In its current available form, Gene Therapy (GT) is an experimental therapy that aims at replacing the defective gene with a copy of the normal gene. This allows the cell to start producing normal protein, which is supposed to cure the disease. One of the most challenging steps in GT is the introduction of the "corrected gene" into the cell. Scientists have found that one of the most efficient ways to introduce the corrected gene into the cell is to use modified viruses. Some viruses, normally insert their own genetic material into the patients genetic material as a way of multiplying themselves. This characteristic is used in GT to incorporate normal genes into the patient’s cells. Scientist first remove the genes in the virus that cause disease and "load" it with the "normal gene" i.e. the WASP Gene in the case of WAS. These "loaded" viruses referred to as "vectors" are then used to introduce the normal gene into the patient. There are four basic steps in gene therapy.
1. A vehicle needs to be found to introduce the corrected gene into the cell. This vehicle is referred to as a vector. For gene therapy of WAS, vectors based of mouse retrovirus or the human immunodeficiency virus (HIV) have been generated. In patients with WAS, a retrovirus called lentivirus is used as the vector. Researchers inactivate the virus, so it does not produce disease in the patient and "load" it with the corrected gene.
2. This vector now needs to be introduced into the patient’s cells. Doctors collect blood forming stem cells (hemaotpoietic stem cells) from the patient's bone marrow or the peripheral blood. These cells are then grown in large numbers outside the body. Next, these cells are mixed with the vector. The virus infects these cells converting them to "repaired cells" .
3. These repaired cells have to be introduced back into the patient. The next step is to make sure that the patient does not reject the "repaired cells" that are introduced engraft into the patient. Doctors use chemotherapy to facilitate engraftment. This process is called "conditioning". The doses of chemotherapy used for gene therapy may be lower than those used for bone marrow transplant.
4. These "repaired cells" are now introduced into the patient in a process similar to blood transfusion. These "repaired cells" are encouraged to grow and multiply in the patient. In theory, the cells should be able to produce normal protein (WASp) and to cure the patient.
These repaired cells then continue to multiply, forming more numbers of normal cells. In patients with WAS these repaired cells are expected to have a selective advantage and over time, the number of repaired cells should increase. These repaired cells produce normal WASp, curing the patient. The regimen for conditioning may vary from one trial center to another. The duration of stay in the hospital, the medications that may be used immediately after gene therapy and the time to become completely normal will vary based on the conditioning regimen that is being used.
Courtesy: National Institute of Health
Gene Therapy has made significant progress in the treatment of patients with SCID(Severe Combine Immune Deficiency, another primary immune disorder). In September of 1990, Dr. Michael Blaese and his colleagues at the NIH were the first1 to apply gene therapy to a genetic disease on a patinet with SCID. The patient still carries the effects of this treatment 19 years later. In 1999, Dr Alain Fischer and his colleagues at Necker Hospital in Paris began a trial for patients with SCID and successfully cured 9 out of 10 patients. Unfortunately, 4 of the patients developed leukemia2 related to the gene therapy itself and further trials were halted. Three of these patients are alive and cured of their SCID and leukemia. Since then, with lessons learned, trials have been restarted with significant advances being made, especially in some types of patients with SCID 3 without any complications from leukemia. This has been very encouraging to the fledgling world of gene therapy and is providing the impetus for further research and cure for other primary immunodeficiency syndromes such as WAS and CGD(Chronic granulomatous disease).
Dr. Christoph Klein from Hannover, Germany is the first physician to use gene therapy in an attempt to cure patients with Wiskott-Aldrich Syndrome4 in 2007. Since then, Dr. Klein has used gene therapy with some efficacy on six patients. The first two of these patients have been described in detail by Dr. Klein and now have a successful reconstitution of the immune system and increase in the platelet counts. No major, untoward side effects have been noted so far. One of his patients had autoimmune thrombocytopenia which resolved with gene therapy. Both patients are doing well more than two years after the procedure (Dr. Klein's personal communication with Dr. Candotti, Washington DC, March 2009). A 12 year old was the oldest child so far to have received gene therapy for WAS. The first patients to have received gene therapy are doing well two years after the procedure. (Verbal Communication-Dr. Candotti). A second set of clinical trials is being planned by Dr. Adrian Thrasher and his colleagues in three centers in Europe - London, Paris and in Milan. These trials are to start towards the end of 2009.
