Purine nucleoside phosphorylase deficiency (PNP-def) presenting with lymphopenia and developmental delay: successful correction with umbilical cord blood transplantation

Neurologic Status of Patients with Purine Nucleoside Phosphorylase Deficiency Before and After Hematopoetic Stem Cell Transplantation

BACKGROUND

Purine nucleoside phosphorylase (PNP) deficiency is a rare autosomal recessive combined immunodeficiency. The phenotype is profound T cell deficiency with variable B and NK cell functions and results in recurrent and persistent infections that typically begin in the first year of life. Neurologic findings occur in approximately two-thirds of patients. The mechanism of neurologic abnormalities is unclear. Hematopoietic stem cell transplantation (HSCT) is the only curative treatment for PNP deficiency.

METHODS

We report here six patients from five unrelated families with PNP deficiency treated in two centers in Turkey. We evaluated the neurological status of patients and compared to post-transplantation period if available. Then, we performed PubMed, Google Scholar, and Researchgate searches using the terms "PNP" and "hematopoietic stem cell transplantation" to find all reported cases of PNP transplantation and compared to our cohort.

RESULTS

Six patients were treated in two centers in Turkey. One patient died from post-transplant complications. The other four patients underwent successful HSCT with good immune reconstitution after transplantation (follow-up 21-48 months) and good neurological outcomes. The other patient with a new mutation is still waiting for a matching HLA donor.

DISCUSSION

In PNP deficiency, clinical manifestations are variable, and this disease should be considered in the presence of many different clinical findings. Despite the comorbidities that occurred before transplantation, HSCT currently appears to be the only treatment option for this disease. HSCT not only cures immunologic disorders, but probably also improves or at least stabilizes the neurologic status of patients.

Purine Nucleoside Phosphorylase Deficient Severe Combined Immunodeficiencies: A Case Report and Systematic Review (1975-2022)

Purine nucleoside phosphorylase deficient severe combined immunodeficiency (PNP SCID) is one of the rare autosomal recessive primary immunodeficiency disease, and the data on epidemiology and outcome are limited. We report the successful management of a child with PNP SCID and present a systematic literature review of published case reports, case series, and cohort studies on PNP SCID listed in PubMed, Web of Science, and Scopus from 1975 until March 2022. Forty-one articles were included from the 2432 articles retrieved and included 100 PNP SCID patients worldwide. Most patients presented with recurrent infections, hypogammaglobulinaemia, autoimmune manifestations, and neurological deficits. There were six reported cases of associated malignancies, mainly lymphomas. Twenty-two patients had undergone allogeneic hematopoietic stem cell transplantation with full donor chimerism seen mainly in those receiving matched sibling donors and/or conditioning chemotherapy before the transplant. This research provides a contemporary, comprehensive overview on clinical manifestations, epidemiology, genotype mutations, and transplant outcome of PNP SCID. These data highlight the importance of screening for PNP SCID in cases presented with recurrent infections, hypogammaglobulinaemia, and neurological deficits.

Awareness and practice of cord blood donation by pregnant women in Lagos Nigeria: Practice implication for future cord blood transplantation in Nigeria

Background:

Poor awareness remains a substantial limitation to harnessing the benefits of umbilical cord blood (UCB) in sub-Saharan Africa. The aim of this study was to determine the level of awareness and factors influencing intention to donate cord blood to blood bank among antenatal clinic attendees at a tertiary hospital in Nigeria.

Methods:

We conducted a questionnaire-based cross-sectional study of 400 women attending the antenatal clinic of a tertiary hospital in Lagos, Nigeria, between February and June 2018. The data were analyzed using Stata version 13; comparisons were conducted with Chi-square, Student's t-test, and Mann–Whitney U-test. Univariable and multivariable binary logistic regression was conducted with “willingness to donate” as the outcome variable.

