No abstract

Natural T cell receptors (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 wild-type 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 favorable 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 favorable binding enthalpy, the A6c134 TCR made increased contacts with the Tax peptide compared with the A6wt/A2-Tax complex, demonstrating a peptide-focused mechanism for the enhanced affinity that directly involved the mutated residues in the A6c134 TCR CDR3β loop. This peptide-focused enhanced TCR binding may represent an important approach for developing antigen specific high affinity TCR reagents for use in T cell based therapies.

Immunotherapeutic strategies have revolutionised cancer therapy in recent years, bringing meaningful improvements in outcomes for patients with previously intractable conditions. These successes have, however, been largely limited to certain types of liquid tumours and a small subset of solid tumours that are known to be particularly immunogenic. Broadening these advances across the majority of tumour indications, which are characterised by an immune-excluded, immune-deserted or immune-suppressed ('cold') phenotype, will require alternative approaches that are able to specifically address this unique biological environment. Several newer therapeutic modalities, including adoptive cell therapy and T cell redirecting bispecific molecules, are considered to hold particular promise and are being investigated in early phase clinical trials across various solid tumour indications. ImmTAC molecules are a novel class of T cell redirecting bispecific biologics that exploit TCR-based targeting of tumour cells; providing potent and highly specific access to the vast landscape of intracellular targets. The first of these reagents to reach the clinic, tebentafusp (IMCgp100), has generated demonstrable clinical efficacy in an immunologically cold solid tumour with a high unmet need. Here, we highlight the key elements of the ImmTAC platform that make it ideally positioned to overcome the cold tumour microenvironment in an off-the-shelf format.

Highlights d Mutations in TCRb and CD3z TMRs that reduce their interaction augment signaling d pMHC and anti-CD3 binding to TCR-CD3 induce similar quaternary structure relaxation d Soluble monovalent pMHC alone signals and reduces TCRab cohesion with CD3z d Allosteric changes in TCR-CD3 dynamics instigate T cell activation