Reticular dysgenesis: HLA non-identical bone marrow transplants in a series of 10 patients

Recent advances in understanding the pathogenesis and management of reticular dysgenesis

Reticular Dysgenesis is a rare immunodeficiency which is clinically characterized by the combination of Severe Combined Immunodeficiency (SCID) with agranulocytosis and sensorineural deafness. Mutations in the gene encoding adenylate kinase 2 (AK2) were identified to cause this phenotype. In this review, we will demonstrate important clinical differences between reticular dysgenesis and other SCID entities and summarize recent concepts in the understanding of the pathophysiology of the disease and the management strategies for this difficult condition.

Reticular dysgenesis-associated AK2 protects hematopoietic stem and progenitor cell development from oxidative stress

Rissone et al. demonstrate that adenylate kinase AK2, an enzyme mutated in reticular dysgenesis (RD) in humans, prevents oxidative stress during hematopoiesis. Using a zebrafish model, as well as induced pluripotent stem cells derived from an RD patient, they find that AK2 deficiency affects hematopoietic stem and progenitor development with increased oxidative stress. Antioxidant treatment rescues the hematopoietic phenotypes.

Adenylate kinases (AKs) are phosphotransferases that regulate the cellular adenine nucleotide composition and play a critical role in the energy homeostasis of all tissues. The AK2 isoenzyme is expressed in the mitochondrial intermembrane space and is mutated in reticular dysgenesis (RD), a rare form of severe combined immunodeficiency (SCID) in humans. RD is characterized by a maturation arrest in the myeloid and lymphoid lineages, leading to early onset, recurrent, and overwhelming infections. To gain insight into the pathophysiology of RD, we studied the effects of AK2 deficiency using the zebrafish model and induced pluripotent stem cells (iPSCs) derived from fibroblasts of an RD patient. In zebrafish, Ak2 deficiency affected hematopoietic stem and progenitor cell (HSPC) development with increased oxidative stress and apoptosis. AK2-deficient iPSCs recapitulated the characteristic myeloid maturation arrest at the promyelocyte stage and demonstrated an increased AMP/ADP ratio, indicative of an energy-depleted adenine nucleotide profile. Antioxidant treatment rescued the hematopoietic phenotypes in vivo in ak2 mutant zebrafish and restored differentiation of AK2-deficient iPSCs into mature granulocytes. Our results link hematopoietic cell fate in AK2 deficiency to cellular energy depletion and increased oxidative stress. This points to the potential use of antioxidants as a supportive therapeutic modality for patients with RD.

Unresolved issues in hematopoietic stem cell transplantation for severe combined immunodeficiency: need for safer conditioning and reduced late effects

In this review we discuss recent outcomes of hematopoietic cell transplantation (HCT) for patients with severe combined immunodeficiency (SCID), including survival, T- and B-cell reconstitution, and late effects, particularly those related to genotype, use of conditioning regimen, and use of alternative donors. We identify the following issues that require additional data, which can be obtained through cooperative studies: outcomes of patients with SCID who did not receive conditioning before alternative donor HCT; outcomes of patients with SCID who did not receive graft-versus-host disease prophylaxis after T cell-replete HCT; late effects of HCT for patients with SCID, including neurocognitive outcomes, growth, and development; and their relationship to genotype and use of alkylating agents for conditioning. Careful follow-up of outcomes of all newborns receiving diagnoses based on newborn screening programs for SCID is essential because data are scarce on the effects of conditioning regimens in very young patients. A consensus on the definition of T- and B-cell recovery, criteria for additional "boosts," pharmacokinetic data of chemotherapy agents used in young children, and uniformity of the use of various chemotherapy agents are needed to compare results among institutions. Finally, development of new nontoxic conditioning regimens for HCT that can be safely used in very young children is required.

Laboratory technology for population-based screening for severe combined immunodeficiency in neonates: the winner is T-cell receptor excision circles

The most profound primary immunodeficiency disease, severe combined immunodeficiency (SCID), is fatal in infancy unless affected infants are provided with an adaptive immune system through allogeneic hematopoietic cell transplantation, enzyme replacement, or gene therapy. However, most infants with SCID lack a family history or any clinical clues before the onset of infections, making this serious but treatable disease a candidate for population-based newborn screening. Of several approaches considered for SCID screening, testing for T-cell receptor excision circles (TRECs), a DNA biomarker of normal T-cell development, has proved successful. TREC numbers can be measured in DNA isolated from the dried bloodspots already routinely collected for newborn screening. Infants with low or absent TRECs can thus be identified and referred for confirmatory testing and prompt intervention. TREC testing of newborns is now being performed in several states, indicating that this addition to the newborn screening panel can be successfully integrated into state public health programs.

