J?rgen Sch?ller, CSO
Immudex, Fruebjergvej 3, 2100 Copenhagen, Denmark

Reliable monitoring of cellular immune responses is important in vaccine and immunotherapeutic development. Flow analysis using conventional MHC multimers like Tetramers and Pentamers has made a great impact on this field, enabling enumeration and phenotypic characterization of antigen-specific T cells. However, it is often difficult to obtain well-separated, distinct negative and positive cell populations when attempting to detect T cells of low affinity for the MHC multimer.
The use of MHC Dextramers can overcome these problems, and provide reliable detection of low-affinity CD8+, CD4+ and iNKT cells. MHC Dextramers are an improved form of MHC multimers that improves staining intensity, resolution and signal-to-noise dramatically under these circumstances.
Cancer vaccines typically stimulate T cells with low affinity for the cognate pMHC class I complex. We show that MHC Dextramers, in contrast to Tetramers, can efficiently stain low-affinity T cells. Thus, using Dextramers, staining is achieved for affinities as low as 500 ?M, and effective separation of the negative and positive cell populations is achieved for affinities as low as 250 ?M.
pMHC class II complexes typically have low affinity for their cognate TCRs, making it difficult to enumerate CD4+ cells involved in e.g. autoimmune or inflammatory disease using conventional MHC multimers. We show that class II Dextramers allow detection of CD4+ T cells that cannot be detected using tetramers.
Finally, CD1d complexes (MHC-like complexes comprising glycolipids rather than peptides) often have low affinity for the TCR of iNKT cells. The use of CD1 Dextramers may be used to enumerate these cells.