Sca-1 is a member of the Ly-6 antigen family which molecular mass of 8 kDa under non-reducing conditions and of 18 kDa under reducing conditions. Mouse hematopoietic stem cells express low levels of Thy-1 antigen (Thy-1lo) and to be negative for lineage markers (Lin-) that is, not expressing markers characteristic of B cells (B220), granulocytes (Gr-1), myelomonocytic cells (Mac-1) and T lymphocytes (CD4 and CD8). Recently, new monoclonal antibody, anti-Sca-1, was used to purify stem cells from the Thy-1lo, Linbone marrow subpopulation. Thy-1lo, Lin-, Sca-1+ (but not the Thy-1lo, Lin-, Sca-1-) population of bone marrow cells are highly purified pluripotent stem cells. They read out with nearly unit efficiency in assays for primitive myeloerythroid and thymic progenitor, and have a capability to admit lethally irradiated mouse to survive and be restored in all blood-cell lineages. The Thy-1lo, Lin-, Sca-1+ subpopulation thought to have all stem cells present in the bone marrow.Synonyms: Ly-6A.2/Ly-6E.1, Lymphocyte antigen 6A-2/6E-1, SCA-1, Stem cell antigen 1, T-cell-activating protein, TAP