Rates of non-confounded HIV-associated neurocognitive disorders in men initiating combination antiretroviral therapy during primary infection

HIV Compartmentalization in the CNS and Its Impact in Treatment Outcomes and Cure Strategies

PURPOSE OF REVIEW

This review focuses on the cerebrospinal fluid (CSF) findings in connection to the central nervous system (CNS) reservoir in treatment-naïve and virally suppressed PLWH, followed by the findings in CSF HIV-1 escape and analytical treatment interruption studies.

RECENT FINDINGS

Compared to chronic infection, initiating antiretroviral therapy (ART) during acute HIV-1 infection results in more homogeneous longitudinal benefits in the CNS. Viral variants in CSF HIV-1 escape are independently linked to infected cells from the systemic reservoir and in the CNS, highlighting the phenomenon as a consequence of different mechanisms. HIV-infected cells persist in CSF in nearly half of the individuals on stable ART and are associated with worse neurocognitive performance. Future studies should probe into the origin of the HIV-infected cells in the CSF. Examining the capacity for viral replication would provide new insight into the CNS reservoir and identify strategies to eradicate it or compensate for the insufficiency of ART.

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.

Cognitive trajectories after treatment in acute HIV infection

OBJECTIVE

People with HIV continue to exhibit cognitive symptoms after suppressive antiretroviral therapy (ART). It remains unclear if initiating ART during acute HIV-1 infection (AHI) uniformly improves cognitive outcomes.

METHODS

Sixty-seven individuals (96% men, median age 28 years) initiated ART immediately after AHI diagnosis and maintained viral suppression for 6 years. They underwent a four-test neuropsychological battery that measured fine motor speed and dexterity, psychomotor speed, and executive functioning at baseline (pre-ART AHI), weeks 12, 24 and 96, and annually thereafter through week 288. Performances were standardized to calculate an overall (NPZ-4) score and frequencies of impaired cognitive performance (≤-1 SD on at least two tests, or ≤-2 SD on at least one test). Group-based trajectory analysis (GBTA) was applied to identify distinct neuropsychological trajectories modelled from baseline to week 288. Posthoc analyses examined HIV-1 and demographic factors that differed between trajectory subgroups.

RESULTS

NPZ-4 scores improved from baseline to week 96 (P < 0.001) and from weeks 96 to 288 (P < 0.001), with frequencies of impaired performance of 30, 6 and 2% at the respective time-points. The amplitude of NPZ-4 improvement throughout the period was more than 0.5 SD and beyond practice effects. GBTA identified three NPZ-4 trajectory subgroups that all showed improvement over-time. The subgroup with lowest baseline performance exhibited worse depressive symptoms at baseline (P = 0.04) and the largest improvement among the three. HIV-1 indices did not differ between the subgroups.

CONCLUSION

Cognitive performance improved in a sustained and stable manner after initiating ART during AHI. Largest improvements were seen in participants with worst baseline cognitive performance.

Effect of human immunodeficiency virus on the brain: A review

Thirty million people are infected with human immunodeficiency virus (HIV) worldwide, and HIV-associated neurocognitive disorder (HAND) is one of the most common comorbidities of HIV. However, the effect of HIV on the brain has not been fully investigated. This article aimed to review the changes to the brain due to HIV in terms of atrophy, diffusion changes, and hyperintensities. Studies have observed significant atrophy in subcortical gray matter, as well as in cortical white and gray matter. Moreover, the ventricles enlarge, and the sulci widen. Although HIV causes changes to the white and gray matter of the brain, few diffusion tensor imaging studies have investigated the changes to gray matter integrity. White and gray matter hyperintensities have frequently been observed in HIV-positive individuals, with the subcortical gray matter (caudate nucleus and putamen) and periventricular white matter frequently affected. In conclusion, subcortical gray matter is the first brain region to be affected and is affected most severely. Additionally, this review highlights the gaps in the literature, since the effect of HIV on the brain is not fully known. Future studies should continue to investigate the effect of HIV on the brain in different stages of the disease, and alternate therapies should be developed since highly active antiretroviral therapy is currently ineffective at treating HAND.

Cognitive disorders in people living with HIV

High rates of cognitive disorders in antiretroviral-treated people living with HIV have been described worldwide. The exact prevalence of such cognitive disorders is determined by the definitions used, and the presence of these cognitive disorders significantly impacts the overall wellbeing of people with HIV. With the cohort of people with HIV becoming increasingly older, and having high rates of comorbidities and concomitant medication use, rates of cognitive disorders are likely to increase. Conversely, interventions are being sought to reduce the size of the latent HIV reservoir. If successful, such interventions are likely to also reduce the HIV reservoir in the brain compartment, which could result in improvements in cognitive function and reduced rates of impairment.

