Scientists working at the University of Bristol and NHS Blood and Transplant recently published their research in the journal Nature. They’ve shown that a virtually unlimited blood supply can be achieved through a process of “immortalizing” stem cells at an early stage.

Previously, researchers have been able to synthesize blood by isolating a type of stem cell that manufactures red blood cells and manipulating it to do its work in a lab. Unfortunately, the stem cells tend to become exhausted when they’ve produced around 50,000 red blood cells. An average bag of blood contains about a trillion red blood cells, making that technique unfeasible for any real-world application.

Through a complicated process, the researchers have found that they can hold the stem cell in its pre-exhausted state and coax it to produce red blood cells indefinitely.

Of course, there’s a catch. The process is expensive and isn’t currently viable for solving the world’s blood supply shortages. The team has only produced “liters” of its own product, thus far.

“The intention is not to replace blood donation but provide specialist treatment for specific patient groups,” Dr. Dave Anstee, director of the NIHR Blood and Transplant Research Unit at Bristol and NHS. According to Anstee, “The patients who stand to potentially benefit most are those with complex and life-limiting conditions like sickle cell disease and thalassemia, which can require multiple transfusions of well-matched blood.”