Sources of diversity in T cell epitope discovery.

CD8-positive T cells respond to small antigenic peptide fragments presented on class I major histocompatibility complexes (MHCs). Those specific T cell epitopes capable of precipitating a cellular immune response are either derived from (altered) self (i.e. they are autoimmune- or cancer-associated) or come from foreign sources (i.e. they are pathogen-associated). Identification of T cell epitopes provides elementary information that can be employed in technologies that monitor and predict the likely outcome of an immune response, as well as in therapeutic and vaccine development efforts. The coexistence between host and pathogen has largely driven the diversification of both their systems of immune surveillance and their antigenic determinants, respectively. In this review, we discuss the multitude of factors that introduce diversity to the T cell response from both sides of the host-pathogen interaction. Furthermore, we provide an overview of a variety of commonly employed methods and tools to characterize class I MHC restricted antigen presentation and recent endeavors towards the harmonization of reporting data concerning T cell responses.