Myeloid dysplasia and bone marrow hypocellularity in adenosine deaminase-deficient severe combined immune deficiency

Long-term and real-world safety and efficacy of retroviral gene therapy for adenosine deaminase deficiency

Adenosine deaminase (ADA) deficiency leads to severe combined immunodeficiency (SCID). Previous clinical trials showed that autologous CD34+ cell gene therapy (GT) following busulfan reduced-intensity conditioning is a promising therapeutic approach for ADA-SCID, but long-term data are warranted. Here we report an analysis on long-term safety and efficacy data of 43 patients with ADA-SCID who received retroviral ex vivo bone marrow-derived hematopoietic stem cell GT. Twenty-two individuals (median follow-up 15.4 years) were treated in the context of clinical development or named patient program. Nineteen patients were treated post-marketing authorization (median follow-up 3.2 years), and two additional patients received mobilized peripheral blood CD34+ cell GT. At data cutoff, all 43 patients were alive, with a median follow-up of 5.0 years (interquartile range 2.4-15.4) and 2 years intervention-free survival (no need for long-term enzyme replacement therapy or allogeneic hematopoietic stem cell transplantation) of 88% (95% confidence interval 78.7-98.4%). Most adverse events/reactions were related to disease background, busulfan conditioning or immune reconstitution; the safety profile of the real world experience was in line with premarketing cohort. One patient from the named patient program developed a T cell leukemia related to treatment 4.7 years after GT and is currently in remission. Long-term persistence of multilineage gene-corrected cells, metabolic detoxification, immune reconstitution and decreased infection rates were observed. Estimated mixed-effects models showed that higher dose of CD34+ cells infused and younger age at GT affected positively the plateau of CD3+ transduced cells, lymphocytes and CD4+ CD45RA+ naive T cells, whereas the cell dose positively influenced the final plateau of CD15+ transduced cells. These long-term data suggest that the risk-benefit of GT in ADA remains favorable and warrant for continuing long-term safety monitoring. Clinical trial registration: NCT00598481 , NCT03478670 .

Updated Management Guidelines for Adenosine Deaminase Deficiency

Inherited defects in the adenosine deaminase (ADA) gene typically cause severe combined immunodeficiency. In addition to infections, ADA-deficient patients can present with neurodevelopmental, behavioral, hearing, skeletal, lung, heart, skin, kidney, urogenital, and liver abnormalities. Some patients also suffer from autoimmunity and malignancies. In recent years, there have been remarkable advances in the management of ADA deficiency. Most ADA-deficient patients can be identified by newborn screening for severe combined immunodeficiency, which facilitates early diagnosis and treatment of asymptomatic infants. Most patients benefit from enzyme replacement therapy (ERT). Allogeneic hematopoietic cell transplantation from an HLA-matched sibling donor or HLA-matched family member donor with no conditioning is currently the preferable treatment. When matched sibling donor or matched family member donor is not available, autologous ADA gene therapy with nonmyeloablative conditioning and ERT withdrawal, which is reported in recent studies to result in 100% overall survival and 90% to 95% engraftment, should be pursued. If gene therapy is not immediately available, ERT can be continued for a few years, although its excessive cost might be prohibitive. The recent improved outcome of hematopoietic cell transplantation using HLA-mismatched family-related donors or HLA-matched unrelated donors, after reduced-intensity conditioning, suggests that such procedures might also be considered rather than continuing ERT for prolonged periods. Long-term follow-up will further assist in determining the optimal treatment approach for ADA-deficient patients.

Outcomes following treatment for ADA-deficient severe combined immunodeficiency: a report from the PIDTC

