Understanding the molecular interaction between unconventional T cell antigen receptors and their ligands; paving the way for future immuno-therapy

Abstract

The ability of the human immune system to coordinate an effective immune response to stress is a complex and tightly regulated process that brings together many different molecules and mechanisms from multiple interconnecting systems. Understanding these mechanisms and pathways is key in developing novel therapeutic targets to combat the wide and ever-growing array of human diseases. Unconventional T cells and their ligands have recently been established as targets for immunotherapy in diseases such as cancer, primarily due to their major histocompatibility (MHC)-unrestricted nature and strong anti-tumour response. They are often described to bridge the gap between innate and adaptive immunity, due to their ability to display characteristics and phenotypes of both these responses. Despite the growing interest in unconventional immune responses, limited structural data currently represents a bottleneck in understanding them fully, thus hindering the development of successful treatments in the field.

My work aims to investigate the hypothesis that CD1 antigen-presenting molecules display substantial conformational plasticity and are thus capable of presenting a wide variety of both stimulatory and inhibitory lipids to diverse TCRs. We utilise structural techniques to investigate the molecular mechanism underpinning CD1 plasticity and unconventional TCR recognition of two CD1 isoforms (CD1d and CD1c) presenting lipid ligands. We also develop an optimised pipeline to generate soluble, refolded gamma delta (γδ) TCRs that can be used to investigate CD1c recognition by the γδ TCR.

This work demonstrates that CD1d can alternate its conformation within the vicinity of the lipid binding site, in a lipid cargo-dependent fashion. We display, using X-ray crystallography and molecular dynamics (MD) simulations, that CD1d can ‘relax’ and ‘constrict’ its lipid binding groove providing potential mechanisms for its ability to accommodate a range of lipid sizes and properties, a feature previously demonstrated in other CD1 isoforms. Furthermore, we use X-ray crystallography to produce structural data of a novel macaque CD1d structure, to explore the conservation of CD1d lipid-binding groove flexibility across species. We also demonstrate successful optimisation of a refolding and purification pipeline to produce soluble, stable CD1c-reactive γδ TCRs. Further to this, we utilise an in-house generated bead display system to confirm the CD1c-reactivity of the refolded γδ TCR. Our findings suggest CD1d shares the same conformational adaptability of other CD1 isoforms such as CD1b and CD1c, providing a potential molecular mechanism to explain CD1d’s ability to bind ligands that exceed the standard groove size. We also show that we can refold stable, CD1c-reactive γδ TCRs that can be used to explore the molecular mechanisms underlying the recognition of CD1c lipid complexes by the γδ TCR. These results can be used to build on a greater understanding of how CD1 antigen-presenting molecules can modulate their conformation to perform different functions, and they pave the way for further studies to unravel CD1 recognition by TCRs.

More information

Identifiers

ORCID for Salah Mansour: orcid.org/0000-0002-5982-734X

ORCID for Ivo Tews: orcid.org/0000-0002-4704-1139

Catalogue record

Export record