Aaron Rosado

PhD Defense Presentation

Date: Tuesday, May 18th, 2021

Time: 10:00 AM

Location: https://bluejeans.com/743201883

Thesis Advisor:

Cheng Zhu, PhD

Georgia Institute of Technology, WH Coulter Department of Biomedical Engineering

Thesis Committee:

Michael Davis, PhD

Georgia Institute of Technology, WH Coulter Department of Biomedical Engineering

Susan Thomas, PhD

Georgia Institute of Technology, WH Coulter Department of Biomedical Engineering

Arash Grakoui, PhD

Emory University School of Medicine, Department of Medicine, Division of Infectious Diseases

Michelle Krogsgaard, PhD

NYU School of Medicine, Department of Pathology

Title: CD28 and TCR In-situ Biophysical Analyses Inform T Cell Immunity Mechanisms

Abstract:

This work investigates two receptors on T lymphocytes that shape immunity, the T cell receptor (TCR) and cluster of differentiation 28 (CD28). T cells coordinate adaptive immunity, but how signaling via TCR and CD28 interactions with peptide-major compatibility complex (pMHC) and B7 family ligands on antigen presenting cells govern T cell function and differentiation remains poorly understood.  In-situ biophysical measurements on live T cell surfaces suggest both B7 family ligands form monomeric bonds with CD28. This work demonstrated CD28 catch bonds with B7 family ligands for the first time. Catch bonds refer to a counter-intuitive phenomenon where force prolongs bond lifetime contrasted with the more intuitive slip bond where force shortens bond lifetime.  Although TCR–pMHC catch bonds on splenic T cells characterize a well-established TCR mechanosensing mechanism, the same interaction on hepatic T cells showed slip bonds correlating with a more activated state among liver T cells.  We also analyzed both short- and long-term memory effects from the same molecular interactions.  Short-term (within seconds) memory analyses found that bond formation increased bond formation likelihood but not dissociation in the immediate future.  Long-term (~5 minutes) memory analyses found that splenic T cells became more activated by repeated ligand engagement and receptor tension resulting in TCR–pMHC catch bond elimination.  Our sensitive assay also revealed subtle T cell activation by piconewton-level T cell pushing and pulling forces as well as changes in short-term memory.  This work suggests biophysical instrumentation employed in-situ can reveal information about dynamic processes mediating important immunological functions.  The findings within this work provide insights into mechanistically how co-stimulation works at a single molecule level as well as how signaling overlap between TCR and CD28 influence receptor localization, mechanosensing, and triggering.  These insights answer longstanding mechanistic questions about how T cells function and provide foundations for future investigations.