Neurocognitive decline in HIV patients is associated with ongoing T-cell activation in the cerebrospinal fluid

Persistent low-level viraemia is associated with non-infectious comorbidities in an observational cohort in four African countries

INTRODUCTION

People living with HIV (PLWH) have higher rates of non-infectious comorbid diseases (NCDs) than individuals without HIV. We characterized the risk of NCDs among PLWH with undetectable viral load and persistent low-level viraemia (pLLV) in the African Cohort Study (AFRICOS). We secondarily quantified the role of immune activation in the association between LLV and NCDs.

METHODS

AFRICOS enrols participants in 12 clinics in Uganda, Kenya, Tanzania and Nigeria. Participants on antiretroviral therapy ≥ 6 months without an NCD at enrolment were included. PLLV was defined as at least two consecutive visits with a detectable viral load <1000 copies/ml. We examined elevated blood pressure, hypercholesterolemia, hyperglycaemia, renal insufficiency and a composite variable of any NCD. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazard modelling. Among a subset of participants with biomarker data, we assessed the interaction between viral load and 13 biomarkers in the association with any NCD.

RESULTS

From 23 January 2013 to 1 December 2022, 1755 participants met the inclusion criteria for these analyses. At the first eligible visit, the majority of participants had an undetectable viral load (n = 1375, 78.35%). Participants with pLLV had an increased rate of developing any NCD (aHR: 1.22, 95% CI: 1.02-1.47) compared to participants with an undetectable viral load. There was a statistically significant interaction between LLV and TNF-α, CCL2/MCP-1 and TNF-RII in the association with any NCD.

CONCLUSIONS

PLLV was significantly associated with NCDs and immune inflammation in this population. Aggressive management of LLV may positively impact NCDs in PLWH.

Dynamics of peripheral T cell exhaustion and monocyte subpopulations in neurocognitive impairment and brain atrophy in chronic HIV infection

BACKGROUND

HIV-associated neurocognitive disorders (HAND) is hypothesized to be a result of myeloid cell-induced neuro-inflammation in the central nervous system that may be initiated in the periphery, but the contribution of peripheral T cells in HAND pathogenesis remains poorly understood.

METHODS

We assessed markers of T cell activation (HLA-DR + CD38+), immunosenescence (CD57 + CD28-), and immune-exhaustion (TIM-3, PD-1 and TIGIT) as well as monocyte subsets (classical, intermediate, and non-classical) by flow cytometry in peripheral blood derived from individuals with HIV on long-term stable anti-retroviral therapy (ART). Additionally, normalized neuropsychological (NP) composite test z-scores were obtained and regional brain volumes were assessed by magnetic resonance imaging (MRI). Relationships between proportions of immune phenotypes (of T-cells and monocytes), NP z-scores, and brain volumes were analyzed using Pearson correlations and multiple linear regression models.

RESULTS

Of N = 51 participants, 84.3% were male, 86.3% had undetectable HIV RNA < 50 copies/ml, median age was 52 [47, 57] years and median CD4 T cell count was 479 [376, 717] cells/uL. Higher CD4 T cells expressing PD-1 + and/or TIM-3 + were associated with lower executive function and working memory and higher CD8 T cells expressing PD-1+ and/or TIM-3+ were associated with reduced brain volumes in multiple regions (putamen, nucleus accumbens, cerebellar cortex, and subcortical gray matter). Furthermore, higher single or dual frequencies of PD-1 + and TIM-3 + expressing CD4 and CD8 T-cells correlated with higher CD16 + monocyte numbers.

CONCLUSIONS

This study reinforces evidence that T cells, particularly those with immune exhaustion phenotypes, are associated with neurocognitive impairment and brain atrophy in people living with HIV on ART. Relationships revealed between T-cell immune exhaustion and inflammatory in CD16+ monocytes uncover interrelated cellular processes likely involved in the immunopathogenesis of HAND.

Strategies to target the central nervous system HIV reservoir

PURPOSE OF THE REVIEW

The central nervous system (CNS) is an hotspot for HIV persistence and may be a major obstacle to overcome for curative strategies. The peculiar anatomical, tissular and cellular characteristics of the HIV reservoir in the CNS may need to be specifically addressed to achieve a long-term HIV control without ART. In this review, we will discuss the critical challenges that currently explored curative strategies may face in crossing the blood-brain barrier (BBB), targeting latent HIV in brain-resident myeloid reservoirs, and eliminating the virus without eliciting dangerous neurological adverse events.

RECENT FINDINGS

Latency reversing agents (LRA), broadly neutralizing monoclonal antibodies (bNabs), chimeric antigen receptor (CAR) T-cells, and adeno-associated virus 9-vectored gene-therapies cross the BBB with varying efficiency. Although brain penetration is poor for bNAbs, viral vectors for in vivo gene-editing, certain LRAs, and CAR T-cells may reach the cerebral compartment more efficiently. All these approaches, however, may encounter difficulties in eliminating HIV-infected perivascular macrophages and microglia. Safety, including local neurological adverse effects, may also be a concern, especially if high doses are required to achieve optimal brain penetration and efficient brain cell targeting.

SUMMARY

Targeting the CNS remains a potential problem for the currently investigated HIV curing strategies. In vivo evidence on CNS effectiveness is limited for most of the investigated strategies, and additional studies should be focused on evaluating the interplay between the cerebral HIV reservoir and treatment aiming to achieve an ART-free cure.

Neurological Complications Caused by Human Immunodeficiency Virus (HIV) and Associated Opportunistic Co-infections: A Review on their Diagnosis and Therapeutic Insights

Neurocognitive disorders associated with human immunodeficiency virus (HIV) infected individuals increase the risk of mortality and morbidity that remain a prevalent clinical complication even in the antiretroviral therapy era. It is estimated that a considerable number of people in the HIV community are developing neurological complications at their early stages of infection. The daily lives of people with chronic HIV infections are greatly affected by cognitive declines such as loss of attention, learning, and executive functions, and other adverse conditions like neuronal injury and dementia. It has been found that the entry of HIV into the brain and subsequently crossing the blood-brain barrier (BBB) causes brain cell damage, which is the prerequisite for the development of neurocognitive disorders. Besides the HIV replication in the central nervous system and the adverse effects of antiretroviral therapy on the BBB, a range of opportunistic infections, including viral, bacterial, and parasitic agents, augment the neurological complications in people living with HIV (PLHIV). Given the immuno-compromised state of PLHIV, these co-infections can present a wide range of clinical syndromes with atypical manifestations that pose challenges in diagnosis and clinical management, representing a substantial burden for the public health system. Therefore, the present review narrates the neurological complications triggered by HIV and their diagnosis and treatment options. Moreover, coinfections that are known to cause neurological disorders in HIV infected individuals are highlighted.

Low levels of peripheral blood activated and senescent T cells characterize people with HIV-1-associated neurocognitive disorders

Background

HIV infection induces a 75% increase in the risk of developing neurocognitive impairment (NCI), which has been linked to immune activation. We therefore looked for immune activation markers correlating with NCI.

