Tat-enhanced delivery of the C terminus of HDAg-L inhibits assembly and secretion of hepatitis D virus

Identification of a novel interaction site between the large hepatitis delta antigen and clathrin that regulates the assembly of genotype III hepatitis delta virus

BACKGROUND

Hepatitis delta virus (HDV), a satellite virus of hepatitis B virus (HBV), is a small, defective RNA virus strongly associated with the most severe form of hepatitis and progressive chronic liver disease and cirrhosis. Chronic hepatitis D, resulting from HBV/HDV coinfection, is considered to be the most severe form of viral hepatitis and affects 12-20 million people worldwide. Involved in the endocytosis and exocytosis of cellular and viral proteins, clathrin contributes to the pathogenesis and morphogenesis of HDV. Previously, we demonstrated that HDV-I and -II large hepatitis delta antigens (HDAg-L) possess a putative clathrin box that interacts with clathrin heavy chain (CHC) and supports HDV assembly.

METHODS

Virus assembly and vesicular trafficking of HDV virus-like particles (VLPs) were evaluated in Huh7 cells expressing HDV-I, -II and -III HDAg-L and hepatitis B surface antigen (HBsAg). To elucidate the interaction motif between HDAg-L and CHC, site-directed mutagenesis was performed to introduce mutations into HDAg-L and CHC and analyzed using coimmunoprecipitation or pull-down assays.

RESULTS

Comparable to HDV-I virus-like particles (VLPs), HDV-III VLPs were produced at a similar level and secreted into the medium via clathrin-mediated post-Golgi vesicular trafficking. Mutation at F27 or E33 of CHC abolished the binding of CHC to the C-terminus of HDV-III HDAg-L. Mutation at W207 of HDV-III HDAg-L inhibited its association with CHC and interfered with HDV-III VLP formation. We elucidated mechanism of the binding of HDV-III HDAg-L to CHC and confirmed the pivotal role of clathrin binding in the assembly of genotype III HDV.

CONCLUSIONS

A novel W box which was identified at the C terminus of HDV-III HDAg-L is known to differ from the conventional clathrin box but also interacts with CHC. The novel W box of HDAg-L constitutes a new molecular target for anti-HDV-III therapeutics.

Peptide-Based Vaccines for Tuberculosis

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis. As a result of the coronavirus disease 2019 (COVID-19) pandemic, the global TB mortality rate in 2020 is rising, making TB prevention and control more challenging. Vaccination has been considered the best approach to reduce the TB burden. Unfortunately, BCG, the only TB vaccine currently approved for use, offers some protection against childhood TB but is less effective in adults. Therefore, it is urgent to develop new TB vaccines that are more effective than BCG. Accumulating data indicated that peptides or epitopes play essential roles in bridging innate and adaptive immunity and triggering adaptive immunity. Furthermore, innovations in bioinformatics, immunoinformatics, synthetic technologies, new materials, and transgenic animal models have put wings on the research of peptide-based vaccines for TB. Hence, this review seeks to give an overview of current tools that can be used to design a peptide-based vaccine, the research status of peptide-based vaccines for TB, protein-based bacterial vaccine delivery systems, and animal models for the peptide-based vaccines. These explorations will provide approaches and strategies for developing safer and more effective peptide-based vaccines and contribute to achieving the WHO’s End TB Strategy.

Cell-Penetrating Peptides-Based Liposomal Delivery System Enhanced Immunogenicity of Peptide-Based Vaccine against Group A Streptococcus

Peptide-based vaccine development represents a highly promising strategy for preventing Group A Streptococcus (GAS) infection. However, these vaccines need to be administered with the help of a delivery system and/or immune adjuvant. Cell-penetrating peptides (CPPs) have been used as a powerful tool for delivering various therapeutic agents, including peptides, as they can overcome the permeability barrier of cell membranes. Here, we used CPPs to deliver our lead lipopeptide-based vaccine (LCP-1). CPPs were anchored through a spacer to LCP-1-bearing multilamellar and unilamellar liposomes and administered to Swiss outbred mice. Tat47-57 conjugated to two palmitic acids via a (Gly)6 spacer (to form a liposome-anchoring moiety) was the most efficient system for triggering immune responses when combined with multilamellar liposomes bearing LCP-1. The immunostimulatory potential of a variety of other CPPs was examined following intranasal administration in mice. Among them, LCP-1/liposomes/Tat47-57 and LCP-1/liposomes/KALA induced the highest antibody titers. The antibodies produced showed high opsonic activity against clinically isolated GAS strains D3840 and GC2 203. The use of the CPP-liposome delivery system is a promising strategy for liposome-based GAS vaccine development.

Cell-penetrating Peptides: Efficient Vectors for Vaccine Delivery

Subunit vaccines are composed of pathogen fragments that, on their own, are generally poorly immunogenic. Therefore, the incorporation of an immunostimulating agent, e.g. adjuvant, into vaccine formulation is required. However, there are only a limited number of licenced adjuvants and their immunostimulating ability is often limited, while their toxicity can be substantial. To overcome these problems, a variety of vaccine delivery systems have been proposed. Most of them are designed to improve the stability of antigen in vivo and its delivery into immune cells. Cell-penetrating peptides (CPPs) are especially attractive component of antigen delivery systems as they have been widely used to enhance drug transport into the cells. Fusing or co-delivery of antigen with CPPs can enhance antigen uptake, processing and presentation by antigen presenting cells (APCs), which are the fundamental steps in initiating an immune response. This review describes the different mechanisms of CPP intercellular uptake and various CPP-based vaccine delivery strategies.