Stem cells in the spleen: therapeutic potential for Sjogren's syndrome, type I diabetes, and other disorders.

The view of the spleen as an unnecessary organ has been shattered. The evidence shows the spleen to be a source of naturally-occurring multipotent stem cells with possibly pluripotent potential. The stem cells are sequestered in the spleen of not only of animals but also of normal human adults. The reservoir of cells is set for differentiation and they need not be manipulated in vitro or ex vivo before autologous or heterologous use. Splenic stem cells, of Hox11 lineage, have been found in disease or injury to differentiate into pancreatic islets, salivary epithelial cells and osteoblast-like cells, cranial neurons, cochlea, lymphocytes, and more differentiated immune cells that repair injured heart cells. Injury or disease in target tissues induces these stem cells, still in the spleen, to upregulate the same embryonic transcription factors artificially introduced into induced pluripotent stem cells (iPS). Splenic stem cells may have broad pluripotent potential, but unlike iPS cells, possess low oncogenic risk.