To develop vaccines capable of stimulating effective T-cell response, it is necessary to understand the factors contributing to the immunodominance of CTL epitopes. During viral infection, a large number of peptides are generated by processing of viral proteins in the proteasomes of infected cells. Only a small fraction of these peptides are presented by MHC class I molecules and subsequently recognized by specific CTL. This hierarchy of CTL response proved in animals [108] and in humans [104] is called immunodominance. There are several factors, which contribute to this phenomenon: HLA haplotype and its binding affinity to individual epitopes, repertoire of T-cell receptors, processing and presentation of viral peptides and interaction of CTL with antigen-presenting cells [109, 110] . It was shown that efficiency of epitope processing is one of the dominant factors affecting immunogenicity of multi-epitope vaccine [111, 112] .