HIV infection is active and progressive in lymphoid tissue during the clinically latent stage of disease

Pneumococcal vaccine hyporesponsiveness in people living with HIV: A narrative review of immunological mechanisms and insights from minimally invasive lymph node sampling

Despite highly effective antiretroviral therapy, people living with HIV (PLWH) remain at elevated risk for invasive pneumococcal disease. Clinical studies show that, even with high CD4+ counts, PLWH exhibit diminished serological responses and rapid antibody decline following pneumococcal vaccination, plausibly due to underlying immune dysfunction. Germinal centers (GCs), located within lymph nodes, are essential for generating high-affinity antibodies, but are structurally and functionally disrupted in PLWH. These local impairments, combined with systemic immune dysregulation, contribute to vaccine hyporesponsiveness in PLWH. This narrative review links immunological findings from experimental and in vivo studies to clinical pneumococcal vaccine trials, to investigate mechanisms that may be leveraged to strengthen vaccine-induced immunity in PLWH. We also highlight the application of fine needle aspiration (FNA) of the lymph node as a way to study pneumococcal vaccine hyporesponsiveness in the GC and provide potential direction to improve responses for next-generation pneumococcal conjugate vaccines in PLWH.

Viral Infection and Dissemination Through the Lymphatic System

Many viruses induce viremia (virus in the blood) and disseminate throughout the body via the bloodstream from the initial infection site. However, viruses must often pass through the lymphatic system to reach the blood. The lymphatic system comprises a network of vessels distinct from blood vessels, along with interconnected lymph nodes (LNs). The complex network has become increasingly appreciated as a crucial host factor that contributes to both the spread and control of viral infections. Viruses can enter the lymphatics as free virions or along with migratory cells. Once virions arrive in the LN, sinus-resident macrophages remove infectious virus from the lymph. Depending on the virus, macrophages can eliminate infection or propagate the virus. A virus released from an LN is eventually deposited into the blood. This unique pathway highlights LNs as targets for viral infection control and for modulation of antiviral response development. Here, we review the lymphatic system and viruses that disseminate through this network. We discuss infection of the LN, the generation of adaptive antiviral immunity, and current knowledge of protection within the infected node. We conclude by sharing insights from ongoing efforts to optimize lymphatic targeting by vaccines and pharmaceuticals. Understanding the lymphatic system's role during viral infection enhances our knowledge of antiviral immunity and virus-host interactions and reveals potential targets for next-generation therapies.

Immune Alterations and Viral Reservoir Atlas in SIV-Infected Chinese Rhesus Macaques

BACKGROUND/OBJECTIVES

Over the last decades, our projects have been dedicated to clarifying immunopathological and virological events associated with Human Immunodeficiency Virus (HIV) infection.

METHODS

By using non-human primate models of pathogenic and non-pathogenic lentiviral infections, we aimed at identifying the cells and tissues in which the virus persists, despite antiretroviral therapy (ART). Indeed, the eradication of viral reservoirs is a major challenge for HIV cure.

RESULTS

We present a series of results performed in rhesus macaques of Chinese origin deciphering the virological and immunological events associated with ART that can be of interest for people living with HIV.

CONCLUSIONS

This model could be of interest for understanding in whole body the clinical alteration that persist despite ART.

Compartmental structure in the secondary lymphoid tissue can slow down in vivo HIV-1 evolution in the presence of strong CTL responses

Human immunodeficiency virus (HIV-1) replicates in the secondary lymphoid tissues, which are characterized by complex compartmental structures. While cytotoxic T lymphocytes (CTL) readily access infected cells in the extrafollicular compartments, they do not home to follicular compartments, which thus represent an immune-privileged site. Using mathematical models, previous work has shown that this compartmental tissue structure can delay the emergence of CTL escape mutants. Here, we show computationally that the compartmental structure can have an impact on the evolution of advantageous mutants that are not related to CTL recognition: (i) compartmental structure can influence the fixation probability of an advantageous mutant, with weakened selection occurring if CTL responses are of intermediate strength; (ii) compartmental structure is predicted to reduce the rate of mutant generation, which becomes more pronounced for stronger CTL responses; and (iii) compartmental structure is predicted to slow down the overall rate of mutant invasion, with the effect becoming more pronounced for stronger CTL responses. Altogether, this work shows that in vivo virus evolution proceeds slower in models with compartmental structure compared with models that assume equivalent virus load in the absence of compartmental structure, especially for strong CTL-mediated virus control. This has implications for understanding the rate of disease progression.

The quality of SIV-specific fCD8 T cells limits SIV RNA production in Tfh cells during antiretroviral therapy

The attack and defense of infected cells and cytotoxic CD8 T cells occur in germinal centers in lymphoid tissue in chronic persistent HIV/SIV infection. Latently infected cells, the therapeutic target of HIV infection, accumulate in follicular helper T (Tfh) cells in lymphoid tissue; the impact of HIV-specific follicular CD8 (fCD8) T cells in lymphoid tissue on the latently infected cells remains unknown. We infected 15 cynomolgus macaques with SIVmac239 and examined the contribution of SIV-Gag-specific fCD8 T cells, defined by activation-induced markers (AIMs), to SIV-infected cells. Eight out of the 15 infected macaques served as progressors; a chronic phase combination antiretroviral therapy (cART) model was established for the eight macaques (progressors) with chronic persistent infection status, wherein cART was started in the chronic phase and discontinued after 27 weeks. Seven macaques that naturally controlled the viremia served as natural controllers. The frequency of SIV-Gag-specific fCD8 T cells was inversely correlated with the amount of cell-associated SIV-gag RNA in the Tfh only under cART or in the controllers but not in untreated progressors. scRNA-seq of SIV-Gag-specific fCD8 T cells in various conditions revealed that the gene expression pattern of SIV-Gag-specific fCD8 T cells in the controllers was closer to that of those under cART than the untreated progressors. Comparing the SIV-Gag-specific fCD8 T cells of those under cART to the controllers revealed their more exhausted and immunosenescent nature under cART. Improving the HIV/SIV-specific fCD8 T cells under cART by targeting those pathways might contribute to the development of potential curative strategies.IMPORTANCEWe infected cynomolgus macaques with SIVmac239 to establish an SIV-chronically infected cART model. We performed an in-depth characterization of Tfh and fCD8 T cells in three conditions-chronic stage of untreated, cART-treated, and natural controller cynomolgus macaques-by combining tissue section analysis and single-cell analyses of sorted cells. We revealed the inverse relationship between Tfh infection and SIV-Gag-specific fCD8 T cell frequencies as observed in HIV-infected individuals, thereby establishing the cynomolgus macaque as a relevant animal model to study the determinants of HIV/SIV persistence in lymphoid tissue. Additionally, scRNA-seq analysis of SIV-Gag-specific fCD8 T cells revealed an enrichment of exhausted or senescent transcriptomic signatures under cART. These data will provide the basic insights into virus-host CD8 T cell interactions, particularly within the follicular region, during latent HIV infection under ART.

Anatomical, subset, and HIV-dependent expression of viral sensors and restriction factors

We developed viral sensor and restriction factor-cytometry by time of flight (VISOR-CyTOF), which profiles 19 viral sensors and restriction factors (VISORs) simultaneously in single cells, and applied it to 41 postmortem tissues from people with HIV. Mucosal myeloid cells are well equipped with SAMHD1 and sensors of viral capsid and DNA while CD4+ T cells are not. In lymph node CD4+ Tfh, VISOR expression patterns reflect those favoring integration but blocking HIV gene expression, thus favoring viral latency. We also identify small subsets of bone marrow-, lung-, and gut-associated CD4+ T and myeloid cells expressing high levels of restriction factors targeting most stages of the HIV replication cycle. In vitro, HIV preferentially fuses to CD4+ T cells with a permissive VISOR profile, but early induction of select VISORs by T1IFN prevents productive HIV infection. Our findings document the diverse patterns of VISOR profiles across tissues and cellular subsets and define their association with susceptibility to HIV.

