PEG-ADA: an alternative to haploidentical bone marrow transplantation and an adjunct to gene therapy for adenosine deaminase deficiency

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.

T cell gene therapy to treat immunodeficiency

The application of therapeutic T cells for a number of conditions has been developed over the past few decades with notable successes including donor lymphocyte infusions, virus-specific T cells and more recently CAR-T cell therapy. Primary immunodeficiencies are monogenetic disorders leading to abnormal development or function of the immune system. Haematopoietic stem cell transplantation and, in specific candidate diseases, haematopoietic stem cell gene therapy has been the only definitive treatment option so far. However, autologous gene-modified T cell therapy may offer a potential cure in conditions primarily affecting the lymphoid compartment. In this review we will highlight several T cell gene addition or gene-editing approaches in different target diseases with a focus on what we have learnt from clinical experience and promising preclinical studies in primary immunodeficiencies. Functional T cells are required not only for normal immune responses to infection (affected in CD40 ligand deficiency), but also for immune regulation [disrupted in IPEX syndrome (immune dysregulation, polyendocrinopathy, enteropathy, X-Linked) due to dysfunctional FOXP3 and CTLA4 deficiency] or cytotoxicity [defective in X-lymphoproliferative disease and familial haemophagocytic lymphohistiocytosis (HLH) syndromes]. In all these candidate diseases, restoration of T cell function by gene therapy could be of great value.

A Novel Approach to the Treatment of Plasma Protein Deficiency: Ex Vivo-Manipulated Adipocytes for Sustained Secretion of Therapeutic Proteins

Despite the critical need for lifelong treatment of inherited and genetic diseases, there are no developmental efforts for most such diseases due to their rarity. Recent progress in gene therapy, including the approvals of two products (Glybera and Strimvelis) that may provide patients with sustained effects, has shed light on the development of gene therapy products. Most gene therapy products are based on either adeno-associated virus-mediated in vivo gene transfer to target tissues or administration of ex vivo gene-transduced hematopoietic cells. In such circumstances, there is room for different approaches to provide clinicians with other therapeutic options through a variety of principles based on studies not only to gain an understanding of the pathological mechanisms of diseases, but also to understand the physiological functions of target tissues and cells. In this review, we summarize recent progress in gene therapy-mediated enzyme replacement and introduce a different approach using adipocytes to enable lifelong treatment for intractable plasma protein deficiencies.

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.

Smart pH-sensitive nanoassemblies with cleavable PEGylation for tumor targeted drug delivery

A new acidly sensitive PEGylated polyethylenimine linked by Schiff base (PEG-s-PEI) was designed to render pH-sensitive PEGylation nanoassemblies through multiple interactions with indomethacin and docetaxel (DTX). DTX nanoassemblies driven by PEG-s-PEI thus formulated exhibited an excellent pH-sensitivity PEGylation cleavage performance at extracellular pH of tumor microenvironment, compared to normal tissues, thereby long circulated in blood but were highly phagocytosed by tumor cells. Consequently, this smart pH-sensitive PEGylation cleavage provided an efficient strategy to target tumor microenvironment, in turn afforded superior therapeutic outcome in anti-tumor activity.

Severe Combined Immunodeficiency Disorders

Severe combined immunodeficiency disorders represent pediatric emergencies due to absence of adaptive immune responses to infections. The conditions result from either intrinsic defects in T-cell development (ie, severe combined immunodeficiency disease [SCID]) or congenital athymia (eg, complete DiGeorge anomaly). Hematopoietic stem cell transplant provides the only clinically approved cure for SCID, although gene therapy research trials are showing significant promise. For greatest survival, patients should undergo transplant before 3.5 months of age and before the onset of infections. Newborn screening programs have yielded successful early identification and treatment of infants with SCID and congenital athymia in the United States.

Sustained Elevated Adenosine via ADORA2B Promotes Chronic Pain through Neuro-immune Interaction

The molecular mechanisms of chronic pain are poorly understood and effective mechanism-based treatments are lacking. Here, we report that mice lacking adenosine deaminase (ADA), an enzyme necessary for the breakdown of adenosine, displayed unexpected chronic mechanical and thermal hypersensitivity due to sustained elevated circulating adenosine. Extending from Ada(-/-) mice, we further discovered that prolonged elevated adenosine contributed to chronic pain behaviors in two additional independent animal models: sickle cell disease mice, a model of severe pain with limited treatment, and complete Freund's adjuvant paw-injected mice, a well-accepted inflammatory model of chronic pain. Mechanistically, we revealed that activation of adenosine A2B receptors on myeloid cells caused nociceptor hyperexcitability and promoted chronic pain via soluble IL-6 receptor trans-signaling, and our findings determined that prolonged accumulated circulating adenosine contributes to chronic pain by promoting immune-neuronal interaction and revealed multiple therapeutic targets.

