Hematopoietic stem cell transplantation for infantile osteopetrosis

Osteopetrosis in the pediatric patient: what the radiologist needs to know

Osteopetrosis describes several types of rare sclerosing bone dysplasias of varying clinical and radiographic severity. The classic autosomal dominant subtype emerges most often in adolescence but can present from infancy through adulthood. The autosomal recessive osteopetrosis, or "malignant infantile osteopetrosis," presents in infancy with a grimmer prognosis, though the autosomal dominant forms (often mislabeled as "benign") actually can have life-threatening consequences as well. Often osteopetrosis is detected due to skeletal findings on radiographs performed to evaluate injury or as an incidental finding during evaluation for illness. Given the varied phenotypic severity and presentations at different ages, radiologists play an integral role in the care of these patients both in diagnosis and in clinical evaluation and monitoring. A deeper understanding of the underlying genetic basis of the disease can aid in the radiologist in diagnosis and in anticipation of unique complications. An overview of current clinical management is also discussed.

Allogenic hematopoietic stem cell transplantation in an Iranian patient with osteopetrosis caused by carbonic anhydrase II deficiency: A case report

BACKGROUND

Osteopetrosis is a group of geneticall heterogeneous disorders resulting from impaired osteoclast function and bone resorption. The identification of specific genetic mutations can yield important prognostic and therapeutic implications. Herein, we present the diagnosis and successful application of hematopoietic stem cell transplantation (HSCT) in a patient with osteopetrosis caused by carbonic anhydrase II deficiency (Intermediate osteopetrosis).

CASE PRESENTATION

Herein, we describe a 2.5-year-old male patient born to consanguineous parents who presented at 8-month-old with hydrocephaly, brain shunt, and developmental delay. Later at 9 months old, he was found to have eye disorder such as nystagmus, fracture of the elbow, abnormal skeletal survey, normal cell blood count (CBC), and severe hypocellularity in the bone marrow. Further evaluation showed renal tubular acidosis type 2. Whole-exome sequencing revealed a pathogenic homozygous variant in intron 2 of the carbonic anhydrase 2 gene (CA2) gene (c.232 + 1 G>T). The diagnosis of intermediate autosomal recessive osteopetrosis was established, and allogenic HSCT from his mother, a full-matched related donor (MRD), was planned. The conditioning regimen included Busulfan, Fludarabine, and Rabbit anti-thymocyte globulin. Cyclosporine and Mycophenolate Mofetil were used for graft-versus-host-disease prophylaxis. He Engrafted on day +13, and 95% chimerism was achieved. He is currently doing well without immunosuppressive therapy, now 12 months post HSCT, with normal calcium level and improving visual quality and FISH analysis revealed complete donor chimerism.

DISCUSSION

HSCT could be a promising curative treatment for intermediate osteopetrosis and can provide long-term survival. Ongoing challenges in various aspects of HSCT remain to be addressed.

Hematopoietic stem cell transplantation, a curative approach in infantile osteopetrosis

Most patients with osteopetrosis (OPT) can be causally and curatively treated with allogeneic hematopoietic stem cell transplantation (HSCT) because osteoclasts are derived from the HSC. However, HSCT is contraindicated in some forms of OPT, namely OPT with neurodegeneration (in all patients with OSTM1 and about half of patients with CLCN7 mutations) and OPT caused by an osteoblast defect (patients with RANKL mutations). HSCT for OPT risks serious side effects, such as transplant failure, venous occlusive disease, pulmonary hypertension, and hypercalcemic crises. Nevertheless, the success rate of HSCT has improved significantly in recent decades. This applies, in particular, to HSCT from non-HLA compatible (haploidentical) donors. Therefore, nowadays an HSCT can be discussed for intermediate OPT forms. After a successful HSCT, most patients have very good quality of life, but about two-thirds are visually impaired, and in rarer cases show motor and neurological disabilities. Early diagnosis, further improvements in transplantation procedures, and advances to improve quality-of-life after transplantation are challenges for the future.

Experimental therapies for osteopetrosis

The medical treatment of osteopetrosis is an ongoing clinical problem. There are no effective and safer therapeutic approaches for all its forms. However, recent discoveries concerning the etiology and the pathogenesis of osteopetrosis, the development of dedicated cellular and animal models, and the advent of new technologies are paving the way for the development of targeted and safer therapies for both lethal and milder osteopetrosis. This review summarizes the huge effort and successes made by researchers to identify and develop new experimental approaches with this objective, such as the use of non-genotoxic myeloablation, gene correction of inducible Pluripotent Stem Cells (iPSCs), lentiviral-based gene therapy, protein replacement, prenatal treatment, osteoclast precursors transplantation and RNA Interference.

Pediatric patient with a bilateral Salter-Harris II fracture and slipped capital femoral epiphysis secondary to autosomal recessive osteopetrosis

Treatment of femoral neck fractures secondary to osteopetrosis is an uncertain and puzzled decision. Experience in the treatment, especially in the pediatric population, is scarcely reported. The duration of conservative treatment is prolonged and poses the risks of non-union and development of coxa vara deformity. The recommended treatment is closed reduction and internal fixation; however, surgery on osteopetrotic bone is challenging due to defective bone marrow function, delayed consolidation and higher risk of intraoperative fractures. Slipped capital femoral epiphysis secondary to osteopetrosis is very rarely reported. This article presents the case of a 5-year-old female patient with rapidly deteriorating physical function due to bilateral proximal femoral Salter-Harris type II fractures with associated slippage of the growth plates secondary to confirmed autosomal recessive osteopetrosis. Operative treatment was performed in a tertiary level orthopedic center with closed reduction and internal fixation with cannulated screws. A loss of fixation with coxa vara deformity was seen on the left side 7 months postoperatively with increasing pain. A revision surgery with reosteosynthesis and a valgus osteotomy was thus performed which showed good subjective and objective results 1 year postoperatively with complete bony union.

Outcomes of blood and marrow transplantation in children less than 2-years of age: 23 years of experience at a single center

Objectives

Allogeneic hematopoietic cell transplantation (Allo-HCT) is a curative option for children with various malignant and non-malignant diseases. Most reports studied all age groups amongst children. Herein we analyzed our data in children transplanted at or less than 2-years of age.

Patients and methods

We reviewed medical charts of 618 patients who underwent 666 transplantation at our center between 1993 and 2015. There were 340 boys and 278 girls. Median age was 0.7 years (range 0.04-2). Stem cell source was bone marrow (BM) in 492 (73.9%), unrelated umbilical cord blood (UCB) in 161 (24.2%) followed by peripheral blood stem cell (PBSC) in 13 (2%) patients. Matched siblings were the most common donors (n = 356, 53.5%), followed by unrelated (n = 161, 24.2%) with haploidentical family member donors in 29 (4.4%) transplants. Disease groups were categorized as benign hematology (Thalassemia, Fanconi, Aplastic anemia etc.), benign neoplasm (Langerhans cell histiocytosis, Hemophagocytic Lymphohistiocytosis etc.), non-neoplasms (metabolic disorders, immunodeficiency disorders etc.) and Leukemia/lymphomas (myeloid and lymphoid malignancies etc.).

Results

Cumulative incidence of acute GvHD (I-IV) was 31.5% (n = 210) and grade III-IV GvHD was 8.7% (n = 58). At median follow-up of 115.1 months, the cumulative probability of overall survival (OS) at 5 years was 70.0% ± 1.9%. Our mortality rate was 31.2% (n = 193). The five-year OS was significantly better in patients transplanted for benign hematological disorders (P = .001). Patients transplanted using BM/PBSC as source of stem cells fared significantly better compared to those in which CB was used (P<.001). Post-transplant graft failure remains the leading cause requiring further transplants in this age group. In conclusion, the cumulative probability of OS at 5 years was about 70.0% for all with an OS of 61% in our haploidentical recipients.

