In a nutshell, pluripotent stem cells can produce any type of cell, whereas tissue stem cells can only produce cells of that tissue type. Embryonic stem cells are pluripotent cells, but as they generally do not exist in the human body after the person is five days old, working with these cells presents ethical and scarcity concerns. Tissue stem cells, on the other hand, are plentiful but only generate cells within a particular tissue line. For example, dermal fibroblasts can differentiate into any skin cell and hematopoietic progenitor cells can differentiate into any blood cell, but neither can differentiate into muscle tissue cells. Naturally, scientists tried, and succeeded, in converting these cells into pluripotent stem cells, by inducing them into that condition, hence the name. As scientists must start from something, obtaining hematopoietic progenitor cells from blood draws is much less painful to the patient than obtaining dermal fibroblasts from a skin biopsy, and hence hematopoietic progenitor cells are preferable starting materials from which to make iPS cells.
Generally speaking, when hematopoietic progenitor cells are expanded (multiplied in a lab setting), they have a tendency to differentiate (configure into a specific type of cell), which makes them less likely to accept reprogramming into iPS cells. The Cellular Dynamics researchers, however, found a way to avoid such a result, thereby allowing the researchers to harvest more hematopoietic progenitor cells from a smaller volume of blood. While beyond the scope of this article, interested readers are encouraged to discover the conditions that brought about this result via U.S. Patent Application Publication No. 2017/0088818 A1. Using, essentially, a combination of conditions, inhibitors, and medium composition, the researchers were able to both expand the hematopoietic progenitor cells while still achieving reprogramming success using known reprogramming techniques (introducing exogenous episomal genetic elements or exogenous RNA genetic elements that express iPS reprogramming factors into the expanded hematopoietic progenitor cells).
More iPS cells mean more breakthroughs, and this patent application may accelerate that process as well.