Bottom-Up Instructive Quality Control in the Biofabrication of Smart Protein Materials

The impact of cell factory quality control on material properties is a neglected but critical issue in the fabrication of protein biomaterials, which are unique in merging structure and function. The molecular chaperoning of protein conformational status is revealed here as a potent molecular instructor of the macroscopic properties of self-assembling, cell-targeted protein nanoparticles, including biodistribution upon in vivo administration.

Toll-like receptor signaling in primary immune deficiencies

Toll-like receptors (TLRs) recognize common microbial or host-derived macromolecules and have important roles in early activation of the immune system. Patients with primary immune deficiencies (PIDs) affecting TLR signaling can elucidate the importance of these proteins to the human immune system. Defects in interleukin-1 receptor-associated kinase-4 and myeloid differentiation factor 88 (MyD88) lead to susceptibility to infections with bacteria, while mutations in nuclear factor-κB essential modulator (NEMO) and other downstream mediators generally induce broader susceptibility to bacteria, viruses, and fungi. In contrast, TLR3 signaling defects are specific for susceptibility to herpes simplex virus type 1 encephalitis. Other PIDs induce functional alterations of TLR signaling pathways, such as common variable immunodeficiency in which plasmacytoid dendritic cell defects enhance defective responses of B cells to shared TLR agonists. Dampening of TLR responses is seen for TLRs 2 and 4 in chronic granulomatous disease (CGD) and X-linked agammaglobulinemia (XLA). Enhanced TLR responses, meanwhile, are seen for TLRs 5 and 9 in CGD, TLRs 4, 7/8, and 9 in XLA, TLRs 2 and 4 in hyper IgE syndrome, and for most TLRs in adenosine deaminase deficiency.

Stem cell transplantation for primary immune deficiency

PURPOSE OF REVIEW

In this article, we summarize the recent advances in treating primary immune deficiency (PID) disorders by stem cell transplantation (SCT); we have focused on articles published in the past 2 years since the last major review of SCT for PID.

RECENT FINDINGS

Analyses of the outcomes of SCT for PID by specific molecular defect have clarified which conditions are receptive to unconditioned transplants and which require more myeloablative conditioning. Improved outcomes for 'difficult' conditions [adenosine deaminase-severe combined immunodeficiency (ADA-SCID), major histocompatibility complex class II deficiency] and potential advantages of using cord blood as a stem cell source have also been described. Newborn screening for SCID identifies well babies with SCID: the optimal SCT protocol for such young infants remains to be determined. Reduced toxicity conditioning has been successfully used to treat conditions such as Wiskott-Aldrich syndrome and chronic granulomatous disease, offering curative engraftment with reduced transplant-related mortality. Similarly, treating children with familial hemophagocytic lymphohistiocytosis using reduced intensity conditioning SCT results in much improved outcomes. Advances in next generation sequencing have identified new diseases amenable to SCT, such as DOCK8 deficiency, resulting in improved quality of life and protection from malignancy.

SUMMARY

Recent studies suggest that further improvements in treating PID with SCT are possible with a greater understanding of the genetics and immunobiology of these diseases, facilitating the matching of donor type and conditioning regimens, or indeed alternative therapies (such as gene therapy) to specific PID disorders.

Outcome of hematopoietic stem cell transplantation for adenosine deaminase–deficient severe combined immunodeficiency

Deficiency of the purine salvage enzyme adenosine deaminase leads to SCID (ADA-SCID). Hematopoietic cell transplantation (HCT) can lead to a permanent cure of SCID; however, little data are available on outcome of HCT for ADA-SCID in particular. In this multicenter retrospective study, we analyzed outcome of HCT in 106 patients with ADA-SCID who received a total of 119 transplants. HCT from matched sibling and family donors (MSDs, MFDs) had significantly better overall survival (86% and 81%) in comparison with HCT from matched unrelated (66%; P < .05) and haploidentical donors (43%; P < .001). Superior overall survival was also seen in patients who received unconditioned transplants in comparison with myeloablative procedures (81% vs 54%; P < .003), although in unconditioned haploidentical donor HCT, nonengraftment was a major problem. Long-term immune recovery showed that regardless of transplant type, overall T-cell numbers were similar, although a faster rate of T-cell recovery was observed after MSD/MFD HCT. Humoral immunity and donor B-cell engraftment was achieved in nearly all evaluable surviving patients and was seen even after unconditioned HCT. These data detail for the first time the outcomes of HCT for ADA-SCID and show that, if patients survive HCT, long-term cellular and humoral immune recovery is achieved.

