Evaluation of the stability of a spray-dried tuberculosis vaccine candidate designed for dry powder respiratory delivery

Particle engineering via spray drying was used to develop a dry powder presentation of an adjuvanted tuberculosis vaccine candidate. This presentation utilizing a trileucine-trehalose excipient system was designed to be both thermostable and suitable for respiratory delivery. The stability of the spray-dried vaccine powder was assessed over one year at various storage temperatures (-20, 5, 25, 40, 50 °C) in terms of powder stability, adjuvant stability, and antigen stability.

Highlights

Liquid vaccines can be spray-dried into a dry powder to enhance thermostability.

These dry vaccine powders can be inhaled directly into the lungs.

The addition of trileucine greatly improves the vaccine powder lung dose.

Lung dose was maintained even after 1 year of storage at 40 °C.

A formulation without trileucine was included as a control. The results showed that the interior particle structure and exterior particle morphology of the powder was maintained for one year at 40 °C, while the control case exhibited a small extent of particle fusing under the same storage conditions. Moisture content was maintained, and powder solid state remained amorphous for all storage temperatures. Aerosol performance was assessed with a commercial dry powder inhaler in combination with a human mouth-throat model. The emitted dose and lung dose were maintained for all samples after one year at temperatures up to 40 °C. Nanoemulsion size and oil content of the adjuvant system were maintained after one year at temperatures up to 40 °C, and the agonist content was maintained after one year at temperatures up to 25 °C.

The antigen was completely degraded in the control formulation at seven months of storage at 40 °C; by contrast, 45% of the antigen was still present in the trehalose-trileucine formulation after one year of storage at 50 °C. Comparatively, the antigen was completely degraded in a liquid sample of the vaccine candidate after only one month of storage at 37 °C. The spray-dried trehalose-trileucine vaccine powder clearly maintained its inhalable properties after one year’s storage at high temperatures and improved overall thermostability of the vaccine.

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Article information: Mellissa Gomez, Joseph McCollum, Hui Wang, Shital Bachchhav, Isobel Tetreau, Alana Gerhardt, Chris Press, Ryan M. Kramer, Christopher B. Fox, Reinhard Vehring, Evaluation of the stability of a spray-dried tuberculosis vaccine candidate designed for dry powder respiratory delivery,
Vaccine, 2021. https://doi.org/10.1016/j.vaccine.2021.07.002.