Method for assessing IFN-γ responses in guinea pigs during TB vaccine trials

Aims:  We sought to develop a new method that enables the assessment of the immune response of guinea pigs during TB vaccine evaluation studies, without the need to cull or anaesthetize animals. Method and Results:  Guinea pigs were vaccinated with five different formulations of oral BCG. One week prior to challenge with Mycobacterium bovis, blood (50–200 μl) was taken from the ears of vaccinated subjects. Host RNA was isolated and amplified following antigenic restimulation of PBMCs for 24 h with 30 μg of bovine PPD. The up- or down-regulation of γ-interferon (IFN-γ), a key cytokine involved in protection against tuberculosis, was assessed using real-time PCR. The relative expression of prechallenge IFN-γ mRNA in the vaccinated groups (n = 5) correlated (P < 0·001) with protection against M. bovis challenge. Conclusion:  We have demonstrated that it is possible to take blood samples and track IFN-γ responses in guinea pigs that then go on to be exposed to M. bovis, thus providing prechallenge vaccine uptake information. Significance and Impact of the Study:  This methodology will also be applicable for tracking the immune responses of vaccinated guinea pigs over time that then go on to be challenged with M. tuberculosis during human TB vaccine evaluation studies.