Hematopoietic stem cell transplantation for Wiskott-Aldrich syndrome: an EBMT inborn errors working party analysis

Wiskott-Aldrich syndrome: a study of 577 patients defines the genotype as a biomarker for disease severity and survival

ABSTRACT

Wiskott-Aldrich syndrome (WAS) is a multifaceted monogenic disorder with a broad disease spectrum and variable disease severity and a variety of treatment options including allogeneic hematopoietic stem cell transplantation (HSCT) and gene therapy (GT). No reliable biomarker exists to predict disease course and outcome for individual patients. A total of 577 patients with a WAS variant from 26 countries and a median follow-up of 8.9 years (range, 0.3-71.1), totaling 6118 patient-years, were included in this international retrospective study. Overall survival (OS) of the cohort (censored at HSCT or GT) was 82% (95% confidence interval, 78-87) at age 15 years and 70% (61-80) at 30 years. The type of variant was predictive of outcome: patients with a missense variant in exons 1 or 2 or with the intronic hot spot variant c.559+5G>A (class I variants) had a 15-year OS of 93% (89-98) and a 30-year OS of 91% (86-97), compared with 71% (62-81) and 48% (34-68) in patients with any other variant (class II; P < .0001). The cumulative incidence rates of disease-related complications such as severe bleeding (P = .007), life-threatening infection (P < .0001), and autoimmunity (P = .004) occurred significantly later in patients with a class I variant. The cumulative incidence of malignancy (P = .6) was not different between classes I and II. It confirms the spectrum of disease severity and quantifies the risk for specific disease-related complications. The class of the variant is a biomarker to predict the outcome for patients with WAS.

Allogeneic hematopoietic stem cell transplantation outcome in oldest known surviving patients with Wiskott-Aldrich syndrome

Regardless of their age, adult patients with Wiskott-Aldrich syndrome should be considered for hematopoietic stem cell transplantation if clinically indicated.

Treosulfan vs busulfan conditioning for allogeneic bmt in children with nonmalignant disease: a randomized phase 2 trial

Optimal conditioning prior to allogeneic hematopoietic stem cell transplantation for children with non-malignant diseases is subject of ongoing research. This prospective, randomized, phase 2 trial compared safety and efficacy of busulfan with treosulfan based preparative regimens. Children with non-malignant diseases received fludarabine and either intravenous (IV) busulfan (4.8 to 3.2 mg/kg/day) or IV treosulfan (10, 12, or 14 g/m2/day). Thiotepa administration (2 × 5 mg/kg) was at the investigator's discretion. Primary endpoint was freedom from transplantation (treatment)-related mortality (freedom from TRM), defined as death between Days -7 and +100. Overall, 101 patients (busulfan 50, treosulfan 51) with at least 12 months follow-up were analyzed. Freedom from TRM was 90.0% (95% CI: 78.2%, 96.7%) after busulfan and 100.0% (95% CI: 93.0%, 100.0%) after treosulfan. Secondary outcomes (transplantation-related mortality [12.0% versus 3.9%]) and overall survival (88.0% versus 96.1%) favored treosulfan. Graft failure was more common after treosulfan (n = 11), than after busulfan (n = 2) while all patients were rescued by second procedures except one busulfan patient. CTCAE Grade III adverse events were similar in both groups. This study confirmed treosulfan to be an excellent alternative to busulfan and can be safely used for conditioning treatment in children with non-malignant disease.

Advances in gene therapy for inborn errors of immunity

PURPOSE OF REVIEW

Provide an overview of the landmark accomplishments and state of the art of gene therapy for inborn errors of immunity (IEI).

RECENT FINDINGS

Three decades after the first clinical application of gene therapy for IEI, there is one market authorized product available, while for several others efficacy has been demonstrated or is currently being tested in ongoing clinical trials. Gene editing approaches using programmable nucleases are being explored preclinically and could be beneficial for genes requiring tightly regulated expression, gain-of-function mutations and dominant-negative mutations.