Intestinal Microbiota and Aging in People with HIV-What We Know and What We Don't

PURPOSE OF REVIEW

People with HIV (PWH) experience premature aging and an elevated risk of age-related comorbidities, even with viral suppression through antiretroviral therapy (ART). We examine gastrointestinal disruptions, specifically impaired intestinal barrier integrity and microbial dysbiosis, as contributors to these comorbidities.

RECENT FINDINGS

HIV infection compromises the intestinal epithelial barrier, increasing permeability and microbial translocation, which trigger inflammation and cellular stress. ART does not fully restore gut barrier integrity, leading to persistent inflammation and cellular stress. Additionally, HIV-associated microbial dysbiosis favors pro-inflammatory bacteria, intensifying inflammation and tissue damage, which may contribute to premature aging in PWH. Understanding the interactions between intestinal microbiota, chronic inflammation, cellular stress, and aging is essential to developing therapies aimed at reducing inflammation and slowing age-related diseases in PWH. In this review, we discuss critical knowledge gaps and highlight the therapeutic potential of microbiota-targeted interventions to mitigate inflammation and delay age-associated pathologies in PWH.

Anti-PD-1 chimeric antigen receptor T cells efficiently target SIV-infected CD4+ T cells in germinal centers

Programmed cell death protein 1 (PD-1) is an immune checkpoint marker commonly expressed on memory T cells and enriched in latently HIV-infected CD4+ T cells. We engineered an anti-PD-1 chimeric antigen receptor (CAR) to assess the impact of PD-1 depletion on viral reservoirs and rebound dynamics in SIVmac239-infected rhesus macaques (RMs). Adoptive transfer of anti-PD-1 CAR T cells was done in 2 SIV-naive and 4 SIV-infected RMs on antiretroviral therapy (ART). In 3 of 6 RMs, anti-PD-1 CAR T cells expanded and persisted for up to 100 days concomitant with the depletion of PD-1+ memory T cells in blood and tissues, including lymph node CD4+ follicular helper T (TFH) cells. Loss of TFH cells was associated with depletion of detectable SIV RNA from the germinal center (GC). However, following CAR T infusion and ART interruption, there was a marked increase in SIV replication in extrafollicular portions of lymph nodes, a 2-log higher plasma viremia relative to controls, and accelerated disease progression associated with the depletion of CD8+ memory T cells. These data indicate anti-PD-1 CAR T cells depleted PD-1+ T cells, including GC TFH cells, and eradicated SIV from this immunological sanctuary.

[Castleman's disease, pathophysiology, advances in diagnosis and treatment]

Castleman's disease (CD) encompasses a heterogeneous set of reactive lymphoproliferative processes that share well-defined histologic features. CD is considered a rare or minority disease. The incidence of CD is not fully known, although it is estimated at less than 1 per 100,000 inhabitants. It has a bimodal distribution (30-40 years and then 60-80 years). The incidence is similar in both sexes, although the unicentric variant seems to have a slight predominance in women with a 2:1 ratio. CD is classified into a hyalinovascular form (this being the most frequent) and a plasmocellular form, related to the HIV and VHH-8 viruses, which together with other autoimmune mechanisms develop hyperproduction of interleukin-6 (IL-6) by B lymphocytes. There are different lines of treatment, where the use of anti IL-6 stands out, being siltuximab the most used as orphan drug in this pathology.

HIV Productively Infects Highly Differentiated and Exhausted CD4+ T Cells During AIDS

Background

Throughout HIV infection, productively infected cells generate billions of viral particles and are thus responsible for body-wide HIV dissemination, but their phenotype during AIDS is unknown. As AIDS is associated with immunological changes, analyzing the phenotype of productively infected cells can help understand HIV production during this terminal stage.

Methods

Blood samples from 15 untreated viremic participants (recent infection, n=5; long-term infection, n=5; active opportunistic AIDS-defining disease, n=5) and 5 participants virologically controlled on antiretroviral therapy (ART) enrolled in the Analysis of the Persistence, Reservoir and HIV Latency (APRIL) study (NCT05752318) were analyzed. Cells expressing the capsid protein p24 (p24+ cells) after 18 hours of resting or 24 hours of stimulation (HIV-Flow) revealed productively infected cells from viremic participants or translation-competent reservoir cells from treated participants, respectively.

Results

The frequency of productively infected cells tended to be higher during AIDS in comparison with recent and long-term infections (median, 340, 72, and 32/million CD4+ T cells, respectively) and correlated with the plasma viral load at all stages of infection. Altogether, these cells were more frequently CD4low, HLA-ABClow, CD45RA-, Ki67+, PD-1+, with a non-negligible contribution from pTfh (CXCR5+PD-1+) cells, and were not significantly enriched in HIV coreceptors CCR5 nor CXCR4 expression. The comparison markers expression between stages showed that productively infected cells during AIDS were enriched in memory and exhausted cells. In contrast, the frequencies of infected pTfh were lower during AIDS compared to non-AIDS stages. A UMAP analysis revealed that total CD4+ T cells were grouped in 7 clusters and that productive p24+ cells were skewed to given clusters throughout the course of infection. Overall, the preferential targets of HIV during the latest stages seemed to be more frequently highly differentiated (memory, TTD-like) and exhausted cells and less frequently pTfh-like cells. In contrast, translation-competent reservoir cells were less frequent (5/million CD4+ T cells) and expressed more frequently HLA-ABC and less frequently PD-1.

Conclusions

In long-term infection and AIDS, productively infected cells were differentiated and exhausted. This could indicate that cells with these given features are responsible for HIV production and dissemination in an immune dysfunction environment occurring during the last stages of infection.

Distinct intestinal microbial signatures linked to accelerated systemic and intestinal biological aging

BACKGROUND

People living with HIV (PLWH), even when viral replication is controlled through antiretroviral therapy (ART), experience persistent inflammation. This inflammation is partly attributed to intestinal microbial dysbiosis and translocation, which may lead to non-AIDS-related aging-associated comorbidities. The extent to which living with HIV - influenced by the infection itself, ART usage, sexual orientation, or other associated factors - affects the biological age of the intestines is unclear. Furthermore, the role of microbial dysbiosis and translocation in the biological aging of PLWH remains to be elucidated. To investigate these uncertainties, we used a systems biology approach, analyzing colon and ileal biopsies, blood samples, and stool specimens from PLWH on ART and people living without HIV (PLWoH) as controls.

RESULTS

PLWH exhibit accelerated biological aging in the colon, ileum, and blood, as measured by various epigenetic aging clocks, compared to PLWoH. Investigating the relationship between microbial translocation and biological aging, PLWH had decreased levels of tight junction proteins in the intestines, along with increased microbial translocation. This intestinal permeability correlated with faster biological aging and increased inflammation. When investigating the relationship between microbial dysbiosis and biological aging, the intestines of PLWH had higher abundance of specific pro-inflammatory bacteria, such as Catenibacterium and Prevotella. These bacteria correlated with accelerated biological aging. Conversely, the intestines of PLWH had lower abundance of bacteria known for producing the anti-inflammatory short-chain fatty acids, such as Subdoligranulum and Erysipelotrichaceae, and these bacteria were associated with slower biological aging. Correlation networks revealed significant links between specific microbial genera in the colon and ileum (but not in feces), increased aging, a rise in pro-inflammatory microbe-related metabolites (e.g., those in the tryptophan metabolism pathway), and a decrease in anti-inflammatory metabolites like hippuric acid.

CONCLUSIONS

We identified specific microbial compositions and microbiota-related metabolic pathways that are intertwined with intestinal and systemic biological aging. This microbial signature of biological aging is likely reflecting various factors including the HIV infection itself, ART usage, sexual orientation, and other aspects associated with living with HIV. A deeper understanding of the mechanisms underlying these connections could offer potential strategies to mitigate accelerated aging and its associated health complications. Video Abstract.