Adenosine deaminase (ADA) deficiency causes ∼13% of cases of severe combined immune deficiency (SCID). Treatments include enzyme replacement therapy (ERT), hematopoietic cell transplant (HCT), and gene therapy (GT). We evaluated 131 patients with ADA-SCID diagnosed between 1982 and 2017 who were enrolled in the Primary Immune Deficiency Treatment Consortium SCID studies. Baseline clinical, immunologic, genetic characteristics, and treatment outcomes were analyzed. First definitive cellular therapy (FDCT) included 56 receiving HCT without preceding ERT (HCT); 31 HCT preceded by ERT (ERT-HCT); and 33 GT preceded by ERT (ERT-GT). Five-year event-free survival (EFS, alive, no need for further ERT or cellular therapy) was 49.5% (HCT), 73% (ERT-HCT), and 75.3% (ERT-GT; P < .01). Overall survival (OS) at 5 years after FDCT was 72.5% (HCT), 79.6% (ERT-HCT), and 100% (ERT-GT; P = .01). Five-year OS was superior for patients undergoing HCT at <3.5 months of age (91.6% vs 68% if ≥3.5 months, P = .02). Active infection at the time of HCT (regardless of ERT) decreased 5-year EFS (33.1% vs 68.2%, P < .01) and OS (64.7% vs 82.3%, P = .02). Five-year EFS (90.5%) and OS (100%) were best for matched sibling and matched family donors (MSD/MFD). For patients treated after the year 2000 and without active infection at the time of FDCT, no difference in 5-year EFS or OS was found between HCT using a variety of transplant approaches and ERT-GT. This suggests alternative donor HCT may be considered when MSD/MFD HCT and GT are not available, particularly when newborn screening identifies patients with ADA-SCID soon after birth and before the onset of infections. This trial was registered at www.clinicaltrials.gov as #NCT01186913 and #NCT01346150.

Targeting the Hematopoietic Stem Cell Niche in β-Thalassemia and Sickle Cell Disease

In the last decade, research on pathophysiology and therapeutic solutions for β-thalassemia (BThal) and sickle cell disease (SCD) has been mostly focused on the primary erythroid defect, thus neglecting the study of hematopoietic stem cells (HSCs) and bone marrow (BM) microenvironment. The quality and engraftment of HSCs depend on the BM microenvironment, influencing the outcome of HSC transplantation (HSCT) both in allogeneic and in autologous gene therapy settings. In BThal and SCD, the consequences of severe anemia alter erythropoiesis and cause chronic stress in different organs, including the BM. Here, we discuss the recent findings that highlighted multiple alterations of the BM niche in BThal and SCD. We point out the importance of improving our understanding of HSC biology, the status of the BM niche, and their functional crosstalk in these disorders towards the novel concept of combined therapies by not only targeting the genetic defect, but also key players of the HSC–niche interaction in order to improve the clinical outcomes of transplantation.

A systematic review and meta-analysis of gene therapy with hematopoietic stem and progenitor cells for monogenic disorders

Ex-vivo gene therapy (GT) with hematopoietic stem and progenitor cells (HSPCs) engineered with integrating vectors is a promising treatment for monogenic diseases, but lack of centralized databases is hampering an overall outcomes assessment. Here we aim to provide a comprehensive assessment of the short and long term safety of HSPC-GT from trials using different vector platforms. We review systematically the literature on HSPC-GT to describe survival, genotoxicity and engraftment of gene corrected cells. From 1995 to 2020, 55 trials for 14 diseases met inclusion criteria and 406 patients with primary immunodeficiencies (55.2%), metabolic diseases (17.0%), haemoglobinopathies (24.4%) and bone marrow failures (3.4%) were treated with gammaretroviral vector (γRV) (29.1%), self-inactivating γRV (2.2%) or lentiviral vectors (LV) (68.7%). The pooled overall incidence rate of death is 0.9 per 100 person-years of observation (PYO) (95% CI = 0.37-2.17). There are 21 genotoxic events out of 1504.02 PYO, which occurred in γRV trials (0.99 events per 100 PYO, 95% CI = 0.18-5.43) for primary immunodeficiencies. Pooled rate of engraftment is 86.7% (95% CI = 67.1-95.5%) for γRV and 98.7% (95% CI = 94.5-99.7%) for LV HSPC-GT (p = 0.005). Our analyses show stable reconstitution of haematopoiesis in most recipients with superior engraftment and safer profile in patients receiving LV-transduced HSPCs.

