Georgia Institute of Technology PS-OP: Mechanobiology of PD-1

Exploiting the Mechanobiology of PD-1 for Cancer Immunotherapy

Programmed cell death 1 (PD-1) is one of the key co-inhibitory molecules upregulated upon T cell activation and is a hallmark of T-cell exhaustion. Despite the fact that PD-1 blockade has become a revolutionary strategy in treating cancer and infectious diseases, the mechanobiology of PD-1 has not been studied. This is a knowledge gap that the present research project is addressing through experimental studies.

The significance of the project’s unique mechanobiology angle lies in the therapeutic potential of targeting the mechanoregulation of PD-1 to treat a wide variety of diseases, including melanoma. The approaches of the multidisciplinary team combine four physical science tools with two mouse models of melanoma. These represent the unique strengths of the Zhu lab and the Ahmed lab, as well as enable the investigation of PD-1 mechanobiology in silico, in vitro, and in vivo.

Physical science tools used in the PS-OP:

• DNA-based mechanical tension probes and tension gauge tethers that report and limit cell-generated forces on PD-1.
• Biomembrane force probe-based single-molecule methods that quantify force regulation of in situ PD-1–PD-ligand interactions with concurrent imaging of intracellular signals in single cells.
• Molecular dynamics simulations that reveal structural changes of PD-1 in complex with its ligands under force and the bonding dynamics at atomic level.
• Microfluidic-based devices for cell trapping, stimulation, and analysis.

Preliminary studies of the project demonstrate that 1) cells actively pull-on PD-1; 2) force on PD-1 elicits catch bonds to regulate ligand bonding; 3) force induces rearrangement of the PD-1–PD-1 Ligand 2 (PD-L2) binding interface to form new atomic-level interactions; 4) mutating specific amino acids on PD-1 alters its force, catch bond and function; and 5) PD-1’s inhibitory signal suppresses antigen recognition by disrupting the synergy between the T cell receptor (TCR) and CD8 in peptide-major histocompatibility complex (MHC binding).

These data support the hypothesis that force critically regulates ligand bonding and signaling of PD-1; as such, targeting the PD-1 mechanoregulation may represent a novel approach to immunotherapy.

This hypothesis is being tested by three specific aims:

• Determine the forces on PD-1 and their impact on PD-1 ligand bonding, signaling and function
• Modulate T cell function by targeting PD-1 mechanoregulation
• Investigate the therapeutic potential of manipulating PD-1 catch bonds in tumor mouse models.

These studies will elucidate the mechanism of PD-1 signaling, improve one’s understanding of CD8 T-cell responses to melanoma, and suggest new immunotherapeutic strategies to treating cancer.

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 opposing surfaces. His lab conceptualized and demonstrated several types of mechanical regulation of protein unbinding and unfolding in a number of receptor–ligand systems.

Rafi Ahmed, Ph.D.
Emory Vaccine Center

Dr. Rafi Ahmed, a member of the National Academy of Science, is a world-renowned immunologist whose work has been highly influential in shaping our understanding of memory T cell differentiation and T and B cell immunity. Dr. Ahmed's research aims to understand the mechanisms of B and T cell memory and to use this information to develop new vaccines for the prevention and treatment of disease.

The Ahmed laboratory uses highly sophisticated cellular and molecular techniques to study antigen-specific immunological memory in murine, primate, and human systems. A major area of focus is identifying cellular molecules that regulate the generation and maintenance of CD8 and CD4 T cell and humoral immunity.