(404e) Area 15DE Plenary Award - the Mechano-Chemistry of Immune Cell Motility

Motility is critical to the function of the immune system. T lymphocytes communicate with antigen presenting cells through the binding of T-cell receptors to antigens held in major histocompatibility complexes. The success of cellular immunotherapies such as chimeric antigen receptor T-cells (CAR T-cells) requires direct binding of CAR T-cells to cancer cells expressing neo-antigens. Molecular contact is achieved when immune cells find their targets through motility. Immune cells are weakly adherent, fast moving migratory cells. We describe our efforts to categorize the mechanics of immune cell motility across many different immune cells, including T-cells, neutrophils, macrophages, and dendritic cells. We find that despite descending from a common progenitor, the hematopoietic stem cell, each of these cells achieve active motion in unique spatial and temporal patterns and exert forces of different magnitudes.

We also consider the fascinating phenomenon of upstream migration of immune cells. During diapedesis, immune cells arrest and migrate on the apical surface of endothelium before transmigrating into tissues. Endothelial cells express intracellular adhesion molecule-1 (ICAM-1), and immune cells express its receptor, lymphocyte functioning antigen-1 (LFA-1). Under flow, LFA-1/ICAM-1 binding leads to upstream migration, in which cells counter the applied force and then exert additional traction stresses to propel themselves against the direction of flow. We hypothesize that upstream migration results from catch binding of LFA-1/ICAM-1, in combination with outside-in signaling through LFA-1. Using CRISPR-Cas9 deletions, we have identified key intracellular signaling molecules downstream of LFA-1 that are critical for upstream migration; their deletion reverses phenotype. Furthermore, using traction force microscopy, we have now for the first time measured that cells exert forces an order of magnitude larger when migrating upstream than they exert moving randomly. We are now examining how intracellular players affect traction stresses through an ever-widening CRISPR molecular screen.