Systems featuring two or more encapsulation devices stacked together. The encapsulation devices house cells, such as but not limited to islet cells or stem cell derived beta cells or the like, e.g., for regulating blood glucose, or other cells or spheroids that can produce and release a therapeutic agent that is useful in the body, etc. The system may feature oxygen delivery, or in some cases no exogenous oxygen is delivered and vascularization of the device can help provide oxygen and other needed nutrient to the cells. The system of the present invention may be used in conjunction with other therapies such as an artificial pancreas. Stacking the devices with blood vessel formation around and in between them may allow for a decrease in the footprint that would be needed for implantation.