Human immunodeficiency virus dynamics in secondary lymphoid tissues and the evolution of cytotoxic T lymphocyte escape mutants

In secondary lymphoid tissues, human immunodeficiency virus (HIV) can replicate in both the follicular and extrafollicular compartments. Yet, virus is concentrated in the follicular compartment in the absence of antiretroviral therapy, in part due to the lack of cytotoxic T lymphocyte (CTL)-mediated activity there. CTLs home to the extrafollicular compartment, where they can suppress virus load to relatively low levels. We use mathematical models to show that this compartmentalization can explain seemingly counter-intuitive observations. First, it can explain the observed constancy of the viral decline slope during antiviral therapy in the peripheral blood, irrespective of the presence of CTL in Simian Immunodeficiency Virus (SIV)-infected macaques, under the assumption that CTL-mediated lysis significantly contributes to virus suppression. Second, it can account for the relatively long times it takes for CTL escape mutants to emerge during chronic infection even if CTL-mediated lysis is responsible for virus suppression. The reason is the heterogeneity in CTL activity and the consequent heterogeneity in selection pressure between the follicular and extrafollicular compartments. Hence, to understand HIV dynamics more thoroughly, this analysis highlights the importance of measuring virus populations separately in the extrafollicular and follicular compartments rather than using virus load in peripheral blood as an observable; this hides the heterogeneity between compartments that might be responsible for the particular patterns seen in the dynamics and evolution of the HIV in vivo.

New Insights into HIV Life Cycle, Th1/Th2 Shift during HIV Infection and Preferential Virus Infection of Th2 Cells: Implications of Early HIV Treatment Initiation and Care

The theory of immune regulation involves a homeostatic balance between T-helper 1 (Th1) and T-helper 2 (Th2) responses. The Th1 and Th2 theories were introduced in 1986 as a result of studies in mice, whereby T-helper cell subsets were found to direct different immune response pathways. Subsequently, this hypothesis was extended to human immunity, with Th1 cells mediating cellular immunity to fight intracellular pathogens, while Th2 cells mediated humoral immunity to fight extracellular pathogens. Several disease conditions were later found to tilt the balance between Th1 and Th2 immune response pathways, including HIV infection, but the exact mechanism for the shift from Th1 to Th2 cells was poorly understood. This review provides new insights into the molecular biology of HIV, wherein the HIV life cycle is discussed in detail. Insights into the possible mechanism for the Th1 to Th2 shift during HIV infection and the preferential infection of Th2 cells during the late symptomatic stage of HIV disease are also discussed.

The latent HIV reservoir: current advances in genetic sequencing approaches

Multiple cellular HIV reservoirs in diverse anatomical sites can undergo clonal expansion and persist for years despite suppressive antiretroviral therapy, posing a major barrier toward an HIV cure. Commonly adopted assays to assess HIV reservoir size mainly consist of PCR-based measures of cell-associated total proviral DNA, intact proviruses and transcriptionally competent provirus (viral RNA), flow cytometry and microscopy-based methods to measure translationally competent provirus (viral protein), and quantitative viral outgrowth assay, the gold standard to measure replication-competent provirus; yet no assay alone can provide a comprehensive view of the total HIV reservoir or its dynamics. Furthermore, the detection of extant provirus by these measures does not preclude defects affecting replication competence. An accurate measure of the latent reservoir is essential for evaluating the efficacy of HIV cure strategies. Recent approaches have been developed, which generate proviral sequence data to create a more detailed profile of the latent reservoir. These sequencing approaches are valuable tools to understand the complex multicellular processes in a diverse range of tissues and cell types and have provided insights into the mechanisms of HIV establishment and persistence. These advancements over previous sequencing methods have allowed multiplexing and new assays have emerged, which can document transcriptional activity, chromosome accessibility, and in-depth cellular phenotypes harboring latent HIV, enabling the characterization of rare infected cells across restrictive sites such as the brain. In this manuscript, we provide a review of HIV sequencing-based assays adopted to address challenges in quantifying and characterizing the latent HIV reservoir.

Distinct Intestinal Microbial Signatures Linked to Accelerated Biological Aging in People with HIV

Background

People with HIV (PWH), even with controlled viral replication through antiretroviral therapy (ART), experience persistent inflammation. This is partly due to intestinal microbial dysbiosis and translocation. Such ongoing inflammation may lead to the development of non-AIDS-related aging-associated comorbidities. However, there remains uncertainty regarding whether HIV affects the biological age of the intestines and whether microbial dysbiosis and translocation influence the biological aging process in PWH on ART. To fill this knowledge gap, we utilized a systems biology approach, analyzing colon and ileal biopsies, blood samples, and stool specimens from PWH on ART and their matched HIV-negative counterparts.

Results

Despite having similar chronological ages, PWH on ART exhibit accelerated biological aging in the colon, ileum, and blood, as measured by various epigenetic aging clocks, compared to HIV-negative controls. Investigating the relationship between microbial translocation and biological aging, PWH on ART had decreased levels of tight junction proteins in the colon and ileum, along with increased microbial translocation. This increased intestinal permeability correlated with faster intestinal and systemic biological aging, as well as increased systemic inflammation. When investigating the relationship between microbial dysbiosis and biological aging, the intestines of PWH on ART had higher abundance of specific pro-inflammatory bacterial genera, such as Catenibacterium and Prevotella. These bacteria significantly correlated with accelerated local and systemic biological aging. Conversely, the intestines of PWH on ART had lower abundance of bacterial genera known for producing short-chain fatty acids and exhibiting anti-inflammatory properties, such as Subdoligranulum and Erysipelotrichaceae, and these bacteria taxa were associated with slower biological aging. Correlation networks revealed significant links between specific microbial genera in the colon and ileum (but not in feces), increased aging, a rise in pro-inflammatory microbial-related metabolites (e.g., those in the tryptophan metabolism pathway), and a decrease in anti-inflammatory metabolites like hippuric acid and oleic acid.

Conclusions

We identified a specific microbial composition and microbiome-related metabolic pathways that are intertwined with both intestinal and systemic biological aging in PWH on ART. A deeper understanding of the mechanisms underlying these connections could potentially offer strategies to counteract premature aging and its associated health complications in PWH.

Lymph node dendritic cells harbor inducible replication-competent HIV despite years of suppressive ART

Although gut and lymph node (LN) memory CD4 T cells represent major HIV and simian immunodeficiency virus (SIV) tissue reservoirs, the study of the role of dendritic cells (DCs) in HIV persistence has long been limited to the blood due to difficulties to access lymphoid tissue samples. In this study, we show that LN migratory and resident DC subpopulations harbor distinct phenotypic and transcriptomic profiles. Interestingly, both LN DC subpopulations contain HIV intact provirus and inducible replication-competent HIV despite the expression of the antiviral restriction factor SAMHD1. Notably, LN DC subpopulations isolated from HIV-infected individuals treated for up to 14 years are transcriptionally silent but harbor replication-competent virus that can be induced upon TLR7/8 stimulation. Taken together, these results uncover a potential important contribution of LN DCs to HIV infection in the presence of ART.

CD3-immunotoxin mediated depletion of T cells in lymphoid tissues of rhesus macaques

Selective T-cell depletion prior to cell or organ transplantation is considered a preconditioning regimen to induce tolerance and immunosuppression. An immunotoxin consisting of a recombinant anti-CD3 antibody conjugated with diphtheria toxin was used to eliminate T-cells. It showed significant T-cell depletion activity in the peripheral blood and lymph nodes in animal models used in previous studies. To date, a comprehensive evaluation of T-cell depletion and CD3 proliferation for all lymphoid tissues has not been conducted. Here, two rhesus macaques were administered A-dmDT390-SCFBdb (CD3-IT) intravenously at 25 μg/kg twice daily for four days. Samples were collected one day prior to and four days post administration. Flow cytometry and immunofluorescence staining were used to evaluate treatment efficiency accurately. Our preliminary results suggest that CD3-IT treatment may induce higher depletion of CD3 and CD4 T-cells in the lymph nodes and spleen, but is ineffective in the colon and thymus. The data showed a better elimination tendency of CD4 T-cells in the B-cell zone relative to the germinal center in the lymph nodes. Further, CD3-IT treatment may lead to a reduction in germinal center T follicular helper CD4 cells in the lymph nodes compared to healthy controls. The number of proliferating CD3 T-cell indicated that repopulation in different lymphoid tissues may occur four days post treatment. Our results provide insights into the differential efficacy of CD3-IT treatment and T-cell proliferation post treatment in different lymphoid tissues. Overall, CD3-IT treatment shows potential efficacy in depleting T-cells in the periphery, lymph nodes, and spleen, making it a viable preconditioning regimen for cell or organ transplantation. Our pilot study provides critical descriptive statistics and can contribute to the design of larger future studies.