Educational paper. The expanding clinical and immunological spectrum of severe combined immunodeficiency

Severe combined immunodeficiency (SCID) is one of the most severe forms of primary immunodeficiency characterized by absence of functional T lymphocytes. It is a paediatric emergency, which is life-threatening when recognized too late. The clinical presentation varies from the classical form of SCID through atypical SCID to Omenn syndrome. In addition, there is a considerable immunological variation, which can hamper the diagnosis. In this educational review, we describe the immunopathological background, clinical presentations and diagnostic process of SCID, as well as the therapeutic possibilities.

Malignancies in the setting of primary immunodeficiency: Implications for hematologists/oncologists

Many primary immunodeficiency disorders (PIDD) are associated with elevated risks for different types of cancer. Defective immunosurveillance mechanisms in PIDD and infection with oncogenic viruses (eg, Epstein Barr, herpesvirus 8) seem to have significant contributory roles in many cases. Non-Hodgkin lymphoma and Hodgkin disease are two of the most common PIDD-associated malignancies. The impact of PIDD-associated malignancy has increased in recent years in parallel with improved patient with PIDD survival and longevity, due largely to effective immunoglobulin replacement therapy. Epidemiologic data, clinical patterns, and management considerations of the common PIDD-associated cancers are reviewed.

Reticular dysgenesis in a preterm infant: a case report

Reticular dysgenesis (RD) is a rare congenital immunodeficiency classified within the severe combined immunodeficiencies (SCIDs) and characterized by impairment of both lymphoid and myeloid cell development. Neutropenia unresponsive to recombinant human granulocyte colony-stimulating factor (rGCSF) is the hallmark of RD and the clinical course is rapidly fatal due to overwhelming infections. The authors report a female newborn at 32 weeks of gestation presenting with severe leukopenia at birth. The bone marrow showed a maturation arrest in the myeloid and lymphoid lineage. She had no response to granulocyte colony stimulating factor (rGCSF) treatment and died with sepsis at age of 2 months.

Systematic evidence review of newborn screening and treatment of severe combined immunodeficiency

CONTEXT

Severe combined immunodeficiency (SCID) is a group of disorders that leads to early childhood death as a result of severe infections. Recent research has addressed potential newborn screening for SCID.

OBJECTIVE

To conduct a systematic review of the evidence for newborn screening for SCID, including test characteristics, treatment efficacy, and cost-effectiveness.

METHODS

We searched Medline and the OVID In-Process & Other Non-Indexed Citations databases. We excluded articles if they were reviews, editorials or other opinion pieces, or case series of fewer than 4 patients or if they contained only adult subjects or nonhuman data. The remaining articles were systematically evaluated, and data were abstracted by 2 independent reviewers using standardized tools. For topics that lacked published evidence, we interviewed experts in the field.

RESULTS

The initial search resulted in 719 articles. Twenty-six met inclusion criteria. The results of several small studies suggested that screening for SCID is possible. Interviews revealed that 2 states have begun pilot screening programs. Evidence from large case series indicates that children receiving early stem-cell transplant for SCID have improved outcomes compared with children who were treated later. There is some inconclusive evidence regarding the need for donor-recipient matching and use of pretransplant chemotherapy. Few data on the cost-effectiveness of a SCID-screening program.

CONCLUSIONS

Evidence indicates the benefits of early treatment of SCID and the possibility of population-based newborn screening. Better information on optimal treatment and the costs of treatment and screening would benefit policy makers deciding among competing health care priorities.

Transplant outcomes in bone marrow failure syndromes and hemoglobinopathies

Allogeneic hematopoietic stem cell transplantation (HSCT) is the only potential cure for most bone marrow (BM) failure syndromes and hemoglobinopathies. Over the past decade, umbilical cord blood (UCB) has been used more frequently as a stem cell source in patients who lack a suitable BM donor. Although graft failure remains a significant problem, UCB transplantation (UCBT) using the optimal conditioning regimen can be a salvage treatment for patients without a suitable BM donor and warrants evaluation in further prospective studies.

