Investigating the role of HLA class I derived peptide in alloreactivity.

The peptide complexed with human leukocyte antigen (HLA) can be said to have a significant role in the generation of alloresponses, both in terms of cellular and humoral alloresponses. Previous researchers have identified minor histocompatibility antigen (mHAG) derived peptides such as HA-1, and their contribution to alloresponses. However, little research has been performed regarding the contribution of peptides, which are themselves derived from HLA molecules. To redress this, this thesis focused upon identifying and assessing the function of endogenous peptides, in particular peptides which are themselves derived from HLA class I molecules, which may have a role in the alloresponses, within the context of clinical transplantation.This research describes the creation of a database of HLA class I derived peptides predicted to bind to HLA-A*02 molecules, and then utilises this database to identify HLA class I derived peptides which are bound by the HLA-A*02 molecule, present upon the surface of the monocytic THP-1 cell line. This process identified two peptides, which were derived from one HLA class I molecule and presented by another (HLA-A*02). One of the identified peptides (VMAPRTLIL) belongs to a group of peptides, known as leader peptides, which have functions in both innate and adaptive immune responses. A clinical audit was performed to assess the effect of mismatching the HLA class I derived leader peptides within the context of renal transplantation and identified a correlation with a poorer functioning allograft at 12 months post transplant, when the donor and recipient have 3 leader peptide mismatches (p=< 0.05).Further experimental work attempted to determine a functional role of the endogenous peptides. In particular seeking to establish if variation within peptides bound by the same HLA molecule can influence the subsequent binding of HLA specific antibodies, and if so, seek to elucidate the mechanisms involved. Using a T2 cell line peptide binding assay, as a target for a HLA-A*02 specific antibody, a variation between the ability of the antibody to bind when alternative peptides were bound was observed. Through the use of structural modelling it was demonstrated that changes within HLA class I bound peptides can induce conformational changes to epitopes,which were previously described for HLA class I molecules as being the targets of HLA class I specific antibodies.These findings suggest an important role for HLA class I derived leader peptides in the outcome of renal transplantation, which requires further study within a validating cohort of patients. While the observation that peptides can induce conformational variation within identified epitopes provides further insight into the complex nature of alloantibody binding, and aides the understanding of this process.