Autologous Gene Therapy for Artemis-Deficient SCID

This study aims to determine if a new method can be used to treat Artemis-deficient Severe Combined Immunodeficiency (ART-SCID), a severe form of primary immunodeficiency caused by mutations in the DCLRE1C gene. This method involves transferring a normal copy of the DCLRE1C gene into stem cells of an affected patient. Participants will receive an infusion of stem cells transduced with a self-inactivating lentiviral vector that contains a normal copy of the DCLRE1C gene. Prior to the infusion they will receive sub-ablative, dose-targeted busulfan conditioning. The study will investigate if the procedure is safe, whether it can be done according to the methods described in the protocol, and whether the procedure will provide a normal immune system for the patient. A total of 25 patients will be enrolled at the University of California San Francisco in this single-site trial, and will be followed for 15 years post-infusion. It is hoped that this type of gene transfer may offer improved outcomes for ART-SCID patients who lack a brother or sister who can be used as a donor for stem cell transplantation or who have failed to develop a functioning immune system after a previous stem cell transplant.

Children with SCID generally do not survive beyond the first year of life without definitive treatment. The most effective current cure is hematopoietic stem cell transplant (HCT) with a human leukocyte antigen (HLA) matched sibling. While a matched sibling HCT can successfully treat ART-SCID, fewer than 20% of affected children have such a donor, and even when a matched sibling donor is available there is often incomplete T and B cell immune reconstitution. ART-SCID is the most difficult type of SCID to cure by hematopoietic stem cell transplant using alternative donors. Engraftment typically requires intensive conditioning with high dose alkylating agents to prevent rejection and to open marrow niches. These patients also have a high risk of developing graft versus host disease (GVHD) when alternative donors are used. The great majority of patients have absent B cell reconstitution and require lifelong administration of immunoglobulin infusions. Patients with ART-SCID who do receive high doses of alkylators, especially when 2 agents are used, have poorer survival, abnormal dental development, endocrinopathies, and short stature in comparison with children exposed to no or limited alkylators or children with SCID types that are not associated with a DNA repair defect. For these reasons, a safer, more effective approach to curing ART-SCID is needed. Autologous gene-corrected hematopoeitic stem cell transplant may eliminate both the risk of GVHD and the need for alkylators to prevent rejection.

The study design is a single-cohort, longitudinal experiment using non-randomized patients treated once with a lentiviral vector for gene-correction of Artemis-deficient SCID after conditioning with low-dose busulfan. No formal control group is planned for gauging safety; rather, intensive monitoring of the initial 6 enrollees will preclude continued accrual in the presence of safety signals, and long-term safety will be monitored for 15 years. Bone marrow stem cells will be harvested from participants who weigh ≤7.5 kilograms or have failed cytokine mobilization previously, and cytokine-mobilized peripheral blood stem cells will be harvested from participants weighing >7.5 kilograms. CD34 cells will be isolated using the CliniMACS® CD34 Reagent System cell sorter device. The cells will be transduced with the AProArt lentiviral vector. Transduction enhancers will be used to increase the transduction efficiency in peripheral blood CD34+ cells from patients who undergo a peripheral blood stem cell collection. These transduced cells will then be cryopreserved, and aliquots of the cells will undergo safety testing and be reserved for potency evaluation. All patients will receive busulfan conditioning targeted over 2 days to achieve a cumulative area under the curve (AUC) of 20 mg*hr/L (an ablative cumulative AUC is 60-90mg*hr/L). Following the infusion of AProArt-transduced cells, patients will be evaluated at 4, 6, 8, 16, and 24 weeks for evidence of gene transduced peripheral blood mononuclear cells and when possible cell lineages including T, B, NK and granulocyte/myeloid cells. If there is no evidence of gene transduced cells at 6 weeks (42 days) post infusion, a decision will be made regarding further therapy.

After day 42 post-transplant, recipients will be followed for toxicity and durable reconstitution of T and B cell immunity. Immune reconstitution of T cells will be monitored on a regular basis. If the absolute neutrophil count is < 200/µl or platelets < 20,000/µl on 3 independent determinations after day 42 post infusion of transduced cells, the patient may receive infusion of the back-up cells or an allogeneic hematopoeitic stem cell transplant. Patients who were neutropenic prior to conditioning (SCID-related neutropenia) but responsive to granulocyte-colony stimulating factor (GCSF) will not be considered to have failed, provided the absolute neutrophil count can be maintained above >500/µl with GCSF.

After day 42, patients will be assessed weekly through 12 weeks post-transplant and at week 16, monthly through month 6 post-transplant, and then 3 monthly through month 24. They will then be assessed at 6 monthly intervals during years 2-5 and annually through year 15. Study follow-up will include completion of Quality of Life questionnaires and administration of neurodevelopmental testing.

Patients with evidence of clinically inadequate reconstitution, low VCN, or any other features suggesting clinically inadequate response to the initial gene therapy procedure will be offered a repeat infusion of gene-transduced cells. Conditioning regimens given prior to a repeat gene therapy procedure may include low-dose busulfan, other conditioning, or no conditioning.

An independent Data Safety Monitoring Board (DSMB) will be appointed for safety monitoring of this trial. The DSMB will review all data for safety on a regular schedule, based on numbers of enrolled subjects and will also conduct special urgent review of any protocol related Serious Adverse Events (SAE). As the trial is initiated, the DSMB will review results of each of the first 3 cases prior to proceeding with subsequent patients.

The investigational product (IND1711) for the ART-SCID gene transfer study is not available for expanded access use. As per 21 CFR Part 312.305(3), the study management team has determined that providing the investigational product for expanded access use at this time would interfere with the conduct and completion of the clinical trial and potential development of future expanded access use. The investigational product is available to eligible patients through participation in this clinical trial.