Method

Sixty-five people aged 55-70 years living with controlled HIV-1 infection were enrolled in the study and their neurocognitive ability was assessed according to the Frascati criteria. Fifty-nine markers of T4 cell, T8 cell, NK cell, and monocyte activation, inflammation and endothelial activation were measured in their peripheral blood. White matter hyperintensities (WMH) were identified by magnetic resonance imaging. Double hierarchical clustering was performed for the activation markers and 240 patients including the 65 whose neurocognitive performance had been evaluated.

Results

Thirty-eight percent of volunteers presented NCI. Twenty-four percent of them were asymptomatic and fourteen percent had a mild disorder. Strikingly, activated (HLA-DR+) as well as senescent (CD57+CD28-CD27±) T4 cells and T8 cells were less prevalent in the peripheral blood of participants with NCI than in participants without the disorder. Accordingly, the percentage of HLA-DR+ T4 cells was lower in volunteers with periventricular and deep WMH. The double hierarchical clustering unveiled six different immune activation profiles. The neurocognitive performances of participants with two of these six profiles were poor. Here again, these two profiles were characterized by a low level of T4 and T8 cell activation and senescence.

Conclusion

Our observation of low circulating levels of activated and senescent T cells in HIV-1 patients with NCI raises the interesting hypothesis that these lymphocytes may be recruited into the central nervous system.

CD3+CD56+ and CD3-CD56+ lymphocytes in the cerebrospinal fluid of persons with HIV-1 subtypes B and C

The transactivator of transcription (Tat) is a HIV regulatory protein which promotes viral replication and chemotaxis. HIV-1 shows extensive genetic diversity, HIV-1 subtype C being the most dominant subtype in the world. Our hypothesis is the frequency of CSF CD3+CD56+ and CD3-CD56dim is reduced in HIV-1C compared to HIV-1B due to the Tat C30S31 substitution in HIV-1C. 34 CSF and paired blood samples (PWH, n = 20; PWoH, n = 14) were studied. In PWH, the percentage of CD3+CD56+ was higher in CSF than in blood (p < 0.001), comparable in both compartments in PWoH (p = 0.20). The proportion of CD3-CD56dim in CSF in PWH was higher than PWoH (p = 0.008). There was no subtype differences. These results showed CNS compartmentalization of NKT cell response in PWH.

Neuroimaging and immunological features of neurocognitive function related to substance use in people with HIV

This study sought to identify neuroimaging and immunological factors associated with substance use and that contribute to neurocognitive impairment (NCI) in people with HIV (PWH). We performed cross-sectional immunological phenotyping, neuroimaging, and neurocognitive testing on virally suppressed PWH in four substance groups: cocaine only users (COC), marijuana only users (MJ), dual users (Dual), and Non-users. Participants completed substance use assessments, multimodal MRI brain scan, neuropsychological testing, and blood and CSF sampling. We employed a two-stage analysis of 305 possible biomarkers of cognitive function associated with substance use. Feature reduction (Kruskal Wallis p-value < 0.05) identified 53 biomarkers associated with substance use (22 MRI and 31 immunological) for model inclusion along with clinical and demographic variables. We employed eXtreme Gradient Boosting (XGBoost) with these markers to predict cognitive function (global T-score). SHapley Additive exPlanations (SHAP) values were calculated to rank features for impact on model output and NCI. Participants were 110 PWH with sustained HIV viral suppression (33 MJ, 12 COC, 22 Dual, and 43 Non-users). The ten highest ranking biomarkers for predicting global T-score were 4 neuroimaging biomarkers including functional connectivity, gray matter volume, and white matter integrity; 5 soluble biomarkers (plasma glycine, alanine, lyso-phosphatidylcholine (lysoPC) aC17.0, hydroxy-sphingomyelin (SM.OH) C14.1, and phosphatidylcholinediacyl (PC aa) C28.1); and 1 clinical variable (nadir CD4 count). The results of our machine learning model suggest that substance use may indirectly contribute to NCI in PWH through both metabolomic and neuropathological mechanisms.

Through the Looking-Glass: Psychoneuroimmunology and the Microbiome-Gut-Brain Axis in the Modern Antiretroviral Therapy Era

OBJECTIVE

Depression, substance use disorders, and other neuropsychiatric comorbidities are common in people with HIV (PWH), but the underlying mechanisms are not sufficiently understood. HIV-induced damage to the gastrointestinal tract potentiates residual immune dysregulation in PWH receiving effective antiretroviral therapy. However, few studies among PWH have examined the relevance of microbiome-gut-brain axis: bidirectional crosstalk between the gastrointestinal tract, immune system, and central nervous system.

METHODS

A narrative review was conducted to integrate findings from 159 articles relevant to psychoneuroimmunology (PNI) and microbiome-gut-brain axis research in PWH.

RESULTS

Early PNI studies demonstrated that neuroendocrine signaling via the hypothalamic-pituitary-adrenal axis and autonomic nervous system could partially account for the associations of psychological factors with clinical HIV progression. This review highlights the need for PNI studies examining the mechanistic relevance of the gut microbiota for residual immune dysregulation, tryptophan catabolism, and oxytocin release as key biological determinants of neuropsychiatric comorbidities in PWH (i.e., body-to-mind pathways). It also underscores the continued relevance of neuroendocrine signaling via the hypothalamic-pituitary-adrenal axis, autonomic nervous system, and oxytocin release in modifying microbiome-gut-brain axis functioning (i.e., mind-to-body pathways).

CONCLUSIONS

Advancing our understanding of PNI and microbiome-gut-brain axis pathways relevant to depression, substance use disorders, and other neuropsychiatric comorbidities in PWH can guide the development of novel biobehavioral interventions to optimize health outcomes. Recommendations are provided for biobehavioral and neurobehavioral research investigating bidirectional PNI and microbiome-gut-brain axis pathways among PWH in the modern antiretroviral therapy era.

Correlation between CD4/CD8 ratio and neurocognitive performance during early HIV infection

INTRODUCTION

CD4/CD8 ratio is a marker of immune activation in HIV infection and has been associated with neurocognitive performance during chronic infection, but little is known about the early phases. The aim of this study was to examine the relationship between blood CD4/CD8 ratio and central nervous system endpoints in primary HIV infection (PHI) before and after antiretroviral treatment (ART).

METHODS

This was a retrospective analysis of the Primary Infection Stage CNS Events Study (PISCES) cohort. We longitudinally assessed blood and cerebrospinal fluid (CSF) markers of inflammation, immune activation and neuronal injury, and neuropsychological testing performance (NPZ4, an average of three motor and one processing speed tests, and a summarized total score, NPZ11, including also executive function, learning and memory) in ART-naïve participants enrolled during PHI. Spearman correlation and linear mixed models assessed the relationships between the trajectory of CD4/CD8 ratio over time and neurocognitive performance, blood and CSF markers of immune activation and neuronal injury.

