Abstract A195: Mechanosensory mechanisms and in vivo tissue topology contribute to rheology of circulating leukocytes resulting in efficient post-capillary vessel wall adhesion and recruitment
Authors: Huang Alex Y. , Benson Bryan L. , Correa Luis , Li Lucy , Myers Jay T. , Gurkan Umut A. , Ransohoff Richard 
Published: February 2019

Abstract
Efficient recruitment of circulating immune cells to various tissues plays a critical role in homeostasis and immune surveillance, a process that serves as the basis of any successful cell-based immunotherapeutic strategies in cancer, particularly for solid tumors and cancers residing in body sites outside of blood vessels and sinusoid network. Clinical and experimental observations suggest that in vivo leukocyte adhesion and extravasation are maximal near the transition from capillary to post-capillary venule, through a multistep process that includes the intravascular capture, rolling, arrest, crawling of cells through interactions of adhesion molecules (selectins, integrins, chemokines/receptors, for example), eventually leading to transcellular or paracellular transmigration through intact endothelium. These cellular and molecular processes are strongly influenced by a confluence of scale-dependent physical effects. Mimicking the scale of physiologic vessels using in vitro microfluidic systems allows the capture and investigation of these effects on leukocyte adhesion assays, but imposes practical limits on reproducibility and reliable quantification. We have developed a microfluidic platform that provides multiple (54-512) technical replicates within a 15-minute sample collection time, coupled with an automated computer vision analysis pipeline that captures leukocyte adhesion probabilities as a function of not only shear stress imposed on leukocytes within the vessels as conventional wisdom dictates, but also of the extensional stresses imposed by the topology of post-capillary venules and the rheology of circulating leukocytes in these vessels. We identified that in post-capillary channels of physiologic scale, efficient leukocyte adhesion requires erythrocytes forcing leukocytes against the wall, a phenomenon that is promoted by the transitional flow in post-capillary venule expansions and highly dependent on the adhesion molecule ICAM-1. These studies help identified a mechanosensory mechanism that determines the increased likelihood of leukocyte adhesion in post-capillary venules, and further suggests a significant role of mechanosensory channel(s) in influencing leukocyte integrin affinity for cellular capture to the vessel wall. Through a series of truncation mutants, we have narrowed down a small region of putative interacting domain between integrin and a candidate mechanosensory channel—PIEZO1—on leukocytes. These ongoing investigations offer new insights into immune cellular recruitment and new molecular targets to enhance leukocyte recruitment to peripheral tumor sites.
Citation Format: Alex Y. Huang, Bryan L. Benson, Luis Correa, Lucy Li, Jay T. Myers, Umut A. Gurkan, Richard Ransohoff. Mechanosensory mechanisms and in vivo tissue topology contribute to rheology of circulating leukocytes resulting in efficient post-capillary vessel wall adhesion and recruitment [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A195.