Allogeneic stem cell transplantation for X-linked agammaglobulinemia using reduced intensity conditioning as a model of the reconstitution of humoral immunity

Neonatal Screening for Spinal Muscular Atrophy and Severe T- and B-Cell Lymphopenias in Andalusia: A Prospective Study

Spinal muscular atrophy (SMA) and severe T- and/or B-cell lymphopenias (STBCL) in the form of severe combined immunodeficiencies (SCID) or X-linked agammaglobulinemia (XLA) are rare but potentially fatal pathologies. In January 2021, we initiated the first pilot study in Spain to evaluate the efficacy of a very early detection technique for SMA and SCID. RT-PCR was performed on prospectively collected dried blood spots (DBSs) from newborns in Western Andalusia (Spain). Internal and external controls (SCID, XLA and SMA) were included. The determination of SMA was relative (positive/negative) and that of TRECs and KRECs was quantitative (copies/punch). A total of 14.035 prospective samples were analysed. All controls were correctly identified while no cases of SMA or SCID/XLA were prospectively identified. DBS analysis of infants with suspected SMA or STBCL that presented to our centre showed pathological values in two cases each for SMA and SCID and one for XLA, all of them being subsequently confirmed genetically. In this prospective pilot study, no infants with SMA or STBCL were detected; however, the technique applied here was shown to be reliable and fast, further supporting the benefits and need to include SMA and SCID in national newborn screening (NBS) programs, as it will allow early supportive and curative therapy.

Gene regulation in inborn errors of immunity: Implications for gene therapy design and efficacy

Inborn errors of immunity (IEI) present a unique paradigm in the realm of gene therapy, emphasizing the need for precision in therapeutic design. As gene therapy transitions from broad-spectrum gene addition to careful modification of specific genes, the enduring safety and effectiveness of these therapies in clinical settings have become crucial. This review discusses the significance of IEIs as foundational models for pioneering and refining precision medicine. We explore the capabilities of gene addition and gene correction platforms in modifying the DNA sequence of primary cells tailored for IEIs. The review uses four specific IEIs to highlight key issues in gene therapy strategies: X-linked agammaglobulinemia (XLA), X-linked chronic granulomatous disease (X-CGD), X-linked hyper IgM syndrome (XHIGM), and immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX). We detail the regulatory intricacies and therapeutic innovations for each disorder, incorporating insights from relevant clinical trials. For most IEIs, regulated expression is a vital aspect of the underlying biology, and we discuss the importance of endogenous regulation in developing gene therapy strategies.

An International Survey of Allogeneic Hematopoietic Cell Transplantation for X-Linked Agammaglobulinemia

PURPOSE

X-linked agammaglobulinemia (XLA) is an inborn error of immunity caused by variants in Bruton's tyrosine kinase (BTK). XLA patients require lifelong immunoglobulin replacement therapy (IgRT). Only few XLA patients are indicated for allogeneic hematopoietic cell transplantation (HCT) because of severe complications. Accordingly, the published transplantation experience in XLA is minimal. We aimed to collect clinical data of XLA patients who received HCT in an international framework and to establish appropriate transplantation criteria and methods for XLA patients.

METHODS

XLA patients were recruited through a questionnaire and a literature review. The data are on patient characteristics and transplantation methods and outcomes.

RESULTS

In this study, twenty-two XLA patients who underwent HCT were recruited. The indication for HCT was recurrent or life-threatening infection in sixteen patients, malignancy in three, and other factors in three. A myeloablative conditioning, reduced toxicity myeloablative conditioning (RT-MAC), and reduced intensity conditioning (RIC) were selected in four, ten, and eight patients, respectively. Engraftment was achieved in 21 patients (95%). In all patients, 2-year overall survival (OS) and event-free survival (EFS) were 86% and 77%, respectively. In patients who received RT-MAC or RIC using treosulfan, busulfan, or melphalan, 2-year OS and EFS were 82% and 71%, respectively. Finally, twenty-one patients (95%) obtained complete or stable high-level mixed chimerism (50-95%), and the 1-year discontinuation rate of IgRT was 89%.

