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X-linked chronic granulomatous disease is an immunodeficiency characterized by defective production of microbicidal reactive oxygen species (ROS) by phagocytes. Causative mutations occur throughout the 13 exons and splice sites of the CYBB gene, resulting in loss of gp91phox protein. Here we report gene correction by homology-directed repair in patient hematopoietic stem/progenitor cells (HSPCs) using CRISPR/Cas9 for targeted insertion of CYBB exon 1–13 or 2–13 cDNAs from adeno-associated virus donors at endogenous CYBB exon 1 or exon 2 sites. Targeted insertion of exon 1–13 cDNA did not restore physiologic gp91phox levels, consistent with a requirement for intron 1 in CYBB expression. However, insertion of exon 2–13 cDNA fully restored gp91phox and ROS production upon phagocyte differentiation. Addition of a woodchuck hepatitis virus post-transcriptional regulatory element did not further enhance gp91phox expression in exon 2–13 corrected cells, indicating that retention of intron 1 was sufficient for optimal CYBB expression. Targeted correction was increased ~1.5-fold using i53 mRNA to transiently inhibit nonhomologous end joining. Following engraftment in NSG mice, corrected HSPCs generated phagocytes with restored gp91phox and ROS production. Our findings demonstrate the utility of tailoring donor design and targeting strategies to retain regulatory elements needed for optimal expression of the target gene.

PurposeHaploidentical related donor (HRD) transplantation was performed in 7 recipients with chronic granulomatous disease (CGD) who had no matched-related or unrelated donor.MethodsPeripheral blood cell (PBC) products were used with a conditioning regimen consisting of low-dose cyclophosphamide, fludarabine, total body irradiation, and busulfan. Graft-versus-host disease (GVHD) prophylaxis consisted of high-dose post-transplant cyclophosphamide and sirolimus. Recipients were ages 14–26 years, and 3 had severe infections active at transplant.ResultsAll 7 recipients achieved full engraftment with complete donor chimerism early in the post-transplant period. Acute GVHD occurred in all cases and was grade 3 or steroid refractory in 3. Two patients with steroid-refractory GVHD died. Three patients with severe infectious complications active at transplant, 1 Nocardia pneumonia and 2 extensive invasive fungal infections), survived and were cured of their infection at last follow-up. Bacterial disease occurred post-transplant in all recipients, and viral infections/reactivation were common, including 4 cases of BK virus–associated hemorrhagic cystitis.ConclusionsSeven patients with CGD achieved rapid and full-donor engraftment from HRDs utilizing PBCs and a conditioning regimen with PTCy and sirolimus GVHD prophylaxis. However, the incidence of grade 3 and steroid-refractory GVHD was high and led to 2 deaths. Patients with active infections at transplant had successful transplant courses and were cured of their disease. Although there was an initial success with this regimen, the cumulative experience does not support its use in CGD due to an unacceptable rate of severe GVHD.

Purpose The purpose of this study was to evaluate engraftment and adverse events with a conditioning and prophylactic regimen intended to achieve high rates of engraftment with minimal graft-versus-host disease (GVHD) in allogeneic transplantation for chronic granulomatous disease in a single center. Methods Forty patients, 37 male, with chronic granulomatous disease were transplanted. Transplant products were matched sibling peripheral blood stem cells (PBSCs) in four and matched unrelated donor (MUD) bone marrow in three, and one patient received mismatched unrelated PBSCs. Thirty-two patients received MUD PBSCs. All patients received a conditioning regimen of busulfan/alemtuzumab (with low-dose total body irradiation for MUD recipients) with sirolimus graft-versus-host disease prophylaxis. Results Engraftment occured in 38/40 recipients (95%). Acute or chronic GVHD occurred in 18 (45%) and 5 (12.5%), respectively, with 6 episodes of grades III–IV and/or steroid refractory GVHD. Overall survival was 33/40 (82.5%) and event-free survival was 30/40 (80%). Successful engraftment was associated with myeloid and NK cell, but not CD3+ chimerism. Myeloid engraftment was greater than 70% in 30/32 recipients at mean follow-up of 3.4 years. Evidence of persistent immunodeficiency was not seen in successful transplants. Attempts to rescue failed or poorly functioning grafts were associated with unacceptable morbidity and mortality. Conclusions A reduced-intensity allogeneic transplant protocol based on alemtuzumab and busulfan with sirolimus GVHD prophylaxis produced high rates of successful engraftment and minimal regimen-related toxicity. Prolonged clinical follow-up has confirmed its efficacy in ameliorating CGD-related disease. Outcomes were not acceptable with donor cell infusion rescue of cause with poor graft function.