HLA-haploidentical donor transplantation in severe combined immunodeficiency

Curative treatment of Severe Combined Immunodeficiency (SCID) by Hematopoietic Cell Transplantation (HCT) remains a challenge, in particular in infants presenting with serious, poorly controllable complications. In the absence of a matched family donor, HLA-haploidentical transplantation from parental donors represents a uniformly and readily available treatment option, offering a high chance to be successful. Concerning outcomes of HCT in SCID, other important parameters beside survival need to be taken into consideration, in particular the stability and robustness of the graft and its function, as well as potential late complications, related either to the disease or to the treatment.

Transplantation immunology: solid organ and bone marrow

Development of the field of organ and tissue transplantation has accelerated remarkably since the human MHC was discovered in 1967. Matching of donor and recipient for MHC antigens has been shown to have a significant positive effect on graft acceptance. The roles of the different components of the immune system involved in the tolerance or rejection of grafts and in graft-versus-host disease have been clarified. These components include antibodies, antigen-presenting cells, helper and cytotoxic T-cell subsets, immune cell-surface molecules, signaling mechanisms, and cytokines. The development of pharmacologic and biological agents that interfere with the alloimmune response has had a crucial role in the success of organ transplantation. Combinations of these agents work synergistically, leading to lower doses of immunosuppressive drugs and reduced toxicity. Reports of significant numbers of successful solid-organ transplantations include those of the kidneys, liver, heart, and lung. The use of bone marrow transplantation for hematologic diseases, particularly hematologic malignancies and primary immunodeficiencies, has become the treatment of choice in many of these conditions. Other sources of hematopoietic stem cells are also being used, and diverse immunosuppressive drug regimens of reduced intensity are being proposed to circumvent the mortality associated with the toxicity of these drugs. Gene therapy to correct inherited diseases by means of infusion of gene-modified autologous hematopoietic stem cells has shown efficacy in 2 forms of severe combined immunodeficiency, providing an alternative to allogeneic tissue transplantation.

Primary Immunodeficiencies

Primary immunodeficiencies (PIDs), once considered to be very rare, are now increasingly recognized because of growing knowledge in the immunological field and the availability of more sophisticated diagnostic techniques and therapeutic modalities [161]. However in a database of >120,000 inpatients of a general hospital for conditions suggestive of ID 59 patients were tested, and an undiagnosed PID was found in 17 (29%) of the subjects tested [107]. The publication of the first case of agammaglobulinemia by Bruton in 1952 [60] demonstrated that the PID diagnosis is first done in the laboratory. However, PIDs require specialized immunological centers for diagnosis and management [33]. A large body of epidemiological evidence supports the hypothesis of the existence of a close etiopathogenetic relation between PID and atopy [73]. In particular, an elevated frequency of asthma, food allergy (FA), atopic dermatitis and enteric pathologies can be found in various PIDs. In addition we will discuss another subject that is certainly of interest: the pseudo-immunodepressed child with recurrent respiratory infections (RRIs), an event that often requires medical intervention and that very often leads to the suspicion that it involves antibody deficiencies [149].

Hematopoietic stem cell transplantation for primary immunodeficiency disease

Hematopoietic stem cell transplantation is the definitive therapy for a variety of rare primary cellular immunodeficiency syndromes diagnosed in children. All primary immunodeficiencies benefit from early diagnosis and transplantation before the development of serious infections, which contribute to a significant increased risk of mortality following transplant. In the absence of a matched sibling, parental haplocompatible, matched unrelated donor and cord blood stem cells have all been utilized with varying degrees of success and immune reconstitution. The role of pretransplant conditioning in patients with SCID disease in terms of its effects upon T- and B-cell immune reconstitution and late effects is still under debate and will require further study.

A molecular classification of congenital neutropenia syndromes

Current knowledge on the molecular pathogenesis of severe congenital neutropenia indicates that the clinical diagnosis includes a heterogeneous group of disorders following different patterns of inheritance. Similarly, multifaceted syndromes associated with neutropenia can be classified molecularly, which in turn allows for a better understanding of the basis of the neutropenia. Many of the neutropenia disorders can be treated with G-CSF (filgrastim) to increase the neutrophil count, thereby reducing infection morbidity and mortality. In some instances hematopoietic stem cell transplantation remains the only curative treatment currently available. This review describes and classifies, on a molecular basis, both primary congenital neutropenia and multifaceted syndromes associated with neutropenia.

