Discovery of CD8 + T cell epitopes in Chlamydia trachomatis infection through use of caged class I MHC tetramers

Abstract

Class I MHC tetramers allow direct phenotypic identification of CD8⁺ T cell populations, but their production remains laborious. A peptide exchange strategy that employs class I MHC products loaded with conditional ligands (caged MHC molecules) provides a fast and straightforward method to obtain diverse arrays of class I MHC tetramers and facilitates CD8⁺ T cell epitope discovery. Here, we describe the development of photocleavable analogs of the FAPGNYPAL (SV9) epitope that bind H-2K^b and H-2D^b with full retention of their structural and functional integrity. We ranked all possible H-2K^b octameric and H-2D^b nonameric epitopes that span the genome of Chlamydia trachomatis and prepared MHC tetramers from ≈2,000 of the highest scoring peptides by replacement of the SV9 analog with the peptide of choice. The resulting 2,000-member class I MHC tetramer array allowed the discovery of two variants of an epitope derived from polymorphic membrane protein I (PmpI) and an assessment of the kinetics of emergence and the effector function of the corresponding CD8⁺ T cells.