Cross correction following haemopoietic stem cell transplant for purine nucleoside phosphorylase deficiency: engrafted donor-derived white blood cells provide enzyme to residual enzyme-deficient recipient cells

Purine nucleoside phosphorylase (PNP) deficiency is an immunodeficiency disorder characterized by recurrent infections, failure to thrive and neurologic symptomatology. While enzyme replacement therapy (ERT) is a therapeutic option for adenine deaminase (ADA) deficiency, a similar disorder, this is not available for PNP deficiency, and bone marrow transplant (BMT) is the only treatment option. Moreover, even with BMT, improvement of neurological deficits is not definite. We describe a 16-month-old boy who underwent BMT for PNP deficiency which resulted not only in freedom from infections but also in neurological improvement and autologous T-cell recovery.Pre-transplant, this child had severe lymphopenia with recurrent infections and psychomotor retardation. Post-transplant, in the presence of mixed chimerism, he had normal lymphocyte count, including presence of recipient T cells and neurological improvement. The re-emergence of recipient T cells, when there were virtually no such cells pre-transplant, and the neurological improvement are indicative of improvement of the enzyme deficiency in tissues which remain genetically enzyme depleted.These defects are not directly corrected by BMT, but are due to delivery of the missing enzyme by the transplanted tissue. In this aspect, transplantation in PNP deficiency is similar to transplantation in other inborn errors of metabolism where the engrafted donor cells deliver enzyme and restore function to deficient tissues. This further lends support to the recommendations that BMT should be the favoured treatment option in disorders like ADA deficiency or Hurler syndrome, where, even though ERT is available, it is limited by inability to correct the central nervous system defects.

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

Genetic deficiency of adenosine deaminase (ADA) can cause profound lymphopenia and result in the clinical presentation of severe combined immune deficiency (SCID). However, because of the ubiquitous expression of ADA, ADA-deficient patients often present also with nonimmunologic clinical problems, affecting the skeletal, central nervous, endocrine, and gastrointestinal systems. We now report that myeloid dysplasia features and bone marrow hypocellularity are often found in patients with ADA-SCID. As a clinical correlate to this finding, we have observed vulnerability to antibiotic-induced myelotoxicity and prolonged neutropenia after nonmyeloablative chemotherapy. We have also noted that, in the absence of enzyme replacement therapy, absolute neutrophil counts of patients with ADA deficiency vary inversely with the accumulation of deoxynucleotides. These data have significant implications for the application of standard and investigational therapies to patients with ADA-SCID and support further studies to investigate the possibility that ADA deficiency is associated with a stem cell defect. These trials were registered at www.clinicaltrials.gov as #NCT00018018 and #NCT00006319.

A2B adenosine receptor-mediated induction of IL-6 promotes CKD

Chronic elevation of adenosine, which occurs in the setting of repeated or prolonged tissue injury, can exacerbate cellular dysfunction, suggesting that it may contribute to the pathogenesis of CKD. Here, mice with chronically elevated levels of adenosine, resulting from a deficiency in adenosine deaminase (ADA), developed renal dysfunction and fibrosis. Both the administration of polyethylene glycol-modified ADA to reduce adenosine levels and the inhibition of the A(2B) adenosine receptor (A(2B)R) attenuated renal fibrosis and dysfunction. Furthermore, activation of A(2B)R promoted renal fibrosis in both mice infused with angiotensin II (Ang II) and mice subjected to unilateral ureteral obstruction (UUO). These three mouse models shared a similar profile of profibrotic gene expression in kidney tissue, suggesting that they share similar signaling pathways that lead to renal fibrosis. Finally, both genetic and pharmacologic approaches showed that the inflammatory cytokine IL-6 mediates adenosine-induced renal fibrosis downstream of A(2B)R. Taken together, these data suggest that A(2B)R-mediated induction of IL-6 contributes to renal fibrogenesis and shows potential therapeutic targets for CKD.

Adenosine deaminase enzyme therapy prevents and reverses the heightened cavernosal relaxation in priapism

INTRODUCTION

Priapism featured with painful prolonged penile erection is dangerous and commonly seen in sickle cell disease (SCD). The preventive approaches or effective treatment options for the disorder are limited because of poor understanding of its pathogenesis. Recent studies have revealed a novel role of excess adenosine in priapism caused by heightened cavernosal relaxation, and therefore present an intriguing mechanism-based therapeutic possibility.

AIM

The aim of this study was to determine the therapeutic effects of adenosine deaminase (ADA) enzyme therapy to lower adenosine in priapism.

METHODS

Both ADA-deficient mice and SCD transgenic (Tg) mice display priapism caused by excessive adenosine. Thus, we used these two distinct lines of mouse models of priapism as our investigative tools. Specifically, we treated both of these mice with different dosages of polyethylene glycol-modified ADA (PEG-ADA) to reduce adenosine levels in vivo. At the end points of the experiments, we evaluated the therapeutic effects of PEG-ADA treatment by measuring adenosine levels and monitoring the cavernosal relaxation.

MAIN OUTCOME MEASURES

Adenosine levels in penile tissues were measured by high-performance liquid chromatography, and cavernosal relaxation was quantified by electrical field stimulation (EFS)-induced corporal cavernosal strip (CCS) assays.

RESULTS

We found that lowering adenosine levels in penile tissues by PEG-ADA treatment from birth in ADA-deficient mice prevented the increased EFS-induced CCS relaxation associated with priapism. Intriguingly, in both ADA-deficient mice and SCD Tg mice with established priapism, we found that normalization of adenosine levels in penile tissues by PEG-ADA treatment relieved the heightened EFS-induced cavernosal relaxation in priapism.