Conclusion

Analyzing our institutional data over time has enabled us to develop tentative strategies to minimize transplant related toxicities in very young children who are candidates for allo-HCT.

Osteoclast rich osteopetrosis due to defects in the TCIRG1 gene

Discovery that mutations in TCIRG1 (also known as Atp6i) gene are responsible for most instances of autosomal recessive osteopetrosis (ARO) heralded a new era for comprehension and treatment of this phenotypically heterogeneous rare bone disease. TCIRG1 encodes the a3 subunit, an essential isoform of the vacuolar ATPase proton pump involved in acidification of the osteoclast resorption lacuna and in secretory lysosome trafficking. TCIRG1 defects lead to inefficient bone resorption by nonfunctional osteoclasts seen in abundance on bone marrow biopsy, delineating this ARO as 'osteoclast-rich'. Presentation is usually in early childhood and features of extramedullary haematopoiesis (hepatosplenomegaly, anaemia, thrombocytopenia) due to bone marrow fibrosis, and cranial nerve impingement (blindness in particular). Impaired dietary calcium uptake due to high pH causes the co-occurrence of rickets, described as "osteopetrorickets". Osteoclast dysfunction leads to early death if untreated, and allogeneic haematopoietic stem cell transplantation is currently the treatment of choice. Studies of patients as well as of mouse models carrying spontaneous (the oc/oc mouse) or targeted disruption of Atp6i (TCIRG1) gene have been instrumental providing insight into disease pathogenesis and development of novel cellular therapies that exploit gene correction.

BHLHE40 promotes osteoclastogenesis and abnormal bone resorption via c-Fos/NFATc1

Background

Dysregulated osteoclast activity due to altered osteoclast differentiation causes multiple bone diseases. Osteoclasts are multinucleated giant cells derived from hematopoietic stem cells and play a major role in bone absorption. However, the mechanisms underlying the tight regulation of osteoclast differentiation in multiple pathophysiological status remain unknown.

Results

We showed that Bhlhe40 upregulation is tightly associated with osteoclast differentiation and osteoporosis. Functionally, Bhlhe40 promoted osteoclast differentiation in vitro, and Bhlhe40 deficiency led to increased bone mass and decreased osteoclast differentiation in vivo. Moreover, Bhlhe40 deficient mice resisted estrogen deficiency and aging-induced osteoporosis. Mechanism study showed that the increase in bone mass due to Bhlhe40 deficiency was a cell intrinsic defect in osteoclast differentiation in these mice. BHLHE40 upregulated the gene expression of Fos and Nfatc1 by directly binding to their promoter regions. Notably, inhibition of Fos/Nfatc1 abrogated the enhanced osteoclast differentiation induced by BHLHE40 overexpression.

Conclusions

Our research reveals a novel Bhlhe40/c-Fos/Nfatc1 axis involved in regulating osteoclastogenesis and shows that osteoporosis caused by estrogen deficiency and aging can be rescued by regulating Bhlhe40 in mice. This may help in the development of a new strategy for the treatment of osteoporosis.

Early treatment of osteopetrosis: Paradigm shift to marrow cell transplantation

The osteopetroses reflect alterations of a special cell type, the osteoclast, belonging to the myeloid lineage. We have known this since the 1970s, confirmed by a myriad of reports featuring details that guided subsequent molecular diagnosis and treatment. This review is a tribute to two pioneers in the field: Donald G. Walker PhD (1925-1979) and Sandy C. Marks Jr. PhD (1937-2002), who explored osteopetrosis pathophysiology and treatment. Using spontaneous mutant models of osteopetrosis in mice, rats, and rabbits, they demonstrated the cellular basis of osteopetrosis while also advancing understanding of the hematological origin of osteoclasts. This became the foundation for life-saving treatment by hematopoietic stem cell transplantation. Their prose was uncomplicated, experiments were straightforward, and conclusions were based on facts explaining why their teaching became influential worldwide. I never met Dr. Walker but spoke with Dr. Marks on several occasions. Both inspired my work and, now appreciating how they shaped the osteoclast/osteopetrosis scientist community, we must thank these eminent scientists for being mentors of all of us.

OSTM1 pleiotropic roles from osteopetrosis to neurodegeneration

Autosomal recessive osteopetroses (ARO) are rare genetic skeletal disorders of high clinical and molecular heterogeneity with an estimated frequency of 1:250,000 worldwide. The manifestations are diverse and although individually rare, the various forms contribute to the prevalence of a significant number of affected individuals with considerable morbidity and mortality. Among the ARO classification, the most severe form is the autosomal recessive-5 (OPTB5) osteopetrosis (OMIM 259720) that results from homozygous mutation in the OSTM1 gene (607649). OSTM1 mutations account for approximately 5 % of instances of autosomal recessive osteopetrosis and lead to a highly debilitating form of the disease in infancy and death within the first few years of life (Sobacchi et al., 2013) [1].

Assessing the Efficacy of Alkylating Agent Regimens in the Treatment of Infantile Malignant Osteopetrosis: Cyclophosphamide, Busulfan, or Thiotepa

Infantile malignant osteopetrosis is a debilitating disease that requires total bone marrow irradiation and transplant procedures for patients to survive. The major complication of this procedure is graft vs host disease (GVHD), followed by infections and end organ toxicity. Therefore, current research efforts into treatment mainly aim to reduce GVHD while limiting infections and organ toxicity. Different regimens of alkylating agents have been used to try to reduce GVHD. The most common regimen is cyclophosphamide (Cy) with busulfan (Bu), followed by Cy with Bu and thiotepa (Thio). This meta-analysis aimed to evaluate the efficacy of different treatments by comparing mortality and morbidity causes and rates across groups. The mean one-year survival rate for the Cy, Bu, Thio regimen studies in the human leukocyte antigen (HLA) unmatched group (45.01%) was statistically lower than the one-year survival rate for the studies using just a Cy, Bu regimen (70.8%) in the HLA unmatched studies (p<0.00142). The one-year survival in the studies which had HLA-matched donors was 80.56%, which is statistically higher (p<0.001) than the one-year survival in the HLA-unmatched studies (53.96%), indicating a benefit of finding HLA-matched donors. It seems that price and availability could be a factor in the widespread use of Cy.

Autoimmune Cytopenias Post Hematopoietic Stem Cell Transplantation in Pediatric Patients With Osteopetrosis and Other Nonmalignant Diseases

Autoimmune cytopenia (AIC) is a rare complication post hematopoietic stem cell transplantation (HSCT), with a higher incidence in nonmalignant diseases. The etiology of post-HSCT AIC is poorly understood, and in many cases, the cytopenia is prolonged and refractory to treatment. Diagnosis of post-HSCT AIC may be challenging, and there is no consensus for a standard of care. In this retrospective study, we summarize our experience over the past five years with post-HSCT AIC in pediatric patients with osteopetrosis and other nonmalignant diseases. All pediatric patients who underwent HSCT for nonmalignant diseases at Hadassah Medical Center over the past five years were screened for post-HSCT AIC, and data were collected from the patient’s medical records. From January 2017 through December 2021, 140 pediatric patients underwent HSCT for osteopetrosis (n=40), and a variety of other nonmalignant diseases. Thirteen patients (9.3%) presented with post-HSCT AIC. Of these, 7 had osteopetrosis (17.5%), and 6 had other underlying nonmalignant diseases. Factors associated with developing AIC included unrelated or non-sibling family donors (n=10), mixed chimerism (n=6), and chronic GvHD (n=5). Treatment modalities included steroids, IVIG, rituximab, bortezomib, daratumumab, eltrombopag, plasmapheresis, and repeated HSCT. Response to treatment was variable; Seven patients (54%) recovered completely, and three patients (23%) recovered partially, still suffering from mild-moderate thrombocytopenia. Three patients died (23%), two following progressive lung disease and one from sepsis and multi-organ failure after a 3^rd HSCT. In our experience, post-HSCT AICs in pediatric patients with nonmalignant diseases may pose a challenging post-transplant complication with a variable presentation and a wide spectrum of severity. A relatively high prevalence is seen in patients with osteopetrosis, possibly due to difficult engraftment and high rates of mixed chimerism. There is a dire need for novel treatment modalities for better management of the more severe and refractory cases.

