Marrow transplantation from human leukocyte antigen-identical or haploidentical donors for correction of Wiskott-Aldrich syndrome

Un-manipulated Haploidentical Transplant in Wiskott-Aldrich Syndrome

BACKGROUND

Allogeneic stem cell transplant is the only curative treatment for Wiskott-Aldrich syndrome.

CASE CHARACTERISTICS

18-months-old boy with no sibling, cord blood or matched unrelated donor transplant options.

OUTCOME

Doing well 7 years after haplo-identical stem cell transplantation using unmanipulated bone marrow as the stem cell source.

MESSAGE

Father as a haplo-identical donor is a feasible option.

Hematopoietic cell transplantation for Wiskott-Aldrich syndrome: advances in biology and future directions for treatment

The Wiskott-Aldrich syndrome (WAS) is an X-linked disorder characterized by a triad of diagnostic clinical elements: immunodeficiency, eczema, and hemorrhage caused by thrombocytopenia with small-sized platelets. The formal proof that hematopoietic cell transplantation (HCT) could be used to cure WAS revealed a requirement for both immunosuppression and myelosuppression that still underlies the standard approach to curative therapy today. The current short- and long-term toxicities of HCT are the main stumbling block for the ability to cure every patient with WAS and X-linked thrombocytopenia, and much remains to be done.

Transplant outcomes for primary immunodeficiency disease

Primary immune deficiencies (PIDs) are rare diseases, and most are lethal without appropriate intervention. Hematopoietic cell transplantation (HCT) can cure the majority of patients, but most lack a suitable matched related donor. Alternative donor stem cells (mismatched related donor bone marrow, unrelated donor bone marrow, and unrelated donor umbilical cord blood [UCB]) are therefore frequently required. Published data comparing outcomes after alternative donor transplant for PID are scarce. The outcomes and potential advantage and disadvantages of each alternative stem cell source are discussed in this chapter. Although there are insufficient prospective data to make meaningful comparisons between the alternative stem cell sources, the results presented here demonstrate clearly that the use of UCB transplantation for PID is a viable option and may be advantageous in many situations.

Results and long-term outcome in 39 patients with Wiskott-Aldrich syndrome transplanted from HLA-matched and -mismatched donors

In this report, we present an analysis in 39 WAS patients treated by hematopoietic stem cell transplantation (HSCT) in our center since 1983. Fifteen patients received transplants from HLA-identical unrelated donors, 15 from nonidentical parental donors, and 9 from matched siblings. The overall survival rate is 90% in patients with matched donors and 50% in patients after nonidentical transplantation, with a mean follow-up time of 11 years. Treatment failures in the latter group were mainly related to graft rejections and to GvHD and infections following repeat transplants. Long-term survivors in both patient groups remain with few exceptions free of late complications and with stable graft function and complete donor cell chimerism. Based on our findings, we recommend early and prompt treatment of each diagnosed WAS patient if an HLA-matched, related or unrelated, donor can be identified. If this is not the case, HLA-nonidentical donor transplantation represents an alternative to be considered early in patients with severe disease.

Long-term outcome following hematopoietic stem-cell transplantation in Wiskott-Aldrich syndrome: collaborative study of the European Society for Immunodeficiencies and European Group for Blood and Marrow Transplantation

Wiskott-Aldrich syndrome (WAS) is a rare X-linked immunodeficiency with microthrombocytopenia, eczema, recurrent infections, autoimmune disorders, and malignancies that are life-threatening in the majority of patients. In this long-term, retrospective, multicenter study, we analyzed events that occurred in 96 WAS patients who received transplants between 1979 and 2001 who survived at least 2 years following hematopoietic stem-cell transplantation (HSCT). Events included chronic graft-versus-host disease (cGVHD), autoimmunity, infections, and sequelae of before or after HSCT complications. Three patients (3%) died 2.1 to 21 years following HSCT. Overall 7-year event-free survival rate was 75%. It was lower in recipients of mismatched related donors, also in relation with an older age at HSCT and disease severity. The most striking finding was the observation of cGVHD-independent autoimmunity in 20% of patients strongly associated with a mixed/split chimerism status (P < .001), suggesting that residual-host lymphocytes can mediate autoimmune disease despite the coexistence of donor lymphocytes. Infectious complications (6%) related to splenectomy were also significant and may warrant a more restrictive approach to performing splenectomy in WAS patients. Overall, this study provides the basis for a prospective, standardized, and more in-depth detailed analysis of chimerism and events in long-term follow-up of WAS patients who receive transplants to design better-adapted therapeutic strategies.