SUMMARY

Gene therapy by modifying autologous hematopoietic stem cells (HSCs) offers an attractive alternative to allogeneic hematopoietic stem cell transplantation (HSCT), the current standard of care to treat severe IEI. This approach does not require availability of a suitable allogeneic donor and eliminates the risk of graft versus host disease (GvHD). Gene therapy can be attempted by using a viral vector to add a copy of the therapeutic gene (viral gene addition) or by using programmable nucleases (gene editing) to precisely correct mutations, disrupt a gene or introduce an entire copy of a gene at a specific locus. However, gene therapy comes with its own challenges such as safety, therapeutic effectiveness and access. For viral gene addition, a major safety concern is vector-related insertional mutagenesis, although this has been greatly reduced with the introduction of safer vectors. For gene editing, the risk of off-site mutagenesis is a main driver behind the ongoing search for modified nucleases. For both approaches, HSCs have to be manipulated ex vivo, and doing this efficiently without losing stemness remains a challenge, especially for gene editing.

Progress in the field of hematopoietic stem cell-based therapies for inborn errors of immunity

PURPOSE OF REVIEW

Hematopoietic stem cell-based therapies, including allogeneic hematopoietic cell transplantation (HCT) and autologous gene therapy (GT), have been used as curative therapy for many inborn errors of immunity (IEI). As the number of genetically defined IEI and the use of HCT and GT increase, valuable data on outcomes and approaches for specific disorders are available. We review recent progress in HCT and GT for IEI in this article.

RECENT FINDINGS

Novel approaches to prevention of allogeneic complications and experience in adolescents and young adults have expanded the use of HCT. Universal newborn screening for severe combined immunodeficiency (SCID) has led to improved outcome after HCT. Analysis of outcomes of HCT and GT for SCID, Wiskott-Aldrich syndrome (WAS) and chronic granulomatous disease (CGD) reveal risk factors for survival, the impact of specific conditioning regimens, and vector- or disease-specific impacts on efficacy and safety. Preclinical studies of GT and gene editing show potential for translation to the clinic.

SUMMARY

Emerging data on outcome after HCT for specific IEI support early evaluation and treatment, before development of co-morbidities. Data in large cooperative retrospective databases continues to yield valuable insights clinicians can use in patient selection and choice of therapy.

Outcome of Second Allogeneic HSCT for Patients with Inborn Errors of Immunity: Retrospective Study of 20 Years' Experience

A significant complication of HSCT is graft failure, although few studies focus on this problem in patients with inborn errors of immunity (IE). We explored outcome of second HSCT for IEI by a retrospective, single-centre study between 2002 and 2022. Four hundred ninety-three patients underwent allogeneic HSCT for severe combined immunodeficiency (SCID; n = 113, 22.9%) or non-SCID IEI (n = 380, 77.1%). Thirty patients (6.0%) required second HSCT. Unconditioned infusion or no serotherapy at first HSCT was more common in patients who required second transplant. Median interval between first and second HSCT was 0.97 years (range: 0.19-8.60 years); a different donor was selected for second HSCT in 24/30 (80.0%) patients. Conditioning regimens for second HSCT were predominately treosulfan-based (with thiotepa: n = 18, 60.0%; without, n = 6, 20.0%). Patients received grafts from peripheral blood stem cell (n = 25, 83.3%) or bone marrow (n = 5, 16.7%) with median stem cell dose 9.5 × 106 CD34 + cells/kilogram (range: 1.4-32.3). Median follow-up was 1.92 years (0.22-16.0). Overall survival was 80.8% and event-free survival was 64.7%. Four patients died, two of early-transplant related complications, and two of late sepsis post-second HSCT. Three patients required third HSCT; all are alive with 100% donor chimerism. Cumulative incidence of acute graft-versus-host disease was 28.4%, (all grade I-II). Viral reactivation was seen in 13/30 (43.3%) patients, including HHV6 (n = 6), CMV (n = 4), and adenovirus (n = 2). At latest follow-up, 25/26 surviving patients have donor chimerism ≥ 90% and 16/25 (64.0%) have discontinued immunoglobulin replacement. Second HSCT offers IEI patients with graft failure curative treatment with good overall survival and immunological recovery.