This is an exciting time and one of great hope for patients with Wiskott-Aldrich Syndrome, particularly for those who are not candidates for a stem cell transplant. With all of this excitement, it is important to keep in mind the words of Dr. Alain Fischer, immunologist and gene therapy expert from Necker Hospital in Paris who said, "........it is absolutely clear that gene therapy is not going to be 'the therapy". It is just one approach among many others." Gene therapy is still experimental and is in its early stages in the treatment of WAS.
Advantages of Gene Therapy
1. It is theoretically available to all patients as the cells are taken from the patient and there is no "donor" required.
2. No risk of GvHD.
3. No expected rejection because the patients own cells are used.
4. In some trials, less chemotherapy is used than used in HCT.
Potential Complications of Gene Therapy
- The body could reject the "repaired cells" and the patient may not engraft
- The body can mount an immune response against the "repaired gene" as it may be seen as foreign and destroy the cells that carry it. A reaction like this was seen in 1999 with Jesse Gelsingher.
- The healthy gene may insert into the wrong spot and cause unintended reactions.
- Too much of WASp may be produced causing other problems
- The virus may cause unintended problems such as the cases of leukemia that were seen with a few patients with SCID5.
- The inactivated HIV virus may become contagious at some point.
- Side effects from the chemotherapy
Inclusion and Exclusion Criteria for the trials
(information obtained from the WAS discussion forum and Dr. Candotti - interested families are encouraged to verify the details directly with the investigators)
1. Patients with Classic WAS are eligible to participate in the trials in both groups.
2. Patients with Classic WAS who are symptomatic with an autoimmune disorder are eligible.
3. Patients with a matched sibling donor are not eligible to participate in the trials from the European Group(Dr. Thrasher et al).
4. Patients with XLT are not eligible to participate at this time.
Differences between the two trials
(Information obtained from the WAS discussion forum and Dr. Candotti)
1. Gene Therapy http://history.nih.gov
2. Lyford, J. Gene therapy 'caused T-cell leukemia' The Scientist. http://cmbi.bjmu.edu.cn
3. Kohn, DB, Candotti, F, Gene Therapy Fulfilling Its Promise. NEJM Volume 360:518-521
4. Boztug, K, Dewey, RA, Diez, IA, Manfred, S, Kerstin, S, Jana, D, Sonja, N, Klaus, K, Irina, K, Lazlo, M, von Kalle, C, Welte, K, Klein, C. Hematopoietic Stem Cell gene Therapy for Wiskott Aldrich Syndrome. American Society of Hematology Conference, December 10, 2007
5. Why Gene Therapy cause Leukemia in some Boy in the Bubble Syndrome patientsCommentary: Case of Leukaemia Associated with SCID-X1 Gene Therapy Trial in London. European Society Of Gene and Cell Therapy. Science News
6. Alessandro Aiuti, Federica Cattaneo, Stefania Galimberti, Ulrike Benninghoff, Barbara Cassani, Luciano Callegaro, Samantha Scaramuzza,, Grazia Andolfi, Massimiliano Mirolo, Immacolata Brigida, Antonella Tabucchi, Filippo Carlucci, Martha Eibl, Memet Aker,Shimon Slavin, Hamoud Al-Mousa, Abdulaziz Al Ghonaium, Alina Ferster, Andrea Duppenthaler, Luigi Notarangelo, Uwe Wintergerst, Rebecca H. Buckley, Marco Bregni, Sarah Marktel,Maria Grazia Valsecchi, Paolo Rossi, Fabio Ciceri, Roberto Miniero, Claudio Bordignon and Maria-Grazia Roncarolo, M.D. Gene Therapy for Immunodeficiency Due to Adenosine Deaminase Deficiency. The New England Journal of Medicine Volume, Jan 29, 2009 ; 360:447-458
7. Development of lentiviral gene therapy for Wiskott Aldrich syndrome Anne Galy, Maria-Grazia Roncarolo & Adrian J Thrasher Expert Opinion on Biological Therapy. February 2008, Vol. 8, No. 2, Pages 181-190
8. Ozsahin H, Cavazzana-Calvo M, Notarangelo LD, Schulz A, Thrasher AJ, Mazzolari E, Slatter MA, Le Deist F, Blanche S, Veys P, Fasth A, Bredius R, Sedlacek P, Wulffraat N, Ortega J, Heilmann C, O'Meara A, Wachowiak J, Kalwak K, Matthes-Martin S, Gungor T, Ikinciogullari A, Landais P, Cant AJ, Friedrich W, Fischer A. Long-term outcome following hematopoietic stem-cell transplantation in Wiskott-Aldrich syndrome: collaborative study of the European Society for Immunodeficiencies and European Group for Blood and Marrow Transplantation. Blood. 2008 Jan 1;111(1):439-45.