- Open Access
Taking stock of gene therapy for cystic fibrosis
© Current Science Ltd 2000
- Received: 28 April 2000
- Accepted: 1 September 2000
- Published: 15 September 2000
The identification of the cystic fibrosis (CF) gene opened the way for gene therapy. In the ten years since then, proof of principle in vitro and then in animal models in vivo has been followed by numerous clinical studies using both viral and non-viral vectors to transfer normal copies of the gene to the lungs and noses of CF patients. A wealth of data have emerged from these studies, reflecting enormous progress and also helping to focus and define key difficulties that remain unresolved. Gene therapy for CF remains the most promising possibility for curative rather than symptomatic therapy.
- cationic lipids
- cystic fibrosis
- gene therapy
- recombinant viruses
The cloning of the CF gene with subsequent characterisation of its protein (CFTR)  opened the way for gene and protein therapy. The idea was simply to administer the normal CF gene or protein, as though it were a drug, to the organ most affected yet apparently quite accessible: the lungs. In theory this should result in the restoration of normal cellular function and thus prevent or treat the disease. A vigorous research effort followed the identification of the gene; the first reports of CFTR gene transfer in vitro appeared in 1990 , only one year later. Further studies in vitro  were followed by gene transfer in vivo to the airway epithelial cells of transgenic CF mice [4,5], confirming that it was possible to achieve some functional restoration of the ion transport defects in these cells after transgene expression. Within four years, four clinical studies of gene therapy in CF patients had been reported; since then there have been over 20 phase I studies.
Several of these trials used adenoviral vectors to transfer CFTR cDNA to adult volunteers with CF; many of these trials have now been reported [6–13]. Some early studies reported acute inflammation, which was probably related to the local instillation of a high viral load. There has been evidence of gene transfer as determined by the detection of mRNA or CFTR protein, although this was not a consistent finding. Electrophysiological correction has been suggested in some studies, but only one study was controlled and this showed limited evidence of gene transfer at the highest dose, with no evidence of functional correction. Two clinical trials with adeno-associated virus (AAV) as the gene transfer agent have also been reported [14,15]. No significant side effects have been observed and some evidence of correction of the chloride defect has been suggested.
Liposome–plasmid complexes have been tested in several clinical trials [16–21]. Of these, five were double-blind placebo-controlled studies. Three trials with a similar design showed a partial correction of the chloride transport defect in the nose [16–18]. In a further study, complexes were delivered to the lungs by nebulisation  with an approximate 20% restoration of chloride transport towards normal values. Administration was associated with a transient febrile reaction that did not occur in the control group, who received only the lipid; this reaction might have been attributable to the bacterial origin of the DNA . None of these studies showed any correction of the sodium defect, and vector-specific mRNA was only inconsistently found.
A wealth of data have emerged from all of these studies, reflecting enormous progress but also helping to focus on the key difficulties. The principal issue is to improve the efficiency of gene transfer, but questions relating to the level of efficiency needed and the target cell population also need addressing. The key problem of efficiency can be considered in terms of either improving vectors or overcoming biological barriers. An intrinsic function of the lining epithelium of the airways is to prevent penetration by foreign materials and invading organisms. Thus, a complex series of epithelial barriers, including a mucous layer that inhibits gene transfer , a glycocalyx, an apical cell membrane and tight junctions between the cells, conspire to keep out intraluminally delivered materials, including both viral and non-viral vectors. This problem is compounded in CF by the presence of thick, infected sputum, also known to inhibit gene transfer , and plugging of the small airways with mucus. The use of adjunctive mucolytic agents or the abrogation of tight junction barrier function either with detergents or with antibodies against intrinsic tight junction components, are just two novel strategies being investigated to overcome these barriers.