Nonconditioned ADA-SCID gene therapy reveals ADA requirement in the hematopoietic system and clonal dominance of vector-marked clones

Two patients with adenosine deaminase (ADA)-deficient severe combined immunodeficiency (ADA-SCID) received stem cell-based gene therapy (SCGT) using GCsapM-ADA retroviral vectors without preconditioning in 2003 and 2004. The first patient (Pt1) was treated at 4.7 years old, and the second patient (Pt2), who had previously received T cell gene therapy (TCGT), was treated at 13 years old. More than 10 years after SCGT, T cells showed a higher vector copy number (VCN) than other lineages. Moreover, the VCN increased with differentiation toward memory T and B cells. The distribution of vector-marked cells reflected variable levels of ADA requirements in hematopoietic subpopulations. Although neither patient developed leukemia, clonal expansion of SCGT-derived clones was observed in both patients. The use of retroviral vectors yielded clonal dominance of vector-marked clones, irrespective of the lack of leukemic changes. Vector integration sites common to all hematopoietic lineages suggested the engraftment of gene-marked progenitors in Pt1, who showed severe osteoblast (OB) insufficiency compared to Pt2, which might cause a reduction in the stem/progenitor cells in the bone marrow (BM). The impaired BM microenvironment due to metabolic abnormalities may create space for the engraftment of vector-marked cells in ADA-SCID, despite the lack of preconditioning.

The Use of Induced Pluripotent Stem Cells to Study the Effects of Adenosine Deaminase Deficiency on Human Neutrophil Development

Inherited defects that abrogate the function of the adenosine deaminase (ADA) enzyme and consequently lead to the accumulation of toxic purine metabolites cause profound lymphopenia and severe combined immune deficiency. Additionally, neutropenia and impaired neutrophil function have been reported among ADA-deficient patients. However, due to the rarity of the disorder, the neutrophil developmental abnormalities and the mechanisms contributing to them have not been characterized. Induced pluripotent stem cells (iPSC) generated from two unrelated ADA-deficient patients and from healthy controls were differentiated through embryoid bodies into neutrophils. ADA deficiency led to a significant reduction in the number of all early multipotent hematopoietic progenitors. At later stages of differentiation, ADA deficiency impeded the formation of granulocyte colonies in methylcellulose cultures, leading to a significant decrease in the number of neutrophils generated from ADA-deficient iPSCs. The viability and apoptosis of ADA-deficient neutrophils isolated from methylcellulose cultures were unaffected, suggesting that the abnormal purine homeostasis in this condition interferes with differentiation or proliferation. Additionally, there was a significant increase in the percentage of hyperlobular ADA-deficient neutrophils, and these neutrophils demonstrated significantly reduced ability to phagocytize fluorescent microspheres. Supplementing iPSCs and methylcellulose cultures with exogenous ADA, which can correct adenosine metabolism, reversed all abnormalities, cementing the critical role of ADA in neutrophil development. Moreover, chemical inhibition of the ribonucleotide reductase (RNR) enzyme, using hydroxyurea or a combination of nicotinamide and trichostatin A in iPSCs from healthy controls, led to abnormal neutrophil differentiation similar to that observed in ADA deficiency, implicating RNR inhibition as a potential mechanism for the neutrophil abnormalities. In conclusion, the findings presented here demonstrate the important role of ADA in the development and function of neutrophils while clarifying the mechanisms responsible for the neutrophil abnormalities in ADA-deficient patients.

Busulfan Pharmacokinetics in Adenosine Deaminase-Deficient Severe Combined Immunodeficiency Gene Therapy

The pharmacokinetics of low-dose busulfan (BU) were investigated as a nonmyeloablative conditioning regimen for autologous gene therapy (GT) in pediatric subjects with adenosine deaminase-deficient severe combined immunodeficiency disease (ADA SCID). In 3 successive clinical trials, which included either γ-retroviral (γ-RV) or lentiviral (LV) vectors, subjects were conditioned with BU using different dosing nomograms. The first cohort received BU doses based on body surface area (BSA), the second cohort received doses based on actual body weight (ABW), and in the third cohort, therapeutic drug monitoring (TDM) was used to target a specific area under the concentration-time curve (AUC). Neither BSA-based nor ABW-based dosing achieved a consistent cumulative BU AUC; in contrast, TDM-based dosing led to more consistent AUC. BU clearance increased as subject age increased from birth to 18 months. However, weight and age alone were insufficient to accurately predict the dose that would consistently achieve a target AUC. Furthermore, various clinical, laboratory, and genetic factors (eg, genotypes for glutathione-S-transferase isozymes known to participate in BU metabolism) were analyzed, but no single finding predicted subjects with rapid versus slow clearance. Analysis of BU AUC and the postengraftment vector copy number (VCN) in granulocytes, a surrogate marker of the level of engrafted gene-modified hematopoietic stem and progenitor cells (HSPCs), demonstrated gene marking at levels sufficient for therapeutic benefit in the subjects who had achieved the target BU AUC. Although many factors determine the ultimate engraftment following GT, this work demonstrates that the BU AUC correlated with the eventual level of engrafted gene-modified HSPCs within a vector group (γ-RV versus LV), with significantly higher levels of granulocyte VCN in the recipients of LV-modified grafts compared to recipients of γ-RV-transduced grafts. Taken together, these findings provide insight into low-dose BU pharmacokinetics in the unique setting of autologous GT for ADA SCID, and these dosing principles may be applied to future GT trials using low-dose BU to open the bone marrow niche.

