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Programmed death-ligand 1 is a glycoprotein expressed on antigen presenting cells, hepatocytes, and tumors which upon interaction with programmed death-1, results in inhibition of antigen-specific T cell responses. Here, we report a mechanism of inhibiting programmed death-ligand 1 through small molecule-induced dimerization and internalization. This represents a mechanism of checkpoint inhibition, which differentiates from anti-programmed death-ligand 1 antibodies which function through molecular disruption of the programmed death 1 interaction. Testing of programmed death ligand 1 small molecule inhibition in a humanized mouse model of colorectal cancer results in a significant reduction in tumor size and promotes T cell proliferation. In addition, antigen-specific T and B cell responses from patients with chronic hepatitis B infection are significantly elevated upon programmed death ligand 1 small molecule inhibitor treatment. Taken together, these data identify a mechanism of small molecule-induced programmed death ligand 1 internalization with potential therapeutic implications in oncology and chronic viral infections. Programmed death-ligand 1 (PD-L1) is involved in the inhibition of antigen specific T cells via ligation of programmed death 1 (PD-1). Here, the authors show checkpoint inhibition by use of small molecule inhibition of PD-L1 which in a humanised mouse model was shown to restore T cell responses and reduced tumour burden.

Chronic hepatitis B (CHB) infection functional cure is defined as sustained loss of HBsAg and several therapeutic strategies are in clinical development designed to pharmacologically reduce serum HBsAg, break immune tolerance, and increase functional cure rates. However, little is known about pre-treatment HBsAg levels as an indicator of HBV immune potential. Here, we compared the phenotypes and HBV-specific response of lymphocytes in CHB patients stratified by serum HBsAg levels <500 (HBs lo ) or >50,000 IU/ml (HBs hi ) using immunological assays (flow cytometry, ICS, ELISPOT). HBs hi patients had significantly higher expression of inhibitory PD-1 on CD4 + T cells, particularly among TEMRA subset, and higher FcRL5 expression on B cells. Upon HBcAg(core) or HBsAg(env)-stimulation, 85% and 60% of HBs lo patients had IFNγ + TNFα + and IFNγ + IL2 + CD4 + T cell responses respectively, in comparison to 33% and 13% of HBs hi patients. Checkpoint blockade with αPD-1 improved HBV-specific CD4 + T cell function only in HBs lo patients. HBsAg-specific antibody-secreting cells (ASCs) response was not different between these groups, yet αPD-1 treatment resulted in significantly higher fold change in ASCs among patients with HBsAg <100 IU/ml compared to patients with HBsAg >5,000 IU/ml. Thus, serum HBsAg correlates with inhibitory receptor expression, HBV-specific CD4 + T cell responses, and augmentation by checkpoint blockade.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Progress in understanding the pathogenesis of hepatitis C virus (HCV) has been slowed by the absence of tractable small animal models. Whereas GB virus B (GBV-B, an unclassified flavivirus) shares a phylogenetic relationship and several biologic attributes with HCV, including hepatotropism, it is not known to cause persistent infection, a hallmark of HCV. Here, we document persistent GBV-B infection in one of two healthy tamarins (Saguinus oedipus) inoculated intrahepatically with infectious synthetic RNA. High-titer viremia (108to 109genome equivalents per ml) and transiently elevated serum alanine transaminase activities were present from weeks 4 to 12 postinoculation in both animals. However, whereas GBV-B was eliminated from one animal by 20 weeks, the second animal remained viremic (103to 107genome equivalents per ml) for >2 years, with alanine transaminase levels becoming elevated again before spontaneous resolution of the infection. A liver biopsy taken late in the course of infection demonstrated hepatitis with periportal mononuclear infiltrates, hepatocellular microvesicular changes, cytoplasmic lipid droplets, and disordered mitochondrial ultrastructure, findings remarkably similar to chronic hepatitis C. GBV-B-infected hepatocytes contained numerous small vesicular membranous structures resembling those associated with expression of HCV nonstructural proteins, and sequencing of GBV-B RNA demonstrated a rate of molecular evolution comparable to that of HCV. We conclude that GBV-B is capable of establishing persistent infections in healthy tamarins, a feature that substantially enhances its value as a model for HCV. Mitochondrial structural changes and altered lipid metabolism leading to steatosis are conserved features of the pathogenesis of chronic hepatitis caused by these genetically distinct flaviviruses.

