pMHC multimers consist of multiple pMHCI or pMHCII that have been chemically linked together and conjugated to a detectable marker for the study of T-cells.
The interaction between the T cell receptor (TCR) and its pMHC ligand is weak compared to antibodies and generally lasts for only seconds at 37°C. The multimerisation of pMHC, usually as avidin-biotin based tetramers, has revolutionised the study of antigen-specific T-cells by enabling their visualization, enumuration, phenotyping and isolation in direct ex vivo samples. Unlike monomeric pMHC, pMHC multimers can bind to the T-cell surface long enough for detection using fluorescent markers. This is because all engaged pMHCI monomers in the multimer are required to dissociate simultaneously to allow its release from the cell surface. Our surface plasmon resonance results using TCR tetramers and surface-bound pMHCI have shown that the ‘avidity’ effect of tetramerizing the TCR/pMHCI interaction can extend the half-life of interaction from less than 7 seconds to over 2.5 hours! This increase in avidity, combined with making the molecules fluorescent, enables the isolation of T-cells that have a TCR that recognises the multimerised antigen by flow cytometry.
We have developed modified multimeric forms of pMHC conjugated to flourochromes that can be used to identify any disease specific T-cell population from cancers, viruses, autoimmune diseases, etc. These T-cells can then be further investigated to gauge the specificity, quality and quantity of T-cell populations, which has revolutionized both diagnostic and analytical approaches. These technologies have significantly improved the sensitivity of pMHCI tetramers for the identification analysis and of CTLs.