Treosulfan-Based Conditioning Regimen In Pediatric Hematopoietic Stem Cell Transplantation: A Retrospective Analysis on Behalf of the Spanish Group for Hematopoietic Transplantation and Cellular Therapy (GETH-TC)

Increasing data on treosulfan-based conditioning regimens before hematopoietic stem cell transplantation (HSCT) demonstrate the consistent benefits of this approach, particularly regarding acute toxicity. This study aimed to describe the results of treosulfan-based conditioning regimens in children, focusing on toxicity and outcomes when used to treat both malignant and nonmalignant diseases. This retrospective observational study of pediatric patients treated in Spain with treosulfan-based conditioning regimens before HSCT was based on data collection from electronic clinical records. We studied a total of 160 treosulfan-based conditioning HSCTs to treat nonmalignant diseases (n = 117) or malignant diseases (n = 43) in 158 children and adolescents. The median patient age at HSCT was 5.1 years (interquartile range, 2 to 10 years). The most frequent diagnoses were primary immunodeficiency (n = 42; 36%) and sickle cell disease (n = 42; 36%) in the nonmalignant disease cohort and acute lymphoblastic leukemia (n = 15; 35%) in the malignant disease cohort. Engraftment occurred in 97% of the patients. The median times to neutrophil engraftment (17 days versus 14 days; P = .008) and platelet engraftment (20 days versus 15 days; P = .002) were linger in the nonmalignant cohort. The 1-year cumulative incidence of veno-occlusive disease was 7.98% (95% confidence interval [CI], 4.6% to 13.6%), with no significant differences between cohorts. The 1-year cumulative incidence of grade III-IV acute graft-versus-host disease (GVHD) was higher in the malignant disease cohort (18% versus 3.2%; P = .011). Overall, the malignant cohort had both a higher total incidence (9% versus 3%; P < .001) and a higher 2-year cumulative incidence (16% versus 1.9%; P < .001) of total chronic GVHD. The 2-year cumulative transplantation-related mortality was 15%, with no difference between the 2 cohorts. The 5-year overall survival was 80% (95% CI, 72% to 86%) and was higher in the nonmalignant cohort (87% versus 61%; P = .01). The 2-year cumulative incidence of relapse was 25% in the malignant cohort. The 5-year cumulative GVHD-free, relapse-free survival rate was 60% (95% CI, 51% to 70%) and was higher in the nonmalignant cohort (72% versus 22%; P < .001). A treosulfan-based radiation-free conditioning regimen is feasible, achieving a high engraftment rate and 5-year overall survival, and is an emerging option for the first HSCT in nonmalignant diseases.

Excellent outcome of stem cell transplantation for sickle cell disease

Many sickle cell disease (SCD) patients lack matched family donors (MFD) or matched unrelated donors (MUD), implying haploidentical donors (MMFD) as a logical donor choice. We used a reduced toxicity protocol for all donor types. We included 31 patients (2-22 years) with MFD (n = 15), MMFD (10), or MUD (6) HSCT and conditioning with alemtuzumab/ATG, thiotepa, fludarabine and treosulfan, and post-transplant cyclophosphamide for MMFD. After the initial six patients, treosulfan was replaced by targeted busulfan (AUC 65-75 ng*h/ml). After a median follow-up of 26 months (6-123), all patients are alive and off immunosuppression. Two MMFD patients experienced secondary graft failure with recurrence of SCD, both after treosulfan conditioning. Neither acute GVHD ≥ °III nor moderate/severe chronic GVHD was observed. The disease-free, severe GVHD-free survival was 100%, 100%, and 80% in the MFD, MUD, and MMFD groups, respectively (p = 0.106). There was a higher rate of virus reactivation in MMFD (100%) and MUD (83%) compared to MFD (40%; p = 0.005), but not of viral disease (20% vs 33% vs 13%; p = 0.576). Six patients had treosulfan-based conditioning, two of whom experienced graft failure (33%), compared to 0/25 (0%) after busulfan-based conditioning (p = 0.032). Donor chimerism was ≥ 80% in 28/31 patients (90%) at last follow-up. Reduced toxicity myeloablative conditioning resulted in excellent overall survival, negligible GVHD, and low toxicity among all donor groups in pediatric and young adult patients with SCD.

