Lentiviral Gene Therapy for X-linked Severe Combined Immunodeficiency

Study Overview
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Brief Summary
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Severe combined immunodeficiency disorder (SCID) is a heterogeneous group of inherited disorders characterized by a profound reduction or absence of T lymphocyte function, resulting in lack of both cellular and humoral immunity. SCID arises from a variety of molecular defects which affect lymphocyte development and function. The most common form of SCID is an X-linked form (SCID-X1), which accounts for 30-50% of all cases. SCID-X1 is caused by defects in the common cytokine receptor gamma chain, which was originally identified as a component of the high affinity interleukin-2 receptor (IL2RG). Allogeneic haematopoietic stem cell transplantation (HSCT), which replaces the patient's bone marrow with that of a healthy donor, is the only treatment that definitively restores the normal function of the bone marrow. HSCT is the first choice of treatment for patients with signs of bone marrow failure and a fully-matched related donor. However, patients without a fully-matched related donor have much worse overall outcomes from HSCT. This study will investigate whether patients with SCID-X1 without a fully matched related donor may benefit from gene therapy. To do this the investigators propose to perform a phase I/II clinical trial to evaluate the safety and efficacy (effect) of gene therapy for SCID-X1 patients using a lentivirus delivery system containing the IL2RG gene. Up to 5 eligible SCID-X1 patients will undergo mobilisation and harvest of their haematopoietic stem precursor cells (HPSCs). In the laboratory the disabled lentivirus will be used to insert a normal human IL2RG gene into the patient's harvested HPSCs. Patients will receive chemotherapy conditioning prior to cell infusion, in order to enhance grafting. The genetically corrected stem cells will then be re-infused into the patient. Patients will be followed up for 2 years. This trial will determine whether gene therapy for SCID-X1 using a lentiviral vector is safe, feasible and effective

Official Title
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Phase I/II Study of Lentiviral Gene Transfer for SCID-X1 With Low Dose Targeted Busulfan

Conditions
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Severe Combined Immunodeficiency, X-Linked

Intervention / Treatment
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* Drug: Lentiviral vector transduced CD34+ cells


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Diagnosis of SCID-X1 based on immunophenotype and lack of T cell function (proliferation to PHA <10% of the lower limit of normal for the laboratory) AND confirmed by a mutation in IL2RG Lack of an HLA identical (A, B, C, DR, DQ) related donor Age <5 years Signed informed consent Documentation of willingness to follow up for 15 years post-infusion If the patient has previously undergone allogeneic transplant or gene therapy, insufficiency of graft-derived T cell engraftment must be documented. Age at least 8 weeks of age by the time of busulfan administration Exclusion Criteria: Patients with an active, therapy-resistant infection. Infections that are known to be highly morbid in SCID patients will be considered active and therapy-resistant if the infectious agent is repeatedly isolated despite a minimum of 2 weeks of appropriate therapy and is associated with significant organ dysfunction (including but not limited to abnormalities listed below). Mechanical ventilation including continuous positive airway pressure Abnormal liver function defined by AST and ALT >10 times the upper range of normal OR Bilirubin >2 mg/dL Shortening fraction on echocardiogram <25% or ejection fraction <50% Renal failure defined as glomerular filtration rate <30 ml/min/1.73 m2 or dialysis dependence Uncontrolled seizure disorder Encephalopathy Documented coexistence of any disorder known to affect DNA repair Diagnosis of active malignant disease other than EBV-associated lymphoproliferative disease Patients with evidence of infection with HIV-1 Previous allogeneic transplant with cytoreductive chemotherapy Major (life-threatening) congenital anomalies. Examples of major (life-threatening) congenital anomalies include, but are not limited to: unrepaired cyanotic heart disease, hypoplastic lungs, anencephaly or other major central nervous system malformations, other severe non-repairable malformations of the gastrointestinal or genitourinary tracts that significantly impair organ function. Other conditions which in the opinion of the P.I. or Co-investigators, contra-indicate collection and/or infusion of transduced cells or indicate patient's inability to follow the protocol. These may include for example clinical ineligibility to receive anaesthesia, severe deterioration of clinical condition of the patient after collection of bone marrow but before infusion of transduced cells, or documented refusal or inability of the family to return for scheduled visits. There may be other unforeseen rare circumstances that would result in exclusion of the patient, such as sudden loss of legal guardianship.