RESULTS

In all, 109 PHI participants were enrolled. The mean CD4/CD8 ratio decreased with longer time from infection to starting treatment (p < 0.001). Every unit increase in NPZ4 score was independently associated with a 0.15 increase in CD4/CD8 ratio (95% CI: 0.002-0.29; p = 0.047), whereas no correlation was found between CD4/CD8 ratio and NPZ11. Among the cognitive domains, only a change in processing speed was correlated with CD4/CD8 ratio over time (p = 0.03). The trajectory of the CD4/CD8 ratio was negatively correlated with change in CSF neurofilament light chain (p = 0.04).

CONCLUSIONS

The trajectory of CD4/CD8 ratio was independently associated with motor/psychomotor speed performance, suggesting that immune activation is involved in brain injury during the early stages of the infection.

Main lymphocyte subpopulations in cerebrospinal fluid and peripheral blood in HIV-1 subtypes C and B

HIV-1 subtype C (HIV-1C) shows reduced Tat protein chemoattractant activity compared with HIV-1B. The impact of HIV-1C Tat on the chemotaxis of the main lymphocyte subpopulations in the cerebrospinal fluid (CSF) and the peripheral blood (PB) is unclear. We hypothesized that there would be a lower frequency of specific lymphocyte subpopulations CD3⁺ or CD19⁺ in CSF in HIV-1C than in HIV-1B. The objectives were to detect the differences in the proportions of main lymphocyte subpopulations in CSF and PB, between people with HIV (PWH) and HIV-1-uninfected volunteers (PWoH) and in HIV-1B and HIV-1C. Lymphocyte immunophenotyping was studied in CSF and paired PB samples of PWH (n = 22) and PWoH (n = 14). Lymphocytes were analyzed within the CD45⁺ gated region. The proportions of CSF CD3⁺CD4⁺, CD3⁺CD8⁺, and CD3^-CD19⁺ lymphocytes in CSF were comparable in HIV-1B and C. There was an increase in the proportion of CD3⁺CD8⁺ cells and a decrease in CD3⁺CD4⁺ T cells (ps = 0.016) in the CSF samples of the PWH compared with the PWoH group. In the PWH group, both CD3⁺CD4⁺ and CD3⁺CD8⁺ lymphocytes were significantly higher in the CSF than in the PB (p = 0.047 and 0.005). The proportion of CD3⁺CD4⁺ was lower and that of CD3⁺CD8⁺ was higher in the CSF samples of the aviremic group than that of HIV-negative control (p = 0.0008 and < 0.0001, respectively). HIV-1C Tat substitution (C30S) did not interfere with the CNS migration of the main lymphocyte subpopulations. This is the first study to evaluate these lymphocytes in CSF and PB of HIV-1C compared with HIV-1B.

Cerebrospinal fluid CD4+ T cell infection in humans and macaques during acute HIV-1 and SHIV infection

HIV-1 replication within the central nervous system (CNS) impairs neurocognitive function and has the potential to establish persistent, compartmentalized viral reservoirs. The origins of HIV-1 detected in the CNS compartment are unknown, including whether cells within the cerebrospinal fluid (CSF) produce virus. We measured viral RNA+ cells in CSF from acutely infected macaques longitudinally and people living with early stages of acute HIV-1. Active viral transcription (spliced viral RNA) was present in CSF CD4+ T cells as early as four weeks post-SHIV infection, and among all acute HIV-1 specimens (N = 6; Fiebig III/IV). Replication-inactive CD4+ T cell infection, indicated by unspliced viral RNA in the absence of spliced viral RNA, was even more prevalent, present in CSF of >50% macaques and human CSF at ~10-fold higher frequency than productive infection. Infection levels were similar between CSF and peripheral blood (and lymph nodes in macaques), indicating comparable T cell infection across these compartments. In addition, surface markers of activation were increased on CSF T cells and monocytes and correlated with CSF soluble markers of inflammation. These studies provide direct evidence of HIV-1 replication in CD4+ T cells and broad immune activation in peripheral blood and the CNS during acute infection, likely contributing to early neuroinflammation and reservoir seeding. Thus, early initiation of antiretroviral therapy may not be able to prevent establishment of CNS viral reservoirs and sources of long-term inflammation, important targets for HIV-1 cure and therapeutic strategies.

Neurological pathologies are associated with HIV-1 infection and remain common in the ongoing AIDS epidemic. Despite the advent of successful viremia suppression by anti-retroviral therapy, increased life expectancies and co-morbidities have led to higher prevalence of milder forms of neurocognitive dysfunction. How HIV-1 causes neurocognitive dysfunction is currently unclear, though it is widely believed that viral replication within the central nervous system (CNS) prior to therapy triggers these detrimental processes. The appearance of HIV-1 in the cerebrospinal fluid during the earliest stages of infection suggests that these processes may begin very early. Here, we use novel techniques to probe cells for viral infection during the first few weeks of infection in the CNS of humans and animals to determine the source of this virus. We found HIV-1 replication in T cells in the cerebrospinal fluid during this early window. In addition, infected T cells were present at similar frequencies in the CNS and other anatomic compartments, suggesting equilibration of T cell infection levels across these sites and potential for establishment of long-term reservoirs in the CNS. Our study provides new insights to the early events of viral entry and replication in the CNS with implications for subsequent viral persistence and neuronal injury.

Soluble Biomarkers of Cognition and Depression in Adults with HIV Infection in the Combination Therapy Era

PURPOSE OF REVIEW

Cognitive impairment and depression continue to be common among people with HIV (PWH) in the combination antiretroviral therapy (ART) era. A better understanding of the biological mechanisms that may underpin these disorders is needed. The purpose of this review is to describe published findings on soluble biomarkers from blood and cerebrospinal fluid (CSF) that have been associated with either cognition or depression among PWH in the setting of ART.

RECENT FINDINGS

Several biomarkers, including those that reflect viral persistence, monocyte/macrophage activation, and other processes, are associated with cognition and depressive symptoms. Some but not all results have been consistent across multiple studies. More research has been published on biomarkers of cognition relative to biomarkers of depression (particularly from CSF). More studies are needed that investigate multiple biomarkers to understand the role of distinct but additive pathways in these disorders and to guide the development of new therapies.

Neurologic Complications of Human Immunodeficiency Virus

PURPOSE OF REVIEW

This article reviews the neurologic complications associated with human immunodeficiency virus (HIV) infection.

RECENT FINDINGS

Neurologic complications of HIV may be caused by direct virally mediated pathology, immune-mediated phenomena in response to viral infection, or opportunistic infections secondary to depletion of lymphocytes. These neurologic disorders may be influenced by the degree of immunosuppression (ie, CD4+ T-cell lymphocyte count) and stage of infection (early versus late), as well as use of antiretroviral therapy, and may manifest as a variety of central and peripheral neurologic syndromes, including the more commonly encountered HIV-associated cognitive disorders and length-dependent sensorimotor polyneuropathy, respectively. Immune dysregulation underlies the majority of these neurologic phenomena, as well as other HIV-associated conditions including immune reconstitution inflammatory syndrome (IRIS), CD8 lymphocytosis, and potentially the development of compartmentalized infection within the CSF, also referred to as CSF escape.

