Mouse cystic fibrosis transmembrane conductance regulator (CFTR) differs from human CFTR in several important respects: altered gating pattern distinguished by prolonged residence in a sub-conductance state, reduced single-channel conductance and strong inward rectification. Transfer of the regulatory (R) domain of mouse CFTR to human CFTR was without effect, whereas transfer of both nucleotide-binding domains (NBDs) endowed human CFTR with greatly prolonged channel openings without conferring human CFTR with the sub-conductance state, single-channel conductance and inward rectification of mouse CFTR. We therefore hypothesised that the membrane-spanning domains (MSDs) determine these differences between human and mouse CFTR. To test this idea, we constructed the human-mouse CFTR (hmCFTR) chimeras hmTM1-6, hmTM7-12 and hmTM1-6:TM7-12 containing MSD1, MSD2 and MSD1+2 of mouse CFTR on a human CFTR background and studied them in excised inside-out membrane patches from transiently transfected CHO cells. For single-channel studies, we used a large Cl- concentration gradient ([Cl-]i, 147 mM; [Cl-]e, 10 mM) and clamped voltage at –50 mV, whereas for macroscopic studies, we used symmetrical Cl--rich solutions. All intracellular solutions contained PKA (75 nM) and ATP (1 mM) to activate and sustain CFTR activity; temperature was 37 °C. The three hmCFTR chimeras possessed a gating pattern intermediate between human and mouse CFTR. Both the single-channel conductance and open probability of the full open-state decreased in the rank order: human CFTR > hmTM7-12 > hmTM1-6 ≥ hmTM1-6:TM7-12 (n = 5-10). Like human CFTR, hmTM7-12 rarely transitioned to sub-conductance states, whereas hmTM1-6 sojourned to multiple sub-conductance states and hmTM1-6:TM7-12 resided in a tiny sub-conductance state resembling that of mouse CFTR. Human CFTR Cl- currents exhibited weak inward rectification, whereas those of mouse CFTR strongly inwardly rectified. Transfer of both MSDs of mouse CFTR to human CFTR in the chimeras hmTM1-6:TM7-12 reproduced the strong inward rectification of mouse CFTR (n = 4). Interestingly, the inward rectification of hmTM1-6 closely resembled that of mouse CFTR, whereas that of hmTM7-12 was intermediate between human and mouse CFTR (n = 6-9). Taken together, our data demonstrate that sequences from both MSDs specify the gating, conduction and rectification properties of CFTR with sequences from MSD1 playing a dominant role in determining the different rectification behaviour of human and mouse CFTR. Supported by the Biotechnology and Biological Sciences Research Council and Cystic Fibrosis Trust. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

We have recently shown that non-viral gene therapy can stabilise the decline of lung function in patients with cystic fibrosis (CF). However, the effect was modest, and more potent gene transfer agents are still required. Fuson protein (F)/Hemagglutinin/Neuraminidase protein (HN)-pseudotyped lentiviral vectors are more efficient for lung gene transfer than non-viral vectors in preclinical models. In preparation for a first-in-man CF trial using the lentiviral vector, we have undertaken key translational preclinical studies. Regulatory-compliant vectors carrying a range of promoter/enhancer elements were assessed in mice and human air-liquid interface (ALI) cultures to select the lead candidate; cystic fibrosis transmembrane conductance receptor (CFTR) expression and function were assessed in CF models using this lead candidate vector. Toxicity was assessed and 'benchmarked' against the leading non-viral formulation recently used in a Phase IIb clinical trial. Integration site profiles were mapped and transduction efficiency determined to inform clinical trial dose-ranging. The impact of pre-existing and acquired immunity against the vector and vector stability in several clinically relevant delivery devices was assessed. A hybrid promoter hybrid cytosine guanine dinucleotide (CpG)- free CMV enhancer/elongation factor 1 alpha promoter (hCEF) consisting of the elongation factor 1α promoter and the cytomegalovirus enhancer was most efficacious in both murine lungs and human ALI cultures (both at least 2-log orders above background). The efficacy (at least 14% of airway cells transduced), toxicity and integration site profile supports further progression towards clinical trial and pre-existing and acquired immune responses do not interfere with vector efficacy. The lead rSIV.F/HN candidate expresses functional CFTR and the vector retains 90-100% transduction efficiency in clinically relevant delivery devices. The data support the progression of the F/HN-pseudotyped lentiviral vector into a first-in-man CF trial in 2017.

