Non-infectious lung disease in patients with adenosine deaminase deficient severe combined immunodeficiency

Delayed-onset adenosine deaminase deficiency with a novel synonymous mutation and a case series from China

BACKGROUND

Adenosine deaminase (ADA) is a key enzyme in the purine salvage pathway. Genetic defects of the ADA gene can cause a subtype of severe combined immunodeficiency. To date, few Chinese cases have been reported.

METHODS

We retrospectively reviewed the medical records of patients diagnosed with ADA deficiency in Beijing Children's Hospital and summarized the previously published ADA deficiency cases from China in the literature.

RESULTS

Nine patients were identified with two novel mutations (W272X and Q202 =). Early-onset infection, thymic abnormalities and failure to thrive were the most common manifestations of Chinese ADA-deficient patients. The ADA genotype has a major effect on the clinical phenotype. Notably, a novel synonymous mutation (c.606G>A, p.Q202=) was identified in a delayed-onset patient, which affected pre-mRNA splicing leading to a frameshift and premature truncation of the protein. Furthermore, the patient showed γδT cells expansion with an increased effect or phenotype, which may be associated with the delayed onset of disease. In addition, we reported cerebral aneurysm and intracranial artery stenosis for the first time in ADA deficiency. Five patients died with a median age of four months, while two patients received stem cell transplantation and are alive.

CONCLUSIONS

This study described the first case series of Chinese ADA-deficient patients. Early-onset infection, thymic abnormalities and failure to thrive were the most common manifestations in our patients. We identified a synonymous mutation that affected pre-mRNA splicing in the ADA gene, which had never been reported in ADA deficiency. Furthermore, we reported cerebral aneurysm in a delayed-onset patient for the first time. Further study is warranted to investigate the underlying mechanisms.

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.

Long-Term Immune Recovery After Hematopoietic Stem Cell Transplantation for ADA Deficiency: a Single-Center Experience

Unconditioned hematopoietic stem cell transplantation (HSCT) is the recommended treatment for patients with adenosine deaminase (ADA)-deficient severe combined immunodeficiency with an HLA-matched sibling donor (MSD) or family donor (MFD). Improved overall survival (OS) has been reported compared to the use of unrelated donors, and previous studies have demonstrated that adequate cellular and humoral immune recovery can be achieved even in the absence of conditioning. Detailed insight of the long-term outcome is still limited. We aim to address this by studying a large single-center cohort of 28 adenosine deaminase-deficient patients who underwent a total of 31 HSCT procedures, of which more than half were unconditioned. We report an OS of 85.7% and event-free survival of 71% for the entire cohort, with no statistically significant differences after procedures using related or unrelated HLA-matched donors. We find that donor engraftment in the myeloid compartment is significantly diminished in unconditioned procedures, which typically use a MSD or MFD. This is associated with poor metabolic correction and more frequent failure to discontinue immunoglobulin replacement therapy. Approximately one in four patients receiving an unconditioned procedure required a second procedure, whereas the use of reduced intensity conditioning (RIC) prior to allogeneic transplantation improves the long-term outcome by achieving better myeloid engraftment, humoral immune recovery, and metabolic correction. Further longitudinal studies are needed to optimize future management and guidelines, but our findings support a potential role for the routine use of RIC in most ADA-deficient patients receiving an HLA-identical hematopoietic stem cell transplant, even when a MSD or MFD is available.

Multicentric dermatofibrosarcoma protuberans in a child with severe combined immunodeficiency due to adenosine deaminase deficiency

We report the case of a 4-year-old boy, post-human stem cell transplantation for severe combined immunodeficiency (SCID) due to adenosine deaminase deficiency (ADA), who developed multiple dermatofibrosarcoma protuberans (DFSP). We hypothesize a role for chimerism leading to accumulation of toxic metabolites which can cause DNA strand breaks and inhibit lymphocyte activation. Patients with ADA-SCID should remain under lifelong dermatologic surveillance as DFSP lesions can be quite inconspicuous.

