The scid mouse as a model to identify and quantify myeloid and lymphoid stem cells

Scid mice are excellent recipients for studying the characteristics of stem cells. Sublethal irradiation not only enhances engraftment of stem cells but enables one to graft limiting numbers of cells without compromising the survival of the recipient. This enables one to estimate the frequency of stem cells by limiting dilution analysis. Compared to fresh bone marrow, LTBMC are slightly enriched for stem cells capable of reconstituting lymphoid function in scid recipients. The stem cells have self-renewal ability since bone marrow from cured primary scid recipients can cure secondary recipients. Our results indicate that lymphoid reconstitution following engraftment with LTBMC occurs from a lymphoid-restricted stem cell; similar restricted stem cells also exist in normal bone marrow.