Respiratory epithelium is the target of therapies, such as gene therapy, for cystic fibrosis (CF) lung disease. To determine the usefulness of the nasal epithelium as a pre-screen for lung-directed therapies, we profiled gene expression in CF and non-CF nasal and bronchial epithelium samples using Illumina HumanRef-8 Expression BeadChips. 863 genes were differentially expressed between CF and non-CF bronchial epithelium but only 15 were differentially expressed between CF and non-CF nasal epithelium ( ≥ 1.5-fold, P ≤ 0.05). The most enriched pathway in CF bronchial epithelium was inflammatory response, whereas in CF nasal epithelium it was amino acid metabolism. We also compared nasal and bronchial epithelium in each group and identified differential expression of cellular movement genes in CF patients and cellular growth genes in non-CF subjects. We conclude that CF and non-CF nasal and bronchial epithelium are transcriptionally distinct and CF nasal epithelium is not a good surrogate for the lung respiratory epithelium.

BACKGROUND:When assessing the efficacy of gene transfer agents (GTAs) for cystic fibrosis (CF) gene therapy, we routinely evaluate gene transfer in the mouse nose and measure transfection efficiency by assessing transgene-specific mRNA using the real-time (TaqMan) quantitative reverse transcriptase-polymerase chain reaction. TaqMan is traditionally used to quantify expression in whole tissue homogenates, which in the nose would contain many cells types, including respiratory and olfactory epithelium. Only the respiratory epithelium is a satisfactory model for human airway epithelium and therefore CFTR gene transfer should be specifically assessed in respiratory epithelial cells (RECs). METHODS:We have compared laser microdissection, pronase digestion and nasal brushing for: (i) the ability to enrich RECs from the wild-type mouse nose and (ii) the length of time to perform the procedure. Using TaqMan, we subsequently assessed gene transfer in enriched RECs after nasal perfusion of GL67A/pCF1-CFTR complexes in a CF mouse model. RESULTS:Laser microdissection successfully isolated RECs; however, time-consuming sample preparation made this technique unsuitable for high-throughput studies. Pronase digestion was sufficiently rapid but only yielded 19% (range = 13%) RECs (n = 6). The nasal brushing method was superior, yielding 92% (range = 15%) RECs (n = 8) and was equally effective in CF knockout mice (91%, range = 14%, n = 10). Importantly, gene transfer was detectable in brushed RECs from 70% of perfused mice and the number of vector-specific transcripts was comparable to 3.5% of endogenous wild-type Cftr levels. CONCLUSIONS:Isolation of RECs by brushing allows accurate assessment of GTA transfection efficiency in an experimental system that is relevant for CF gene therapy.

A clinical program to assess whether lipid GL67A-mediated gene transfer can ameliorate cystic fibrosis (CF) lung disease is currently being undertaken by the UK CF Gene Therapy Consortium. We have evaluated GL67A gene transfer to the murine nasal epithelium of wild-type and CF knockout mice to assess this tissue as a test site for gene transfer agents. The plasmids used were regulated by either (1) the commonly used short-acting cytomegalovirus promoter/enhancer or (2) the ubiquitin C promoter. In a study of approximately 400 mice with CF, vector-specific CF transmembrane conductance regulator (CFTR) mRNA was detected in nasal epithelial cells of 82% of mice treated with a cytomegalovirus-plasmid (pCF1-CFTR), and 62% of mice treated with an ubiquitin C-plasmid. We then assessed whether CFTR gene transfer corrected a panel of CFTR-specific endpoint assays in the murine nose, including ion transport, periciliary liquid height, and ex vivo bacterial adherence. Importantly, even with the comparatively large number of animals assessed, the CFTR function studies were only powered to detect changes of more than 50% toward wild-type values. Within this limitation, no significant correction of the CF phenotype was detected. At the current levels of gene transfer efficiency achievable with nonviral vectors, the murine nose is of limited value as a stepping stone to human trials.