Too much of a good thing: a review of primary immune regulatory disorders

Primary immune regulatory disorders (PIRDs) are inborn errors of immunity caused by a loss in the regulatory mechanism of the inflammatory or immune response, leading to impaired immunological tolerance or an exuberant inflammatory response to various stimuli due to loss or gain of function mutations. Whilst PIRDs may feature susceptibility to recurrent, severe, or opportunistic infection in their phenotype, this group of syndromes has broadened the spectrum of disease caused by defects in immunity-related genes to include autoimmunity, autoinflammation, lymphoproliferation, malignancy, and allergy; increasing focus on PIRDs has thus redefined the classical 'primary immunodeficiency' as one aspect of an overarching group of inborn errors of immunity. The growing number of genetic defects associated with PIRDs has expanded our understanding of immune tolerance mechanisms and prompted identification of molecular targets for therapy. However, PIRDs remain difficult to recognize due to incomplete penetrance of their diverse phenotype, which may cross organ systems and present to multiple clinical specialists prior to review by an immunologist. Control of immune dysregulation with immunosuppressive therapies must be balanced against the enhanced infective risk posed by the underlying defect and accumulated end-organ damage, posing a challenge to clinicians. Whilst allogeneic hematopoietic stem cell transplantation may correct the underlying immune defect, identification of appropriate patients and timing of transplant is difficult. The relatively recent description of many PIRDs and rarity of individual genetic entities that comprise this group means data on natural history, clinical progression, and treatment are limited, and so international collaboration will be needed to better delineate phenotypes and the impact of existing and potential therapies. This review explores pathophysiology, clinical features, current therapeutic strategies for PIRDs including cellular platforms, and future directions for research.

Outcomes of hematopoietic stem cell gene therapy for Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is a rare X-linked disorder characterized by combined immunodeficiency, eczema, microthrombocytopenia, autoimmunity, and lymphoid malignancies. Gene therapy (GT) to modify autologous CD34+ cells is an emerging alternative treatment with advantages over standard allogeneic hematopoietic stem cell transplantation for patients who lack well-matched donors, avoiding graft-versus-host-disease. We report the outcomes of a phase 1/2 clinical trial in which 5 patients with severe WAS underwent GT using a self-inactivating lentiviral vector expressing the human WAS complementary DNA under the control of a 1.6-kB fragment of the autologous promoter after busulfan and fludarabine conditioning. All patients were alive and well with sustained multilineage vector gene marking (median follow-up: 7.6 years). Clinical improvement of eczema, infections, and bleeding diathesis was universal. Immune function was consistently improved despite subphysiologic levels of transgenic WAS protein expression. Improvements in platelet count and cytoskeletal function in myeloid cells were most prominent in patients with high vector copy number in the transduced product. Two patients with a history of autoimmunity had flares of autoimmunity after GT, despite similar percentages of WAS protein-expressing cells and gene marking to those without autoimmunity. Patients with flares of autoimmunity demonstrated poor numerical recovery of T cells and regulatory T cells (Tregs), interleukin-10-producing regulatory B cells (Bregs), and transitional B cells. Thus, recovery of the Breg compartment, along with Tregs appears to be protective against development of autoimmunity after GT. These results indicate that clinical and laboratory manifestations of WAS are improved with GT with an acceptable safety profile. This trial is registered at clinicaltrials.gov as #NCT01410825.

Population pharmacokinetic modeling of treosulfan and rationale for dose recommendation in children treated for conditioning prior to allogeneic hematopoietic stem cell transplantation

Intravenously infused treosulfan was evaluated in adult and pediatric patients for conditioning regimen prior to allogeneic hematopoietic stem cell transplantation. A population pharmacokinetic (PK) model was initially developed on 116 adult and pediatric PK profiles from historical trials, to support treosulfan dose recommendations for children in 2 prospective trials. The aim was to assess and update the initial population PK model by inclusion of additional 83 pediatric PK profiles from these 2 trials. The final population PK model was 2-compartmental with dosing in the central compartment, linear elimination, and inter-compartmental clearance. Inter-individual variability was included on clearance (CL), central volume (V1), peripheral volume (V2), and inter-compartmental clearance (Q). The final model described an effect of the body surface area (BSA) on CL, V1, V2, and Q. The final model resulted in a modified dose recommendation for children and advises treosulfan doses of 10 g/m2, 12 g/m2, and 14 g/m2 for BSAs of <0.4 m2, ≥0.4 to <0.9 m2, and ≥0.9 m2, respectively. This simplified BSA-dependent dose recommendation was developed for children, ensuring a well comparable treosulfan exposure as a dose of 14 g/m2 in adults - irrespective of their age and without applying individual therapeutic drug monitoring.