Results:

Majority (n = 287/331 [86.2%, 95% confidence interval [CI]: 76.4–84.9]) of the participants had some knowledge of UCB, almost half intended future donation of UCB (n = 161/333, [48.3%, 95% CI: 42.9–53.6]). Based on our findings, factors such as religion (P = 0.001), education (P = 0.03), information from health-care provider (P < 0.001) appear to influence awareness, and the decision to donate UCB.

Conclusion:

Although the awareness of the clinical uses of UCB is very limited in Nigeria, the intent to participate in UCB donation is high. Factors such as religion, education, and prior information about UCB donation by health-care providers have been identified in this study to have an influence on the decision to donate UCB.

Partial Purine Nucleoside Phosphorylase Deficiency Helps Determine Minimal Activity Required for Immune and Neurological Development

Introduction: Complete or near complete absence of the purine nucleoside phosphorylase (PNP) enzyme causes a profound T cell immunodeficiency and neurological abnormalities that are often lethal in infancy and early childhood. We hypothesized that patients with partial PNP deficiency, characterized by a late and mild phenotype due to residual PNP enzyme, would provide important information about the minimal PNP activity needed for normal development. Methods: Three siblings with a homozygous PNP gene mutation (c.769C>G, p.His257Asp) resulting in partial PNP deficiency were investigated. PNP activity was semi-quantitively assayed by the conversion of [14C]inosine in hemolysates, mononuclear cells, and lymphoblastoid B cells. PNP protein expression was determined by Western Blotting in lymphoblastoid B cells. DNA repair was quantified by measuring viability of lymphoblastoid B cells following ionizing irradiation. Results: A 21-year-old female was referred for recurrent sino-pulmonary infections while her older male siblings, aged 25- and 28- years, did not suffer from significant infections. Two of the siblings had moderately reduced numbers of T, B, and NK cells, while the other had near normal lymphocyte subset numbers. T cell proliferations were normal in the two siblings tested. Hypogammaglobulinemia was noted in two siblings, including one that required immunoglobulin replacement. All siblings had typical (normal) neurological development. PNP activity in various cells from two patients were 8-11% of the normal level. All siblings had normal blood uric acid and increased PNP substrates in the urine. PNP protein expression in cells from the two patients examined was similar to that observed in cells from healthy controls. The survival of lymphoblastoid B cells from 2 partial PNP-deficient patients after irradiation was similar to that of PNP-proficient cells and markedly higher than the survival of cells from a patient with absent PNP activity or a patient with ataxia telangiectasia. Conclusions: Patients with partial PNP deficiency can present in the third decade of life with mild-moderate immune abnormalities and typical development. Near-normal immunity might be achieved with relatively low PNP activity.

The Broad Clinical Spectrum and Transplant Results of PNP Deficiency

PURPOSE

Purine nucleoside phosphorylase (PNP) is a known yet rare cause of combined immunodeficiency with a heterogeneous clinical presentation. We aim to add to the expanding clinical spectrum of disease, and to summarize the available data on bone marrow transplant for this condition.

METHODS

Data was collected from patient files retrospectively. A review of the literature of hematopoietic stem cell transplantation (HSCT) for PNP deficiency was conducted.

RESULTS

Four patients were treated in two centers in Israel. One patient died of EBV-related lymphoma with CNS involvement prior to transplant. The other three patients underwent successful HSCT with good immune reconstitution post-transplant (follow-up 8-108 months) and excellent neurological outcomes.

CONCLUSION

PNP is a variable immunodeficiency and should be considered in various clinical contexts, with or without neurological manifestations. HSCT offers a good treatment option, with excellent clinical outcomes, when preformed in a timely manner.

