mechanism. However, one cannot neglect the abundance of cell necrosis-mediated death of cells via CNC, especially at higher concentrations.

Elevated cerebrospinal fluid Galectin-9 is associated with central nervous system immune activation and poor cognitive performance in older HIV-infected individuals.

We previously reported that galectin-9 (Gal-9), a soluble lectin with immunomodulatory properties, is elevated in plasma during HIV infection and induces HIV transcription. The link between Gal-9 and compromised neuronal function is becoming increasingly evident; however, the association with neuroHIV remains unknown. We measured Gal-9 levels by ELISA in cerebrospinal fluid (CSF) and plasma of 70 HIV-infected (HIV+) adults stratified by age (older > 40 years and younger < 40 years) either ART suppressed or with detectable CSF HIV RNA, including a subgroup with cognitive assessments, and 18 HIV uninfected (HIV-) controls. Gal-9 tissue expression was compared in necropsy brain specimens from HIV- and HIV+ donors using gene datasets and immunohistochemistry. Among older HIV+ adults, CSF Gal-9 was elevated in the ART suppressed and CSF viremic groups compared to controls, whereas in the younger group, Gal-9 levels were elevated only in the CSF viremic group (p < 0.05). CSF Gal-9 positively correlated with age in all groups (p < 0.05). CSF Gal-9 tracked with CSF HIV RNA irrespective of age (ß = 0.33; p < 0.05). Higher CSF Gal-9 in the older viremic HIV+ group correlated with worse neuropsychological test performance scores independently of age and CSF HIV RNA (p < 0.05). Furthermore, CSF Gal-9 directly correlated with myeloid activation (CSF-soluble CD163 and neopterin) in both HIV+ older groups (p < 0.05). Among HIV+ necropsy specimens, Gal-9 expression was increased in select brain regions compared to controls (p < 0.05). Gal-9 may serve as a novel neuroimmuno-modulatory protein that is involved in driving cognitive deficits in those aging with HIV and may be valuable in tracking cognitive abnormalities.

Breaking the Glyco-Code of HIV Persistence and Immunopathogenesis.

PURPOSE OF REVIEW: Glycoimmunology is an emerging field focused on understanding how immune responses are mediated by glycans (carbohydrates) and their interaction with glycan-binding proteins called lectins. How glycans influence immunological functions is increasingly well understood. In a parallel way, in the HIV field, it is increasingly understood how the host immune system controls HIV persistence and immunopathogenesis. However, what has mostly been overlooked, despite its potential for therapeutic applications, is the role that the host glycosylation machinery plays in modulating the persistence and immunopathogenesis of HIV. Here, we will survey four areas in which the links between glycan-lectin interactions and immunology and between immunology and HIV are well described. For each area, we will describe these links and then delineate the opportunities for the HIV field in investigating potential interactions between glycoimmunology and HIV persistence/immunopathogenesis. RECENT FINDINGS: Recent studies show that the human glycome (the repertoire of human glycan structures) plays critical roles in driving or modulating several cellular processes and immunological functions that are central to maintaining HIV infection. Understanding the links between glycoimmunology and HIV infection may create a new paradigm for discovering novel glycan-based therapies that can lead to eradication, functional cure, or improved tolerance of lifelong infection.

Glycosylation of Zika Virus is Important in Host-Virus Interaction and Pathogenic Potential.

Zika virus (ZIKV) is a global public health issue due to its association with severe developmental disorders in infants and neurological disorders in adults. ZIKV uses glycosylation of its envelope (E) protein to interact with host cell receptors to facilitate entry; these interactions could also be important for designing therapeutics and vaccines. Due to a lack of proper information about Asn-linked (N-glycans) on ZIKV E, we analyzed ZIKV E of various strains derived from different cells. We found ZIKV E proteins being extensively modified with oligomannose, hybrid and complex N-glycans of a highly heterogeneous nature. Host cell surface glycans correlated strongly with the glycomic features of ZIKV E. Mechanistically, we observed that ZIKV N-glycans might play a role in viral pathogenesis, as mannose-specific C-type lectins DC-SIGN and L-SIGN mediate host cell entry of ZIKV. Our findings represent the first detailed mapping of N-glycans on ZIKV E of various strains and their functional significance.

Cytokines Elevated in HIV Elite Controllers Reduce HIV Replication In Vitro and Modulate HIV Restriction Factor Expression.

A subset of HIV-infected individuals termed elite controllers (ECs) maintain CD4+ T cell counts and control viral replication in the absence of antiretroviral therapy (ART). Systemic cytokine responses may differentiate ECs from subjects with uncontrolled viral replication or from those who require ART to suppress viral replication. We measured 87 cytokines in four groups of women: 73 ECs, 42 with pharmacologically suppressed viremia (ART), 42 with uncontrolled viral replication (noncontrollers [NCs]), and 48 HIV-uninfected (NEG) subjects. Four cytokines were elevated in ECs but not NCs or ART subjects: CCL14, CCL21, CCL27, and XCL1. In addition, median stromal cell-derived factor-1 (SDF-1) levels were 43% higher in ECs than in NCs. The combination of the five cytokines suppressed R5 and X4 virus replication in resting CD4+ T cells, and individually SDF-1ß, CCL14, and CCL27 suppressed R5 virus replication, while SDF-1ß, CCL21, and CCL14 suppressed X4 virus replication. Functional studies revealed that the combination of the five cytokines upregulated CD69 and CCR5 and downregulated CXCR4 and CCR7 on CD4+ T cells. The CD69 and CXCR4 effects were driven by SDF-1, while CCL21 downregulated CCR7. The combination of the EC-associated cytokines induced expression of the anti-HIV host restriction factors IFITM1 and IFITM2 and suppressed expression of RNase L and SAMHD1. These results identify a set of cytokines that are elevated in ECs and define their effects on cellular activation, HIV coreceptor expression, and innate restriction factor expression. This cytokine pattern may be a signature characteristic of HIV-1 elite control, potentially important for HIV therapeutic and curative strategies.IMPORTANCE Approximately 1% of people infected with HIV control virus replication without taking antiviral medications. These subjects, termed elite controllers (ECs), are known to have stronger immune responses targeting HIV than the typical HIV-infected subject, but the exact mechanisms of how their immune responses control infection are not known. In this study, we identified five soluble immune signaling molecules (cytokines) in the blood that were higher in ECs than in subjects with typical chronic HIV infection. We demonstrated that these cytokines can activate CD4+ T cells, the target cells for HIV infection. Furthermore, these five EC-associated cytokines could change expression levels of intrinsic resistance factors, or molecules inside the target cell that fight HIV infection. This study is significant in that it identified cytokines elevated in subjects with a good immune response against HIV and defined potential mechanisms as to how these cytokines could induce resistance to the virus in target cells.