New Potential Axes of HIV Neuropathogenesis with Relevance to Biomarkers and Treatment

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) affect approximately half of people living with HIV despite viral suppression with antiretroviral therapies and represent a major cause of morbidity. HAND affects activities of daily living including driving, using the Internet and, importantly, maintaining drug adherence. Whilst viral suppression with antiretroviral therapies (ART) has reduced the incidence of severe dementia, mild neurocognitive impairments continue to remain prevalent. The neuropathogenesis of HAND in the context of viral suppression remains ill-defined, but underlying neuroinflammation is likely central and driven by a combination of chronic intermittent low-level replication of whole virus or viral components, latent HIV infection, peripheral inflammation possibly from a disturbed gut microbiome or chronic cellular dysfunction in the central nervous system. HAND is optimally diagnosed by clinical assessment with imaging and neuropsychological testing, which can be difficult to perform in resource-limited settings. Thus, the identification of biomarkers of disease is a key focus of the field. In this chapter, recent advances in the pathogenesis of HAND and biomarkers that may aid its diagnosis and treatment will be discussed.

Central Nervous System Inflammation and Infection during Early, Nonaccelerated Simian-Human Immunodeficiency Virus Infection in Rhesus Macaques

Studies utilizing highly pathogenic simian immunodeficiency virus (SIV) and simian-human immunodeficiency virus (SHIV) have largely focused on the immunopathology of the central nervous system (CNS) during end-stage neurological AIDS and SIV encephalitis. However, this may not model pathophysiology in earlier stages of infection. In this nonaccelerated SHIV model, plasma SHIV RNA levels and peripheral blood and colonic CD4⁺ T cell counts mirrored early human immunodeficiency virus (HIV) infection in humans. At 12 weeks postinfection, cerebrospinal fluid (CSF) detection of SHIV RNA and elevations in IP-10 and MCP-1 reflected a discrete neurovirologic process. Immunohistochemical staining revealed a diffuse, low-level CD3⁺ CD4⁻ cellular infiltrate in the brain parenchyma without a concomitant increase in CD68/CD163⁺ monocytes, macrophages, and activated microglial cells. Rare SHIV-infected cells in the brain parenchyma and meninges were identified by RNAScope in situ hybridization. In the meninges, there was also a trend toward increased CD4⁺ infiltration in SHIV-infected animals but no differences in CD68/CD163⁺ cells between SHIV-infected and uninfected control animals. These data suggest that in a model that closely recapitulates human disease, CNS inflammation and SHIV in CSF are predominantly mediated by T cell-mediated processes during early infection in both brain parenchyma and meninges. Because SHIV expresses an HIV rather than SIV envelope, this model could inform studies to understand potential HIV cure strategies targeting the HIV envelope.

IMPORTANCE Animal models of the neurologic effects of HIV are needed because brain pathology is difficult to assess in humans. Many current models focus on the effects of late-stage disease utilizing SIV. In the era of antiretroviral therapy, manifestations of late-stage HIV are less common. Furthermore, new interventions, such as monoclonal antibodies and therapeutic vaccinations, target HIV envelope. We therefore describe a new model of central nervous system involvement in rhesus macaques infected with SHIV expressing HIV envelope in earlier, less aggressive stages of disease. Here, we demonstrate that SHIV mimics the early clinical course in humans and that early neurologic inflammation is characterized by predominantly T cell-mediated inflammation accompanied by SHIV infection in the brain and meninges. This model can be utilized to assess the effect of novel therapies targeted to HIV envelope on reducing brain inflammation before end-stage 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.

Neurologic Complications in Treated HIV-1 Infection

Effective combination antiretroviral therapy has transformed HIV infection into a chronic disease, with HIV-infected individuals living longer and reaching older age. Neurological disease remains common in treated HIV, however, due in part to ongoing inflammation and immune activation that persist in chronic infection. In this review, we highlight recent developments in our understanding of several clinically relevant neurologic complications that can occur in HIV infection despite treatment, including HIV-associated neurocognitive disorders, symptomatic CSF escape, cerebrovascular disease, and peripheral neuropathy.

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.

Guidelines for Evaluation and Management of Cognitive Disorders in HIV-Positive Individuals

Antiretroviral therapy has revolutionised the treatment for people living with HIV (PLWH). Where antiretroviral coverage is high, the treatment paradigm for HIV-disease is now one of managing the long-term consequences of the virus and its treatment rather than the consequences of untreated HIV-disease such as immunosuppression and opportunistic infections. One such long-term consequence is HIV-associated cognitive impairment which is reported to occur in up to 50 % of treated PLWH and has been associated with poorer outcomes. Given the ageing cohort and increased frequency of comorbidities, the prevalence of symptomatic cognitive impairment may increase with time. High quality evidence for management strategies including screening, diagnosis and treatment of HIV-associated cognitive impairment are lacking and in general guidelines are based on best clinical practice. In this article, we assessed recent guidelines concerning the management of HIV-associated cognitive impairment by performing a systematic review of the MEDLINE database using PubMed. We report that, in general, guidelines from around the world regarding the management of HIV-associated cognitive impairment are converging. Screening is generally not recommended in asymptomatic PLWH. Diagnosis of HIV-associated cognitive impairment should be made only after a comprehensive assessment and exclusion of other potential causes. Antiretroviral therapy forms the cornerstone of management of HIV-associated cognitive impairment and should be guided by plasma and cerebrospinal fluid (CSF) genotype(s).