Increased peptide contacts govern high affinity binding of a modified TCR whilst maintaining a native pMHC docking mode

• Main Author: David Kenneth Cole
• Format: Article
• Language: English
• Published: Frontiers Media S.A. 2013-06-01
• Series: Frontiers in Immunology
• Subjects: crystal structure; T cell; T cell receptor (TCR); Human T leukocyte virus type 1 (HTLV-1); peptide-major histocompatibility complex (pMHC); surface plasmon resonance (SPR)
• Online Access: http://journal.frontiersin.org/Journal/10.3389/fimmu.2013.00168/full

Natural TCRs generally bind to their cognate pMHC molecules with weak affinity and fast kinetics, limiting their use as therapeutic agents. Using phage display, we have engineered a high affinity version of the A6 wildtype TCR (A6wt), specific for the human leukocyte antigen (HLA-A*0201) complexed with human T cell lymphotropic virus type 111-19 peptide (A2-Tax). Mutations in just 4 residues in the CDR3β loop region of the A6wt TCR were selected that improved binding to A2-Tax by nearly 1000-fold. Biophysical measurements of this mutant TCR (A6c134) demonstrated that the enhanced binding was derived through favourable enthalpy and a slower off-rate. The structure of the free A6c134 TCR and the A6c134/A2-Tax complex revealed a native binding mode, similar to the A6wt/A2-Tax complex. However, concordant with the more favourable binding enthalpy, the A6c134 TCR made increased contacts with the Tax peptide compared with the A6wt/A2-Tax complex, demonstrating a peptide-focussed mechanism for the enhanced affinity that directly involved the mutated residues in the A6c134 TCR CDR3β loop. This peptide-focussed enhanced TCR binding may represent an important approach for developing antigen specific high affinity TCR reagents for use in T cell based therapies.