Rare solid tumors in a patient with Wiskott-Aldrich syndrome after hematopoietic stem cell transplantation: case report and review of literature

Background and aims

Wiskott-Aldrich syndrome (WAS) is an X-linked recessive primary immunodeficiency disorder characterized by severe eczema, recurrent infections, and micro-thrombocytopenia. Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative therapeutic option for patients with classic form. The risk of developing post-transplant tumors appears to be higher in patients with WAS than in other inborn errors of immunity (IEIs), but the actual incidence is not well defined, due to the scarcity of published data.

Methods

Herein, we describe a 10-year-old patient diagnosed with WAS, treated with HSCT in the first year of life, who subsequently developed two rare solid tumors, kaposiform hemangioendothelioma and desmoid tumor. A review of the literature on post-HSCT tumors in WAS patients has been performed.

Results

The patient received diagnosis of classic WAS at the age of 2 months (Zhu score = 3), confirmed by WAS gene sequencing, which detected the nonsense hemizygous c.37C>T (Arg13X) mutation. At 9 months, patient underwent HSCT from a matched unrelated donor with an adequate immune reconstitution, characterized by normal lymphocyte subpopulations and mitogen proliferation tests. Platelet count significantly increased, even though platelet count never reached reference values. A mixed chimerism was also detected, with a residual WASP- population on monocytes (27.3%). The patient developed a kaposiform hemangioendothelioma at the age of 5. A second abdominal tumor was identified, histologically classified as a desmoid tumor when he reached the age of 10 years. Both hematopoietic and solid tumors were identified in long-term WAS survivors after HSCT.

Conclusion

Here, we describe the case of a patient with WAS who developed two rare solid tumors after HSCT. An active surveillance program for the risk of tumors is necessary in the long-term follow-up of post-HSCT WAS patients.

Case report: Allogeneic stem cell transplantation for type B insulin resistance

Type B insulin resistance (TBIR) is a rare, often fulminant form of insulin resistance caused by autoantibodies against the insulin receptor. If left untreated, its mortality is high. Various immunosuppressive regimens have shown efficacy, but treatment effects are variable and time-delayed, and drug-induced complications may arise. We report a patient with TBIR arising as a complication of Wiskott-Aldrich syndrome. Stable remission of TBIR was achieved through allogeneic peripheral blood stem cell transplantation (PBSCT) over a follow-up period of more than 1.5 years. We thus demonstrate that PBSCT can be considered a treatment option in TBIR where conventional immunosuppressive therapy is ineffective or contraindicated.

Activated PI3Kδ syndrome - reviewing challenges in diagnosis and treatment

Activated PI3Kδ syndrome (APDS) is a rare inborn error of immunity (IEI) characterized primarily by frequent infections, lymphoproliferation and autoimmunity. Since its initial description in 2013, APDS has become part of the growing group of nearly 500 IEIs affecting various components of the immune system. The two subtypes of APDS - APDS1 and APDS2 - are caused by variants in the PIK3CD and PIK3R1 genes, respectively. Due to the rarity of the disease and the heterogeneous clinical picture, many patients are not diagnosed until years after symptom onset. Another challenge is the large number of PIK3CD and PIK3R1 variants whose functional significance for developing APDS is inconclusive. Treatment of APDS has so far been mostly symptom-oriented with immunoglobulin replacement therapy, immunosuppressive therapies and antibiotic or antiviral prophylaxes. Additionally, allogeneic stem cell transplantation as well as new targeted therapies are options targeting the root cause that may improve patients' quality of life and life expectancy. However, the clinical course of the disease is difficult to predict which complicates the choice of appropriate therapies. This review article discusses diagnostic procedures and current and future treatment options, and highlights the difficulties that physicians, patients and their caretakers face in managing this complex disease. This article is based on cohort studies, the German and US guidelines on the management of primary immunodeficiencies as well as on published experience with diagnosis and compiled treatment experience for APDS.