The First Purine Nucleoside Phosphorylase Deficiency Patient Resembling IgA Deficiency and a Review of the Literature

Purine nucleoside phosphorylase (PNP) deficiency is a rare autosomal recessive primary immunodeficiency disorder characterized by decreased numbers of T-cells, variable B-cell abnormalities, decreased amount of serum uric acid and PNP enzyme activity. The affected patients usually present with recurrent infections, neurological dysfunction and autoimmune phenomena. In this study, whole-exome sequencing was used to detect mutation in the case suspected of having primary immunodeficiency. We found a homozygous mutation in PNP gene in a girl who is the third case from the national Iranian registry. She had combined immunodeficiency, autoimmune hemolytic anemia and a history of recurrent infections. She developed no neurological dysfunction. She died at the age of 11 after a severe chicken pox infection. PNP deficiency should be considered in late-onset children with recurrent infections, autoimmune disorders without typical neurologic impairment.

Immunodeficiency, Motor Delay, and Hypouricemia Caused by a Novel Mutation of Purine Nucleoside Phosphorylase Gene in an Indian Infant

We describe an 11-month-old boy who presented with recurrent respiratory infections from 6 months of age. His elder sister died at 10 months with severe septicemia and meningitis. The boy had a mild motor delay. Investigations revealed T cell deficiency and very low serum uric acid suggestive of purine nucleoside phosphorylase (PNP) deficiency - a rare variant of severe combined immunodeficiency disease. A novel homozygous missense mutation of c.597C>G(p. S199R) of exon 5 on PNP gene confirmed the diagnosis. We suggest that uric acid should be a part of investigation profile for unidentified motor delay, as recurrent infections can be late presentation.

Neurologic Involvement in Primary Immunodeficiency Disorders

The nervous system may be affected in primary immune deficiency (PID) syndromes through infectious, autoimmune, neoplastic mechanisms, or as a primary feature of the syndrome. However certain neurologic problems do not conform to these etiopathogenetic groups. We retrospectively examined PID patients seen in neurology consultation between 2014 and 2017 in order to determine the spectrum of nervous system involvement. Among patients with confirmed neurologic problems (n = 35), common manifestations were encephalopathy and global developmental/cognitive delay. In 13 (37%) instances, the neurologic signs had no apparent relation with a treatment-related, infectious, or vascular complication and were considered as primary findings: acquired microcephaly, central nervous system malformation, or peripheral neuropathy. The diagnosis of PID was made after, and based on, the neurologic manifestation in 6 of 35 (17%) patients. Neurologic presentation may constitute the initial manifestation in some types of primary immune deficiency.

Infusion of Sibling Marrow in a Patient with Purine Nucleoside Phosphorylase Deficiency Leads to Split Mixed Donor Chimerism and Normal Immunity

Purine nucleoside phosphorylase (PNP) deficiency, a rare autosomal recessive metabolic disease causes combined immunodeficiency and developmental delay, hypotonia, and spasticity. Patients present with recurrent infections associated with T-lymphocytopenia, characteristically presenting later than patients with classical severe combined immunodeficiency (SCID). PNP, with adenosine deaminase (ADA), is part of the purine salvage pathway. The only curative therapy is hematopoietic stem cell transplantation. Myeloablative conditioning is recommended to prevent rejection caused by residual immune function. However, HLA-identical sibling stem cell infusions in ADA-SCID result in some donor stem cell engraftment and long-term thymopoiesis. We report a patient with PNP deficiency, who received HLA-identical sibling marrow without chemotherapy because of disseminated cytomegalovirus (CMV) infection. The patient presented at 14 months of age following recurrent infections, from early infancy, with persistent irritability, developmental delay, and hypotonia. She had neutropenia, pan-lymphocytopenia, and hypogammaglobulinemia with low plasma urate and erythrocyte PNP activity. Diagnosis was confirmed with a homozygous mutation in PNP. The patient was viremic with CMV detected in blood and CSF by PCR. Dual antiviral therapy improved the clinical condition and reduced the viral load. In view of the disseminated CMV infection, the decision was made to infuse stem cells without any pre-conditioning chemotherapy. She received a matched sibling donor unconditioned stem cell infusion at 16 months of age. The post-transplant course was uneventful. Blood PCR became negative for CMV. Global hypotonia persisted, although with significant improvement in irritability. At 4 years of age and 29 months post-transplant, the patient demonstrated normal T-lymphocyte and natural killer cell numbers. Recent thymic emigrants represented 12% of the total T-lymphocyte population. Lymphocyte proliferative responses to phytohemagglutinin were normal. Memory and class-switched B-lymphocytes were present. Immunoglobulin replacement had been discontinued, and there were normal IgG responses to tetanus vaccine, Haemophilus influenzae type B and pneumococcal conjugate vaccine antigens. There was 93% donor T-lymphocytes, 20% donor B-lymphocytes, and 5% donor myeloid cells, indicative of some donor stem cell engraftment. There was no significant infection history despite regular nursery attendance. Height and weight were following the 50th centile. Split mixed donor chimerism has corrected the immunological defect.