Gene delivery using AAV8 in vivo for disease stabilization in a bimodal gene therapy approach for the treatment of ADA-deficient SCID

Adenosine deaminase (ADA) deficiency is an inborn error of metabolism affecting multiple systems and causing severe combined immunodeficiency. We tested intravenous administration of recombinant adeno-associated virus (AAV) 2/8-ADA vector in ADA-deficient neonate and adult mice or as part of a bimodal approach comprised of rAAV treatment at birth followed by infusion of lentiviral vector (LV)-modified lineage-depleted bone marrow cells at 8 weeks. ADA^−/− mice treated with rAAV and enzyme replacement therapy (ERT) for 30 days were rescued from the lethal pulmonary insufficiency, surviving out to 180 days without further treatment. rAAV vector copy number (VCN) was highest in liver, lung, and heart and was associated with near-normal ADA activity and thymocyte development. In the bimodal approach, rAAV-mediated ADA expression supported survival during the 4 weeks before infusion of the LV-modified bone marrow cells and during the engraftment period. Conditioning prior to infusion may have resulted in the replacement of rAAV marked cells in marrow and liver, with LV VCN 100- to 1,000-fold higher in hematopoietic tissue compared with rAAV VCN, and was associated with immune cell reconstitution. In conclusion, a bimodal approach may be an alternative for patients without reliable access to ERT before receiving a stem cell transplant or gene therapy.

Pulmonary Manifestations of Immunodeficiency and Immunosuppressive Diseases Other than Human Immunodeficiency Virus

Immune deficiencies may alter normal lung function and protective mechanisms, resulting in a myriad of pulmonary manifestations. Primary immunodeficiencies involve multiple branches of the immune system, and defects may predispose to recurrent upper and lower respiratory infections by common pathogens; opportunistic infections; and autoimmune, inflammatory, and malignant processes that may result in interstitial pneumonias. Secondary immunodeficiencies may result from neoplasms or their treatment, organ transplant and immunosuppression, and from autoimmune diseases and their treatments. Primary and secondary immunodeficiencies and their pulmonary manifestations may be difficult to diagnose and treat. A multidisciplinary approach to evaluation is essential.

Chest Radiographs for Distinguishing ADA-SCID from Other Forms of SCID

PURPOSE

Early differentiation of adenosine deaminase deficient severe combined immunodeficiency (ADA-SCID) from other forms of SCID may initiate appropriate treatment interventions with the aim of metabolic detoxification and improved outcome. Our hypothesis was that previously described radiological features (inferior scapular angle squaring and spurring and costochondral cupping) can differentiate ADA-SCID from other forms of SCID.

METHODS

Chest radiographs at clinical presentation between 2000 and 2017 of children with ADA-SCID were retrospectively included, provided that the radiological features were assessable. Random chest radiographs of children with other forms of SCID were included for comparison. Three paediatric radiologists (2 senior, 1 junior) assessed the radiographs for the specific radiological features and stated their diagnosis (ADA-SCID or non-ADA-SCID). An optimal threshold for test performance was defined using a ROC curve.

RESULTS

Thirty-six patients with ADA-SCID and twenty-five patients with non-ADA-SCID were included (median age 3.8 months). The optimal threshold for test performance was at approximately < 7 months old: sensitivity 91.7%, specificity 80.7%, interreader agreement was k = 0.709, AUC 0.862. The positive likelihood ratio for scapular squaring, scapular spur, and costochondral cupping was 4.0, 54.6 and 7.8, respectively. The test was valid when performed by both senior and junior paediatric radiologists.

CONCLUSION

Radiological features such as scapular spurring, scapular squaring and costochondral cupping can reliably differentiate between ADA-SCID and other forms of SCID. This is true for children aged approximately < 7 months, and this is reliable when assessed by both senior and junior paediatric radiologists.

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.

Heterozygous Mutation in Adenosine Deaminase Gene in a Patient With Severe Lymphopenia Following Corticosteroid Treatment of Autoimmune Hemolytic Anemia

We describe a previously healthy 14-year-old girl with acute onset autoimmune hemolytic anemia, associated with severe but transient lymphopenia during corticosteroid therapy, without infectious episodes during follow-up. After detailed investigations to rule out an underlying immunodeficiency, we detected a heterozygous ADA gene mutation. This was associated with slightly increased blood levels of adenosine and deoxyadenosine nucleotides and with reduced ADA activity in red blood cells, but within the normal range. This observation suggests that heterozygous ADA mutation might be a predisposing factor for lymphopenia in patients receiving corticosteroid therapy.

