Assessing the role of peripheral CD8 T cells in neurocognitive impairment in HIV-infected men who have sex with men: data from the MSM Neurocog Study

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.

HIV-Associated Neurocognitive Impairment in the Modern ART Era: Are We Close to Discovering Reliable Biomarkers in the Setting of Virological Suppression?

The prevalence of the most severe forms of HIV-associated neurocognitive disorders (HAND) is decreasing due to worldwide availability and high efficacy of antiretroviral treatment (ART). However, several grades of HIV-related cognitive impairment persist with effective ART and remain a clinical concern for people with HIV (PWH). The pathogenesis of these cognitive impairments has yet to be fully understood and probably multifactorial. In PWH with undetectable peripheral HIV-RNA, the presence of viral escapes in cerebrospinal fluid (CSF) might explain a proportion of cases, but not all. Many other mechanisms have been hypothesized to be involved in disease progression, in order to identify possible therapeutic targets. As potential indicators of disease staging and progression, numerous biomarkers have been used to characterize and implicate chronic inflammation in the pathogenesis of neuronal injuries, such as certain phenotypes of activated monocytes/macrophages, in the context of persistent immune activation. Despite none of them being disease-specific, the correlation of several CSF cellular biomarkers to HIV-induced neuronal damage has been investigated. Furthermore, recent studies have been evaluating specific microRNA (miRNA) profiles in the CSF of PWH with neurocognitive impairment (NCI). The aim of the present study is to review the body of evidence on different biomarkers use in research and clinical settings, focusing on PWH on ART with undetectable plasma HIV-RNA.

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.

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.

Virologically suppressed patients with asymptomatic and symptomatic HIV-associated neurocognitive disorders do not display the same pattern of immune activation

OBJECTIVES

Inversion of the CD4:CD8 ratio is a marker of immune activation and age-associated disease. We measured the CD4:CD8 ratio as a marker of cognitive impairment in HIV-infected patients and explored differences according to clinical severity.

METHODS

Post hoc analysis of data from two prospective cohorts of HIV-infected patients randomly selected to undergo neuropsychological tests was performed. Test scores were adjusted for age, gender and education. Inclusion criteria were undetectable viral load and stable treatment for at least 6 months. Subjects with HIV-associated dementia were excluded. Patients were divided into an unimpaired group, a group with asymptomatic neurocognitive disorder (ANI) and a group with symptomatic HIV-associated neurocognitive disorder (sHAND), represented by mild neurocognitive disorder (MND). Demographic and background parameters, immune activation markers and the CD4:CD8 ratio were recorded.

RESULTS

Two hundred patients were included in the study. The mean age was 52 years, 78% were male, the mean CD4 count was 624 cells/μL, the mean nadir CD4 count was 240 cells/μL, 27% were hepatitis C virus (HCV)-coinfected, the mean duration of HIV infection was 16 years, and the mean time on current combination antiretroviral therapy (cART) was 2.9 years. Twenty-nine per cent of subjects had HAND (21% had ANI and 8% had MND). In multivariate analysis, a CD4:CD8 ratio < 1 was associated with a nadir CD4 count < 200 cells/μL [odds ratio (OR) 3.68] and with the presence of CD4(+) CD38(+) HLA(+) cells (OR 1.23). Multinominal logistic regression showed that, in comparison with the unimpaired group, diagnosis of sHAND was associated with a CD4:CD8 ratio < 1 (OR 10.62), longer HIV infection (OR 1.15) and longer current cART (OR 1.34), while the ANI group differed from the unimpaired group only for education level.

CONCLUSIONS

Aviraemic patients with sHAND did not display the same pattern of immune activation as subjects with ANI, suggesting that the underlying pathophysiological mechanisms could be different.

Immune system's role in viral encephalitis

Viral infections can be a major thread for the central nervous system (CNS), therefore, the immune system must be able to mount a highly proportionate immune response, not too weak, which would allow the virus to proliferate, but not too strong either, to avoid collateral damages. Here, we aim at reviewing the immunological mechanisms involved in the host defense in viral CNS infections. First, we review the specificities of the innate as well as the adaptive immune responses in the CNS, using several examples of various viral encephalitis. Then, we focus on three different modes of interactions between viruses and immune responses, namely human Herpes virus-1 encephalitis with the defect in innate immune response which favors this disease; JC virus-caused progressive multifocal leukoencephalopathy and the crucial role of adaptive immune response in this example; and finally, HIV infection with the accompanying low grade chronic inflammation in the CNS in some patients, which may be an explanation for the presence of cognitive disorders, even in some well-treated HIV-infected patients. We also emphasize that, although the immune response is generally associated with viral replication control and limited cellular death, an exaggerated inflammatory reaction can lead to tissue damage and can be detrimental for the host, a feature of the immune reconstitution inflammatory syndrome (IRIS). We will briefly address the indication of steroids in this situation.