Hematopoietic stem-cell transplantation for the treatment of severe combined immunodeficiency

Prediction of Viable CD34 Count in Harvested Product by Peripheral Blood Hematopoietic Progenitor Count of Automated Hematology Analyzer Undergoing Hematopoietic Stem Cell Transplantation

Introduction

The CD34+ hematopoietic cell count was used to define cell harvest goals. Successful peripheral blood stem cell transplantation depends on infusion of an appropriate number of HPCs to achieve rapid and durable hematologic recovery.

Purpose

In this study, we evaluated the use of the Hematopoietic Progenitor Cell count program on the Sysmex XN-3000 hematology analyzer as an effective parameter for enumerating CD34+ cells.

Patients and Methods

Whole blood samples from 144 subjects who are either healthy donors or patients scheduled to undergo peripheral blood stem cell collection were collected and hemopoietic stem cells were quantified using CD34 cell enumeration by flow cytometry and XN-HPC by hematology analyzer.

Results

The correlation between the two methods was high (r = 0.766; 95% CI: 0.702-0.818). Passing-Bablok showed an intercept at 3.45 (2.54 to 4.74) with a slope of 0.78 (95% CI 0.69 to 0.89). Residual analysis of this model indicated no significant deviation from linearity (p = 0.360). The receiver operating characteristic curve demonstrated an area under curve to be 0.88 (0.82 to 0.92), with a positive predictive value of 80.3%. The correlation between CD34+ and XN-HPC showed a strong relationship and good agreement with minimal bias.

Conclusion

The XN-HPC showed good analytical performance. With the increasing requirements for stem cell transplantation, a technically simple and rapid alternative for stem cell enumeration that is sustainable is highly useful.

Opening SCID newborn screening for novel exon genetic variants through whole-exome sequencing in China

BACKGROUND

Severe combined immunodeficiency (SCID) is the most fatal form of inherited primary immunodeficiency disease. Known molecular defect mutations occur in most children with SCID.

METHODS

Herein, we report Adenosine Deaminase-SCID (ADA-SCID) using whole-exome sequencing (WES), explore exome mutational landscape and significance for 17 SCID samples, and verify the mutated exon genes using the Gene Expression Omnibus (GEO) datasets. A total of 250 patients, who were hospitalized at the Neonatal Intensive Care Unit (NICU) of The Seventh Medical Center of the PLA General Hospital for 3 years (from 2017 to 2020), were screened for SCID. We collected mutated genes from the WES data of 17 SCID children. GSE609 and GSE99176 cohorts were used to identify the expressions of mutated exon genes and molecular features in SCID. Gene set variation analyses (GSVA) and correlation analyses were performed.

RESULTS

The detection rate with approximately 6.8 % (17/250) of SCID is high in the NICU. A total of 16 genes were identified among 17 SCID samples, of which the Top 2 genes (MUC6 and RP11-683L23.1) might be crucial in the progression of SCID with 94 % mutation frequency. Furthermore, CNN2 and SCGB1C1 had significant co-mutations and may cooperate to affect SCID development. Importantly, the phylogenetic tree classification results of 17 SCID samples are more correlated to MUC6 with the most significant mutations. Expression profiles of seven mutated genes and five mutated genes were documented in GSE609 and GSE99176 cohorts based on microarray, respectively. Several immune-related pathways were significantly enriched, and Foxd4, differing from the other four mutated genes, was inversely correlated with the GSVA-enriched pathway.

CONCLUSION

Due to its high detection rate (6.8%) and fatality rate (100%), the inclusion of SCID in newborn screening (NBS) is urgent for children in China. The WES successfully identified several common exonic variants (e.g., MUC6) and depicted the feature of mutations and evolution, which will help develop new diagnostic methods for SCID.

Haploidentical HSCT in the Treatment of Pediatric Hematological Disorders

Allogeneic hematopoietic stem cell transplantation has become a treatment option for otherwise non-curative conditions, both malignant and benign, affecting children and adults. Nevertheless, the latest research has been focusing extensively on transplantation from related and unrelated haploidentical donors, suitable for patients requiring emergent hematopoietic stem cell transplantation (HSCT) in the absence of an HLA-matched donor. Haploidentical HSCT (haplo-HSCT) can be an effective treatment for non-malignant pediatric disorders, such as primary immunodeficiencies or hemoglobinopathies, by enabling a much quicker selection of the appropriate donor for virtually all patients, low incidence of graft-versus-host disease (GVHD), and transplant-related mortality (TRM). Moreover, the outcomes of haplo-HSCT among children with hematological malignancies have improved radically. The most demanding tasks for clinicians are minimizing T-cell-mediated alloreactivity as well as early GVHD prevention. As a result, several T-cell depletion approaches, such as ex vivo T-cell depletion (TCD), and T-cell replete approaches, such as a combination of anti-thymocyte globulin (ATG), post-transplantation cyclophosphamide (PTCy), cyclosporine/tacrolimus, mycophenolate mofetil, or methotrexate, have been taken up. As more research is needed to establish the most beneficial form of therapy, haplo-HSCT is currently considered an alternative donor strategy for pediatric and adult patients with complications like viral and bacterial infections, invasive fungal disease, and GVHD.

Uncertainties experienced by parents of children diagnosed with severe combined immunodeficiency through newborn screening

Individuals with severe combined immunodeficiency (SCID), a group of rare, genetic conditions, are at risk for life-threatening illnesses unless diagnosed and treated early. Even after early identification through newborn screening, parents of children with SCID embark on a complex journey marked by a variety of informational and emotional support needs. This paper explored the types of uncertainties experienced by parents of a child with SCID diagnosed through newborn screening. We conducted semi-structured interviews with 26 parents to discuss the types of uncertainty experienced, including scientific, practical, personal, and existential. Each interview was recorded, transcribed, and coded. Using deductive and inductive content analysis, we describe the type of uncertainty experienced across each stage of the SCID journey. We found that uncertainties in the SCID journey were chronic and multifaceted. Some uncertainties were more prominent at certain points of the journey whereas others spanned multiple stages. Parents expressed a variety of negative emotional reactions to uncertainty, from anxiety, worry, and fear, to doubt, guilt, or grief, and even anger, frustration, and depression. The results speak to the need for healthcare providers to prepare parents for the SCID journey by providing resources to help manage and cope with uncertainty.

CRISPR/Cas9-Based Disease Modeling and Functional Correction of Interleukin 7 Receptor Alpha Severe Combined Immunodeficiency in T-Lymphocytes and Hematopoietic Stem Cells

Interleukin 7 Receptor alpha Severe Combined Immunodeficiency (IL7R-SCID) is a life-threatening disorder caused by homozygous mutations in the IL7RA gene. Defective IL7R expression in humans hampers T cell precursors' proliferation and differentiation during lymphopoiesis resulting in the absence of T cells in newborns, who succumb to severe infections and death early after birth. Previous attempts to tackle IL7R-SCID by viral gene therapy have shown that unregulated IL7R expression predisposes to leukemia, suggesting the application of targeted gene editing to insert a correct copy of the IL7RA gene in its genomic locus and mediate its physiological expression as a more feasible therapeutic approach. To this aim, we have first developed a CRISPR/Cas9-based IL7R-SCID disease modeling system that recapitulates the disease phenotype in primary human T cells and hematopoietic stem and progenitor cells (HSPCs). Then, we have designed a knockin strategy that targets IL7RA exon 1 and introduces through homology-directed repair a corrective, promoterless IL7RA cDNA followed by a reporter cassette through AAV6 transduction. Targeted integration of the corrective cassette in primary T cells restored IL7R expression and rescued functional downstream IL7R signaling. When applied to HSPCs further induced to differentiate into T cells in an Artificial Thymic Organoid system, our gene editing strategy overcame the T cell developmental block observed in IL7R-SCID patients, while promoting full maturation of T cells with physiological and developmentally regulated IL7R expression. Finally, genotoxicity assessment of the CRISPR/Cas9 platform in HSPCs using biased and unbiased technologies confirmed the safety of the strategy, paving the way for a new, efficient, and safe therapeutic option for IL7R-SCID patients.