CONCLUSIONS

Our studies have identified that PEG-ADA is a novel, safe, and mechanism-based drug to prevent and correct excess adenosine-mediated increased cavernosal relaxation seen in two independent priapic animal models, and suggested its therapeutic possibility in men suffering from priapism.

Retroviral vectors encoding ADA regulatory locus control region provide enhanced T-cell-specific transgene expression

Background

Murine retroviral vectors have been used in several hundred gene therapy clinical trials, but have fallen out of favor for a number of reasons. One issue is that gene expression from viral or internal promoters is highly variable and essentially unregulated. Moreover, with retroviral vectors, gene expression is usually silenced over time. Mammalian genes, in contrast, are characterized by highly regulated, precise levels of expression in both a temporal and a cell-specific manner. To ascertain if recapitulation of endogenous adenosine deaminase (ADA) expression can be achieved in a vector construct we created a new series of Moloney murine leukemia virus (MuLV) based retroviral vector that carry human regulatory elements including combinations of the ADA promoter, the ADA locus control region (LCR), ADA introns and human polyadenylation sequences in a self-inactivating vector backbone.

Methods

A MuLV-based retroviral vector with a self-inactivating (SIN) backbone, the phosphoglycerate kinase promoter (PGK) and the enhanced green fluorescent protein (eGFP), as a reporter gene, was generated. Subsequent vectors were constructed from this basic vector by deletion or addition of certain elements. The added elements that were assessed are the human ADA promoter, human ADA locus control region (LCR), introns 7, 8, and 11 from the human ADA gene, and human growth hormone polyadenylation signal. Retroviral vector particles were produced by transient three-plasmid transfection of 293T cells. Retroviral vectors encoding eGFP were titered by transducing 293A cells, and then the proportion of GFP-positive cells was determined using fluorescence-activated cell sorting (FACS). Non T-cell and T-cell lines were transduced at a multiplicity of infection (MOI) of 0.1 and the yield of eGFP transgene expression was evaluated by FACS analysis using mean fluorescent intensity (MFI) detection.

Results

Vectors that contained the ADA LCR were preferentially expressed in T-cell lines. Further improvements in T-cell specific gene expression were observed with the incorporation of additional cis-regulatory elements, such as a human polyadenylation signal and intron 7 from the human ADA gene.

Conclusion

These studies suggest that the combination of an authentically regulated ADA gene in a murine retroviral vector, together with additional locus-specific regulatory refinements, will yield a vector with a safer profile and greater efficacy in terms of high-level, therapeutic, regulated gene expression for the treatment of ADA-deficient severe combined immunodeficiency.

A novel mutation in the ADA gene causing severe combined immunodeficiency in an Arab patient: a case report

INTRODUCTION

About 20% of the cases of human severe combined immunodeficiency are the result of the child being homozygous for defective genes encoding the enzyme adenosine deaminase. To our knowledge, the mutation pattern in Arab patients with severe combined immunodeficiency has never been reported previously.

CASE PRESENTATION

A 14-month-old Arab boy had clinical features typical of severe combined immunodeficiency. His clinical picture and flow cytometric analysis raised the diagnosis of adenosine deaminase deficiency and prompted us to screen the adenosine deaminase gene for mutation(s). We detected a novel mutation in exon 9 of the adenosine deaminase gene (p.Arg282>Gln), which we believe is the cause of the severe combined immunodeficiency phenotype observed in our patient.

CONCLUSION

This is the first report of adenosine deaminase mutation in an Arab patient with severe combined immunodeficiency due to a novel pathogenic mutation in the adenosine deaminase gene.

Excess adenosine in murine penile erectile tissues contributes to priapism via A2B adenosine receptor signaling

Priapism, abnormally prolonged penile erection in the absence of sexual excitation, is associated with ischemia-mediated erectile tissue damage and subsequent erectile dysfunction. It is common among males with sickle cell disease (SCD), and SCD transgenic mice are an accepted model of the disorder. Current strategies to manage priapism suffer from a poor fundamental understanding of the molecular mechanisms underlying the disorder. Here we report that mice lacking adenosine deaminase (ADA), an enzyme necessary for the breakdown of adenosine, displayed unexpected priapic activity. ADA enzyme therapy successfully corrected the priapic activity both in vivo and in vitro, suggesting that it was dependent on elevated adenosine levels. Further genetic and pharmacologic evidence demonstrated that A2B adenosine receptor-mediated (A2BR-mediated) cAMP and cGMP induction was required for elevated adenosine-induced prolonged penile erection. Finally, priapic activity in SCD transgenic mice was also caused by elevated adenosine levels and A2BR activation. Thus, we have shown that excessive adenosine accumulation in the penis contributes to priapism through increased A2BR signaling in both Ada -/- and SCD transgenic mice. These findings provide insight regarding the molecular basis of priapism and suggest that strategies to either reduce adenosine or block A2BR activation may prove beneficial in the treatment of this disorder.