HIV infection

The AIDS epidemic has been a global public health issue for more than 40 years and has resulted in ~40 million deaths. AIDS is caused by the retrovirus, HIV-1, which is transmitted via body fluids and secretions. After infection, the virus invades host cells by attaching to CD4 receptors and thereafter one of two major chemokine coreceptors, CCR5 or CXCR4, destroying the host cell, most often a T lymphocyte, as it replicates. If unchecked this can lead to an immune-deficient state and demise over a period of ~2-10 years. The discovery and global roll-out of rapid diagnostics and effective antiretroviral therapy led to a large reduction in mortality and morbidity and to an expanding group of individuals requiring lifelong viral suppressive therapy. Viral suppression eliminates sexual transmission of the virus and greatly improves health outcomes. HIV infection, although still stigmatized, is now a chronic and manageable condition. Ultimate epidemic control will require prevention and treatment to be made available, affordable and accessible for all. Furthermore, the focus should be heavily oriented towards long-term well-being, care for multimorbidity and good quality of life. Intense research efforts continue for therapeutic and/or preventive vaccines, novel immunotherapies and a cure.

HIV-1 activates oxidative phosphorylation in infected CD4 T cells in a human tonsil explant model

Introduction

Human immunodeficiency virus type 1 (HIV-1) causes a chronic, incurable infection leading to immune activation and chronic inflammation in people with HIV-1 (PWH), even with virologic suppression on antiretroviral therapy (ART). The role of lymphoid structures as reservoirs for viral latency and immune activation has been implicated in chronic inflammation mechanisms. Still, the specific transcriptomic changes induced by HIV-1 infection in different cell types within lymphoid tissue remain unexplored.

Methods

In this study, we utilized human tonsil explants from healthy human donors and infected them with HIV-1 ex vivo. We performed single-cell RNA sequencing (scRNA-seq) to analyze the cell types represented in the tissue and to investigate the impact of infection on gene expression profiles and inflammatory signaling pathways.

Results

Our analysis revealed that infected CD4+ T cells exhibited upregulation of genes associated with oxidative phosphorylation. Furthermore, macrophages exposed to the virus but uninfected showed increased expression of genes associated with the NLRP3 inflammasome pathway.

Discussion

These findings provide valuable insights into the specific transcriptomic changes induced by HIV-1 infection in different cell types within lymphoid tissue. The activation of oxidative phosphorylation in infected CD4+ T cells and the proinflammatory response in macrophages may contribute to the chronic inflammation observed in PWH despite ART. Understanding these mechanisms is crucial for developing targeted therapeutic strategies to eradicate HIV-1 infection in PWH.

Cytolytic CD8+ T cells infiltrate germinal centers to limit ongoing HIV replication in spontaneous controller lymph nodes

Follicular CD8⁺ T cells (fCD8) mediate surveillance in lymph node (LN) germinal centers against lymphotropic infections and cancers, but the precise mechanisms by which these cells mediate immune control remain incompletely resolved. To address this, we investigated functionality, clonotypic compartmentalization, spatial localization, phenotypic characteristics, and transcriptional profiles of LN-resident virus-specific CD8⁺ T cells in persons who control HIV without medications. Antigen-induced proliferative and cytolytic potential consistently distinguished spontaneous controllers from noncontrollers. T cell receptor analysis revealed complete clonotypic overlap between peripheral and LN-resident HIV-specific CD8⁺ T cells. Transcriptional analysis of LN CD8⁺ T cells revealed gene signatures of inflammatory chemotaxis and antigen-induced effector function. In HIV controllers, the cytotoxic effectors perforin and granzyme B were elevated among virus-specific CXCR5⁺ fCD8s proximate to foci of HIV RNA within germinal centers. These results provide evidence consistent with cytolytic control of lymphotropic infection supported by inflammatory recruitment, antigen-specific proliferation, and cytotoxicity of fCD8s.

HIV Never Sleeps: Evidence to Support Early Antiretroviral Treatment

This Pillars of Immunology article is a commentary on “HIV infection is active and progressive in lymphoid tissue during the clinically latent stage of disease,” a pivotal article written by G. Pantaleo, C. Graziosi, J. F. Demarest, L. Butini, M. Montroni, C. H. Fox, J. M. Orenstein, D. P. Kotler, and A. S. Fauci, and published in Nature, in 1993. https://www.nature.com/articles/362355a0. The Journal of Immunology, 2023, 210: 1181–1182

Persons with HIV Develop Spike-Specific Lymph Node Germinal Center Responses following SARS-CoV-2 Vaccination

COVID-19 disproportionately affects persons with HIV (PWH) in worldwide locations with limited access to SARS-CoV-2 vaccines. PWH exhibit impaired immune responses to some, but not all, vaccines. Lymph node (LN) biopsies from PWH demonstrate abnormal LN structure, including dysregulated germinal center (GC) architecture. It is not clear whether LN dysregulation prevents PWH from mounting Ag-specific GC responses in the draining LN following vaccination. To address this issue, we longitudinally collected blood and draining LN fine needle aspiration samples before and after SARS-CoV-2 vaccination from a prospective, observational cohort of 11 PWH on antiretroviral therapy: 2 who received a two-dose mRNA vaccine series and 9 who received a single dose of the Ad26.COV2.S vaccine. Following vaccination, we observed spike-specific Abs, spike-specific B and T cells in the blood, and spike-specific GC B cell and T follicular helper cell responses in the LN of both mRNA vaccine recipients. We detected spike-specific Abs in the blood of all Ad26.COV2.S recipients, and one of six sampled Ad26.COV2.S recipients developed a detectable spike-specific GC B and T follicular helper cell response in the draining LN. Our data show that PWH can mount Ag-specific GC immune responses in the draining LN following SARS-CoV-2 vaccination. Due to the small and diverse nature of this cohort and the limited number of available controls, we are unable to elucidate all potential factors contributing to the infrequent vaccine-induced GC response observed in the Ad26.COV2.S recipients. Our preliminary findings suggest this is a necessary area of future research.

Profound phenotypic and epigenetic heterogeneity of the HIV-1-infected CD4+ T cell reservoir

Understanding the complexity of the long-lived HIV reservoir during antiretroviral therapy (ART) remains a considerable impediment in research towards a cure for HIV. To address this, we developed a single-cell strategy to precisely define the unperturbed peripheral blood HIV-infected memory CD4+ T cell reservoir from ART-treated people living with HIV (ART-PLWH) via the presence of integrated accessible proviral DNA in concert with epigenetic and cell surface protein profiling. We identified profound reservoir heterogeneity within and between ART-PLWH, characterized by new and known surface markers within total and individual memory CD4+ T cell subsets. We further uncovered new epigenetic profiles and transcription factor motifs enriched in HIV-infected cells that suggest infected cells with accessible provirus, irrespective of reservoir distribution, are poised for reactivation during ART treatment. Together, our findings reveal the extensive inter- and intrapersonal cellular heterogeneity of the HIV reservoir, and establish an initial multiomic atlas to develop targeted reservoir elimination strategies.

