Gene Therapy for WAS*

Image courtesy of: Arlabosse T, et al  Gene Therapy for Inborn Errors of Immunity. J Allergy Clin Immunol Pract. 2023 Jun;11(6):1592-1601. doi: 10.1016/j.jaip.2023.04.001. Epub 2023 Apr 20. PMID: 37084938.

Determination of eligibility for GT:   Once it is determined that the best clinical management option for a patient is to undergo HSCT or GT, the assessment begins as to what is the best procedure for the patient. Patients over the age of 6 months who do not have a fully matched donor are eligible for consideration for GT.  Other factors such as age of the patient, their general health, presence of complication, etc. could also contribute to making the determination if a patient is eligible for GT.  In concert with the patient and his family, the treating transplant physician weighs several factors and makes the determination if HSCT or GT is best suited for the patient.  Determination is made on a case-by-case basis.   

Availability of GT:  Currently, GT for WAS, Waskyra is only available at the San Rafaelle Telethon Institute for Gene Therapy in Milan, Italy.  Following the approval of this therapy by the FDA and the European Medicines Agency (EMA), there are likely to be a few more centers in the USA and EU in the near future.  Over time, we hope that access to GT will be available also at other centers around the world.

Pre gene therapy evaluation 

Once it is determined that a patient is eligible for GT, the pre-gene therapy evaluation begins.  Similar to the pre-transplant evaluation, several tests are done to evaluate the function of major organs, such as the kidneys, heart, lungs, etc. to determine that the patient will be able to withstand the medical interventions needed by the GT process and to have a baseline recording for further evaluation.  Financial planning is done at this point and measures are set in place for the emotional support of the parents during the process.  Going through a GT is challenging and can be emotionally exhausting.  Having a local support group through family, friends and religious affiliations can help to ease the process.  The hospital GT team will be there to guide you through the process physically and emotionally. Once all the evaluations and support systems are in place, the patient is ready for GT.

Gene therapy procedure

There are four steps in GT.

1.  1.  Collection of hematopoietic stem cells from the patient:  As the patient’s own stem cells are used in GT, these stem cells must be collected from the patient.  Hematopoietic stem cells are found in large numbers in the bone marrow.  To collect enough numbers of stem cells, patients are injected with medications such as G-CSF (Granulocyte Colony Stimulating Factor) and Plerixafor that causes the stem cells to increase in numbers and move from the bone marrow to the peripheral blood from where they can be easily collected over several days. These stem cells are then sent to the lab for processing.  This is done approximately 5-10 weeks [FC1] [SI2] before the GT procedure and a part of this is cryopreserved as a backup, in case there is a need for it.  

2. Genetic Modification of the stem cells:  GT for WAS uses a GT technique referred to as gene addition: In gene addition, a normal, functional copy of the WAS gene (without mutations)  is inserted into the patients stem cells by a process called transduction.  A vehicle, referred to as a vector is needed is used to introduce the normal copy of the WAS gene into the patients cells.  The vector used for WAS GT is an inactivated lentivirus⁹.  As the virus is inactivated, it cannot replicate and cause infection in the patient.  

To introduce the normal copy of the gene the patients, stem cells that have been collected are processed in the lab and are mixed with the vector containing to the normal WAS gene. As this process is done in a lab and not directly in the patient, it is referred to as ex-vivo gene therapy (see image [FC3] [SI4] above).  Once copies of the normal WAS gene are integrated into the patient’s stem cells, they enables the production of normal WASp leading to correction of the immune cells and platelets thereby correcting the underlying disease.  As the corrected stem cells grow and multiply, all the cells they give rise to, the stem cells and blood cells that have the corrected WAS gene.  It is a one time treatment that, when successful, enables patients to live a normal life.  

Depending on how many vector particles enter each cell, the stem cells can have have multiple copies of the normal WAS gene. This number of copies of the normal WAS gene in each cell is referred to as the vector copy number.  It is an important determinant of how effective the treatment is. In general, the higher the vector copy number, the better the correction is¹ 

3. Re-infusion of corrected stem cells into the patient:  The gene-corrected cells are now to be re-infused into the patient. As part of the preparation for gene thrapy a medication called Rituximab may be given to the patient three weeks before GT.  This is to prevent the occurrence of autoimmunity which is a common complication in patients with WAS. 

