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.

Current status of a unique vaccine preventing pregnancy.

The ability of a vaccine linking beta hCG to a carrier to generate antibodies against hCG, its reversibility and safety was established by Phase I clinical trials conducted in India, Finland, Sweden, Chile and Brazil. Employing a hetero-species dimer (beta hCG-αoLH) linked to tetanus toxoid further improved the immunogenicity of the vaccine. Phase II clinical trials showed that anti-hCG titres above 50 ng/ml prevented pregnancy of sexually active fertile women without derangement of ovulation and menstrual regularity. On decline of antibodies, women conceived again to give birth to normal progeny. A genetically engineered vaccine consisting of beta hCG linked to B subunit of heat labile enterotoxin of E. coli has been made. It is expressed as DNA as well as protein. Priming with DNA followed by protein version of the vaccine generates very high titres against hCG in mice. Extensive toxicology studies in 2 species of rodents, and marmosets have shown complete safety of the vaccine. The vaccine is cleared for Clinical trials by the National Review committee on Genetic Manipulation and Drugs Controller General of India.

Advances in development of a contraceptive vaccine against human chorionic gonadotropin.

INTRODUCTION: There is continuing need for contraceptives. According to World Health Organization, 210 million pregnancies occur each year, out of which some 80 million are unintended. A vaccine offering privacy and periodic intake would be an attractive proposition. AREAS COVERED: The article is a brief review of three vaccines developed against human chorionic gonadotropin (hCG) with progressively better attributes. Clinical trials have proven in more than one country the complete safety and reversibility of the anti-hCG vaccine(s) in women. Vaccination does not entail any disturbance in levels of reproductive tract hormones of the woman or any disturbance in menstrual regularity and bleeding profiles. Phase II clinical trials show the effective prevention of pregnancy in sexually active women of proven fertility. A recombinant vaccine amenable to industrial production has been developed; it induces substantially higher antibody titers in mice of four different genetic strains than those required to prevent pregnancy in women. Rigorous toxicology studies have been completed on this vaccine in rodents and marmosets. EXPERT OPINION: This unique vaccine, requiring periodic intake and demonstrating no impairment of ovulation, hormonal profiles and menstrual regularity, is on the verge of final clinical trials under the aegis of the Indian Council of Medical Research and should be a valuable addition to the available contraceptives.

Priming with DNA Enhances Considerably the Immunogenicity of hCG ß-LTB Vaccine.

PROBLEM: Necessity to elicit antibody response above the protective threshold titres by sexually active women immunized to prevent pregnancy. METHOD OF STUDY: Recombinant hCGß-LTB vaccine expressed as both DNA and protein. Balb C mice employed for testing immunogenicity. RESULTS: Necessity to give three primary injections of the vaccine to elicit proper antibody response. Immunization twice with DNA form of the vaccine at fortnightly interval followed by the protein elicits a distinctly higher antibody response than proteinic vaccine alone. Antibodies generated are bio-effective against hCG. CONCLUSION: Immunization with the DNA form of the recombinant hCGß-LTB vaccine twice at fortnightly interval followed by the proteinic form of the vaccine induces distinctly higher antibody response.

Development of a recombinant hCG-specific single chain immunotoxin cytotoxic to hCG expressing cancer cells.

A large number of cancers express human chorionic gonadotropin (hCG) or its subunits ectopically. Patients harboring such cancers have poor prognosis and adverse survival. PiPP is a monoclonal antibody of high affinity and specificity for hCGß/hCG. Work was carried out to develop a PiPP based recombinant immunotoxin for the immunotherapy of hCG expressing cancers. Recombinant PiPP antibody was constructed in scFv format in which gene encoding the VH and VL domains were joined through a linker. This scFv gene was fused to the gene expressing Pseudomonas exotoxin (PE38), and cloned in a Escherichia coli based expression vector under the control of strong bacteriophage T7 promoter. Immunotoxin conjugating scFv(PiPP) and PE38, was expressed in E. coli as recombinant protein. Recombinant PiPP immunotoxin was purified from the bacterial cell lysate and tested for binding and killing of hCGß expressing lymphoma, T-lymphoblastic leukemia and lung carcinoma cells in vitro. Immunotoxin showed nearly 90% killing on the cells. This is the first ever report on recombinant immunotoxin for binding and cytotoxicity to hCG expressing cancer cells, and thus can be a potential candidate for the immunotherapy of hCG expressing cells.