Early Enzyme Replacement Therapy Improves Hearing and Immune Defects in Adenosine Deaminase Deficient-Mice

Background: Inherited defects in adenosine deaminase (ADA) cause severe immune deficiency, which can be corrected by ADA enzyme replacement therapy (ERT). Additionally, ADA-deficient patients suffer from hearing impairment. We hypothesized that ADA-deficient (-/-) mice also exhibit hearing abnormalities and that ERT from an early age will improve the hearing and immune defects in these mice. Methods: Auditory brainstem evoked responses, organ weights, thymocytes numbers, and subpopulations, lymphocytes in peripheral blood as well as T lymphocytes in spleen were analyzed in ADA-/- and ADA-proficient littermate post-partum (pp). The cochlea was visualized by scanning electron microscopy (SEM). The effects of polyethylene glycol conjugated ADA (PEG-ADA) ERT or 40% oxygen initiated at 7 days pp on the hearing and immune abnormalities were assessed. Results: Markedly abnormal hearing thresholds responses were found in ADA-/- mice at low and medium tone frequencies. SEM demonstrated extensive damage to the cochlear hair cells of ADA-/- mice, which were splayed, short or missing, correlating with the hearing deficits. The hearing defects were not reversed when hypoxia in ADA-/- mice was corrected. Progressive immune abnormalities were detected in ADA-/- mice from 4 days pp, initially affecting the thymus followed by peripheral lymphocytes and T cells in the spleen. ERT initiated at 7 days pp significantly improved the hearing of ADA-/- mice as well as the number of thymocytes and T lymphocytes, although not all normalized. Conclusions: ADA deficiency is associated with hearing deficits and damage to cochlear hair cells. Early initiation of ERT improves the hearing and immune abnormalities.

Consensus approach for the management of severe combined immune deficiency caused by adenosine deaminase deficiency

Inherited defects in adenosine deaminase (ADA) cause a subtype of severe combined immunodeficiency (SCID) known as severe combined immune deficiency caused by adenosine deaminase defects (ADA-SCID). Most affected infants can receive a diagnosis while still asymptomatic by using an SCID newborn screening test, allowing early initiation of therapy. We review the evidence currently available and propose a consensus management strategy. In addition to treatment of the immune deficiency seen in patients with ADA-SCID, patients should be followed for specific noninfectious respiratory, neurological, and biochemical complications associated with ADA deficiency. All patients should initially receive enzyme replacement therapy (ERT), followed by definitive treatment with either of 2 equal first-line options. If an HLA-matched sibling donor or HLA-matched family donor is available, allogeneic hematopoietic stem cell transplantation (HSCT) should be pursued. The excellent safety and efficacy observed in more than 100 patients with ADA-SCID who received gammaretrovirus- or lentivirus-mediated autologous hematopoietic stem cell gene therapy (HSC-GT) since 2000 now positions HSC-GT as an equal alternative. If HLA-matched sibling donor/HLA-matched family donor HSCT or HSC-GT are not available or have failed, ERT can be continued or reinstituted, and HSCT with alternative donors should be considered. The outcomes of novel HSCT, ERT, and HSC-GT strategies should be evaluated prospectively in "real-life" conditions to further inform these management guidelines.