A Foxo1-Klf2-S1pr1-Gnai1-Rac1 signaling axis is a critical mediator of Ostm1 regulatory network in T lymphopoiesis

Ostm1 mutations cause the severe form of osteopetrosis with bone marrow deficiency in humans and mice, yet a role in T cell ontogeny remains to be determined. Herein, we show that thymi of the Ostm1-null mice (gl/gl) from P8-to-P15 become markedly hypocellular with disturbed architecture. Analysis of gl/gl early T cell program determined a major decrease of 3-fold in bone marrow common lymphoid precursors (CLP), 35-fold in early thymic precursors (ETPs) and 100-fold in T cell double positive subpopulations. Ostm1 ablation in T cell double negative (DN) also appears to induce fast-paced differentiation kinetics with a transitory intermediate CD44⁺CD25^int subpopulation. Transgenic targeting Ostm1 expression from the gl/gl DN1 population partially rescued T cell subpopulations from ETP onwards and normalized the accelerated DN differentiation, indicating a cell-autonomous role for Ostm1. Transcriptome of early DN1 population identified an Ostm1 crosstalk with a Foxo1-Klf2-S1pr1-Gnai1-Rac1 signaling axis. Our findings establish that Ostm1 is an essential regulator of T cell ontogeny.

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Loss of Ostm1 causes severe thymus hypocellularity

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Ostm1 is a modulator of the T cell differentiation program from the CLPs onwards

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Targeted CD2-Ostm1 in Ostm1 null mice leads to partial rescue of DN differentiation

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Ostm1 null DN1 transcriptome identifies a Foxo1-Klf2-S1pr1-Gnai1-Rac1 signaling axis

Low frequency of treatable pediatric disease alleles in gnomAD: An opportunity for future genomic screening of newborns

Hematopoietic stem cell transplant (HSCT) can prevent progression of several genetic disorders. Although a subset of these disorders are identified on newborn screening panels, others are not identified until irreversible symptoms develop. Genetic testing is an efficient methodology to ascertain pre-symptomatic children, but the penetrance of risk-associated variants in the general population is not well understood. We developed a list of 127 genes associated with disorders treatable with HSCT. We identified likely pathogenic or pathogenic (LP/P) and loss-of-function (LoF) variants in these genes in the Genome Aggregation Database (gnomAD), a dataset containing exome and genome sequencing data from 141,456 healthy adults. Within gnomAD, we identified 59 individuals with a LP/P or LoF variant in 15 genes. Genes were associated with bone marrow failure syndromes, bleeding disorders, primary immunodeficiencies, osteopetrosis, metabolic disorders, and epidermolysis bullosa. In conclusion, few ostensibly healthy adults had genotypes associated with pediatric disorders treatable with HSCTs. Given that most of these disorders do not have biomarkers that could be cheaply and universally assessed on a standard newborn screen, our data suggest that genetic testing may be a complementary approach to traditional newborn screening methodology that has the potential to improve mortality and is not expected to lead to a high burden of false-positive results.

Clinical presentation and analysis of genotype-phenotype correlations in patients with malignant infantile osteopetrosis

Malignant infantile osteopetrosis (MIOP) is the autosomal recessive, severe form of osteopetrosis. This rare genetic syndrome usually presents soon after birth and is often fatal if left untreated. Early diagnosis is key for proper management but clinical presentation is diverse, and oftentimes diagnosis may be challenging. In this study, we retrospectively collected data of genetic mutations and phenotypic characteristics at the initial presentation of 81 MIOP patients and analyzed genotype-phenotype correlations. The most common genetic mutation was in the TCIRG1 gene (n = 46, 56.8%), followed by SNX10 (n = 20, 25%). Other genetic mutations included RANK (n = 7, 8.7%), CLCN7 (n = 5, 6.2%) and CA2 (n = 3, 3.7%). More than half of the patients presented with growth retardation (n = 46, 56.8%). Twenty-one of the patients were blind (26%) and thirty-seven patients had other neurological deficits (45.7%) at the time of initial presentation. Most patients presented with hematological signs of bone marrow failure including anemia (n = 69, 85.2%) and thrombocytopenia (n = 33, 40.7%). Thrombocytopenia at initial presentation was significantly more prevalent in patients with mutations in the TCIRG1 gene (p = 0.036). Other phenotypic presenting features were not found to be significantly correlated to specific gene mutations. In conclusion, the initial presentation of MIOP is variable, but some features are common such as growth retardation, visual impairment, and cytopenias. High awareness of MIOP presenting signs is essential for prompt diagnosis of this challenging disease.

Intermediate Autosomal Recessive Osteopetrosis With an Unusual Absence of Fractures

Background: Osteopetrosis includes a variety of rare inherited skeletal disorders characterized by increased bone density and thickness. It has different clinical forms, including infantile autosomal recessive, intermediate autosomal recessive, and late-onset autosomal dominant forms. Intermediate autosomal recessive osteopetrosis (IARO) displays high variability. Case Report: A 10-year-old male presented to our pediatrics emergency department with abdominal distension, low-grade fever, and swelling of the right maxilla with associated discharge. His local physician had treated the lesion with drainage and aspiration of pus without improvement. Examination revealed pallor, hepatosplenomegaly, poor dentition, and dental caries. Eye examination showed reduced visual acuity, absent color vision, nystagmus, and bilateral optic nerve atrophy. Laboratory investigations showed anemia and thrombocytopenia. Radiography yielded classic features of osteopetrosis. Detailed intraoral examination revealed an area of exposed necrotic bone in the alveolar region of the right maxilla, leading to a diagnosis of IARO with underlying osteomyelitis. The intraoral wound was treated with bismuth iodoform paraffin paste dressing, and the infection was treated with antibiotics. Anemia and thrombocytopenia were managed supportively by transfusion of packed red blood cells and platelets. Conclusion: IARO commonly presents with multiple fractures, so the absence of fractures in our patient was unusual. Studies evaluating the intermediate variant are meager; hence, documenting its various presentations is essential to aid physicians in making early diagnoses. Osteomyelitis of the jaws is a feared complication in these patients. Therefore, practitioners need to be cautious of infections of dental origin.

OUP accepted manuscript

Osteopetrosis is a rare inherited disease characterized by impaired osteoclast activity causing defective bone resorption and bone marrow aplasia. It is fatal in early childhood unless hematopoietic stem cell transplantation is performed. But, the transplant course is complicated with engraftment failure. Recently, osteoclasts have been described as the potential regulators of hematopoietic stem cell (HSC) niche. Here we investigated the alterations in the HSC and mesenchymal stromal cell (MSC) components of osteopetrotic niche and their interactions to mimic the stem cell dynamics/trafficking in the BM niche after HSC transplantation. Induced pluripotent stem cells were generated from peripheral blood mononuclear cells of patients with osteopetrosis carrying TCIRG1 mutation. iPSC lines were differentiated into hematopoietic and myeloid progenitors, then into osteoclasts using a step-wise protocol. We first demonstrated a shift toward monocyte-macrophages lineage regarding hematopoietic differentiation potential of osteopetrotic iPSC-derived hematopoietic progenitors (HPCs) and phenotypically normal and functionally defective osteoclast formation. The expression of the genes involved in HSC homing and maintenance (Sdf-1, Jagged-1, Kit-L, and Opn) in osteopetrotic MSCs recovered significantly after coculture with healthy HPCs. Similarly, the restoration of phenotype, impaired differentiation, and migratory potential of osteopetrotic iHPCs were observed upon interaction with healthy MSCs. Our results establish significant alterations in both MSC and HPC compartments of the osteopetrotic niche, and support the impact of functionally impaired osteoclasts in defective niche formation.

