MDR1-positive colonies from different transduction medium and plating conditions. The transduction results from a group of 99 hematopoietic colonies, previously described in Fig 2, is shown here in grid format. The colonies are divided into transduction conditions, four cytokines or in medium alone, along the vertical axis. Cells are then further divided, along the horizontal axis, into the colony assay conditions in which they were grown, HPP-CFC (6 or 7 factor) and high–CSF-1. The number of colonies in each group appears in parentheses. The percent positive is listed in bold in each section. This illustrates the efficient transfer of the vector into the HPP-CFC regardless of transduction conditions or plating assay; colonies are 83% to 97% positive. Interestingly, both transduction conditions resulted in lower transfer into the macrophage colonies; 45% were positive from the four cytokine transductions and 57% were positive from the transduction in medium alone.