SUMMARY

This article reviews a spectrum of clinical syndromes and related neuropathologic states associated with HIV infection.

CD4/CD8 ratio, comorbidities, and aging in treated HIV infected individuals on viral suppression

The progression of the human immunodeficiency virus (HIV) infection to acquired immunodeficiency syndrome (AIDS) can be efficiently interrupted by antiretroviral therapy (ART). However, even successfully treated HIV-infected individuals are prone to develop non-AIDS-related diseases that affect the metabolism and several organs and systems. Biomarkers that predict the occurrence of comorbidities may help develop preventive measures. Current research shows that CD4+ T cell counts and viral load do not predict the development of non-AIDS-related diseases. The CD4/CD8 ratio has been indicated as a suitable marker of persistent immune dysfunction and the occurrence of non-AIDS-related events in treated HIV-positive patients. In this study, we explored the relationship between CD4/CD8 ratios, comorbidities, and aging in ART-treated HIV patients on viral suppression. We collected and evaluated data from 352 HIV-positive adults who were virologically suppressed (<40 copies/mL) on ART and with CD4 counts above 350 cells/mm3 . The median age for participants was 46 years, 218 individuals had at least one comorbidity, and 239 had inverted CD4/CD8 ratios (<1). Current CD4/CD8 ratios were predicted by baseline CD4/CD8 ratios and nadir CD4 counts. Despite the high rates of inverted CD4/CD8 ratios and prevalence of comorbidities, no association between them was observed. The prevalence of comorbidities was significantly higher in older individuals, though aging alone did not explain the rate of all individual comorbidities. Low CD4/CD8 ratios were linked to neurocognitive disorders, suggesting that persistent T cell dysfunction contributes to neurocognitive decline.

Global prevalence and burden of HIV-associated neurocognitive disorder

Objective

To characterize the prevalence and burden of HIV-associated neurocognitive disorder (HAND) and assess associated factors in the global population with HIV.

Methods

We searched PubMed and Embase for cross-sectional or cohort studies reporting the prevalence of HAND or its subtypes in HIV-infected adult populations from January 1, 1996, to May 15, 2020, without language restrictions. Two reviewers independently undertook the study selection, data extraction, and quality assessment. We estimated pooled prevalence of HAND by a random effects model and evaluated its overall burden worldwide.

Results

Of 5,588 records identified, we included 123 studies involving 35,513 participants from 32 countries. The overall prevalence of HAND was 42.6% (95% confidence interval [CI] 39.7–45.5) and did not differ with respect to diagnostic criteria used. The prevalence of asymptomatic neurocognitive impairment, mild neurocognitive disorder, and HIV-associated dementia were 23.5% (20.3–26.8), 13.3% (10.6–16.3), and 5.0% (3.5–6.8) according to the Frascati criteria, respectively. The prevalence of HAND was significantly associated with the level of CD4 nadir, with a prevalence of HAND higher in low CD4 nadir groups (mean/median CD4 nadir <200 45.2% [40.5–49.9]) vs the high CD4 nadir group (mean/median CD4 nadir ≥200 37.1% [32.7–41.7]). Worldwide, we estimated that there were roughly 16,145,400 (95% CI 15,046,300–17,244,500) cases of HAND in HIV-infected adults, with 72% in sub-Saharan Africa (11,571,200 cases, 95% CI 9,600,000–13,568,000).

Conclusions

Our findings suggest that people living with HIV have a high burden of HAND in the antiretroviral therapy (ART) era, especially in sub-Saharan Africa and Latin America. Earlier initiation of ART and sustained adherence to maintain a high-level CD4 cell count and prevent severe immunosuppression is likely to reduce the prevalence and severity of HAND.

Monocyte and CD4+ T-cell antiviral and innate responses associated with HIV-1 inflammation and cognitive impairment

OBJECTIVE

Mechanisms underlying immune activation and HIV-associated neurocognitive disorders (HAND) in untreated chronic infection remain unclear. The objective of this study was to identify phenotypic and transcriptional changes in blood monocytes and CD4 T cells in HIV-1-infected and uninfected individuals and elucidate processes associated with neurocognitive impairment.

DESIGN

A group of chronically HIV-1-infected Thai individuals (n = 19) were selected for comparison with healthy donor controls (n = 10). Infected participants were further classified as cognitively normal (n = 10) or with HAND (n = 9). Peripheral monocytes and CD4 T cells were phenotyped by flow cytometry and simultaneously isolated for multiplex qPCR-targeted gene expression profiling directly ex vivo. The frequency of HIV-1 RNA-positive cells was estimated by limiting dilution cell sorting.

RESULTS

Expression of genes and proteins involved in cellular activation and proinflammatory immune responses was increased in monocytes and CD4 T cells from HIV-1-infected relative to uninfected individuals. Gene expression profiles of both CD4 T cells and monocytes correlated with soluble markers of inflammation in the periphery (P < 0.05). By contrast, only modest differences in gene programs were observed between cognitively normal and HAND cases. These included increased monocyte surface CD169 protein expression relative to cognitively normal (P = 0.10), decreased surface CD163 expression relative to uninfected (P = 0.02) and cognitively normal (P = 0.06), and downregulation of EMR2 (P = 0.04) and STAT1 (P = 0.02) relative to cognitively normal.

CONCLUSION

Our data support a model of highly activated monocytes and CD4 T cells associated with inflammation in chronic HIV-1 infection, but impaired monocyte anti-inflammatory responses in HAND compared with cognitively normal.

Harnessing regulatory T cell neuroprotective activities for treatment of neurodegenerative disorders

Emerging evidence demonstrates that adaptive immunity influences the pathobiology of neurodegenerative disorders. Misfolded aggregated self-proteins can break immune tolerance leading to the induction of autoreactive effector T cells (Teffs) with associated decreases in anti-inflammatory neuroprotective regulatory T cells (Tregs). An imbalance between Teffs and Tregs leads to microglial activation, inflammation and neuronal injury. The cascade of such a disordered immunity includes the drainage of the aggregated protein antigens into cervical lymph nodes serving to amplify effector immune responses. Both preclinical and clinical studies demonstrate transformation of this altered immunity for therapeutic gain. We posit that the signs and symptoms of common neurodegenerative disorders such as Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, and stroke can be attenuated by boosting Treg activities.

Distinct cellular immune properties in cerebrospinal fluid are associated with cognition in HIV-infected individuals initiating antiretroviral therapy

We examined the relationship between CSF immune cells and neurocognition and neuronal damage in HIV+ individuals before and after initiating antiretroviral therapy. Multivariate analysis at baseline indicated that greater CD4+ T cell abundance was associated with better cognition (p = .017), while higher CSF HIV RNA was associated with increased neuronal damage (p = .014). Following 24 weeks of antiretroviral therapy, CD8+ T cells, HLA-DR expressing CD4+ and CD8+ T cells, B cells, NK cells, and non-classical monocyte percentage decreased in CSF. Female gender was negatively associated with cognitive performance over time, as was higher percentage of HLA-DR expressing CD8+ T cells at baseline.

