Bovine T cells preferentially recognize non-viral spacer epitopes in a putative FMDV vaccinal peptide

In a group of immunized cattle with a variety of MHC class II types, T-cell responses were detected to a synthetic peptide (FMDV15) proposed as a basis for a vaccine against foot-and-mouth disease. This peptide combines the loop region of VP1 with the C-terminal sequence connected by a spacer (PPS). Two major immunodominant regions of FMDV15 for bovine T cells were detected, one within the loop region and the other around the spacer. A substantial proportion of the T-cell response to FMDV15 was directed to the spacer region in 5/12 animals, and in vitro generation of FMDV15-specific T cells preferentially selected for spacer-specific T cells. This pattern of response was associated with a particular MHC class II type which is very common in cattle. Focusing of the T-cell response to non-native virus epitopes may explain why FMDV15 is inefficient at inducing protection.