Allogeneic hemopoietic stem cell transplantation (HSCT) for Wiskott-Aldrich syndrome: a report of the Spanish Working Party for Blood and Marrow Transplantation in Children (GETMON)

Allogeneic stem cell transplantation is the only curative treatment for Wiskott-Aldrich syndrome. The authors retrospectively analyzed the outcome with this procedure in 13 patients with severe Wiskott-Aldrich syndrome transplanted in 5 Spanish centers from 1989 to 2006. A patient was transplanted twice from the same donor due to a late engraftment failure. Age at transplant ranged from 7 to 192 months (median 30 months). There were 10 matched donors (3 related and 7 unrelated), 2 mismatched unrelated, and 1 haploidentical. Conditioning regimen consisted of busulfan and cyclophosphamide (BuCy) in 11 cases and fludarabine and melfalan (1) or BuCy (1). ATG was added in transplants from non-genetically matched donors. GvHD prophylaxis consisted of cyclosporine and methotrexate in most patients plus T-cell depletion in the haploidentical HSCT. Nine of the 13 transplanted patients are alive with complete clinical, immunologic, and hematologic recovery 8-204 months (median 101 months) after HSCT. Eight surviving patients had been transplanted from matched donors (3 related and 5 unrelated) and 1 from a haploidentical donor. Four patients died, 2 transplanted from matched donors (1 from acute GvHD and organ failure, 1 from a lymphoproliferative disorder after a second transplant), and 2 transplanted from mismatched unrelated donors (1 from acute GvHD and organ failure, 1 from graft failure and infection). Allogeneic hemopoietic stem cell transplantation must be utilized in all patients with severe Wisckott-Aldrich syndrome, using the most suitable graft variant for each patient.

Outcome in patients with Wiskott-Aldrich syndrome following stem cell transplantation: an analysis of 57 patients in Japan

A total of 57 patients with Wiskott-Aldrich syndrome (WAS) were studied after undergoing stem cell transplantation (SCT) in Japan between January 1985 and December 2004. Eleven patients received transplants from human leucocyte antigen (HLA)-matched related donors, 10 from HLA-mismatched related donors, 21 from unrelated bone marrow donors, and 15 from unrelated cord blood donors. Nine of the 57 patients rejected the initial graft. The overall 5-year survival rate was 73.7% and the 5-year failure-free survival rate was 65.7% (failure was defined as rejection or death). The overall 5-year survival rates for patients receiving bone marrow and cord blood from unrelated donors were both 80.0%. Based on univariate analysis, the factors associated with poor survival were: transplantation from an HLA-mismatched related donor, patient age of more than 5 years at the time of transplantation, and a conditioning regimen other than busulfan and cyclophosphamide (BU-CY) or busulfan, cyclophosphamide and antithymocyte globulin (BU-CY-ATG). In a multivariate analysis, a conditioning regimen other than BU-CY and BU-CY-ATG was the only independent factor associated with transplantation failure. Given the improved outcome for WAS patients following transplantation from an unrelated donor, we conclude that patients with WAS should receive SCT as soon as possible after diagnosis.

Stem cell transplantation for the Wiskott-Aldrich syndrome: a single-center experience confirms efficacy of matched unrelated donor transplantation

The treatment of Wiskott-Aldrich syndrome (WAS), a once uniformly fatal disorder, has evolved considerably as the use of hematopoietic stem cell transplant has become more widespread. For the majority of patients who lack an human leukocyte antigen-identical sibling, closely matched unrelated donor bone marrow transplant (MUD BMT) at an early age is an excellent option that nevertheless is not uniformly chosen. We retrospectively analyzed our experience with transplantation in 23 patients with WAS from 1990 to 2005 at the University of Brescia, Italy, of whom 16 received MUD BMT. Myeloablative chemotherapy was well tolerated with median neutrophil engraftment at day 18, and no cases of grade III or IV graft-vs-host disease. Overall survival was very good with 78.2% (18/23) of the whole cohort and 81.2% (13/16) of MUD BMT recipients surviving. Among 18 survivors, full donor engraftment was detected in 12 patients, and stable mixed chimerism in all blood lineages in four patients. Deaths were limited to patients who had received mismatched related BMT or who had severe clinical symptomatology at the time of transplantation, further emphasizing the safety and efficacy of MUD BMT when performed early in the clinical course of WAS.

