Lymphocyte-Dominant Encephalitis and Meningitis in Simian Immunodeficiency Virus-Infected Macaques Receiving Antiretroviral Therapy

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.

Clinical Signs, Prevention and Treatment of Viral Infections in Infants

Certain infectious diseases are common in infants than any other age groups and are associated with morbidities in childhood and adulthood, and even mortality in severe cases. Environment, epidemic and maternal immunity are the main causes of these infections. Early diagnosis using molecular methods and treatment is therefore important to prevent future complications. Vaccines are recommended during infancy and childhood to prevent these infections. This review highlights some of the most commonly reported viral infections in children, their clinical signs, prevention and treatment.

Pharmacologic approaches to HIV-associated neurocognitive disorders

Antiretroviral therapy in people living with HIV can achieve potent, long-term suppression of HIV plasma viremia and has increased life expectancy. The central nervous system is infected early after virus acquisition and remains a reservoir for HIV. HIV-associated neurocognitive disorders (HAND) are an end-organ manifestation of HIV infection. The need to address neurological complications caused by HAND is significant as approximately 50% of people living with HIV on suppressive antiretroviral therapy are estimated to have some form of HAND. This review discusses the pathophysiology of HAND, CSF/CNS penetration and clinical pharmacology of antiretrovirals including pharmacokinetic/pharmacodynamic relationships, the persistence of HIV in the brain, and future therapeutic approaches to preserve and improve sustained viral suppression in the brain.

The Glutamate System as a Crucial Regulator of CNS Toxicity and Survival of HIV Reservoirs

Glutamate (Glu) is the most abundant excitatory neurotransmitter in the central nervous system (CNS). HIV-1 and viral proteins compromise glutamate synaptic transmission, resulting in poor cell-to-cell signaling and bystander toxicity. In this study, we identified that myeloid HIV-1-brain reservoirs survive in Glu and glutamine (Gln) as a major source of energy. Thus, we found a link between synaptic compromise, metabolomics of viral reservoirs, and viral persistence. In the current manuscript we will discuss all these interactions and the potential to achieve eradication and cure using this unique metabolic profile.

Chronic HIV-1 Tat exposure alters anterior cingulate cortico-basal ganglia-thalamocortical synaptic circuitry, associated behavioral control, and immune regulation in male mice

HIV-1 selectively disrupts neuronal integrity within specific brain regions, reflecting differences in viral tropism and/or the regional differences in the vulnerability of distinct neuronal subpopulations within the CNS. Deficits in prefrontal cortex (PFC)-mediated executive function and the resultant loss of behavioral control are a particularly debilitating consequence of neuroHIV. To explore how HIV-1 disrupts executive function, we investigated the effects of 48 h, 2 and/or 8 weeks of HIV-1 Tat exposure on behavioral control, synaptic connectivity, and neuroimmune function in the anterior cingulate cortex (ACC) and associated cortico-basal ganglia (BG)-thalamocortical circuitry in adult, Tat transgenic male mice. HIV-1 Tat exposure increased novelty-exploration in response to novel food, flavor, and environmental stimuli, suggesting that Tat triggers increased novelty-exploration in situations of competing motivation (e.g., drive to feed or explore vs. fear of novel, brightly lit open areas). Furthermore, Tat induced adaptability in response to an environmental stressor and pre-attentive filtering deficits. The behavioral insufficiencies coincided with decreases in the inhibitory pre- and post-synaptic proteins, synaptotagmin 2 and gephyrin, respectively, in the ACC, and alterations in specific pro- and anti-inflammatory cytokines out of 23 assayed. The interaction of Tat exposure and the resultant time-dependent, selective alterations in CCL4, CXCL1, IL-12p40, and IL-17A levels in the PFC predicted significant decreases in adaptability. Tat decreased dendritic spine density and cortical VGLUT1 inputs, while increasing IL-1β, IL-6, CCL5, and CCL11 in the striatum. Alternatively, IL-1α, CCL5, and IL-13 were decreased in the mediodorsal thalamus despite the absence of synaptic changes. Thus, HIV-1 Tat appears to uniquely and systematically disrupt immune regulation and the inhibitory and excitatory synaptic balance throughout the ACC-BG-thalamocortical circuitry resulting in a loss of behavioral control.

Nef-induced CCL2 Expression Contributes to HIV/SIV Brain Invasion and Neuronal Dysfunction

C-C motif chemokine ligand 2 (CCL2) is a chemoattractant for leukocytes including monocytes, T cells, and natural killer cells and it plays an important role in maintaining the integrity and function of the brain. However, there is accumulating evidence that many neurological diseases are attributable to a dysregulation of CCL2 expression. Acquired immune deficiency syndrome (AIDS) encephalopathy is a severe and frequent complication in individuals infected with the human immunodeficiency virus (HIV) or the simian immunodeficiency virus (SIV). The HIV and SIV Nef protein, a progression factor in AIDS pathology, can be transferred by microvesicles including exosomes and tunneling nanotubes (TNT) within the host even to uninfected cells, and Nef can induce CCL2 expression. This review focuses on findings which collectively add new insights on how Nef-induced CCL2 expression contributes to neurotropism and neurovirulence of HIV and SIV and elucidates why adjuvant targeting of CCL2 could be a therapeutic option for HIV-infected persons.

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.

Visualizing the Immune System: Providing Key Insights into HIV/SIV Infections

Immunological inductive tissues, such as secondary lymphoid organs, are composed of distinct anatomical microenvironments for the generation of immune responses to pathogens and immunogens. These microenvironments are characterized by the compartmentalization of highly specialized immune and stromal cell populations, as well as the presence of a complex network of soluble factors and chemokines that direct the intra-tissue trafficking of naïve and effector cell populations. Imaging platforms have provided critical contextual information regarding the molecular and cellular interactions that orchestrate the spatial microanatomy of relevant cells and the development of immune responses against pathogens. Particularly in HIV/SIV disease, imaging technologies are of great importance in the investigation of the local interplay between the virus and host cells, with respect to understanding viral dynamics and persistence, immune responses (i.e., adaptive and innate inflammatory responses), tissue structure and pathologies, and changes to the surrounding milieu and function of immune cells. Merging imaging platforms with other cutting-edge technologies could lead to novel findings regarding the phenotype, function, and molecular signatures of particular immune cell targets, further promoting the development of new antiviral treatments and vaccination strategies.