**7. Conclusions**

Aerosolizing catheters convert liquids into particles at the point of expulsion. Typically, an aerosolizing catheter is first passed into the trachea and then the vector is instilled. The Microsprayer® (PennCentury) and the AeroProbe® catheter (Trudell Medical International) are examples of delivery systems for this application. According to the manufacturer, it is possible to generate particles with aerodynamic diameters of 4–8 μm. The Trudell AeroProbe was previously used to aerosolize helper-dependent adenovirus vectors to rabbit airways [136, 137] and to deliver Sendai virus vectors to sheep [138]. Since Sendai virus and lentiviruses are both enveloped, it is likely that this approach is feasible with lentiviral vectors. In addition,

aerosolized VSVG-LVs have been successfully delivered to the airways of mice [139].

segments.

338 Cystic Fibrosis in the Light of New Research

lulose.

**6.2. Insertional mutagenesis**

the least economic delivery strategy for LVs.

Successful vector aerosolization has been reported in mice [140], rabbits,[136, 137], pig [141] and sheep airways [142, 143]. By 2–3 weeks of age, wild type pigs are large enough to be sedated and have a pediatric bronchoscope passed into the trachea. The AeroProbe® catheter can be passed to the carina via the bronchoscope suction channel with the animal breathing sponta‐ neously. In this way, an integrating vector can be aerosolized and targeted to specific bronchial

In the case of nebulizers, the liquid is first converted into mist and then passively inhaled. Using this strategy, a plasmid-based vector was delivered to the airways of CF patients in a phase IIB gene therapy trial [144]. This approach could potentially be used to deliver DNA transposon or hybrid vectors. However, this strategy may not be feasible with enveloped viral vectors because this class of vectors may not be stable enough to withstand nebulization. In addition, nebulization requires a large volume of concentrated material; therefore, would be

Atomizers are a subclass of aerosolizing catheters that deliver larger sized particles. An atomizer, such as the MADgicTM (LMA) atomizer, delivers large droplets (~30–90 μm in diameter), which may vary in size depending on the force applied to the syringe plunger. This type of device is often used to topically deliver medications to the airways [145]. Our group has observed that this type of atomizer is an effective delivery device for multiple viral vectors including FIV, particularly when formulated with a viscoelastic material such as methylcel‐

Since persistent gene expression from lentiviral vectors requires genomic integration, they show promise for treating life-long genetic diseases; however, there is inherent risk when introducing a transgene with integrating vectors. Insertional mutagenesis may disrupt normal cell functions by inactivating an essential host gene or inappropriately causing expression of an undesirable gene. The risk will vary depending on the vector used, the transgene cassette, and the cell type targeted. In many cases, enhancer effects pose the greatest danger. So far, malignant cell transformation after vector-mediated insertional mutagenesis has only been observed in three clinical entities (X-linked severe combined immunodeficiency (SCID-X1), chronic granulomatous disease (CGD), and Wiskott–Aldrich syndrome (WAS)), all of which occurred in conjunction with the use of first-generation gamma-retroviral vectors harboring LTRs with strong enhancer/promoter sequences [146-150]. These studies were conducted in

Within a year of the discovery of CFTR, investigators validated the concept that gene replacement could reverse the ion transport defect *in vitro*, suggesting that gene therapy may be possible [164, 165]. We and others have demonstrated that CFTR delivery by integrating vectors can correct the CF anion defect *in vitro* and *in vivo*, and although further pre-clinical trials are warranted, there is great potential for translating this strategy to the clinic. As discussed, estimates of the percent of CF epithelia requiring correction vary and there is debate about which cell types must be corrected to achieve phenotypic correc‐ tion; however, interest in CF gene therapy remains strong as barriers to gene transfer are identified, outcome measures are established, CF animal models with lung disease are developed, and better delivery systems are engineered. Demonstration of corrective gene transfer to pristine newborn lungs in CF animal models is a vital first step before looking ahead to correcting more diseased lungs. Newborn screening for CF is now established in all 50 states, allowing early disease detection. This offers an opportunity to introduce an integrating therapeutic gene transfer vector to the airway epithelium prior to the onset of chronic infection and inflammation. This strategy is a potentially life-long curative therapy regardless of the disease-causing mutation.
