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February 13, 2008

New implantable device can extract stem cells from the bloodstream

Cell Traffix, using a microtube device coated with the protein P-selectin, has isolated and collected adult stem cells residing in human bone marrow to eight times greater purity than can be obtained through traditional centrifugation.

The device, a length of plastic tubing coated with proteins, could lead to better bone-marrow transplants and stem-cell therapies, and it also shows promise as a way to capture and reprogram cancer cells roaming the bloodstream. The system could capture and differentiate stem cells and other cells in the body and allow them to altered or replaced inside or outside the body. It is a path to killing cancer and removing aged cells with rejuvenated cells. There has also been promising work in reprogramming adult stem cells to revert to embryonic stem cells

Researchers used genetic alteration to turn back the clock on human skin cells and create cells that are nearly identical to human embryonic stem cells, which have the ability to become every cell type found in the human body. Reprogramming adult stem cells into embryonic stem cells could generate a potentially limitless source of immune-compatible cells for tissue engineering and transplantation medicine.


The behavior of stem cells, or any new tissue, in the body has a great deal to do with the holistic functioning of signaling networks and the cellular environment. The Cell Traffix device can enable alterations in the signaling to regular cells, cancer cells and stem cells.


Direct capture of blood-borne nucleated cells from circulation using P-selectin and non-coated control surfaces in implanted devices. Following incorporation into the femoral artery of anesthetized rats and 1-h blood perfusion, P-selectin coated tubes (A) showed a significantly greater average concentration of captured nucleated cells than non-coated control tubes (B) [184·6 ± 19·9 cells/mm2 for P-selectin tubes (40 μg/ml) vs. 4·7 ± 1·4 cells/mm2 for control surfaces (P < 0·01), bar = 50 μm]. (C) Total cell yields from 50 cm implanted tubes with cell adhesion molecule surfaces were significantly greater than the yield from non-specific binding in control tubes (**P < 0·01).

The new device mimics a small blood vessel: it's a plastic tube a few hundred micrometers in diameter that's coated with proteins called selectins. The purpose of selectins in the body seems to be to slow down a few types of cells so that they can receive other chemical signals. A white blood cell, for instance, might be instructed to leave the circulation and enter a wound, where it would protect against infection. "Selectins cause [some] cells to stick and slow down," says Michael King, a chemical engineer at the University of Rochester who's developing the cell-capture devices. Different types of selectins associate with different kinds of cells, including platelets, bone-marrow-derived stem cells, and immune cells such as white cells.


Nanowerk describes and ridicules a pure brute force nanotechnology robot approach to cellular repair. The new work by Cell Traffix shows that there could be other more clever paths to being able to achieve cellular rejuvenation.

Twenty-eight percent of the cells captured by King's implants were stem cells. "This is astounding given how rare they are in the bloodstream," says King. Implants would probably not be able to capture enough stem cells for transplant. But King believes that filtering a donor's blood through a long stretch of selectin-coated tubing outside the body, in a process similar to dialysis, would be very efficient. "This technique will clearly be useful outside the body" as a means of purifying bone-marrow-derived stem cells, says Daniel Hammer, chair of bioengineering at the University of Pennsylvania.


Mike King holding the cell capture device
Hammer believes that King's devices will also have broader applications as implants that serve to mobilize a person's own stem cells to regenerate damaged tissues. By slowing down cells with selectins and then exposing them to other kinds of signals, says Hammer, King's devices "could capture stem cells, concentrate them, and differentiate them, without ever having to take the cells out of the body." There might be a way to use selectins to extract neural stem cells, too. "This is a very broad-reaching discovery," says Hammer. Indeed, King says that he has already had some success using selectin coatings to reprogram cancer cells. Leukemia is a blood cancer, but King expects that the anticancer coating would work for solid tumors as well. Devices lined with these coatings might be implanted into cancer patients to prevent or slow metastasis. The company hopes to begin clinical testing of the anticancer coatings by early 2010.



FURTHER READING
Implanted CellTraffix Device Extracts Adult Stem Cells Directly from the Bloodstream, online in the British Journal of Haematology

Cancer killing invention also harvest stem cells

Other stem cell work: embryonic stem cells can be used to create functional immune system blood cells, a finding which is an important step in the utilisation of embryonic stem cells as an alternative source of cells for bone marrow transplantation.

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