Hematopoietic cell transplantation for a child with OSTM1 osteopetrosis

HCT prior to onset of neurologic symptoms in children with OSTM1 osteopetrosis does not halt neurologic progression.

Expanded newborn screening by mass spectrometry: New tests, future perspectives

Tandem mass spectrometry (MS/MS) has become a leading technology used in clinical chemistry and has shown to be particularly sensitive and specific when used in newborn screening (NBS) tests. The success of tandem mass spectrometry is due to important advances in hardware, software and clinical applications during the last 25 years. MS/MS permits a very rapid measurement of many metabolites in different biological specimens by using filter paper spots or directly on biological fluids. Its use in NBS give us the chance to identify possible treatable metabolic disorders even when asymptomatic and the benefits gained by this type of screening is now recognized worldwide. Today the use of MS/MS for second-tier tests and confirmatory testing is promising especially in the early detection of new disorders such as some lysosomal storage disorders, ADA and PNP SCIDs, X-adrenoleucodistrophy (X-ALD), Wilson disease, guanidinoacetate methyltransferase deficiency (GAMT), and Duchenne muscular dystrophy. The new challenge for the future will be reducing the false positive rate by using second-tier tests, avoiding false negative results by using new specific biomarkers and introducing new treatable disorders in NBS programs.

Novel Genetic Mutations in the First Swedish Patient with Purine Nucleoside Phosphorylase Deficiency and Clinical Outcome After Hematopoietic Stem Cell Transplantation with HLA-Matched Unrelated Donor

Purine nucleoside phosphorylase (PNP) is an enzyme active in the purine salvage pathway. PNP deficiency caused by autosomal recessive mutations in the PNP gene leads to severe combined immunodeficiency (SCID) and in two thirds of cases also to neurological effects such as developmental delay, ataxia, and motor impairment.PNP deficiency has a poor outcome, and the only curative treatment is allogenic hematopoietic stem cell transplantation (HSCT). We present the first Swedish patient with PNP deficiency with novel mutations in the PNP gene and the immunological results of the HSCT and evaluate the impact of HSCT on the neurological symptoms. The patient presented early in life with neurological symptoms and suffered later from repeated serious respiratory tract infections. Biochemical tests showed severe reduction in PNP activity (1% residual activity). Genetic testing revealed two new mutations in the PNP gene: c.729C>G (p.Asn243Lys) and c.746A>C (p.Tyr249Cys). HSCT was performed with an unrelated donor, resulting in prompt and sustained engraftment and complete donor chimerism. There was no further aggravation of the patient's neurological symptoms at 21 months post HSCT, and appropriate developmental milestones were achieved. HSCT is curative for the immunological defect caused by PNP deficiency, and our case strengthens earlier reports that HSCT is effective as a treatment even for neurological symptoms in PNP deficiency.