We have assessed whether viscoelastic gels known to inhibit mucociliary clearance can increase lipid-mediated gene transfer. Methylcellulose or carboxymethylcellulose (0.25–1.5%) was mixed with complexes of the cationic lipid GL67A and plasmids encoding luciferase and perfused onto the nasal epithelium of mice. Survival after perfusion with 1% CMC or 1% MC was 90 and 100%, respectively. In contrast 1.5% CMC was uniformly lethal likely due to the viscous solution blocking the airways. Perfusion with 0.5% CMC containing lipid/DNA complexes reproducibly increased gene expression by approximately 3-fold (n=16, p<0.05). Given this benefit, likely related to increased duration of contact, we also assessed the effect of prolonging contact time of the liposome/DNA complexes by delivering our standard 80μg DNA dose over either approximately 22 or 60min of perfusion. This independently increased gene transfer by 6-fold (n=8, p<0.05) and could be further enhanced by the addition of 0.5% CMC, leading to an overall 25-fold enhancement (n=8, p<0.001) in gene expression. As a result of these interventions CFTR transgene mRNA transgene levels were increased several logs above background. Interestingly, this did not lead to correction of the ion transport defects in the nasal epithelium of cystic fibrosis mice nor for immunohistochemical quantification of CFTR expression. To assess if 0.5% CMC also increased gene transfer in the mouse lung, we used whole body nebulisation chambers. CMC was nebulised for 1h immediately before, or simultaneously with GL67A/pCIKLux. The former did not increase gene transfer, whereas co-administration significantly increased gene transfer by 4-fold (p<0.0001, n=18). This study suggests that contact time of non-viral gene transfer agents is a key factor for gene delivery, and suggests two methods which may be translatable for use in man.

Carpenter, Jane MSN, RN; Stevenson, Barbara MS, RN; Carson, Ellen PhD, ARNP,BC Author Information

An innovative family of tridentate-cationic "single-chained lipids" designed to enhance DNA compaction and to promote endosomal escape was synthesized by coupling various lipids to a multibranched scaffold. DNA retardation assays confirmed the ability of the most members of the library to complex DNA. Classical molecular dynamics simulations performed on the lauryl derivative, bound to a short strand of DNA in aqueous solution supported these observations. These showed that two "arms" of the tripodal molecule are ideally suited to forming strong Coulombic interactions with two contiguous phosphate groups from the DNA backbone while the lipophilic tail stays perpendicular to the DNA helix. Gene transfer abilities of the library were assessed in multiple cell lines (CHO, Cos7, and 16HBE14o-) with some library members giving excellent transfection abilities and low cytotoxicity, supporting the use of this tripodal approach for the development of efficient gene delivery agents.

The Portland Fish Exchange, opened in 1986 has grown into a highly su ccessful auction. During the same period other auctions in New England have diminished in their importance. Other attempted display auctions on both the east and west coast of the United States have failed. What factors have made the Portland auction a su ccess and are those factors transferable?

The creation of precise clinical mutations by gene targeting is important in elucidating disease pathogenesis using mouse models. 'Hit and run' gene targeting is an elegant method to achieve this goal. This uses first a positive selection to introduce the targeting vector carrying the required mutation and then a negative selection to identify clones which have removed vector and wild-type sequences by intrachromosomal recombination. However, this approach has only been successfully used in a handful of cases. We used this procedure to introduce precise clinical mutations into the exon 10 region of the cystic fibrosis transmembrane conductance regulator (Cftr) gene. Using a CMV promoter driven hygromycin/thymidine kinase (hyg/tk) fusion gene as both our dominant and negative selectable marker, we targeted the Cftr locus very efficiently but only identified false runs after the negative selection step. This defect in thymidine kinase induced toxicity to gancyclovir correlated with methylation of the transgene. Consequently we devised a stringent screening procedure to select only true 'run' clones. Unfortunately these 'run' clones had lost the mutation so we altered the vector design to bias the run step to retain the mutation and used a different tk selection cassette with a HSVtk promoter sequence. This new vector design allowed both efficient 'hit and run' for two cystic fibrosis (CF) mutations with no false positives and successful germline transmission of the novel G480C missense mutation.

In the January issue of Nature Medicine, an error in typography resulted in the incorrect printing of the Greek characters and μ. This error affected several papers. Nature Medicine regrets the errors, and all reprints of the articles have been corrected. Liposome-mediated CFTR gene transfer to the nasal epithelium of patients with cystic fibrosis Natasha J.