Reducing Mortality and Morbidity in Children with Severe Combined Immunodeficiency in Switzerland: the Role of Newborn Screening

Newborn screening (NBS) for severe combined immunodeficiency (SCID) has been introduced in various countries with the aim of reducing morbidity and mortality. However, studies analyzing outcomes before and after the implementation of NBS programs remain limited. This study sought to compare the outcomes of SCID patients identified through Switzerland's national SCID NBS program, introduced in January 2019, with those of a historical cohort diagnosed between 2007 and 2019. The study included seven patients (32%) identified through NBS, and 15 (68%) born before NBS implementation and diagnosed based on clinical signs. Children in the NBS group were younger at diagnosis (median age 9 days vs 9 months, P = .002) and at hematopoietic stem cell transplantation (HSCT, median age 5 months vs 11 months, P = .003) compared to the clinical group. The NBS group had a lower incidence of infections before HSCT (29% vs 93%, P = .004). Although not statistically significant, the overall survival rate on last follow-up was higher in the NBS group (86% vs 67%, P = .62). Importantly, patients with active infections undergoing HSCT had a significantly lower overall survival probability compared to those without (P = .01). In conclusion, the introduction of NBS in Switzerland has led to earlier and often asymptomatic diagnosis of affected children, enabling timely intervention, infection prevention, and prompt treatment. These factors have contributed to higher survival rates in the NBS group. These findings underscore the critical importance of NBS for SCID, offering potential life-saving benefits through early detection and intervention.

Severe Combined Immunodeficiency (SCID) and Its New Treatment Modalities

Severe combined immunodeficiency (SCID) is a rare condition with very high mortality. SCID is mainly caused by the multiple mutations of genes affecting the entire immune cells. Children with this disease are born with an impaired immune system. The child appears healthy but the consequences of the impaired immune system lead to various secondary infections such as meningeal infections and respiratory infections further leading to consolidation, diarrhea, inflammation of skin and other systemic diseases. Severe combined immunodeficiency is also known as "bubble boy disease" or "living in the bubble" syndrome, as in early days for treatment the physicians decided to completely isolate them until they got the perfect match for the bone marrow transplantation. It is one of the pediatric emergencies and is to be treated as soon as possible. SCID involves multiple genes which leads to makes diagnosis of the disease cumbersome. In early years many infants were diagnosed almost after half a year and in severe conditions which led to the decrease in the survival rate of the children. But now due to advanced newborn screening modalities and other monitoring systems it can be diagnosed as early as within three months of age. The various treatment modalities include hematopoietic stem cell transplantation, gene therapy, enzyme replacement therapy and chemotherapy. This narrative review article describes about the severe combined immunodeficiency and its newer treatment modalities.

Nanobody-derived bispecific CAR-T cell therapy enhances the anti-tumor efficacy of T cell lymphoma treatment

T cell lymphoma (TCL) is a highly heterogeneous group of diseases with a poor prognosis and low 5-year overall survival rate. The current therapeutic regimens have relatively low efficacy rates. Clinical studies of single-target chimeric antigen receptor T cell (CAR-T cell) therapy in T lymphocytes require large and multiple infusions, increasing the risks and cost of treatment; therefore, optimizing targeted therapy is a way to improve overall prognosis. Despite significant advances in bispecific CAR-T cell therapy to avoid antigen escape in treatment of B cell lymphoma, applying this strategy to TCL requires further investigation. Here, we constructed an alpaca nanobody (Nb) phage library and generated high-affinity and -specificity Nbs targeting CD30 and CD5, respectively. Based on multiple rounds of screening, bispecific NbCD30-CD5-CAR T cells were constructed, and their superior anti-tumor effect against TCL was validated in vitro and in vivo. Our findings demonstrated that Nb-derived bispecific CAR-T cells significantly improved anti-tumor efficacy in TCL treatment compared with single-target CAR-T cells and bispecific single chain variable fragment (scFv)-derived CAR-T cells. Because Nbs are smaller and less immunogenic, the synergistic effect of Nb-based bispecific CAR-T cells may improve their safety and efficacy in future clinical applications.

The impact of Treosulfan-based conditioning for inborn errors of immunity: Is dose monitoring crucial?

INTRODUCTION

In children with inborn errors of immunity (IEI) who will receive a hematopoietic stem cell transplant (HSCT) treosulfan-based conditioning is currently preferred. The aim of this study was to investigate early and late outcomes in pediatric IEI patients receiving pre-HSCT treosulfan and to examine the effect of treosulfan dose monitoring on outcomes.

METHODS

Seventy-three pediatric patients receiving this management between 2015 and 2022 were included.

RESULTS

Overall survival rate was 80%, and event-free survival was 67.8%. A larger treosulfan dose AUC after first application increased the rate of early toxicity (p = .034) and slowed lymphocyte engraftment (r = .290; p = .030). Underlying disease, treosulfan AUC, donor type, stem cell type, number of immunosuppressive agents, the dose of anti-thymocyte globulin, and post-transplantation cyclophosphamide did not to increase risk of acute graft-versus-host disease. The risk of mixed chimerism (MC) in patients with autoimmune lymphoproliferative syndrome and leukocyte adhesion deficiency were higher than those with severe combined immunodeficiency (p = .021 and p = .014, respectively). The risk of MC was lower in those receiving peripheral blood stem cells (SC) compared with bone marrow derived SC (OR = .204, p = .022).

CONCLUSION

The AUC of the treosulfan dose was not associated with poorer late outcomes. Treosulfan is an agent that can be used safely in the IEI patient group,  level measurement appears essential to identify early toxicities. Prospective studies with more extended follow-up periods are needed.

Measuring the effect of newborn screening on survival after haematopoietic cell transplantation for severe combined immunodeficiency: a 36-year longitudinal study from the Primary Immune Deficiency Treatment Consortium

BACKGROUND

Severe combined immunodeficiency (SCID) is fatal unless durable adaptive immunity is established, most commonly through allogeneic haematopoietic cell transplantation (HCT). The Primary Immune Deficiency Treatment Consortium (PIDTC) explored factors affecting the survival of individuals with SCID over almost four decades, focusing on the effects of population-based newborn screening for SCID that was initiated in 2008 and expanded during 2010-18.

METHODS

We analysed transplantation-related data from children with SCID treated at 34 PIDTC sites in the USA and Canada, using the calendar time intervals 1982-89, 1990-99, 2000-09, and 2010-18. Categorical variables were compared by χ2 test and continuous outcomes by the Kruskal-Wallis test. Overall survival was estimated by the Kaplan-Meier method. A multivariable analysis using Cox proportional hazards regression models examined risk factors for HCT outcomes, including the variables of time interval of HCT, infection status and age at HCT, trigger for diagnosis, SCID type and genotype, race and ethnicity of the patient, non-HLA-matched sibling donor type, graft type, GVHD prophylaxis, and conditioning intensity.

