HIV variability in the liver and evidence of possible compartmentalization

The multifaceted nature of HIV tissue reservoirs

PURPOSE OF REVIEW

To underline the complexity and the heterogeneity of the HIV reservoir.

RECENT FINDINGS

While lymphoid tissues (spleen, lymph nodes, gut-associated lymphoid tissue) harbor specific subsets of specialized CD4 +  T cells enriched in HIV-infected cells, non-CD4 +  T cell reservoirs such as tissue-resident macrophages and dendritic cells have also been implicated to contribute to viral persistence. Moreover, studies have applied highly sensitive tools to detect transcriptional activity within HIV-infected cells during prolonged ART and revealed a broader spectrum of transcriptional activity for proviruses than previously thought. Finally, while a combination of factors might be involved in the regulation of HIV persistence within different tissues and remains to be fully elucidated, recent results from autopsy samples of HIV-infected ART suppressed individuals indicate extensive clonality of HIV reservoirs in multiple tissues and suggest that the recirculation of HIV-infected cells and their local expansions in tissues may also contribute to the complexity of the HIV reservoirs in humans.

SUMMARY

HIV persistence in blood and multiple tissues despite long-standing and potent therapy is one of the major barriers to a cure. Given that the HIV reservoir is established early and is highly complex based on its composition, viral diversity, tissue distribution, transcriptional activity, replication competence, migration dynamics and proliferative potential across the human body and possible compartmentalization in specific tissues, combinatorial therapeutic approaches are needed that may synergize to target multiple viral reservoirs to achieve a cure for HIV infection.

Acute Hepatitis due to Primary Human Immunodeficiency Virus Infection

The acute retroviral syndrome may present with diverse systemic manifestations and laboratory abnormalities. Here we present a rare case of primary human immunodeficiency virus (HIV) infection causing severe acute hepatitis. Liver histopathology demonstrated a pattern of lymphocytic inflammation consistent with acute hepatitis, high levels of HIV proviral DNA were detected within liver tissue, and immunofluorescence showed HIV p24 antigen within immune and parenchymal cells including hepatocytes. We review the literature pertaining to HIV infection of cell compartments within the liver and discuss the implications for HIV-associated acute liver disease.

Near full-length HIV sequencing in multiple tissues collected postmortem reveals shared clonal expansions across distinct reservoirs during ART

HIV persists in tissues during antiretroviral therapy (ART), but the relative contribution of different anatomical compartments to the viral reservoir in humans remains unknown. We performed an extensive characterization of HIV reservoirs in two men who donated their bodies to HIV cure research and who had been on suppressive ART for years. HIV DNA is detected in all tissues, with large variations across anatomical compartments and between participants. Intact HIV genomes represent 2% and 25% of all proviruses in the two participants and are mainly detected in secondary lymphoid organs, with the spleen and mediastinal lymph nodes harboring intact viral genomes in both individuals. Multiple copies of identical HIV genomes are found in all tissues, indicating that clonal expansions are common in anatomical sites. The majority (>85%) of these expanded clones are shared across multiple tissues. These findings suggest that infected cells expand, migrate, and possibly circulate between anatomical sites.

A Pathogenic Role of Non-Parenchymal Liver Cells in Alcohol-Associated Liver Disease of Infectious and Non-Infectious Origin

Now, much is known regarding the impact of chronic and heavy alcohol consumption on the disruption of physiological liver functions and the induction of structural distortions in the hepatic tissues in alcohol-associated liver disease (ALD). This review deliberates the effects of alcohol on the activity and properties of liver non-parenchymal cells (NPCs), which are either residential or infiltrated into the liver from the general circulation. NPCs play a pivotal role in the regulation of organ inflammation and fibrosis, both in the context of hepatotropic infections and in non-infectious settings. Here, we overview how NPC functions in ALD are regulated by second hits, such as gender and the exposure to bacterial or viral infections. As an example of the virus-mediated trigger of liver injury, we focused on HIV infections potentiated by alcohol exposure, since this combination was only limitedly studied in relation to the role of hepatic stellate cells (HSCs) in the development of liver fibrosis. The review specifically focusses on liver macrophages, HSC, and T-lymphocytes and their regulation of ALD pathogenesis and outcomes. It also illustrates the activation of NPCs by the engulfment of apoptotic bodies, a frequent event observed when hepatocytes are exposed to ethanol metabolites and infections. As an example of such a double-hit-induced apoptotic hepatocyte death, we deliberate on the hepatotoxic accumulation of HIV proteins, which in combination with ethanol metabolites, causes intensive hepatic cell death and pro-fibrotic activation of HSCs engulfing these HIV- and malondialdehyde-expressing apoptotic hepatocytes.

