Stem cell biology and cell transplantation therapy in the retina

Abstract

Embryonic stem (ES) cells, which are derived from the inner cell mass of mammalian blastocyst stage embryos, have the ability to differentiate into any cell type in the body and to grow indefinitely while maintaining pluripotency. During development, cells undergo progressive and irreversible differentiation into specialized adult cell types. Remarkably, in spite of this restriction in potential, adult somatic cells can be reprogrammed and returned to the naive state of pluripotency found in the early embryo simply by forcing expression of a defined set of transcription factors. These induced pluripotent stem (iPS) cells are molecularly and functionally equivalent to ES cells and provide powerful in vitro models for development, disease, and drug screening, as well as material for cell replacement therapy. Since functional impairment results from cell loss in most central nervous system (CNS) diseases, recovery of lost cells In addition to donor cell or tissue preparation, manipulation of the host conditions is essential for successful transplantation. Diseased host tissue may exhibit pathological conditions that differ from normal physiological conditions. For instance, inflammation affects the survival, synapse formation, and neural activity of transplanted cells, and except in cases of autotransplantation, immune rejection occurs following cell transplantation. The optimal time windows for photoreceptor transplantation should be determined for every type of retinal degeneration. A better understanding of the pathological host conditions, including immune responses, will be essential for regeneration of retinal function. Optimization of pharmacological drugs and transplantation materials are therefore crucial for successful transplantation. © 2009 Taylor & Francis Group, LLC.