A successful unrelated peripheral blood stem cell transplantation with reduced intensity-conditioning regimen in a patient with late-onset purine nucleoside phosphorylase deficiency

PNP deficiency is a rare combined immunodeficiency with autosomal recessive mode of inheritance. The immunodeficiency is progressive with normal immune functions at birth, but then, T-cell deficiency with variable B-cell functions usually presents by the age of two yr. The only curative treatment for PNP deficiency is hematopoietic stem cell transplantation. Here, we present a 13-yr-old girl with late-onset PNP deficiency. Despite many complications of infections, she was successfully transplanted with a reduced intensity-conditioning regimen from an HLA-identical unrelated donor.

Inborn errors of metabolism underlying primary immunodeficiencies

A number of inborn errors of metabolism (IEM) have been shown to result in predominantly immunologic phenotypes, manifesting in part as inborn errors of immunity. These phenotypes are mostly caused by defects that affect the (i) quality or quantity of essential structural building blocks (e.g., nucleic acids, and amino acids), (ii) cellular energy economy (e.g., glucose metabolism), (iii) post-translational protein modification (e.g., glycosylation) or (iv) mitochondrial function. Presenting as multisystemic defects, they also affect innate or adaptive immunity, or both, and display various types of immune dysregulation. Specific and potentially curative therapies are available for some of these diseases, whereas targeted treatments capable of inducing clinical remission are available for others. We will herein review the pathogenesis, diagnosis, and treatment of primary immunodeficiencies (PIDs) due to underlying metabolic disorders.

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.

CoQ(10) deficiencies and MNGIE: two treatable mitochondrial disorders

BACKGROUND

Although causative mutations have been identified for numerous mitochondrial disorders, few disease-modifying treatments are available. Two examples of treatable mitochondrial disorders are coenzyme Q(10) (CoQ(10) or ubiquinone) deficiency and mitochondrial neurogastrointestinal encephalomyopathy (MNGIE).

SCOPE OF REVIEW

Here, we describe clinical and molecular features of CoQ(10) deficiencies and MNGIE and explain how understanding their pathomechanisms have led to rationale therapies. Primary CoQ(10) deficiencies, due to mutations in genes required for ubiquinone biosynthesis, and secondary deficiencies, caused by genetic defects not directly related to CoQ(10) biosynthesis, often improve with CoQ(10) supplementation. In vitro and in vivo studies of CoQ(10) deficiencies have revealed biochemical alterations that may account for phenotypic differences among patients and variable responses to therapy. In contrast to the heterogeneous CoQ(10) deficiencies, MNGIE is a single autosomal recessive disease due to mutations in the TYMP gene encoding thymidine phosphorylase (TP). In MNGIE, loss of TP activity causes toxic accumulations of the nucleosides thymidine and deoxyuridine that are incorporated by the mitochondrial pyrimidine salvage pathway and cause deoxynucleoside triphosphate pool imbalances, which, in turn cause mtDNA instability. Allogeneic hematopoetic stem cell transplantation to restore TP activity and eliminate toxic metabolites is a promising therapy for MNGIE.

MAJOR CONCLUSIONS

CoQ(10) deficiencies and MNGIE demonstrate the feasibility of treating specific mitochondrial disorders through replacement of deficient metabolites or via elimination of excessive toxic molecules.

GENERAL SIGNIFICANCE

Studies of CoQ(10) deficiencies and MNGIE illustrate how understanding the pathogenic mechanisms of mitochondrial diseases can lead to meaningful therapies. This article is part of a Special Issue entitled: Biochemistry of Mitochondria, Life and Intervention 2010.

Purine nucleoside phosphorylase deficiency with a novel PNP gene mutation: a first case report from India

The authors report a case of purine nucleoside phosphorylase (PNP) deficiency for the first time from India. The case presented with recurrent severe infections, developmental delays, seizures and progressive neurological deterioration. The diagnosis of primary immunodeficiency disorder was delayed in spite of recurrent infection due to predominant neurological symptoms. Sequencing of the PNP gene revealed a novel mutation resulting in a premature stop codon.