Adenosine deaminase deficiency: a review

Adenosine deaminase (ADA) deficiency leads to an accumulation of toxic purine degradation by-products, most potently affecting lymphocytes, leading to adenosine deaminase-deficient severe combined immunodeficiency. Whilst most notable affects are on lymphocytes, other manifestations include skeletal abnormalities, neurodevelopmental affects and pulmonary manifestations associated with pulmonary-alveolar proteinosis. Affected patients present in early infancy, usually with persistent infection, or with pulmonary insufficiency. Three treatment options are currently available. Initial treatment with enzyme replacement therapy may alleviate acute symptoms and enable partial immunological reconstitution, but treatment is life-long, immune reconstitution is incomplete, and the reconstituted immune system may nullify the effects of the enzyme replacement. Hematopoietic stem cell transplant has long been established as the treatment of choice, particularly where a matched sibling or well matched unrelated donor is available. More recently, the use of gene addition techniques to correct the genetic defect in autologous haematopoietic stem cells treatment has demonstrated immunological and clinical efficacy. This article reviews the biology, clinical presentation, diagnosis and treatment of ADA-deficiency.

Adenosine Deaminase (ADA)-Deficient Severe Combined Immune Deficiency (SCID): Molecular Pathogenesis and Clinical Manifestations

Deficiency of adenosine deaminase (ADA, EC3.5.4.4), a housekeeping enzyme of purine metabolism encoded by the Ada gene, is a cause of human severe combined immune deficiency (SCID). Numerous deleterious mutations occurring in the ADA gene have been found in patients with profound lymphopenia (T^- B^- NK^-), thus underscoring the importance of functional purine metabolism for the development of the immune defense. While untreated ADA SCID is a fatal disorder, there are multiple life-saving therapeutic modalities to restore ADA activity and reconstitute protective immunity, including enzyme replacement therapy (ERT), allogeneic hematopoietic stem cell transplantation (HSCT) and gene therapy (GT) with autologous gene-corrected hematopoietic stem cells (HSC). We review the pathogenic mechanisms and clinical manifestations of ADA SCID.

Alterations in the brain adenosine metabolism cause behavioral and neurological impairment in ADA-deficient mice and patients

Adenosine Deaminase (ADA) deficiency is an autosomal recessive variant of severe combined immunodeficiency (SCID) caused by systemic accumulation of ADA substrates. Neurological and behavioral abnormalities observed in ADA-SCID patients surviving after stem cell transplantation or gene therapy represent an unresolved enigma in the field. We found significant neurological and cognitive alterations in untreated ADA-SCID patients as well as in two groups of patients after short- and long-term enzyme replacement therapy with PEG-ADA. These included motor dysfunction, EEG alterations, sensorineural hypoacusia, white matter and ventricular alterations in MRI as well as a low mental development index or IQ. Ada-deficient mice were significantly less active and showed anxiety-like behavior. Molecular and metabolic analyses showed that this phenotype coincides with metabolic alterations and aberrant adenosine receptor signaling. PEG-ADA treatment corrected metabolic adenosine-based alterations, but not cellular and signaling defects, indicating an intrinsic nature of the neurological and behavioral phenotype in ADA deficiency.

Adenosine Deaminase Deficiency - More Than Just an Immunodeficiency

Adenosine deaminase (ADA) deficiency is best known as a form of severe combined immunodeficiency (SCID) that results from mutations in the gene encoding ADA. Affected patients present with clinical and immunological manifestations typical of a SCID. Therapies are currently available that can target these immunological disturbances and treated patients show varying degrees of clinical improvement. However, there is now a growing body of evidence that deficiency of ADA has significant impact on non-immunological organ systems. This review will outline the impact of ADA deficiency on various organ systems, starting with the well-understood immunological abnormalities. We will discuss possible pathogenic mechanisms and also highlight ways in which current treatments could be improved. In doing so, we aim to present ADA deficiency as more than an immunodeficiency and suggest that it should be recognized as a systemic metabolic disorder that affects multiple organ systems. Only by fully understanding ADA deficiency and its manifestations in all organ systems can we aim to deliver therapies that will correct all the clinical consequences.