Seronegative MSM at high risk of HIV-1 acquisition show an immune quiescent profile with a normal immune response against common antigens

Human immunodeficiency virus (HIV) infection still represents a major public health problem worldwide, and its vaccine remains elusive. The study of HIV-exposed seronegative individuals (HESN) brings important information about the natural resistance to HIV, allows a better understanding of the infection, and opens doors for new preventive and therapeutic strategies. Among HESN groups, there are some men who have sex with men (MSM) with high-risk sexual behaviors, who represent an adequate cohort for HESN study because of their major HIV exposure without infection. This study aimed to compare the immunological profile of Colombian seronegative MSM with different risk sexual behaviors. This study included 60 MSM at high-risk (n = 16) and low-risk (n = 44) of HIV-1 acquisition. No sex worker nor homozygous delta 32 mutation subjects were included. All participants were negative for anti-HIV-1/2 antibodies and HIV-1 proviral DNA. A higher frequency of sexual partners in the last 3 months before the study participation (median, 30 vs. 2), lifetime sexual partners (median, 1,708 vs. 26), and unprotected anal intercourse (median 12.5 vs. 2) was determined in high-risk MSM than low-risk MSM. High-risk MSM also showed a quiescent profile of T cells and natural killer (NK) cells, with a significantly lower percentage of CD4+CD38+, CD4+HLADR-CD38+, CD4+Ki67+ T cells, and NKG2D+ NK cells (CD3-CD16+CD56+), a significantly higher percentage of CD4+HLADR-CD38-, and a tendency to show a higher percentage of CD8+HLADR+CD38- T cells than the low-risk group. Likewise, they showed higher mRNA levels of Serpin A1 from PBMCs. The results suggest that this MSM cohort could be HESN individuals and their resistance would be explained by a quiescent profile of T cells and NK cells and an increased Serpin A1 expression. Further study on MSM at high risk of exposure to HIV-1 is necessary to better understand the natural resistance to HIV.

HIV-1 infected humanized DRAGA mice develop HIV-specific antibodies despite lack of canonical germinal centers in secondary lymphoid tissues

A major barrier in the use of humanized mice as models of HIV-1 (HIV) infection is the inadequate generation of virus-specific antibody responses. Humanized DRAGA (hDRAGA) mice generate antigen-specific class switched antibodies to several pathogens, but whether they do so in HIV infection and the extent to which their secondary lymphoid tissues (sLT) support germinal center responses is unknown. hDRAGA mice were evaluated for their ability to support HIV replication, generate virus-specific antibody responses, develop splenocyte subsets, and organize sLT architecture. hDRAGA mice supported persistent HIV replication and developed modest levels of gp41-specific human IgM and IgG. Spleens from uninfected and HIV infected hDRAGA mice contained differentiated B and CD4+ T cell subsets including germinal center (GC) B cells and T follicular helper cells (TFH); relative expansions of TFH and CD8+ T cells, but not GC B cells, occurred in HIV-infected hDRAGA mice compared to uninfected animals. Immunofluorescent staining of spleen and mesenteric lymph node sections demonstrated atypical morphology. Most CD4+ and CD8+ T cells resided within CD20hi areas. CD20hi areas lacked canonical germinal centers, as defined by staining for IgD-Ki67+cells. No human follicular dendritic cells (FDC) were detected. Mouse FDC were distributed broadly throughout both CD20hi and CD20lo regions of sLT. HIV RNA particles were detected by in situ hybridization within CD20+ areas and some co-localized with mouse FDC. Viral RNA+ cells were more concentrated within CD20hi compared to CD20lo areas of sLT, but differences were diminished in spleen and eliminated in mesenteric lymph nodes when adjusted for CD4+ cell frequency. Thus, hDRAGA mice recapitulated multiple aspects of HIV pathogenesis including HIV replication, relative expansions in TFH and CD8+ T cells, and modest HIV-specific antibody production. Nevertheless, classical germinal center morphology in sLT was not observed, which may account for the inefficient expansion of GC B cells and generation of low titer human antibody responses to HIV-1 in this model.

CD8 lymphocytes mitigate HIV-1 persistence in lymph node follicular helper T cells during hyperacute-treated infection

HIV persistence in tissue sites despite ART is a major barrier to HIV cure. Detailed studies of HIV-infected cells and immune responses in native lymph node tissue environment is critical for gaining insight into immune mechanisms impacting HIV persistence and clearance in tissue sanctuary sites. We compared HIV persistence and HIV-specific T cell responses in lymph node biopsies obtained from 14 individuals who initiated therapy in Fiebig stages I/II, 5 persons treated in Fiebig stages III-V and 17 late treated individuals who initiated ART in Fiebig VI and beyond. Using multicolor immunofluorescence staining and in situ hybridization, we detect HIV RNA and/or protein in 12 of 14 Fiebig I/II treated persons on suppressive therapy for 1 to 55 months, and in late treated persons with persistent antigens. CXCR3+ T follicular helper cells harbor the greatest amounts of gag mRNA transcripts. Notably, HIV-specific CD8+ T cells responses are associated with lower HIV antigen burden, suggesting that these responses may contribute to HIV suppression in lymph nodes during therapy. These results reveal HIV persistence despite the initiation of ART in hyperacute infection and highlight the contribution of virus-specific responses to HIV suppression in tissue sanctuaries during suppressive ART.

Active PD-L1 incorporation within HIV virions functionally impairs T follicular helper cells

The limited development of broadly neutralizing antibodies (BnAbs) during HIV infection is classically attributed to an inadequate B-cell help brought by functionally impaired T follicular helper (Tfh) cells. However, the determinants of Tfh-cell functional impairment and the signals contributing to this condition remain elusive. In the present study, we showed that PD-L1 is incorporated within HIV virions through an active mechanism involving p17 HIV matrix protein. We subsequently showed that in vitro produced PD-L1high but not PD-L1low HIV virions, significantly reduced Tfh-cell proliferation and IL-21 production, ultimately leading to a decreased of IgG1 secretion from GC B cells. Interestingly, Tfh-cell functions were fully restored in presence of anti-PD-L1/2 blocking mAbs treatment, demonstrating that the incorporated PD-L1 proteins were functionally active. Taken together, the present study unveils an immunovirological mechanism by which HIV specifically exploits the regulatory potential of PD-L1 to suppress the immune system during the course of HIV infection.

During HIV infection, the development of effective BnAbs remains a rare phenomenon, occurring in only 15–20% of HIV-infected individuals after years of infection. Although multiple mechanisms may be involved, recent studies have suggested that functional impairment of Tfh cells, through immune checkpoint (IC)/IC-Ligand (IC-L) interactions, may lead to a decrease in B-cell help leading to low BnAbs production. Our laboratory recently showed that PD-L1 was predominantly expressed on lymph node (LN) migratory dendritic cells located predominantly in extra-follicular areas, implying that the source of IC-L contributing to Tfh-cell functional impairment may be independent of cellular expression of IC-L. These observations prompted us to investigate the potential contribution of IC-L incorporated within HIV virion envelope to Tfh-cell functional impairment. We subsequently demonstrated that PD-L1 was incorporated into a large fraction of HIV virions in the plasma of viremic HIV-infected individuals. Interestingly, PD-L1 remains active when incorporated into HIV virions envelope and could impaired Tfh-cell proliferation, resulting in decreased IgG1 production by B cells in vitro. These findings demonstrate an unsuspected mechanism contributing to the regulation of Tfh-cell function, which may contribute to the low production of BnAbs by B cells during HIV infection.

Subsets of Tissue CD4 T Cells Display Different Susceptibilities to HIV Infection and Death: Analysis by CyTOF and Single Cell RNA-seq

CD4 T lymphocytes belong to diverse cellular subsets whose sensitivity or resistance to HIV-associated killing remains to be defined. Working with lymphoid cells from human tonsils, we characterized the HIV-associated depletion of various CD4 T cell subsets using mass cytometry and single-cell RNA-seq. CD4 T cell subsets preferentially killed by HIV are phenotypically distinct from those resistant to HIV-associated cell death, in a manner not fully accounted for by their susceptibility to productive infection. Preferentially-killed subsets express CXCR5 and CXCR4 while preferentially-infected subsets exhibit an activated and exhausted effector memory cell phenotype. Single-cell RNA-seq analysis reveals that the subsets of preferentially-killed cells express genes favoring abortive infection and pyroptosis. These studies emphasize a complex interplay between HIV and distinct tissue-based CD4 T cell subsets, and the important contribution of abortive infection and inflammatory programmed cell death to the overall depletion of CD4 T cells that accompanies untreated HIV infection.

