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Update on the safety and efficacy of retroviral gene therapy for immunodeficiency due to adenosine deaminase deficiency.

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Published:25th Mar 2020
Author: Cicalese MP, Ferrua F, Castagnaro L, Pajno R, Barzaghi F, Giannelli S et al.
Source: Blood Journal
Ref.:Blood. 2016 Apr 29. pii: blood-2016-01-688226. [Epub ahead of print]

Adenosine deaminase (ADA) deficiency is a rare, autosomal recessive systemic metabolic disease characterized by severe combined immunodeficiency (SCID). The treatment of choice for ADA-deficient SCID (ADA-SCID) is hematopoietic stem cell transplant (SCT) from a human leukocyte antigen (HLA)-matched sibling donor, although fewer than 25% of patients have such a donor available. Enzyme replacement therapy (ERT) partially and temporarily relieves immunodeficiency. We investigated the medium-term outcome of gene therapy (GT) in 18 patients with ADA-SCID for whom an HLA-identical family donor was not available; most were not responding well to ERT. Patients were treated with an autologous CD34+ enriched cell fraction that contained CD34+ cells transduced with a retroviral vector encoding the human ADA cDNA sequence (GSK2696273) as part of single-arm, open-label studies or compassionate use programs. Overall survival was 100% over 2.3 to 13.4 years (median: 6.9 years). Gene-modified cells were stably present in multiple lineages throughout follow up. GT resulted in a sustained reduction in the severe infection rate from 1.17 events per person-year to 0.17 events per person-year (n=17, Patient 1 data not available). Immune reconstitution was demonstrated by normalization of T cell subsets (CD3+, CD4+, and CD8+), evidence of thymopoiesis, and sustained T cell proliferative capacity. B cell function was evidenced by immunoglobulin production, decreased intravenous immunoglobulin use, and antibody response after vaccination. All 18 patients reported infections as adverse events; infections of respiratory and gastrointestinal tracts were reported most frequently. No events indicative of leukemic transformation were reported. Trial details are registered at as #NCT00598481.


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