Mankind's first natural stem cell transplant

The timing of the umbilical cord clamping at birth is still controversial. In the modern era of medicine, the cord has been clamped early to facilitate resuscitation and stabilization of infants. However, recently delayed cord clamping has been supported by physicians because it allows for the physiological transfer of blood from the placenta to the infant. Many clinical studies have revealed that the delayed cord clamping elevates blood volume and haemoglobin and prevents anaemia in infants. Moreover, since it was known that umbilical cord blood contains various valuable stem cells such as haematopoietic stem cells, endothelial cell precursors, mesenchymal progenitors and multipotent/pluripotent lineage stem cells, the merit of delayed cord clamping has been magnified. In this review, we discuss the advantages and disadvantages of delayed cord clamping at birth. We highlight the importance of delayed cord clamping in realizing mankind's first stem cell transfer and propose that it should be encouraged in normal births.

Lentivirus gene therapy for purine nucleoside phosphorylase deficiency

BACKGROUND

Purine nucleoside phosphorylase (PNP) deficiency causes the accumulation of toxic purine metabolites and lethal T cell immune defects, which might be corrected by expressing PNP by transplanting bone marrow (BM) cells transduced with lentiviral vectors containing the human PNP gene (lentiPNP).

METHODS

Lymphocytes from a single PNP-deficient patient as well as lymphocytes, fibroblasts and BM from PNP-deficient (PNP (-/-)) mice were transduced with lentiPNP. Female PNP (-/-) mice were transplanted with lentiPNP transduced BM cells from male PNP (-/-) mice or normal BM.

RESULTS

LentiPNP transduction significantly increased PNP expression in PNP-deficient human lymphocytes, murine lymphocytes, fibroblasts and BM cells. LentiPNP transduction also significantly improved the proliferation of PNP (-/-) murine lymphocyte and survival of irradiated PNP (-/-) fibroblasts. Polymerase chain reaction analysis demonstrated efficient transduction of lentiPNP into total and lineage-depleted BM cells grown ex vivo. LentiPNP transduced PNP (-/-) BM cells transplanted into PNP (-/-) mice expressed PNP in vivo, partially restored urinary uric acid secretion, improved thymocytes maturation, increased weight gain and extended survival of the mice. However, 12 weeks after transplant, the benefit of lentiPNP transduced cells and normal BM diminished and the percentage of engrafted donor cells decreased.

CONCLUSIONS

This short-term observational study provides the first in vivo proof that gene therapy may correct some of the abnormalities associated with PNP deficiency. Better gene transduction and expression, as well as improved cell engraftment, are required to further advance PNP gene therapy.

An unconditioned bone marrow transplantation in a child with purine nucleoside phosphorylase deficiency and its unique complication

Purine nucleoside phosphorylase deficiency is a rare immunodeficiency syndrome characterized by recurrent infections, neurological dysfunction, and autoimmunity. Early diagnosis and hematopoietic stem cell transplantation may reverse the dismal prognosis in PNP deficiency. This report presents a new PNP deficiency case successfully transplanted without a conditioning regimen from an HLA-identical family donor, who developed a complication of disseminated BCG infection.

Cord blood stem cell transplantation in primary immune deficiencies

PURPOSE OF REVIEW

Umbilical cord haematopoietic stem cell transplantation for primary immunodeficiencies is examined with other developments in treatment. Cord blood biology is reviewed, and advantages and disadvantages of umbilical cord blood stem cell transplantation for primary immunodeficiencies discussed. Clinical outcome data and future developments are reviewed.

RECENT FINDINGS

Cord blood T lymphocytes become tolerant to host human leukocyte antigen antigens, but retain alloreactivity to other antigens, in part due to immaturity of cord blood T lymphocytes and dendritic cells. Although naïve T lymphocytes can generate herpes virus specificity after transplantation, the risk of viral death is increased within the first 100 days. The clinical success of umbilical cord blood stem cell transplantation for primary immunodeficiencies is reviewed and new methods for expanding the stem cell number or encouraging engraftment with the use of third-party haematopoietic or mesenchymal stem cells examined.

