Graduate Thesis Or Dissertation
Physical and Chemical Stability of Antigens and Emulsified Adjuvants for Filovirus Vaccines Public Deposited
Vaccine antigens experience physical and chemical instability in liquid formulations due to a variety of degradation processes that are often accelerated by elevated temperatures. In lyophilized formulations, the removal of bulk water helps to avoid or inhibit many of these degradation processes, thus significantly enhancing the stability of the vaccine. This may lead to less stringent cold-chain storage requirements, which offers facilitated distribution to resource-poor areas, especially in low- and middle-income countries (LMICs). The filoviruses Zaire ebolavirus, Marburg marburgvirus, and Sudan ebolavirus are some of the most lethal pathogens known and are endemic in hot, remote LMICs where poor access to electricity and healthcare infrastructure complicates vaccine distribution. To improve the thermostability of filovirus vaccines in order to potentially relax or eliminate cold-chain requirements, a trivalent filovirus vaccine was stabilized as a glassy solid through lyophilization.
Initial studies focused on formulating monovalent vaccines consisting of filovirus glycoproteins from each of the three species and subjecting the formulations to accelerated stability studies. Lyophilized filovirus glycoproteins retained quaternary protein structure and immunogenicity after high temperature incubation. Further work was completed to combine all three antigens and emulsion adjuvant into a dry single-vial presentation. Single-vial trivalent vaccines retained adjuvant properties after co-lyophilization and were found to elicit high antibody levels against all three antigens in mice and non-human primates (NHPs). A subsequent NHP study utilized single-vial formulations with a higher concentration of adjuvant, but these vaccines elicited lower neutralizing antibody titers in NHPs than previously tested formulations. Exploratory studies suggested that peroxide-induced oxidation of the glycoproteins was responsible for the diminished antibody responses in NHPs due to formulations containing higher amounts of adjuvant. Further studies probed the critical factors for colloidal stability during lyophilization using a model emulsion system. It was determined that slower cooling rates in conjunction with lower ratios of adjuvant to sucrose stabilized the emulsion during freezing.
Although no dry single-vial adjuvanted vaccines are commercially available, the work presented in this thesis provides evidence that lyophilization can be used to successfully stabilize vaccine formulations containing emulsion adjuvants.
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