Development of a Thermostable Tuberculosis Vaccine Candidate Suitable for Pulmonary Delivery through Particle Engineering

• Author / Creator

  Gomez, Mellissa

• Tuberculosis (TB) is a preventable and curable highly infectious respiratory disease that is responsible for the deaths of approximately 1.5 million people every year. However, vaccination programs are hindered by refrigeration requirements for vaccines during transportation and storage. Additionally, research has shown that administration of vaccines via inhalation may be more effective at conferring protection against respiratory illnesses. A promising subunit TB vaccine candidate, ID93+GLA-SE, consisting of an antigen, ID93, and adjuvant system, GLA-SE, has been developed; however, the vaccine candidate is stable only under refrigeration. This thesis details how particle engineering via spray drying was implemented to convert ID93+GLA-SE into a thermostable, inhalable dry powder format suitable for global health applications.
  First, ID93+GLA-SE was converted into a thermostable dry powder composed of many microparticles via spray drying. In silico modelling was used to develop an appropriate formulation and calculate spray drying processing parameters to effectively encapsulate and stabilize the vaccine nanoemulsion droplets within a trehalose matrix. A one-year stability study was conducted, with powders held at multiple temperatures up to 40 °C. Physical stability of the powder was assessed in terms of particle morphology, moisture content, and solid state. Vaccine chemical properties were assessed in terms of nanoemulsion droplet size, adjuvant system concentration, antigen presence, pH, and osmolality. Results showed that overall physical stability was maintained for all storage temperatures. Nanoemulsion droplet size, oil component of the adjuvant system, pH, and osmolality were within the preset stability criteria. Similarly, the antigen was shown to be present even after one year of storage at 40 °C. The agonist showed 17-25% and 56-58% loss after 13.5 months of storage at 25 and 40 °C, respectively; however, high temperature degradation results were comparable to a lyophilized presentation of the vaccine candidate.
  Second, an inhalable presentation of the spray-dried vaccine was investigated. Leucine, pullulan, and trileucine were explored as dispersibility enhancing agents. Six inhalable candidates were designed and spray-dried. The aerosol performance results showed that the leucine- and trileucine- containing candidates improved aerosol performance (32% and 33-34% lung dose, respectively) as compared to a formulation without a dispersibility enhancer (18% lung dose). The pullulan- containing candidates did not improve the aerosol performance significantly (19-25% lung dose). Chemical analysis indicated that the leucine- and pullulan-containing formulations did not effectively preserve vaccine integrity. These results established trileucine as the lead dispersibility enhancing agent.
  Third, the lead inhalable vaccine candidate containing trileucine was spray-dried and placed on a seven-month stability study at storage temperatures up to 50 °C. A trileucine-free version of the formulation was also spray-dried and included in the study for comparison. The physical stability of both powder formulations was assessed in terms of particle morphology, solid state, moisture content, and aerosol performance. Results showed that both spray-dried formulations maintained particle morphology, solid state, and moisture content for the duration of the stability study at all temperatures. However, aerosol performance for the trileucine-free vaccine powder decreased when it was stored at high temperatures. By comparison, the trileucine-containing formulation was shown to maintain aerosol performance even after high-temperature storage.
  Finally, due to the overall success in spray drying the ID93+GLA-SE vaccine candidate, preclinical trials with mice were planned to assess immunogenicity and protective efficacy. The preclinical trials were designed to evaluate administration of the inhalable candidate through both the intranasal and pulmonary routes. The spray-dried inhalable vaccine was adapted to be suitable for inhalation by mice in order to complete these trials. Two formulations were developed, one designed for deposition in the nose only, and the other designed for deposition in the nose and lungs. Characterization confirmed that the mouse-inhalable vaccine candidates retained key vaccine properties post-spray drying. An aerosol delivery system was also designed and characterized for use in the preclinical trials for both administration routes. Processing conditions were optimized such that approximately 10% and 44% of the maximum possible dose could be delivered, respectively. However, results showed that even with optimized parameters, the system would be unable to deliver the target powder dose without placing restrained mice under considerable stress. It is recommended that the antigen and agonist concentrations be increased to achieve target delivered dose.

• Subjects / Keywords

  • spray drying
  • tuberculosis
  • vaccine
  • inhalable
  • thermostable
  • particle engineering
  • microparticles
  • nanoemulsion

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-ym0a-p454

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.