Sensitivity tuning of TCR-engineered T-cells using CD8 co-receptor variants

Abstract

TCR-engineered T-cells are a promising tool for the treatment of haematological and solid malignancies. The key to the success of T-cell therapy lies in the discovery of high affinity TCRs that target tumour cells, while leaving healthy tissues intact. However, the majority of tumour-targeting TCRs are of low affinity due to negative selection during thymic development. Strategies such as affinity maturation can enhance the affinity of the TCR for its target antigen, but are laborious and can result in unpredicted T-cell crossreactivity. The CD8 co-receptor binds to MHCI at a site that is distant and distinct from the TCR binding site and acts to tune the antigen sensitivity of T-cells. Previous research has defined a “therapeutic affinity window” within which the pMHCI affinity for CD8 can be enhanced, resulting in increased T-cell sensitivity without reducing T-cell specificity. Based on these findings, I used molecular modelling to predict a panel of CD8 variants with affinities within this “therapeutic window”, with the aim of using the CD8 co-receptor to enhance the sensitivity of TCR-engineered T-cells. These CD8 variants were then functionally characterised in a Jurkat model system, and the two best performing variants selected for further biophysical evaluation. Once it was confirmed that the two variants had enhanced affinity for pMHCI, they were functionally evaluated in combination with clinically relevant tumour targeting TCRs in both Jurkat and primary T-cells. It was established that only TCRs of low affinity could benefit from enhanced affinity CD8 variants, and that in primary CD4 T-cells, the two variants substantially increased the recognition of tumour lines expressing target antigens, without inducing non-specific recognition of antigen negative tumour lines. These results indicate that CD8 co-receptor variants could be used as a novel strategy to modify the sensitivity of TCR-engineered T-cells to tumour associated antigens. With further functional and safety data, such a strategy would have an advantage over affinity maturation tools, as it would provide a universal and safe sensitivity enhancement of TCR-engineered T-cells.

Date of Award	28 Sept 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Linda Wooldridge (Supervisor)