Georgia Tech PS-OP: Impaired T-cell Mechanosensing

Mechanisms of Impaired T-cell Mechanosensing of Melanoma Antigens

This PS-OP investigates how the tumor microenvironment (TME) impairs interactions of T-cell surface molecules with counter-molecules on melanoma cells to suppress anti-tumor immunity.

Detailed mechanistic understanding is being obtained by an integrated approach that combines physical science-based tools with complementary pre-clinical mouse models of melanoma T cell immunity, which are being further tested using biospecimens from melanoma patients. The molecular focus is the T-cell receptor (TCR) that initiates the T-cell antigen recognition upon binding to peptide-major histocompatibility complex (pMHC), and the co-receptor CD8 that co-ligates with the pMHC.

Physical sciences tools being used in the PS-OP include:

• Single-molecule force techniques for quantifying TCR mechanosensing through in situ kinetic analyses of molecular interactions with concurrent imaging of intracellular signals on a single cell
• DNA-based digital tension probes that report cell generated pulling forces on the TCR and CD8 via engaged pMHC

Animal models include:

• A mouse model that uses melanoma conjugated with a chicken ovalbumin antigen recognized by the OT-I TCR
• A humanized transgenic mouse model with melanoma self-antigen gp100 in conjunction with JR209

By analyzing the mechanically regulated 2D ligand binding of TCR and/or CD8 at the T-cell membrane, we observed that the TCR avidities for the pMHC of CD8 T cells infiltrating primary murine melanomas grown in vivo are significantly reduced relative to T cells within non-tumor associated tissues. Such differential avidities were not detected by the conventional assay using pMHC tetramer, attesting to the power of our mechanics-based methods for analyzing TCR–pMHC interactions.

We also found melanomas to substantially alter the force-dependent TCR–pMHC bond durability. In tumor-free animals, the TCR and pMHC formed a catch-slip bond whose lifetime first increased and then decreased with increasing force, which we have previously demonstrated to govern T cell signaling and effector function. Whereas in melanoma-bearing animals, the TCR–pMHC bond lifetime only decreased with increasing force (i.e., behaved as a slip bond and were associated with reduced T cell effector functions).

We hypothesize that deficient CD8 T cell immunity in melanoma results, at least in part, from impaired antigen recognition within the TME, as manifested by the altered TCR mechanosensing of pMHC.

Three specific aims are proposed to test this hypothesis:

• Determine the molecular interactions crucial to T cell antigen recognition that are impaired by the TME
• Define the functional consequences of suppressed T cell antigen recognition
• Elucidate the mechanisms underlying the TME suppression of T cell antigen recognition

This PS-OP has the potential to identify new immunotherapeutic targets for the treatment of melanoma to improve the outcomes of patients with advanced disease.

Investigators

Cheng Zhu, Ph.D.
Georgia Institute of Technology

Dr. Cheng Zhu is a Regents’ Professor of Biomedical Engineering at the Georgia Institute of Technology. He received his Ph.D. from Columbia University in 1988.

Dr. Zhu is interested in the molecular biophysics of the immune and vascular systems, with a focus on the mechanobiology of T-cells and platelets, with respective applications to tumor immunology and thrombosis. He pioneered the in situ analysis of interactions at the junctional interface between molecules anchored to two apposing surfaces. His lab conceptualized and demonstrated several types of mechanical regulation of protein unbinding and unfolding in a number of receptor–ligand systems.

Michelle Krogsgaard, Ph.D.
New York University

Dr. Michelle Krogsgaard’s laboratory at the Perlmutter Cancer Center at New York University School of Medicine combines cell biology, biochemistry and biophysics to explore mechanisms of T cell recognition, activation and function in mouse models of disease and in human tissues.

Previously she did thesis work at University of Copenhagen in Denmark where she studied mechanisms of multiple sclerosis. Her postdoctoral work at Stanford University focused on mechanisms of T cell activation and contributed to understanding mediators of T cell sensitivity. She has received awards from the Pew Trust, the American Cancer Society, the Cancer Research Institute and the NIH.

Susan Napier Thomas, Ph.D.
Georgia Institute of Technology

Dr. Susan Napier Thomas is an Assistant Professor of Mechanical Engineering at the Georgia Institute of Technology and a member of the Winship Cancer Center at Emory University. Integrating engineering tools and advanced preclinical cancer models, her laboratory investigates mechanisms of cancer progression including metastasis and in particular the role of lymphatics in directing immune suppression within the tumor microenvironment, as well as develops drug delivery strategies and technologies to enhance cancer immunotherapy.

She trained as a Whitaker postdoctoral scholar at École Polytechnique Fédérale de Lausanne and received her Ph.D. from The Johns Hopkins University.