Successful unmanipulated haploidentical bone marrow transplantation from an HLA 2-locus-mismatched mother for Wiskott-Aldrich syndrome after unrelated cord blood stem cell transplantation

The authors describe a boy with Wiskott-Aldrich syndrome (WAS) who was diagnosed immediately after birth using flow cytometric and genetic analysis. At 1 year of age he received unrelated cord blood stem cell transplantation (UCBSCT); however, the sex chromosomes of the peripheral blood mononuclear cells showed that the recipient type was over 70%. This rate gradually increased to over 90% after immunosuppressant therapy was discontinued. Clinical manifestations, including high fever, graft-versus-host disease (GVHD)-like eruptions, and signs of infection recurred. Results of flow cytometric and genetic analysis of mononuclear cells from the boy's mother were normal with no mutation. Three months after UCBSCT, he received an unmanipulated HLA-haploidentical 2-locus-mismatched bone marrow transplant (BMT) from his mother. The prophylaxis against GVHD was tacrolimus and short-term methotrexate. Hematopoietic reconstitution was rapid and fluorescence in situ hybridization analysis revealed sustained engraftment. Grade II acute GVHD developed but improved rapidly with the administration of methylprednisolone. The patient is progressing well and displays complete chimerism 2 years after the BMT. This case suggests that unmanipulated haploidentical BMT from the mother might be feasible not only for malignant disease but also for immunodeficiency disease patients who urgently need stem cell transplants and have no HLA-identical donors.

Allogeneic stem cell transplantation for treatment of immunodeficiency

Primary immunodeficiencies constitute a group of highly complex congenital disorders commonly characterized by an extremely poor prognosis. Allogeneic hematopoietic stem cell transplantation has the potential to establish a permanently functioning immune system and represents a curative approach in many of these disorders. In this review several aspects of stem cell transplantation are presented, with an emphasis on the mechanism of immune reconstitution in severe combined immunodeficiency diseases. In this disorder transplant modalities vary, and also include transplantation without cytoreductive conditioning. Clinical results are summarized based on recent analysis performed in large patient cohorts, which have shown steady improvements and have led to a marked change in the prognosis of patients with primary immunodeficiencies.

Umbilical cord blood transplantation in Wiskott Aldrich syndrome

OBJECTIVE

To report the use of umbilical cord blood (UCB) stem cell transplantation in Wiskott Aldrich syndrome (WAS) when a matched sibling donor was unavailable.

METHODS

Three children with WAS received unrelated umbilical cord blood stem cell transplantation after a preparative regimen for the treatment of combined immunodeficiency diseases. The patients ranged in age from 1.9 to 7.9 years. The cord blood units were 4/6 HLA antigen matches in 2 children and 5/6 in 1 child, with molecular HLA-DR match in all 3 children.

RESULTS

The time for neutrophil engraftment (ANC >500/mm(3)) was 11 to 16 days, and the average time for platelet engraftment was 36 to 49 days. One patient had no evidence of GvHD, 1 patient grade I, and 1 patient grade II. No patient had chronic GvHD. The patient with grade II GvHD also had gut involvement. Immunologic reconstitution demonstrated that cord blood stem cell transplantation resulted in consistent and stable T-, B-, and NK-cell development. Functional B-cell antibody responses revealed that 2 of the patients in whom IVIG has been discontinued had low detectable antibody responses to tetanus and diphtheria toxoid immunizations at 18 to 24 months after transplantation.

CONCLUSIONS

Unrelated umbilical donor cord blood is an alternative source of stem cells for transplantation in children with WAS when a suitable HLA-matched donor is not available. Benefits of UCB include rapid and reliable recovery of immune function, low risk of GvHD, and low viral transmission rate.

Retrovirus-mediated WASP gene transfer corrects Wiskott-Aldrich syndrome T-cell dysfunction