CONCLUSION

Based on the concept in which IgRT is the standard treatment for XLA, HCT may be an effective and safe alternative treatment option for XLA patients, and IgRT can be discontinued following transplantation. It is ideal to perform HCT in XLA patients for whom transplantation is indicated before they develop organ damage.

A Registry Study of 240 Patients with X-Linked Agammaglobulinemia Living in the USA

PURPOSE

To understand the natural history and clinical outcomes for patients with X-linked agammaglobulinemia (XLA) in the United States utilizing the United States Immunodeficiency Network (USIDNET) patient registry.

METHODS

The USIDNET registry was queried for data from XLA patients collected from 1981 to 2019. Data fields included demographics, clinical features before and after diagnosis of XLA, family history, genetic mutation in Bruton's tyrosine kinase (BTK), laboratory findings, treatment modalities, and mortality.

RESULTS

Data compiled through the USIDNET registry on 240 patients were analyzed. Patient year of birth ranged from 1945 to 2017. Living status was available for 178 patients; 158/178 (88.8%) were alive. Race was reported for 204 patients as follows: White, 148 (72.5%); Black/African American, 23 (11.2%); Hispanic, 20 (9.8%); Asian or Pacific Islander, 6 (2.9%), and other or more than one race, 7 (3.4%). The median age at last entry, age at disease onset, age at diagnosis, and length of time with XLA diagnosis was 15 [range (r) = 1-52 years], 0.8 [r = birth-22.3 years], 2 [r = birth-29 years], and 10 [r = 1-56 years] years respectively. One hundred and forty-one patients (58.7%) were < 18 years of age. Two hundred and twenty-one (92%) patients were receiving IgG replacement (IgGR), 58 (24%) were on prophylactic antibiotics, and 19 (7.9%) were on immunomodulatory drugs. Eighty-six (35.9%) patients had undergone surgical procedures, two had undergone hematopoietic cell transplantation, and two required liver transplantation. The respiratory tract was the most affected organ system (51.2% of patients) followed by gastrointestinal (40%), neurological (35.4%), and musculoskeletal (28.3%). Infections were common both before and after diagnosis, despite IgGR therapy. Bacteremia/sepsis and meningitis were reported more frequently before XLA diagnosis while encephalitis was more commonly reported after diagnosis. Twenty patients had died (11.2%). The median age of death was 21 years (range = 3-56.7 years). Neurologic condition was the most common underlying co-morbidity for those XLA patients who died.

CONCLUSIONS

Current therapies for XLA patients reduce early mortality, but patients continue to experience complications that impact organ function. With improved life expectancy, more efforts will be required to improve post-diagnosis organ dysfunction and quality of life. Neurologic manifestations are an important co-morbidity associated with mortality and not yet clearly fully understood.

Genes as Medicine: The Development of Gene Therapies for Inborn Errors of Immunity

The field of gene therapy has experienced tremendous growth in the last decade ranging from improvements in the design of viral vectors for gene addition of therapeutic gene cassettes to the discovery of site-specific nucleases targeting transgenes to desired locations in the genome. Such advancements have not only enabled the development of disease models but also created opportunities for the development of tailored therapeutic approaches. There are 3 main methods of gene modification that can be used for the prevention or treatment of disease. This includes viral vector-mediated gene therapy to supply or bypass a missing/defective gene, gene editing enabled by programmable nucleases to create sequence-specific alterations in the genome, and gene silencing to reduce the expression of a gene or genes. These gene-modification platforms can be delivered either in vivo, for which the therapy is injected directed into a patient's body, or ex vivo, in which cells are harvested from a patient and modified in a laboratory setting, and then returned to the patient.