HIV DNA persists in hepatocytes in people with HIV-hepatitis B co-infection on antiretroviral therapy

BACKGROUND

HIV can infect multiple cells in the liver including hepatocytes, Kupffer cells and infiltrating T cells, but whether HIV can persist in the liver in people with HIV (PWH) on suppressive antiretroviral therapy (ART) remains unknown.

METHODS

In a prospective longitudinal cohort of PWH and hepatitis B virus (HBV) co-infection living in Bangkok, Thailand, we collected blood and liver biopsies from 18 participants prior to and following ART and quantified HIV and HBV persistence using quantitative (q)PCR and RNA/DNAscope. Antiretroviral (ARV) drug levels were quantified using mass spectroscopy.

FINDINGS

In liver biopsies taken prior to ART, HIV DNA and HIV RNA were detected by qPCR in 53% (9/17) and 47% (8/17) of participants respectively. Following a median ART duration of 3.4 years, HIV DNA was detected in liver in 61% (11/18) of participants by either qPCR, DNAscope or both, but only at very low and non-quantifiable levels. Using immunohistochemistry, HIV DNA was observed in both hepatocytes and liver infiltrating CD4+ T cells on ART. HIV RNA was not detected in liver biopsies collected on ART, by either qPCR or RNAscope. All ARVs were clearly detected in liver tissue.

INTERPRETATION

Persistence of HIV DNA in liver in PWH on ART represents an additional reservoir that warrants further investigation.

FUNDING

National Health and Medical Research Council of Australia (Project Grant APP1101836, 1149990, and 1135851); This project has been funded in part with federal funds from the National Cancer Institute, National Institutes of Health, under Contract No. 75N91019D00024.

Pancreatogenic Diabetes: Triggering Effects of Alcohol and HIV

Multiorgan failure may not be completely resolved among people living with HIV despite HAART use. Although the chances of organ dysfunction may be relatively low, alcohol may potentiate HIV-induced toxic effects in the organs of alcohol-abusing, HIV-infected individuals. The pancreas is one of the most implicated organs, which is manifested as diabetes mellitus or pancreatic cancer. Both alcohol and HIV may trigger pancreatitis, but the combined effects have not been explored. The aim of this review is to explore the literature for understanding the mechanisms of HIV and alcohol-induced pancreatotoxicity. We found that while premature alcohol-inducing zymogen activation is a known trigger of alcoholic pancreatitis, HIV entry through C-C chemokine receptor type 5(CCR5)into pancreatic acinar cells may also contribute to pancreatitis in people living with HIV (PLWH). HIV proteins induce oxidative and ER stresses, causing necrosis. Furthermore, infiltrative immune cells induce necrosis on HIV-containing acinar cells. When necrotic products interact with pancreatic stellate cells, they become activated, leading to the release of both inflammatory and profibrotic cytokines and resulting in pancreatitis. Effective therapeutic strategies should block CCR5 and ameliorate alcohol's effects on acinar cells.

Tissue reservoirs of HIV

PURPOSE OF REVIEW

Tissue reservoirs of HIV may promote the persistent immunopathology responsible for non-AIDS morbidity and data support multifocal reactivation from tissues as the source of viral rebound during antiretroviral therapy (ART) interruption. The heterogeneity of tissue reservoirs and incomplete knowledge about their composition are obstacles to an HIV cure.

RECENT FINDINGS

In addition to the higher concentration of infected CD4 T cells found in both central lymphoid tissues and gut, specific subsets of CD4 T cells appear to play a disproportionate role in HIV persistence. Recently, a subset of central memory T cells enriched in lymph node germinal centers called T-follicular helper cells has been identified that expresses more viral RNA and occupies an anatomic niche inaccessible to cytotoxic T lymphocyte killing. Additional observations suggest that antiretroviral drug (ARV) concentrations may be lower in some tissues, raising the possibility for localized, low-level viral replication. Finally, some recent data implicate the persistence of infected, non-CD4 T-cell types in tissues during ART.