X-linked Severe Combined Immunodeficiency (SCID-X1) due to IL2RG mutations is potentially fatal in infancy where ‘emergency’ life-saving stem cell transplant may only achieve incomplete immune reconstitution following transplant. Salvage therapy SCID-X1 patients over 2 years old (NCT01306019) is a non-randomized, open-label, phase I/II clinical trial for administration of lentiviral-transduced autologous hematopoietic stem cells following busulfan (6 mg/kg total) conditioning. The primary and secondary objectives assess efficacy in restoring immunity and safety by vector insertion site analysis (VISA). In this ongoing study (19 patients treated), we report VISA in blood lineages from first eight treated patients with longer follow up found a > 60-fold increase in frequency of forward-orientated VIS within intron 3 of the High Mobility Group AT-hook 2 gene. All eight patients demonstrated emergence of dominant HMGA2 VIS clones in progenitor and myeloid lineages, but without disturbance of hematopoiesis. Our molecular analysis demonstrated a cryptic splice site within the chicken β-globin hypersensitivity 4 insulator element in the vector generating truncated mRNA transcripts from many transcriptionally active gene containing forward-oriented intronic vector insert. A two base-pair change at the splice site within the lentiviral vector eliminated splicing activity while retaining vector functional capability. This highlights the importance of functional analysis of lentivectors for cryptic splicing for preclinical safety assessment and a redesign of clinical vectors to improve safety. De Ravin et al. report an unplanned interim analysis of a secondary safety outcome for an ongoing clinical trial on lentiviral gene therapy for the treatment of X-linked Severe Combined Immunodeficiency (NCT01306019). Vector induced alternative splicing events are identified that cause aberrant fusion transcripts, leading to clonal dominance in a single patient and clonal expansion in others. This can be mitigated by the removal of the lentivector cryptic splice acceptor.

Targeted genetic correction of hematopoietic stem cells is applied to X-linked chronic granulomatous disease. Gene therapy with genetically modified human CD34 + hematopoietic stem and progenitor cells (HSPCs) may be safer using targeted integration (TI) of transgenes into a genomic 'safe harbor' site rather than random viral integration. We demonstrate that temporally optimized delivery of zinc finger nuclease mRNA via electroporation and adeno-associated virus (AAV) 6 delivery of donor constructs in human HSPCs approaches clinically relevant levels of TI into the AAVS1 safe harbor locus. Up to 58% Venus + HSPCs with 6–16% human cell marking were observed following engraftment into mice. In HSPCs from patients with X-linked chronic granulomatous disease (X-CGD), caused by mutations in the gp91phox subunit of the NADPH oxidase, TI of a gp91phox transgene into AAVS1 resulted in ∼15% gp91phox expression and increased NADPH oxidase activity in ex vivo –derived neutrophils. In mice transplanted with corrected HSPCs, 4–11% of human cells in the bone marrow expressed gp91phox. This method for TI into AAVS1 may be broadly applicable to correction of other monogenic diseases.

