Our priority is to develop a PrPSc-specific prion vaccine based on epitopes that are uniquely exposed upon misfolding. and specificity. leukotoxin (Lkt) as a carrier molecule for prion peptide epitopes. Leukotoxin has proven to be a potent immunogen capable of vectoring a variety of peptide self-epitopes such as GnRH.44-46 In addition, Lkt has considerable advantages in terms of cost, demonstrated safety and efficacy in livestock vaccines, and ease of production and licensing for use in veterinary vaccines. The Lkt platform has proven to be a safe and efficient platform to induce strong immune responses against various peptide-epitopes of PrP in a variety of species including mice, sheep, cattle, deer and elk. There are, however, limitations to the ability of the Lkt system to overcome self-tolerance. The initial efforts of our group to develop prion vaccines based on select epitopes of PrPC coupled to the Lkt carrier failed to induce epitope-specific immune responses. As such, the Lkt carrier is not a magic bullet for delivery of peptide self-epitopes. This highlights the importance of epitope optimization in Rabbit Polyclonal to C-RAF (phospho-Ser301) parallel with efforts to optimize formulation and delivery. While the Lkt carrier has proven valuable in the context of an injectable vaccine, it is not an ideal carrier for the development of an oral CWD vaccine. While an injected prion vaccine for farmed livestock is a priority, ultimately an oral vaccine will be required to manage the propagation and amplification of prions in wild cervid populations. Our group is investigating alternate carrier proteins that may be more appropriate for an oral prion vaccine. Disease-specific epitopes Therapeutic strategies based on the induction of immune responses to self-antigens are complicated by the potential for pathological consequences as a result of autoreactive antibodies. As GW4064 such there is appropriate concern over the induction of immune responses to PrPC, a widely expressed cell surface protein. These concerns are supported by the observation that PrPC-reactive antibodies induce extensive apoptosis of neurons in the brain and instigate inappropriate cell signal activation and cellular function of suppressor T-cell lymphocytes.47,48 The limited phenotypic consequences associated with genetic deletion of PrPC could be interpreted to predict minimal consequence of autoantibodies to PrPC. However changes to PrPC function as a consequence of antibody binding, particularly from a signaling perspective, may be distinct from the loss-of-function associated with genetic knockouts. Although it is reassuring that there have been no reports of significant pathology associated with the induction of PrPC-reactive immune responses, it is important to appreciate that antibodies to different GW4064 regions of PrPC may have distinct functional consequences for the target protein. This hypothesis is supported by the recent report of unique outcomes, some of which are pathological, as a result of antibody binding to distinct regions of PrPC.49 As such, the safety of autoreactive antibodies to PrPC is most appropriately evaluated on a case-by-case basis and, ideally, reactivity to PrPC is avoided altogether (Fig.?2). Open in a separate window Figure?2. Effect of conformation-specific immunotherapy on endogenous PrPC and PrPSc. Given the potential pathologies associated with the induction of immune responses to the native conformation of a self-protein, there is considerable appeal to selectively stimulating immune responses to the misfolded species. Conformation-specific immunotherapy is enabled by the unique molecular mechanism of prion diseases whereby the misfolding of PrPC into the pathological conformation results in the surface exposure of protein regions that are normally buried within the native structure. These DSEs represent highly attractive targets for vaccine development. To date, three PrP DSEs have been proposed. Their sequences and positioning with respect to the primary and tertiary structure GW4064 of PrPC are presented in (Fig.?3).50 While efforts are underway to translate each of these epitopes into vaccines, the scope of this review will be on efforts relating GW4064 to the YYR epitope. Open GW4064 in a separate window Figure?3. Mapping of PrPSc DSEs. Location of YML (green), YYR (orange), and RL (red) disease-specific epitopes within tertiary and primary structure of PrP. Adapted from James et al.50 YYR disease-specific epitope The first DSE of PrP was identified through biophysical investigations of the refolding of PrPC into PrPSc. Specifically, the increased solvent exposure of tyrosine residues as a consequence of misfolding was mapped.