Abstract: There is provided a microfluidic device comprising a first region configured to hold target cells, e.g., tumor cells, a second region configured to hold effector cells, e.g., immune cells, and an array of microstructures disposed between the first and second regions, wherein the first region is in fluid communication with the second region, and wherein the array of microstructures is configured to selectively allow movement of immune cells, from the second region to an interaction zone that is at least partially disposed within the first region, for interaction with tumor cells in the interaction zone. The array of microstructures can be an array of micropillars. Also provided is a chip comprising a plurality of the device and a method of studying interactions of a first cell type with a second cell type.