Inborn errors of immunity to infection: the rule rather than the exception

The immune system's function is to protect against microorganisms, but infection is nonetheless the most frequent cause of death in human history. Until the last century, life expectancy was only approximately 25 years. Recent increases in human life span primarily reflect the development of hygiene, vaccines, and anti-infectious drugs, rather than the adjustment of our immune system to coevolving microbes by natural selection. We argue here that most individuals retain a natural vulnerability to infectious diseases, reflecting a great diversity of inborn errors of immunity.

Congenital immunodeficiencies and sepsis

OBJECTIVE

Because a hallmark of congenital immunodeficiency disorders is susceptibility to recurrent, unusual and/or severe infections, an effort was undertaken to identify a subset of these patients with an increased risk for sepsis.

DESIGN

Literature review.

RESULTS

Twenty congenital immunodeficiency disorders were identified with increased sepsis susceptibility.

CONCLUSION

Distinguishing patients with congenital immunodeficiencies from others with sepsis has important implications for the future well-being of the immunodeficient patient because many of the diseases are modified favorably by appropriate treatment. In addition, better understanding of sepsis in the setting of congenital immunodeficiency has numerous implications for both immunodeficiency and sepsis research. As a group, these disorders define components of the human immune system that are essential for defense against severe infection and demonstrate immunologic themes underlying sepsis susceptibility.

Development of population-based newborn screening for severe combined immunodeficiency

BACKGROUND

Severe combined immunodeficiency (SCID) is a treatable, inherited lack of cellular and humoral immunity caused by diverse mutations in several different genes and leading to death in infancy unless immune reconstitution is provided. Currently no population screening exists for SCID, but early diagnosis would improve outcome.

OBJECTIVE

Because all patients with SCID make few or no T cells, we asked whether the absence of T-cell receptor excision circles (TRECs), DNA episomes in newly formed T cells, could identify SCID regardless of genotype.

METHODS

DNA isolated from dried blood spots was assayed by real-time PCR to quantitate TRECs. Control PCR was performed on a segment of the beta-actin gene. After pilot studies with adult and cord blood control subjects, blood from SCID patients was spotted onto filters and tested, followed by screening of actual blood spots from the Maryland Newborn Screening Program. Finally, newborn blood spots were recovered and tested from 2 infants after their diagnosis of SCID.

RESULTS

In contrast to filters from the newborn screening program, which had a mean of 1020 TRECs in two 3-mm punches, samples from 23 infants with SCID had <30 TRECs. The newborn screening filter was retrieved from a state laboratory for one of these infants plus another infant who had died of SCID previously; although both samples had detectable beta-actin DNA, neither had TRECs.

CONCLUSION

TRECs are a stable analyte that can identify T-cell lymphopenia in newborn dried blood spots so that infants with SCID can receive early, life-saving treatment.

Hematopoietic cell transplantation for congenital bone marrow failure

PURPOSE OF REVIEW

Congenital bone marrow failure is rare and multifactorial. This review focuses on the outcome after allogeneic hematopoietic cell transplantation for the treatment of these disorders, with particular emphasis on recent discoveries and the challenges.

RECENT FINDINGS

In the treatment of congenital bone marrow failure disorders, the goals are to eliminate or reduce early and late toxicities and the risk of graft-versus-host disease. Novel nonmyeloablative fludarabine-based preparative regimens have demonstrated low risks of toxicity and acceptable engraftment rates for several congenital bone marrow failure disorders. Although there seems to be less early toxicity, longer follow-up is needed to determine late effects, especially the development of malignancy. T cell depletion of the bone marrow or peripheral blood, or the use of umbilical cord blood, has decreased the risk of graft-versus-host disease. Together, reduced toxicity and low rates of graft-versus-host disease have at least minimized the morbidity early after transplantation, with promising early survival.

SUMMARY

With marked improvement in rates of survival after allogeneic hematopoietic cell transplantation for selected congenital bone marrow failure disorders, emphasis is now being placed on improving quality of life and reducing late effects. Multicenter collaborative trials will determine the best treatment for these rare disorders.

Update on childhood neutropenia: molecular and clinical advances

Congenital and inherited disorders are important differential diagnoses of neutropenia, particularly in neonates and children, although acquired causes are more common. This article focuses on recent advances in understanding the cellular and molecular defects in inherited neutropenias as well as issues that are related to clinical presentation, diagnosis, and complications.