In addition, much effort is being devoted to the modification of vectors. For adenovirus, AAV and other viruses, the appropriate receptors are largely confined to the basolateral cell membrane. Thus, attempts are now being made to adapt viral entry by using apically sited receptors such as the UTP-binding P2Y2 receptor. Novel viruses are increasingly being investigated, and cationic liposomes and polymers are increasingly being coupled to peptides, sugars and viral particles to try to increase gene transfer efficiency. The vexing question of how much effective gene delivery and expression is required to achieve clinical benefit remains unresolved, but the level is likely to be low. If gene transfer is achieved in only a certain proportion of cells within the airway epithelium, then studies suggest that 6–10% of cells need to be corrected to reverse the chloride defect and 100% for the sodium defect [25,26]. If, in contrast, delivery occurs to every cell, then levels of approximately 5% of normal CFTR mRNA can correct the chloride defect and reverse the intestinal pathology in CF mice . These goals have not yet been reached but the relatively low levels that might be needed are encouraging.
CF affects the conducting airways rather than the alveoli. These include both the larger bronchial regions lined by a pseudostratified columnar epithelium and containing numerous submucosal glands, and the small bronchiolar regions lined by a simple columnar epithelium devoid of glands. A central question for CF gene therapy is which cell type and which region (large or small airways) to target. Although ciliated superficial epithelium is abundant and displays the ion transport defects in patients with CF, the submucosal glands are the cells expressing the highest CFTR levels in the lung and might well need to be targeted for clinical benefit. This raises considerations of delivery, because topical application is unlikely to reach these cells. Further, most results suggest that small airways are both the initial and the major site of disease in CF. Again, the effective delivery of cDNA to these areas is difficult with present nebuliser technology and remains an important strategic issue.
A final important issue relates to repeated application. All of the current vectors are likely to produce episomal gene transfer, and the current duration of expression after a single application is measurable in weeks. This does not matter as long as multiple applications are feasible. In this regard, cationic liposomes seem to have an important advantage, with a third application having been shown to be as effective as the first in a recent trial of multiple applications of liposome-mediated gene therapy to the nasal epithelium of CF patients . The repeated administration of viral vectors results in the production of neutralising antibodies that limit reapplication efficiency, and considerable effort is being expended to reduce this problem.
Gene therapy will probably prove to be most beneficial if given very early, before the onset of established infection or inflammation in the lungs. Thus, questions about the execution and design of trials in the paediatric population are likely to become the focus of new efforts . The rigorous measurement of gene transfer efficiency in vivo and the development of markers – both real and surrogate – of clinical benefit also remain important challenges.
In conclusion, CFTR gene therapy has proved to be safe so far and has produced a proof of principle with respect to CFTR function in the target organ in humans, an encouraging position in a young field. Nevertheless, it is not yet a clinically effective treatment for CF lung disease. The inevitable pessimism that follows unrealistic expectations of a rapid cure has dogged the recent media view of gene therapy. Gene therapy is clearly at the typical stage of new drug development where considerable and unglamorous effort needs to be expended to move from proof of principle to clinical product. Encouraging progress in gene therapy can clearly be found both within the CF field and in parallel areas. Thus, a clinical study of intramuscular injection of an AAV vector expressing factor IX in adults with severe haemophilia B  demonstrated prolonged expression of the protein and positive changes in clinical endpoints, including circulating levels of factor IX and the frequency of infusion of factor IX protein. The questions that remain to be answered for successful CF gene therapy have now been clearly defined, and gene therapy for CF remains the most promising possibility for curative rather than symptomatic therapy.