The significance of mixed chimaerism and cell lineage chimaerism monitoring in paediatric patients post haematopoietic stem cell transplant

Haematopoietic stem cell transplants (HSCTs) are carried out across the world to treat haematological and immunological diseases which would otherwise prove fatal. Certain diseases are predominantly encountered in paediatric patients, such severe primary immunodeficiencies (PID) and diseases of inborn errors of metabolism (IEM). Chimaerism testing for these disorders has different considerations compared to adult diseases. This review focuses on the importance of cell-lineage-specific chimaerism testing and examines the appropriate cell populations to be assessed in individual paediatric patient groups. By analysing disease-associated subpopulations, abnormalities are identified significantly earlier than in whole samples and targeted clinical decisions can be made. Chimaerism methods have evolved over time and lead to an ever-increasing level of sensitivity and biomarker arrays to distinguish between recipient and donor cells. Short tandem repeat (STR) is still the gold standard for routine chimaerism assessment, and hypersensitive methods such as quantitative and digital polymerase chain reaction (PCR) are leading the forefront of microchimaerism testing. The rise of molecular methods operating with minute DNA amounts has been hugely beneficial to chimaerism testing of paediatric samples. As HSCTs are becoming increasingly personalised and risk-adjusted towards a child's individual needs, chimaerism testing needs to adapt alongside these medical advances ensuring the best possible care.

Cost Utility of Lifelong Immunoglobulin Replacement Therapy vs Hematopoietic Stem Cell Transplant to Treat Agammaglobulinemia

IMPORTANCE

Lifelong immunoglobulin replacement therapy (IRT) is standard-of-care treatment for congenital agammaglobulinemia but accrues high annual costs ($30 000-$90 000 per year) and decrements to quality of life over patients' life spans. Hematopoietic stem cell transplant (HSCT) offers an alternative 1-time therapy, but has high morbidity and mortality.

OBJECTIVE

To evaluate the cost utility of IRT vs matched sibling donor (MSD) and matched unrelated donor (MUD) HSCT to treat patients with agammaglobulinemia in the US.

DESIGN, SETTING, AND PARTICIPANTS

This economic evaluation used Markov analysis to model the base-case scenario of a patient aged 12 months with congenital agammaglobulinemia receiving lifelong IRT vs MSD or MUD HSCT. Costs, probabilities, and quality-of-life measures were derived from the literature. Microsimulations estimated premature deaths for each strategy in a virtual cohort. One-way sensitivity and probabilistic sensitivity analyses evaluated uncertainty around parameter estimates performed from a societal perspective over a 100-year time horizon. The threshold for cost-effective care was set at $100 000 per quality-adjusted life-year (QALY). This study was conducted from 2020 across a 100-year time horizon.

EXPOSURES

Immunoglobulin replacement therapy vs MSD or MUD HSCT for treatment of congenital agammaglobulinemia.

MAIN OUTCOMES AND MEASURES

The primary outcomes were incremental cost-effectiveness ratio (ICER) expressed in 2020 US dollars per QALY gained and premature deaths associated with each strategy.

RESULTS

In this economic evaluation of patients with congenital agammaglobulinemia, lifelong IRT cost more than HSCT ($1 512 946 compared with $563 776 [MSD] and $637 036 [MUD]) and generated similar QALYs (20.61 vs 17.25 [MSD] and 17.18 [MUD]). Choosing IRT over MSD or MUD HSCT yielded ICERs of $282 166 per QALY gained over MSD and $255 633 per QALY gained over MUD HSCT, exceeding the US willingness-to-pay threshold of $100 000/QALY. However, IRT prevented at least 2488 premature deaths per 10 000 microsimulations compared with HSCT. When annual IRT price was reduced from $60 145 to below $29 469, IRT became the cost-effective strategy. Findings remained robust in sensitivity and probabilistic sensitivity analyses.

CONCLUSIONS AND RELEVANCE

In the US, IRT is more expensive than HSCT for agammaglobulinemia treatment. The findings of this study suggest that IRT prevents more premature deaths but does not substantially increase quality of life relative to HSCT. Reducing US IRT cost by 51% to a value similar to IRT prices in countries implementing value-based pricing may render it the more cost-effective strategy.

