Expansion of hematopoietic stem cells would, at face value, allow the possibility of curing many hematological diseases by the process of selecting non-leukemic stem cells, ex vivo expanding them, and providing them back to the patient after myeloablation has destroyed the resident malignant cells.
Pluristem (Nasdaq:PSTI) is developing adult stem cell based therapeutics for a variety of conditions using their proprietary PluriX Bioreactor System. The current patent granted to the company covers the expansion of undifferentiated hematopoietic stem cells using what appears to be a bioreactor set up involving stromal feeder cells.
The concept of using stromal cells to prevent differentiation of the expanded cell is very common in the area of embryonic stem cells, where murine feeder layers, as well as other types of feeders such as foreskin fibroblasts, and keloid tissue are used.
Other methods of expanding hematopoietic stem cells are known in the art, for example, patent #6,413,509 covering use of IL-3 for expansion, #6,241,984 covering an IL-3/GM-CSF fusion protein, and #6,054,465 which covers a wide variety of hematopoietic stimulatory small molecules.
The first independent claim of the patent is:
"A method of expanding an undifferentiated hemopoietic stem cell population to increase the number of the hemopoietic stem cells without the undifferentiated hemopoietic stem cells undergoing differentiation, the method comprising: (a) culturing stromal cells to confluence in a stationary phase plug-flow bioreactor under continuous flow of medium on a substrate in the form of a sheet, said substrate including a non-woven fibrous matrix forming a physiologically acceptable three-dimensional network of fibers to thereby generate a stationary phase three-dimensional confluent stromal cell culture; (b) separating a stromal cell conditioned medium from said stationary phase three-dimensional confluent stromal cell culture; (c) collecting said stromal cell conditioned medium; (d) obtaining an undifferentiated hemopoietic stem cell population; (e) adding said undifferentiated hemopoietic stem cell population to a medium containing said stromal cell conditioned medium; and (f) culturing said undifferentiated hemopoietic stem cell populations in a medium containing said stromal cell conditioned medium, thereby expanding the undifferentiated hemopoietic stem cell population to increase the number of undifferentiated hemopoietic stem cells without the undifferentiated hemopoietic stem cells undergoing differentiation to obtain an expanded undifferentiated hematopoietic stem cell population"
It would be interesting to see if Pluristem considered using their device for expansion of embryonic stem cells or iPS cells !