Neuroprotective effects of adenosine deaminase in the striatum

Adenosine deaminase (ADA) is a ubiquitous enzyme that catabolizes adenosine and deoxyadenosine. During cerebral ischemia, extracellular adenosine levels increase acutely and adenosine deaminase catabolizes the increased levels of adenosine. Since adenosine is a known neuroprotective agent, adenosine deaminase was thought to have a negative effect during ischemia. In this study, however, we demonstrate that adenosine deaminase has substantial neuroprotective effects in the striatum, which is especially vulnerable during cerebral ischemia. We used temporary oxygen/glucose deprivation (OGD) to simulate ischemia in rat corticostriatal brain slices. We used field potentials as the primary measure of neuronal damage. For stable and efficient electrophysiological assessment, we used transgenic rats expressing channelrhodopsin-2, which depolarizes neurons in response to blue light. Time courses of electrically evoked striatal field potential (eFP) and optogenetically evoked striatal field potential (optFP) were recorded during and after oxygen/glucose deprivation. The levels of both eFP and optFP decreased after 10 min of oxygen/glucose deprivation. Bath-application of 10 µg/ml adenosine deaminase during oxygen/glucose deprivation significantly attenuated the oxygen/glucose deprivation-induced reduction in levels of eFP and optFP. The number of injured cells decreased significantly, and western blot analysis indicated a significant decrease of autophagic signaling in the adenosine deaminase-treated oxygen/glucose deprivation slices. These results indicate that adenosine deaminase has protective effects in the striatum.

Impulse oscillometry identifies peripheral airway dysfunction in children with adenosine deaminase deficiency

Adenosine deaminase-deficient severe combined immunodeficiency (ADA-SCID) is characterized by impaired T-, B- and NK-cell function. Affected children, in addition to early onset of infections, manifest non-immunologic symptoms including pulmonary dysfunction likely attributable to elevated systemic adenosine levels. Lung disease assessment has primarily employed repetitive radiography and effort-dependent functional studies. Through impulse oscillometry (IOS), which is effort-independent, we prospectively obtained objective measures of lung dysfunction in 10 children with ADA-SCID. These results support the use of IOS in the identification and monitoring of lung function abnormalities in children with primary immunodeficiencies.

Adenosine deaminase deficient severe combined immunodeficiency presenting as atypical haemolytic uraemic syndrome

PURPOSE

Adenosine deaminase (ADA) deficiency is a systemic disorder of purine metabolism. Deficiency of the purine salvage enzyme ADA leads to the build-up of the toxic metabolites, deoxyadenosine triphosphate and deoxyadenosine. ADA is ubiquitously expressed in all tissues of the body but most profoundly affects lymphocyte development and function leading to severe combined immunodeficiency (SCID). Unlike most other forms of SCID, ADA deficiency also results in non-immunologic manifestations. Associations between ADA deficiency and sensorineural hearing loss, behavioural abnormalities, non-infectious pulmonary disease and skeletal dysplasia are all recognised, and affect the long term outcome for these patients. Identification of new non-immunological manifestations and clinical presentations of ADA deficiency is essential to allow early optimisation of supportive care.

METHODS AND RESULTS

Here we report four patients with ADA deficiency whose presenting feature was haemolytic uremic syndrome (HUS). 3 of 4 patients were diagnosed with ADA deficiency only after developing HUS, and one diagnosis was made post mortem, after a sibling was diagnosed with SCID. Shiga-toxigenic organisms were not isolated from any of the patients. 2 patients made a good recovery from their HUS with supportive treatment and initiation of PEG-ADA. Both remain well on enzyme replacement with mild or no residual renal impairment.

CONCLUSIONS

Clinicians should be aware of this previously unreported non-immunologic manifestation of ADA deficiency.

Hematopoietic stem cell transplantation for primary immunodeficiencies

Allogeneic hematopoietic stem cell transplantation has been shown to be curative for well-described as well as newly discovered immunodeficiencies. However, it is difficulty to define a universal transplant regimen given the rarity of these disorders and the varied pathophysiology these disorders encompass. This article discusses those primary immunodeficiencies most commonly treated by hematopoietic stem cell transplant and describes the transplant issues specific to these disorders.