Insights into the HIV-1 Latent Reservoir and Strategies to Cure HIV-1 Infection

Since the first discovery of human immunodeficiency virus 1 (HIV-1) in 1983, the targeted treatment, antiretroviral therapy (ART), has effectively limited the detected plasma viremia below a very low level and the technique has been improved rapidly. However, due to the persistence of the latent reservoir of replication-competent HIV-1 in patients treated with ART, a sudden withdrawal of the drug inevitably results in HIV viral rebound and HIV progression. Therefore, more understanding of the HIV-1 latent reservoir (LR) is the priority before developing a cure that thoroughly eliminates the reservoir. HIV-1 spreads through both the release of cell-free particles and by cell-to-cell transmission. Mounting evidence indicates that cell-to-cell transmission is more efficient than cell-free transmission of particles and likely influences the pathogenesis of HIV-1 infection. This mode of viral transmission also influences the generation and maintenance of the latent reservoir, which represents the main obstacle for curing the infection. In this review, the definition, establishment, and maintenance of the HIV-1 LR, along with the state-of-the-art quantitative approaches that directly quantify HIV-1 intact proviruses, are elucidated. Strategies to cure HIV infection are highlighted. This review will renew hope for a better and more thorough cure of HIV infection for mankind and encourage more clinical trials to achieve ART-free HIV remission.

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.

Do spatiotemporal units matter for exploring the microgeographies of epidemics?

From the onset of the COVID-19 pandemic in 2020, studies on the microgeographies of epidemics have surged. However, studies have neglected the significant impact of multiple spatiotemporal units, such as report timestamps and spatial scales. This study examines three cities with localized COVID-19 resurgence after the first wave of the pandemic in mainland China to estimate the differential impact of spatiotemporal unit on exploring the influencing factors of epidemic spread at the microscale. The quantitative analysis results suggest that future spatial epidemiology research should give greater attention to the "symptom onset" timestamp instead of only the "confirmed" data and that "spatial transmission" should not be confused with "spatial sprawling" of epidemics, which can greatly reduce comparability between epidemiology studies. This research also highlights the importance of considering the modifiable areal unit problem (MAUP) and the uncertain geographic context problem (UGCoP) in future studies.

CAR/CXCR5-T cell immunotherapy is safe and potentially efficacious in promoting sustained remission of SIV infection

During chronic human immunodeficiency virus (HIV) or simian immunodeficiency virus (SIV) infection prior to AIDS progression, the vast majority of viral replication is concentrated within B cell follicles of secondary lymphoid tissues. We investigated whether infusion of T cells expressing an SIV-specific chimeric antigen receptor (CAR) and the follicular homing receptor, CXCR5, could successfully kill viral-RNA+ cells in targeted lymphoid follicles in SIV-infected rhesus macaques. In this study, CD4 and CD8 T cells from rhesus macaques were genetically modified to express antiviral CAR and CXCR5 moieties (generating CAR/CXCR5-T cells) and autologously infused into a chronically infected animal. At 2 days post-treatment, the CAR/CXCR5-T cells were located primarily in spleen and lymph nodes both inside and outside of lymphoid follicles. Few CAR/CXCR5-T cells were detected in the ileum, rectum, and lung, and no cells were detected in the bone marrow, liver, or brain. Within follicles, CAR/CXCR5-T cells were found in direct contact with SIV-viral RNA+ cells. We next infused CAR/CXCR5-T cells into ART-suppressed SIV-infected rhesus macaques, in which the animals were released from ART at the time of infusion. These CAR/CXCR5-T cells replicated in vivo within both the extrafollicular and follicular regions of lymph nodes and accumulated within lymphoid follicles. CAR/CXR5-T cell concentrations in follicles peaked during the first week post-infusion but declined to undetectable levels after 2 to 4 weeks. Overall, CAR/CXCR5-T cell-treated animals maintained lower viral loads and follicular viral RNA levels than untreated control animals, and no outstanding adverse reactions were noted. These findings indicate that CAR/CXCR5-T cell treatment is safe and holds promise as a future treatment for the durable remission of HIV.

Physiologically Based Pharmacokinetic Modeling of 3 HIV Drugs in Combination and the Role of Lymphatic System after Subcutaneous Dosing. Part 1: Model for the Free-Drug Mixture

Drug-combination nanoparticles (DcNP) allow the formulation of multiple HIV drugs in one injectable. In nonhuman primates (NHP), all drugs in DcNP have demonstrated long-acting pharmacokinetics (PK) in the blood and lymph nodes, rendering it suitable for a Targeted Long-acting Antiretroviral Therapy (TLC-ART). To support the translation of TLC-ART into the clinic, the objective is to present a physiologically based PK (PBPK) model tool to control mechanisms affecting the rather complex DcNP-drug PK. Two species contribute simultaneously to the drug PK: drugs that dissociate from DcNP (Part 1) and drugs retained in DcNP (Part 2, presented separately). Here, we describe the PBPK modeling of the nanoparticle-free drugs. The free-drug model was built on subcutaneous injections of suspended lopinavir, ritonavir, and tenofovir in NHP, and validated by external experiments. A novelty was the design of a lymphatic network as part of a whole-body PBPK system which included major lymphatic regions: the cervical, axillary, hilar, mesenteric, and inguinal nodes. This detailed/regionalized description of the lymphatic system and mononuclear cells represents an unprecedented level of prediction that renders the free-drug model extendible to other small-drug molecules targeting the lymphatic system at both the regional and cellular levels.

Real-Time Infectious Disease Modeling to Inform Emergency Public Health Decision Making

Infectious disease transmission is a nonlinear process with complex, sometimes unintuitive dynamics. Modeling can transform information about a disease process and its parameters into quantitative projections that help decision makers compare public health response options. However, modelers face methodologic challenges, data challenges, and communication challenges, which are exacerbated under the time constraints of a public health emergency. We review methods, applications, challenges and opportunities for real-time infectious disease modeling during public health emergencies, with examples drawn from the two deadliest pandemics in recent history: HIV/AIDS and coronavirus disease 2019 (COVID-19).

Expected final online publication date for the Annual Review of Public Health, Volume 43 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Hypermethylation at the CXCR5 gene locus limits trafficking potential of CD8+ T cells into B-cell follicles during HIV-1 infection

CD8+ T-cells play an important role in HIV control. However, in human lymph nodes (LNs), only a small subset of CD8+ T-cells expresses CXCR5, the chemokine receptor required for cell migration into B cell follicles, which are major sanctuaries for HIV persistence in individuals on therapy. Here, we investigate the impact of HIV infection on follicular CD8+ T-cells (fCD8s) frequencies, trafficking pattern and CXCR5 regulation. We show that, although HIV infection results in a marginal increase of fCD8s in LN, the majority of HIV-specific CD8+ T-cells are CXCR5 negative (non-fCD8s) (p<0.003). Mechanistic investigations using ATAC-seq showed that non-fCD8s have closed chromatin at the CXCR5 transcriptional start site (TSS). DNA bisulfite sequencing identified DNA hypermethylation at the CXCR5 TSS as the most probable cause of closed chromatin. Transcriptional factor footprints analysis revealed enrichment of transforming growth factors (TGFs) at the TSS of fCD8s. In-vitro stimulation of non-fCD8s with recombinant TGF-β resulted in significant increase in CXCR5 expression (fCD8s). Thus, this study identifies TGF-β signaling as a viable strategy for increasing fCD8s frequencies in follicular areas of the LN where they are needed to eliminate HIV infected cells, with implications for HIV cure strategies.

Accurate Enumeration of Apoptotic Cancer Cells Using Flow Cytometry

The frequency of apoptotic cells in a given phenotypically defined population is usually calculated the apoptotic index (AI), i.e., the percentage of apoptotic cells displaying a specific linage antigen (LAg) within a population of cells that remain unfragmented and retain the expression of the LAg. However, this approach has two major limitations. Firstly, apoptotic cells fragment into apoptotic bodies that later disintegrate. Secondly, apoptotic cells frequently lose, partially or even completely, the cell surface expression of the LAg used for the identification of specific cell subsets. The present chapter will describe a flow cytometry method to calculate the apoptotic rate (AR) that takes into account both cell fragmentation and loss of lineage antigen expression on measurement of apoptosis using flow cytometry ratiometric cell enumeration that emerges as a more accurate method of measurement of the occurrence of apoptosis in normal and tumoral cell cultures.

