The impact of accessory receptors on T cell activation by chimeric antigen receptors

Thesis

T-cells can be redirected against novel targets, such as cancer cells, by engineering them to express alternative antigen recognition machinery in the form of chimeric antigen receptors (CARs). Despite promising results in treating blood cancers, their efficacy is limited and this has partly been traced to their poor antigen sensitivity. The reason for this is unclear. We show that CARs have a 46–2800 fold lower sensitivity than the T-cell receptor (TCR) when antigen is presented by antigen presenting cells (APCs) but have a similar 0.83–3.5 fold change in sensitivity when antigen is presented as purified protein in isolation. By systematically adding purified ligands to other, accessory, receptors expressed on CD8+ T cells, we identify that the CD2 and LFA-1 co-signalling receptors dramatically improve TCR antigen sensitivity (125 and 22-fold respectively) but not CAR antigen sensitivity (<5-fold). We found that CAR antigen sensitivity can be improved by fusing the CAR variable domains to the CD3ε subunit of the TCR (a TRuC), and restored to TCR levels by exchanging the variable regions of the TCRαβ chains with those of a CAR (a STAR). These improvements are predicted by the improved ability of these receptors to exploit CD2 and LFA-1. The binding of CD2 to its ligand CD58 is thought to improve antigen recognition by precisely aligning membranes to the ∼14 nm spanned by the TCR/pMHC interaction. We hypothesised that the CAR/antigen interaction may have a size incompatible with CD2/CD58 and therefore, engineered a panel of elongated CD2 receptors. We find that the antigen sensitivity increases by elongating CD2, with a different elongated CD2 being optimal for different antigen receptors. Taken together, CARs display a large defect in antigen sensitivity by their inefficient exploitation of the CD2 and LFA-1 interaction and engineered CD2 molecules can rescue their antigen sensitivity.

Authors: Burton, J

• DOI: 10.5287/ora-pmybd7ao9
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: Immunology; T cells; T cells--Receptors; Immunotherapy