Longevity of airway gene therapy for cystic fibrosis : single and repeat lentiviral dosing.

The promise of gene therapy as a treatment and/or cure for cystic fibrosis (CF) airway disease is yet to be fulfilled. Lentiviral (LV) vectors possess many of the properties that would satisfy the requirements for an effective clinical gene correction treatment; the capacity to hold the large CF transmembrane conductance regulator (CFTR) gene, pseudotyped envelopes that provide broad tropism for a range of cells and tissue types, the ability to transduce dividing and non-dividing cells, the potential for long-term gene expression from genomic integration, and the lack of pre-existing blocking antibodies for majority of the CF population. To determine the persistence of LV gene expression, the same mice were repeatedly assessed throughout their lifetimes. The utilization of the biological compound lysophosphatidylcholine (LPC) as a pre-treatment enhanced nasal airway gene expression of the HIV-1 based LV vector containing reporter genes, or the functional CFTR gene, in normal and CF mice in vivo. Nasal luciferase (Luc) gene expression from a single LPC/LV nasal dose was sustained for the life time of normal mice, possibly suggesting an involvement of stem/progenitor cells or long-lived terminally differentiated cells. In contrast, stable long-term Luc gene expression was detected in the lung airways without the requirement of LPC pre-treatment. The loss then re-emergence of lung luminescence in CF mice demonstrated that stem/progenitor cells were transduced. This was the first examination of persistence of LV reporter gene and functional gene expression, in individual CF mice over their lifetimes. CF mice treated with LPC/LV-CFTR demonstrated a significant partial functional correction of the nasal CFTR electrophysiological defect that was sustained for up to 1 year. Importantly, this significantly increased survival, close to that observed in normal mice. Since the level of functional expression diminished over time in CF mice the ability to re-dose and evade blocking host immune responses was addressed. Multiple doses of a LV vector over a short time frame were feasible but did not significantly increase expression compared to a single dose. Circulating antibodies to both the vector envelope and the transgene protein were detected after repeat dosing conducting over a longer time frame. The timing of additional LV vector doses may be crucial for effective boosting of waning gene expression. The addition of a transient immunosuppressive treatment did not significantly enhance the level of gene expression produced by a single dose, but did reduce circulating antibodies to both the delivered foreign transgene and to the pseudotyped envelope protein. The demonstration of longevity of gene expression, the functional correction of the CFTR defect, the substantial increase in CF animal survival, the ability to re-dose and the use of immune-suppression to reduce antibody production provides strong and specific support for the continued investigation of LV CFTR gene transfer towards a clinical gene therapy treatment for CF airway disease.

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