IL3 and leukemia: To serve as baseline comparators for our analysis of leukaemia progression, we elected to sample two controls: (i) the lineage negative/c-kit positive (lin-/kit+) compartment of wild-type bone-marrow mononuclear cells (WT) representing the target cells transduced by the leukaemogenic retroviruses [6], and (ii) the Factor-Dependent Cells Patterson-Mix (FDCP-mix) cell-line, a non-transformed IL3 dependent murine progenitor cell-line, capable of haematopoietic multi-lineage differentiation and, importantly, lacking leukaemogenic potential [21].