Transient versus stable transfection. Multiple methods for achieving transgenesis are shown. Column 1 – plasmids. Multiple copies found transiently, and multiple integration sites upon stable transfection. Column 2 – lentivirus (LV), adeno-associated virus (AAV) and herpes simplex virus (HSV). Transduction is long term and not of a transient nature. LV integrates with several copies; AAV and HSV are both non-integrative. Column 3 – adenovirus. Virus usually lacks replication ability, thus only transient transduction, at multiple copies, is achieved. Column 4 – bacterial artificial chromosomes (BACs). Transient expression results in low copy number within the nucleus, stable expression is integrative at a low copy number also. Column 5 – episomal vectors. Transient expression of several copies, vector associates with chromosome and nuclear matrix. For stable expression, the vector continues to associate with the chromosomal regions and nuclear matrix but does not integrate. Column 6 – gene knockin or targeted integration. These are stable only approaches and involve targeting either the endogenous gene locus or a predetermined locus.