Combination nanovaccines against respiratory pathogens
Evidence of mass pandemic plagues dates back to the earliest recorded history, with the Book of Exodus describing plagues inflicted upon Egypt that devastated citizens and livestock. Since then, countless plagues have been recorded, including the Plague of Athens (430-416 BCE), Justinian’s plague (541-542 AD), and the Black Death (1346-1352 AD), which are responsible for the deaths of hundreds of millions of people throughout history.
Among the deadliest pathogens are Yersinia pestis, the causative agent of the plague, and Bacillus anthracis, the causative agent of anthrax. Y. pestis is responsible for Justinian’s plague and the Black Death and is estimated to have accounted for over 200 million human deaths throughout history, while B. anthracis has been suggested to have caused the Plague of Athens, which wiped out 100,000 people, a quarter of the city’s population, over a three year period. Beyond their dark past, both of these pathogens have been used as biological weapons to cause harm to civilians and military personnel, with the most recent being the 9/11 attacks in the United States in 2001, in which 22 citizens were infected with B. anthracis spores that were delivered in letters in the mail, resulting in the deaths of five individuals. These pathogens are highly lethal if inhaled, with mortality rates approaching 100% if untreated after only a few days.
Unfortunately, there is no FDA-approved vaccine against Y. pestis. There is an FDA-approved AVA vaccine against B. anthracis, the AVA vaccine, however it has limitations. The AVA vaccine requires multiple immunizations to achieve purported protective immunity, and hence is insufficient in the event of mass exposure to civilian populations and warfighters of B. anthracis. In addition, the AVA vaccine has been reported to induce injection site reactogenicity due to its aluminum-based alhydrogel adjuvant, and there are concerns of thermal stability with proteins adsorbed to aluminum-based adjuvants.
In addition to these deadly pathogens, human respiratory syncytial virus (RSV) is a devastating disease that is the leading cause of severe acute lower respiratory tract disease in infants and young children worldwide, accounting for up to 70% of hospitalized bronchiolitis cases in industrialized countries. Globally, there are an estimated 33 million new episodes of HRSV-associated disease in children under five years of age with more than 100,000 resultant deaths. Severe RSV infection has been linked with the development and exacerbation of recurrent wheezing and asthma, and is a predisposing factor to the development of otitis media. RSV infection has a devastating, worldwide impact on human health and despite significant efforts, no approved vaccine currently exists for use against the disease in humans. Hence, there is a need to design and develop vaccines against RSV that are capable of providing robust immune responses against this pathogen and reduce the prevalence of this disease.
One final consideration for vaccine design against such dangerous respiratory pathogens is thermal stability. As all World Health Organization prequalified vaccines currently require refrigeration, obviating the cold chain would enable delivery of vaccines to refrigeration-scarce zones around the world, reduce cost, and improve stockpiling capabilities. Therefore, it is imperative to develop vaccines that are capable of eliciting rapid and long-lived protective immunity to both civilian and warfighters, ideally in a single dose, as well as obviate the cold chain.
Polyanhydride nanoparticle-based vaccines (i.e., nanovaccines) are a promising next-generation vaccine platform for safe and effective single-dose vaccines against such pathogens. These materials are safe and biocompatible, have demonstrated adjuvant properties, enable dose sparing, and have enhanced shelf stability of labile proteins. These characteristics are needed for the next generation of vaccine formulations, which will allow for the production of safe and highly effective vaccines that can be administered in a single dose, have reduced cost and the ability to obviate the cold chain for vaccine stockpiling.
The goal of the work described in this thesis is the design and evaluation of a single dose combination-adjuvant polyanhydride-based nanovaccine formulation that is capable of providing rapid and long-lived protective immunity against multiple respiratory pathogens, including the inhaled forms of Y. pestis and B. anthracis, pneumonic plague and inhalation anthrax, respectively, as well as against RSV. This was achieved by encapsulating the Y. pestis fusion protein F1-V and B. anthracis protective antigen (PA) into polyanhydride nanoparticles, which were co-administered with the cyclic di-nucleotide adjuvant cyclic di-guanosine monophosphate, and evaluating the protective efficacy following lethal intranasal (IN) challenge of the respective fully virulent pathogens. For RSV, the RSV-specific post-fusion proteins, F and G, were encapsulated into polyanhydride nanoparticles and administered intranasally in a neonatal calf model in order to evaluate the protective efficacy of IN RSV challenge. In addition, this report describes the rational design of polyanhydride nanovaccines for enhanced adjuvanticity and shelf stability.