If successful, the implant could eliminate the need for these patients to inject themselves with insulin.
The World Health Organisation reports that more than 422 million people worldwide are living with diabetes, a condition that can take two forms.
In the first, the body's immune system attacks cells in the pancreas, preventing the organ from producing enough insulin [type 1 diabetes (T1D)]. In the second, the body doesn't know how to use the insulin that is produced [type 2 diabetes (TD2)].
T1D accounts for roughly 10 percent of diabetes cases, and unlike T2D, which can often be reversed through lifestyle changes such as weight loss or increased exercise, scientists have yet to figure out how to prevent or cure T1D.
Right now, insulin injections are the best way to manage T1D, but this method can be problematic in high-risk cases - patients with hypoglycemia (low glucose) unawareness, for example, may have trouble adjusting their insulin dosage.
Each of these credit card-sized implants carries cells derived from stem cells. These cells are designed to mature inside the human body into the specialised pancreas cells the immune system destroys in those with T1D. The implant is placed just below the skin and releases insulin whenever necessary.
"Patients with high-risk type 1 diabetes complications, such as hypoglycemia unawareness, are at constant risk of life-threatening low blood glucose," clinical trial investigator Jeremy Pettus from University of California, San Diego, said in a ViaCyte press release.
"The PEC-Direct islet cell replacement therapy is designed to help patients with the most urgent medical need."
"There are limited treatment options for patients with high-risk type 1 diabetes to manage life-threatening hypoglycemic episodes," added ViaCyte president and CEO Paul Laikind.
"We believe that the PEC-Direct product candidate has the potential to transform the lives of these patients."
Truly, freeing T1D patients from the need for constant insulin shots hasn't been an easy task. Researchers in Finland have been looking into it for 25 years and only recently did they manage to develop a vaccine for preventing type 1 diabetes - that breakthrough will go to clinical trials by 2018.
ViaCyte's device is another promising discovery.
Prior to last week's clinical trial, PEC-Direct implants using smaller amounts of stem cells were tested in 19 diabetes patients. Although these did mature into the desired islet cells, the limited number wasn't designed to treat the condition.
The PEC-Direct implants received by the two patients last week contain more cells. The hope is that three months from now, when the cells have matured, they'll be able to take the place of injections by releasing insulin automatically when needed.
If it does work, the only thing T1D patients will have to do is take immunosuppressant drugs to make sure their bodies don't reject the new cells. That's a small price to pay to be freed of daily injections.
As James Shapiro at the University of Alberta, Canada, told New Scientist, "A limitless source of human insulin-producing cells would be a major step forward on the journey to a potential cure for diabetes."
Correction (8.08.2017): An earlier version of this article incorrectly stated that hypoglycemia requires an immediate insulin shot. The wording has been updated to better reflect the problems around hypo unawareness and insulin dosage.