CROI 2024 Abstract eBook

Abstract eBook

Invited Session

conserved capsid features with recruitment of a series of specific host cofactor proteins in the cytoplasm, in nuclear pores and in the nucleus and pioneering microscopy techniques have clearly illustrated intact capsids in the nucleus and associated them with successful infection. We have shown that the single pandemic HIV-1(M) lineage capsid has unique features that promote evasion from innate immune sensors. We hypothesise that this is explained by a more sophisticated regulation of the timing and location of capsid uncoating and genome release by the cofactors. This more effectively hides viral DNA and therefore permits more effective innate immune evasion. We hypothesise that this in turn promotes human-to-human transmission because innate immune activation is expected to reduce viral replication at the site of exposure and therefore establishment of infection. In collaboration with David Jacques and Till Boecking of the University of New South Wales we have also discovered that, despite their huge size, intact capsids can traverse nuclear pores through mimicking karyopherin nuclear transport proteins. Capsids do this by recruiting the FG motifs found in the nuclear pore diffusion barrier to a conserved binding pocket found in each capsid monomer. Thus, HIV capsids are molecular machines that have evolved to protect the process of viral genome synthesis from innate immune detection and to transport the genome across the cytoplasm, through nuclear pores, and to chromatin where they uncoat, and release genome, in exactly the right location and at exactly the right time for successful, undetected integration into host chromatin. Novel Markers of Hepatitis B: Clinical Utility For New Treatment Strategies Fabien Zoulim Institut National de la Santé et de la Recherche Médicale; Université Claude Bernard Lyon 1 , Lyon, France Background: In the context of novel treatment strategies aimed at HBV cure by eliminating or silencing the cccDNA reservoir, its non-invasive evaluation with blood viral biomarkers is critical to monitor intrahepatic viral clearance and guide treatment cessation. One of the caveats of these biomarkers is their ability to accurately distinguish biomarkers expressed from cccDNA versus those expressed from integrated viral sequences. HBsAg can be expressed from viral sequences integrated in the host genome which undermines its value in predicting cccDNA levels and transcriptional activity, particularly in HBeAg(−) patients and in patients under NUC therapy. Circulating HBV RNA (cirB-RNA) concentration is a promising novel biomarker for antiviral treatment monitoring. Quantification of cirB-RNA, measured with research laboratory developed assays, have good predictive power for both on treatment serological response and off-treatment durability. New generation investigational assays allowed the quantification of cccDNA derived viral RNAs in serum but not from integrated sequences. CirB-RNA detection correlates with cccDNA transcriptional activity in NUC treated or untreated patients. HBV core-related antigen (HBcrAg), a composite biomarker of core/pre-core derived proteins, is thought to be mainly expressed from cccDNA derived RNA template and was also shown to have a good predictive value for antiviral treatment response. cirB-RNA and HBcrAg are usually correlated. The combination of undetectable cirB-RNA and HBcrAg at the end of treatment is more predictive for sustained suppression of replication off-treatment compared with either biomarker alone. Other biomarkers are in development to assess the cccDNA reservoir, e.g. the quantification of phosphorylated and non-phosphorylated HBc in the blood circulation. These investigational biomarkers are now used for the evaluation of target engagement and antiviral efficacy to assist the development of new antivirals (Capsid Assembly Modulators, SiRNA, antisense oligonucleotides, etc.) and immunomodulatory agents (check point inhibitors, TLR agonists, therapeutic vaccines, etc.). Altogether, these non-invasive viral markers show promise for a deep phenotyping of patients and show potential for patient stratification and novel treatment evaluation. Advances in HBV Immunotherapy: The Beginning of the End? Adam Gehring University Health Network, Toronto, Canada Background: Encouraging data demonstrates that new combination therapies are beginning to achieve HBsAg loss in a significant proportion of chronic hepatitis B (CHB) patients. In some patients, HBsAg loss is durable, achieving functional cure, while others relapse, with HBsAg becoming detectable again during follow up. What determines cure vs. relapse remains unclear but, in the absence of a sterilizing cure, the immune system is believed by many to