Effects of the Lysine Methyltransferase Inhibitor AZ505 on Bone Metabolism

Background

Protein methylation has important role in regulating diverse cellular responses, including differentiation, by affecting protein activity, stability, and interactions. AZ505 is an inhibitor of the SET and MYND domain-containing protein 2 lysine methylase. In this study, we investigated the effect of AZ505 on osteoblast and osteoclast differentiation in vitro and evaluated the effect of AZ505 in vivo on the long bones in mice.

Methods

Osteoblast differentiation was assessed by alkaline phosphatase (ALP) and Alizarin red staining after culturing calvarial preosteoblasts in an osteogenic medium. Osteoclast differentiation was analyzed by tartrate-resistant acid phosphatase (TRAP) staining in bone marrow-derived macrophages cultured with macrophage-colony stimulating factor and receptor activator of nuclear factor-κB ligand (RANKL). For in vivo experiments, mice were intraperitoneally injected with AZ505 and femurs were examined by micro-computed tomography.

Results

AZ505 increased ALP and Alizarin red staining in cultured osteoblasts and the expression of osteoblast marker genes, including Runx2 and osteocalcin. AZ505 resulted in decreased TRAP-staining of osteoclasts and expression of c-Fos and nuclear factor of activated T cells transcription factors and osteoclast marker genes, including cathepsin K and dendritic cell-specific transmembrane protein. Unexpectedly, in vivo administration of AZ505 markedly decreased the trabecular bone mass of femurs. In support of this catabolic result, AZ505 strongly upregulated RANKL expression in osteoblasts.

Conclusions

The results indicate that AZ505 has a catabolic effect on bone metabolism in vivo despite its anabolic effect in bone cell cultures. The findings indicate that cell culture data should be extrapolated cautiously to in vivo outcomes for studying bone metabolism.

Hematopoietic stem cell-derived functional osteoblasts exhibit therapeutic efficacy in a murine model of osteogenesis imperfecta

Currently, there is no cure for osteogenesis imperfecta (OI)-a debilitating pediatric skeletal dysplasia. Herein we show that hematopoietic stem cell (HSC) therapy holds promise in treating OI. Using single-cell HSC transplantation in lethally irradiated oim/oim mice, we demonstrate significant improvements in bone morphometric, mechanics, and turnover parameters. Importantly, we highlight that HSCs cause these improvements due to their unique property of differentiating into osteoblasts/osteocytes, depositing normal collagen-an attribute thus far assigned only to mesenchymal stem/stromal cells. To confirm HSC plasticity, lineage tracing was done by transplanting oim/oim with HSCs from two specific transgenic mice-VavR, in which all hematopoietic cells are GFP+ and pOBCol2.3GFP, where GFP is expressed only in osteoblasts/osteocytes. In both models, transplanted oim/oim mice demonstrated GFP+ HSC-derived osteoblasts/osteocytes in bones. These studies unequivocally establish that HSCs differentiate into osteoblasts/osteocytes, and HSC transplantation can provide a new translational approach for OI.

Brain Abscess in a Patient with Osteopetrosis: A Rare Complication

Brain abscess formation is extremely rare in patients with osteopetrosis. Herein, we report a case of viridans streptococci brain abscess in an immunocompromised child diagnosed with osteopetrosis. The patient presented with a sudden change in mental status and convulsions. Radiological evaluation revealed a temporal lobe brain abscess, and intravenous antibiotherapy was started immediately. The patient underwent abscess drainage, and laboratory investigation of pus material revealed viridans streptococci.

Clinical Development of Cell Therapies to Halt Lysosomal Storage Diseases: Results and Lessons Learned

Although cross-correction was discovered more than 50 years ago, and held the promise of drastically improving disease management, still no cure exists for lysosomal storage diseases (LSDs). Cell therapies hold the potential to halt disease progression: either a subset of autologous cells can be ex vivo/ in vivo transfected with the functional gene or allogenic wild type stem cells can be transplanted. However, majority of cell-based attempts have been ineffective, due to the difficulties in reversing neuronal symptomatology, in finding appropriate gene transfection approaches, in inducing immune tolerance, reducing the risk of graft versus host disease (GVHD) when allogenic cells are used and that of immune response when engineered viruses are administered, coupled with a limited secretion and uptake of some enzymes. In the last decade, due to advances in our understanding of lysosomal biology and mechanisms of cross-correction, coupled with progresses in gene therapy, ongoing pre-clinical and clinical investigations have remarkably increased. Even gene editing approaches are currently under clinical experimentation. This review proposes to critically discuss and compare trends and advances in cell-based and gene therapy for LSDs. Systemic gene delivery and transplantation of allogenic stem cells will be initially discussed, whereas proposed brain targeting methods will be then critically outlined.

Haploidentical haematopoietic stem cell transplantation for malignant infantile osteopetrosis and intermediate osteopetrosis: a retrospective analysis of a single centre

OBJECTIVE

To evaluate the clinical efficacy of haploidentical haematopoietic stem cell transplantation (haplo-HSCT) for the treatment of malignant infantile osteopetrosis (MIOP) and intermediate osteopetrosis.

METHODS

Children with MIOP and IOP who underwent haplo-HSCT in Beijing Children's Hospital, Capital Medical University, from January 2010 to May 2018 were retrospectively analysed. Data relating to the clinical manifestations, engraftment, and prognosis of the children were extracted from medical records.

RESULTS

Twenty-seven patients, including 18 males and 9 females, with an onset age of 12 (0.04-72) months were enrolled in this study. The median time from diagnosis to transplantation was 4 (1-23) months. All patients received haplo-HSCT with a myeloablative conditioning regimen (including fludarabine, busulfan, and cyclophosphamide). Graft versus host disease (GVHD) prophylaxis was based on anti-human T lymphocyte porcine immunoglobulin/anti-human thymus globulin, methotrexate, and mycophenolate mofetil. The median observation time was 55.2 (0.3-126.2) months. By the end of follow-up, twenty patients survived and seven patients died. The 5 year overall survival rate was 73.9%. Stage I-II acute GVHD was observed in 20 patients, stage III GVHD in 1 patient and no patients had stage IV disease. Chronic GVHD was observed in 11 patients (40.7%) and was controlled by anti-GVHD therapy.

CONCLUSIONS

Haplo-HSCT was an effective treatment for MIOP and IOP, with a high survival rate and significantly improved clinical symptoms. For patients with a vision impairment before HSCT, the improvement was slow after transplantation. The incidence of GVHD was high but mild and was effectively controlled by appropriate treatment. These data indicated that haplo-HSCT was a feasible treatment for MIOP and IOP.

