Synthetic T cell receptor engagers to overcome suppression of the function of human anti-tumour T cells

Abstract

Cytotoxic T cells (CTL) play a key role in the tumour microenvironment (TME), as they have the ability to recognize and kill tumour target cells. Yet, that ability is largely suppressed. The suppression of CTL function is difficult to study within the entire complex TME. Therefore, we built a reductionist experimental system for the investigation of the molecular and cellular mechanism of CTL suppression in their direct interaction with tumour target cells using 3D tumour cell spheroids.
We incubated human CTL transduced to express a transgenic TCR with tumour cell spheroids in the presence of cognate antigen. This resulted in suppression of CTL function with impaired target cell killing and diminished IFNγ secretion. Moreover, induction of an exhaustion phenotype in spheroid-infiltrating lymphocytes was detected by the elevated frequency of the expression of suppression markers.
We also investigated the mechanism of action of a TCR-based therapeutic called ImmTAC. ImmTAC-NYE combines a high-affinity TCR extracellular domain for a defined tumour-associated epitope (NY-ESO-1) with a humanised anti-CD3ε antibody single chain Fv fragment to activate T cells (pHLA:ImmTAC:CD3). We determined T cell activation by ImmTAC-NYE against a panel of cell lines expressing medium, low and limiting levels of the targeted NY-ESO antigen. Our data demonstrate a positive correlation between NY-ESO-1 abundance and CD8+ CTL activation in tumour cell killing and IFNγ release. ImmTAC-NYE treated T cells showed greater tumour target cell killing with enhanced T cell infiltration into spheroids as compared to CD8+ T cells expressing a TCR, 1G4, recognising the same antigen. Comparing ImmTAC-NYE variants with different affinities for CD3ε, an ImmTAC with intermediate-affinity anti-CD3e showed the best balance between sensitivity and specificity.
Collectively, our 3D spheroid system allowed for a physiologically relevant investigation of the activation of T cell responses to tumour target cell by the ImmTAC-NYE.

Date of Award	17 Jun 2025
Original language	English
Awarding Institution	University of Bristol
Sponsors	the Cultural Bureau at the Royal Saudi Embassy in the United Kingdom and the Saudi Ministry of Education
Supervisor	Christoph Wuelfing (Supervisor) & Linda Wooldridge (Supervisor)