Follicular dendritic cells

Follicular dendritic cells (FDCs) are unique accessory immune cells that contribute to the regulation of humoral immunity. They are multitasker cells essential for the organization and maintenance of the lymphoid architecture, induction of germinal center reaction, production of B memory cells, and protection from autoimmune disorders. They perform their activities through both antigen-driven and chemical signaling to B cells. FDCs play a crucial role in the physiological regulation of the immune response. Dis-regulation of this immune response results when FDCs retain antigens for years. This provides a constant antigenic stimulation for B cells resulting in the development of immune disorders. Antigen trapped on FDCs is resistant to therapeutic intervention causing chronicity and recurrences. Beyond their physiological immunoregulatory functions, FDCs are involved in the pathogenesis of several immune-related disorders including HIV/AIDS, prion diseases, chronic inflammatory, and autoimmune disorders. FDCs have also been recently implicated in rare neoplasms of lymphoid and hematopoietic tissues. Understanding FDC biology is essential for better control of humoral immunity and opens the gate for therapeutic management of FDC-mediated immune disorders. Thus, the biology of FDCs has become a hot research area in the last couple of decades. In this review, we aim to provide a comprehensive overview of FDCs and their role in physiological and pathological conditions.

Roles of Virion-Incorporated CD162 (PSGL-1), CD43, and CD44 in HIV-1 Infection of T Cells

Nascent HIV-1 particles incorporate the viral envelope glycoprotein and multiple host transmembrane proteins during assembly at the plasma membrane. At least some of these host transmembrane proteins on the surface of virions are reported as pro-viral factors that enhance virus attachment to target cells or facilitate trans-infection of CD4⁺ T cells via interactions with non-T cells. In addition to the pro-viral factors, anti-viral transmembrane proteins are incorporated into progeny virions. These virion-incorporated transmembrane proteins inhibit HIV-1 entry at the point of attachment and fusion. In infected polarized CD4⁺ T cells, HIV-1 Gag localizes to a rear-end protrusion known as the uropod. Regardless of cell polarization, Gag colocalizes with and promotes the virion incorporation of a subset of uropod-directed host transmembrane proteins, including CD162, CD43, and CD44. Until recently, the functions of these virion-incorporated proteins had not been clear. Here, we review the recent findings about the roles played by virion-incorporated CD162, CD43, and CD44 in HIV-1 spread to CD4⁺ T cells.

Intra- and extra-cellular environments contribute to the fate of HIV-1 infection

HIV-1 entry into host cells leads to one of the following three alternative fates: (1) HIV-1 elimination by restriction factors, (2) establishment of HIV-1 latency, or (3) active viral replication in target cells. Here, we report the development of an improved system for monitoring HIV-1 fate at single-cell and population levels and show the diverse applications of this system to study specific aspects of HIV-1 fate in different cell types and under different environments. An analysis of the transcriptome of infected, primary CD4+ T cells that support alternative fates of HIV-1 identifies differential gene expression signatures in these cells. Small molecules are able to selectively target cells that support viral replication with no significant effect on viral latency. In addition, HIV-1 fate varies in different tissues following infection of humanized mice in vivo. Altogether, these studies indicate that intra- and extra-cellular environments contribute to the fate of HIV-1 infection.

Interests of the Non-Human Primate Models for HIV Cure Research

Non-human primate (NHP) models are important for vaccine development and also contribute to HIV cure research. Although none of the animal models are perfect, NHPs enable the exploration of important questions about tissue viral reservoirs and the development of intervention strategies. In this review, we describe recent advances in the use of these models for HIV cure research and highlight the progress that has been made as well as limitations using these models. The main NHP models used are (i) the macaque, in which simian immunodeficiency virus (SIVmac) infection displays similar replication profiles as to HIV in humans, and (ii) the macaque infected by a recombinant virus (SHIV) consisting of SIVmac expressing the HIV envelope gene serving for studies analyzing the impact of anti-HIV Env broadly neutralizing antibodies. Lessons for HIV cure that can be learned from studying the natural host of SIV are also presented here. An overview of the most promising and less well explored HIV cure strategies tested in NHP models will be given.

Visualization of HIV-1 reservoir: an imaging perspective

PURPOSE OF REVIEW

The persistence of HIV-1-infected cells, despite the introduction of the combinatorial antiretroviral therapy, is a major obstacle to HIV-1 eradication. Understanding the nature of HIV reservoir will lead to novel therapeutic approaches for the functional cure or eradication of the virus. In this review, we will update the recent development in imaging applications toward HIV-1/simian immunodeficiency virus (SIV) viral reservoirs research and highlight some of their limitations.

RECENT FINDINGS

CD4 T cells are the primary target of HIV-1/SIV and the predominant site for productive and latent reservoirs. This viral reservoir preferentially resides in lymphoid compartments that are difficult to access, which renders sampling and measurements problematical and a hurdle for understanding HIV-1 pathogenicity. Novel noninvasive technologies are needed to circumvent this and urgently help to find a cure for HIV-1. Recent technological advancements have had a significant impact on the development of imaging methodologies allowing the visualization of relevant biomarkers with high resolution and analytical capacity. Such methodologies have provided insights into our understanding of cellular and molecular interactions in health and disease.

SUMMARY

Imaging of the HIV-1 reservoir can provide significant insights for the nature (cell types), spatial distribution, and the role of the tissue microenvironment for its in vivo dynamics and potentially lead to novel targets for the virus elimination.

Similar Frequency and Inducibility of Intact Human Immunodeficiency Virus-1 Proviruses in Blood and Lymph Nodes

BACKGROUND

The human immunodeficiency virus (HIV)-1 latent reservoir (LR) in resting CD4+ T cells is a barrier to cure. LR measurements are commonly performed on blood samples and therefore may miss latently infected cells residing in tissues, including lymph nodes.

METHODS

We determined the frequency of intact HIV-1 proviruses and proviral inducibility in matched peripheral blood (PB) and lymph node (LN) samples from 10 HIV-1-infected patients on antiretroviral therapy (ART) using the intact proviral DNA assay and a novel quantitative viral induction assay. Prominent viral sequences from induced viral RNA were characterized using a next-generation sequencing assay.

RESULTS

The frequencies of CD4+ T cells with intact proviruses were not significantly different in PB versus LN (61/106 vs 104/106 CD4+ cells), and they were substantially lower than frequencies of CD4+ T cells with defective proviruses. The frequencies of CD4+ T cells induced to produce high levels of viral RNA were not significantly different in PB versus LN (4.3/106 vs 7.9/106), but they were 14-fold lower than the frequencies of cells with intact proviruses. Sequencing of HIV-1 RNA from induced proviruses revealed comparable sequences in paired PB and LN samples.

CONCLUSIONS

These results further support the use of PB as an appropriate proxy for the HIV-1 LR in secondary lymphoid organs.

Abundant HIV-infected cells in blood and tissues are rapidly cleared upon ART initiation during acute HIV infection

The timing and location of the establishment of the viral reservoir during acute HIV infection remain unclear. Using longitudinal blood and tissue samples obtained from HIV-infected individuals at the earliest stage of infection, we demonstrate that frequencies of infected cells reach maximal values in gut-associated lymphoid tissue and lymph nodes as early as Fiebig stage II, before seroconversion. Both tissues displayed higher frequencies of infected cells than blood until Fiebig stage III, after which infected cells were equally distributed in all compartments examined. Initiation of antiretroviral therapy (ART) at Fiebig stages I to III led to a profound decrease in the frequency of infected cells to nearly undetectable level in all compartments. The rare infected cells that persisted were preferentially found in the lymphoid tissues. Initiation of ART at later stages (Fiebig stages IV/V and chronic infection) induced only a modest reduction in the frequency of infected cells. Quantification of HIV DNA in memory CD4⁺ T cell subsets confirmed the unstable nature of most of the infected cells at Fiebig stages I to III and the emergence of persistently infected cells during the transition to Fiebig stage IV. Our results indicate that although a large pool of cells is infected during acute HIV infection, most of these early targets are rapidly cleared upon ART initiation. Therefore, infected cells present after peak viremia have a greater ability to persist.