Agammaglobulinemia: from X-linked to Autosomal Forms of Disease

Interruptions or alterations in the B cell development pathway can lead to primary B cell immunodeficiency with resultant absence or diminished immunoglobulin production. While the most common cause of congenital agammaglobulinemia is X-linked agammaglobulinemia (XLA), accounting for approximately 85% of cases, other genetic forms of agammaglobulinemia have been identified. Early recognition and diagnosis of these conditions are pivotal for improved outcomes and prevention of sequelae and complications. The diagnosis of XLA is often delayed, and can be missed if patient has a mild phenotype. The lack of correlation between phenotype and genotype in this condition makes management and predicting outcomes quite difficult. In contrast, while less common, autosomal recessive forms of agammaglobulinemia present at younger ages and with typically more severe clinical features resulting in an earlier diagnosis. Some diagnostic innovations, such as KREC level measurements and serum BCMA measurements, may aid in facilitating an earlier identification of agammaglobulinemia leading to prompt treatment. Earlier diagnosis may improve the overall health of patients with XLA.

Whole genome sequencing identifies novel structural variant in a large Indian family affected with X-linked agammaglobulinemia

X-linked agammaglobulinemia (XLA, OMIM #300755) is a primary immunodeficiency disorder caused by pathogenic variations in the BTK gene, characterized by failure of development and maturation of B lymphocytes. The estimated prevalence worldwide is 1 in 190,000 male births. Recently, genome sequencing has been widely used in difficult to diagnose and familial cases. We report a large Indian family suffering from XLA with five affected individuals. We performed complete blood count, immunoglobulin assay, and lymphocyte subset analysis for all patients and analyzed Btk expression for one patient and his mother. Whole exome sequencing (WES) for four patients, and whole genome sequencing (WGS) for two patients have been performed. Carrier screening was done for 17 family members using Multiplex Ligation-dependent Probe Amplification (MLPA) and haplotype ancestry mapping using fineSTRUCTURE was performed. All patients had hypogammaglobulinemia and low CD19+ B cells. One patient who underwent Btk estimation had low expression and his mother showed a mosaic pattern. We could not identify any single nucleotide variants or small insertion/ deletions from the WES dataset that correlates with the clinical feature of the patient. Structural variant analysis through WGS data identifies a novel large deletion of 5,296 bp at loci chrX:100,624,323-100,629,619 encompassing exons 3-5 of the BTK gene. Family screening revealed seven carriers for the deletion. Two patients had a successful HSCT. Haplotype mapping revealed a South Asian ancestry. WGS led to identification of the accurate genetic mutation which could help in early diagnosis leading to improved outcomes, prevention of permanent organ damage and improved quality of life, as well as enabling genetic counselling and prenatal diagnosis in the family.

Haematopoietic Stem Cell Transplant for Norovirus-Induced Intestinal Failure in X-linked Agammaglobulinemia

Since the first clinical description in 1952, immunoglobulin replacement therapy remains the mainstay of treatment of patients with X-linked agammaglobulinemia (XLA). However, this therapy only replaces IgG isotype and does not compensate for the loss of Bruton tyrosine kinase in non-B-lymphocytes. Patients may still therefore develop complications despite current standard of care. Here, we describe an XLA patient with persistent chronic norovirus infection, refractory to treatment and causing intestinal failure. The patient underwent haematopoietic stem cell transplantation, curing XLA and allowed clearance of norovirus prior to humoral immunoreconstitution, suggesting non-humoral immunodeficiency in these patients.

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.

Hematopoietic Stem Cell Transplantation for Children With Inborn Errors of Immunity

This is a retrospective analysis of clinical characteristics of children with inborn errors of immunity who underwent hematopoietic stem cell transplant (HSCT). Although the mean age at diagnosis was 24.4 months, it was 51.9 months at HSCT. There is an urgent need to improve awareness, expand donor registries and initiate newborn screening for inborn errors or immunity.