Early Inflammatory Signatures Predict Subsequent Cognition in Long-Term Virally Suppressed Women With HIV

Immunologic function is an important determinant of cognition. Here we examined the contribution of early immune signatures to cognitive performance among HIV-infected, virally suppressed women (HIV+VS) and in HIV-uninfected (HIV-) women. Specifically, we measured serum inflammatory markers, developed combinatory immune signatures, and evaluated their associations with cognition. Forty-nine HIV+VS women in the Women’s Interagency HIV Study (WIHS) who achieved viral suppression shortly after effective antiretroviral therapy (ART) initiation, and 56 matched HIV− women were selected. Forty-two serum inflammatory markers were measured within 2 years of effective ART initiation for HIV+VS women, and at an initial timepoint for HIV− women. The same inflammatory markers were also measured approximately 1, 7, and 12 years later for all women. Of the 105 women with complete immune data, 83 (34 HIV+VS, 49 HIV−) also had cognitive data available 12 years later at ≥1 time points (median = 3.1). We searched for combinatory immune signatures by adapting a dynamic matrix factorization analytic method that builds upon Tucker decomposition followed by Ingenuity^® Pathway Analysis to facilitate data interpretation. Seven combinatory immune signatures emerged based on the Frobenius residual. Three signatures were common between HIV+VS and HIV− women, while four signatures were unique. These inflammatory signatures predicted subsequent cognitive performance in both groups using mixed-effects modeling, but more domain-specific associations were significant in HIV+VS than HIV− women. Leukocyte influx into brain was a major contributor to cognitive function in HIV+VS women, while T cell exhaustion, inflammatory response indicative of depressive/psychiatric disorders, microglial activity, and cytokine signaling predicted both global and domain-specific performance for HIV− women. Our findings suggest that immune signatures may be useful diagnostic, prognostic, and immunotherapeutic targets predictive of subsequent cognitive performance. Importantly, they also provide insight into common and distinct inflammatory mechanisms underlying cognition in HIV− and HIV+VS women.

Role of T Lymphocytes in HIV Neuropathogenesis

PURPOSE OF REVIEW

The purpose of this review is to summarize the current knowledge on the role of CD4⁺ T lymphocytes leading to HIV assault and persistence in the central nervous system (CNS) and the elimination of HIV-infected CNS resident cells by CD8⁺ T lymphocytes.

RECENT FINDINGS

HIV targets the CNS early in infection, and HIV-infected individuals suffer from mild forms of neurological impairments even under antiretroviral therapy (ART). CD4⁺ T cells and monocytes mediate HIV entry into the brain and constitute a source for HIV persistence and neuronal damage. HIV-specific CD8⁺ T cells are also massively recruited in the CNS in acute infection to control viral replication but cannot eliminate HIV-infected cells within the CNS. This review summarizes the involvement of CD4⁺ T cells in seeding and maintaining HIV infection in the brain and describes the involvement of CD8⁺ T cells in HIV neuropathogenesis, playing a role still to be deciphered, either beneficial in eliminating HIV-infected cells or deleterious in releasing inflammatory cytokines.

Altered Brain Function in Young HIV Patients with Syphilis Infection: A Voxel-Wise Degree Centrality Analysis

Objective

This study assessed the possible effect of syphilis co-infection in the brain function in young HIV patients by using voxel-wise degree centrality (DC) analysis.

Methods

Forty-four syphilis-co-infected HIV patients (HIV+/syphilis+), 45 HIV patients without syphilis history (HIV+/syphilis-) and 43 matched healthy controls (HC) underwent resting-state fMRI examinations. Laboratory tests and a battery of neuropsychological tests were performed before each MRI examination. One-way ANOVA was used to compare the differences of DC among the three groups. The correlations between MRI metrics and laboratory/neuropsychological tests in each patient's group were performed by Pearson correlation analysis.

Results

Compared with HIV+/syphilis-, worse performance in complex motor skills was found in HIV+/syphilis+. Compared with HC, HIV+/syphilis+ and HIV+/syphilis- groups showed attenuated DC in the right orbital frontal cortex and increased DC in the left parietal/temporal cortex. Besides, we also found increased DC in the left inferior frontal cortex and bilateral posterior cingulated cortex/precuneus in HIV+/syphilis+ compared with HC. Moreover, compared with HIV+/syphilis-, HIV+/syphilis+ displayed decreased DC in the left middle occipital cortex. Additionally, in HIV+/syphilis+ group, the mean z value of DC was correlated to the CD4+ cell counts and the learning and delayed recall score.

Conclusion

Syphilis co-infection might be related to more brain functional reorganization in young HIV patients which could be reflected by DC value.

Recall Responses from Brain-Resident Memory CD8+ T Cells (bTRM) Induce Reactive Gliosis

HIV-associated neurocognitive disorders (HAND) persist even during effective combination antiretroviral therapy (cART). Although the cause of HAND is unknown, studies link chronic immune activation, neuroinflammation, and cerebrospinal fluid viral escape to disease progression. In this study, we tested the hypothesis that specific, recall immune responses from brain-resident memory T cells (bT_RM) could activate glia and induce neurotoxic mediators. To address this question, we developed a heterologous prime-central nervous system (CNS) boost strategy in mice. We observed that the murine brain became populated with long-lived CD8⁺ bT_RM, some being specific for an immunodominant Gag epitope. Recall stimulation using HIV-1 AI9 peptide administered in vivo resulted in microglia displaying elevated levels of major histocompatibility complex class II and programmed death-ligand 1, and demonstrating tissue-wide reactive gliosis. Immunostaining further confirmed this glial activation. Taken together, these results indicate that specific, adaptive recall responses from bT_RM can induce reactive gliosis and production of neurotoxic mediators.

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Heterologous prime-CNS boost induced HIV-1-specific bT_RM, which persisted long term

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Recall responses from HIV-specific bT_RM induced tissue-wide reactive gliosis

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bT_RM induced-reactive gliosis likely has cumulative neurotoxic consequences

Neurocognitive dysfunction in HIV-infected youth: investigating the relationship with immune activation

BACKGROUND

HIV-infected individuals are at increased risk of neurocognitive impairment compared to the general population. Studies suggest that, despite combination antiretroviral therapy (cART), HIV infection causes immune activation which results in neural damage; however, few data exist in HIV-infected youth.

METHODS

HIV-infected youth 8-26-years-old on cART with virological suppression were prospectively enrolled along with healthy controls. Neurocognitive performance was assessed by age-appropriate Wechsler Intelligence Scales. Soluble and cellular markers of T-lymphocyte and monocyte activation were measured by ELISA and flow cytometry, respectively.

