Co-culture experiments were set up to compare PERV transmission from two independently derived PK-15 clones expressing human APOBEC3G and two vector expressing controls. Remarkably, the human APOBEC3G expressing PK-15 clones showed levels of PERV transmission that were lower than the Q-PCR detection threshold of approximately 10 copies ( Figure 2B ; . This graph summarizes data for two independently derived PK-15 clones, V1 (squares) and V2 (diamonds). All data points were calculated using results from duplicate Q-PCR reactions of genomic DNA from three parallel (but independent) co-cultures. The error bars indicate the SEM. See the Materials and Methods and Online Figure S1 for additional details, representative raw data and controls. doi:10.1371/journal.pone.0000893.g001