SUMMARY

The retention of infected cells in a wide variety of tissues, often with distinct viral and cellular characteristics, underscores the importance of studying tissue reservoirs in the development and assessment of cure strategies. Both inhibitory ARVs and latency-reversing drugs must reach these sites, and novel strategies may be needed to attack virus in cells as variable as T-follicular helper cells and macrophages.

Mechanisms of HIV persistence in HIV reservoirs

The establishment and maintenance of HIV reservoirs that lead to persistent viremia in patients on antiretroviral drugs remains the greatest challenge of the highly active antiretroviral therapy era. Cellular reservoirs include resting memory CD4+ T lymphocytes, implicated as the major HIV reservoir, having a half-life of approximately 44 months while this is less than 6 hours for HIV in plasma. In some individuals, persistent viremia consists of invariant HIV clones not detected in circulating resting CD4+ T lymphocytes suggesting other possible sources of residual viremia. Some anatomical reservoirs that may harbor such cells include the brain and the central nervous system, the gastrointestinal tract and the gut-associated lymphoid tissue and other lymphoid organs, and the genital tract. The presence of immune cells and other HIV susceptible cells, occurring in differing compositions in anatomical reservoirs, coupled with variable and poor drug penetration that results in suboptimal drug concentrations in some sites, are all likely factors that fuel the continued low-level replication and persistent viremia during treatment. Latently, HIV-infected CD4+ T cells harboring replication-competent virus, HIV cell-to-cell spread, and HIV-infected T cell homeostatic proliferation due to chronic immune activation represent further drivers of this persistent HIV viremia during highly active antiretroviral therapy.

Understanding HIV compartments and reservoirs

The spectrum of HIV-1 cellular reservoirs is highly diversified, and their role varies according to the milieu of the anatomical sites in which the virus replicates. In this light, mechanisms underlying HIV-1 persistence in anatomical compartments may be profoundly different from what is observed in peripheral blood. This scenario is further complicated by sub-optimal drug penetration in tissues allowing persistent and cryptic HIV-1 replication in body districts despite undetectable viremia. On this basis, this review aims at providing recent insights regarding the critical role of HIV-1 cellular reservoirs in different anatomical compartments, and their relationship with the pathogenesis of HIV-1 infection. A comprehensive definition of the complex interplay between the virus and its reservoir is critical in order to set up prophylactic and therapeutic strategies aimed at achieving the maximal virological suppression and hopefully in the near future the cure of HIV-1 infection (either functional or biological).

Analysis of HIV quasispecies suggests compartmentalization in the liver

Liver disease is now a major cause of morbidity and mortality among persons infected with the human immunodeficiency virus (HIV). An increasing body of evidence suggests that HIV infection is associated with exacerbated liver fibrosis and that HIV has the ability to infect several hepatic cell types. Despite the recognized existence of genetically distinct subpopulations of HIV in the central nervous system and genital tract, viral diversity and compartmentalization in the liver have not been explored extensively. Therefore, phylogenetic analysis was performed on full-length env and nef sequences for four patients. Distinct clustering of viral variants was observed for all patients in both areas of the genome. Statistical evidence of HIV compartmentalization in the liver was demonstrated in 85.4% of comparisons. Signature sequence analysis identified several liver-specific amino acids in all patients. Thus, the current study demonstrates statistically significant evidence for HIV compartmentalization in the liver. Additionally, these data suggest that the hepatic microenvironment harbors unique selective pressures that drive viral adaptation.

Low-level HIV infection of hepatocytes

BACKGROUND

There are only limited data on whether HIV infection occurs within the liver; therefore, we explored early and late stages of the HIV life cycle in two hepatocyte cell lines--Huh7.5 and Huh7.5JFH1--as well as in primary human hepatocytes.

RESULTS

Integrated HIV DNA was detected in Huh7.5 and Huh7.5JFH1 cells, as well as in primary hepatocytes, and was inhibited by the integrase inhibitor raltegravir in a dose-dependent manner. HIV p24 protein was also detected in cell culture supernatants at days 1, 3, 5, and 7 post-infection and was inhibited by AZT, although levels were modest compared to those in a lymphocyte cell line. Culture supernatants from HIV-infected hepatocytes were capable of infecting a non-hepatic HIV indicator cell line.

CONCLUSIONS

These results indicating low-level HIV replication in hepatoctyes in vitro complement evidence suggesting that HIV has deleterious effects on the liver in vivo.