The Wiskott-Aldrich syndrome (WAS) is an X-linked disorder characterized by thrombocytopenia, eczema, and immunodeficiency. At present, the only definitive therapy for the disease is allogeneic bone marrow transplantation (BMT). Because of the frequent lack of suitable donors and the potential severe complications associated with BMT, the development of gene-based therapeutic strategies for WAS is highly desirable. To study whether corrective gene transfer into WAS T cells can lead to restoration of the immunologic defects of WAS, a retroviral vector expressing the WAS protein (WASP) gene was used to transduce human T-lymphotropic virus type 1-transformed T-cell lines and primary T lymphocytes from patients with WAS. After transduction, WAS T cells showed levels of WASP expression similar to those found in cells from normal individuals. In addition, the reconstituted WASP interacted in vitro with proteins containing SH3 domain such as Grb2, PLC-gamma1, and Fyn, each of which are connected to signaling pathways linked to the actin cytoskeleton. Furthermore, after CD3 cross-linking, transduced WAS T lines showed improvement of actin polymerization and T-cell receptor/CD3 down-regulation. More importantly, primary WAS T lymphocytes transduced with WASP acquired the ability to proliferate in response to anti-CD3 stimulation. These findings suggest that biologic defects of WAS T cells can be corrected in vitro by retrovirus-mediated gene transfer and pose the basis for future investigation of gene therapy as treatment for WAS.

Treatment of severe thrombocytopenia with IL-11 in children with Wiskott-Aldrich syndrome

This report examines the safety and efficacy of IL-11 in treating severe thrombocytopenia secondary to Wiskott-Aldrich syndrome in two pediatric patients before allogeneic stem cell transplantation (SCT). Both patients had a substantial increase in their platelet counts and a decrease in bleeding episodes and platelet transfusions. The median platelet count increased from 32,000/mm3 to 64,000/mm3. Each subsequently received allogeneic SCT; 1 year after transplantation, both are reconstituted with 100% donor hematopoietic stem cells with sustained normal platelet counts (>200 K/mm3). Larger studies are required to confirm this observation of the safety and efficacy of IL-11 in this setting.

Non-myeloablative bone marrow transplantation in an adult with Wiskott-Aldrich syndrome

Early bone marrow transplant is now standard treatment for infants with severe immunodeficiencies such as Wiskott-Aldrich Syndrome (WAS), but results in older children and adults are poor. Non-myeloablative transplant has shown promise in the treatment of older children, who are likely to have active infections and organ damage. We describe a non-myeloablative transplant of a 26-year-old man with WAS, undertaken because of severe infections and vasculitis. Partial engraftment and immunorestoration were achieved. The patient is well 1 year post transplantation.

Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is an X-linked immunodeficiency characterized by thrombocytopenia with small platelets, eczema, recurrent infections, autoimmune disorders, IgA nephropathy, and an increased incidence of hematopoietic malignancies. The identification of the responsible gene, WASP (Wiskott-Aldrich Syndrome Protein), revealed clinical heterogeneity of the syndrome, and showed that X-linked thrombocytopenia without, or with only mild immunodeficiency and eczema, is also caused by mutations of WASP. The study of WASP and its mutations demonstrates how a single gene defect can cause multiple and complex clinical symptoms.

Stem-cell transplantation for inherited immunodeficiency disorders

For patients with well-characterized, rapidly fatal, nonmalignant immunodeficiency disorders, such as SCID, the decision to proceed with allogeneic SCT is clear-cut. For patients with many other disorders, this decision can be extremely difficult. Disorders such as LAD or CGD have a variable natural history. Each patient must be considered individually, with the risk for SCT-related morbidity and mortality carefully weighed against that of the underlying disease. Significant advances during the past 10 years have made SCT a much safer procedure. Use of nonmyeloablative conditioning regimens as a means of reducing toxicity of high-dose chemotherapy and irradiation hold great promise. Highly immunosuppressive, nonchemotherapeutic agents that inhibit graft rejection or GVHD by blocking the critical costimulatory component of the T-cell receptor-antigen interaction are beginning to emerge and may be ideal for SCT of nonmalignant diseases. Therefore, the risk-benefit equation must be reassessed each year as the severity of patients' disorders is better defined and techniques of SCT improve.

Stem cell transplantation for non-malignant disorders

Stem cell transplantation (SCT) can be used to cure or ameliorate a wide variety of non-malignant diseases. These range from inherent defects of haemopoietic cell production or function, through metabolic diseases (where blood cells are providing in vivo enzyme therapy to solid organs), to severe autoimmune diseases. However, although transplantation has revolutionized the treatment of many of the diseases discussed, severe toxicities remain. In some cases these are inherent to the disease concerned but frequently they relate to the conditioning regime or post-transplant complications such as graft-versus-host disease (GvHD). This chapter concentrates on the indications for transplant, outcome statistics and problems inherent in particular conditions, seen in the light of technological improvements during the 1990s and the potential impact of enzyme and gene therapies.