Synergistic Chromatin-Modifying Treatments Reactivate Latent HIV and Decrease Migration of Multiple Host-Cell Types

Upon infection of its host cell, human immunodeficiency virus (HIV) establishes a quiescent and non-productive state capable of spontaneous reactivation. Diverse cell types harboring the provirus form a latent reservoir, constituting a major obstacle to curing HIV. Here, we investigate the effects of latency reversal agents (LRAs) in an HIV-infected THP-1 monocyte cell line in vitro. We demonstrate that leading drug treatments synergize activation of the HIV long terminal repeat (LTR) promoter. We establish a latency model in THP-1 monocytes using a replication incompetent HIV reporter vector with functional Tat, and show that chromatin modifiers synergize with a potent transcriptional activator to enhance HIV reactivation, similar to T-cells. Furthermore, leading reactivation cocktails are shown to differentially affect latency reactivation and surface expression of chemokine receptor type 4 (CXCR4), leading to altered host cell migration. This study investigates the effect of chromatin-modifying LRA treatments on HIV latent reactivation and cell migration in monocytes. As previously reported in T-cells, epigenetic mechanisms in monocytes contribute to controlling the relationship between latent reactivation and cell migration. Ultimately, advanced “Shock and Kill” therapy needs to successfully target and account for all host cell types represented in a complex and composite latency milieu.

HIV-1 Latency and Viral Reservoirs: Existing Reversal Approaches and Potential Technologies, Targets, and Pathways Involved in HIV Latency Studies

Eradication of latent human immunodeficiency virus (HIV) infection is a global health challenge. Reactivation of HIV latency and killing of virus-infected cells, the so-called "kick and kill" or "shock and kill" approaches, are a popular strategy for HIV cure. While antiretroviral therapy (ART) halts HIV replication by targeting multiple steps in the HIV life cycle, including viral entry, integration, replication, and production, it cannot get rid of the occult provirus incorporated into the host-cell genome. These latent proviruses are replication-competent and can rebound in cases of ART interruption or cessation. In general, a very small population of cells harbor provirus, serve as reservoirs in ART-controlled HIV subjects, and are capable of expressing little to no HIV RNA or proteins. Beyond the canonical resting memory CD4⁺ T cells, HIV reservoirs also exist within tissue macrophages, myeloid cells, brain microglial cells, gut epithelial cells, and hematopoietic stem cells (HSCs). Despite a lack of active viral production, latently HIV-infected subjects continue to exhibit aberrant cellular signaling and metabolic dysfunction, leading to minor to major cellular and systemic complications or comorbidities. These include genomic DNA damage; telomere attrition; mitochondrial dysfunction; premature aging; and lymphocytic, cardiac, renal, hepatic, or pulmonary dysfunctions. Therefore, the arcane machineries involved in HIV latency and its reversal warrant further studies to identify the cryptic mechanisms of HIV reservoir formation and clearance. In this review, we discuss several molecules and signaling pathways, some of which have dual roles in maintaining or reversing HIV latency and reservoirs, and describe some evolving strategies and possible approaches to eliminate viral reservoirs and, ultimately, cure/eradicate HIV infection.

HIV-1 tracing method of systemic viremia in vivo using an artificially mutated virus pool

The appearance of human immunodeficiency virus type 1 (HIV-1) plasma viremia is associated with progression to symptomatic disease and CD4⁺ T cell depletion. To locate the source of systemic viremia, this study employed a novel method to trace HIV-1 infection in vivo. We created JRCSFξnef, a pool of infectious HIV-1 (strain JR-CSF) with highly mutated nef gene regions by random mutagenesis PCR and infected this mutated virus pool into both Jurkat-CCR5 cells and hematopoietic stem cell-transplanted humanized mice. Infection resulted in systemic plasma viremia in humanized mice and viral RNA sequencing helped us to identify multiple lymphoid organs such as spleen, lymph nodes, and bone marrow but not peripheral blood cells as the source of systemic viremia. Our data suggest that this method could be useful for the tracing of viral trafficking in vivo.

Mechanistic Modeling of Maternal Lymphoid and Fetal Plasma Antiretroviral Exposure During the Third Trimester

Pregnancy-induced changes in plasma pharmacokinetics of many antiretrovirals (ARV) are well-established. Current knowledge about the extent of ARV exposure in lymphoid tissues of pregnant women and within the fetal compartment is limited due to their inaccessibility. Subtherapeutic ARV concentrations in HIV reservoirs like lymphoid tissues during pregnancy may constitute a barrier to adequate virological suppression and increase the risk of mother-to-child transmission (MTCT). The present study describes the pharmacokinetics of three ARVs (efavirenz, dolutegravir, and rilpivirine) in lymphoid tissues and fetal plasma during pregnancy using materno-fetal physiologically-based pharmacokinetic models (m-f-PBPK). Lymphatic and fetal compartments were integrated into our previously validated adult PBPK model. Physiological and drug disposition processes were described using ordinary differential equations. For each drug, virtual pregnant women (n = 50 per simulation) received the standard dose during the third trimester. Essential pharmacokinetic parameters, including Cmax, Cmin, and AUC (0-24), were computed from the concentration-time data at steady state for lymph and fetal plasma. Models were qualified by comparison of predictions with published clinical data, the acceptance threshold being an absolute average fold-error (AAFE) within 2.0. AAFE for all model predictions was within 1.08-1.99 for all three drugs. Maternal lymph concentration 24 h after dose exceeded the reported minimum effective concentration (MEC) for efavirenz (11,514 vs. 800 ng/ml) and rilpivirine (118.8 vs. 50 ng/ml), but was substantially lower for dolutegravir (16.96 vs. 300 ng/ml). In addition, predicted maternal lymph-to-plasma AUC ratios vary considerably (6.431-efavirenz, 0.016-dolutegravir, 1.717-rilpivirine). Furthermore, fetal plasma-to-maternal plasma AUC ratios were 0.59 for efavirenz, 0.78 for dolutegravir, and 0.57 for rilpivirine. Compared with rilpivirine (0 h), longer dose forgiveness was observed for dolutegravir in fetal plasma (42 h), and for efavirenz in maternal lymph (12 h). The predicted low lymphoid tissue penetration of dolutegravir appears to be significantly offset by its extended dose forgiveness and adequate fetal compartment exposure. Hence, it is unlikely to be a predictor of maternal virological failure or MTCT risks. Predictions from our m-f-PBPK models align with recommendations of no dose adjustment despite moderate changes in exposure during pregnancy for these drugs. This is an important new application of PBPK modeling to evaluate the adequacy of drug exposure in otherwise inaccessible compartments.

MAVSCOT: A fuzzy logic-based HIV diagnostic system with indigenous multi-lingual interfaces for rural Africa

HIV still constitutes a major public health problem in Africa, where the highest incidence and prevalence of the disease can be found in many rural areas, with multiple indigenous languages being used for communication by locals. In many rural areas of the KwaZulu-Natal (KZN) in South Africa, for instance, the most widely used languages include Zulu and Xhosa, with only limited comprehension in English and Afrikaans. Health care practitioners for HIV diagnosis and treatment, often, cannot communicate efficiently with their indigenous ethnic patients. An informatics tool is urgently needed to facilitate these health care professionals for better communication with their patients during HIV diagnosis. Here, we apply fuzzy logic and speech technology and develop a fuzzy logic HIV diagnostic system with indigenous multi-lingual interfaces, named Multi-linguAl HIV indigenouS fuzzy logiC-based diagnOstic sysTem (MAVSCOT). This HIV multilingual informatics software can facilitate the diagnosis in underprivileged rural African communities. We provide examples on how MAVSCOT can be applied towards HIV diagnosis by using existing data from the literature. Compared to other similar tools, MAVSCOT can perform better due to its implementation of the fuzzy logic. We hope MAVSCOT would help health care practitioners working in indigenous communities of many African countries, to efficiently diagnose HIV and ultimately control its transmission.