Methods of delivering transgenes to target cells using plasmids comprising viral inverted terminal repeat (ITR) sequences are described. Such plasmids are capable of directing sustained transgene expression in target cells in rats provided that at least one adeno-associated virus (AAV) ITR sequence is present in the plasmid, regardless of whether that ITR is located upstream or downstream of the transgene. In a particular embodiment, plasmids comprising one or more AAV ITR sequence and an IL-10 transgene are shown to be effective in sustained reversal of pain in an animal model of neuropathic pain.