Sorting Nexin 10 as a Key Regulator of Membrane Trafficking in Bone-Resorbing Osteoclasts: Lessons Learned From Osteopetrosis

Bone homeostasis is a complex, multi-step process, which is based primarily on a tightly orchestrated interplay between bone formation and bone resorption that is executed by osteoblasts and osteoclasts (OCLs), respectively. The essential physiological balance between these cells is maintained and controlled at multiple levels, ranging from regulated gene expression to endocrine signals, yet the underlying cellular and molecular mechanisms are still poorly understood. One approach for deciphering the mechanisms that regulate bone homeostasis is the characterization of relevant pathological states in which this balance is disturbed. In this article we describe one such “error of nature,” namely the development of acute recessive osteopetrosis (ARO) in humans that is caused by mutations in sorting nexin 10 (SNX10) that affect OCL functioning. We hypothesize here that, by virtue of its specific roles in vesicular trafficking, SNX10 serves as a key selective regulator of the composition of diverse membrane compartments in OCLs, thereby affecting critical processes in the sequence of events that link the plasma membrane with formation of the ruffled border and with extracellular acidification. As a result, SNX10 determines multiple features of these cells either directly or, as in regulation of cell-cell fusion, indirectly. This hypothesis is further supported by the similarities between the cellular defects observed in OCLs form various models of ARO, induced by mutations in SNX10 and in other genes, which suggest that mutations in the known ARO-associated genes act by disrupting the same plasma membrane-to-ruffled border axis, albeit to different degrees. In this article, we describe the population genetics and spread of the original arginine-to-glutamine mutation at position 51 (R51Q) in SNX10 in the Palestinian community. We further review recent studies, conducted in animal and cellular model systems, that highlight the essential roles of SNX10 in critical membrane functions in OCLs, and discuss possible future research directions that are needed for challenging or substantiating our hypothesis.

Autosomal recessive osteopetrosis: mechanisms and treatments

Autosomal recessive osteopetrosis (ARO) is a severe inherited bone disease characterized by defective osteoclast resorption or differentiation. Clinical manifestations include dense and brittle bones, anemia and progressive nerve compression, which hamper the quality of patients' lives and cause death in the first 10 years of age. This Review describes the pathogenesis of ARO and highlights the strengths and weaknesses of the current standard of care, namely hematopoietic stem cell transplantation (HSCT). Despite an improvement in the overall survival and outcomes of HSCT, transplant-related morbidity and the pre-existence of neurological symptoms significantly limit the success of HSCT, while the availability of human leukocyte antigen (HLA)-matched donors still remains an open issue. Novel therapeutic approaches are needed for ARO patients, especially for those that cannot benefit from HSCT. Here, we review preclinical and proof-of-concept studies, such as gene therapy, systematic administration of deficient protein, in utero HSCT and gene editing.

Summary: Autosomal recessive osteopetrosis is a heterogeneous and rare bone disease for which effective treatments are still lacking for many patients. Here, we review the literature on clinical, preclinical and proof-of-concept studies.

Gene therapy for infantile malignant osteopetrosis: review of pre-clinical research and proof-of-concept for phenotypic reversal

Infantile malignant osteopetrosis is a devastating disorder of early childhood that is frequently fatal and for which there are only limited therapeutic options. Gene therapy utilizing autologous hematopoietic stem and progenitor cells represents a potentially advantageous therapeutic alternative for this multisystemic disease. Gene therapy can be performed relatively rapidly following diagnosis, will not result in graft versus host disease, and may also have potential for reduced incidences of other transplant-related complications. In this review, we have summarized the past sixteen years of research aimed at developing a gene therapy for infantile malignant osteopetrosis; these efforts have culminated in the first clinical trial employing lentiviral-mediated delivery of TCIRG1 in autologous hematopoietic stem and progenitor cells.

How we approach malignant infantile osteopetrosis

Malignant infantile osteopetrosis (MIOP) is a rare hereditary disorder characterized by excessive bone overgrowth due to a defect in bone marrow resorption by osteoclasts. In most cases, hematopoietic stem cell transplantation (HSCT) may correct bone metabolism but the rapidly progressing nature of this condition necessitates early diagnosis and prompt treatment to minimize irreversible cranial nerve damage. The management of patients with MIOP presents many unique challenges. In this review, the clinical management of patients with MIOP is discussed, including diagnosis, preparation for HSCT and special transplant considerations, management of unique HSCT complications, and long-term follow-up.

Two macrophages, osteoclasts and microglia: from development to pleiotropy

Tissue-resident macrophages are highly specialized to their tissue-specific microenvironments, activated by various inflammatory signals and modulated by genetic and environmental factors. Osteoclasts and microglia are distinct tissue-resident cells of the macrophage lineage in bone and brain that are responsible for pathological changes in osteoporosis and Alzheimer’s disease (AD), respectively. Osteoporosis is more frequently observed in individuals with AD compared to the prevalence in general population. Diagnosis of AD is often delayed until underlying pathophysiological changes progress and cause irreversible damages in structure and function of brain. As such earlier diagnosis and intervention of individuals at higher risk would be indispensable to modify clinical courses. Pleiotropy is the phenomenon that a genetic variant affects multiple traits and the genetic correlation between two traits could suggest a shared molecular mechanism. In this review, we discuss that the Pyk2-mediated actin polymerization pathway in osteoclasts and microglia in bone and brain, respectively, is the horizontal pleiotropic mediator of shared risk factors for osteoporosis and AD.

Expanded circulating hematopoietic stem/progenitor cells as novel cell source for the treatment of TCIRG1 osteopetrosis

Allogeneic hematopoietic stem cell transplantation is the treatment of choice for autosomal recessive osteopetrosis caused by defects in the TCIRG1 gene. Despite recent progress in conditioning, a relevant number of patients are not eligible for allogeneic stem cell transplantation because of the severity of the disease and significant transplant-related morbidity. We exploited peripheral CD34+ cells, known to circulate at high frequency in the peripheral blood of TCIRG1-deficient patients, as a novel cell source for autologous transplantation of gene corrected cells. Detailed phenotypical analysis showed that circulating CD34+ cells have a cellular composition that resembles bone marrow, supporting their use in gene therapy protocols. Transcriptomic profile revealed enrichment in genes expressed by hematopoietic stem and progenitor cells (HSPCs). To overcome the limit of bone marrow harvest/ HSPC mobilization and serial blood drawings in TCIRG1 patients, we applied UM171-based ex-vivo expansion of HSPCs coupled with lentiviral gene transfer. Circulating CD34+ cells from TCIRG1-defective patients were transduced with a clinically-optimized lentiviral vector (LV) expressing TCIRG1 under the control of phosphoglycerate promoter and expanded ex vivo. Expanded cells maintained long-term engraftment capacity and multi-lineage repopulating potential when transplanted in vivo both in primary and secondary NSG recipients. Moreover, when CD34+ cells were differentiated in vitro, genetically corrected osteoclasts resorbed the bone efficiently. Overall, we provide evidence that expansion of circulating HSPCs coupled to gene therapy can overcome the limit of stem cell harvest in osteopetrotic patients, thus opening the way to future gene-based treatment of skeletal diseases caused by bone marrow fibrosis.

Challenges in long-term control of hypercalcaemia with denosumab after haematopoietic stem cell transplantation for TNFRSF11A osteoclast-poor autosomal recessive osteopetrosis

Autosomal recessive osteopetrosis (ARO) is rare, involving increased bone density due to defective osteoclast differentiation or function, with several genetic subtypes.

Case

This child with compound heterozygous novel loss-of-function TNFRSF11A pathogenic variants causing osteoclast-poor ARO underwent haematopoietic stem cell transplantation (HSCT) aged 3.1 years and experienced episodic severe hypercalcaemia over 2.5 years. She initially presented aged 8 months with craniosynostosis and visual impairment and underwent surgery; no increased bone density evident on skull imaging nor variants in genes associated with craniosynostosis identified. She was subsequently referred for investigation of poor linear growth and low alkaline phosphatase. Clinical abnormalities included asymmetric pectus carinatum, thickened anterior tibia and wrists, and markedly delayed dentition. Skeletal survey revealed generalised osteosclerosis with undertubulation.

