Direct visualization of antigen-specific T cells using peptide-MHC-class I tetrameric complexes.

Peptide-major histocompatibility complexes (MHC) class I tetrameric complexes ("tetramers") are proving invaluable as fluorescent reagents for enumeration, characterization, and isolation of peptide-specific T cells and have afforded many advantages over previous techniques, particularly the ability to directly quantify and phenotype antigen-specific T cells with minimal in vitro manipulation. Recently, various technical peculiarities of tetramers have led to modifications within this important immunoassay. The current manuscript details potential pitfalls and provides guidance for interpretation of results.