Lipidated brartemicin adjuvant p-C18Brar is a promising a,a'-trehalose 6,6'-dilipid for use in ovine pneumonia vaccines

Ovine pneumonia is a disease in sheep that is associated with major animal welfare issues and economic losses and for which there is no effective vaccine. We tested the adjuvanticity of our most promising a,a'-trehalose 6,6'-glycolipids, lipidated brartemicin adjuvants p-C18Brar (3), o-C18Brar (4), and amide-TDB (5) in vaccines for ovine pneumonia containing Mannheimia haemolytica and Mycoplasma ovipneumoniae whole cell antigens. p-C18Brar (3) and o-C18Brar (4) led to strong antigen-specific IgG antibody titres that were better than those elicited by the prototypical a,a'-trehalose glycolipid trehalose dibehenate (TDB, 2) and amide-TDB (5). T-cell responses, as determined by measuring IFN-gamma and IL-17A production from antigen-stimulated whole blood cultures, revealed that p-C18Brar (3), but not TDB (2), o-C18Brar (4), or amide-TDB (5), led to statistically significant increases in these cytokines. We then optimised the synthesis of p-C18Brar (3) (3 steps, 72% overall yield) and undertook further vaccination studies to determine the optimal dose of p-C18Brar (3) that would be used for future large scale ovine pneumonia field trials. At a dose of 3.75 mg per vaccine, the adjuvanticity of p-C18Brar (3), as measured by levels of anti-M. haemolytica IgG antibody and T-cell responses (IFN-gamma and IL-17A) was better than that elicited by the commercially available adjuvant Quil-A, and had reduced reactogenicity. Taken together, the excellent immunological profile of p-C18Brar (3) and its ease and efficiency of synthesis makes it an attractive adjuvant for use in veterinary vaccines.