Little is known about the potential for engraftment of autologous hematopoietic stem cells in human adults not subjected to myeloablative conditioning regimens. Five adult patients with the p47phoxdeficiency form of chronic granulomatous disease received intravenous infusions of autologous CD34+peripheral blood stem cells (PBSCs) that had been transduced ex vivo with a recombinant retrovirus encoding normal p47phox. Although marrow conditioning was not given, functionally corrected granulocytes were detectable in peripheral blood of all five patients. Peak correction occurred 3-6 weeks after infusion and ranged from 0.004 to 0.05% of total peripheral blood granulocytes. Corrected cells were detectable for as long as 6 months after infusion in some individuals. Thus, prolonged engraftment of autologous PBSCs and continued expression of the transduced gene can occur in adults without conditioning. This trial also piloted the use of animal protein-free medium and a blood-bank-compatible closed system of gas-permeable plastic containers for culture and transduction of the PBSCs. These features enhance the safety of PBSCs directed gene therapy.

Purpose We describe haploidentical hematopoietic cell transplantation (HCT) with high-dose post-transplant cyclophosphamide (PTCy) in a boy with x-linked chronic granulomatous disease (CGD). Methods A persistent and life-threatening fungal infection was the indication for HSCT. Non-myeloablative conditioning with PTCy (50 mg/kg days 3 and 4) was used in the absence of fully matched donors. Results Engraftment occurred on day 24. The patient experienced Grade 2 graft-versus-host disease of the skin and gastrointestinal tract and CMV infection, both of which were controlled. Chimerism was 100 % at days 30 and 6 months. Cessation of antifungal therapy was consistent with cure of the infection. Conclusions Haploidentical HCT with high-dose PTCy for CGD is feasible and succeeded even in the context of active infection.

A prominent feature of WHIM syndrome (an immune deficiency) is myelokathexis (a type of premature apoptosis) of mature myeloid cells in bone marrow (BM) together with an associated peripheral blood (PB) neutropenia. WHIM syndrome is caused by autosomal dominant heterozygous C-truncation mutations in CXC chemokine receptor 4 (CXCR4), the receptor for stromal cell-derived factor-1 (SDF1) important in marrow trafficking. We have previously reported that healthy human CD34 hematopoietic stem cells transduced with retrovirus encoding one of CXCR4 mutations causing WHIM (R334X; referred to hereafter as mutated-CXCR4) demonstrate enhanced chemotaxis and calcium-flux responses to SDF1, resulting from a failure to downregulate and internalize mutated-CXCR4. In the current study we explore the mechanism for induction of myelokathexis by mutated-CXCR4. We generated IRES-containing bifunctional retrovirus vectors encoding mutated-CXCR4 or wild-type (wt-) CXCR4 together with a green fluorescent protein (GFP) construct. Retrovirus encoding GFP alone was used as negative control. Healthy human GCSF mobilized peripheral blood stem cells (PBSCs) transduced with either mutated-CXCR4 or wt-CXCR4 demonstrated enhanced migration and calcium flux in response to SDF1 compared to the control GFP construct, with the mutated-CXCR4 showing a demonstrably greater functional effect. However, there was no difference in rates of apoptosis in culture (Annexin assay). These transduced human PBSC were transplanted into NOD/SCID mice and human cells appearing in BM and PB assessed at 6 wks. There was enhanced engraftment of human CD45+ cells in the BM of mice transplanted with mutated-CXCR4 and wt-CXCR4 transduced PBSCs compared to GFP alone transduced PBSCs, with the mutated-CXCR4 group showing a greater level of human cell engraftment. However, assessing only GFP+ cells (to focus only on transduced cells in all groups) in BM and PB we showed a highly significant increase in the rate of apoptosis of GFP+ cells in BM of the mutated-CXCR4 group compared to the other groups together with a significantly lower ratio of PB GFP+ CD45+ human leukocytes/GFP+ BM compared to the other groups. These results suggest that mutated-CXCR4 does not itself induce an increased rate of apoptosis, but that the positive dominant functional effect of this receptor causes mature myeloid cells to remain in BM beyond the time of normal release. This increases the frequency of post-mature myeloid cells undergoing apoptosis in BM with an associated neutropenia due to failed release into the PB.