Unrelated partially matched peripheral blood stem cell transplantation with highly purified CD34+ cells in a child with Wiskott-Aldrich syndrome

Stem cell transplantation is the only curative approach to the treatment of Wiskott-Aldrich syndrome. However, using grafts from partially matched unrelated donors is associated with increased risk of graft rejection and graft-versus-host disease. In an attempt to prevent these problems, a 6-year-old boy with Wiskott-Aldrich syndrome lacking a suitable family donor, was transplanted with large numbers of unrelated highly purified CD34+ peripheral blood stem cells mismatched at one C locus. Conditioning consisted of busulfan 16 mg/kg body weight, cyclophosphamide 200 mg/kg body weight and antithymocyte globulin 20 mg/kg body weight x 3 days. The boy had a rapid hematopoietic engraftment and showed immunologic reconstitution by day +92. Although he did not receive prophylactic immunosuppression he did not develop any graft-versus-host disease and is well and alive up to now, 25 months after transplantation.

Retrovirus-mediated WASP gene transfer corrects defective actin polymerization in B cell lines from Wiskott-Aldrich syndrome patients carrying 'null' mutations

Boys affected with Wiskott-Aldrich syndrome (WAS) present with variable association of thrombocytopenia, eczema and immune deficiency. If untreated, WAS patients may succumb to intracerebral hemorrhages, severe infections or malignancies. Allogeneic bone marrow transplantation (BMT) can cure all aspects of the disease, but HLA-identical donors are not available to all patients and mismatched BMTs are unfortunately associated with high mortality and morbidity. The good success of HLA-matched BMT, however, makes WAS a potential candidate for hematopoietic stem cell gene therapy. WAS patients carry mutations of the Wiskott-Aldrich syndrome protein gene encoding WASP, a 502-amino acid proline-rich protein with demonstrated involvement in the organization of the actin cytoskeleton. To verify the feasibility of genetic correction for this disease, the WASP cDNA was expressed in EBV-immortalized B cell lines obtained from WAS patients using a retroviral vector. Transduced WAS cells showed levels of WASP expression similar to those found in cells from normal donors, without detectable effects on viability or growth characteristics. In addition, retrovirus-mediated expression of WASP led to improvement of cytoplasmic F-actin expression and formation of F-actin-positive microvilli, a process shown to be defective in untransduced WAS cell lines. These preliminary results indicate a potential use for retrovirus-mediated gene transfer as therapy for WAS.

Intravenous immunoglobulin, splenectomy, and antibiotic prophylaxis in Wiskott-Aldrich syndrome

AIM

To assess the results of supportive treatment with intravenous immunoglobulin (IVIG) and antibiotic prophylaxis in combination with splenectomy in patients with Wiskott-Aldrich syndrome.

STUDY DESIGN

Retrospective review of case records of 21 patients from March 1984 to February 1996.

RESULTS

Thrombocytopenia was cured in 14 of 15 patients who had splenectomy, but it recurred intermittently in three. Mean platelet volume (MPV) was normal transiently in some patients, but all MPV values were subnormal 8-23 months after splenectomy. Antibiotic and IVIG prophylaxis may have contributed to the lack of a detectable increase in the number of severe acute bacterial infections in the 451 months after splenectomy. Four patients died in 2205 months of observation before and after splenectomy (median 82, range 16-248): two of cerebral B cell lymphoma, one of progressive multifocal leucoencephalopathy, and one with severe chronic chest disease of pneumonia.

CONCLUSION

Adequate supportive treatment with IVIG and antibiotic prophylaxis together with splenectomy enables good survival and quality of life in the short and medium term in patients with Wiskott-Aldrich syndrome. Persistence of infection, bleeding, and vasculitic and allergic symptoms in a significant minority and the risk of development of lymphoma, however, suggest that bone marrow transplantation may be indicated if an HLA identical donor is available.

Bone marrow transplantation in 26 patients with Wiskott-Aldrich syndrome from a single center