Gene Therapy for Inborn Errors of Immunity

In the early 1990s, gene therapy (GT) entered the clinical arena as an alternative to hematopoietic stem cell transplantation for forms of inborn errors of immunity (IEIs) that are not medically manageable because of their severity. In principle, the use of gene-corrected autologous hematopoietic stem cells presents several advantages over hematopoietic stem cell transplantation, including making donor searches unnecessary and avoiding the risks for graft-versus-host disease. In the past 30 years or more of clinical experience, the field has witnessed multiple examples of successful applications of GT to a number of IEIs, as well as some serious drawbacks, which have highlighted the potential genotoxicity of integrating viral vectors and stimulated important progress in the development of safer gene transfer tools. The advent of gene editing technologies promises to expand the spectrum of IEIs amenable to GT to conditions caused by mutated genes that require the precise regulation of expression or by dominant-negative variants. Here, we review the main concepts of GT as it applies to IEIs and the clinical results obtained to date. We also describe the challenges faced by this branch of medicine, which operates in the unprofitable sector of human rare diseases.

Effect of busulfan and treosulfan on gonadal function after allogeneic stem cell transplantation in children and adolescents with nonmalignant diseases is not exposure-dependent

With an increasing number of young patients surviving into adulthood after hematopoietic stem cell transplantation (HSCT), gonadal dysfunction becomes an important late effect with significant impact on quality of life. In this retrospective study, we evaluated the exposure of busulfan (BU) and treosulfan (TREO) in relation to gonadal function in pediatric patients transplanted for a nonmalignant disease between 1997 and 2018. In the BU cohort, 56 patients could be evaluated and gonadal dysfunction occurred in 35 (63%) patients. Lower BU exposure (cumulative area under the curve cAUC <70 mg*h/L) was not associated with a reduced risk of gonadal dysfunction (OR 0.92 95% confidence interval (CI) 0.25-3.49, p=0.90). In the TREO cohort, 32 patients were evaluable and gonadal insufficiency occurred in 9 patients (28%). Lower TREO exposure (AUC <1750 mg*h/L on day 1) was not associated with a reduced risk of gonadal dysfunction (OR 1.6 95%CI 0.16-36.6, p=0.71). Our data do not support the premise that reduced intensity BU-based conditioning lowers the risk for gonadal toxicity and it is unlikely that TDM-based reduced treosulfan exposure will further limit the risk for gonadal dysfunction.

Allogeneic Hematopoietic Stem Cell Transplantation Activity in Inborn Errors of Immunity in Russian Federation

PURPOSE

Allogeneic hematopoietic stem cell transplantation (HSCT) is an established therapy for many inborn errors of immunity (IEI). The indications for HSCT have expanded over the last decade. The study aimed to collect and analyze the data on HSCT activity in IEI in Russia.

METHODS

The data were collected from the Russian Primary Immunodeficiency Registry and complemented with information from five Russian pediatric transplant centers. Patients diagnosed with IEI by the age of 18 years and who received allogeneic HSCT by the end of 2020 were included.

RESULTS

From 1997 to 2020, 454 patients with IEI received 514 allogeneic HSCT. The median number of HSCTs per year has risen from 3 in 1997-2009 to 60 in 2015-2020. The most common groups of IEI were immunodeficiency affecting cellular and humoral immunity (26%), combined immunodeficiency with associated/syndromic features (28%), phagocyte defects (21%), and diseases of immune dysregulation (17%). The distribution of IEI diagnosis has changed: before 2012, the majority (65%) had severe combined immunodeficiency (SCID) and hemophagocytic lymphohistiocytosis (HLH), and after 2012, only 24% had SCID and HLH. Of 513 HSCTs, 48.5% were performed from matched-unrelated, 36.5% from mismatched-related (MMRD), and 15% from matched-related donors. In 349 transplants T-cell depletion was used: 325 TCRαβ/CD19+ depletion, 39 post-transplant cyclophosphamide, and 27 other. The proportion of MMRD has risen over the recent years.

CONCLUSION

The practice of HSCT in IEI has been changing in Russia. Expanding indications to HSCT and SCID newborn screening implementation may necessitate additional transplant beds for IEI in Russia.

