The invention provides a quiescent stem cell having the capacity to differentiate into ectoderm, mesoderm and endoderm, and which does not express cell surface markers including MHC class I, MHC class II, CD44, CD45, CD13, CD34, CD49c, CD73, CD105 CD90, CD66A, CD66E, CXCR4, CD133 or an SSEA. The invention further provides a proliferative stem cell, which expresses genes including Oct-4, Nanog, Sox2, GDF3, P16INK4, BMI, Notch, HDAC4, TERT, Rex-1, TWIST, KLF-4 and Stella but does not express cell surface markers including MHC class I, MHC class II, CD44, CD45, CD13, CD34, CD49c, CD73, CD105, CD90, CD66A, CD66E, CXCR4, CD133 or an SSEA. The cells of the invention can be isolated from adult mammals, have embryonic cell characteristics, and can form embryoid bodies. Methods for obtaining the stem cells, as well as methods of treating diseases and differentiated the stem cells, are also provided.