Management

She received haploidentical HSCT aged 3.1 years and developed hypercalcaemia (adjusted calcium 4.09mmol/L = 16.4mg/dL) Day 18 post-HSCT, unresponsive to hyperhydration and diuretics. Denosumab achieved normocalcaemia, which required 0.6mg/kg every 6 weeks long-term. The ensuing 2.75 years feature full donor engraftment, good HSCT graft function, skeletal remodelling with 2.5 years recurrent severe hypercalcaemia and nine fragility long bone fractures.

Conclusion

This case illustrates challenges of bone and calcium management in ultrarare TNFRSF11A-related OP-ARO. Craniosynostosis was an early feature, evident pre-sclerosis in osteopetrosis. Following HSCT, restoration of osteoclast activity in the context of elevated bone mass produced severe and prolonged (2.5 years) hypercalcaemia. Denosumab was effective medium-term, but required concurrent long duration (11 months) zoledronic acid to manage recurrent hypercalcaemia. Fragility fractures brought appreciable additional morbidity in the post-HSCT phase.

Major skull manifestations of skeletal dysplasias - pictorial essay

Skeletal dysplasias are a large group of rare conditions with widely heterogeneous manifestations and a reputation for being diagnostically difficult. Involvement of the brain and craniovertebral junction are features familiar to the paediatric neuroradiologist. Involvement of the skull itself represents an area of overlap between the domains of the neuroradiologist and the skeletal dysplasia radiologist. In this pictorial essay, we review the principal skull manifestations of skeletal dysplasias as they present to the neuroradiologist.

The synergistic role of Pu.1 and Fms in zebrafish osteoclast-reducing osteopetrosis and possible therapeutic strategies

Osteoclasts are bone resorption cells of myeloid origin. Osteoclast defects can lead to osteopetrosis, a genetic disorder characterized by bone sclerosis for which there is no effective drug treatment. It is known that Pu.1 and Fms are key regulators in myelopoiesis, and their defects in mice can lead to reduced osteoclast numbers and consequent osteopetrosis. Yet how Pu.1 and Fms genetically interact in the development of osteoclasts and the pathogenesis of osteopetrosis is still unclear. Here, we characterized pu.1^G242D;fms^j4e1 double-deficient zebrafish, which exhibited a greater deficiency of functional osteoclasts and displayed more severe osteopetrotic symptoms than the pu.1^G242D or fms^j4e1 single mutants, suggesting a synergistic function of Pu.1 and Fms in the regulation of osteoclast development. We further demonstrated that Pu.1 plays a dominant role in osteoclastogenesis, whereas Fms plays a dominant role in osteoclast maturation. Importantly, treatment with the drug retinoic acid significantly relieved the different degrees of osteopetrosis symptoms in these models by increasing the number of functional osteoclasts. Thus, we report the development of valuable animal models of osteopetrosis, and our results shed light on drug development for antiosteopetrosis therapy.

Skeletal Changes After Hematopoietic Stem Cell Transplantation in Osteopetrosis

Osteopetrosis is a rare skeletal dysplasia resulting from an osteoclast defect leading to increased bone mass and density. Hematopoietic stem cell transplantation can rescue the disease phenotype and prevent complications. However, little is known about the skeletal changes hematopoietic stem cell transplantation induces in patients with this disease. The purpose of this study was to describe the skeletal changes after hematopoietic stem cell transplantation in a retrospective cohort of patients diagnosed with osteopetrosis in one medical center over 13 years. For this purpose, all available epidemiological, hematological, biochemical, and radiographic data were collected and quantitatively analyzed. We found a significant early change in bone metabolism markers coinciding with hematopoietic recovery after stem cell transplantation. Hematopoietic stem cell transplantation induced a later significant improvement in both skeletal mineral distribution and morphology but did not lead to complete radiological normalization. Presumably, changes in bone metabolism, skeletal mineral distribution, and morphology were the result of renewed osteoclast function enabling bone remodeling. We propose that biochemical bone metabolism markers and radiological indices be routinely used to evaluate response to hematopoietic stem cell transplantation in patients with osteopetrosis. © 2020 American Society for Bone and Mineral Research.

Haploidentical stem cell transplantation with post-transplant cyclophosphamide for osteopetrosis and other nonmalignant diseases

Allogeneic hematopoietic stem cell transplantation (HSCT) is curative for a variety of nonmalignant disorders including osteopetrosis, bone marrow failures, and immune deficiencies. Haploidentical HSCT is a readily available option in the absence of a matched donor, but engraftment failure and other post-transplant complications are a concern. Post-transplant cyclophosphamide (PT-Cy) regimens are gaining popularity and recent reports show promising results. We report our experience with nine pediatric patients with nonmalignant diseases who were transplanted from a haploidentical donor with PT-Cy. From 2015 to 2019, nine children with nonmalignant diseases underwent haploidentical HSCT with PT-Cy, two as a second transplant and seven as primary grafts after upfront serotherapy and busulfan-based myeloablative conditioning. Patient’s diseases included osteopetrosis (n = 5), congenital amegakaryocytic thrombocytopenia (n = 2), hemophagocytic lymphohistiocytosis (n = 1), and Wiskott Aldrich syndrome (n = 1). Two patients failed to engraft following upfront PT-Cy transplants, one was salvaged with a second PT-Cy transplant, and the other with a CD34+ selected graft. None of the patients suffered from graft-versus-host disease. Three patients died from early posttransplant infectious complications and six patients are alive and well. In conclusion, haploidentical HSCT with PT-Cy is a feasible option for pediatric patients with nonmalignant diseases lacking a matched donor.

Chimerism in the Realm of Hematopoietic Stem Cell Transplantation for Non-malignant Disorders-A Perspective

Hematopoietic stem cell transplantation (HCT) is a curative intervention in non-malignant disorders (NMD) that benefit from donor-derived hematopoiesis, immunity, and establishment of vital cells or enzyme systems. Stability or reversal of disease symptoms depends on adequacy and long-term stability of donor cell engraftment in the compartment of interest. Unlike hematologic malignancies where complete replacement with donor derived hematopoiesis is desirable for a cure, NMD manifestations can often be controlled in the presence of mixed chimerism. This allows for exploration of reduced intensity conditioning regimens that can limit organ toxicity, late effects, and increase tolerability especially in young recipients or those with a large burden of disease related morbidity. However, the levels of donor chimerism conducive to disease control vary between NMD, need to focus on the hematopoietic lineage necessary to correct individual disorders, and need to be assessed for stability over time, i.e., a whole lifespan. An enhanced ability to reject grafts due to recipient immune competence, alloimmunization, and autoimmunity add to the complexity of this balance making NMD a highly diverse group of unrelated disorders. The addition of donor factors such as stem cell source and Human-Leukocyte-Antigen match extend the complexity such that 'one size does not fit all'. In this perspective, we will discuss current knowledge of the role of chimerism and goals, approach to HCT, and emerging methods of boosting engraftment and graft function, and monitoring recommendations. We draw attention to knowledge gaps and areas of necessity for further research and research support.

Ostm1 from Mouse to Human: Insights into Osteoclast Maturation

The maintenance of bone mass is a dynamic process that requires a strict balance between bone formation and resorption. Bone formation is controlled by osteoblasts, while osteoclasts are responsible for resorption of the bone matrix. The opposite functions of these cell types have to be tightly regulated not only during normal bone development, but also during adult life, to maintain serum calcium homeostasis and sustain bone integrity to prevent bone fractures. Disruption of the control of bone synthesis or resorption can lead to an over accumulation of bone tissue in osteopetrosis or conversely to a net depletion of the bone mass in osteoporosis. Moreover, high levels of bone resorption with focal bone formation can cause Paget’s disease. Here, we summarize the steps toward isolation and characterization of the osteopetrosis associated trans-membrane protein 1 (Ostm1) gene and protein, essential for proper osteoclast maturation, and responsible when mutated for the most severe form of osteopetrosis in mice and humans.