Understanding immunoactinopathies: A decade of research on WAS gene defects

Immunoactinopathies caused by mutations in actin-related proteins are a growing group of inborn errors of immunity (IEI). Immunoactinopathies are caused by a dysregulated actin cytoskeleton and affect hematopoietic cells especially because of their unique capacity to survey the body for invading pathogens and altered self, such as cancer cells. These cell motility and cell-to-cell interaction properties depend on the dynamic nature of the actin cytoskeleton. Wiskott-Aldrich syndrome (WAS) is the archetypical immunoactinopathy and the first described. WAS is caused by loss-of-function and gain-of-function mutations in the actin regulator WASp, uniquely expressed in hematopoietic cells. Mutations in WAS cause a profound disturbance of actin cytoskeleton regulation of hematopoietic cells. Studies during the last 10 years have shed light on the specific effects on different hematopoietic cells, revealing that they are not affected equally by mutations in the WAS gene. Moreover, the mechanistic understanding of how WASp controls nuclear and cytoplasmatic activities may help to find therapeutic alternatives according to the site of the mutation and clinical phenotypes. In this review, we summarize recent findings that have added to the complexity and increased our understanding of WAS-related diseases and immunoactinopathies.

Correcting inborn errors of immunity: From viral mediated gene addition to gene editing

Allogeneic hematopoietic stem cell transplantation is an effective treatment to cure inborn errors of immunity. Remarkable progress has been achieved thanks to the development and optimization of effective combination of advanced conditioning regimens and use of immunoablative/suppressive agents preventing rejection as well as graft versus host disease. Despite these tremendous advances, autologous hematopoietic stem/progenitor cell therapy based on ex vivo gene addition exploiting integrating γ-retro- or lenti-viral vectors, has demonstrated to be an innovative and safe therapeutic strategy providing proof of correction without the complications of the allogeneic approach. The recent advent of targeted gene editing able to precisely correct genomic variants in an intended locus of the genome, by introducing deletions, insertions, nucleotide substitutions or introducing a corrective cassette, is emerging in the clinical setting, further extending the therapeutic armamentarium and offering a cure to inherited immune defects not approachable by conventional gene addition. In this review, we will analyze the current state-of-the art of conventional gene therapy and innovative protocols of genome editing in various primary immunodeficiencies, describing preclinical models and clinical data obtained from different trials, highlighting potential advantages and limits of gene correction.

Second allogeneic hematopoietic stem cell transplantation in patients with inborn errors of immunity

Graft failure (GF) remains a serious issue of hematopoietic stem cell transplantation (HSCT) in inborn errors of immunity (IEI). Second HSCT is the only salvage therapy for GF. There are no uniform strategies for the second HSCTs and limited data are available on the second HSCT outcomes. 48 patients with various IEI received second allogeneic HSCT from 2013 to 2020. Different conditioning regimens were used, divided into two main groups: containing myeloablative doses of busulfan/treosulfan (n = 19) and lymphoid irradiation 2-6 Gy (n = 22). Irradiation-containing conditioning was predominantly used in suspected immune-mediated rejection of the first graft. Matched unrelated donor was used in 28 patients, mismatched related in 18, and matched related in 1. 35 patients received TCRαβ/CD19 graft depletion. The median follow-up time was 2.4 years post-HSCT. One patient died at conditioning. The OS was 0.63 (95% CI: 0.41-0.85) after busulfan/treosulfan and 0.68 (95% CI: 0.48-0.88) after irradiation-based conditioning, p = 0.66. Active infection at HSCT significantly influenced OS: 0.43 (95% CI: 0.17-0.69) versus 0.73 (95% CI: 0.58-0.88) without infection, p = 0.004. The cumulative incidence of GF was 0.15 (95% CI: 0.08-0.29). To conclude, an individualized approach is required for the second HSCT in IEI. Low-dose lymphoid irradiation in suspected immune-mediated GF may be a feasible option.

Transplant for non-malignant disorders: an International Society for Cell & Gene Therapy Stem Cell Engineering Committee report on the role of alternative donors, stem cell sources and graft engineering

Hematopoietic stem cell transplantation (HSCT) is curative for many non-malignant disorders. As HSCT and supportive care technologies improve, this life-saving treatment may be offered to more and more patients. With the development of new preparative regimens, expanded alternative donor availability, and graft manipulation techniques, there are many options when choosing the best regimen for patients. Herein the authors review transplant considerations, transplant goals, conditioning regimens, donor choice, and graft manipulation strategies for patients with non-malignant disorders undergoing HSCT.

