The present invention provides an integration-defective lentiviral vector based on a parental lentivirus and related methods, the integration-defective lentiviral vector including one or more of the following: (a) a mutation, deletion or other modification of one or more binding sites for a host factor involved in gene silencing; (b) an addition of one or more binding sites for a transcription activator, which can be natural (such as but not limited to ubiquitous and/or tissue/cell type specific) including but not limited to SP1 NFkB, or synthetic including but not limited to binding sites for tetracycline regulated trans activators tTA, rtTA, tT65, and/or rtT65; (c) one or more nucleic acid sequences from a SV40 genome, wherein the one or more sequences are obtained from a region of the SV40 genome upstream to the SV40 poly-adenylation signal; (d) a shRNA expression cassette, which encodes a shRNA directed to a host gene involved in epigenetic silencing and/or in DNA repair pathways; or (e) any combination of (a), (b), (c) and (d), wherein as compared to the parental lentivirus, the integration-defective lentiviral vector resists gene silencing.