2003; baxter - Supplements - Haematologica

[Gene Therapy]review paperGene therapy for hemophilia A:immune consequences of viralvectormediated factor VIIIgene transferhaematologica 2003; 88(suppl. n. 12):115-121http://www.haematologica.org/free/immunotolerance2001.pdfTHIERRY VANDENDRIESSCHE, DESIRE COLLEN,MARINEE K.L. CHUAHCenter for Transgene Technology and Gene Therapy,Flanders Interuniversity Institute for Biotechnology-Universityof Leuven, BelgiumObjective. Hemophilia A is potentially amenable fortreatment by gene therapy. We have been exploringthe use of different viral vectors including onco-retroviral,lentiviral and high-capacity adenoviral (HC-Ad),each with their own advantages and limitations, forhemophilia A gene therapy.Study design. Injection of onco-retroviral vectorsencoding the B-domain deleted human FVIII cDNAinto neonatal hemophilia A mice resulted in longtermexpression of therapeutic and even supra-physiologicFVIII levels that stably corrected the bleedingdiathesis in 50% of the recipient mice. The lack ofneutralizing antibodies specific for human FVIII inthese animals, may have been due to the inductionof neonatal tolerance. However, in the remainingrecipient mice, a humoral and possibly also a cellularimmune response developed which thwarted phenotypiccorrection. Since onco-retroviral transductionis restricted to rapidly dividing target cells, efficienthepatic gene transfer could only be achievedin neonates but not in adult mice. To overcome thislimitation, lentiviral vectors were employed instead.Results. Non-dividing hepatocytes in adult recipientmice can be efficiently transduced (5-10%) usingimproved lentiviral vector designs, leading to longtermtransgene expression with only limited and transienthepatotoxicity. This underscores the potentialof lentiviral vectors for hemophilia gene therapy.However, efficient gene transfer was also apparentin antigen-presenting cells (APCs), particularly inKupffer cells, splenic macrophages and B-lymphocytes.Since it has previously been shown that inadvertenttransgene expression in APC triggers thedevelopment of neutralizing antibodies, the use ofCorrespondence: Thierry VandenDriessche, MD, Center forTransgene Technology and Gene Therapy, Flanders InteruniversityInstitute for Biotechnology, University of Leuven, 49 HerestraatB-3000 Leuven, Belgium. Phone: international+32.16.346144. Fax: international +32.16.34599. E-mail:thierry.vandendriessche@med.kuleuven.ac.be ormarineekhim.chuah@med.kuleuven.ac.behepatocyte-specific promoters may be warranted tocircumvent this potential risk. Finally, we have shownthat high-capacity adenoviral vectors can be used toachieve unprecedented high levels of human FVIIIexpression in hemophilic mice but that humoral andpossibly also cellular immune responses precludedlong-term gene expression.Conclusions. In conclusion, the use of different replication-deficientviral vectors that do not encode viralantigens can be used to express therapeutic levelsof human FVIII in hemophilic mice with varying efficiencies.However, the development of neutralizingantibodies following gene therapy in conjunctionwith the induction of cellular immune responsesagainst the transduced target cells, remains a concernthat will need to be addressed further in largeanimal models, such as hemophilic dogs, withspecies-specific transgenes.©2003, Ferrata Storti FoundationKey words: hemophilia; factor VIII; coagulation; genetherapy; inhibitory antibodies.Though factor VIII (FVIII) substitution therapyhas greatly improved the lives of patientssuffering from hemophilia A, there are stilllimitations to the current treatment that havetriggered interest in alternative treatments bygene therapy. Significant progress has recentlybeen made in the development of gene therapyfor the treatment of hemophilia A that serves asan ideal trailblazer for the treatment of other diseasesby gene therapy. These advances parallelthe technical improvements of existing viral vectorsystems and the development of new deliverymethods. 1-3 Both viral vectors as well as non-viralvectors have been considered for the developmentof hemophilia gene therapy. In general,viral vector-mediated gene transfer is far moreefficient than non-viral gene transfer and hastherefore been the method of choice.What is the ideal gene therapy vector forhemophilia A? The ideal gene therapy vectorwould need to have the following properties:haematologica vol. 88(supplement n. 12):september 2003