Towards Human Translation of Lentiviral Airway Gene Delivery for Cystic Fibrosis: A One-Month CFTR and Reporter Gene Study in Marmosets

Adeno-Associated Virus-Mediated Gene Therapy

Choice of vector is the most critical step in gene therapy. Adeno-associated viruses (AAV); third generation vectors, are getting much attention of scientists to be used as vehicles due to their non-pathogenicity, excellent safety profile, low immune responses, great efficiency to transduce non-dividing cells, large capacity to transfer genetic material and long-term expression of genetic payload. AAVs have multiple serotypes and each serotype shows tropism for a specific cell. Different serotypes are used to target liver, lungs, muscles, retina, heart, CNS, kidneys, etc. Furthermore, AAV based gene therapies have tremendous marketing applications that can be perfectly incorporated in the anticipated sites of the host target genome resulting in life long expression of transgenes. Some therapeutic products use AAV vectors that are used to treat lipoprotein lipase deficiency (LPLD) and it is injected intramuscularly, to treat mutated retinal pigment epithelium RPE65 (RPE65) that is introduced to subretinal space, an intravenous infusion to treat spinal muscular atrophy and rAAV2-CFTR vector is introduced into nasal epithelial cells to treat cystic fibrosis. AAV therapies and other such interdisciplinary methodologies can create the miracles for the generation of precision gene therapies for the treatment of most serious and sometimes fatal disorders.

Comparison of physical perturbation devices for enhancing lentiviral vector-mediated gene transfer to the airway epithelium

Natural airway defences currently impede the efficacy of viral vector-mediated airway gene therapy. Conditioning airways prior to vector delivery can disrupt these barriers, improving viral vector access to target receptors and airway stem cells. This study aimed to assess and quantify the in vivo histological and gene transfer effects of physical perturbation devices to identify effective conditioning approaches. A range of flexible wire baskets with varying configurations, a Brush, biopsy forceps, and a balloon catheter were examined. We first evaluated the histological effects of physical perturbation devices in rat tracheas that were excised 10 minutes after conditioning. Based on the histological findings, a selection of devices were used to condition rat tracheas in vivo before delivering a lentiviral vector containing the LacZ reporter gene. After 7 days, excised tracheas were X-gal processed and examined en face to quantify the area of LacZ staining. Histological observations 10 minutes after conditioning found that physical perturbation dislodged cells from the basement membrane to varying degrees, with some producing significant levels of epithelial cell removal. When a subset of devices were assessed for their ability to enhance gene transfer, only the NGage® wire basket (Cook Medical) produced a significant increase in the proportion of X-gal-stained area when compared to unconditioned tracheas (8-fold, p = 0.00025). These results suggest that a range of factors contribute to perturbation-enhanced gene transfer. Overall, this study supports existing evidence that physical perturbation can assist airway gene transfer, and will help to identify the characteristics of an effective device for airway gene therapy.

Effective viral-mediated lung gene therapy: is airway surface preparation necessary?

Gene-based therapeutics are actively being pursued for the treatment of lung diseases. While promising advances have been made over the last decades, the absence of clinically available lung-directed genetic therapies highlights the difficulties associated with this effort. Largely, progress has been hindered by the presence of inherent physical and physiological airway barriers that significantly reduce the efficacy of gene transfer. These barriers include surface mucus, mucociliary action, cell-to-cell tight junctions, and the basolateral cell membrane location of viral receptors for many commonly used gene vectors. Accordingly, airway surface preparation methods have been developed to disrupt these barriers, creating a more conducive environment for gene uptake into the target airway cells. The two major approaches have been chemical and physical methods. Both have proven effective for increasing viral-mediated gene transfer pre-clinically, although with variable effect depending on the specific strategy employed. While such methods have been explored extensively in experimental settings, they have not been used clinically. This review covers the airway surface preparation strategies reported in the literature, the advantages and disadvantages of each method, as well as a discussion about applying this concept in the clinic.

In vitro optimization of miniature bronchoscope lentiviral vector delivery for the small animal lung

Current gene therapy delivery protocols for small animal lungs typically utilize indirect dose delivery via the nasal airways, or bolus delivery directly into the trachea. Both methods can result in variable transduction throughout the lung, as well as between animals, and cannot be applied in a targeted manner. To minimize variability and improve lung coverage we previously developed and validated a method to visualize and dose gene vectors into pre-selected lobes of rat lungs using a mini-bronchoscope. Lentiviral (LV) vectors are known to be fragile and can be inactivated easily by temperature or the application of shear stresses. There are several ways that the bronchoscope could be configured to deliver the LV vector, and these could result in different amounts of functional LV vector being delivered to the lung. This study evaluated several methods of LV vector delivery through the bronchoscope, and how flow rates and LV vector stabilizing diluents impact LV vector delivery. NIH-3T3 cells were exposed to LV vector containing the green fluorescent protein (GFP) reporter gene using various bronchoscopic delivery techniques and the number of GFP-positive cells produced by each was quantified by flow cytometry. The results showed that directly drawing the LV vector into the bronchoscope tip resulted in 80-90% recovery of viable vector, and was also the simplest method of delivery. The fluid delivery rate and the use of stabilizing serum in the vector diluent had no effect on the viability of the LV vector delivered. These findings can be used to optimize LV vector dose delivery into individual lung lobes of small animal models.

The Effects of Conditioning and Lentiviral Vector Pseudotype on Short- and Long-Term Airway Reporter Gene Expression in Mice

A gene addition therapy into the conducting airway epithelium is a potential cure for cystic fibrosis lung disease. Achieving sustained lung gene expression has proven difficult due to the natural barriers of the lung. The development of lentiviral (LV) vectors pseudotyped with viral envelopes that have a natural tropism to the airway has enabled persistent gene expression to be achieved in vivo. The aims of this study were to compare the yields of hemagglutinin (HA) and vesicular stomatitis virus-glycoprotein (VSV-G) pseudotyped HIV-1 vectors produced under the same conditions by our standard LV vector production method. We then sought to measure gene expression in mouse airways and to determine whether lysophosphatidylcholine (LPC) conditioning enhances short- and long-term gene expression. C57Bl/6 mouse airways were conditioned with 10 μL of 0.1% LPC or saline control, followed 1 h later by a 30 μL dose of an HA or VSV-G pseudotyped vector carrying either the LacZ or luciferase reporter genes. LacZ expression was assessed by X-gal staining after 7 days, while lung luminescence was quantified regularly for up to 18 months by bioluminescent imaging. The HA pseudotyped vectors had functional titers 25 to 60 times lower than the VSV-G pseudotyped vectors. Conditioning the lung with LPC significantly increased the total number of LacZ-transduced cells for both pseudotypes compared to saline control. Regardless of LPC conditioning, the VSV-G pseudotype produced higher initial levels of gene expression compared to HA. LPC conditioning did not increase the number of transduced basal cells for either pseudotype compared to saline, and was not required for long-term gene expression. Both pseudotyped vectors effectively transduced the upper conducting airways of wild-type mice. The use of LPC conditioning before vector delivery was not required in mouse lungs to produce long-term gene expression, but did improve short-term gene expression.