FINDINGS

For 902 children with confirmed SCID, 5-year overall survival remained unchanged at 72%-73% for 28 years until 2010-18, when it increased to 87% (95% CI 82·1-90·6; n=268; p=0·0005). For children identified as having SCID by newborn screening since 2010, 5-year overall survival was 92·5% (95% CI 85·8-96·1), better than that of children identified by clinical illness or family history in the same interval (79·9% [69·5-87·0] and 85·4% [71·8-92·8], respectively [p=0·043]). Multivariable analysis demonstrated that the factors of active infection (hazard ratio [HR] 2·41, 95% CI 1·56-3·72; p<0·0001), age 3·5 months or older at HCT (2·12, 1·38-3·24; p=0·001), Black or African-American race (2·33, 1·56-3·46; p<0·0001), and certain SCID genotypes to be associated with lower overall survival during all time intervals. Moreover, after adjusting for several factors in this multivariable analysis, HCT after 2010 no longer conveyed a survival advantage over earlier time intervals studied (HR 0·73, 95% CI 0·43-1·26; p=0·097). This indicated that younger age and freedom from infections at HCT, both directly driven by newborn screening, were the main drivers for recent improvement in overall survival.

INTERPRETATION

Population-based newborn screening has facilitated the identification of infants with SCID early in life, in turn leading to prompt HCT while avoiding infections. Public health programmes worldwide can benefit from this definitive demonstration of the value of newborn screening for SCID.

FUNDING

National Institute of Allergy and Infectious Diseases, Office of Rare Diseases Research, and National Center for Advancing Translational Sciences.

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.

Early Is the Key for Treatment of Severe Combined Immunodeficiency

This Pillars of Immunology article is a commentary on “Hematopoietic stem cell transplantation for severe combined immunodeficiency in the neonatal period leads to superior thymic output and improved survival,” a pivotal article written by L. A. Myers, D. D. Patel, J. M. Puck, and R. H. Buckley, and published in Blood, in 2002. https://pubmed.ncbi.nlm.nih.gov/11806989/.

Blocking common γ chain cytokine signaling ameliorates T cell-mediated pathogenesis in disease models

The common γ chain (γc; IL-2RG) is a subunit of the interleukin (IL) receptors for the γc cytokines IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21. The lack of appropriate neutralizing antibodies recognizing IL-2RG has made it difficult to thoroughly interrogate the role of γc cytokines in inflammatory and autoimmune disease settings. Here, we generated a γc cytokine receptor antibody, REGN7257, to determine whether γc cytokines might be targeted for T cell-mediated disease prevention and treatment. Biochemical, structural, and in vitro analysis showed that REGN7257 binds with high affinity to IL-2RG and potently blocks signaling of all γc cytokines. In nonhuman primates, REGN7257 efficiently suppressed T cells without affecting granulocytes, platelets, or red blood cells. Using REGN7257, we showed that γc cytokines drive T cell-mediated disease in mouse models of graft-versus-host disease (GVHD) and multiple sclerosis by affecting multiple aspects of the pathogenic response. We found that our xenogeneic GVHD mouse model recapitulates hallmarks of acute and chronic GVHD, with T cell expansion/infiltration into tissues and liver fibrosis, as well as hallmarks of immune aplastic anemia, with bone marrow aplasia and peripheral cytopenia. Our findings indicate that γc cytokines contribute to GVHD and aplastic anemia pathology by promoting these characteristic features. By demonstrating that broad inhibition of γc cytokine signaling with REGN7257 protects from immune-mediated disorders, our data provide evidence of γc cytokines as key drivers of pathogenic T cell responses, offering a potential strategy for the management of T cell-mediated diseases.

Multiplex HDR for disease and correction modeling of SCID by CRISPR genome editing in human HSPCs

Severe combined immunodeficiency (SCID) is a group of disorders caused by mutations in genes involved in the process of lymphocyte maturation and function. CRISPR-Cas9 gene editing of the patient's own hematopoietic stem and progenitor cells (HSPCs) ex vivo could provide a therapeutic alternative to allogeneic hematopoietic stem cell transplantation, the current gold standard for treatment of SCID. To eliminate the need for scarce patient samples, we engineered genotypes in healthy donor (HD)-derived CD34⁺ HSPCs using CRISPR-Cas9/rAAV6 gene-editing, to model both SCID and the therapeutic outcomes of gene-editing therapies for SCID via multiplexed homology-directed repair (HDR). First, we developed a SCID disease model via biallelic knockout of genes critical to the development of lymphocytes; and second, we established a knockin/knockout strategy to develop a proof-of-concept single-allelic gene correction. Based on these results, we performed gene correction of RAG2-SCID patient-derived CD34⁺ HSPCs that successfully developed into CD3⁺ T cells with diverse TCR repertoires in an in vitro T cell differentiation platform. In summary, we present a strategy to determine the optimal configuration for CRISPR-Cas9 gene correction of SCID using HD-derived CD34⁺ HSPCs, and the feasibility of translating this gene correction approach in patient-derived CD34⁺ HSPCs.

Review of Treatment for Adenosine Deaminase Deficiency (ADA) Severe Combined Immunodeficiency (SCID)

Adenosine deaminase deficiency (ADA) is a purine salvage pathway deficiency that results in buildup of toxic metabolites causing death in rapidly dividing cells, especially lymphocytes. The most complete form of ADA leads to severe combined immune deficiency (SCID). Treatment with enzyme replacement therapy (ERT) was developed in the 1970s and became the treatment for ADA SCID by the 1980s. It remains an option for some infants with SCID, and a stopgap measure for others awaiting curative therapy. For some infants with ADA SCID who have matching family donors hematopoietic stem cell transplant (HSCT) is an option for cure. Gene therapy for ADA SCID, approved in some countries and in trials in others, is becoming possible for more infants with this disorder. This review covers the history of ADA SCID, the treatment options to date and particularly the history of the development of gene therapy for ADA SCID and the current state of the risks and benefits of the gene therapy option.

Experimental and clinical progress of in utero hematopoietic cell transplantation therapy for congenital disorders

In utero hematopoietic cell transplantation (IUHCT) is considered a potentially efficient therapeutic approach with relatively few side effects, compared to adult hematopoietic cell transplantation, for various hematological genetic disorders. The principle of IUHCT has been extensively studied in rodent models and in some large animals with close evolutionary similarities to human beings. However, IUHCT has only been used to rebuild human T cell immunity in certain patients with inherent immunodeficiencies. This review will first summarize the animal models utilized for IUHCT investigations and describe the associated outcomes. Recent advances and potential barriers for successful IUHCT are discussed, followed by possible strategies to overcome these barriers experimentally. Lastly, we will outline the progress made towards utilizing IUHCT to treat inherent disorders for patients, list out associated limitations and propose feasible means to promote the efficacy of IUHCT clinically.

Outcomes following treatment for ADA-deficient severe combined immunodeficiency: a report from the PIDTC

Adenosine deaminase (ADA) deficiency causes ∼13% of cases of severe combined immune deficiency (SCID). Treatments include enzyme replacement therapy (ERT), hematopoietic cell transplant (HCT), and gene therapy (GT). We evaluated 131 patients with ADA-SCID diagnosed between 1982 and 2017 who were enrolled in the Primary Immune Deficiency Treatment Consortium SCID studies. Baseline clinical, immunologic, genetic characteristics, and treatment outcomes were analyzed. First definitive cellular therapy (FDCT) included 56 receiving HCT without preceding ERT (HCT); 31 HCT preceded by ERT (ERT-HCT); and 33 GT preceded by ERT (ERT-GT). Five-year event-free survival (EFS, alive, no need for further ERT or cellular therapy) was 49.5% (HCT), 73% (ERT-HCT), and 75.3% (ERT-GT; P < .01). Overall survival (OS) at 5 years after FDCT was 72.5% (HCT), 79.6% (ERT-HCT), and 100% (ERT-GT; P = .01). Five-year OS was superior for patients undergoing HCT at <3.5 months of age (91.6% vs 68% if ≥3.5 months, P = .02). Active infection at the time of HCT (regardless of ERT) decreased 5-year EFS (33.1% vs 68.2%, P < .01) and OS (64.7% vs 82.3%, P = .02). Five-year EFS (90.5%) and OS (100%) were best for matched sibling and matched family donors (MSD/MFD). For patients treated after the year 2000 and without active infection at the time of FDCT, no difference in 5-year EFS or OS was found between HCT using a variety of transplant approaches and ERT-GT. This suggests alternative donor HCT may be considered when MSD/MFD HCT and GT are not available, particularly when newborn screening identifies patients with ADA-SCID soon after birth and before the onset of infections. This trial was registered at www.clinicaltrials.gov as #NCT01186913 and #NCT01346150.

