Retroviral vector insertion site (RVIS) distribution according to gene classes and type of transgene. (A) RVISs in known proto-oncogenes (POGs) increase in frequency over serial BMT and are most pronounced in leukemic clones. (B) No major impact of the transgene class was found except when the vector encoded a potent oncogene (TAg), which increased the probability to select for RVIS in POGs. SIGs indicates signaling genes; OGs, other genes.