Low binding capacity of murine tetramers mutated at residue 227 does not preclude the ability to efficiently activate CD8+ T lymphocytes

Bi-specific MHC heterodimers for characterization of cross-reactive T cells

T cell cross-reactivity describes the phenomenon whereby a single T cell can recognize two or more different peptide antigens presented in complex with MHC proteins. Cross-reactive T cells have previously been characterized at the population level by cytokine secretion and MHC tetramer staining assays, but single-cell analysis is difficult or impossible using these methods. In this study, we describe development of a novel peptide-MHC heterodimer specific for cross-reactive T cells. MHC-peptide monomers were independently conjugated to hydrazide or aldehyde-containing cross-linkers using thiol-maleimide coupling at cysteine residues introduced into recombinant MHC heavy chain proteins. Hydrazone formation provided bi-specific MHC heterodimers carrying two different peptides. Using this approach we prepared heterodimers of the murine class I MHC protein H-2K(b) carrying peptides from lymphocytic choriomeningitis virus and vaccinia virus, and used these to identify cross-reactive CD8+ T cells recognizing both lymphocytic choriomeningitis virus and vaccinia virus antigens. A similar strategy could be used to develop reagents to analyze cross-reactive T cell responses in humans.

Analytical performance of a standardized single-platform MHC tetramer assay for the identification and enumeration of CMV-specific CD8+ T lymphocytes

Major histocompatibility complex (MHC) multimers that identify antigen-specific T cells, coupled with flow cytometry, have made a major impact on immunological research. HLA Class I multimers detect T cells directed against viral, tumor, and transplantation antigens with exquisite sensitivity. This technique has become an important standard for the quantification of a T cell immune response. The utility of this method in multicenter studies, however, is dependant on reproducibility between laboratories. As part of a clinical study using a standardized two-tube three-color single-platform method, we monitored and characterized performance across multiple sites using tetramers against the T cell receptors (TCR) specific for MHC Class I, A*0101--VTEHDTLLY, A*0201--NLVPMVATV and B*0702--TPRVTGGGAM CMV peptides. We studied the analytical performance of this method, focusing on reducing background, maximizing signal intensity, and ensuring that sufficient cells are enumerated to provide meaningful statistics. Inter and intra-assay performance were assessed, which included inherent variability introduced by shipping, type of flow cytometer used, protocol adherence, and analytical interpretation across a range of multiple sample levels and specificities under routine laboratory testing conditions. Using the described protocol, it is possible to obtain intra- and interlab CV's of <20%, with a functional sensitivity for absolute tetramer counts of 1 cell/microL and 0.2% tetramer+ percent for A*0101, A*0201, and B*0702 alleles. The standardized single-platform MHC tetramer assay is simple, rapid, reproducible, and useful for assessing CMV-specific T cells, and will allow for reasonable comparisons of clinical evaluations across multiple centers at clinically relevant thresholds (2.0-10.0 cells/microL).