Carrier frequency of a nonsense mutation in the adenosine deaminase (ADA) gene implies a high incidence of ADA-deficient severe combined immunodeficiency (SCID) in Somalia and a single, common haplotype indicates common ancestry

Inherited adenosine deaminase (ADA) deficiency is a rare metabolic disorder that causes immunodeficiency, varying from severe combined immunodeficiency (SCID) in the majority of cases to a less severe form in a small minority of patients. Five patients of Somali origin from four unrelated families, with severe ADA-SCID, were registered in the Greater London area. Patients and their parents were investigated for the nonsense mutation Q3X (ADA c7C>T), two missense mutations K80R (ADA c239A>G) and R142Q (ADA c425G>A), and a TAAA repeat located at the 3' end of an Alu element (AluVpA) positioned 1.1 kb upstream of the ADA transcription start site. All patients were homozygous for the haplotype ADA-7T/ADA-239G/ADA-425G/AluVpA7. Among 207 Somali immigrants to Denmark, the frequency of ADA c7C>T and the maximum likelihood estimate of the frequency of the haplotype ADA-7T/ADA-239G/ADA-425G/AluVpA7 were both 0.012 (carrier frequency 2.4%). Based on the analysis of AluVpA alleles, the ADA c7C/T mutation was estimated to be approximately 7,100 years old. Approximately 1 out of 5 - 10000 Somali children will be born with ADA deficiency due to an ADA c7C/T mutation, although within certain clans the frequency may be significantly higher. ADA-SCID may be a frequent immunodeficiency disorder in Somalia, but will be underdiagnosed due to the prevailing socioeconomic and nutritional deprivation.

Effect of site-directed PEGylation of trichosanthin on its biological activity, immunogenicity, and pharmacokinetics

Trichosanthin (TCS) is a type I ribosome-inactivating protein (RIP) with multiple biological and pharmacological activities. It has been approved effective in the clinical treatment of AIDS and tumor, but its strong immunogenicity and short plasma half-life have limited the clinical administration. To reduce the immunogenicity and prolong the plasma half-life of this compound, three TCS muteins (M(1), M(2) and M(3)) and two PEGylated TCS muteins (PM(1) and PM(2)) were constructed by site-directed mutagenesis and PEGylation, respectively. Compared with the unmodified TCS, both PEGylated TCS showed a 3- to 4-fold decrease in immunogenicity, a 0.5- to 0.8-fold decrease in non-specific toxicity, and a 4.5- to 6-fold increase in plasma half-life. But there is a problem of activity reduction. The increased circulating half-life in vivo may compensate for the reduced activity. Together with the other benefits of PEGylation such as reduced immunogenicity and toxicity, it is worthwhile to further explore the potential application of the PEGylated TCS as a better therapeutic agent for AIDS and tumor.

Tailoring structure-function properties of L-asparaginase: engineering resistance to trypsin cleavage

Bacterial L-ASNases (L-asparaginases) catalyse the conversion of L-asparagine into L-aspartate and ammonia, and are widely used for the treatment of ALL (acute lymphoblastic leukaemia). In the present paper, we describe an efficient approach, based on protein chemistry and protein engineering studies, for the construction of trypsin-resistant PEGylated L-ASNase from Erwinia carotovora (EcaL-ASNase). Limited proteolysis of EcaL-ASNase with trypsin was found to be associated with a first cleavage of the peptide bond between Lys53 and Gly54, and then a second cleavage at Arg206-Ser207 of the C-terminal fragment, peptide 54-327, showing that the initial recognition sites for trypsin are Lys53 and Arg206. Site-directed mutagenesis of Arg206 to histidine followed by covalent coupling of mPEG-SNHS [methoxypoly(ethylene glycol) succinate N-hydroxysuccinimide ester] to the mutant enzyme resulted in an improved modified form of EcaL-ASNase that retains 82% of the original catalytic activity, exhibits enhanced resistance to trypsin degradation, and has higher thermal stability compared with the wild-type enzyme.

Patients with adenosine deaminase deficiency surviving after hematopoietic stem cell transplantation are at high risk of CNS complications

Adenosine deaminase (ADA) deficiency is a systemic metabolic disease that causes an autosomal recessive variant of severe combined immunodeficiency (SCID) and less consistently other complications including neurologic abnormalities. Hematopoietic stem cell transplantation (HSCT) is able to correct the immunodeficiency, whereas control of nonimmunologic complications has not been extensively explored. We applied HSCT in 15 ADA-deficient patients consecutively treated at our institutions since 1982 and analyzed long-term outcome. Seven patients received transplants without conditioning from HLA-matched family donors (MFDs); the other 8 patients received conditioning and were given transplants either from HLA-mismatched family donors (MMFDs; n = 6) or from matched unrelated donors (MUDs; n = 2). At a mean follow-up period of 12 years (range, 4-22 years), 12 patients are alive with stable and complete immune reconstitution (7 of 7 after MFD, 4 of 6 after MMFD, and 1 of 2 after MUD transplantation). Six of 12 surviving patients show marked neurologic abnormalities, which include mental retardation, motor dysfunction, and sensorineural hearing deficit. We were unable to identify disease or transplantation-related factors correlating with this divergent neurologic outcome. The high rate of neurologic abnormalities observed in long-term surviving patients with ADA deficiency indicates that HSCT commonly fails to control CNS complications in this metabolic disease.

