Mariusz Ratajczak, director of the Developmental Biology Research Program at the University of Louisville, is widely credited as the discoverer of VSELs. He has claimed to isolate VSELs from mouse and human tissues, estimating them to be 3–5 micrometers in size and noting that they express pluripotent marker genes. Ratajczak has suggested that VSELs may possess embryonic-stem-cell-like qualities and has argued that finding such cells in an adult could have strong potential in research and medicine. Indeed, there is already at least one commercial venture that has stemmed from the discovery of VSELs: NeoStem, a New York City-based biopharmaceutical company launched in 2006, uses VSEL Technology licensed from Ratajczak to explore the use of VSELs as human therapies, and is backed by the Vatican, which has declared these cells to be an ethical alternative to ESCs. However, recent studies that isolated VSELs from mouse and human cord blood have showed a lack of stem cell characteristics.