Differential Cultivation of Induces Changes in the Immune Response to and Protective Efficacy of Whole Cell-Based Inactivated Vaccines.

() is a category A biothreat agent for which there is no Food and Drug Administration-approved vaccine. can survive in a variety of habitats with a remarkable ability to adapt to changing environmental conditions. Furthermore, expresses distinct sets of antigens (Ags) when inside of macrophages (its host) as compared to those grown with Mueller Hinton Broth (MHB). However, in contrast to MHB-grown grown in Brain-Heart Infusion (BHI) more closely mimics the antigenic profile of macrophage-grown . Thus, we anticipated that when used as a vaccine, BHI-grown would provide better protection compared to MHB-grown , primarily due to its greater antigenic similarity to circulating inside the host (macrophages) during natural infection. Our investigation, however, revealed that inactivated (i) grown in MHB (iMHB) exhibited superior protective activity when used as a vaccine, as compared to i grown in BHI (iBHI). The superior protection afforded by i-MHB compared to that of i-BHI was associated with significantly lower bacterial burden and inflammation in the lungs and spleens of vaccinated mice. Moreover, i-MHB also induced increased levels of specific IgG. Further evaluation of early immunological cues also revealed that i-MHB exhibits increased engagement of Ag-presenting cells including increased i binding to dendritic cells, increased expression of costimulatory markers, and increased secretion of pro-inflammatory cytokines. Importantly, these studies directly demonstrate that growth conditions strongly impact vaccine efficacy and that the growth medium used to produce whole cell vaccines to must be a key consideration in the development of a tularemia vaccine.