Comparison of peptide–major histocompatibility complex tetramers and dextramers for the identification of antigen‐specific T cells

Summary Fluorochrome‐conjugated peptide–major histocompatibility complex (p MHC ) multimers are widely used for flow cytometric visualization of antigen‐specific T cells. The most common multimers, streptavidin–biotin‐based ‘tetramers’, can be manufactured readily in the laboratory. Unfortunately, there are large differences between the threshold of T cell receptor ( TCR ) affinity required to capture p MHC tetramers from solution and that which is required for T cell activation. This disparity means that tetramers sometimes fail to stain antigen‐specific T cells within a sample, an issue that is particularly problematic when staining tumour‐specific, autoimmune or MHC class II‐restricted T cells, which often display TCR s of low affinity for p MHC . Here, we compared optimized staining with tetramers and dextramers (dextran‐based multimers), with the latter carrying greater numbers of both p MHC and fluorochrome per molecule. Most notably, we find that: (i) dextramers stain more brightly than tetramers; (ii) dextramers outperform tetramers when TCR –p MHC affinity is low; (iii) dextramers outperform tetramers with p MHC class II reagents where there is an absence of co‐receptor stabilization; and (iv) dextramer sensitivity is enhanced further by specific protein kinase inhibition. Dextramers are compatible with current state‐of‐the‐art flow cytometry platforms and will probably find particular utility in the fields of autoimmunity and cancer immunology.