Encapsulation is not desirable when appropriate therapy requires the long-term integration or migration of cells into tissues. The use of fetal tissues, including embryonic stem cells, can obviate the need for antirejection drugs because these cells can adapt immunologically to the host organism. One of the promising aspects of stem cell use is their ability to differentiate into a variety of tissue types with the appropriate encouragement, either in the laboratory or in vivo. The attempt to create useful and stable immortal stem cell lines and to harvest adult stem cells from the patients themselves or from donors is a prominent area for research, not merely for the functional benefits that would accrue, but because of the moral and sometimes political controversy over the use of fetal tissues. Brain cell transplants from aborted fetuses have also proved moderately effective in treating some of the symptoms of Parkinson’s disease in patients younger than 59. The list of diseases and disorders for which stem cells are beingexamined in animal and clinical trial systems is too great to be covered here.
In a Phase I clinical trial completed in 1999 by researches at the University of Pittsburgh Medical Center, 6 of 12 patients who had “naked” (i.e., nonencapsulated) LBS-Neurons (derived from a human tumor cell line) transplanted into sites within and near stroke-damaged areas of the brain, showed substantial improvement on tests of disability; and PET scans showed apparent integration and functioning of the new cells (www.laytonbio.com/whats new.htm).
Cancer is also a target of nonencapsulated cells. Neurotech S.A. is conducting the first Phase I/II clinical studies of the use of genetically engineered naked endothelial cells for the treatment of brain cancer. Its NTC-121 cell therapy consists of a stable brain endothelial cell line engineered to produce the human cytokine IL-2.>
According to a March 2000 Neurotech press release, “Endothelial cells will migrate to and survive in an angiogenic environment associated with cancer and will provide a local sustained release of protein therapeutic molecules. . . . This provides a dynamic method of locally targeting the immunotherapy, human IL-2, to tumor cells in the brain, and the local application limits systemic adverse effects.” The unique properties of these endothelial cells allow them to be used without encapsulation.
Whether naked cells or encapsulated ones will ultimately dominate the future of cellular therapeutics is still an open question. |