Newborn Tandem Mass Spectroscopy Screening for Adenosine Deaminase Deficiency-First Two Years' Experience

BACKGROUND

Newborn screening (NBS) via T-cell receptor excision circles (TREC) is now universal in the United States, Puerto Rico, and the Navajo Nation as a strategy to identify severe combined immunodeficiency (SCID) in newborns. Due to the characteristics of adenosine deaminase (ADA) deficiency, small but significant number of cases can be missed by this screening.

OBJECTIVE

To evaluate the results of the first year of statewide NBS for ADA via dried blood spot newborn screening.

METHODS

On October 7, 2019, the state of Michigan began screening newborn dried blood spots for ADA deficiency via the Neobase-2 tandem mass spectroscopy (TMS) kit. We report one known case of ADA deficiency in the 18 months prior to screening. We then reviewed the results of the first two years of TMS ADA screening in Michigan.

RESULTS

There was one ADA deficient patient known to our centers in the 18 months before initiation of TMS ADA screening, this patient died of complications of their disease. In the first two years of TMS ADA NBS, 206,321 infants were screened, and two patients had positive ADA screens. Both patients had ADA deficiency confirmed through biochemical and genetic testing. One patient identified also had a positive TREC screen and was confirmed to have ADA SCID.

CONCLUSION

In our first two years, TMS NBS for ADA deficiency identified two patients with ADA deficiency at negligible cost; including one patient who would not have been identified by TREC NBS. This report provides initial evidence of the value of specific NBS for ADA deficiency.

Emerging approaches to improve allogeneic hematopoietic cell transplantation outcomes for nonmalignant diseases

Many congenital or acquired nonmalignant diseases (NMDs) of the hematopoietic system can be potentially cured by allogeneic hematopoietic cell transplantation (HCT) with varying types of donor grafts, degrees of HLA matching, and intensity of conditioning regimens. Unique features that distinguish the use of allogeneic HCT in this population include higher rates of graft failure, immune-mediated cytopenias, and the potential to achieve long-term disease-free survival in a mixed chimerism state. Additionally, in contrast to patients with hematologic malignancies, a priority is to completely avoid graft-versus-host disease in patients with NMD because there is no theoretical beneficial graft-versus-leukemia effect that can accompany graft-versus-host responses. In this review, we discuss the current approach to each of these clinical issues and how emerging novel therapeutics hold promise to advance transplant care for patients with NMDs.

Defects in mucosal immunity and nasopharyngeal dysbiosis in HSC-transplanted SCID patients with IL2RG/JAK3 deficiency

Both innate and adaptive lymphocytes have critical roles in mucosal defense that contain commensal microbial communities and protect against pathogen invasion. Here we characterize mucosal immunity in patients with severe combined immunodeficiency (SCID) receiving hematopoietic stem cell transplantation (HSCT) with or without myeloablation. We confirmed that pretransplant conditioning had an impact on innate (natural killer and innate lymphoid cells) and adaptive (B and T cells) lymphocyte reconstitution in these patients with SCID and now show that this further extends to generation of T helper 2 and type 2 cytotoxic T cells. Using an integrated approach to assess nasopharyngeal immunity, we identified a local mucosal defect in type 2 cytokines, mucus production, and a selective local immunoglobulin A (IgA) deficiency in HSCT-treated SCID patients with genetic defects in IL2RG/GC or JAK3. These patients have a reduction in IgA-coated nasopharyngeal bacteria and exhibit microbial dysbiosis with increased pathobiont carriage. Interestingly, intravenous immunoglobulin replacement therapy can partially normalize nasopharyngeal immunoglobulin profiles and restore microbial communities in GC/JAK3 patients. Together, our results suggest a potential nonredundant role for type 2 immunity and/or of local IgA antibody production in the maintenance of nasopharyngeal microbial homeostasis and mucosal barrier function.

Long-Term Clinical Outcomes of Severe Combined Immunodeficiency Patients Given Nonablative Marrow Transplants

BACKGROUND

Severe combined immunodeficiency (SCID) is a syndrome characterized by profound T-cell deficiency that is universally fatal in infancy unless immune reconstitution is achieved by hematopoietic stem cell transplantation, gene therapy, or enzyme replacement. Published long-term clinical follow-up is limited for transplanted patients with SCID.

OBJECTIVE

To characterize the long-term outcomes of patients with SCID treated at a single center.

METHODS

We examined the clinical outcomes of 177 successive SCID infants given allogeneic bone marrow over 38 years without pretransplant chemotherapy or post-transplant graft-versus-host disease prophylaxis. A total of 90% received T-cell-depleted haploidentical parental marrow. Clinical status was assessed by questionnaires delivered by mail or electronically. Molecular type of SCID, demographics, and type, date and age of transplant were obtained from a database.

RESULTS

Eighty-eight questionnaires were completed for survivors ranging in age from 2 to 38 years. Survival remained higher in those transplanted before 3.5 months of age. Half of the cohort remained on immunoglobulin replacement. Health conditions reported included rashes, anxiety, depression, warts, and mouth ulcers. Most reported that these were transient, self-resolving issues. Attention-deficit/hyperactivity disorder, warts, and learning disabilities were reportedly more prevalent than in the general population. Most reported having no active concerns about their health. We found substantial scholastic achievement, with half of adult patients reporting college attendance. Most patients had a healthy body mass index.

CONCLUSIONS

Overall, our findings are consistent with those in the last update in 2009 in this population. Age at transplant remains a key variable in survival.

Analysis of the TREC and KREC Levels in the Dried Blood Spots of Healthy Newborns with Different Gestational Ages and Weights

Inborn errors of immunity can be detected by evaluating circular DNA (cDNA) fragments of T- and B-cell receptors (TREC and KREC) resulting from the receptor gene rearrangement in T and B cells. Maturation and activation of the fetal immune system is known to proceed gradually according to the gestational age, which highlights the importance of the immune status in premature infants at different gestational ages. In this article, we evaluated TREC and KREC levels in infants of various gestational ages by real-time PCR with taking into account the newborn’s weight and sex. The 95% confidence intervals for TREC and KREC levels (expressed in the number of cDNA copies per 105 cells) were established for different gestational groups. The importance of studying immune system development in newborns is informed by the discovered dependence of the level of naive markers on the gestational stage in the early neonatal period.