Ages Eligible for Study
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Minimum Age: 8 Weeks
Maximum Age: 5 Years

Sexes Eligible for Study
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Male

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Intervention Model: Single Group Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Lentiviral vector transduced CD34+ cells<br>Single arm, non-randomised cohort of up to 5 patients with X-linked Severe Combined Immunodeficiency. CD34+ cells will be collected via bone marrow harvest or leukapheresis. The collected cells will then be purified, cultured and transduced with the G2SCID lentiviral vector. Transduced cells will be frozen. A minimum of 2.5 x 106/kg CD34+ cells after transduction with a minimum transduction efficiency of 0.7 copies/cell is required for infusion into the patient. The patient will receive non-myeloablative conditioning with intravenous busulfan the two or three days prior to cell infusion. The frozen cells will be thawed on the day of infusion and the cells administered according to hospital procedures. The patient will remain in hospital until sufficient cover of the patient's immune system | Drug: Lentiviral vector transduced CD34+ cells<br>* Gene therapy for X-linked Severe Combined Immunodeficiency will be performed by introduction a normal copy of the IL2RG gene into the blood forming stem cells (CD34+ cells) of the patient's bone marrow by using a type of gene delivery system (in this trial called a lentiviral vector). The gene corrected cells are then transplanted back into the patient.<br>* Other names: G2SCID lentiviral vector transduced CD34+ cells;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Measure event-free survival after 1 year after gene transfer | Event-free survival at 1 year post-infusion. Events will include death, infusion of unmanipulated back-up product for failure of haematopoietic recovery, and allogeneic transplant performed for poor immune reconstitution | 1 year | 
| Measure T cell immune reconstitution: CD3+ T cell count | T cell reconstitution at 1 year post-infusion: CD3+ T cell count ≥300 cells/microliter in peripheral blood | 1 year | 
| Measure T cell immune reconstitution; gene marking | T cell reconstitution at 1 year post-infusion: Gene marking ≥0.1 copies/cell in sorted CD3+ T cells | 1 year | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Measure overall survival | Measure overall survival at 2 years post-infusion | 2 years | 
| Measure event-free survival | Measure event-free survival at 2 years post-infusion | 2 years | 
| Incidence of adverse events related to gene therapy | Incidence of adverse events related to gene therapy | up to 2 years post-infusion of gene therapy | 
| Enumeration of absolute lymphocyte count determined by routine complete reconstitution | Enumeration of absolute lymphocyte count determined by routine complete blood counts (CBC) | up to 2 years post-infusion of gene therapy | 
| Haematopoietic recovery after receipt of busulfan | Haematopoietic recovery is defined as absolute neutrophil count above 0.5 x10^9 /l for three consecutive days, achieved within 6 weeks following infusion. | up to 6 weeks post-infusion of gene therapy | 
| Measure absolute numbers of T, B and NK lymphocytes | Absolute numbers of T, B and NK lymphocytes | up to 2 years post-infusion of gene therapy | 
| Calculate percentage of naïve and memory T cell subsets | Percentage of naïve and memory T cell subsets | up to 2 years post-infusion of gene therapy | 
| Measure laboratory results which correlates with efficacious immune reconstitution | Percentage of naïve and memory B cell subsets | up to 2 years post-infusion of gene therapy | 
| Determine Freedom from immunoglobulin substitution for at least 9 months | Freedom from immunoglobulin substitution for at least 9 months | 2 years post-infusion of gene therapy | 
| Measure serum immunoglobulin levels reconstitution | Serum immunoglobulin levels | up to 2 years post-infusion of gene therapy | 
| Measure proliferation of lymphocytes to phytohaemagglutinin determined by titrated thymidine incorporation reconstitution | Proliferation of lymphocytes to phytohaemagglutinin determined by titrated thymidine incorporation | up to 2 years post-infusion of gene therapy | 
| Measure antigen specific antibody titres to tetanus toxoid reconstitution | Measure antigen specific antibody titres to tetanus toxoid | up to 2 years post-infusion of gene therapy | 
| Measure T cell receptor excision circles (TREC) | Measure T cell receptor excision circles (TREC) | up to 2 years post-infusion of gene therapy | 
| Measure T cell receptor Vb family usage | Measure T cell receptor Vb family usage | up to 2 years post-infusion of gene therapy | 
| To assess the efficacy of stem cell transduction/engraftment by measuring the frequency of gene marking in peripheral blood cells | Gene marking in specific lineages of peripheral blood cells. Genomic DNA isolated from each population will be assayed for VCN by quantitative PCR (qPCR). The results will be aggregated to determine the effectiveness of gene marking in the peripheral blood cells. | up to 2 years post-infusion of gene therapy | 
| Measure clonal diversity of vector integrants | Clonal diversity will be quantitated and used to estimate the number of transduced haematopoietic stem cells that have engrafted in the subjects. Number of sequence reads and unique integration sites will be assessed to quantify population clone diversity, distribution of integration sites and relative abundance. | up to 2 years post-infusion of gene therapy |