Hidden in Plain Sight: Encapsulating Islets to Outsmart the Immune System

Islet cell transplantation is a treatment option for some individuals living with Type 1 Diabetes (T1D). However, lifelong suppression of the immune system is required to prevent it from attacking the transplanted islets. Because suppressing the immune system can lead to other health problems, researchers are exploring ways to “hide” transplanted islet cells from the immune system, so that they will not be attacked by it. 

One promising strategy is encapsulation. This entails surrounding islet cells with protective materials that allow them to function while shielding them from immune attack. Broadly, there are three main encapsulation approaches. These are called macroencapsulation, microencapsulation, and nanoencapsulation.

Macroencapsulation involves transplanting a substantial number of islet cells inside a device. These devices protect islets while allowing nutrients and oxygen to diffuse inward and insulin to diffuse outward. But they also promote the formation of scar tissue and protein buildup that can limit oxygen and nutrient supply. This damages the islets. Modifications to the shape of the device may minimize this problem.

Microencapsulation uses smaller capsules that each contain a small number of islet cells. These are typically made from jello-like substances called hydrogels that allow nutrients and oxygen to surround the cells, and insulin to leave the cells and enter the bloodstream. Hydrogels are particularly attractive because they can be modified to optimize their flexibility, water absorption, and stability. All these changes may improve its ability to maintain the health of the transplanted islets.

Nanoencapsulation takes a different approach. It applies extremely thin coatings directly onto the surface of individual islets. These coatings allow interaction with the surrounding environment while reducing exposure to the immune system. Ongoing challenges remain. These include concerns regarding the long-term stability of the coatings and the possibility of foreign body reactions to it.

So, can transplanted islets truly be hidden from the immune system? Encapsulation strategies can reduce immune recognition, but transplanted islets still need access to oxygen, nutrients, and blood supply to function properly. These requirements make complete immune isolation difficult, and some level of immune interaction may still occur. While these approaches have yet to eliminate the need for immunosuppression, ongoing research continues to improve these technologies. Encapsulation remains a promising pathway toward safer and more widely accessible islet transplantation therapies.

About the author

Evan Pullishy

Evan Pullishy is a graduate student in the department of surgery at the University of Alberta. He studies localized drug delivery as a method to improve islet cell survival and function after islet cell transplantation.