Engraftment and multilineage repopulation potential of MGMTP140K gene-modified cells in secondary recipients after in vivo selection. (A) Schematic representation of secondary transplantation in DLA-matched dogs. The white dog represents the initial recipient of the gene-marked hematopoietic cells from the black dog (1°). The 2° transfer of the MGMTP140K gene-modified cells back into the original donor (black dog). (B,C top panels) Percentage of donor-positive WBC (----) and donor gene-modified WBC (●) in primary recipients (white dogs) is shown as a function of time. Chemotherapy denoted by small black arrows above the graph. Large black arrow indicates the time point at which the bone marrow was transplanted back into the original donors (black dogs). (B,C bottom panels) Percentage of gene-modified WBC in the secondary recipients (black dogs). Bar graphs to the right of the gene-marking plots are an alternate representation of hematopoietic contribution from each dog (white and black).