Similar to HSCT, medications (chemotherapy) are given to destroy the patient’s blood forming cells and to make place in the bone marrow for the gene-corrected cells.  Usually, the patient is hospitalized the day before the chemotherapy is started.  Some patients may have to be hospitalized earlier to get them ready for the GT.  The chemotherapy process is called conditioning.  While the chemotherapy used for GT is similar to HSCT, the chemotherapy doses used for GT are significantly lower than those used for HSCT.  The conditioning regimen used for GT is referred to as a reduced intensity conditioning using busulfan and fludarabine which is started 3 days prior to GT, referred to a “Day -3”.  On “Day 0" the corrected stem cells are infused into the patient. The days after this are counted as day +1, +2 etc. The corrected cells are infused into the blood in a simple process similar to a regular blood transfusion.  Several medications are given while the patient is in the hospital and lab work is done frequently, up to every day at times.  To prevent the patient from having numerous pokes every day, sturdier, temporary IV lines (referred to as a Broviac or a Hickman Catheter) are implanted in a vein in the patient’s chest. 

Blood are needed to check for normal functioning of the body and to follow the presence and growth of gene corrected cells. Due to the chemotherapy, the patient will have a lower number of red blood cells, white blood cells and platelets in the blood for the first few weeks. Over the next several weeks after GT, the corrected cells grow and make new blood cells that produce normal WASp. This is called "engraftment" and is an important milestone in the transplant journey.  

4. Engraftment and production of healthy cells: Engraftment is the process whereby the gene corrected stem cells settle successfully into the patient’s marrow and begin to produce new, healthy blood cells. The average time to engraftment after GT is 26 days⁴.  Until such time that the corrected cells grow and make enough cells, the patients are given transfusions of red blood cells and platelets, as needed.  IVIG is given as a replacement on a regular basis, until such time that the gene-corrected B cells are functioning well.

During this process, the patients are on several different medications. Because the patients have no immune system until the gene-corrected cells are well established, they are highly prone to infections.  Antibiotics, antivirals and antifungals are given for the prevention of infection and aggressive treatments are started, if the patient develops a fever. Visitors are restricted to reduce the exposure to potential infections.  To decrease the chance of infection, patients are put in rooms with special air filters.  They may also be in a room with a positive pressure air system to make sure that the air from the outside does not enter the room.  These methods to reduce infection are referred to as "protective or reverse isolation".  It is important to follow the reverse isolation procedures outlined by the GT team hospital scrupulously, as infections can be serious and cause significant setbacks in the gene-therapy path. Once the patient blood cell counts are stable and indicate that the infused cells have engrafted , the patient is discharged from the hospital.

After discharge:  :  Patients are usually in the hospital for a median of 52 days until engraftment happens and the doctors determine that they are ready to be discharged.  Until 100 days have passed after the GT, if possible, patients stay within a 20-minute reach of the hospital in case an emergency were to arise.  During this time labs are done very frequently, up to everyday.  After the 100-day milestone, patients may be able to return to their homes, if all is stable.  Labs and visits to the hospital are done on a weekly basis until the blood counts have stabilized and the immune system is improved.  Because they are at high risk for infections, patients’ movement outside the home is restricted and visitors to the home are limited.  With all going well, patients have a normally functioning immune system (full immune reconstitution) by 1 years after GT and can lead a normal life.  These numbers are just averages and it may vary significantly from patient to patient, depending on the circumstances and the complications that may arise.

Advantages and potential complications of gene therapy 

Advantages:

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, so, there is no need for immunosuppressive medications after GT.

3. No expected rejection because the patients own cells are used.

4. In the Waskyra trials, less chemotherapy is used than used in HSCT, therefore reducing organ toxicity, and leading to a smoother recovery after GT.

Potential Complications of Gene Therapy

While the complications listed below are possible, it is important to note that the first three complications were not seen in any of the 45 patients enrolled in the 4 lentiviral vector trials for WAS to date ¹⁰ ¹ ⁸.  

1. The insertion of the vector in the patient cells may cause unintended  consequences such as genetic damage that can lead to the development of leukemia, a complication that was seen with the retroviral vector trials⁷.  

