A stable live bacterial vaccine.

Area of Science:

• Vaccinology
• Microbial Pathogenesis
• Biotechnology

Background:

• Thermal instability of vaccines necessitates complex cold-chain logistics, increasing costs and limiting accessibility.
• Existing dry-form vaccines lack long-term stability at elevated temperatures, hindering global distribution.
• Recombinant live attenuated Listeria monocytogenes (Lm) vaccines offer potential but require improved formulation for stability.

Purpose of the Study:

• To develop a thermostable dry powder formulation of a recombinant Lm vaccine expressing a Francisella tularensis antigen.
• To assess the long-term viability and antigenicity of the spray-dried Lm vaccine under various storage conditions.

Main Methods:

• Spray-drying technique was employed to formulate the Lm vaccine using stabilizing excipients (sugars and an amino acid).
• Viability of the dry vaccine powder was evaluated after storage at ambient room temperature and 40°C.
• In vitro antigenicity was confirmed using dendritic cell infection assays to detect the expressed protective antigen.

Main Results:

• The spray-dried Lm vaccine powder demonstrated minimal viability loss after over a year at ambient temperature and 180 days at 40°C.
• High-temperature stability was attributed to an inert atmosphere and removal of oxygen free radicals.
• In vitro studies confirmed the antigenicity of the vaccine derived from the spray-dried formulation.

Conclusions:

• Spray-drying, combined with appropriate excipients and storage, yields a thermostable dry vaccine.
• This formulation strategy offers a cost-effective solution for producing, storing, and transporting heat-sensitive vaccines.
• The approach holds significant promise for improving vaccine accessibility, particularly in resource-limited regions.