RESULTS

45 HIV-infected subjects and 21 controls were enrolled. Markers of T-cell and monocyte activation were higher in the HIV-infected subjects compared to controls, but proportions of inflammatory and patrolling monocytes were similar. Although there were no significant differences in neurocognitive scores between the HIV-infected and control groups, scores were low-average for four of five testing domains for the HIV-infected subjects and average for all five in the controls, and % of HIV-infected subjects with scores classified as 'low average' or below was higher than in the controls. Variables most associated with neurocognitive performance among HIV-infected subjects included activated CD4⁺ T-cells (% CD4+CD38+HLA-DR), monocyte activation (soluble CD14), HIV duration, age and sex.

CONCLUSIONS

HIV-infected youth on cART with virological suppression show subtle evidence of neurocognitive impairment compared to healthy controls, and increased immune activation appears to play a role. Additional studies are needed to develop strategic interventions beyond cART to potentially improve neurocognitive performance and/or minimize further impairment in this vulnerable population. ClinicalTrials.gov Identifier: NCT01523496.

Glial Cell Expression of PD-L1

The programmed death (PD)-1/PD-L1 pathway is a well-recognized negative immune checkpoint that results in functional inhibition of T-cells. Microglia, the brain-resident immune cells are vital for pathogen detection and initiation of neuroimmune responses. Moreover, microglial cells and astrocytes govern the activity of brain-infiltrating antiviral T-cells through upregulation of PD-L1 expression. While T-cell suppressive responses within brain are undoubtedly beneficial to the host, preventing cytotoxic damage to this vital organ, establishment of a prolonged anti-inflammatory milieu may simultaneously lead to deficiencies in viral clearance. An immune checkpoint blockade targeting the PD-1: PD-L1 (B7-H1; CD274) axis has revolutionized contemporary treatment for a variety of cancers. However, the therapeutic potential of PD1: PD-L1 blockade therapies targeting viral brain reservoirs remains to be determined. For these reasons, it is key to understand both the detrimental and protective functions of this signaling pathway within the brain. This review highlights how glial cells use PD-L1 expression to modulate T-cell effector function and limit detrimental bystander damage, while still retaining an effective defense of the brain.

Single-cell RNA sequencing reveals microglia-like cells in cerebrospinal fluid during virologically suppressed HIV

Central nervous system (CNS) immune activation is an important driver of neuronal injury during several neurodegenerative and neuroinflammatory diseases. During HIV infection, CNS immune activation is associated with high rates of neurocognitive impairment, even during sustained long-term suppressive antiretroviral therapy (ART). However, the cellular subsets that drive immune activation and neuronal damage in the CNS during HIV infection and other neurological conditions remain unknown, in part because CNS cells are difficult to access in living humans. Using single-cell RNA sequencing (scRNA-seq) on cerebrospinal fluid (CSF) and blood from adults with and without HIV, we identified a rare (<5% of cells) subset of myeloid cells that are found only in CSF and that present a gene expression signature that overlaps significantly with neurodegenerative disease-associated microglia. This highlights the power of scRNA-seq of CSF to identify rare CNS immune cell subsets that may perpetuate neuronal injury during HIV infection and other conditions.

Characterization of Cellular Immune Responses in Thai Individuals With and Without HIV-Associated Neurocognitive Disorders

HIV-associated neurocognitive disorder (HAND) remains a challenge despite antiretroviral therapy (ART), and has been linked to monocyte/macrophage (M/M) migration to the brain. Due to the potential impact of T cell effector mechanisms in eliminating activated/HIV-infected M/M, T cell activation may play a role in the development of HAND. We sought to investigate the relationship between cognition and both CD8⁺ T cell activation (HLA-DR⁺/CD38⁺) and HIV-specific CD8⁺ T cell responses at the time of HIV diagnosis and 12 months postinitiation of ART. CD8⁺ T cell activation was increased in HAND compared to cognitive normal (NL) individuals and correlated directly with plasma viral load and inversely with the cognitive status. In addition, Gag-specific cytolytic activity (CD107a/b⁺) was decreased in HAND compared with NL individuals and correlated with their neurological testing, suggesting a potential role of cytotoxic CD8⁺ T cells in the mechanism of HAND development.

Peripheral and cerebrospinal fluid immune activation and inflammation in chronically HIV-infected patients before and after virally suppressive combination antiretroviral therapy (cART)

Cerebrospinal fluid (CSF)/plasma HIV-RNA ratio has been associated with residual neurocognitive impairment on cART, leading us to hypothesize a specific peripheral and/or CSF immune feature in patients with high CSF/plasma ratio (≥ 1). In patients with diverse pre-cART CSF/plasma ratio (61/70 with CSF/plasma ratio < 1, L-CSF, 9/70 with CSF/plasma ratio ≥ 1, H-CSF), we investigated the effects of 12 months of effective cART on peripheral and CSF inflammatory markers, on T cell activation/maturation and HIV/CMV-specific intracellular cytokine pattern. We also studied the possible clinical association between peripheral/CSF pro-inflammatory milieu and neurocognitive screening tests (MMSE, FAB, IHDS). Prior to cART, the two groups were comparable for peripheral and CSF inflammation, T cell activation/proliferation and maturation, and HIV/CMV-specific response. Upon cART initiation, both H-CSF and L-CSF featured a significant reduction in plasma TNF-α and circulating CD8 activation, with a redistribution of memory/naïve T cell subsets in L-CSF alone. In the CSF compartment, cART seemed able to reduce pro-inflammatory cytokine/chemokine levels in both H-CSF and L-CSF patients. Interestingly, despite a reduction in the pro-inflammatory milieu, no changes were shown in neurocognitive screening tests in both patients' groups. We hereby show that 12-month cART is able to reduce intratechal and peripheral pro-inflammatory burden; a longer cART exposure and a more comprehensive neuropsychological evaluation might be necessary to gain a broader insight into the possible effects on neurocognitive performance.

Heme oxygenase-1 promoter region (GT)n polymorphism associates with increased neuroimmune activation and risk for encephalitis in HIV infection

BACKGROUND

Heme oxygenase-1 (HO-1) is a critical cytoprotective enzyme that limits oxidative stress, inflammation, and cellular injury within the central nervous system (CNS) and other tissues. We previously demonstrated that HO-1 protein expression is decreased within the brains of HIV+ subjects and that this HO-1 reduction correlates with CNS immune activation and neurocognitive dysfunction. To define a potential CNS protective role for HO-1 against HIV, we analyzed a well-characterized HIV autopsy cohort for two common HO-1 promoter region polymorphisms that are implicated in regulating HO-1 promoter transcriptional activity, a (GT)n dinucleotide repeat polymorphism and a single nucleotide polymorphism (A(-413)T). Shorter HO-1 (GT)n repeats and the 'A' SNP allele associate with higher HO-1 promoter activity.

