The Evidence for Allogeneic Hematopoietic Stem Cell Transplantation for Congenital Neutrophil Disorders: A Comprehensive Review by the Inborn Errors Working Party Group of the EBMT

Clinical and transcriptomic characteristics of a novel SMARCD2 mutation that disrupts neutrophil maturation and function

We report a novel case of SMARCD2 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily D, member 2) mutation successfully treated with hematopoietic stem cell transplantation. The female patient presented delayed cord separation, chronic diarrhea, skin abscesses, skeletal dysmorphisms, and neutropenia with specific granule deficiency. Analysis of the transcriptomic profile of peripheral blood sorted mature and immature SMARCD2 neutrophils showed defective maturation process that associated with altered expression of genes related to specific, azurophilic, and gelatinase granules, such as LTF, CRISP3, PTX3, and CHI3L1. These abnormalities account for the prevalence of immature neutrophils in the peripheral blood, impaired function, and deregulated inflammatory responses.

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

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

Precision medicine: The use of tailored therapy in primary immunodeficiencies

Primary immunodeficiencies (PID) are rare, complex diseases that can be characterised by a spectrum of phenotypes, from increased susceptibility to infections to autoimmunity, allergy, auto-inflammatory diseases and predisposition to malignancy. With the introduction of genetic testing in these patients and wider use of next-Generation sequencing techniques, a higher number of pathogenic genetic variants and conditions have been identified, allowing the development of new, targeted treatments in PID. The concept of precision medicine, that aims to tailor the medical interventions to each patient, allows to perform more precise diagnosis and more importantly the use of treatments directed to a specific defect, with the objective to cure or achieve long-term remission, minimising the number and type of side effects. This approach takes particular importance in PID, considering the nature of causative defects, disease severity, short- and long-term complications of disease but also of the available treatments, with impact in life-expectancy and quality of life. In this review we revisit how this approach can or is already being implemented in PID and provide a summary of the most relevant treatments applied to specific diseases.

Case report: HLA-haploidentical hematopoietic cell transplant with posttransplant cyclophosphamide in a patient with leukocyte adhesion deficiency type I

Leukocyte adhesion deficiency type I (LAD-I) is a rare autosomal recessive inborn error of immunity (IEI) caused by the defects in CD18, encoded by the ITGB2 gene. LAD-I is characterized by defective leukocyte adhesion to the vascular endothelium and impaired migration of leukocytes. Allogeneic hematopoietic cell transplant (HCT) is the only curative treatment for LAD-I. In an absence of ideal donor for HCT, human leukocyte antigen (HLA)-haploidentical HCT is performed. Posttransplant cyclophosphamide (PT-CY) is a relatively new graft-versus-host disease (GVHD) prophylactic measure and has been increasingly used in HLA-haploidentical HCT for malignant and nonmalignant diseases. However, experience in using PT-CY for rare IEIs, such as LAD-I, is very limited. We report a case of LAD-I successfully treated with HLA-haploidentical HCT with PT-CY. Complete chimerism was achieved, and the patient was cured. Her transplant course was complicated by mild GVHD, cytomegalovirus reactivation and veno-occlusive disease/sinusoidal obstruction syndrome, which were successfully treated. HLA-haploidentical HCT with PT-CY is a safe and effective option for patients with LAD-I when HLA-matched donors are unavailable.

SLGT2 Inhibitor Rescues Myelopoiesis in G6PC3 Deficiency

The energy metabolism of myeloid cells depends primarily on glycolysis. 1,5-Anhydroglucitol (1,5AG), a natural monosaccharide, is erroneously phosphorylated by glucose-phosphorylating enzymes to produce 1,5-anhydroglucitol-6-phosphate (1,5AG6P), a powerful inhibitor of hexokinases. The endoplasmic reticulum transporter (SLC37A4/G6PT) and the phosphatase G6PC3 cooperate to dephosphorylate 1,5AG6P. Failure to eliminate 1,5AG6P is the mechanism of neutrophil dysfunction and death in G6PC3-deficient mice. Sodium glucose cotransporter 2 (SLGT2) inhibitor reduces 1,5AG level in the blood and restores the neutrophil count in G6PC3-deficient mice. In the investigator-initiated study, a 30-year-old G6PC3-deficient woman with recurrent infections, distressing gastrointestinal symptoms, and multi-lineage cytopenia was treated with an SLGT2-inhibitor. A significant increase in all the hematopoietic cell lineages and substantial improvement in the quality of life was observed.

Specific Granule Deficiency Due To Novel Homozygote SMARCD2 Variant

Background: Specific granule deficiency (SGD) is a rare immunodeficiency associated with CCAT/enhancer-binding protein epsilon (CEBPE) gene variants. It can cause severe recurrent infections and is lethal without successful stem cell transplantation. Few cases with SGD of both type 1 and type 2 have been described in the literature. In this study, we present the first report of a case with a novel homozygous c.511 C > T (p.Gln171Ter) mutation in the SMARCD2 gene of SGD type 2, which was successfully treated with bone marrow transplantation. Case: A male infant presented to our neonatal intensive care unit on the second day of life with an icteric appearance and mild hypotonia. He was evaluated for immunodeficiency as the cause of delayed cord separation and refractory neutropenia. At 6 weeks of age, SGD type 2 with a new variant was diagnosed and successfully treated by bone marrow transplantation. Conclusion: SGD is an immunodeficiency disease that is quite rare. However, we believe that SGD diagnosis and associated new variants can be detected more frequently with the widespread use of all whole-exome sequencing techniques.

Pediatric immune deficiencies: current treatment approaches

PURPOSE OF REVIEW

To summarize the currently available definitive therapies for patients with inborn errors of immunity (IEIs) with a strong focus on recent advances in allogeneic hematopoietic cell transplantation (HCT) and gene therapy, including the use of alternative donors, graft manipulation techniques, less toxic approaches for pretransplant conditioning and gene transfer using autologous hematopoietic stem cells.

RECENT FINDINGS

In the absence of a matched sibling or a matched related donor, therapeutic alternatives for patients with IEIs include alternative donor transplantation or autologous gene therapy, which is only available for selected IEIs. In recent years, several groups have published their experience with haploidentical hematopoietic cell transplantation (HHCT) using different T-cell depletion strategies. Overall survival and event free survival results, although variable among centers, are encouraging. Preliminary results from autologous gene therapy trials with safer vectors and low-dose busulfan conditioning have shown reproducible and successful results. Both strategies have become valid therapeutic options for patients with IEIs. A new promising and less toxic conditioning regimen strategy is also discussed.

SUMMARY

Definitive therapies for IEIs with HCT and gene therapy are in stage of evolution, not only to refine their efficacy and safety but also their reach to a larger number of patients.