Picornaviruses constitute a medically important family of RNA viruses in which genome replication critically depends on a small RNA element, the cis-acting replication element (cre), that templates 3 Dpolpolymerase-catalyzed uridylylation of the protein primer for RNA synthesis, VPg. We report the solution structure of the 33-nt cre of human rhinovirus 14 under solution conditions optimal for uridylylation in vitro. The cre adopts a stem-loop conformation with an extended duplex stem supporting a novel 14-nt loop that derives stability from base-stacking interactions. Base-pair interactions are absent within the loop, and base substitutions within the loop that favor such interactions are detrimental to viral RNA replication. Conserved adenosines in the 5′ loop sequence that participate in a slide-back mechanism of VPg-pUpU synthesis are oriented to the inside of the loop but are available for base templating during uridylation. The structure explains why substitutions of the 3′ loop nucleotides have little impact on conformation of the critical 5′ loop bases and accounts for wide variation in the sequences of cres from different enteroviruses and rhinoviruses.

Complex, multilayered nanoparticles hold great promise for more sophisticated drug/gene delivery systems to single cells. Outermost layers can include cell targeting and cell-entry facilitating molecules. The next layer can include intracellular targeting molecules for precise delivery of the nanoparticle complex inside the cell of interest. Molecular biosensors can be used to confirm the presence of expected molecules (for example, reactive oxygen species (ROS) as a surrogate molecule for signs of infection, or for activation in radiation damage, etc.) prior to delivery of counter-measure molecules such as drugs or gene therapy. They can also be used as a feedback control mechanism to control the proper amount of drug/gene delivery for each cell. Importantly, the full nanoparticle system can be used to prevent any cells from encountering the drug unless that cell is specifically targeted. Thus, if a cell is initially non-specifically targeted, a secondary check for other molecular targets which must also be present inside the target cell of interest can be used to catch initial targeting mistakes and prevent subsequent delivery of treatment molecules to the wrong cells. The precise intracellular location of nanoparticles within specific regions of a cell can be confirmed by 3D multispectral confocal microscopy. These single cell molecular morphology measurements can be extended from individual cells, to other cells in a tissue in tissue monolayers or tissue sections.

Noncanonical poly(A) polymerases PAPD5 and PAPD7 (PAPD5/7) stabilize HBV RNA via the interaction with the viral post-transcriptional regulatory element (PRE), representing new antiviral targets to control HBV RNA metabolism, HBsAg production and viral replication. Inhibitors targeting these proteins are being developed as antiviral therapies, therefore it is important to understand how PAPD5/7 coordinate to stabilize HBV RNA. Here, we utilized a potent small-molecule AB-452 as a chemical probe, along with genetic analyses to dissect the individual roles of PAPD5/7 in HBV RNA stability. AB-452 inhibits PAPD5/7 enzymatic activities and reduces HBsAg both in vitro (EC50 ranged from 1.4 to 6.8 nM) and in vivo by 0.93 log10. Our genetic studies demonstrate that the stem-loop alpha sequence within PRE is essential for both maintaining HBV poly(A) tail integrity and determining sensitivity towards the inhibitory effect of AB-452. Although neither single knock-out (KO) of PAPD5 nor PAPD7 reduces HBsAg RNA and protein production, PAPD5 KO does impair poly(A) tail integrity and confers partial resistance to AB-452. In contrast, PAPD7 KO could not result in any measurable phenotypic changes, but displays a similar antiviral effect as AB-452 treatment when PAPD5 is depleted simultaneously. PAPD5/7 double KO confers complete resistance to AB-452 treatment. Our results thus indicate that PAPD5 plays a dominant role in stabilizing viral RNA by protecting the integrity of its poly(A) tail, while PAPD7 serves as a second line of protection. These findings inform PAPD5 targeted therapeutic strategies and open avenues for further investigating PAPD5/7 in HBV replication. Chronic hepatitis B affects more than 250 million patients and is a major public health concern worldwide. HBsAg plays a central role in maintaining HBV persistence and as such, therapies reducing HBsAg have been extensively investigated. PAPD5/7 targeting inhibitors, with oral bioavailability, represent an opportunity to reduce both HBV RNA and HBsAg. Here we uncover that the SLα sequence is required for HBV poly(A) tail integrity and RNA stability, and that the antiviral activity of AB-452 mimics the SLα mutants. Although PAPD5 and PAPD7 regulate HBV RNA stability, it remains unclear how they coordinate in stabilizing HBV RNA. Based on our studies, PAPD5 plays a dominant role to stabilize viral RNA by protecting the integrity of its poly(A) tail, while PAPD7 serves as a backup protection mechanism. Our studies may point out a direction towards developing PAPD5-selective inhibitors that could be used effectively to treat chronic hepatitis B.