T-cell depleted haploidentical hematopoietic cell transplantation for pediatric malignancy

Access to allogenic hematopoietic cell transplantation (HCT), a potentially curative treatment for chemotherapy-resistant hematologic malignancies, can be limited if no human leukocyte antigen (HLA) identical related or unrelated donor is available. Alternative donors include Cord Blood as well as HLA-mismatched unrelated or related donors. If the goal is to minimize the number of HLA disparities, partially matched unrelated donors are more likely to share 8 or 9 of 10 HLA alleles with the recipient. However, over the last decade, there has been success with haploidentical HCT performed using the stem cells from HLA half-matched related donors. As the majority of patients have at least one eligible and motivated haploidentical donor, recruitment of haploidentical related donors is frequently more rapid than of unrelated donors. This advantage in the accessibility has historically been offset by the increased risks of graft rejection, graft-versus-host disease and delayed immune reconstitution. Various ex vivo T-cell depletion (TCD) methods have been investigated to overcome the immunological barrier and facilitate immune reconstitution after a haploidentical HCT. This review summarizes historical and contemporary clinical trials of haploidentical TCD-HCT, mainly in pediatric malignancy, and describes the evolution of these approaches with a focus on serial improvements in the kinetics of immune reconstitution. Methods of TCD discussed include in vivo as well as ex vivo positive and negative selection. In addition, haploidentical TCD as a platform for post-HCT cellular therapies is discussed. The present review highlights that, as a result of the remarkable progress over half a century, haploidentical TCD-HCT can now be considered as a preferred alternative donor option for children with hematological malignancy in need of allogeneic HCT.

Primary immunodeficiencies: HSCT experiences of a single center in Turkey

BACKGROUND

Primary immunodeficiency diseases (PID) are characterized by the occurrence of frequent infections and are caused by many genetic defects. Hematopoietic stem cell transplantation (HSCT) is the only curative treatment option for the majority of PID. As a Pediatric Hematology-Oncology-Immunology Transplantation Unit, we wanted to present our HSCT experience regarding treatment of primary immunodeficiency diseases.

METHODS

58 patients were included in the study between January 2014 and June 2019. We searched 9/10 or 10/10 matched-related donor (MRD) firstly, in the absence of fully matched-related donor. We screened matched unrelated donor (MUD) from donor banks. MRD was used in 24 (41.3%) patients, MUD in 20 (34.4%) patients, and haploidentical donors in 14 (24.1%) patients. Demographic data, HSCT characteristics, and outcome were evaluated. While 16 patients had severe combined immunodeficiency (SCID), the remaining was non-SCID.

RESULTS

Of the 58 patients, 38 were male and 20 were female. Median age at transplantation was 12 months (range: 2.5-172 months). Combined immunodeficiencies consisted 67.2% of patients. Mean follow-up time was 27 months (6 months-5 years). Median neutrophil, lymphocyte, and thrombocyte engraftment days were similar in comparison of both donor type and stem cell source. The most common complication was acute GvHD in 15 (25.8%) patients. In total, five patients (31%) belonging to the SCID group and 10 patients (23.8%) belonging to the non-SCID group died. Our total mortality rate was 15 (25.8%) in all patients.

CONCLUSIONS

We would like to present our HSCT experiences as a pediatric immunology transplantation center. Existing severe infections before transplantation period, BCGitis, and CMV are important issues of transplantation in Turkey. However, the follow-up time is shorter than some studies, our results regarding complications and survival are similar to previous reports.

Long-term outcomes after gene therapy for adenosine deaminase severe combined immune deficiency

Patients lacking functional adenosine deaminase activity have severe combined immunodeficiency (ADA SCID), which can be treated with ADA enzyme replacement therapy (ERT), allogeneic hematopoietic stem cell transplantation (HSCT), or autologous HSCT with gene-corrected cells (gene therapy [GT]). A cohort of 10 ADA SCID patients, aged 3 months to 15 years, underwent GT in a phase 2 clinical trial between 2009 and 2012. Autologous bone marrow CD34+ cells were transduced ex vivo with the MND (myeloproliferative sarcoma virus, negative control region deleted, dl587rev primer binding site)-ADA gammaretroviral vector (gRV) and infused following busulfan reduced-intensity conditioning. These patients were monitored in a long-term follow-up protocol over 8 to 11 years. Nine of 10 patients have sufficient immune reconstitution to protect against serious infections and have not needed to resume ERT or proceed to secondary allogeneic HSCT. ERT was restarted 6 months after GT in the oldest patient who had no evidence of benefit from GT. Four of 9 evaluable patients with the highest gene marking and B-cell numbers remain off immunoglobulin replacement therapy and responded to vaccines. There were broad ranges of responses in normalization of ADA enzyme activity and adenine metabolites in blood cells and levels of cellular and humoral immune reconstitution. Outcomes were generally better in younger patients and those receiving higher doses of gene-marked CD34+ cells. No patient experienced a leukoproliferative event after GT, despite persisting prominent clones with vector integrations adjacent to proto-oncogenes. These long-term findings demonstrate enduring efficacy of GT for ADA SCID but also highlight risks of genotoxicity with gRVs. This trial was registered at www.clinicaltrials.gov as #NCT00794508.

CAR-T cell therapy in T-cell malignancies: Is success a low-hanging fruit?

Chimeric antigen receptor T-cell (CAR-T) therapy has been prosperous in the treatment of patients with various types of relapsed/refractory (R/R) B-cell malignancies including diffuse large B-cell lymphoma (DLBCL), B-cell acute lymphoblastic leukemia (B-ALL), follicular lymphoma (FL), mantle cell lymphoma (MCL), and multiple myeloma (MM). However, this type of therapy has faced serious hindrances in combating T-cell neoplasms. R/R T-cell malignancies are generally associated with poor clinical outcomes, and the available effective treatment approaches are very limited. CAR-T therapy of T-cell malignancies has unique impediments in comparison with that of B-cell malignancies. Fratricide, T-cell aplasia, and product contamination with malignant T cells when producing autologous CAR-Ts are the most important challenges of CAR-T therapy in T-cell malignancies necessitating in-depth investigations. Herein, we highlight the preclinical and clinical efforts made for addressing these drawbacks and also review additional potent stratagems that could improve CAR-T therapy in T-cell malignancies.

CAR-T cell therapy in T-cell malignancies: Is success a low-hanging fruit?

Chimeric antigen receptor T-cell (CAR-T) therapy has been prosperous in the treatment of patients with various types of relapsed/refractory (R/R) B-cell malignancies including diffuse large B-cell lymphoma (DLBCL), B-cell acute lymphoblastic leukemia (B-ALL), follicular lymphoma (FL), mantle cell lymphoma (MCL), and multiple myeloma (MM). However, this type of therapy has faced serious hindrances in combating T-cell neoplasms. R/R T-cell malignancies are generally associated with poor clinical outcomes, and the available effective treatment approaches are very limited. CAR-T therapy of T-cell malignancies has unique impediments in comparison with that of B-cell malignancies. Fratricide, T-cell aplasia, and product contamination with malignant T cells when producing autologous CAR-Ts are the most important challenges of CAR-T therapy in T-cell malignancies necessitating in-depth investigations. Herein, we highlight the preclinical and clinical efforts made for addressing these drawbacks and also review additional potent stratagems that could improve CAR-T therapy in T-cell malignancies.

Primary immunodeficiency diseases in the newborn

The normal neonate’s immune system is anatomically completed but antigenically inexperienced and shows somewhat decreased role of a number of immunological pathways. Aside from anatomic characteristics (e.g., thin skin and mucosal barriers) of newborn, weakened pro-inflammatory and T-helper cell type 1 cytokine release and lessened cell-mediated immunity predispose the neonate more susceptible to all types of infections. Furthermore, many types of primary immunodeficiency diseases (PIDs) that present in neonatal period are potentially life threatening. However, most of the newborns stand this period without sickness due to complete innate immunity with other adaptive immune system mechanisms and transferred maternal immunoglobulin G. Besides unique immunity of the preterm and normal newborns; risk factors, clinical features, and laboratory evaluation of most common PIDs in newborn are told in this article. The range of PIDs is growing, and the diagnosis and management of these disorders continues to increase in complexity. The most common PID types of the newborn including antibody deficiencies, cellular/combined immunodeficiencies, phagocytic diseases, complement deficiencies, and innate immune system and other disorders are briefly mentioned here as well.