Long-Term Outcome of Adenosine Deaminase-Deficient Patients-a Single-Center Experience

PURPOSE

Inherited defects in the adenosine deaminase (ADA) enzyme can cause severe combined immune deficiency (SCID) and systemic abnormalities. Management options for ADA-deficient patients include enzyme replacement therapy (ERT), hematopoietic stem cell transplantation (HSCT), and gene therapy (GT). Here, we describe the long-term benefits of these treatments.

METHODS

Survival, infections, systemic sequelae, and laboratory assessments were recorded for all ADA-deficient SCID patients, managed at a single center since 1985, who survived 5 or more years following treatment.

RESULTS

Of 20 ADA-deficient patients, the 8 (40%) who survived 5 or more years (range 6-29.5 years, median 14 years) were included in the study. Among the long-term survivors, two patients were treated exclusively with ERT, five underwent HSCT (three from HLA-matched sibling donors, two from HLA-mismatched related donors), and one received GT. The long-term survivors often suffered from recurrent respiratory infections; however, opportunistic infections occurred in only one patient. Systemic sequelae included lung disease such as bronchiectasis and asthma (four patients), neurologic abnormalities (six patients), metabolic disturbances (two patients), allergy and autoimmunity (six patients), and neoplasms (three patients). Normal CD4⁺ T cell numbers and function, as well as antibody production, were usually observed after HSCT and GT, but not after ERT. Late deaths occurred in two patients at 15 and 25 years after HSCT, respectively, and were attributed to respiratory failure.

CONCLUSIONS

ADA-deficient patients commonly suffer from long-term complications, emphasizing the need for improved management and for multi-disciplinary follow-up.

Clinical efficacy of gene-modified stem cells in adenosine deaminase-deficient immunodeficiency

BACKGROUND

Autologous hematopoietic stem cell transplantation (HSCT) of gene-modified cells is an alternative to enzyme replacement therapy (ERT) and allogeneic HSCT that has shown clinical benefit for adenosine deaminase-deficient (ADA-deficient) SCID when combined with reduced intensity conditioning (RIC) and ERT cessation. Clinical safety and therapeutic efficacy were evaluated in a phase II study.

METHODS

Ten subjects with confirmed ADA-deficient SCID and no available matched sibling or family donor were enrolled between 2009 and 2012 and received transplantation with autologous hematopoietic CD34+ cells that were modified with the human ADA cDNA (MND-ADA) γ-retroviral vector after conditioning with busulfan (90 mg/m2) and ERT cessation. Subjects were followed from 33 to 84 months at the time of data analysis. Safety of the procedure was assessed by recording the number of adverse events. Efficacy was assessed by measuring engraftment of gene-modified hematopoietic stem/progenitor cells, ADA gene expression, and immune reconstitution.

RESULTS

With the exception of the oldest subject (15 years old at enrollment), all subjects remained off ERT with normalized peripheral blood mononuclear cell (PBMC) ADA activity, improved lymphocyte numbers, and normal proliferative responses to mitogens. Three of nine subjects were able to discontinue intravenous immunoglobulin replacement therapy. The MND-ADA vector was persistently detected in PBMCs (vector copy number [VCN] = 0.1-2.6) and granulocytes (VCN = 0.01-0.3) through the most recent visits at the time of this writing. No patient has developed a leukoproliferative disorder or other vector-related clinical complication since transplant.

CONCLUSION

These results demonstrate clinical therapeutic efficacy from gene therapy for ADA-deficient SCID, with an excellent clinical safety profile.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00794508.

FUNDING

Food and Drug Administration Office of Orphan Product Development award, RO1 FD003005; NHLBI awards, PO1 HL73104 and Z01 HG000122; UCLA Clinical and Translational Science Institute awards, UL1RR033176 and UL1TR000124.

The Signaling Pathways Involved in Chondrocyte Differentiation and Hypertrophic Differentiation

Chondrocytes communicate with each other mainly via diffusible signals rather than direct cell-to-cell contact. The chondrogenic differentiation of mesenchymal stem cells (MSCs) is well regulated by the interactions of varieties of growth factors, cytokines, and signaling molecules. A number of critical signaling molecules have been identified to regulate the differentiation of chondrocyte from mesenchymal progenitor cells to their terminal maturation of hypertrophic chondrocytes, including bone morphogenetic proteins (BMPs), SRY-related high-mobility group-box gene 9 (Sox9), parathyroid hormone-related peptide (PTHrP), Indian hedgehog (Ihh), fibroblast growth factor receptor 3 (FGFR3), and β-catenin. Except for these molecules, other factors such as adenosine, O₂ tension, and reactive oxygen species (ROS) also have a vital role in cartilage formation and chondrocyte maturation. Here, we outlined the complex transcriptional network and the function of key factors in this network that determine and regulate the genetic program of chondrogenesis and chondrocyte differentiation.

