Characterization of the dengue virus envelope glycoprotein expressed in Pichia pastoris

Yeast-Based Virus-like Particles as an Emerging Platform for Vaccine Development and Delivery

Virus-like particles (VLPs) are empty, nanoscale structures morphologically resembling viruses. Internal cavity, noninfectious, and particulate nature with a high density of repeating epitopes, make them an ideal platform for vaccine development and drug delivery. Commercial use of Gardasil-9 and Cervarix showed the usefulness of VLPs in vaccine formulation. Further, chimeric VLPs allow the raising of an immune response against different immunogens and thereby can help reduce the generation of medical or clinical waste. The economically viable production of VLPs significantly impacts their usage, application, and availability. To this end, several hosts have been used and tested. The present review will discuss VLPs produced using different yeasts as fermentation hosts. We also compile a list of studies highlighting the expression and purification of VLPs using a yeast-based platform. We also discuss the advantages of using yeast to generate VLPs over other available systems. Further, the issues or limitations of yeasts for producing VLPs are also summarized. The review also compiles a list of yeast-derived VLP-based vaccines that are presently in public use or in different phases of clinical trials.

Dengue Virus

Dengue virus (DENV) belongs to the family Flaviviridae, genus Flavivirus. It is a single-stranded positive-sense ribonucleic acid virus with 10,700 bases. The genus Flavivirus includes other arthropod borne viruses such as yellow fever virus, West Nile virus, Zika virus, tick-borne encephalitis virus. It infects ~50–200 million people annually, putting over 3.6 billion people living in tropical regions at risk and causing ~20,000 deaths annually. The expansion of dengue is attributed to factors such as the modern dynamics of climate change, globalization, travel, trade, socioeconomics, settlement, and also viral evolution. There are four antigenically different serotypes of DENV based on the differences in their viral structural and nonstructural proteins. DENV infection causes a spectrum of illness ranging from asymptomatic to dengue fever to severe dengue shock syndrome. Infection with one serotype confers lifelong immunity against that serotype, but heterologus infection leads to severe dengue hemorrhagic fever due to antibody-dependent enhancement. Diagnosis of dengue infections is based mainly on serological detection of either antigen in acute cases or antibodies in both acute and chronic infection. Viral detection and real-time PCR detection though helpful is not feasible in resource poor setup. Treatment of dengue depends on symptomatic management along with fluid resuscitation and may require platelet transfusion. Although vaccine development is in late stages of development, developing a single vaccine against four serotypes often causes serious challenges to researchers; hence, the main stay of prevention is vector control and management.

Virus-Like Particle Systems for Vaccine Development against Viruses in the Flaviviridae Family

Viruses in the Flaviviridae family are important human and animal pathogens that impose serious threats to global public health. This family of viruses includes emerging and re-emerging viruses, most of which are transmitted by infected mosquito or tick bites. Currently, there is no protective vaccine or effective antiviral treatment against the majority of these viruses, and due to their growing spread, several strategies have been employed to manufacture prophylactic vaccines against these infectious agents including virus-like particle (VLP) subunit vaccines. VLPs are genomeless viral particles that resemble authentic viruses and contain critical repetitive conformational structures on their surface that can trigger the induction of both humoral and cellular responses, making them safe and ideal vaccine candidates against these viruses. In this review, we focus on the potential of the VLP platform in the current vaccine development against the medically important viruses in the Flaviviridae family.

Recent Developments in Recombinant Protein-Based Dengue Vaccines

Recombinant proteins are gaining enormous importance these days due to their wide application as biopharmaceutical products and proven safety record. Various recombinant proteins of therapeutic and prophylactic importance have been successfully produced in microbial and higher expression host systems. Since there is no specific antiviral therapy available against dengue, the prevention by vaccination is the mainstay in reducing the disease burden. Therefore, efficacious vaccines are needed to control the spread of dengue worldwide. Dengue is an emerging viral disease caused by any of dengue virus 1-4 serotypes that affects the human population around the globe. Dengue virus is a single stranded RNA virus encoding three structural proteins (capsid protein, pre-membrane protein, and envelope protein) and seven non-structural proteins (NS1, NS2a, NS2b, NS3, NS4a, NS4b, NS5). As the only licensed dengue vaccine (Dengvaxia) is unable to confer balanced protection against all the serotypes, therefore various approaches for development of dengue vaccines including tetravalent live attenuated, inactivated, plasmid DNA, virus-vectored, virus-like particles, and recombinant subunit vaccines are being explored. These candidates are at different stages of vaccine development and have their own merits and demerits. The promising subunit vaccines are mainly based on envelope or its domain and non-structural proteins of dengue virus. These proteins have been produced in different hosts and are being investigated for development of a successful dengue vaccine. Novel immunogens have been designed employing various strategies like protein engineering and fusion of antigen with various immunostimulatory motif to work as self-adjuvant. Moreover, recombinant proteins can be formulated with novel adjuvants to enhance the immunogenicity and thus conferring better protection to the vaccinees. With the advent of newer and safer host systems, these recombinant proteins can be produced in a cost effective manner at large scale for vaccine studies. In this review, we summarize recent developments in recombinant protein based dengue vaccines that could lead to a good number of efficacious vaccine candidates for future human use and ultimately alternative dengue vaccine candidates.

Viral glycoproteins: biological role and application in diagnosis

The viruses that infect humans cause a huge global disease burden and produce immense challenge towards healthcare system. Glycoproteins are one of the major components of human pathogenic viruses. They have been demonstrated to have important role(s) in infection and immunity. Concomitantly high titres of antibodies against these antigenic viral glycoproteins have paved the way for development of novel diagnostics. Availability of appropriate biomarkers is necessary for advance diagnosis of infectious diseases especially in case of outbreaks. As human mobilization has increased manifold nowadays, dissemination of infectious agents became quicker that paves the need of rapid diagnostic system. In case of viral infection it is an emergency as virus spreads and mutates very fast. This review encircles the vast arena of viral glycoproteins, their importance in health and disease and their diagnostic applications.