Hematopoietic cell gene therapy using retroviral vectors has achieved success in clinical trials. However, safety issues regarding vector insertional mutagenesis have emerged. In two different trials, vector insertion resulted in the transcriptional activation of proto-oncogenes. One strategy for potentially diminishing vector insertional mutagenesis is through the use of self-inactivating lentiviral vectors containing the 1.2-kb insulator element derived from the chicken beta-globin locus. However, use of this element can dramatically decrease both vector titer and transgene expression, thereby compromising its practical use. Here, we studied lentiviral vectors containing either the full-length 1.2-kb insulator or the smaller 0.25-kb core element in both orientations in the partially deleted long-terminal repeat. We show that use of the 0.25-kb core insulator rescued vector titer by alleviating a postentry block to reverse transcription associated with the 1.2-kb element. In addition, in an orientation-dependent manner, the 0.25-kb core element significantly increased transgene expression from an internal promoter due to improved transcriptional termination. This element also demonstrated barrier activity, reducing variability of expression due to position effects. As it is known that the 0.25-kb core insulator has enhancer-blocking activity, this particular insulated lentiviral vector design may be useful for clinical application.

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IT injection of AAV1 vector is a useful and non-invasive method for widespread gene delivery to the brain and dorsal root ganglia.

As both the immune system and the blood-brain barrier (BBB) are likely to be developmentally immature in the perinatal period, neonatal gene transfer may be useful for the treatment of lysosomal storage disease (LSD) with neurological involvements such as metachromatic leukodystrophy (MLD). In this experiment, we examined the feasibility of single-strand adeno-associated viral serotype-9 (ssAAV9)-mediated systemic neonatal gene therapy of MLD mice. ssAAV9 vector expressing human arylsulfatase A (ASA) and green fluorescent protein (GFP) (ssAAV9/ASA) was injected into the jugular vein of newborn MLD mice. High levels of ASA expression were observed in the muscle and heart for at least 15 months. ASA was continuously secreted into plasma without development of antibodies against ASA. Global gene transfer into the brain and spinal cord (SC), across the BBB, and long-term ASA expression in the central nervous system were detected in treated mice. Significant inhibition of the accumulation of sulfatide (Sulf) in the brain and cervical SC was confirmed by Alcian blue staining and biochemical analysis of the Sulf content. In a behavior test, treated mice showed a greater ability to traverse narrow balance beams than untreated mice. These data clearly demonstrate that MLD mice model can be effectively treated through neonatal systemic injection of ssAAV9/ASA.

Lentiviral vectors, including double internal promoters, can be used to express two transgenes in a single vector construct; however, transcriptional activities from double internal promoters are often inhibited by promoter interference. To determine whether the chicken hypersensitivity site 4 insulator (cHS4) could block promoter interference, lentiviral vectors including an MSCV-U3 promoter (Mp) and an EF1a promoter (Ep) were generated, and transgene expression was evaluated among transduced cells. In the Ep-Mp configuration, transcriptional activity from Mp was much lower, while Mp-Ep had similar transcription levels from both promoters. The cHS4 core insulator increased expression levels from Mp in HeLa cells, hematopoietic cell lines, and mouse peripheral blood cells following hematopoietic stem cell transplantation transduced with the Mp-Ep configured vector. This blocking function was mainly mediated by barrier activity regions in the insulator but not by CCCTC-binding factor (CTCF) binding sites. Cytosine-phosphate-guanine (CpG) methylation did not contribute to this barrier activity. In summary, combining the cHS4 insulator in double promoter vectors can improve transgene expression levels in various cell lines and mouse hematopoietic repopulating cells. These findings are useful for developing hematopoietic stem cell gene therapy.