Gene Therapy with Hematopoietic Stem Cells: The Diseased Bone Marrow's Point of View

When considering inherited diseases that can be treated by gene transfer into hematopoietic stem cells (HSCs), there are only two in which the HSC and progenitor cell distribution inside the bone marrow and its microenvironment are exactly the same as in a healthy subject: metachromatic leukodystrophy (MLD) and adrenoleukodystrophy (ALD). In all other settings [X-linked severe combined immunodeficiency (X-SCID), adenosine deaminase deficiency, Wiskott-Aldrich syndrome, and β-hemoglobinopathies], the bone marrow content of the different stem and precursor cells and the cells' relationship with the stroma have very specific characteristics. These peculiarities can influence the cells' harvesting and behavior in culture, and the postgraft uptake and further behavior of the gene-modified hematopoietic/precursor cells. In the present mini-review, we shall briefly summarize these characteristics and outline the possible consequences and challenges.

Gene Therapy for the Treatment of Primary Immune Deficiencies

The use of gene therapy in the treatment of primary immune deficiencies (PID) has advanced significantly in the last decade. Clinical trials for X-linked severe combined immunodeficiency, adenosine deaminase deficiency (ADA), chronic granulomatous disease, and Wiskott-Aldrich syndrome have demonstrated that gene transfer into hematopoietic stem cells and autologous transplant can result in clinical improvement and is curative for many patients. Unfortunately, early clinical trials were complicated by vector-related insertional mutagenic events for several diseases with the exception of ADA-deficiency SCID. These results prompted the current wave of clinical trials for primary immunodeficiency using alternative retro- or lenti-viral vector constructs that are self-inactivating, and they have shown clinical efficacy without leukemic events thus far. The field of gene therapy continues to progress, with improvements in viral vector profiles, stem cell culturing techniques, and site-specific genome editing platforms. The future of gene therapy is promising, and we are quickly moving towards a time when it will be a standard cellular therapy for many forms of PID.

Eliminating SCID row: new approaches to SCID

Treatments for patients with SCID by hematopoietic stem cell transplantation (HSCT) have changed this otherwise lethal primary immune deficiency disorder into one with an increasingly good prognosis. SCID has been the paradigm disorder supporting many key advances in the field of HSCT, with first-in-human successes with matched sibling, haploidentical, and matched unrelated donor allogeneic transplantations. Nevertheless, the optimal approaches for HSCT are still being defined, including determining the optimal stem cell sources, the use and types of pretransplantation conditioning, and applications for SCID subtypes associated with radiosensitivity, for patients with active viral infections and for neonates. Alternatively, autologous transplantation after ex vivo gene correction (gene therapy) has been applied successfully to the treatment of adenosine deaminase-deficient SCID and X-linked SCID by vector-mediated gene addition. Gene therapy holds the prospect of avoiding risks of GVHD and would allow each patient to be their own donor. New approaches to gene therapy by gene correction in autologous HSCs using site-specific endonuclease-mediated homology-driven gene repair are under development. With newborn screening becoming more widely adopted to detect SCID patients before they develop complications, the prognosis for SCID is expected to improve further. This chapter reviews recent advances and ongoing controversies in allogeneic and autologous HSCT for SCID.

Recent advances in understanding and managing adenosine deaminase and purine nucleoside phosphorylase deficiencies

PURPOSE OF THE REVIEW

To review the recent advances in the understanding and management of the immune and nonimmune effects of inherited adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) deficiencies.