may reduce the impact of drug-drug interactions with antiretrovirals. This plenary talk will summarize the most recent research evidence on the shorter course TB prevention and treatment, several of which have now informed the WHO guidelines. Further, the talk will provide an updated information on the drug-drug interactions between ATT and antiretrovirals as well as briefly discuss the recent rapid expansion of TB therapeutics pipeline. HIV-1 Genome Packaging During Virion Assembly: Selecting the Right RNA Wei-Shau Hu National Cancer Institute, Frederick, MD, USA Background: During virus assembly, HIV-1 must identify and selectively package the unspliced viral RNA into nascent virions to transfer genetic information to its progeny. A vast majority of HIV-1 virions contain two copies of full-length unspliced HIV-1 RNA that form a dimer, indicating that the RNA packaging is a regulated and efficient process. The viral polyprotein Gag orchestrates virus assembly and mediates RNA genome packaging. During this process, Gag preferentially binds unpaired guanosines within the highly structured 5' untranslated region (UTR) of HIV-1 RNA. Additionally, the HIV-1 unspliced RNA provides a scaffold that promotes Gag:Gag interactions and virus assembly, thereby ensuring its packaging. However, not all HIV-1 unspliced RNAs are created equal. Recent studies showed that HIV-1 uses neighboring sequences as transcription start sites to generate multiple unspliced RNA species with a few nucleotides difference at the 5' end. However, these 99.9% identical RNAs can differ functionally, and one species of unspliced HIV-1 RNA is preferentially packaged over other nearly identical RNAs. These studies reveal the complex regulation of HIV-1 genome packaging process. Background: HIV-1 capsid is a closed conical structure formed during virion maturation. It houses the viral RNA genome and key viral enzymes reverse transcriptase and integrase needed for conversion of the single stranded viral RNA into double stranded DNA and its subsequent integration into a host cell chromosome. The viral capsid consists of the capsid protein (CA) arranged predominantly into hexameric lattices, as well as into 12 pentamers, which introduce curvatures at the capsid periphery to completely close the conical structure. The capsid assembly is mediated by the cellular polyanion inositol hexakisphosphate (IP6), which binds to central arginine rings in pentamers and hexamers to stabilize these crucial assembly intermediates. Recent structural studies have elucidated a molecular switch that directs CA assembly into pentamers and hexamers. Lenacapavir (LEN, Gilead Sciences) is the first-in-class capsid targeting, long-acting and highly potent antiretroviral. Mechanistic and structural studies have revealed a multimodal mechanism of action of the inhibitor. LEN inhibits both early and late steps of HIV-1 replication with picomolar concentrations. Yet, the underlying mechanism for such a high potency of LEN is unclear. We have developed a LC-MS/MS based methodology to quantitate LEN concentrations in virions and found that sub-stoichiometric inhibitor to CA ratios hyper-stabilize HIV-1 capsid and block infection. The inhibitor remains stably bound to HIV-1 capsid for >24 h. Furthermore, we have investigated an additional antiviral activity of LEN during virion maturation. Our biochemical assays uncovered that LEN binding to CA monomers specifically interfered with the formation of pentamers, whereas the inhibitor promoted the assembly of hyper-stable hexametric lattices. The ability of LEN to offset the delicate balance between pentamers and hexamers resulted in formation of defective or atypical assemblies of CA both in vitro and in virions. These findings provide a new insight into molecular mechanisms of action of LEN. Intact HIV Capsids facilitate innate immune evasion and enter the nucleus via karyopherin mimicry Gregory Towers University College London, London, UK Background: HIV has a core built of around 250 capsid protein hexamers and exactly 12 pentamers. This cone shaped core contains the viral single stranded RNA genome which is converted into a double stranded DNA genome by encapsidated reverse transcription, catalysed by viral reverse transcriptase. Early data suggested that viral capsids come apart or "uncoat" before viral DNA synthesis, but we now understand that the infectious cores are the ones that remain intact until after nuclear entry. Genetic studies have associated Virion Maturation: Folding Into the Right Shape Mamuka Kvaratskhelia University of Colorado, Aurora, CO, USA

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CROI 2024