Adenovirus-mediated in utero expression of CFTR does not improve survival of CFTR knockout mice.

Davies L, Varathalingam A, Painter H, Lawton A, Sumner-Jones SG, Nunez-Alonso GA, Chan M, Munkonge F, Alton EW, Hyde S, Gill D

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The British Society of Gene Therapy Annual Conference, Edinburgh, 2008

Gene therapy is being investigated to treat lung aspects of the genetic disease Cystic Fibrosis (CF) and several clinical studies have demonstrated CFTR expression in the airways of adults with CF using a variety of gene transfer agents. In utero gene therapy has been proposed as an alternative approach, with the potential for increasing gene transfer efficiencies and avoiding immune recognition of the vector. In CF, in utero gene transfer could also potentially delay the early onset of disease symptoms in childhood. Previously published studies have suggested that transient expression of CFTR in utero was sufficient to rescue the fatal intestinal defect in S489X Cftrtm1Unc/Cftrtm1Unc CF knockout mice. We replicated these studies using an identical CFTR-expressing adenoviral vector (Av1CF2) and CF mouse strain in sufficiently large numbers to provide robust Kaplan-Meier survival data. Initial studies in C57BL6 mice confirmed that intra amniotic injection of vectors at day 16 of gestation resulted in vector uptake into both the lungs and intestines of developing fetuses and dose-dependent luciferase gene expression was observed in these organs following administration of between 10e6 and 10e8 pfu of the AdLuc luciferase expression vector. Intra-amniotic injection of 10e8 pfu Av1CF2 into CF knockout mice resulted in robust CFTR mRNA expression in both the lungs (130 ± 10e5 mRNA copies/ng total RNA) and intestines (3 ± 1 copies/ng) of treated animals compared to untreated CF mice (0.001 ± 0.001 copies/ng). However, no statistically significant improvement in median survival age was observed in Av1CF2 treated animals (9 ± 7.8 days) compared to untreated control mice (13 ± 2.5 days) or contemporaneous AdLacZ control treated animals (7 ± 6.7 days). This confirms that transient adenovirus-mediated in utero expression of human CFTR does not improve survival of CF knockout mice, although alternative gene transfer vectors need further investigation in this model.