We retrospectively analyzed the outcome of bone marrow transplantation (BMT) performed in 26 patients with Wiskott-Aldrich syndrome (WAS) in one center. Twenty-eight transplantation procedures were performed. Ten unselected patients received unmanipulated marrow from a donor with genetically identical human leukocyte antigen (HLA). Eight patients were cured and survive 1.5 to 16.5 years after BMT. One patient successfully received a T-cell-depleted marrow from a matched unrelated donor. Sixteen patients were selected to receive a related HLA partially incompatible BMT because of the occurrence of life-threatening complications from the WAS (i.e., refractory thrombocytopenia, autoimmunity including vasculitis and sepsis). All but one received T-cell-depleted marrow after a conditioning regimen of busulfan and cyclophosphamide. One patient had two BMTs. Engraftment occurred in 12 of 17 attempts. The addition of monoclonal antibodies to lymphocyte function-associated antigen-1 and CD2 molecules appeared to improve engraftment. Six patients were long-term survivors, whereas others died of viral infections (n = 7), among which Epstein-Barr virus-induced B-lymphocyte proliferative disorder was predominant. Delay in development of full T- and B-cell functions accounted for severe infectious complications. These results confirm the excellent outcome of HLA genetically identical BMT in WAS, whereas BMT from HLA partially incompatible donors should be strictly restricted to patients with severe complications of WAS.

Significant and persistent improvement of thrombocytopenia after splenectomy in an adult with the Wiskott-Aldrich Syndrome and intra-cerebral bleeding

The Wiskott-Aldrich syndrome is an X-linked inherited immunodeficiency disorder characterized by thrombocytopenia, recurrent infections and eczema. Its best management option is HLA-identical bone marrow transplantation; when this is not feasible, splenectomy, followed by continuous prophylactic antibiotics, represents the alternative of choice. The present case report relates the excellent outcome of an adult with the Wiskott-Aldrich syndrome who suffered his first major complication of the disease at age 33 years, an intracerebral hemorrhage. Since an uneventfull splenectomy, thrombocytopenia has significantly improved, and he has remained free of infections for a follow-up period of 3 years while being treated with prophylactic antibiotics.

Update on selected inherited immunodeficiency syndromes

Non-acquired immunodeficiency syndrome disorders in children frequently have cutaneous manifestations that allow initial diagnosis to be suspected by the dermatologist and require continuing dermatologic management. Many recent developments have occurred in understanding the underlying gene defects, diagnosis of patients and carrier mothers of X-linked disorders, prenatal diagnosis, and new means of therapy of selected inherited immunodeficiency disorders.

A multiinstitutional survey of the Wiskott-Aldrich syndrome

The Wiskott-Aldrich syndrome is an X-linked primary immunodeficiency originally characterized by the clinical triad of thrombocytopenia, eczema, and immunodeficiency. We collected clinical and laboratory information on 154 unselected patients with Wiskott-Aldrich syndrome to define better the clinical expression of this disorder. The classic triad of thrombocytopenia with small platelets, recurrent otitis media, and eczema was seen in only 27% of the study population; 5% of the study population had only infectious manifestations, and 20% of the study group had only hematologic manifestations before diagnosis. The results of immunologic evaluations varied from one patient to another and the course of the disorder varied tremendously, even within a single kindred. We conclude that many patients with Wiskott-Aldrich syndrome have an atypical presentation and that a panel of diagnostic tests is often required to establish the diagnosis. Two high-risk subgroups were identified in the study population: patients with platelet counts < 10 x 10(9)/L (< 10,000/mm3) at the time of diagnosis were at high risk of bleeding, and patients with autoimmune disorders were at increased risk of having a malignancy.

Isolation of a novel gene mutated in Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is an X-linked recessive immunodeficiency characterized by eczema, thrombocytopenia, and recurrent infections. Linkage studies have placed the gene at Xp11.22-p11.23. We have isolated from this interval a novel gene, WASP, which is expressed in lymphocytes, spleen, and thymus. The gene is not expressed in two unrelated WAS patients, one of whom has a single base deletion that produces a frame shift and premature termination of translation. Two additional patients have been identified with point mutations that change the same arginine residue to either a histidine or a leucine. WASP encodes a 501 amino acid proline-rich protein that is likely to be a key regulator of lymphocyte and platelet function.

Allogeneic bone marrow transplantation

From highly investigational to standardized therapy, allogeneic BMT has established its role in the treatment of selected diseases. Continued refinements in bone marrow transplantation will increase the number of potential candidates, reduce associated risks, and improve disease-free survival rates. With further exploration into its efficacy, allogeneic BMT will bring new challenges and opportunities for patients, families, and health care providers.

Genetic immunodeficiencies: both the lumpers and the splitters can claim victory

Over the last few years, molecular approaches to analysis of genetic immunodeficiencies have made it clear that different mutations of the same gene may result in very different clinical presentations. On the other hand, a single clinical syndrome is sometimes due to mutations in a variety of independent genes. In the future, appropriate treatment, particularly gene therapy, will depend on a precise genetic diagnosis.