A Rare Case of Malignant Infantile Osteopetrosis Presenting as Frontal Lobe Hemorrhage

Osteopetrosis comprises a group of rare inherited disorders of the bones characterized by a common radiographic finding of increased bone thickness. The disorders vary genetically as well as clinically, and range in severity from mild manifestations to fatal complications based on the type of the disorder. Malignant infantile osteopetrosis (MIOP) is a less common, more severe form of the disease with most affected individuals surviving up to only the first few years of life if left untreated. We present a previously diagnosed case of the malignant infantile type who was brought to our attention for convulsions. Antiepileptic medications were started along with supportive therapy. CT scan revealed a large frontal lobe hemorrhage, which was suspected as a possible cause of the seizures, other than the progressively worsening hypocalcemia. Laboratory investigations also revealed pancytopenia and blood cultures positive for staphylococci, which were treated accordingly. Genetic testing and hematopoietic stem cell transplantation could not be performed due to financial constraints and the rapidly deteriorating condition of the patient. Unfortunately, the baby expired two weeks from the day of admission. This case highlights a rare and grave clinical manifestation of MIOP and brings to attention the significance of bone marrow transplantation as the only curative therapy of the disease.

Osteopetrorickets Presenting with Failure to Thrive and Hypophosphatemia

Osteopetrosis is a rare group of bone disorders characterized by defective osteoclast bone resorption causing high bone mineral density. A high bone mineral density in combination with defective skeletal mineralization results in a phenotype of osteopetrorickets. We present a rare presentation of infantile osteopetrorickets in an 8-week-old female who presented with failure to thrive, hypophosphatemia, anemia, and thrombocytopenia. A skeletal survey showed increased bone density with rachitic changes. She was found to have a homozygous T-cell immune regulator 1 (TCIRG1) pathogenic mutation consistent with osteopetrosis. This highlights the importance of a clinical suspicion of osteopetrosis with this symptom constellation.

Stem cell transplantation for osteopetrosis in patients beyond the age of 5 years

Osteopetrosis (OP) is a rare disease caused by defective osteoclast differentiation or function. Hematopoietic stem cell transplantation (HSCT) is the only curative treatment available in the infantile "malignant" form of OP. Improved clinical and genetic diagnosis of OP has seen the emergence of a cohort of patients with less severe and heterogeneous clinical presentations. This intermediate form of OP does not call for urgent intervention, but patients accumulate debilitating skeletal complications over years and decades, which are severe enough to require curative treatment and may also require intermittent transfusion of blood products. Here we present data from 7 patients with intermediate OP caused by mutations in TCIRG1 (n = 2), CLCN7 (n = 2), RANK (n = 1), SNX10 (n = 1), and CA2 (n = 1), who were transplanted between the ages of 5 to 30 years (mean, 15; median, 12). Donors were matched siblings or family (n = 4), matched unrelated (n = 2), or HLA haploidentical family donors (n = 1). Conditioning was fludarabine and treosulfan based. All 6 patients transplanted from matched donors are currently alive with a follow-up period between 1 and 8 years at time of publication (median, 4 years) and have demonstrated a significant improvement in symptoms and quality of life. Patients with intermediate OP should be considered for HSCT.

TCIRG1 Transgenic Rescue of Osteoclast Function Using Induced Pluripotent Stem Cells Derived from Patients with Infantile Malignant Autosomal Recessive Osteopetrosis

BACKGROUND

Osteoclasts are hematopoietic stem cell-derived multinucleated cells necessary for bone remodeling and resorption. TCIRG1 encodes a protein that is an adenosine triphosphate (ATP)-dependent vacuolar proton pump required for this process. Recessive loss-of-function mutations in both copies of this gene lead to impairment of osteoclast function, with increased bone density, increased skeletal mass, and early mortality.

METHODS

We isolated fibroblasts from a patient with the compound heterozygous TCIRG1 mutations c.1549G>A (p.517D>N) and c.2236C>T (p.746Q>X), and reprogrammed them into iPS (induced pluripotent stem) cells. The function of osteoclasts derived from these cells was then rescued by transgenic expression of TCIRG1 cDNA.

RESULTS

In addition to the known effects of TCIRG1 loss of function, iPS cell-derived osteoclasts from this patient had reduced expression of the bone remodeling enzymes cathepsin K (CTSK) and tartrate-resistant acid phosphatase (TRAP), leading to reduced in vitro bone remodeling. Expression of both genes and pit formation were restored in iPS cell-derived osteoclasts following transgenic restoration of TCIRG1 expression.

CONCLUSIONS

Transgenic overexpression of TCIRG1 was sufficient to restore osteoclast function in iPS cell-derived osteoclasts from a patient with infantile malignant autosomal-recessive osteopetrosis.

CLINICAL RELEVANCE

This work provides a proof of concept for an autologous approach to treating osteopetrosis, potentially avoiding the risks associated with hematopoietic stem cell transplantation in a young patient population.

Current status of umbilical cord blood transplantation in children

The first umbilical cord blood (UCB) transplantation was performed 30 years ago. UCB transplantation (UCBT) is now widely used in children with malignant and non-malignant disorders who lack a matched family donor. UCBT affords a lower incidence of graft-versus-host disease compared to alternative stem cell sources, but also presents a slower immune recovery and a high risk of infections if serotherapy is not omitted or targeted within the conditioning regimen. The selection of UCB units with high cell content and good human leucocyte antigen match is essential to improve the outcome. Techniques, such as double UCBT, ex vivo stem cell expansion and intra-bone injection of UCB, have improved cord blood engraftment, but clinical benefit remains to be demonstrated. Cell therapies derived from UCB are under evaluation as potential novel strategies to reduce relapse and viral infections following transplantation. In recent years, improvements within haploidentical transplantation have reduced the overall use of UCBT as an alternative stem cell source; however, each may have its relative merits and disadvantages and tailored use of these alternative stem cell sources may be the optimal approach.

Hematopoietic Stem Cell Transplantation: A Neonatal Perspective

Allogeneic hematopoietic stem cell transplantation (HSCT) is indicated in various nonmalignant disorders that arise from genetic, hematopoietic, and immune system defects. Many of the disorders described here have life-threatening consequences in the absence of HSCT, a curative intervention. However, timing and approach to HSCT vary by disorder and optimum results are achieved by performing transplantation before irreversible disease-related morbidity or infectious complications. This article details the principles of HSCT in the very young, lists indications, and explores the factors that contribute to successful outcomes based on transplantation and disease-related nuances. It provides an overview into the HSCT realm from a neonatologist's perspective, describes the current status of transplantation for relevant disorders of infancy, and provides a glimpse into future efforts at improving on current success.

Survival Trends in Infants Undergoing Allogeneic Hematopoietic Cell Transplant

IMPORTANCE

Studies demonstrating improved survival after allogeneic hematopoietic cell transplant generally exclude infants.

OBJECTIVE

To analyze overall survival trends and other outcomes among infants who undergo allogeneic hematopoietic cell transplant.

DESIGN, SETTING, AND PARTICIPANTS

In this cohort study, we used time-trend analysis to evaluate 3 periods: 2000 through 2004, 2005 through 2009, and 2010 through 2014. The study was conducted in a multicenter setting through the Center for International Blood and Marrow Transplant Research, which is made up of a voluntary working group of more than 450 transplant centers worldwide. Two groups of infants aged 1 year or younger in 2 cohorts were included: those with malignant conditions, such as leukemia, and those with nonmalignant disorders, including immunodeficiencies. Data analysis was conducted from July 2017 to December 2018.