Gene therapy for severe combined immunodeficiencies

Severe combined immune deficiencies (SCIDs) are a group of monogenic diseases resulting in profound disturbances of lymphocyte development and function. Affected individuals are prone to life-threatening infections and without treatment do not survive beyond the first year of life. Haematopoietic stem cell transplantation from a well-matched donor offers high rates of survival, but in the absence of a suitable matched donor, parental haploidentical transplants are associated with greater complications, lower success rates and in some instances poor long-term immune recovery. Alternative therapeutic options based on correction of the defective gene by retroviral gene delivery have been used to correct X-linked SCID (SCID-X1) and adenosine deaminase-deficient SCID (ADA-SCID). A number of clinical trials have established that ex vivo gene transfer into haematopoietic progenitor cells allows effective recovery of immune defects and that gene therapy can offer a successful alternative to transplantation. The development of leukaemia as a result of insertional mutagenesis in one trial of gene therapy for SCID-X1 has raised concerns regarding the toxicity of retroviral vector-based gene delivery. These side effects are now being studied in detail and measures to prevent such events through alternative vectors delivery systems are in development at present.

Successful reconstitution of immunity in ADA-SCID by stem cell gene therapy following cessation of PEG-ADA and use of mild preconditioning

Gene therapy is a promising treatment option for monogenic diseases, but success has been seen in only a handful of studies thus far. We now document successful reconstitution of immune function in a child with the adenosine deaminase (ADA)-deficient form of severe combined immunodeficiency (SCID) following hematopoietic stem cell (HSC) gene therapy. An ADA-SCID child who showed a poor response to PEG-ADA enzyme replacement was enrolled into the clinical study. Following cessation of enzyme replacement therapy, autologous CD34(+) HSCs were transduced with an ADA-expressing gammaretroviral vector. Gene-modified cells were reinfused following one dose of preconditioning chemotherapy. Two years after the procedure, immunological and biochemical correction has been maintained with progressive increase in lymphocyte numbers, reinitiation of thymopoiesis, and systemic detoxification of ADA metabolites. Sustained vector marking with detection of polyclonal vector integration sites in multiple cell lineages and detection of ADA activity in red blood cells suggests transduction of early hematopoietic progenitors. No serious side effects were seen either as a result of the conditioning procedure or due to retroviral insertion. Gene therapy is an effective treatment option for the treatment of ADA-SCID.

Cerebral lymphoma in an adenosine deaminase-deficient patient with severe combined immunodeficiency receiving polyethylene glycol-conjugated adenosine deaminase

Polyethylene glycol-conjugated adenosine deaminase (PEG-ADA) provides an alternate therapy to mismatched stem cell transplantation for patients with ADA-deficient severe combined immunodeficiency. Although replacement therapy with PEG-ADA is effective in preventing infections, immune function does not return to normal, and most patients remain lymphopenic. Information is limited regarding the prognosis of patients on long-term ADA-replacement therapy. Here we present a case of a 10-year-old child who was diagnosed with ADA-severe combined immunodeficiency at 4 weeks of age after contracting pneumonia. Treatment with PEG-ADA was begun, the biochemical markers of ADA deficiency normalized, and his clinical progress was very good without significant infections. At 10 years of age, after presenting with headaches and cranial nerve deficits, he was diagnosed with Epstein-Barr virus-positive malignant brain lymphoma. It did not respond to various regimens of aggressive chemotherapy, and the patient expired 5 months later. We speculate that in this patient the immunologic surveillance by T cells may have been defective with respect to elimination of Epstein-Barr virus-infected cells, hence the formation of neoplasm. The possible mechanisms underlying such pathology are reviewed.

Site-directed PEGylation of trichosanthin retained its anti-HIV activity with reduced potency in vitro