RECENT FINDINGS

Abnormal thymocyte development and peripheral T-cell activation in ADA-deficient and PNP-deficient patients cause increased susceptibility to infections and immune dysregulation. The impaired purine homeostasis also damages many other cell types and tissues. Animal studies suggest that defects in surfactant metabolism by alveolar macrophages cause the pulmonary alveolar proteinosis commonly seen in ADA-deficient infants, while toxicity of purine metabolites to cerebellar Purkinje cells may lead to the ataxia frequently observed in PNP deficiency. Patients' outcome with current treatments including enzyme replacement and stem cell transplantations are inferior to those achieved in most severe immunodeficiency conditions. New strategies, including intracellular enzyme replacement, gene therapy and innovative protocols for stem cell transplantations hold great promise for improved outcomes in ADA and PNP deficiency. Moreover, newborn screening and early diagnosis will allow prompt application of these novel treatment strategies, further improving survival and reducing morbidity.

SUMMARY

Better understanding of the complex immune and nonimmune effects of ADA and PNP deficiency holds great promise for improved patients' outcome.

Newborn screening for severe combined immunodeficiency: an opportunity for intervention

Severe combined immunodeficiency (SCID) is a potentially fatal disorder characterized by defective T- and B-lymphocyte function. We describe a 34-week female twin who had developed feeding intolerance, perioral cyanosis, abdominal distension and neutropenia at 1 month of age. Despite several evaluations including an 'inconclusive' newborn screening result for SCID, the presence of profound lymphopenia was unappreciated. Eventually a diagnosis of SCID in association with adenosine deaminase deficiency was made. This case serves to emphasize the importance of newborn screening for SCID in the context of careful evaluation of clinical and laboratory findings that may be overlooked and result in a delay in the diagnosis of a potentially life-threatening condition.

Current progress on gene therapy for primary immunodeficiencies

Primary immunodeficiencies have played a major role in the development of gene therapy for monogenic diseases of the bone marrow. The last decade has seen convincing evidence of long-term disease correction as a result of ex vivo viral vector-mediated gene transfer into autologous haematopoietic stem cells. The success of these early studies has been balanced by the development of vector-related insertional mutagenic events. More recently the use of alternative vector designs with self-inactivating designs, which have an improved safety profile has led to the initiation of a wave of new studies that are showing early signs of efficacy. The ongoing development of safer vector platforms and gene-correction technologies together with improvements in cell-transduction techniques and optimised conditioning regimes is likely to make gene therapy amenable for a greater number of PIDs. If long-term efficacy and safety are shown, gene therapy will become a standard treatment option for specific forms of PID.

Neutropenia in primary immunodeficiency

PURPOSE OF REVIEW

Neutropenia is a feature of several primary immunodeficiency diseases (PIDDs). Because of the diverse pathophysiologies of the PIDDs and the rarity of each disorder, data are often lacking, leading to the necessity of empiric treatment. Recent developments in the understanding of neutropenia in several of the PIDDs make a review of the data timely.

RECENT FINDINGS

The category of severe congenital neutropenia continues to expand. Mutations in G6PC3 have been identified as the cause of neutropenia in a minority of previously molecularly undefined cases. Recent advances have broadened our understanding of the pathophysiology and the clinical expression of this disorder. A possible function of the C16orf57 gene has been hypothesized that may explain the clinical overlap between Clerucuzio-type poikiloderma with neutropenia and other marrow diseases. Plerixafor has been shown to be a potentially useful treatment in the warts, hypogammaglobulinemia, infection, and myelokathexis syndrome. Investigations of patients with adenosine deaminase deficient severe combined immunodeficiency have identified neutropenia, and particularly susceptibility to myelotoxins, as a feature of this disorder. Granulocyte-colony stimulating factor is the treatment of choice for neutropenia in PIDD, whereas hematopoietic cell transplantation is the only curative option.

SUMMARY

The number of PIDDs associated with neutropenia has increased, as has our understanding of the range of phenotypes. Additional data and hypotheses have been generated helping to explain the diversity of presentations of neutropenia in PIDDs.

