Microfluidic Strategies for Studying Communication Between Cells and Tissues

Abstract

Understanding communication between cells and tissues is critical for treating human diseases, as communication is key for a coordinated response of many single cells into a population-wide response. Oscillations of signaling molecules, known as cytokines, can transform a heterogeneous population into an entrained population with the goal of, for example, organizing the response of the immune system against an infection. Further, including communication in multi-tissue models is critical in accurately predicting the pharmacokinetics and pharmacodynamics of drugs in patients. Multi-tissue models are needed to better understand how a drug interacts with a patient, from absorption into the body and hepatic activation into a drug’s active form, until a drug’s final excretion from the patient’s body. Microfluidics is a powerful technology that can be used to gain a better understanding of communication dynamics at the scale of single cells and up to microtissues. In this thesis, two types of microfluidics technology were used for studying communication between small populations of cells and microtissues: (1) valve-based microfluidics with high spatiotemporal resolution, and (2) tilting-based microfluidics with easy-to-use hardware. The objective of each platform is described below: 1. Interrogation of cytokine secretion dynamics: The goal of this platform was to understand how immune cells respond to dynamic inputs. A valve-based microfluidic platform was designed that can be used to automatically (1) pattern an immunoassay, (2) culture cells, and (3) expose and measure the response of cells to dynamic inputs. This is the first microfluidic platform developed with the ability to integrate these three tasks inside of the same chip. As a proof of concept experiment, the device was used to measure how a macrophage cell line responses to a dynamic stimulus of lipopolysaccharide (LPS) by quantifying transcription factor NF-кB activity and cytokine TNF secretion. The chip was able to confirm previous findings that a high stimulus of LPS results in a single peak in both NF-кB activity and TNF secretion. 2. Prediction of drug efficacy on patient-derived samples: A tilting-based microfluidic “leukemia-on-a-chip” device was developed with the objective of measuring the effect of both, standard drugs and prodrugs, the latter of which require hepatic bio-activation, on patient-derived leukemia samples. A key component of the leukemia-on-a-chip platform is a metabolic compartment to culture liver microtissues. In contrast to standard well plate experimental setups lacking a metabolic compartment, the leukemia-on-a-chip platform was able to measure the effect of a prodrug on patient derived leukemia samples. The simplicity of the leukemia-on-a-chip devices gives it the potential to be used directly in the clinic to advise treatment decisions. The overarching goal of both platforms was to improve patient outcomes in the clinic. For instance, the cytokine secretion dynamics platform can be used to screen the potential of novel drugs to cause cytokine storms, characterized by uncontrolled cytokine secretion, which can result in organ failure, and, in some cases, death. Further, the objective of the leukemia-on-a-chip device is to predict the efficacy of prodrugs in high-risk leukemia patients. Increased throughput is critical for transforming each device from a proof-of-concept platform into a platform that can be used to advise clinical decisions. Through increased throughput, the devices will be able to achieve increased statistical confidence needed to inform decisions and make a patient-specific impact in the clinic.