METHODS

Brain dorsolateral prefrontal cortex tissue samples from an autopsy cohort of HIV-, HIV+, and HIV encephalitis (HIVE) subjects (n = 554) were analyzed as follows: HO-1 (GT)n polymorphism allele lengths were determined by PCR and capillary electrophoresis, A(-413)T SNP alleles were determined by PCR with allele specific probes, and RNA expression of selected neuroimmune markers was analyzed by quantitative PCR.

RESULTS

HIV+ subjects with shorter HO-1 (GT)n alleles had a significantly lower risk of HIVE; however, shorter HO-1 (GT)n alleles did not correlate with CNS or peripheral viral loads. In HIV+ subjects without HIVE, shorter HO-1 (GT)n alleles associated significantly with lower expression of brain type I interferon response markers (MX1, ISG15, and IRF1) and T-lymphocyte activation markers (CD38 and GZMB). No significant correlations were found between the HO-1 (GT)n repeat length and brain expression of macrophage markers (CD163, CD68), endothelial markers (PECAM1, VWF), the T-lymphocyte marker CD8A, or the B-lymphocyte maker CD19. Finally, we found no significant associations between the A(-413)T SNP and HIVE diagnosis, HIV viral loads, or any neuroimmune markers.

CONCLUSION

Our data suggest that an individual's HO-1 promoter region (GT)n polymorphism allele repeat length exerts unique modifying risk effects on HIV-induced CNS neuroinflammation and associated neuropathogenesis. Shorter HO-1 (GT)n alleles increase HO-1 promoter activity, which could provide neuroprotection through decreased neuroimmune activation. Therapeutic strategies that induce HO-1 expression could decrease HIV-associated CNS neuroinflammation and decrease the risk for development of HIV neurological disease.

HIV-associated neurocognitive disorder

PURPOSE OF REVIEW

HIV-associated neurocognitive disease is the most active topic for neuroAIDS investigations at present. Although impairment is mild in patients successfully treated with modern antiviral regimens, it remains an ongoing problem for HIV patients. It is important to update the emerging research concerning HIV-associated neurocognitive disease.

RECENT FINDINGS

The virus enters the brain during acute infection, with evidence for abnormal functioning that may occur early and often persists. Direct relationships with ongoing viral infection continue to be monitored, but chronic inflammation often associated with monocytes and macrophages appears to be the most likely driver of cognitive dysfunction. Appreciation for cerebrovascular disease as a significant comorbidity that is associated with cognitive deficits is increasing. Neuroimaging is actively being developed to address detection and measurement of changes in the brain. Optimal combined antiretroviral treatment therapy has vastly improved neurologic outcomes, but so far has not been demonstrated to reverse the remaining mild impairment. Inflammatory and vascular mechanisms of cerebral dysfunction may need to be addressed to achieve better outcomes.

SUMMARY

Ongoing research is required to improve neurological outcomes for persons living with HIV. It is likely that interventions beyond antiviral approaches will be required to control or reverse HIV-associated neurocognitive disease.

Neurological Complications of HIV Infection

PURPOSE OF REVIEW

HIV-associated neurocognitive disorders (HAND) are common in patients with HIV disease, even during suppressive combination antiretroviral therapy (cART). This review article addresses the pathogenesis of HAND, focusing on important findings from the last 5 years.

RECENT FINDINGS

While HIV-associated dementia is now rare in settings with cART availability, mild forms of HAND are increasing in prevalence. Biomarkers of cellular injury, such as neurofilament light chain and neopterin, can detect early stages of neuroinflammation associated with HIV infection and are increased even in asymptomatic individuals with chronic HIV infection. Several recent studies form a growing body of evidence that HIV can infect and replicate in monocytes and that blocking monocyte activity can potentially improve neurological outcomes in HIV. Early cART may also prevent HAND. Understanding the multifactorial causes of CNS infection and inflammation is critical to devising treatment and preventive strategies for HAND.

Cognitive Impairment and Persistent CNS Injury in Treated HIV

The implementation of combination antiretroviral therapy (cART) has changed HIV infection into a chronic illness, conveying extensive benefits, including greater longevity and advantages for the central nervous system (CNS). However, studies increasingly confirm that the CNS gains are incomplete, with reports of persistent immune activation affecting the CNS despite suppression of plasma HIV RNA. The rate of cognitive impairment is unchanged, although severity is generally milder than in the pre-cART era. In this review, we discuss cognitive outcomes from recently published clinical HIV studies, review observations on HIV biomarkers for cognitive change, and emphasize longitudinal imaging findings. Additionally, we summarize recent studies on CNS viral invasion, CD8 encephalitis, and how CNS involvement during the earliest stages of infection may set the stage for later cognitive manifestations.

Childhood maltreatment and HIV-associated neurocognitive disorders share similar pathophysiology: a potential sensitisation mechanism?

HIV-associated neurocognitive disorders (HAND) are increasingly prevalent despite the use of antiretroviral therapies. Previous research suggests that individual host factors play an important role in determining susceptibility to HAND. In this review, we propose that childhood trauma (CT) and HAND share several common aetiological mechanisms, namely hypothalamic-pituitary-adrenal axis dysregulation, neuroinflammation and oxidative stress. These convergent and consequent mechanisms may translate into an increased risk of developing HAND in individuals who have experienced early life stress. We provide an overview of basic and clinical research relating to these pathophysiological mechanisms and suggest that further research examine brain-derived neurotrophic factor and telomere length as common mediating factors and potential therapeutic targets for HAND and CT. Graphical abstract Both childhood trauma and HIV-associated neurocognitive disorders are associated with HPA axis dysregulation, inflammation and oxidative stress.

High Number of Activated CD8+ T Cells Targeting HIV Antigens Are Present in Cerebrospinal Fluid in Acute HIV Infection

BACKGROUND

Central nervous system (CNS) infiltration by CD8 T cells is associated with neuroinflammation in many neurodegenerative diseases, including HIV-associated dementia. However, the role of CD8 T cells in the CNS during acute HIV infection (AHI) is unknown.

METHODS

We analyzed the phenotype, gene expression, T cell receptor (TCR) repertoire, and HIV specificity of CD8 T cells in cerebrospinal fluid (CSF) of a unique cohort captured during the earliest stages of AHI (n = 26), chronic (n = 23), and uninfected (n = 8).

RESULTS

CSF CD8 T cells were elevated in AHI compared with uninfected controls. The frequency of activated CSF CD8 T cells positively correlated to CSF HIV RNA and to markers of CNS inflammation. In contrast, activated CSF CD8 T cells during chronic HIV infection were associated with markers of neurological injury and microglial activation. CSF CD8 T cells in AHI exhibited increased functional gene expression profiles associated with CD8 T cells effector function, proliferation, and TCR signaling, a unique restricted TCR Vbeta repertoire and contained HIV-specific CD8 T cells directed to unique HIV epitopes compared with the periphery.

CONCLUSIONS

These results suggest that CSF CD8 T cells in AHI expanding in the CNS are functional and directed against HIV antigens. These cells could thus play a beneficial role protective of injury seen in chronic HIV infection if combination antiretroviral therapy is initiated early.