Effects of vector backbone and pseudotype on lentiviral vector-mediated gene transfer: studies in infant ADA-deficient mice and rhesus monkeys

Systemic delivery of a lentiviral vector carrying a therapeutic gene represents a new treatment for monogenic disease. Previously, we have shown that transfer of the adenosine deaminase (ADA) cDNA in vivo rescues the lethal phenotype and reconstitutes immune function in ADA-deficient mice. In order to translate this approach to ADA-deficient severe combined immune deficiency patients, neonatal ADA-deficient mice and newborn rhesus monkeys were treated with species-matched and mismatched vectors and pseudotypes. We compared gene delivery by the HIV-1-based vector to murine γ-retroviral vectors pseudotyped with vesicular stomatitis virus-glycoprotein or murine retroviral envelopes in ADA-deficient mice. The vesicular stomatitis virus-glycoprotein pseudotyped lentiviral vectors had the highest titer and resulted in the highest vector copy number in multiple tissues, particularly liver and lung. In monkeys, HIV-1 or simian immunodeficiency virus vectors resulted in similar biodistribution in most tissues including bone marrow, spleen, liver, and lung. Simian immunodeficiency virus pseudotyped with the gibbon ape leukemia virus envelope produced 10- to 30-fold lower titers than the vesicular stomatitis virus-glycoprotein pseudotype, but had a similar tissue biodistribution and similar copy number in blood cells. The relative copy numbers achieved in mice and monkeys were similar when adjusted to the administered dose per kg. These results suggest that this approach can be scaled-up to clinical levels for treatment of ADA-deficient severe combined immune deficiency subjects with suboptimal hematopoietic stem cell transplantation options.

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.

Animal models in chronic obstructive pulmonary disease-an overview

ABSTRACT Chronic obstructive pulmonary disease (COPD) is characterized by progressive airway obstruction resultant from an augmented inflammatory response of the respiratory tract to noxious particles and gases. Previous reports present a number of different hypotheses about the etiology and pathophysiology of COPD. The generating mechanisms of the disease are subject of much speculation, and a series of questions and controversies among experts still remain. In this context, several experimental models have been proposed in order to broaden the knowledge on the pathophysiological characteristics of the disease, as well as the search for new therapeutic approaches for acute or chronically injured lung tissue. This review aims to present the main experimental models of COPD, more specifically emphysema, as well as to describe the main characteristics, advantages, disadvantages, possibilities of application, and potential contribution of each of these models for the knowledge on the pathophysiological aspects and to test new treatment options for obstructive lung diseases.

Preclinical demonstration of lentiviral vector-mediated correction of immunological and metabolic abnormalities in models of adenosine deaminase deficiency

Gene transfer into autologous hematopoietic stem cells by γ-retroviral vectors (gRV) is an effective treatment for adenosine deaminase (ADA)-deficient severe combined immunodeficiency (SCID). However, current gRV have significant potential for insertional mutagenesis as reported in clinical trials for other primary immunodeficiencies. To improve the efficacy and safety of ADA-SCID gene therapy (GT), we generated a self-inactivating lentiviral vector (LV) with a codon-optimized human cADA gene under the control of the short form elongation factor-1α promoter (LV EFS ADA). In ADA(-/-) mice, LV EFS ADA displayed high-efficiency gene transfer and sufficient ADA expression to rescue ADA(-/-) mice from their lethal phenotype with good thymic and peripheral T- and B-cell reconstitution. Human ADA-deficient CD34(+) cells transduced with 1-5 × 10(7) TU/ml had 1-3 vector copies/cell and expressed 1-2x of normal endogenous levels of ADA, as assayed in vitro and by transplantation into immune-deficient mice. Importantly, in vitro immortalization assays demonstrated that LV EFS ADA had significantly less transformation potential compared to gRV vectors, and vector integration-site analysis by nrLAM-PCR of transduced human cells grown in immune-deficient mice showed no evidence of clonal skewing. These data demonstrated that the LV EFS ADA vector can effectively transfer the human ADA cDNA and promote immune and metabolic recovery, while reducing the potential for vector-mediated insertional mutagenesis.

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.