Enhanced protection against tuberculosis (TB) has been shown by several groups using a human and chimpanzee adenoviral-vectored TB vaccine, however, cryopreservation is required for the long-term stability and efficacy of these vaccine formulations. This can be quite difficult, especially in resource-poor countries which are in most need of these vaccines. To address this issue, doctoral student Sam Afkhami and colleagues, were able to utilize a spray drying process that demonstrated the thermostability and in vivo immunogenicity of spray dried human and chimpanzee adenoviral-vectored tuberculosis vaccines. They showed that the spray dried powders containing the vaccines had the chemical and morphological properties desired for long-term thermostability and vaccination. Following in vivo vaccination in mice, the spray dried vaccines were as immunogenic as the cryopreserved liquid vaccines, as levels of antigen-specific CD8+ T cells were comparable between the two groups in the spleen, blood and lung tissue. Remarkably, unlike the cryopreserved liquid vaccines, which lost their immunogenicity when stored at ambient temperature (20°C) for 30 days, the spray dried vaccines retained immunogenicity in vivo even when stored at ambient temperature for up to 90 days; thus, demonstrating the thermostability of the spray dried vaccines. This work has tremendous implications in regard to the development of spray drying technologies, which can generate thermally stable viral-vectored vaccines for clinical applications.

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