ImmTAC? - Engineering High-Affinity, Soluble TCRs

摘要

T cell receptors (TCRs) are able to recognise a wide range of intracellular protein targets, through the presentation of peptide fragments on the cell surface by human leukocyte antigens (HLAs). Intracellular proteins provide a wider spectrum of targets than is available to antibodies, which are restricted to binding to cell surface and secreted proteins. This makes TCRs an attractive targeting molecule for use in immunotherapy. Due to thymic selection, naturally occurring TCRs tend to have weak affinity to self-peptides. At Immunocore, we are engineering soluble TCRs with high affinity to specific, validated, cancer peptides and are using these TCRs to develop Immune-mobilising monoclonal TCRs Against Cancer (ImmTAC) molecules. ImmTAC molecules are a unique platform of bi-specific biologies, comprising a high-affinity TCR fused to anti-CD3 scFv domain, which can drive activation of cytotoxic T cells to eradicate cancer cells. The development of ImmTAC molecules requires four key steps. First, T cell clones that recognise the desired peptide-HLA complex are identified and their TCR sequence determined. Second, TCR alpha and beta chains are synthesised, re-folded in vitro and tested for binding to the peptide-HLA complex. Third, mutagenesis of the complementarity determining regions (CDRs) is used to increase the affinity of the TCR by up to a million fold. Fourth, an additional disulphide bond is introduced to increase stability and an anti-CD3 domain is fused to the TCR. The completed ImmTAC then undergoes a range of cellular and molecular assays to confirm its efficacy and specificity. This process has been successfully applied to produce ImmTAC molecules for a number of targets, demonstrating the robustness of the platform. Our lead candidate, IMCgp100, which recognises a melanoma associated gp100 peptide, is currently undergoing clinical trials in advanced melanoma. Our poster describes the protein engineering technologies used at Immunocore to develop ImmTAC molecules.