Subdermal implant could boost islet cell therapy for diabetics
While islet cell transplants allow some diabetics to forgo daily insulin injections, those people have to take immunosuppressive drugs in order to keep the cells from being rejected. A new implant, however, could administer the drugs for them – in much smaller quantities than is currently required.
In Type 1 diabetes, the islet cells produced by the pancreas are destroyed by an autoimmune reaction. They therefore aren't able to produce blood-sugar-regulating insulin, as they normally would. As a result, patients typically have to give themselves daily insulin injections. Not only is this task painful, but it can also often be difficult to work into one's busy routine every single day.
One alternative involves harvesting islet cells from a deceased donor and transplanting them into the patient's liver. For several years, those cells proceed to produce insulin, eliminating the need for daily injections.
Unfortunately, though, in order to keep the body's immune system from identifying the introduced islet cells as foreign bodies that must be neutralized, the patient has to take immunosuppressive drugs on an ongoing basis. Because these drugs are taken orally, and are thus distributed throughout the body, relatively large doses are required – and the larger the dosage, the more severe the unwanted side effects, such as a compromised overall immune system.
It was with these problems in mind that scientists at Houston Methodist Hospital created an experimental implant known as the NICHE (Neovascularized Implantable Cell Homing and Encapsulation).
Similar in size to a US quarter-dollar coin, the flat polyamide-bodied device is designed to be implanted under the skin. It contains two reservoirs – a rectangular inner one for islet cells, and a U-shaped outer one which is filled with immunosuppressive drugs.
Approximately four weeks after the NICHE has been implanted, and oxygen-providing blood vessels have grown into its inside reservoir, that reservoir gets filled with islet cells. This is done by poking a hypodermic needle through the patient's skin and through a self-sealing silicone plug at the end of the reservoir (the same process is used to refill the implant with cells and drugs, as needed).
Within the implant, the cells proceed to produce insulin, which enters the bloodstream through the blood vessels that have grown into the reservoir. The drugs, meanwhile, gradually pass through a porous membrane between the two reservoirs, preventing an immune reaction from taking place. Because those drugs are already present right where they're needed, only a small amount of them is required.
In tests performed on diabetic rats, the NICHE reportedly restored normal blood glucose levels and eliminated Type 1 diabetes symptoms for over 150 days, without producing any severe side effects. The device was refilled once every 28 days, although the scientists are now working on a version that could go for up to six months between refills when used in humans. It's even possible that changes in drug formulations could extend those intervals to just once a year.
"A key result of our research is that local immunosuppression for cell transplantation is effective," said the lead scientist, Prof. Alessandro Grattoni. "This device could change the paradigm of how patients are managed and can have massive impact on treatment efficacy and improvement of patients’ quality of life."
The research is described in a paper that was recently published in the journal Nature Communications.
Source: Houston Methodist