Detection of neo gene by PCR analysis of primary colonies isolated from the BM of SCID mice transplanted with HFBM transduced with a retroviral vector. HFBM was transduced with LN, a retroviral vector containing the neo gene as described in the Materials and Methods section and then transplanted into irradiated SCID mice. Two months later the BM of the mice was procured, placed in clonogenic assays, and the colonies were assessed for incorporated neo gene by PCR. A representative Southern blot using an intervening sequence probe specific for the neo primer pair-amplified product in randomly picked colonies is shown.