Newborn Screening for SCID. Experience in Spain (Catalonia)

Newborn screening (NBS) for severe combined immunodeficiency (SCID) started in Catalonia in January-2017, being the first Spanish and European region to universally include this testing. In Spain, a pilot study with 5000 samples was carried out in Seville in 2014; also, a research project with about 35,000 newborns will be carried out in 2021-2022 in the NBS laboratory of Eastern Andalusia. At present, the inclusion of SCID is being evaluated in Spain. The results obtained in the first three and a half years of experience in Catalonia are presented here. All babies born between January-2017 and June-2020 were screened through TREC-quantification in DBS with the Enlite Neonatal TREC-kit from PerkinElmer. A total of 222,857 newborns were screened, of which 48 tested positive. During the study period, three patients were diagnosed with SCID: an incidence of 1 in 74,187 newborns; 17 patients had clinically significant T-cell lymphopenia (non-SCID) with an incidence of 1 in 13,109 newborns who also benefited from the NBS program. The results obtained provide further evidence of the benefits of early diagnosis and curative treatment to justify the inclusion of this disease in NBS programs. A national NBS program is needed, also to define the exact SCID incidence in Spain.

Alternative pathways for the development of lymphoid structures in humans

Lymphoid tissue inducer (LTi) cells are critical for inducing the differentiation of most secondary lymphoid organs (SLOs) in mice. In humans, JAK3 and γc deficiencies result in severe combined immunodeficiency (SCIDs) characterized by an absence of T cells, natural killer cells, innate lymphoid cells (ILCs), and presumably LTi cells. Some of these patients have undergone allogeneic stem cell transplantation (HSCT) in the absence of myeloablation, which leads to donor T cell engraftment, while other leukocyte subsets are of host origin. By using MRI to look for SLOs in nine of these patients 16 to 44 y after HSCT, we discovered that SLOs were exclusively found in the three areas of the abdomen that drain the intestinal tract. A postmortem examination of a child with γc-SCID who had died 3.5 mo after HSCT showed corticomedullary differentiation in the thymus, T cell zones in the spleen, and the appendix, but in neither lymph nodes nor Peyer patches. Tertiary lymphoid organs were observed in the lung. No RAR-related orphan receptor-positive LTi cells could be detected in the existing lymphoid structures. These results suggest that while LTi cells are required for the genesis of most SLOs in humans, SLO in the appendix and in gut-draining areas, as well as tertiary lymphoid organs, can be generated likely by LTi cell-independent mechanisms.

Neonatal Screening for SCID: The French Experience

After it was demonstrated in 2005 that T cell receptor excision circle (TREC) quantification for dried blood spot (DBS) samples on Guthrie cards is an effective means of SCID screening and following several pilot studies, the practice was formally recommended in the US in 2010. More and more countries have adopted it since then. In France, before the health authorities could recommend adding SCID to the list of five diseases that were routinely screened for, feasibility and cost-effectiveness studies had to be conducted with a sufficiently large cohort of neonates. We carried out three such studies: The first sought to verify the effectiveness of the assay. The second, DEPISTREC, evaluated the feasibility of universal SCID screening in France and assessed the clinical benefit and economic advantage it would provide. Through the third study, NeoSKID, still under way and to continue until recommendations are issued, we have been offering SCID screening in the Pays de la Loire region of France. This review briefly describes routine newborn screening (NBS) and management of primary immunodeficiency diseases (PIDs) in France, and then considers the lessons from our studies and the status of SCID screening implementation within the country.

Lifelong Immune Modulation Versus Hematopoietic Cell Therapy for Inborn Errors of Immunity

Advances in diagnosis of inborn errors of immunity (IEI) and an understanding of the molecular and immunologic mechanisms of these disorders have led to both the development of new therapies and improved approaches to hematopoietic cell transplantation (HCT). For example, monoclonal antibodies (mAbs) and small molecules, such as Janus tyrosine kinase inhibitors, that can modulate immunologic pathways have been designed for or repurposed for management of IEI. A better understanding of molecular mechanisms of IEI has led to use of drugs typically considered "immunosuppressive" to modulate the immune response, such as mammalian target of rapamycin inhibitors in disorders of phosphoinositide 3-kinase gain of function. Since the first HCT in a patient with severe combined immunodeficiency (SCID) in 1968, transplantation strategies have improved, with more than 90% probability of survival after allogeneic HCT in SCID and hence HCT is now the therapeutic standard for SCID and many other IEI. When tailoring treatment for IEI, multiple disease-specific and individual factors should be considered. In diseases such as SCID or agammaglobulinemia, the choice between HCT or medical management is straightforward. However, in many IEI, the choice between the options is challenging. This review focuses on the factors that should be taken into account in the quest for the optimal treatment for patients with IEI.

Fetal interventions for congenital renal anomalies

Congenital abnormalities of the kidney and urinary tract (CAKUT) represent 20% of prenatally diagnosed congenital abnormalities. Although the majority of these abnormalities do not require intervention either pre or postnatally, there is a subset of patients whose disease is so severe that it may warrant intervention prior to delivery to prevent morbidity and mortality. These cases consist of patients with moderate lower urinary tract obstruction (LUTO) in which vesicocentesis, shunting or cystoscopy are options and patients with early pregnancy renal anhydramnios (EPRA) in whom amnioinfusion therapy may be an option. The main causes of EPRA are congenital bilateral renal agenesis (CoBRA), cystic kidney disease (CKD) and severe LUTO. Untreated, EPRA is universally fatal secondary to anhydramnios induced pulmonary hypoplasia. The evidence regarding therapy for LUTO is limited and the stopped early PLUTO (Percutaneous Shunting in Lower Urinary Tract Obstruction) trial was unable to provide definitive answers about patient selection. Evidence for EPRA therapy is also scant. Serial amnioinfusions have shown promise in cases of EPRA due to CoBRA or renal failure and this treatment modality forms the basis of the ongoing NIH funded RAFT (Renal Anhydramnios Fetal Therapy) trial. At present, there is consensus that treatment for EPRA should only occur in the setting of a clinical trial.

Correction to: Treating primary immunodeficiencies with defects in NK cells: from stem cell therapy to gene editing

An amendment to this paper has been published and can be accessed via the original article.

Case Report: A Novel IL2RG Frame-Restoring Rescue Mutation Mimics Early T Cell Engraftment Following Haploidentical Hematopoietic Stem Cell Transplantation in a Patient With X-SCID

Mutations of the interleukin 2 receptor γ chain (IL2RG) result in the most common form of severe combined immunodeficiency (SCID), which is characterized by severe and persistent infections starting in early life with an absence of T cells and natural killer cells, normal or elevated B cell counts and hypogammaglobulinemia. SCID is commonly fatal within the first year of life, unless the immune system is reconstituted by hematopoietic stem cell transplantation (HSCT) or gene therapy. We herein describe a male infant with X-linked severe combined immunodeficiency (X-SCID) diagnosed at 5 months of age. Genetic testing revealed a novel C to G missense mutation in exon 1 resulting in a 3' splice site disruption with premature stop codon and aberrant IL2 receptor signaling. Following the diagnosis of X-SCID, the patient subsequently underwent a TCRαβ/CD19-depleted haploidentical HSCT. Post transplantation the patient presented with early CD8⁺ T cell recovery with the majority of T cells (>99%) being non-donor T cells. Genetic analysis of CD4⁺ and CD8⁺ T cells revealed a spontaneous 14 nucleotide insertion at the mutation site resulting in a novel splice site and restoring the reading frame although defective IL2RG function was still demonstrated. In conclusion, our findings describe a spontaneous second-site mutation in IL2RG as a novel cause of somatic mosaicism and early T cell recovery following haploidentical HSCT.