2. The gene-corrected cells may not engraft or the body could reject the "repaired cells" by mounting an immune response against the WASp protein that may be seen as foreign and destroying the cells that carry it.  

3. Too much of WASp may be produced causing other problems affecting the viability of gene-corrected cells.

4. Chemotherapy can lead to short and/or long-term side effects.   

5. Inadequate vector copy number in the stem cells can lead to less robust restoration of immune function and platelet count⁶. 

Comparison of HSCT and GT   

Feature HSCT GT

Donor required? Yes No

Risk of GVHD Yes None

Track record Decades of data       15+ years of modern data

Ideal candidates Younger patients with matched donors Patients without a fully matched donor

Conditioning chemo Yes, intensity varies Yes, lower intensity than HSCT

Availability Widely available Limited centers (but growing)

Immune recovery Strong, well-established Strong, rapid improvement

Platelet correction Platelet correction good with good full Platelet numbers are often below normal,  no moderate
(Number & function) donor myeloid chimerism or severe bleeds noted and patients are 

                                                                              (Busulfan based conditioning)¹¹,¹² transfusion  free³.  

Reduction in severe bleeding episodes Yes Yes

Risks GVHD, graft failure, infections Chemo side effects,  limited long-term data

Long term follow up Extensive experience >50 years Very encouraging (15 years) but still maturing

History and results of GT Trials 

Waskyra Trial Results³⁴  Clinical trials for Waskyra started at SR-TIGET in Milan, Italy in 2010, enrolling 33 patients³⁴ in the last 15 years including two adults.  Overall data⁸ show that survival is 97% (calculated), the rate of infections decreased from 2.0 events/year? in the 12 months before treatment to 0.15 in the 12 years post Waskyra and to 0.12 in the 2-3 years post Waskyra.  Similarly, the rate of moderate and severe bleeding episodes decreased from 2.0 events/year in the 12 months before treatment to 0.16 in the 2-3 years post Waskyra.  No major gene therapy associated serious events were noted.  No leukemogenic events or vector related toxicity was noted. The most common side effects were due to the medications received as the conditioning regimen.  One patient died due to neurological complications that existed prior to Waskyra treatment and were determined not to be related to Waskyra.  

Three other lentiviral trials were started in 2010 in Paris, London and Boston.  

Publication on the trials from London and Paris 

Publication on the trials from Boston

Results Publication on the trials from Munich

Trials that are to start in the US:  There are two lentiviral gene addition trials that are slated to start in the US. 

CSL Behring is in collaboration with Seattle Children's Research Institute to start a rial based on a novel GT technology developed there.  

Immunovec is in collaboration with the NIH to start a trial based on a novel GT technology developed there. 

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Publications and References

1. Ferrua F, Marangoni F, Aiuti A, Roncarolo MG. Gene therapy for Wiskott-Aldrich syndrome: History, new vectors, future directions. J Allergy Clin Immunol. 2020 Aug;146(2):262-265. doi: 10.1016/j.jaci.2020.06.018. Epub 2020 Jul 2. PMID: 32623069; PMCID: PMC7453879.

2. Lentiviral haemopoietic stem/progenitor cell gene therapy for treatment of Wiskott-Aldrich syndrome: interim results of a non-randomised, open-label, phase 1/2 clinical study, Ferrua, Francesca et al. The Lancet Haematology, Volume 6, Issue 5, e239 - e253
   
   

3. Lentiviral hematopoietic stem cell and progenitor cell gene therapy with Etuvetidigene autotemcel for the treatment of Wiskott-Aldrich Syndrome
   
   

4.  Abstract Title : Lentiviral hematopoietic stem and progenitor cell gene therapy for Wiskott-Aldrich Syndrome: Early access experience in Italian patients based on 648/1996 law

5. Hacein-Bey Abina S, Gaspar HB, Blondeau J, et al. Outcomes Following Gene Therapy in Patients With Severe Wiskott-Aldrich Syndrome. JAMA. 2015;313(15):1550–1563. doi:10.1001/jama.2015.3253

6. Labrosse R, Chu JI, et al Outcomes of hematopoietic stem cell gene therapy for Wiskott-Aldrich syndrome. Blood. 2023 Oct 12;142(15):1281-1296. doi: 10.1182/blood.2022019117. PMID: 37478401; PMCID: PMC10731922.
   
