The use of cells in reparative medicine

Cells are the functional elements of reparative medicine and tissue engineering. The use of living cells as a therapy presents several challenges. These include identification of a suitable source, development of adequate methods, and proof of safety and efficacy. We are now well aware that stem or pluripotent cells offer an exciting potential source for a host of functional cell types. Their true potential will only be realized through continued effort to increase basic scientific understanding at all levels, the development of adequate methods to achieve a functional phenotype, and attention to safety issues associated with adequate control of cell localization, proliferation, and differentiation. There is also new understanding regarding the immunology of parenchymal cells and new promising approaches to immune modulation, which will open the door to broader therapies using allogeneic cell sources without prohibitive immune suppression. Control of cell growth and phenotypic expression does not end in the culture vessel, but goes beyond to the patient. A living therapy is not static but dynamic, as is the host response. The cells or tissue construct in most cases will not behave as a whole-organ transplant. It is therefore important that we understand a cell or tissue therapy's ability to react and interact within the host since clinical effectiveness has proven to be one of the most difficult milestones to achieve. A living cell therapy offers great potential to alter the human condition, encompassing alteration of the current biological state of a targeted tissue or organ, augmentation of depleted or lost function, or absolute functional tissue replacement. The extent to which we are able to achieve effective cell therapies will depend on assimilating a rapidly developing base of scientific knowledge with the practical considerations of design, delivery, and host response.