SUMMARY

Many advantages make umbilical cord blood an attractive source of stem cells; over 100 umbilical cord blood stem cell transplantations have been performed for primary immunodeficiencies, with low rates of significant graft vs. host disease, despite significant human leukocyte antigen mismatch. Immune reconstitution is as good as for other stem cell sources: use of nascent stem cells in young recipients may have long-term advantages. Stem cell engineering to improve engraftment will expand potential beneficiaries of umbilical cord blood stem cell transplantation to older patients.

Current perspectives on primary immunodeficiency diseases

Since the original description of X-linked agammaglobulinemia in 1952, the number of independent primary immunodeficiency diseases (PIDs) has expanded to more than 100 entities. By definition, a PID is a genetically determined disorder resulting in enhanced susceptibility to infectious disease. Despite the heritable nature of these diseases, some PIDs are clinically manifested only after prerequisite environmental exposures but they often have associated malignant, allergic, or autoimmune manifestations. PIDs must be distinguished from secondary or acquired immunodeficiencies, which are far more common. In this review, we will place these immunodeficiencies in the context of both clinical and laboratory presentations as well as highlight the known genetic basis.

Cord blood banking for potential future transplantation

In recent years, umbilical cord blood, which contains a rich source of hematopoietic stem and progenitor cells, has been used successfully as an alternative allogeneic donor source to treat a variety of pediatric genetic, hematologic, immunologic, and oncologic disorders. Because there is diminished risk of graft-versus-host disease after transplantation of cord stem cells using matched related donors, the use of less-than-completely matched HLA cord blood stem cells may incur less risk of graft-versus-host disease than mismatched cells from either a related or unrelated "walking" donor, although this remains to be proven. Gene-therapy research involving modification of autologous cord blood stem cells for the treatment of childhood genetic disorders, although experimental at the present time, may prove to be of value. These scientific advances have resulted in the establishment of not-for-profit and for-profit cord blood-banking programs for allogeneic and autologous cord blood transplantation. Many issues confront institutions that wish to establish or participate in such programs. Parents often seek information from their physicians about this new biotechnology option. This document is intended to provide information to guide physicians in responding to parents' questions about cord blood donation and banking and the types and quality of cord blood banks. Provided also are recommendations about appropriate ethical and operational standards, including informed consent policies, financial disclosures, and conflict-of-interest policies for physicians, institutions, and organizations that operate or have a relationship with cord blood-banking programs.

TAT-mediated intracellular delivery of purine nucleoside phosphorylase corrects its deficiency in mice

Defects in purine nucleoside phosphorylase (PNP) enzyme activity result in abnormal nucleoside homeostasis, severe T cell immunodeficiency, neurological dysfunction, and early death. Protein transduction domain (PTD) can transfer molecules into cells and may help restore PNP activity in cases of PNP deficiency. However, long-term use of PTD to replace enzymes in animal models or patients has not previously been described. We fused human PNP to the HIV-TAT PTD and found that the fusion with TAT changed the retention and distribution of PNP in PNP-deficient mice. TAT induced rapid intracellular delivery of PNP into tissues, including the brain, prevented urinary excretion of PNP, and protected PNP from neutralizing antibodies, resulting in significant extension of the enzyme's biological activity in vivo. Frequent TAT-PNP injections in PNP-deficient mice corrected the metabolic disorder and immune defects with no apparent toxicity. TAT-PNP remained effective over 24 weeks of treatment, resulting in continued improvement in immune function and extended survival. Our data demonstrate that TAT changes the properties of PNP in vivo and that long-term intracellular delivery of PNP by TAT corrects PNP deficiency in mice. We provide evidence to promote further use of PTD to treat diseases that require repeated intracellular enzyme or protein delivery.