- Riordan JR, Rommens JM, Kerem B, Alon N, Rozmahel R, Grzelczak Z, Zielenski J, Lok S, Plavsic N, Chou JL, Drumm ML, Iannuzzi MC, Collins FS, Tsui LC: Identification of the cystic fibrosis gene: cloning and characterization of complementary DNA. Science 1989, 245:1066–1073.View ArticlePubMedGoogle Scholar
- Drumm ML, Pope HA, Cliff WH, Rommens JM, Marvin SA, Tsui LC, Collins FS, Frizzell RA, Wilson JM: Correction of the CF defect in vitro by retrovirus-mediated gene transfer. Cell 1990, 62:1227–1233.View ArticlePubMedGoogle Scholar
- Rich DP, Anderson MP, Gregory RJ, Cheng SH, Paul S, Jefferson DM, McCann JD, Klinger KW, Smith AE, Welsh MJ: Expression of cystic fibrosis transmembrane conductance regulator corrects defective chloride channel regulation in cystic fibrosis airway epithelial cells. Nature 1990, 347:358–363.View ArticlePubMedGoogle Scholar
- Hyde SC, Gill DR, Higgins CF, Trezise AE, MacVinish LJ, Cuthbert AW, Ratcliff R, Evans MJ, Colledge WH: Correction of the ion transport defect in cystic fibrosis transgenic mice by gene therapy. Nature 1993, 362:250–255.View ArticlePubMedGoogle Scholar
- Alton EWFW, Middleton PG, Caplen NJ, Smith SN, Steel DM, Munkonge FM, Jeffery PK, Geddes DM, Hart SL, Williamson R, Fasold KI, Miller AD, Dickinson P, Stevenson BJ, McLachlan G, Dorin JR, Porteous DJ: Non-invasive liposome-mediated gene delivery can correct the ion transport defect in cystic fibrosis mice. Nat Genet 1993, 5:135–142.View ArticlePubMedGoogle Scholar
- Zabner J, Couture RA, Gregory RJ, Graham SM, Smith AE, Welsh MJ: Adenovirus-mediated gene transfer transiently corrects the chloride transport defect in nasal epithelia of patients with cystic fibrosis. Cell 1993, 75:207–216.View ArticlePubMedGoogle Scholar
- Crystal RG, McElvaney NG, Rosenfeld MA, Chu CS, Mastrangeli A, Hay JG, Brody SL, Jaffe HA, Eissa NT, Danel C: Administration of an adenovirus containing the human CFTR cDNA to the respiratory tract of individuals with cystic fibrosis. Nat Genet 1994, 8:42–51.View ArticlePubMedGoogle Scholar
- Knowles MR, Hohneker KW, Zhou Z, Olsen JC, Noah TL, Hu PC, Leigh MW, Engelhardt JF, Edwards LJ, Jones KR, Grossman M, Wilson JM: A controlled study of adenoviral-vector-mediated gene transfer in the nasal epithelium of patients with cystic fibrosis. N Engl J Med 1995, 333:823–831.View ArticlePubMedGoogle Scholar
- Zabner J, Ramsey BW, Meeker DP, Aitken ML, Balfour RP, Gibson RL, Launspach J, Moscicki RA, Richards SM, Standaert TA, Williams-Warren J, Wadsworth SC, Smith AE, Welsh MJ: Repeat administration of an adenovirus vector encoding cystic fibrosis transmemebrane conductance regulator to the nasal epithelium of patients with cystic fibrosis. J Clin Invest 1996, 97:1504–1511.View ArticlePubMedPubMed CentralGoogle Scholar
- Bellon G, Michel-Calemard L, Thouvenot D, Jagneaux V, Poitevin F, Malcus C, Accart N, Layani MP, Aymard M, Bernon H, Bienvenu J, Courtney M, Doring G, Gilly B, Gilly R, Lamy D, Levrey H, Morel Y, Paulin C, Perraud F, Rodillon L, Sene C, So S, Touraine-Moulin F, Pavirani A: Aerosol administration of a recombinant adenovirus expressing CFTR to cystic fibrosis patients: a phase I clinical trial. Hum Gene Ther 1997, 1:15–25.View ArticleGoogle Scholar