Trichosanthin (TCS) was the first ribosome inactivating protein found to possess anti-HIV-1 activity. Phase I/II clinical trial of this compound had been done. Antigenicity and short plasma half-life were the major side effects preventing further clinical trial. Modification of TCS is therefore necessary to revive the interest to develop this compound as an anti-HIV agent. Three potential antigenic sites (Ser-7, Lys-173, and Gln-219) were identified by computer modeling. Through site-directed mutagenesis, these three antigenic amino acids were mutated to a cysteine residue resulting in 3 TCS mutants, namely S7C, K173C, and Q219C. These mutants were further coupled to polyethylene glycol with a molecular size of 20kDa (PEG) via the cysteine residue. This produced another three TCS derivatives, namely PEG20k-S7C, PEG20k-K173C, and PEG20k-Q219C. PEGylation had been widely used recently to decrease immunogenicity by masking the antigenic sites and prolong plasma half-life by expanding the molecular size. The in vitro anti-HIV-1 activity of these mutants and derivatives was tested. Results showed that the anti-HIV-1 activity of S7C, K173C, and Q219C was decreased by about 1.5- to 5.5-fold with slightly lower cytotoxicity. On the other hand, PEGylation produced larger decrease (20- to 30-fold) in anti-HIV activity. Cytotoxicity was, however, weakened only slightly by about 3-fold. The in vitro study showed that the anti-HIV activity of PEGylated TCS was retained with reduced potency. The in vivo activity is expected to have only slightly changed due to other beneficial effects like prolonged half-life.

Mutations in genes required for T-cell development:IL7R, CD45, IL2RG, JAK3, RAG1, RAG2, ARTEMIS, and ADA and severe combined immunodeficiency: HuGE review

Severe combined immunodeficiency (SCID) is an inherited immune disorder characterized by T-cell lymphopenia (TCLP), a profound lack of cellular (T-cell) and humoral (B-cell) immunity and, in some cases, decreased NK-cell number and function. Affected children develop severe bacterial and viral infections within the first 6 months of life and die before 1 year of age without treatment. Mutations in any of eight known genes: IL2RG, ARTEMIS, RAG1, RAG2, ADA, CD45, JAK3, and IL7R cause SCID. Mutations in unidentified genes may also cause SCID. Population-based genotype and allelic frequencies of these gene defects have not been measured. Some minimal estimates of SCID prevalence are presented. Currently, hematopoietic stem cell transplants are the standard treatment. In clinical trials, gene therapy has been used to reconstitute immune function in patients with IL2RG and ADA defects. The availability of effective therapies, plus the short asymptomatic period after birth, (when stem-cell transplantation is most effective), make SCID a potentially good candidate for newborn screening. Dried blood spots are currently collected from all infants at birth for newborn metabolic screening. Tests for TCLP on dried blood spots could be developed as a screen for SCID. Because SCID may be unrecognized, with infant deaths from infection attributed to other causes, newborn screening is the only way to ascertain true birth prevalence. Validated tests and pilot population studies are necessary to determine newborn screening's potential for identifying infants with SCID.

Bilateral sensorineural deafness in adenosine deaminase-deficient severe combined immunodeficiency

Adenosine deaminase deficiency presents with severe combined immunodeficiency and is treatable by bone marrow transplantation. With improved survival, the nonimmunologic manifestations of this condition are becoming apparent. We report a high incidence of bilateral sensorineural deafness in transplanted patients, which highlights the systemic nature of the disease.

Primary cellular immunodeficiencies

Genetic defects in T-cell function lead to susceptibility to infections or to other clinical problems that are more grave than those seen in disorders resulting in antibody deficiency alone. Those affected usually present during infancy with either common or opportunistic infections and rarely survive beyond infancy or childhood. The spectrum of T-cell defects ranges from the syndrome of severe combined immunodeficiency, in which T-cell function is absent, to combined immunodeficiency disorders in which there is some, but not adequate, T-cell function for a normal life span. Recent discoveries of the molecular causes of many of these defects have led to a new understanding of the flawed biology underlying the ever-growing number of defects. Most of these conditions could be diagnosed by means of screening for lymphopenia or for T-cell deficiency in cord blood at birth. Early recognition of those so afflicted is essential to the application of the most appropriate treatments for these conditions at a very early age. The latter treatments include both transplantation and gene therapy in addition to immunoglobulin replacement. Fully defining the molecular defects of such patients is also essential for genetic counseling of family members and prenatal diagnosis.

Cognitive and behavioral abnormalities in adenosine deaminase deficient severe combined immunodeficiency

OBJECTIVE

The objective was to evaluate the cognitive, behavioral, and neurodevelopmental function in patients with adenosine deaminase deficient severe combined immunodeficiency (ADA-SCID) and to compare the findings with those of a case control group of patients without ADA-SCID.

STUDY DESIGN

Case-matched pairs of patients with ADA-SCID (n = 11) and patients without ADA-SCID who had undergone bone marrow transplantation were recruited. Subjects were assessed by age-appropriate standard tests of intelligence, behavior, and neurodevelopment.

RESULTS

Cognitive ability was not significantly different between the 2 groups, but patients with ADA-SCID showed a significant inverse correlation between deoxyadenosinetrisphosphate levels at diagnosis and IQ (P =.048). Behavioral assessment showed that patients with ADA-SCID functioned in the pathologic range on all domains, whereas mean scores for the control group were within normal limits. Behavioral impairment in patients with ADA-SCID also showed a significant positive correlation with age (P =.026).

CONCLUSIONS

Cognitive function in ADA deficiency is adversely affected by the severity of metabolic derangement at the time of diagnosis. In addition, patients with ADA-SCID have significant behavioral abnormalities after transplantation. These defects are not due to the transplant procedure but reflect the systemic nature of ADA deficiency. These findings have important implications for future medical and nonmedical management strategies.