Gene therapy for adenosine deaminase-deficient severe combined immune deficiency: clinical comparison of retroviral vectors and treatment plans

We conducted a gene therapy trial in 10 patients with adenosine deaminase (ADA)-deficient severe combined immunodeficiency using 2 slightly different retroviral vectors for the transduction of patients' bone marrow CD34(+) cells. Four subjects were treated without pretransplantation cytoreduction and remained on ADA enzyme-replacement therapy (ERT) throughout the procedure. Only transient (months), low-level (< 0.01%) gene marking was observed in PBMCs of 2 older subjects (15 and 20 years of age), whereas some gene marking of PBMC has persisted for the past 9 years in 2 younger subjects (4 and 6 years). Six additional subjects were treated using the same gene transfer protocol, but after withdrawal of ERT and administration of low-dose busulfan (65-90 mg/m(2)). Three of these remain well, off ERT (5, 4, and 3 years postprocedure), with gene marking in PBMC of 1%-10%, and ADA enzyme expression in PBMC near or in the normal range. Two subjects were restarted on ERT because of poor gene marking and immune recovery, and one had a subsequent allogeneic hematopoietic stem cell transplantation. These studies directly demonstrate the importance of providing nonmyeloablative pretransplantation conditioning to achieve therapeutic benefits with gene therapy for ADA-deficient severe combined immunodeficiency.

Gene therapy/bone marrow transplantation in ADA-deficient mice: roles of enzyme-replacement therapy and cytoreduction

Gene therapy (GT) for adenosine deaminase-deficient severe combined immune deficiency (ADA-SCID) can provide significant long-term benefit when patients are given nonmyeloablative conditioning and ADA enzyme-replacement therapy (ERT) is withheld before autologous transplantation of γ-retroviral vector-transduced BM CD34+ cells. To determine the contributions of conditioning and discontinuation of ERT to the therapeutic effects, we analyzed these factors in Ada gene knockout mice (Ada(-/-)). Mice were transplanted with ADA-deficient marrow transduced with an ADA-expressing γ-retroviral vector without preconditioning or after 200 cGy or 900 cGy total-body irradiation and evaluated after 4 months. In all tissues analyzed, vector copy numbers (VCNs) were 100- to 1000-fold greater in mice receiving 900 cGy compared with 200 cGy (P < .05). In mice receiving 200 cGy, VCN was similar whether ERT was stopped or given for 1 or 4 months after GT. In unconditioned mice, there was decreased survival with and without ERT, and VCN was very low to undetectable. When recipients were conditioned with 200 cGy and received transduced lineage-depleted marrow, only recipients receiving ERT (1 or 4 months) had detectable vector sequences in thymocytes. In conclusion, cytoreduction is important for the engraftment of gene-transduced HSC, and short-term ERT after GT did not diminish the capacity of gene-corrected cells to engraft and persist.

Pulmonary alveolar proteinosis in patients with adenosine deaminase deficiency

BACKGROUND

Inherited defects in the function of adenosine deaminase (ADA) cause severe combined immunodeficiency (SCID) and affect many other cells and tissues.

OBJECTIVES

We sought to characterize the frequency and features of pulmonary alveolar proteinosis (PAP) in patients with ADA deficiency.

METHODS

Clinical and laboratory features of all patients with SCID caused by ADA deficiency in a single center were analyzed. Bronchoalveolar lavage (BAL) fluid and lung biopsy specimens were stained with hematoxylin and eosin and periodic acid-Schiff, visualized by means of electron microscopy, and studied for associated infections. As a control group, BAL fluid and biopsy specimens from 22 patients with SCID caused by other genetic abnormalities were similarly assessed.

RESULTS

Among 16 consecutive patients with ADA deficiency, 7 had BAL fluid containing periodic acid-Schiff-positive surfactant-like material with macrophages engulfing degenerating lamellar bodies and/or lung biopsy specimens with alveolar spaces filled with homogeneous granular eosinophilic material and large macrophages. The lung pathology was typical of PAP. Identification of various pathogens coincided with PAP in 3 of these patients. We have diagnosed PAP among patients with ADA deficiency more commonly in the last 10 years than previously (P= .05), likely reflecting increased awareness of this condition. There were no significant differences in the clinical or immunologic characteristics between patients with ADA deficiency with or without PAP. Similar findings of PAP were not found among patients with SCID caused by other genetic abnormalities (P= .001). ADA coupled to polyethylene glycol or allogeneic hematopoietic stem cell transplantation rapidly corrected this pulmonary complication. PAP seems to have contributed to the death of only 1 patient with ADA deficiency.

CONCLUSIONS

ADA deficiency predisposes to the development of PAP, which could be reversed after enzyme replacement or transplantation.