- Harvey BG, Leopold PL, Hackett NR, Grasso TM, Williams PM, Tucker AL, Kaner RJ, Ferris B, Gonda I, Sweeney TD, Ramalingam R, Kovesdi I, Shak S, Crystal RG: Airway epithelial CFTR mRNA expression in cystic fibrosis patients after repetitive administration of a recombinant adenovirus. J Clin Invest 1999, 4:1245–1255.View ArticleGoogle Scholar
- Zuckerman JB, Robinson CB, McCoy KS, Shell R, Sferra TJ, Chirmule N, Magosin SA, Propert KJ, Brown-Parr EC, Hughes JV, Tazelaar J, Baker C, Goldman MJ, Wilson JM: A phase I study of adenovirus-mediated transfer of the human cystic fibrosis transmembrane conductance regulator gene to a lung segment of individuals with cystic fibrosis. Hum Gene Ther 1999, 18:2973–2985.View ArticleGoogle Scholar
- Bellon G, Fau C, Michel L, Thouvenot D, Rodillon L, Bienvenue J, Malcus C, Levery H, Squiban P, Pavirani A: CFTR gene transfer by repeated administration of recombinant adenovirus to the nasal mucosa of cystic fibrosis patients. Paediatr Pulmonol Suppl 1999, 9:210.Google Scholar
- Wagner JA, Reynolds T, Moran ML, Moss RB, Wine JJ, Flotte TR, Gardner P: Efficient and persistent gene transfer of AAV-CFTR in the maxillary. Lancet 1998, 651:1702–1703.View ArticleGoogle Scholar
- Wagner JA, Messner AH, Moran ML, Guggino WB, Flotte TR, Wine JJ, Carter BJ, Batson EP, Moss RB, Gardner P: A phase II double-blind randomised controlled clinical trial of tgAVCF using maxillary sinus delivery in CF patients with antrostomies. Paediatr Pulmonol Suppl 1999, 19:209.Google Scholar
- Caplen NJ, Alton EW, Middleton PG, Dorin JR, Stevenson BJ, Gao X, Durham SR, Jeffery PK, Hodson ME, Coutelle C, Huang L, Porteous DJ, Williamson R, Geddes DM: Liposome mediated CFTR gene transfer to the nasal epithelium of patients with cystic fibrosis. Nat Med 1995, 1:39–46.View ArticlePubMedGoogle Scholar
- Gill DR, Southern KW, Mofford KA, Seddon T, Huang L, Sorgi F, Thomson A, MacVinish LJ, Ratcliff R, Bilton D, Lane DJ, Littlewood JM, Webb AK, Middleton PG, Colledge WH, Cuthbert AW, Evans MJ, Higgins CF, Hyde SC: A placebo controlled study of liposome-mediated gene transfer to the nasal epithelium of patients with cystic fibrosis. Gene Ther 1997, 4:199–209.View ArticlePubMedGoogle Scholar
- Porteous DJ, Dorin JR, McLachlan G, Davidson-Smith H, Davidson H, Stevenson BJ, Carothers AD, Wallace WA, Moralee S, Hoenes C, Kallmeyer G, Michaelis U, Naujoks K, Ho LP, Samways JM, Imrie M, Greening AP, Innes JA: Evidence for safety and efficacy of DOTAP cationic liposome-mediated CFTR gene transfer to the nasal epithelium of patients with cystic fibrosis. Gene Ther 1997, 4:210–218.View ArticlePubMedGoogle Scholar
- Zabner J, Cheng SH, Meeker D, Launspach J, Balfour R, Perricone MA, Morris JE, Marshall J, Fasbender A, Smith AE, Welsh MJ: Comparison of DNA-lipid complexes and DNA alone for gene transfer to cystic fibrosis airway epithelium in vivo. J Clin Invest 1997, 100:1529–1537.View ArticlePubMedPubMed CentralGoogle Scholar
