University of Cambridge
Exploiting the Molecular Mechanisms of TAPBPR for use in Cancer Immunotherapy
Abstract
dc:description.abstractTAPBPR is a chaperone within the MHC-I antigen processing and presentation pathway, responsible for shaping the immunopeptidome via MHC-I peptide editing and the recycling of sub-optimally loaded MHC-I to the peptide loading complex. As such, TAPBPR plays an essential role in the activation of the immune system against infection and cancer, ensuring that only high affinity peptides are presented at the cell surface to induce activation of CD8+ T cells. It has previously been shown that a recombinant soluble TAPBPR (sTAPBPR) molecule is capable of catalysing peptide exchange when applied to cells exogenously, with a further antibody-conjugated modification permitting the targeted delivery of an sTAPBPR fusion protein. This unveils therapeutic promise, with the potential to load exogenous immunoreactive peptide onto the surface of cells expressing an antibody target with the sTAPBPR fusion protein. I initially confirmed the ability of two sTAPBPR fusion proteins – one bound to an anti-PDL1 nanobody, the other to an anti-CD19 single chain variable fragment – to bind to their respective targets, as well as their propensity to catalyse peptide exchange on the surface of target cells. Immunoreactive antigen loaded by the fusion proteins lead to the activation and degranulation of CD8+ T cells. I also investigated the ability of the surface TAPBPR to induce NK cell activation via both the direct recognition of TAPBPR by activating receptors, as well as the blocking of inhibitory receptors to their MHC-I ligands through binding competition. While surface TAPBPR did block the binding of inhibitory NK cell receptors to MHC-I and sTAPBPR was directly recognised by a surface molecule other than MHC-I, surface TAPBPR was unable to stimulate NK cell activation or degranulation. Interestingly however, surface TAPBPR was capable of inhibiting NK cell activation against target cells with a non-self MHC-I signature. Lastly, the role of R27 in the function of TAPBPR was explored. The R27A mutation, among others investigated, affected the peptide loading function of TAPBPR as revealed by functional assays and immunopeptidomics analysis. The R27H and R27S mutations were also examined due to their presence in human polymorphism and cancer respectively. These mutations imparted similar effects as the R27A mutation, indicating that these too impact peptide loading. This has implications in cancer, as a restriction of the cancer cell immunopeptidome perhaps enable immune escape. The role of the K22-D35 loop more generally was also explored in the context of MHC-II, with immunopeptidomics analysis also showing R27 to play a key function in the potential peptide exchange function of TAPBPR on MHC-II molecules. Overall, this thesis has advanced our understanding of the therapeutic promise of the sTAPBPR fusion protein for use in immunotherapy via the activation of CD8+ T cells and NK cells. It has also given insight into the role of individual residues in the function of TAPBPR on both MHC-I and MHC-II to gain insight into potential modifications that could improve its therapeutic aptitude.
Degree
thesis:*- Name dc:type.qualificationname
- Doctor of Philosophy (PhD)
- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 2025
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Morley, Jack
- Advisor dc:contributor.advisor
-
- Boyle, Louise
Subjects
dc:subject × 8Rights
dc:rightsIdentifiers
dc:identifier.*- DOI dc:identifier.doi
- https://doi.org/10.17863/CAM.121160
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/389117