At present, effective vaccination strategies for the prevention and control of PRRSV infection are not available. Vaccines based on inactivated PRRSV virus have been ineffective at inducing protective immune responses. Live-attenuated PRRSV vaccines can provide protection against this pathogen, but have been observed to revert to virulence [5] , restricting the application of this vaccination approach. The rational development of future PRRSV vaccines will necessitate a systematic understanding of the protective humoral and cellular immune responses that occur during PRRSV infection, and should aim to induce a broad immune responses that accommodates the plasticity of the major antigenic sites. Recent research has indicated that cell-mediated immunity may play a very important role in the clearance of PRRSV [6] . Major histocompatibility complex (MHC) I restricted cytotoxic T lymphocytes (CTLs) can kill virus-infected cells and eliminate potential sources of new virus [7] . Hence, identification of CTL epitopes is crucial in the design of synthetic vaccines, and a number of studies have successfully identified pathogen-derived T cell epitopes [8] [9] [10] [11] .