Human Galectin-9 Is a Potent Mediator of HIV Transcription and Reactivation.

Identifying host immune determinants governing HIV transcription, latency and infectivity in vivo is critical to developing an HIV cure. Based on our recent finding that the host factor p21 regulates HIV transcription during antiretroviral therapy (ART), and published data demonstrating that the human carbohydrate-binding immunomodulatory protein galectin-9 regulates p21, we hypothesized that galectin-9 modulates HIV transcription. We report that the administration of a recombinant, stable form of galectin-9 (rGal-9) potently reverses HIV latency in vitro in the J-Lat HIV latency model. Furthermore, rGal-9 reverses HIV latency ex vivo in primary CD4+ T cells from HIV-infected, ART-suppressed individuals (p = 0.002), more potently than vorinostat (p = 0.02). rGal-9 co-administration with the latency reversal agent "JQ1", a bromodomain inhibitor, exhibits synergistic activity (p<0.05). rGal-9 signals through N-linked oligosaccharides and O-linked hexasaccharides on the T cell surface, modulating the gene expression levels of key transcription initiation, promoter proximal-pausing, and chromatin remodeling factors that regulate HIV latency. Beyond latent viral reactivation, rGal-9 induces robust expression of the host antiviral deaminase APOBEC3G in vitro and ex vivo (FDR<0.006) and significantly reduces infectivity of progeny virus, decreasing the probability that the HIV reservoir will be replenished when latency is reversed therapeutically. Lastly, endogenous levels of soluble galectin-9 in the plasma of 72 HIV-infected ART-suppressed individuals were associated with levels of HIV RNA in CD4+ T cells (p<0.02) and with the quantity and binding avidity of circulating anti-HIV antibodies (p<0.009), suggesting a role of galectin-9 in regulating HIV transcription and viral production in vivo during therapy. Our data suggest that galectin-9 and the host glycosylation machinery should be explored as foundations for novel HIV cure strategies.

TIGIT Marks Exhausted T Cells, Correlates with Disease Progression, and Serves as a Target for Immune Restoration in HIV and SIV Infection.

HIV infection induces phenotypic and functional changes to CD8+ T cells defined by the coordinated upregulation of a series of negative checkpoint receptors that eventually result in T cell exhaustion and failure to control viral replication. We report that effector CD8+ T cells during HIV infection in blood and SIV infection in lymphoid tissue exhibit higher levels of the negative checkpoint receptor TIGIT. Increased frequencies of TIGIT+ and TIGIT+ PD-1+ CD8+ T cells correlated with parameters of HIV and SIV disease progression. TIGIT remained elevated despite viral suppression in those with either pharmacological antiretroviral control or immunologically in elite controllers. HIV and SIV-specific CD8+ T cells were dysfunctional and expressed high levels of TIGIT and PD-1. Ex-vivo single or combinational antibody blockade of TIGIT and/or PD-L1 restored viral-specific CD8+ T cell effector responses. The frequency of TIGIT+ CD4+ T cells correlated with the CD4+ T cell total HIV DNA. These findings identify TIGIT as a novel marker of dysfunctional HIV-specific T cells and suggest TIGIT along with other checkpoint receptors may be novel curative HIV targets to reverse T cell exhaustion.

HIV Antibody Level as a Marker of HIV Persistence and Low-Level Viral Replication.

Background: Human immunodeficiency virus (HIV) antibodies are generated and maintained by ongoing systemic expression of HIV antigen. We investigated whether HIV antibody responses as measured by high-throughput quantitative and qualitative assays could be used to indirectly measure persistent HIV replication in individuals receiving antiretroviral therapy (ART). Methods: HIV antibody responses were measured over time in the presence or absence of suppressive ART and were compared to the HIV reservoir size and expression of antiviral restriction factors. Results: Among untreated individuals, including both elite controllers (ie, persons with a viral load of ≤40 copies/mL) and noncontrollers, antibody parameters were stable over time and correlated with the individual viral load. Viral suppression with ART led to a progressive decline in antibody responses after treatment induction that persisted for 5-7 years. Higher levels of HIV antibodies during suppressive therapy were associated with later initiation of ART after infection, with higher DNA and cell-associated RNA levels, and with lower expression of multiple anti-HIV host restriction factors. Discussion: These findings suggest that declining antibody levels during ART reflect lower levels of antigen production and/or viral replication in the persistent HIV reservoir. Results of relatively inexpensive and quantitative HIV antibody assays may be useful indirect markers that enable efficient monitoring of the viral reservoir and suppression during functional-cure interventions.