In a mouse model of multiple sclerosis (MS), researchers funded by the National Institutes of Health have developed innovative technology to selectively inhibit the part of the immune system responsible for attacking myelin-the insulating material that encases nerve fibers and facilitates electrical communication between brain cells.
Autoimmune disorders occur when T-cells-a type of white blood cell within the immune system-mistake the body's own tissues for a foreign substance and attack them. Current treatment for autoimmune disorders involves the use of immunosuppressant drugs which tamp down the overall activity of the immune system. However, these medications leave patients susceptible to infections and increase their risk of cancer as the immune system's normal ability to identify and destroy aberrant cells within the body is compromised.
Supported by the National Institute of Biomedical Imaging and Bioengineering (NIBIB) at NIH, Drs. Stephen Miller and Lonnie Shea at Northwestern University, Evanston, teamed up with researchers at the University of Sydney, and the Myelin Repair Foundation in Saratoga, Calif. to come up with a novel way of repressing only the part of the immune system that causes autoimmune disorders while leaving the rest of the system intact.
The new research takes advantage of a natural safeguard employed by the body to prevent autoreactive T-cells-which recognize and have the potential to attack the body's healthy tissues-from becoming active. They report their results in the Nov. 18 online edition of Nature Biotechnology.
"We're trying to do something that interfaces with the natural processes in the body," said Shea. "The body has natural mechanisms for shutting down an immune response that is inappropriate, and we're really just looking to tap into that."
One of these natural mechanisms involves the ongoing clearance of apoptotic, or dying, cells from the body. When a cell dies, it releases chemicals that attract specific cells of the immune system called macrophages. These macrophages gobble up the dying cell and deliver it to the spleen where it presents self-antigens-tiny portions of proteins from the dying cell-to a pool of T-cells. In order to prevent autoreactive T-cells from being activated, macrophages initiate the repression of any T-cells capable of binding to the self-antigens.
Dr. Miller was the first to demonstrate that by coupling a specific self-antigen such as myelin to apoptotic cells, one could tap into this natural mechanism to suppress T-cells that would normally attack the myelin. The lab spent decades demonstrating that they could generate antigen-specific immune suppression in various animal models of autoimmune diseases. Recently, they initiated a preliminary clinical trial with collaborators in Germany to test the safety of injecting the antigen-bound apoptotic cells into patients with MS. While the trial successfully demonstrated that the injections were safe, it also highlighted a key problem with using cells as a vehicle for antigen delivery:
"Cellular therapy is extremely expensive as it needs to be carried out in a large medical center that has the capability to isolate patient's white blood cells under sterile conditions and to re-infuse those antigen-coupled cells back into the patients," said Miller. "It's a costly, difficult, and time-consuming procedure."
Thus began a collaboration with Dr. Shea, a bioengineer at Northwestern University, to discuss the possibility of developing a surrogate for the apoptotic cells. After trying out various formulations, his lab successfully linked the desired antigens to microscopic, biodegradable particles which they predicted would be taken up by circulating macrophages similar to apoptotic cells.