Chin-Shyan Chu

Administration of an adenovirus containing the human CFTR cDNA to the respiratory tract of individuals with cystic fibrosis.

We have administered a recombinant adenovirus vector (AdCFTR) containing the normal human CFTR cDNA to the nasal and bronchial epithelium of four individuals with cystic fibrosis (CF). We show that this vector can express the CFTR cDNA in the CF respiratory epithelium in vivo. With doses up to 2 × 109 pfu, there was no recombination/complementation or shedding of the vector or rise of neutralizing antibody titres. At 2 × 109 pfu, a transient systemic and pulmonary syndrome was observed, possibly mediated by interleukin-6. Follow-up at 6–12 months demonstrated no long term adverse effects. Thus, it is feasible to use an adenovirus vector to transfer and express the CFTR cDNA in the respiratory epithelium of individuals with CF. Correction of the CF phenotype of the airway epithelium might be achieved with this strategy.

Genetic basis of variable exon 9 skipping in cystic fibrosis transmembrane conductance regulator mRNA

Variable in–frame skipping of exon 9 in cystic fibrosis transmembrane conductance regulator (CFTR) mRNA transcripts (exon 9−) occurs in the respiratory epithelium. To explore the genetic basis of this event, we evaluated respiratory epithelial cells and blood leukocytes from 124 individuals (38 with cystic fibrosis (CF), 86 without CF). We found an inverse relationship between the length of the polythymidine tract at the exon 9 splice branch/acceptor site and the proportion of exon 9− CFTR mRNA transcripts. These results strongly indicate a genetic basis in vivo modulating post–transcriptional processing of CFTR mRNA transcripts.

Variable deletion of exon 9 coding sequences in cystic fibrosis transmembrane conductance regulator gene mRNA transcripts in normal bronchial epithelium.

The predicted protein domains coded by exons 9–12 and 19–23 of the 27 exon cystic fibrosis transmembrane conductance regulator (CFTR) gene contain two putative nucleotide‐binding fold regions. Analysis of CFTR mRNA transcripts in freshly isolated bronchial epithelium from 12 normal adult individuals demonstrated that all had some CFTR mRNA transcripts with exon 9 completely deleted (exon 9‐ mRNA transcripts). In most (9 of 12), the exon 9‐ transcripts represented less than or equal to 25% of the total CFTR transcripts. However, in three individuals, the exon 9‐ transcripts were more abundant, comprising 39, 62 and 66% of all CFTR transcripts. Re‐evaluation of the same individuals 2–4 months later showed the same proportions of exon 9‐ transcripts. Of the 24 CFTR alleles in the 12 individuals, the sequences of the exon‐intron junctions relevant to exon 9 deletion (exon 8‐intron 8, intron 8‐exon 9, exon 9‐intron 9, and intron 9‐exon 10) were identical except for the intron 8‐exon 9 region sequences. Several individuals had varying lengths of a TG repeat in the region between splice branch and splice acceptor consensus sites. Interestingly, one allele in each of the two individuals with 62 and 66% exon 9‐ transcripts had a TT deletion in the splice acceptor site for exon 9. These observations suggest either the unlikely possibility that sequences in exon 9 are not critical for the functioning of the CFTR or that only a minority of the CFTR mRNA transcripts need to contain exon 9 sequences to produce sufficient amounts of a normal CFTR to maintain a normal clinical phenotype.

Extensive posttranscriptional deletion of the coding sequences for part of nucleotide-binding fold 1 in respiratory epithelial mRNA transcripts of the cystic fibrosis transmembrane conductance regulator gene is not associated with the clinical manifestations of cystic fibrosis.

Cystic fibrosis (CF) is a recessive hereditary disorder, requiring both parental cystic fibrosis conductance transmembrane regulator (CFTR) genes to carry mutations for clinical disease to manifest, i.e., only 50% of normal CFTR gene expression is required to maintain a normal phenotype. To help define the minimum amount of normal CFTR gene expression necessary to maintain normalcy, we have capitalized on our prior observation (Chu, C.-S., B. C. Trapnell, J. J. Murtagh, Jr., J. Moss, W. Dalemans, S. Jallat, A. Mercenier, A. Pavirani, J.-P. Lecocq, G. R. Cutting, et al. 1991. EMBO [Eur. Mol. Biol. Organ] J. 10:1355-1363) that normal individuals can have up to 66% of bronchial CFTR mRNA transcripts that are missing exon 9, a region representing 21% of the sequence coding for the critical nucleotide (ATP)-binding fold 1 (NBF1) of the predicted CFTR protein. The study population included 78 individuals with no prior diagnosis of CF. Evaluation of bronchial epithelial cells (obtained by bronchoscopy) revealed that exon 9 was variably deleted in all individuals. Remarkably, there were four individuals, all greater than or equal to 35 yr, in whom bronchial epithelial cells exhibited 73, 89, 90, and 92% CFTR transcripts with inframe deletion of exon 9, respectively, despite normal sweat Cl- and no clinical manifestation of CF. In the context that only 8% or less of bronchial CFTR transcripts need exon 9 to maintain normal airway function, these observations strongly suggest that either exon 9 is not necessary for CFTR structure and/or function or that only a very small fraction of bronchial epithelial cells need to express normal CFTR mRNA transcripts with exon 9 to perform the function of CFTR sufficient to maintain a normal phenotype in vivo.