Exploring genetic defects in adults who were clinically diagnosed as severe combined immune deficiency during infancy

Genetic diagnostic tools including whole-exome sequencing (WES) have advanced our understanding in human diseases and become common practice in diagnosing patients with suspected primary immune deficiencies. Establishing a genetic diagnosis is of paramount importance for tailoring adequate therapeutic regimens, including identifying the need for hematopoietic stem cell transplantation (HSCT) and genetic-based therapies. Here, we genetically studied two adult patients who were clinically diagnosed during infancy with severe combined immune deficiency (SCID). Two unrelated patients, both of consanguineous kindred, underwent WES in adulthood, 2 decades after their initial clinical manifestations. Upon clinical presentation, immunological workup was performed, which led to a diagnosis of SCID. The patients presented during infancy with failure to thrive, generalized erythematous rash, and recurrent gastrointestinal and respiratory tract infections, including episodes of Pneumocystis pneumonia infection and Candida albicans fungemia. Hypogammaglobulinemia and T-cell lymphopenia were detected. Both patients were treated with a 10/10 HLA matched sibling donor unconditioned HSCT. Retrospective genetic workup revealed homozygous bi-allelic mutations in IL7RA in one patient and in RAG2 in the other. Our study exemplifies the impact of retrospectively establishing a genetic diagnosis. Pinpointing the genetic cause raises several issues including optimized surveillance and treatment, understanding disease mechanisms and outcomes, future family planning, and social and psychological considerations.

Gene Therapy for Primary Immunodeficiency

Over the past 3 decades, there has been significant progress in refining gene therapy technologies and procedures. Transduction of hematopoietic stem cells ex vivo using lentiviral vectors can now create a highly effective therapeutic product, capable of reconstituting many different immune system dysfunctions when reinfused into patients. Here, we review the key developments in the gene therapy landscape for primary immune deficiency, from an experimental therapy where clinical efficacy was marred by adverse events, to a commercialized product with enhanced safety and efficacy. We also discuss progress being made in preclinical studies for challenging disease targets and emerging gene editing technologies that are showing promising results, particularly for conditions where gene regulation is important for efficacy.

The case for severe combined immunodeficiency (SCID) and T cell lymphopenia newborn screening: saving lives…one at a time

Severe combined immunodeficiency (SCID) is a group of syndromes resulting from genetic defects causing severe deficiency in T cell and B cell function. These conditions are life-threatening and result in susceptibility to serious infections. SCID is often fatal in the first year of life if not detected and properly treated. SCID and related T cell lymphopenias can be detected in newborns by a simple screening test, the T cell receptor excision circle (TREC) assay, using the same dried blood spot samples already collected from newborns to screen for other genetic disorders. The TREC assay facilitates the earliest possible identification of cases of SCID before opportunistic infections, irreversible organ damage, or death, thus allowing for the possibility of curative treatment through hematopoietic stem cell transplant and gene therapy. Infants receiving hematopoietic stem cell transplant in the first few months of life, after being identified through screening, have a high probability of survival (95-100%), along with lower morbidity. The TREC assay has proven to have outstanding specificity and sensitivity to accurately identify almost all infants with SCID (the primary targets) as well as additional infants having other select immunologic abnormalities (secondary targets). The TREC assay is inexpensive and has been effectively integrated into many public health programs. Without timely treatment, SCID is a fatal disease that causes accrual of exorbitant healthcare costs even in just 1 year of life. The cost of care for just one infant with SCID, not diagnosed through newborn screening, could be more than the cost of screening for an entire state or regional population. Continued implementation of TREC screening will undoubtedly enhance early diagnosis, application of treatment, and healthcare cost savings. The Jeffrey Modell Foundation helped initiate newborn screening for SCID in the USA in 2008 and continues its efforts to advocate for SCID screening worldwide. Today, all 50 states and Puerto Rico are screening for SCID and T cell lymphopenia, with 27 million newborns screened to date, and hundreds diagnosed and treated. Additionally, there are at least 20 countries around the world currently conducting screening for SCID at various stages. Newborn screening for SCID and related T cell lymphopenia is cost-effective, and most importantly, it is lifesaving and allows children with SCID the opportunity to live a healthy life.

Allogeneic hematopoietic stem cell transplantation in adults with primary immunodeficiency

With recent advances in genetic sequencing and its widespread adoption for clinical diagnostics, the identification of a primary immunodeficiency (PID) as the underlying cause of diseases presenting to hematologists including refractory autoimmunity, cytopenias, immune dysregulation, and hematologic malignancy, is increasing, particularly in the adult population. Where the pathogenic genetic variants are restricted to the hematopoietic system, selected patients may benefit from allogeneic hematopoietic stem cell transplantation (allo-HSCT). Although it is generally accepted that early allo-HSCT (ie, in infancy or childhood) for PID is preferable, this is not always possible. The clinical phenotype of non-severe combined immune deficiency forms of PID can be very heterogeneous, in part because of the high number of genetic and functional defects affecting T, B, and natural killer cells, neutrophils, and/or antigen presentation. As a result, some patients have less severe disease manifestations in childhood and/or a later de novo presentation. For others, a delayed diagnosis, lack of a genetic diagnosis, or a previous lack of a suitable donor has precluded prior allo-HSCT. Specific issues which make transplantation for adult PID patients particularly challenging are discussed, including understanding the natural history of rare diseases and predicting outcome with conservative management alone; indications for and optimal timing of transplant; donor selection; conditioning regimens; and PID-specific transplant management. The role of gene therapy approaches as an alternative to allo-HSCT in high-risk monogenic PID is also discussed.

History of hematopoietic cell transplantation: challenges and progress

After more than 60 years of research in allogeneic hematopoietic cell transplantation (HCT), this therapy has advanced from one that was declared dead in the 1960s to a standard treatment of otherwise fatal malignant and non-malignant blood diseases. To date, close to 1.5 million hematopoietic cell transplants have been performed in more than 1,500 transplantation centers worldwide. This review will highlight the enormous efforts by numerous investigators throughout the world who have brought the experimental field of HCT to clinical reality, examine ongoing challenges, and provide insights for the future.

Gene therapy for primary immunodeficiencies: up-to-date

INTRODUCTION

Primary immunodeficiencies (PIDs) are monogenic disorders of the immune system associated with increased susceptibility to life-threatening infection. Curative treatment has been limited to hematopoietic stem cell transplant (HSCT), however toxic immunosuppression, graft failure, and graft versus host disease greatly reduce overall survival rates. Gene therapy is a targeted curative therapy that reduces these risks by utilizing autologous hematopoietic stem cells. The treatment has found significant success and is anticipated to become the standard of care in a number of PIDs.

AREAS COVERED

This review is a summary of the developments in gene therapy, gene editing, and current gene therapy approaches in specific PIDs.

EXPERT OPINION

The field of gene therapy has rapidly developed over the last three decades, with the first licensed pharmaceutical gene therapy product now available. After initial clinical trials discovered serious adverse events in the form of insertional oncogenesis, significant improvements in vector design have made the treatment a viable curative therapy. Cryopreservation has expanded the scope of gene therapy by increasing accessibility of the product to wider geographic locations. Targeted gene editing using engineered nucleases, while still in early stages of development, will further add to the repertoire of potential treatments available for PIDs.