- Alton EW, Stern M, Farley R, Jaffe A, Chadwick SL, Phillips J, Davies J, Smith SN, Browning J, Davies MG, Hodson ME, Durham SR, Li D, Jeffery PK, Scallan M, Balfour R, Eastman SJ, Cheng SH, Smith AE, Meeker D, Geddes DM: Cationic lipid-mediated CFTR gene transfer to the lungs and nose of patients with cystic fibrosis: a double-blind placebo-controlled trial. Lancet 1999, 353:947–954.View ArticlePubMedGoogle Scholar
- Noone PG, Hohneker KW, Zhou Z, Johnson LG, Foy C, Gipson C, Jones K, Noah TL, Leigh MW, Schwartzbach C, Efthimiou J, Pearlman R, Boucher RC, Knowles MR: Safety and efficacy of a lipid-CFTR complex for gene transfer in the nasal epithelium of adult patients with cystic fibrosis. Mol Ther 2000, 1:105–114.View ArticlePubMedGoogle Scholar
- Schwartz DA, Quinn TJ, Thorne PS, Sayeed S, Yi AK, Krieg AM: CpG motifs in bacterial DNA cause inflammation in the lower respiratory tract. J Clin Invest 1997, 100:68–73.View ArticlePubMedPubMed CentralGoogle Scholar
- Kitson C, Angel B, Judd D, Rothery S, Severs NJ, Dewar A, Huang L, Wadsworth SC, Cheng SH, Geddes DM, Alton EW: The extra- and intracellular barriers to lipid and adenovirus-mediated pulmonary gene transfer in native sheep airway epithelium. Gene Ther 1999, 6:534–546.View ArticlePubMedGoogle Scholar
- Stern M, Caplen NJ, Browning JE, Griesenbach U, Sorgi F, Huang L, Gruenert DC, Marriot C, Crystal RG, Geddes DM, Alton EW: The effect of mucolytic agents on gene transfer across a CF sputum barrier in vitro. Gene Ther 1998, 5:91–98.View ArticlePubMedGoogle Scholar
- Johnson LG, Olsen JC, Sarkadi B, Moore KL, Swanstrom R, Boucher RC: Efficiency of gene transfer for restoration of normal airway epithelial function in cystic fibrosis. Nat Genet 1992, 2:21–25.View ArticlePubMedGoogle Scholar
- Johnson LG, Boyles SE, Wilson J, Boucher RC: Normalisation of raised sodium absorption and raised calcium-mediated chloride secretion by adenovirus-mediated expression of cystic fibrosis transmembrane conductance regulator in primary human cystic fibrosis airway epithelial cells. J Clin Invest 1995, 95:1377–1382.View ArticlePubMedPubMed CentralGoogle Scholar
- Dorin JR, Farley R, Webb S, Smith SN, Farini E, Delaney SJ, Wainwright BJ, Alton EW, Porteous DJ: A demonstration using mouse models that successful gene therapy for cystic fibrosis requires only partial gene correction. Gene Ther 1996, 3:797–801.PubMedGoogle Scholar
- Hyde SC, Southern KW, Gileadi U, Fitzjohn EM, Mofford KA, Waddell BE, Gooi HC, Goddard CA, Hannavy K, Smyth SE, Egan JJ, Sorgi FL, Huang L, Cuthbert AW, Evans MJ, Colledge WH, Higgins CF, Webb AK, Gill DR: Repeat administration of DNA liposomes to the nasal epithelium of patients with cystic fibrosis. Gene Ther 2000, 13:1156–1165.View ArticleGoogle Scholar
- Jaffe A, Bush A, Geddes DM, Alton EW: Prospects for gene therapy in cystic fibrosis. Arch Dis Child 1999, 80:286–289.View ArticlePubMedPubMed CentralGoogle Scholar
- Kay MA, Manno CS, Ragni MV, Larson PJ, Couto LB, McClelland A, Glader B, Chew AJ, Tai SJ, Herzog RW, Arruda V, Johnson F, Scallan C, Skarsgard E, Flake AW, High KA: Evidence for gene transfer and expression of factor IX in haemophilia B patients treated with an AAV vector. Nat Genet 2000, 24:257–261.View ArticlePubMedGoogle Scholar