Umbilical cord stem cell transplantation for primary immunodeficiencies

Primary immunodeficiencies (PIDs) are a rare but important cause of mortality and morbidity in childhood: the most severe--known as severe combined immunodeficiency (SCID)--are fatal within the first year of life; other PIDs are less immediately life-threatening, but have a poor long-term outlook. Haematopoietic stem cell transplantation (HSCT) is the best treatment for SCID and is increasingly offered for other PIDs. The best results are achieved with an HLA-matched family donor. Umbilical cord stem cells (UCSCs) are an alternative stem cell source. Results using UCSCs in the treatment of haematological disorders and malignancy are as good as those for which marrow is the stem cell source. Although PIDs make up a small proportion of disorders amenable to treatment by HSCT, UCSCs are an ideal source of haematopoietic stem cells for many of these patients. Of the 52 patients with SCID or other PIDs for whom detailed information on outcome is available, results of engraftment, immune reconstitution, incidence of graft-versus-host disease and survival are comparable with other stem cell sources. Small stem cell dose and prolonged time to viral immunity limit the patients for whom UCSCs can be used. Newer methods of achieving better engraftment, ex vivo expansion of stem cells and generation of antigen-specific cytotoxic T cells are being developed at present, and will widen the application of UCSCs as a viable source for more patients.

Untying the Gordian knot: policies, practices, and ethical issues related to banking of umbilical cord blood

Since the first successful transplantation of umbilical cord blood in 1988, cord blood has become an important source of hematopoietic stem and progenitor cells for the treatment of blood and genetic disorders. Significant progress has been accompanied by challenges for scientists, ethicists, and health policy makers. With the recent recognition of the need for a national system for the collection, banking, distribution, and use of cord blood and the increasing focus on cord blood as an alternative to embryos as a source of tissue for regenerative medicine, cord blood has garnered significant attention. We review the development of cord blood banking and transplantation and then discuss the scientific and ethical issues influencing both established and investigational practices surrounding cord blood collection, banking, and use.

Paradoxical CD4+ T-cell decline in HIV-infected patients with complete virus suppression taking tenofovir and didanosine

BACKGROUND

Tenofovir (TDF) and didanosine (ddI) are both adenosine analogues with convenient posology, strong potency and a relatively high genetic barrier for resistance. The popularity of this combination, however, has been questioned due to concerns about pharmacokinetic interactions and increased risk of pancreatitis and hyperglycemia. Less information is available about other possible side effects.

PATIENTS AND METHODS

HIV-infected individuals who initiated a protease inhibitor-sparing regimen between September 2002 and June 2003 at five hospitals, and had at least one subsequent visit within the next 12 months, always with complete virus suppression, were retrospectively assessed. Only drug-naive individuals and patients who simplified a prior successful antiretroviral regimen were analysed.

RESULTS

Outcomes were analysed in 570 individuals according to treatment modality (98 drug-naive versus 472 simplified); the nucleoside analogue (NA) backbone (298 with TDF + ddI, 88 with ddI, 44 with TDF, and 140 with neither ddI nor TDF); and the third agent used (378 with non-nucleoside analogues versus 192 with NA). Significant CD4+ T-cell declines were seen in patients taking ddI + TDF with respect to all other NA combinations, including ddI or TDF separately. Patients exposed to high ddI doses or taking a third NA showed more pronounced CD4 declines. Plasma levels of ddI correlated with the extent of CD4+ T-cell loss.

CONCLUSION

Patients receiving ddI + TDF-based combinations show CD4+ T-cell declines despite achieving complete virus suppression. This effect generally progresses with time. An imbalance in adenosine metabolites within CD4+ T lymphocytes may explain this phenomenon, which resembles the genetic purine nucleoside phosphorylase deficiency syndrome.