Treating primary immunodeficiencies with defects in NK cells: from stem cell therapy to gene editing

Primary immunodeficiency diseases (PIDs) are rare diseases that are characterized by genetic mutations that damage immunological function, defense, or both. Some of these rare diseases are caused by aberrations in the normal development of natural killer cells (NKs) or affect their lytic synapse. The pathogenesis of these types of diseases as well as the processes underlying target recognition by human NK cells is not well understood. Utilizing induced pluripotent stem cells (iPSCs) will aid in the study of human disorders, especially in the PIDs with defects in NK cells for PID disease modeling. This, together with genome editing technology, makes it possible for us to facilitate the discovery of future therapeutics and/or cell therapy treatments for these patients, because, to date, the only curative treatment available in the most severe cases is hematopoietic stem cell transplantation (HSCT). Recent progress in gene editing technology using CRISPR/Cas9 has significantly increased our capability to precisely modify target sites in the human genome. Among the many tools available for us to study human PIDs, disease- and patient-specific iPSCs together with gene editing offer unique and exceptional methodologies to gain deeper and more thorough understanding of these diseases as well as develop possible alternative treatment strategies. In this review, we will discuss some immunodeficiency disorders affecting NK cell function, such as classical NK deficiencies (CNKD), functional NK deficiencies (FNKD), and PIDs with involving NK cells as well as strategies to model and correct these diseases for further study and possible avenues for future therapies.

The challenges presented by haematopoietic stem cell transplantation in children with primary immunodeficiency

INTRODUCTION OR BACKGROUND

For many primary immunodeficiencies (PIDs), haematopoietic stem cell transplantation (HSCT) offers treatment to cure disease. However, patients with PID present a unique set of challenges when considering HSCT.

SOURCES OF DATA

Review of recent literature.

AREAS OF AGREEMENT

The most significant recent impact on successful outcome is introduction of newborn screening programmes for diagnosis of severe combined immunodeficiency-wider adoption of screening in an increasing number of countries will see further improvements. Other PIDs have better outcomes when treated earlier, before development of co-morbidities-early referral for consideration of HSCT is important. Evolution of conditioning regimens is improving short- and long-term toxicities-targeted busulfan and low-toxicity myeloablative treosulfan regimens deliver good survival with reduced short-term toxicities.

AREAS OF CONTROVERSY

The most radical development, still in clinical trials, is the use of mono-antibody-based conditioning, which eliminates the requirement for chemotherapy and is likely to become much more important in HSCT for non-malignant disease in the future.

GROWING POINTS

Multidisciplinary working for optimum care is essential.

AREAS TIMELY FOR DEVELOPING RESEARCH

International collaborations are important to learn about rare presentations and complications, and to formulate the most effective and safe treatment strategies.

Human inborn errors of immunity caused by defects of receptor and proteins of cellular membrane

Inborn errors of immunity are diseases of the immune system resulting from mutations that alter the expression of encoded proteins or molecules. Total updated number of these disorders is currently 406, with 430 different identified gene defects involved. Studies of the underlying mechanisms have contributed in better understanding the pathophysiology of the diseases, but also the complexity of the biology of innate and adaptive immune system and its interaction with microbes. In this review we present and briefly discuss Inborn Errors of Immunity caused by defects in genes encoding for receptors and protein of cellular membrane, including cytokine receptors, T cell antigen receptor (TCR) complex, cellular surface receptors or receptors signaling causing predominantly antibody deficiencies, co-stimulatory receptors and others. These alterations impact many biological processes of immune-system cells, including development, proliferation, activation and down-regulation of the immunological response, and result in a variety of diseases that present with distinct clinical features or with overlapping signs and symptoms.

Management of PTLD After Hematopoietic Stem Cell Transplantation: Immunological Perspectives

Post-transplant lymphoproliferative disorders (PTLDs) are life-threatening complications of iatrogenic immune impairment after allogeneic hematopoietic stem cell transplantation (HSCT). In the pediatric setting, the majority of PTLDs are related to the Epstein-Barr virus (EBV) infection, and present as B-cell lymphoproliferations. Although considered rare events, PTLDs have been increasingly observed with the widening application of HSCT from alternative sources, including cord blood and HLA-haploidentical stem cell grafts, and the use of novel agents for the prevention and treatment of rejection and graft-vs.-host disease. The higher frequency initially paralleled a poor outcome, due to limited therapeutic options, and scarcity of controlled trials in a rare disease context. In the last 2 decades, insight into the relationship between EBV and the immune system, and advances in early diagnosis, monitoring and treatment have changed the approach to the management of PTLDs after HSCT, and significantly ameliorated the prognosis. In this review, we summarize literature on the impact of combined viro-immunologic assessment on PTLD management, describe the various strategies for PTLD prevention and preemptive/curative treatment, and discuss the potential of novel immune-based therapies in the containment of this malignant complication.

Gene therapy for severe combined immunodeficiencies and beyond

This review describes how gene therapy of severe combined immunodeficiency became a reality, primarily based on the expected selective advantage conferred by transduction of hematopoietic progenitor cells. Thus, it resulted in a progressive extension to the treatment of other primary immunodeficiencies.

Ex vivo retrovirally mediated gene therapy has been shown within the last 20 yr to correct the T cell immunodeficiency caused by γc-deficiency (SCID X1) and adenosine deaminase (ADA) deficiency. The rationale was brought up by the observation of the revertant of SCIDX1 and ADA deficiency as a kind of natural gene therapy. Nevertheless, the first attempts of gene therapy for SCID X1 were associated with insertional mutagenesis causing leukemia, because the viral enhancer induced transactivation of oncogenes. Removal of this element and use of a promoter instead led to safer but still efficacious gene therapy. It was observed that a fully diversified T cell repertoire could be generated by a limited set (<1,000) of progenitor cells. Further advances in gene transfer technology, including the use of lentiviral vectors, has led to success in the treatment of Wiskott–Aldrich syndrome, while further applications are pending. Genome editing of the mutated gene may be envisaged as an alternative strategy to treat SCID diseases.

Establishing Simultaneous T Cell Receptor Excision Circles (TREC) and K-Deleting Recombination Excision Circles (KREC) Quantification Assays and Laboratory Reference Intervals in Healthy Individuals of Different Age Groups in Hong Kong

The clinical experience gathered throughout the years has raised awareness of primary immunodeficiency diseases (PIDD). T cell receptor excision circles (TREC) and kappa-deleting recombination excision circles (KREC) assays for thymic and bone marrow outputs measurement have been widely implemented in newborn screening (NBS) programs for Severe Combined Immunodeficiency. The potential applications of combined TREC and KREC assay in PIDD diagnosis and immune reconstitution monitoring in non-neonatal patients have been suggested. Given that ethnicity, gender, and age can contribute to variations in immunity, defining the reference intervals of TREC and KREC levels in the local population is crucial for setting up cut-offs for PIDD diagnosis. In this retrospective study, 479 healthy Chinese sibling donors (240 males and 239 females; age range: 1 month-74 years) from Hong Kong were tested for TREC and KREC levels using a simultaneous quantitative real-time PCR assay. Age-specific 5th-95th percentile reference intervals of TREC and KREC levels (expressed in copies per μL blood and copies per 106 cells) were established in both pediatric and adult age groups. Significant inverse correlations between age and both TREC and KREC levels were observed in the pediatric age group. A significant higher KREC level was observed in females than males after 9-12 years of age but not for TREC. Low TREC or KREC levels were detected in patients diagnosed with mild or severe PIDD. This assay with the established local reference intervals would allow accurate diagnosis of PIDD, and potentially monitoring immune reconstitution following haematopoietic stem cell transplantation or highly active anti-retroviral therapy in the future.