Update on Infections in Primary Antibody Deficiencies

Bacterial respiratory tract infections are the hallmark of primary antibody deficiencies (PADs). Because they are also among the most common infections in healthy individuals, PADs are usually overlooked in these patients. Careful evaluation of the history, including frequency, chronicity, and presence of other infections, would help suspect PADs. This review will focus on infections in relatively common PADs, discussing diagnostic challenges, and some management strategies to prevent infections.

Hematopoietic Stem Cell Transplantation for Children With Inborn Errors of Immunity

This is a retrospective analysis of clinical characteristics of children with inborn errors of immunity who underwent hematopoietic stem cell transplant (HSCT). Although the mean age at diagnosis was 24.4 months, it was 51.9 months at HSCT. There is an urgent need to improve awareness, expand donor registries and initiate newborn screening for inborn errors or immunity.

Molecular requirements for human lymphopoiesis as defined by inborn errors of immunity

Hematopoietic stem cells (HSCs) are the progenitor cells that give rise to the diverse repertoire of all immune cells. As they differentiate, HSCs yield a series of cell states that undergo gradual commitment to become mature blood cells. Studies of hematopoiesis in murine models have provided critical insights about the lineage relationships among stem cells, progenitors, and mature cells, and these have guided investigations of the molecular basis for these distinct developmental stages. Primary immune deficiencies are caused by inborn errors of immunity that result in immune dysfunction and subsequent susceptibility to severe and recurrent infection(s). Over the last decade there has been a dramatic increase in the number and depth of the molecular, cellular, and clinical characterization of such genetically defined causes of immune dysfunction. Patients harboring inborn errors of immunity thus represent a unique resource to improve our understanding of the multilayered and complex mechanisms underlying lymphocyte development in humans. These breakthrough discoveries not only enable significant advances in the diagnosis of such rare and complex conditions but also provide substantial improvement in the development of personalized treatments. Here, we will discuss the clinical, cellular, and molecular phenotypes, and treatments of selected inborn errors of immunity that impede, either intrinsically or extrinsically, the development of B- or T-cells at different stages.

Clinical and Genetic Profile of X-Linked Agammaglobulinemia: A Multicenter Experience From India

BACKGROUND

There is paucity of literature on XLA from developing countries. Herein we report the clinical and molecular profile and outcome in a multicenter cohort of patients with XLA from India.

METHODS

Data on XLA from all regional centers supported by the Foundation for Primary Immunodeficiency Diseases (FPID), USA and other institutions providing care to patients with PIDs were collated. Diagnosis of XLA was based on European Society for Immunodeficiencies (ESID) criteria.

RESULTS

We received clinical details of 195 patients with a provisional diagnosis of XLA from 12 centers. At final analysis, 145 patients were included (137 'definite XLA' and eight 'probable/possible XLA'). Median age at onset of symptoms was 12.0 (6.0, 36.0) months and median age at diagnosis was 60.0 (31.5, 108) months. Pneumonia was the commonest clinical manifestation (82.6%) followed by otitis media (50%) and diarrhea (42%). Arthritis was seen in 26% patients while 23% patients developed meningitis. Bronchiectasis was seen in 10% and encephalitis (likely viral) in 4.8% patients. Pseudomonas aeruginosa was the commonest bacterial pathogen identified followed by Streptococcus pneumoniae, Staphylococcus aureus and Klebsiella pneumoniae. Molecular analysis revealed 86 variants in 105 unrelated cases. Missense variants in BTK gene were the most common (36%) followed by frameshift (22%) and nonsense variants (21%). Most pathogenic gene variants (53%) were clustered in the distal part of gene encompassing exons 14-19 encoding for the tyrosine kinase domain. Follow-up details were available for 108 patients. Of these, 12% had died till the time of this analysis. The 5-year and 10-year survival was 89.9% and 86.9% respectively. Median duration of follow-up was 61 months and total duration of follow-up was 6083.2 patient-months. All patients received intravenous immunoglobulin (IVIg) replacement therapy. However, in many patients IVIg could not be given at recommended doses or intervals due to difficulties in accessing this therapy because of financial reasons and lack of universal health insurance in India. Hematopoietic stem cell transplant was carried out in four (2.8%) patients.