Active drug targeting with immunoconjugates to choroidal neovascularization

PURPOSE

Active drug targeting with monoclonal antibody to neovascular vessels may be a potential treatment for choroidal neovascularization (CNV) in age-related macular degeneration (AMD). Endoglin (CD105) is a proliferating endothelial cell marker with excellent potential for targeting. The goals of this study were to investigate the expression of CD105 in CNV membranes surgically excised from patients with AMD and CNV lesions induced by intense laser photocoagulation in a cynomolgus monkey and to evaluate the in vitro effect of immunoconjugates on endothelial cells.

METHODS

CNV membranes were surgically excised from 10 patients with AMD. Experimental CNV was induced by intense laser photocoagulation in a cynomolgus monkey. Immunolocalization of CD105 on frozen sections of CNV lesions was studied by immunohistochemical evaluation. Anti-von Willebrand's factor antibody was used as an endothelial cell marker. The cytotoxic effect of immunoconjugates of anti-CD105 monoclonal antibody and dextran binding mitomycin C on human umbilical vein endothelial cells (HUVECs) was evaluated in vitro.

RESULTS

Endothelial cells demonstrated strong immunoreactivity of CD105 in all surgically excised CNV membranes. In the monkey eye, CD105-positive cells were detected only in CNV lesions but not in normal chorioretinal tissues. Immunoconjugates with anti-CD105 monoclonal antibody showed a specific inhibitory effect on proliferating HU-VECs.

CONCLUSIONS

These results suggest that anti-CD105 monoclonal antibody-mediated drug targeting has a potential to treat CNV in AMD.

White blood cells 1: non-malignant disorders

Disorders of white cells are very common in clinical practice. White-cell development and numbers are controlled by a mixture of external stimuli including cytokines, matrix proteins, and accessory cells. Several different white-cell lineages are recognised; each has a role in host defence. Both white-cell deficiency and overproduction can lead to disease. Some forms of inherited white-cell deficiency are potentially treatable with gene therapy.

T lymphocytes with a normal ADA gene accumulate after transplantation of transduced autologous umbilical cord blood CD34+ cells in ADA-deficient SCID neonates

Adenosine deaminase-deficient severe combined immunodeficiency was the first disease investigated for gene therapy because of a postulated production or survival advantage for gene-corrected T lymphocytes, which may overcome inefficient gene transfer. Four years after three newborns with this disease were given infusions of transduced autologous umbilical cord blood CD34+ cells, the frequency of gene-containing T lymphocytes has risen to 1-10%, whereas the frequencies of other hematopoietic and lymphoid cells containing the gene remain at 0.01-0.1%. Cessation of polyethylene glycol-conjugated adenosine deaminase enzyme replacement in one subject led to a decline in immune function, despite the persistence of gene-containing T lymphocytes. Thus, despite the long-term engraftment of transduced stem cells and selective accumulation of gene-containing T lymphocytes, improved gene transfer and expression will be needed to attain a therapeutic effect.

Clinical expression, genetics and therapy of adenosine deaminase (ADA) deficiency

Adenosine deaminase (ADA) deficiency was the first known cause of primary immunodeficiency. Over the past 25 years the basis for immune deficiency has largely been established. Now it appears that ADA deficiency may also cause hepatic toxicity, raising new questions about its pathogenesis. The ADA gene has been sequenced and the ADA three-dimensional structure solved. The relationship between genotype and phenotype is being analysed, and ADA deficiency has become a focus for novel approaches to enzyme replacement and gene therapy.

Adenosine Deaminase Deficiency in Adults

Adenosine deaminase (ADA) deficiency typically causes severe combined immunodeficiency (SCID) in infants. We report metabolic, immunologic, and genetic findings in two ADA-deficient adults with distinct phenotypes. Patient no. 1 (39 years of age) had combined immunodeficiency. She had frequent infections, lymphopenia, and recurrent hepatitis as a child but did relatively well in her second and third decades. Then she developed chronic sinopulmonary infections, including tuberculosis, and hepatobiliary disease; she died of viral leukoencephalopathy at 40 years of age. Patient no. 2, a healthy 28-year-old man with normal immune function, was identified after his niece died of SCID. Both patients lacked erythrocyte ADA activity but had only modestly elevated deoxyadenosine nucleotides. Both were heteroallelic for missense mutations: patient no. 1, G216R and P126Q (novel); patient no. 2, R101Q and A215T. Three of these mutations eliminated ADA activity, but A215T reduced activity by only 85%. Owing to a single nucleotide change in the middle of exon 7, A215T also appeared to induce exon 7 skipping. ADA deficiency is treatable and should be considered in older patients with unexplained lymphopenia and immune deficiency, who may also manifest autoimmunity or unexplained hepatobiliary disease. Metabolic status and genotype may help in assessing prognosis of more mildly affected patients.