Blood-Brain Barrier Disruption Is Initiated During Primary HIV Infection and Not Rapidly Altered by Antiretroviral Therapy

Background

We explored the establishment of abnormal blood-brain barrier (BBB) permeability and its relationship to neuropathogenesis during primary human immunodeficiency virus (HIV) infection by evaluating the cerebrospinal fluid (CSF) to serum albumin quotient (QAlb) in patients with primary HIV infection. We also analyzed effects of initiating combination antiretroviral therapy (cART).

Methods

The QAlb was measured in longitudinal observational studies of primary HIV infection. We analyzed trajectories of the QAlb before and after cART initiation, using mixed-effects models, and associations between the QAlb and the CSF level of neurofilament light chain (NFL), the ratio of N-acetylaspartate to creatinine levels (a magnetic resonance spectroscopy neuronal integrity biomarker), and neuropsychological performance.

Results

The baseline age-adjusted QAlb was elevated in 106 patients with primary HIV infection (median time of measurement, 91 days after infection), compared with that in 64 controls (P = .02). Before cART initiation, the QAlb increased over time in 84 participants with a normal baseline QAlb (P = .006) and decreased in 22 with a high baseline QAlb (P = .011). The QAlb did not change after a median cART duration of 398 days, initiated at a median interval of 225 days after infection (P = .174). The QAlb correlated with the NFL level at baseline (r = 0.497 and P < .001) and longitudinally (r = 0.555 and P < .001) and with the ratio of N-acetylaspartate to creatinine levels in parietal gray matter (r = -0.352 and P < .001 at baseline and r = -0.387 and P = .008 longitudinally) but not with neuropsychological performance.

Conclusion

The QAlb rises during primary HIV infection, associates with neuronal injury, and does not significantly improve over a year of treatment. BBB-associated neuropathogenesis in HIV-infected patients may initiate during primary infection.

Clinical and viro-immunological correlates of HIV associated neurocognitive disorders (HAND) in a cohort of antiretroviral-naïve HIV-infected patients

The multifactorial pathogenesis of HIV-associated neurocognitive disorders may explain the inconsistent association between neurocognitive impairment and cerebrospinal fluid (CSF) HIV RNA. Clinical and viro-immunological (CSF and plasma HIV RNA, CSF/plasma HIV RNA ratio, circulating T-cell phenotypes) parameters were investigated in 155 HIV-infected, antiretroviral-naïve, asymptomatic study participants undergoing a neuropsychological evaluation. HIV associated neurocognitive disorders (HAND) was independently associated with AIDS events and a CSF/plasma ratio of at least one, after adjustment for CD4 nadir of less than 200 cells/mmc, suggesting a role for active central nervous system (CNS) viral replication in the pathogenesis of neurocognitive impairment.

A decreasing CD4/CD8 ratio over time and lower CSF-penetrating antiretroviral regimens are associated with a higher risk of neurocognitive deterioration, independently of viral replication

Persistent immune activation is one of the suspected causes of HIV-associated neurocognitive disorders (HAND) in cART era. The CD4/CD8 ratio has been recently showed as a marker of immune activation and HAND. Our aim was to analyze if a decrease in the CD4/CD8 ratio over time could have an impact on neurocognitive deterioration. Randomly selected HIV-infected patients were followed for neuropsychological (NP) testing during a period of almost 2 years. Tests were adjusted for age, gender, and education. Patients were divided into 5 groups: normal tests (NT), neuropsychological deficit (ND, one impaired cognitive domain), asymptomatic neurocognitive disorders (ANI), mild neurocognitive disorders (MND), and HIV-associated dementia (HAD). Risk factors for neurocognitive deterioration were analyzed. Two hundred fifty-six patients underwent NP tests and 94 participated in the follow-up. The groups were comparable. Upon neuropsychological re-testing, six patients showed clinical improvement, 30 had worsened, and 58 were stable, resulting in 42 patients presenting with HAND (45 %). The majority of HAND cases consisted of ANI (26 %) and MND (16 %). In patients whose NP performance worsened, CPE 2010 score was lower at inclusion (7.13 vs 8.00, p = 0.003) and CD4/CD8 decrease more frequent (60 vs 31 %, p = 0.008) than in those who were stable or improved. Multivariate analysis confirmed these results. A decreasing CD4/CD8 ratio during a longitudinal follow-up of randomly selected HIV-infected patients and lower CSF-penetrating regimens were independently associated with cognitive decline. Monitoring trends in CD4/CD8 ratio could contribute to identifying patients at higher risk of neurocognitive deterioration.

Immune activation in the central nervous system throughout the course of HIV infection

PURPOSE OF REVIEW

Robust and dynamic innate and adaptive responses characterize the acute central nervous system (CNS) response to HIV and other viral infections. In a state of chronic infection or viral latency, persistent immune activation associates with abnormality in the CNS. Understanding this process is critical, as immune-mediated abnormality in nonrenewable CNS cells may result in long-term neurologic sequelae for HIV-infected individuals.

RECENT FINDINGS

In humans, immune activation is reduced by suppressive combination antiretroviral therapy, but persists at abnormally elevated levels on treatment. CNS immune activation is initiated in acute infection and progressively increases until combination antiretroviral therapy is started. Newly identified characteristics of the CNS immune surveillance network include features of homeostasis and function of brain microglial cells, lymphatic drainage from CNS to cervical lymph nodes, and cells in cerebrospinal fluid associated with neurocognitive impairment.

SUMMARY

More research is required to determine whether early intervention to reduce infection limits the immunopathology established by sustained immune responses that ultimately fail to resolve infection, and to unravel mechanisms of persistent immune activation during treated HIV so that strategies can be developed to therapeutically protect the brain.

CROI 2016: Neurologic Complications of HIV Infection

The brain remains a major target for HIV infection and a site of potential complications for HIV-infected individuals. Emerging data presented at the 2016 Conference on Retroviruses and Opportunistic Infections suggest that during the early stages of infection, activated CD4+ cells may traffic the virus into the central nervous system (CNS). HIV is detectable in cells and tissues of the CNS in some individuals despite suppressive antiretroviral treatment. A potential source of cerebrospinal fluid HIV escape may be compartmentalized HIV replication within macrophage lineage cells. Virally infected cells can traffic out of the CNS and may have the potential to reseed the systemic compartment. Additional modifiers of HIV-associated neurocognitive disorder (HAND) were identified, including female sex and hepatic dysfunction. Large epidemiologic studies reported an elevated risk of stroke among HIV-infected individuals, related to traditional vascular risk factors, history of recreational drug use, and HIV measures (lower CD4+ cell nadir and higher viral load). Brain imaging may provide a noninvasive means for detecting early changes in the brain associated with HIV infection and may assist in prognosis of HAND. Some potential adjunctive therapies to standard antiretroviral therapy for HIV-infected individuals were considered.