Evaluation of TCR-pMHC affinity and its implications for T cell responsiveness

In the adaptive immune response, interactions between the T cell receptor (TCR) and the major histocompatibility complex (MHC) are crucial for immune system development, maturation, surveillance, and protection against pathogens and cancer. The primary function of the TCR is to recognise antigens presented by the MHC (or pMHC for peptide-MHC complex) and transmit an activation signal inside the effector T cell . This recognition is highly specific and forms the foundation of the adaptive immune response. Several studies have identified two types of MHC molecules: MHC class I and MHC class II, each recognised by different classes of T cells. Cytotoxic CD8+ T lymphocytes recognise peptides presented by MHC class I molecules, while CD4+ T helper lymphocytes recognise peptides presented by MHC class II molecules. MHC class I molecules are found on most nucleated cells, whereas MHC class II molecules are restricted to antigen-presenting cells (APCs), including dendritic cells, macrophages, and B lymphocytes.

The interaction between TCR and pMHC is a key determinant of T cell activation. When the TCR binds to a pMHC complex, in conjunction with co-stimulatory signals and environmental cytokines, it triggers a cascade of intracellular signalling events that ultimately lead to T cell activation. Understanding the TCR-pMHC interaction is essential for developing new therapies for autoimmune disorders, infectious diseases, and cancers, as well as for the development of screening and diagnostic tools. TCR affinity for pMHC is relatively weak in vivo, with a KD in the micromolar range. By modifying this interaction, it is possible to enhance or suppress the immune response, providing a powerful tool for therapeutic intervention.

In this application note, we studied the interaction between a modified affinity-enhanced TCR (expected to have nanomolar affinity) targeting the NY-ESO I antigen (Immudex cat. no. CSS009M) and pMHC (MHC Monomer, HLA-A*0201/SLLMWITQC, cat. no. WB02696M) in terms of affinity and kinetics using surface plasmon resonance (SPR, Biacore) and biolayer interferometry (BLI, Octet) techniques. Both TCR and pMHC monomers were manufactured and supplied by Immudex through their Custom Solutions and Services. The TCR was provided in a biotinylated form, while the pMHC was provided either as a biotinylated or His-tagged unbiotinylated form. SPR and BLI are two methods available at Quality Assistance for the characterisation of intermolecular interactions. SPR and BLI can be considered orthogonal analytical methods, i.e. different methods intended to measure the same attribute. Both instruments are qualified for cGMP and comply with 21CFR/Part 11 requirements.

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