Editor's Note: During the EBMT Annual Meeting, Dr. Francesca Ferrua from the IRCCS San Raffaele Scientific Institute presented an integrated analysis of the lentiviral hematopoietic stem and progenitor cell (HSPC) gene therapy, etuvetidigene autotemcel (ototemcel), for the treatment of Wiskott-Aldrich Syndrome (WAS). The report highlighted remarkable efficacy and safety outcomes with a follow-up period extending up to 13 years. 01. Disease Background and Etuvetidigene Autotemcel Mechanism
Wiskott-Aldrich Syndrome (WAS) is a rare X-linked primary immunodeficiency disorder caused by loss-of-function mutations in the WAS gene, leading to the deficiency or absence of the WAS protein (WASp). Clinically, it is characterized by thrombocytopenia, eczema, recurrent severe infections, and an increased risk of autoimmunity and malignancies. Without curative intervention, the prognosis remains poor.
Etuvetidigene autotemcel (formerly OTL-103) is an autologous gene therapy product consisting of CD34+ HSPCs transduced ex vivo with a self-inactivating lentiviral vector encoding the human WAS cDNA under the control of its endogenous promoter. The therapy has been approved by both the EMA and FDA for patients with WAS who lack a suitable HLA-matched hematopoietic stem cell donor.
02. Study Design: Integrated Analysis of 27 Patients
The presentation integrated data from two clinical trials and an expanded access program, involving 27 patients treated between 2010 and 2022.
- Patient Baseline: Median age at treatment was 2.6 years (range: 1–35 years), with one-third of the cohort aged 5 years or older.
- Cell Source: 21 patients used mobilized peripheral blood (MPB), 5 used bone marrow (BM), and 1 used both.
- Conditioning Regimen: All patients received a single dose of rituximab followed by reduced-intensity conditioning (RIC) with sub-myeloablative busulfan and fludarabine.
- Follow-up: The median follow-up for surviving patients was 5.7 years (range: 2.3–13.3 years).
03. Safety Profile: No Evidence of Insertional Mutagenesis
Etuvetidigene autotemcel demonstrated a favorable safety profile. No cases of engraftment failure, insertional mutagenesis-related malignancies, abnormal clonal proliferation, or replication-competent lentivirus (RCL) were observed.
- Adverse Events (AEs): No AEs related to the drug product were reported.
- Common AEs: The most frequent Grade 3 or higher AEs were central venous catheter (CVC)-related infections, consistent with expectations for hematological reconstitution following RIC.
- Outcomes: One patient died early post-treatment due to the deterioration of a pre-existing neurological condition, which was assessed as unrelated to the gene therapy.
04. Clinical Efficacy: Significant Reduction in Infection and Bleeding
The study met its primary efficacy endpoints, showing significant clinical improvement following a single infusion:
- Overall Survival (OS): 96% at the data cut-off.
- Infection Control: The annualized rate of severe infections was reduced by 93% in the 6–18 month period post-gene therapy compared to the year prior to treatment. This low rate was sustained throughout the long-term follow-up.
- Bleeding Events: The annualized rate of moderate-to-severe bleeding events decreased by 60% within the first 12 months post-treatment and continued to decline thereafter.
05. Biological Reconstitution: Stable Engraftment and WASp Restoration
Gene-corrected cells showed robust and stable engraftment across all tested lineages in both bone marrow and peripheral blood.
- Protein Expression: Stable restoration of WASp expression was observed in lymphocytes, monocytes, and platelets.
- Immune Reconstitution: 100% of patients successfully discontinued immunoglobulin replacement therapy (IgRT), and 93% were able to stop continuous antimicrobial prophylaxis.
- Platelet Recovery: At the last follow-up, 96% of patients achieved a platelet count ≥50,000/μL. Furthermore, improvements in mean platelet volume (MPV), morphology, and function allowed all patients to achieve independence from platelet transfusions.
06. Quality of Life: Resolution of Eczema and Social Normalization
Beyond hematological markers, patients experienced significant systemic improvements:
- Eczema: Complete resolution of eczema was observed in all treated patients.
- Immune Dysregulation: Symptoms of immune dysregulation improved significantly, eliminating the need for prolonged immunosuppression post-treatment.
- Social Impact: Hospitalization rates declined sharply, and patients were able to return to normal social activities and schooling, positively impacting the quality of life for both patients and their families.
Conclusion and Outlook
Dr. Francesca Ferrua concluded that with up to 13 years of follow-up, etuvetidigene autotemcel combined with RIC demonstrates a sustained and favorable risk-benefit profile for patients with WAS. As a landmark gene therapy, it provides a critical curative alternative for patients lacking matched donors, offering long-term clinical stabilization and functional recovery.