CONCLUSION

There was a significant delay in the diagnosis and facilities for molecular diagnosis were not available at many centers. Optimal immunoglobulin replacement is still a challenge.

Molecular mechanisms underlining the role of metformin as a therapeutic agent in lung cancer

BACKGROUND

Metformin, a first-line therapeutic for type 2 diabetes, has been studied for its potential use in cancer treatment following a number of epidemiological studies that have demonstrated reduced cancer incidence and mortality rates among patients treated with the drug. As yet, however, there remains significant uncertainty about the molecular mechanisms by which metformin exerts its anti-cancer effects. Herein, we summarize the evidence surrounding the anti-lung cancer effects of metformin.

CONCLUSIONS

Specifically, we explore protein targets of metformin, including AMPK, PP2A, IRF-1/YAP and HGF and we outline the proposed mechanisms of action for metformin in lung cancer, with particular attention given to apoptosis and autophagy. We also closely examine the synergistic activity of metformin with existing cancer treatment regimens, such as TKI's, platinum-based agents and immune therapeutics. In addition to considering preclinical and clinical studies, we also dissect and contextualize the limitations and inconsistencies of the current literature, especially those of epidemiological studies. Finally, we offer a potential trajectory for future research in this rapidly evolving area of basic and clinical oncology.

[Peripheral blood stem cell transplantation from HLA-mismatched unrelated donor or haploidentical donor for the treatment of X-linked agammaglobulinemia]

Allogeneic stem cell transplantation (allo-SCT) is currently the only curative option for patients with X-linked agammaglobulinemia (XLA). In this study, patient 1 aged 4 years who underwent allogeneic peripheral blood stem cell transplantation (allo-PBSCT) from HLA-mismatched unrelated donor; patient 2 aged 24 years (childhood onset) with primary cutaneous acral CD8⁺ T cell lymphoma who underwent allo-PBSCT from haploidentical relative donor. Both were treated by reduced toxicity myeloablative conditioning with post-transplantation cyclophosphamide (PTCy), anti-thymocyte globulin (ATG), methotrexate (MTX) and cyclosporine (CsA) for graft-versus-host-disease (GVHD) prophylaxis. In patient 1, neutrophil and platelet engraftment were observed on day 11 post-transplantation; the donor chimerism dropped on day 90 post-transplantation, and recovered on day 150 with donor lymphocyte infusion (DLI). In patient 2, neutrophil and platelet engraftment were observed on days 20 and 87 post-transplantation respectively, with complete donor chimerism on day 30 post-transplantation. The serum levels of IgG, IgM and IgA and the percentage of CD19⁺ B cells in peripheral blood of patients 1 and 2 returned to normal within 2 months and more than 1 year after transplantation respectively. There was no evidence of acute GVHD for the two patients. Patient 1 developed a limited type of skin chronic GVHD after DLI, which disappeared after anti-GVHD treatment. This is the first report of successful treatment for two XLA patients using PTCy with allo-PBSCT from HLA-mismatched unrelated donor or haploidentical donor, combining with improved conditioning, which expands the pool of eligible donors for patients with XLA.

