In contrast to inbred mice, the search for CTL epitopes suitable for development of CTL epitope-based vaccine in humans is more complicated [113] . The main reason is that HLA genes in humans are extremely polymorphic. Therefore, the knowledge of HLA restriction in population, which will be vaccinated, is necessary. The complexity of HLA molecules could be reduced by clustering them into sets of molecules that bind largely overlapping peptides. Such clustering was introduced by Sette and Sidney in 1999. They defined HLA supertypes as a set of HLA molecules that have similar peptide binding motifs and overlapping peptide binding repertoires [117] . Nine different supertypes (A1, A2, A3, A24, B7, B27, B44, B58, B62) were defined on the basis of their specifity for the main anchor positions of presented peptides. Later, other three HLA I supertypes (A26, B8 and B39) were described by Lund et al. [118] . Recent analysis provided an update of HLA I alleles classification into supertypes and is expected to facilitate epitope identification and vaccine design studies [119] .