Tailored treatments in inborn errors of immunity associated with atopy (IEIs-A) with skin involvement

Inborn errors of immunity associated with atopy (IEIs-A) are a group of inherited monogenic disorders that occur with immune dysregulation and frequent skin involvement. Several pathways are involved in the pathogenesis of these conditions, including immune system defects, alterations of skin barrier and metabolism perturbations. Current technological improvements and the higher accessibility to genetic testing, recently allowed the identification of novel molecular pathways involved in IEIs-A, also informing on potential tailored therapeutic strategies. Compared to other systemic therapy for skin diseases, biologics have the less toxic and the best tolerated profile in the setting of immune dysregulation. Here, we review IEIs-A with skin involvement focusing on the tailored therapeutic approach according to their pathogenetic mechanism.

Frontier and hotspot evolution in Wiskott-Aldrich syndrome: A bibliometric analysis from 2001 to 2021

BACKGROUND

Wiskott-Aldrich syndrome (WAS) is a rare X-linked primary immunodeficiency disorder. Despite our enormous progress in the strategies used to diagnose, treat, and cure WAS, no bibliometric studies have been performed in this research field. This study explored the trends in WAS research through a bibliometric analysis evaluating relevant literature quantitatively and qualitatively.

METHODS

The literature concerning WAS from 2001 to 2021 was retrieved from the Science Citation Index Expanded (SCI-expanded) of the Web of Science Core Collection database. Acquired data were then visually analyzed using CiteSpace and VOSviewer.

RESULTS

2036 papers were included in the final analysis. The annual publication outputs reached its peak in 2013 but declined in recent years. The dominant position of the United States in WAS research was quite obvious. Harvard University (USA), University College London (UK), and Inserm (France) were the three most prolific institutions. Adrian J. Thrasher exerted significant publication impact and made the most notable contributions in the field of WAS. Blood was the most influential journal with the highest publication outputs, and nearly all the top 10 journals and co-cited journals belonged to Q1. Immune dysregulation, thrombocytopenia, syndrome protein deficiency, stem cell, mutation, and diagnosis were the keywords with the strongest citation burst.

CONCLUSION

From 2001 to 2021, the United States was a global leader in the WAS research. Collaboration between countries and institutions is expected to deepen and strengthen in the future. Research hotspots included pathogenesis, clinical manifestations, diagnosis, and therapy. Our results suggest a greater understanding of the mechanistic underpinnings of immune dysfunction in WAS patients, the application of targeted therapies for individual complications, and the development of curative approaches, which will remain research hotspots in the future.

Genome editing for primary immunodeficiencies: A therapeutic perspective on Wiskott-Aldrich syndrome

Primary immunodeficiency diseases (PIDs) are a group of rare inherited disorders affecting the immune system that can be conventionally treated with allogeneic hematopoietic stem cell transplantation and with experimental autologous gene therapy. With both approaches still facing important challenges, gene editing has recently emerged as a potential valuable alternative for the treatment of genetic disorders and within a relatively short period from its initial development, has already entered some landmark clinical trials aimed at tackling several life-threatening diseases. In this review, we discuss the progress made towards the development of gene editing-based therapeutic strategies for PIDs with a special focus on Wiskott - Aldrich syndrome and outline their main challenges as well as future directions with respect to already established treatments.

Treatment of inherited thrombocytopenias

The new techniques of genetic analysis have made it possible to identify many new forms of inherited thrombocytopenias (IT) and study large series of patients. In recent years, this has changed the view of IT, highlighting the fact that, in contrast to previous belief, most patients have a modest bleeding diathesis. On the other hand, it has become evident that some of the mutations responsible for platelet deficiency predispose the patient to serious, potentially life-threatening diseases. Today's vision of IT is, therefore, very different from that of the past and the therapeutic approach must take these changes into account while also making use of the new therapies that have become available in the meantime. This review, the first devoted entirely to IT therapy, discusses how to prevent bleeding in those patients who are exposed to this risk, how to treat it if it occurs, and how to manage the serious illnesses to which patients with IT may be predisposed.