[Peripheral blood stem cell transplantation from HLA-mismatched unrelated donor or haploidentical donor for the treatment of X-linked agammaglobulinemia]

Allogeneic stem cell transplantation (allo-SCT) is currently the only curative option for patients with X-linked agammaglobulinemia (XLA). In this study, patient 1 aged 4 years who underwent allogeneic peripheral blood stem cell transplantation (allo-PBSCT) from HLA-mismatched unrelated donor; patient 2 aged 24 years (childhood onset) with primary cutaneous acral CD8+ T cell lymphoma who underwent allo-PBSCT from haploidentical relative donor. Both were treated by reduced toxicity myeloablative conditioning with post-transplantation cyclophosphamide (PTCy), anti-thymocyte globulin (ATG), methotrexate (MTX) and cyclosporine (CsA) for graft-versus-host-disease (GVHD) prophylaxis. In patient 1, neutrophil and platelet engraftment were observed on day 11 post-transplantation; the donor chimerism dropped on day 90 post-transplantation, and recovered on day 150 with donor lymphocyte infusion (DLI). In patient 2, neutrophil and platelet engraftment were observed on days 20 and 87 post-transplantation respectively, with complete donor chimerism on day 30 post-transplantation. The serum levels of IgG, IgM and IgA and the percentage of CD19+ B cells in peripheral blood of patients 1 and 2 returned to normal within 2 months and more than 1 year after transplantation respectively. There was no evidence of acute GVHD for the two patients. Patient 1 developed a limited type of skin chronic GVHD after DLI, which disappeared after anti-GVHD treatment. This is the first report of successful treatment for two XLA patients using PTCy with allo-PBSCT from HLA-mismatched unrelated donor or haploidentical donor, combining with improved conditioning, which expands the pool of eligible donors for patients with XLA.

Treosulfan-based reduced toxicity hematopoietic stem cell transplantation in X-linked agammaglobulinemia: A cost-effective alternative to long-term immunoglobulin replacement in developing countries

X-linked agammaglobulinemia (XLA) is a primary antibody disorder due to a mutation in the Bruton tyrosine kinase gene that requires lifelong immunoglobulin replacement resulting in a significant economic burden and treatment abandonment. Hematopoietic stem cell transplantation (HSCT) offers an alternative option for complete cure. In our series, two children with XLA underwent successful HSCT using a myeloablative conditioning with thiotepa, treosulfan, and fludarabine from a matched sibling donor. The second child had rejected his first graft following a busulfan-based regimen with resultant autologous reconstitution. At 6 months post-HSCT, serum IgG were normal, off IVIG, and had no infections. Both children after a median follow-up of 20 months have 100% chimerism. Treosulfan-based reduced toxicity myeloablative HSCT has encouraging results with a positive impact on the socioeconomics in developing countries.

Functional Antibody Responses Following Allogeneic Stem Cell Transplantation for TP53 Mutant pre-B-ALL in a Patient With X-Linked Agammaglobulinemia

Patients with X-linked agammaglobulinemia (XLA) have failure of B-cell development with lack of immunoglobulin (Ig) production. While immunoglobulin replacement therapy (IgRT) is beneficial, XLA patients remain at risk for infections, structural lung damage, and rarely, neoplasia. Allogeneic stem cell transplantation (alloSCT) may offer a potential cure, but is associated with significant life-threatening complications. Here, we present a 25-year old XLA patient who developed pre-B acute lymphocytic leukemia (ALL) with somatic TP53 mutation, and treatment for this high-risk malignancy involved full myeloablative conditioning and a HLA-matched sibling alloSCT. Full donor chimerism was achieved for CD3+ and CD3- cell fractions. The patient remains in morphological and flow cytometric remission 14 months post-transplant, with late-onset oral GvHD requiring low dose prednisolone and cyclosporin. Following IgRT discontinuation at 4 months post-transplantation, humoral immunity was established within 14 months as reflected by normal numbers of total B cells, memory B cells, serum IgG, IgM, and IgA, and production of specific IgG responses to Prevenar-13 vaccination. This is only the second reported case of an XLA patient with pre-B-ALL, and the most detailed report of engraftment following alloSCT in XLA. Together with the two previous XLA cases treated with alloSCT, our report provides evidence for the potential for successful humoral reconstitution with alloSCT in patients with B-cell intrinsic antibody deficiency. These observations may be relevant given IgRT, while beneficial, remains an imperfect solution to long-term infectious complications.