Publication Date


Document Type

Doctoral Dissertation

Academic Program

Immunology and Microbiology



First Thesis Advisor

Eric Huseby


T cell, TCR, MHC, Peptide, Treg, T cell receptor, T Regulatory Cell, Alloreactivity, Immune Response


T cells use their highly variable T cell receptor (TCR) to engage major histocompatibility molecules (MHC) presenting peptides on the surface of antigen presenting cells during an immune response. The TCR repertoire of developing T cells is shaped by thymic selection, resulting in a self-tolerant and foreign peptide specific naïve T cell population. However, naive T cells are alloreactive and generate immune responses towards foreign MHC alleles in clinical settings involving transplantation. While T cell immune responses towards foreign pathogens are peptide specific, the overall specificity of allo-responses is still debated.

Under normal circumstances, immune system homeostasis and self-tolerance is maintained by specialized natural T regulatory cells (nTregs) that develop in the thymus. nTregs respond to self-peptide MHC they encountered in peripheral tissues with immune-suppressive activities. However, the identify of self-peptides that stimulate nTregs, specificity towards these self-peptides, and the method nTreg TCRs engage self-peptide MHC molecules is not clear.

Here, we built a library of defined MHC-linked self-peptides eluted from the I-Ab MHC molecule to screen alloreactive T cells and self-reactive nTregs for activating self-peptides. We used this library to show that negative selection shapes the TCR repertoire’s specificity to self-peptides. We also provide evidence that alloreactive T cells have degenerate self and foreign peptide recognition if the foreign MHC allele is largely different from the host’s MHC allele. Finally, we identified a self-peptide that activates an nTreg, and present protein crystal structures that reveal its TCR engages self and foreign peptide MHC complexes via fairly conventional mechanisms.



Rights and Permissions

Copyright is held by the author, with all rights reserved.