   

7. Braun CJ, Boztug K, et al Gene therapy for Wiskott-Aldrich syndrome--long-term efficacy and genotoxicity. Sci Transl Med. 2014 Mar 12;6(227):227ra33. doi: 10.1126/scitranslmed.3007280. PMID: 24622513.

8.  EMA announcement: First gene therapy to treat rare disease Wiskott-Aldrich syndrome

9. Galy A, Roncarolo MG, Thrasher AJ. Development of lentiviral gene therapy for Wiskott Aldrich syndrome. Expert Opin Biol Ther. 2008 Feb;8(2):181-90. doi: 10.1517/14712598.8.2.181. PMID: 18194074; PMCID: PMC2789278.

10. Magnani, A., Semeraro, M., Adam, F. et al. Long-term safety and efficacy of lentiviral hematopoietic stem/progenitor cell gene therapy for Wiskott–Aldrich syndrome. Nat Med 28, 71–80 (2022). https://doi.org/10.1038/s41591-021-01641-x

11. Ferrua F,  et al Lentiviral haemopoietic stem/progenitor cell gene therapy for treatment of Wiskott-Aldrich syndrome: interim results of a non-randomised, open-label, phase 1/2 clinical study. Lancet Haematol. 2019 May;6(5):e239-e253. doi: 10.1016/S2352-3026(19)30021-3. Epub 2019 Apr 10. PMID: 30981783; PMCID: PMC6494976.

12. Jessie L Alexander, et al Hematopoietic Cell Transplantation for Wiskott-Aldrich syndrome: A PIDTC Report. Blood Adv 2025; bloodadvances.2025017662. doi: https://doi.org/10.1182/bloodadvances.2025017662Hematopoietic Cell Transplantation for Wiskott-Aldrich syndrome: A PIDTC Report

13. Albert MH, Slatter MA, et al  Hematopoietic stem cell transplantation for Wiskott-Aldrich syndrome: an EBMT Inborn Errors Working Party analysis. Blood. 2022 Mar 31;139(13):2066-2079. doi: 10.1182/blood.2021014687. PMID: 35100336.

14.  Image courtesy of: Arlabosse T, Booth C, Candotti F. Gene Therapy for Inborn Errors of Immunity. J Allergy Clin Immunol Pract. 2023 Jun;11(6):1592-1601. doi: 10.1016/j.jaip.2023.04.001. Epub 2023 Apr 20. PMID: 37084938.

Further Reading

1. Candotti F. Gene therapy for Wiskott-Aldrich syndrome: here to stay. Lancet Haematol. 2019 May;6(5):e230-e231. doi: 10.1016/S2352-3026(19)30066-3. Epub 2019 Apr 10. PMID: 30981782.

2. Gene therapy for Wiskott-Aldrich syndrome: History, new vectors, future directions, Ferrua, Francesca et al. Journal of Allergy and Clinical Immunology, Volume 146, Issue 2, 262 - 265

3. Evidence for Long-term Efficacy and Safety of Gene Therapy for Wiskott–Aldrich Syndrome in Preclinical Models, Marangoni, Francesco et al., Molecular Therapy, Volume 17, Issue 6, 1073 - 1082

4. Lentiviral-mediated gene therapy restores B cell tolerance in Wiskott-Aldrich syndrome patients. Francesca Pala,1,2 Henner Morbach,2 Maria Carmina Castiello,1 Jean-Nicolas Schickel,2 Samantha Scaramuzza,1 Nicolas Chamberlain,2 Barbara Cassani,3,4 Salome Glauzy,2 Neil Romberg,5 Fabio Candotti,6 Alessandro Aiuti,1,7 Marita Bosticardo,1 Anna Villa,1,4 and Eric Meffre2 iJ Clin Invest. 2015;125(10):3941-3951. http://doi.org/10.1172/JC182249.  Copyright © 2015, American Society for Clinical Investigation                                                                                                                        

*Author:  Sumathi Iyengar, M.D., Reviewed by Dr. Fabio Candotti, December 2025