EXPOSURES

Allogeneic hematopoietic cell transplant.

MAIN OUTCOMES AND MEASURES

Survival trends, disease relapse, and toxicity.

RESULTS

A total of 2498 infants with a median age of 7 months (range, <1-12 months) were included. In the nonmalignant cohort (n = 472), survival rates improved from the first to the second period (hazard ratio, 0.77 [95% CI, 0.63-0.93]; P = .007) but did not change after 2004. Compared with infants with nonmalignant diseases (n = 2026; 3-year overall survival: 2000-2004, 375/577 [65.0%]; 2005-2009, 503/699 [72.0%]; and 2010-2014, 555/750 [74.0%]), those with malignant conditions had poorer survival rates, without improvement over time (3-year overall survival: 2000-2004, 109/199 [54.8%]; 2005-2009, 104/161 [64.6%]; and 2010-2014, 66/112 [58.9%]). From 2000 through 2014, relapse rates increased in infants with malignant conditions (3-year relapse rate: 2000-2004, 19% [95% CI, 14%-25%]; 2005-2009, 23% [95% CI, 17%-30%]; 2010-2014, 36% [95% CI, 27%-46%]; P = .01). Sinusoidal obstruction syndrome was frequent, occurring with a cumulative incidence of 13% (95% CI, 11%-16%) of infants with nonmalignant diseases and 32% (95% CI, 22%-42%) of those with malignant diseases. Generally, recipients of human leukocyte antigen-identical sibling bone marrow grafts had the best outcomes.

CONCLUSIONS AND RELEVANCE

Survival rates have not improved for infants with malignant diseases over the 15-year study period. Infants with nonmalignant diseases had improved survival rates in the earlier but not the later study period. Higher relapses for the malignant cohort and toxicities for all infants remain significant challenges. Strategies to reduce relapse and toxicity and optimize donor and graft selection may improve outcomes in the future.

Hepatic late adverse effects after antineoplastic treatment for childhood cancer

BACKGROUND

Survival rates have greatly improved as a result of more effective treatments for childhood cancer. Unfortunately, the improved prognosis has been accompanied by the occurrence of late, treatment-related complications. Liver complications are common during and soon after treatment for childhood cancer. However, among long-term childhood cancer survivors, the risk of hepatic late adverse effects is largely unknown. To make informed decisions about future cancer treatment and follow-up policies, it is important to know the risk of, and associated risk factors for, hepatic late adverse effects. This review is an update of a previously published Cochrane review.

OBJECTIVES

To evaluate all the existing evidence on the association between antineoplastic treatment (that is, chemotherapy, radiotherapy involving the liver, surgery involving the liver and BMT) for childhood cancer and hepatic late adverse effects.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2018, Issue 1), MEDLINE (1966 to January 2018) and Embase (1980 to January 2018). In addition, we searched reference lists of relevant articles and scanned the conference proceedings of the International Society of Paediatric Oncology (SIOP) (from 2005 to 2017) and American Society of Pediatric Hematology/Oncology (ASPHO) (from 2013 to 2018) electronically.

SELECTION CRITERIA

All studies, except case reports, case series, and studies including fewer than 10 patients that examined the association between antineoplastic treatment for childhood cancer (aged 18 years or less at diagnosis) and hepatic late adverse effects (one year or more after the end of treatment).

DATA COLLECTION AND ANALYSIS

Two review authors independently performed the study selection and 'risk of bias' assessment. The 'risk of bias' assessment was based on earlier checklists for observational studies. For the original version of the review, two review authors independently performed data extraction. For the update of the review, the data extraction was performed by one reviewer and checked by another reviewer.

MAIN RESULTS

Thirteen new studies were identified for the update of this review. In total, we included 33 cohort studies including 7876 participants investigating hepatic late adverse effects after antineoplastic treatment (especially chemotherapy and radiotherapy) for different types of childhood cancer, both haematological and solid malignancies. All studies had methodological limitations. The prevalence of hepatic late adverse effects, all defined in a biochemical way, varied widely, between 0% and 84.2%. Selecting studies where the outcome of hepatic late adverse effects was well-defined as alanine aminotransferase (ALT) above the upper limit of normal, indicating cellular liver injury, resulted in eight studies. In this subgroup, the prevalence of hepatic late adverse effects ranged from 5.8% to 52.8%, with median follow-up durations varying from three to 23 years since cancer diagnosis in studies that reported the median follow-up duration. A more stringent selection process using the outcome definition of ALT as above twice the upper limit of normal, resulted in five studies, with a prevalence ranging from 0.9% to 44.8%. One study investigated biliary tract injury, defined as gamma-glutamyltransferase (γGT) above the upper limit of normal and above twice the upper limit of normal and reported a prevalence of 5.3% and 0.9%, respectively. Three studies investigated disturbance in biliary function, defined as bilirubin above the upper limit of normal and reported prevalences ranging from 0% to 8.7%. Two studies showed that treatment with radiotherapy involving the liver (especially after a high percentage of the liver irradiated), higher BMI, and longer follow-up time or older age at evaluation increased the risk of cellular liver injury in multivariable analyses. In addition, there was some suggestion that busulfan, thioguanine, hepatic surgery, chronic viral hepatitis C, metabolic syndrome, use of statins, non-Hispanic white ethnicity, and higher alcohol intake (> 14 units per week) increase the risk of cellular liver injury in multivariable analyses. Chronic viral hepatitis was shown to increase the risk of cellular liver injury in six univariable analyses as well. Moreover, one study showed that treatment with radiotherapy involving the liver, higher BMI, higher alcohol intake (> 14 units per week), longer follow-up time, and older age at cancer diagnosis increased the risk of biliary tract injury in a multivariable analysis.

AUTHORS' CONCLUSIONS

The prevalence of hepatic late adverse effects among studies with an adequate outcome definition varied considerably from 1% to 53%. Evidence suggests that radiotherapy involving the liver, higher BMI, chronic viral hepatitis and longer follow-up time or older age at follow-up increase the risk of hepatic late adverse effects. In addition, there may be a suggestion that busulfan, thioguanine, hepatic surgery, higher alcohol intake (>14 units per week), metabolic syndrome, use of statins, non-Hispanic white ethnicity, and older age at cancer diagnosis increase the risk of hepatic late adverse effects. High-quality studies are needed to evaluate the effects of different therapy doses, time trends, and associated risk factors after antineoplastic treatment for childhood cancer.

Developmental origin, functional maintenance and genetic rescue of osteoclasts

Osteoclasts are multinucleated giant cells that resorb bone, ensuring development and continuous remodelling of the skeleton and the bone marrow haematopoietic niche. Defective osteoclast activity leads to osteopetrosis and bone marrow failure^1-9, whereas excess activity can contribute to bone loss and osteoporosis¹⁰. Osteopetrosis can be partially treated by bone marrow transplantation in humans and mice^11-18, consistent with a haematopoietic origin of osteoclasts^13,16,19 and studies that suggest that they develop by fusion of monocytic precursors derived from haematopoietic stem cells in the presence of CSF1 and RANK ligand^1,20. However, the developmental origin and lifespan of osteoclasts, and the mechanisms that ensure maintenance of osteoclast function throughout life in vivo remain largely unexplored. Here we report that osteoclasts that colonize fetal ossification centres originate from embryonic erythro-myeloid progenitors^21,22. These erythro-myeloid progenitor-derived osteoclasts are required for normal bone development and tooth eruption. Yet, timely transfusion of haematopoietic-stem-cell-derived monocytic cells in newborn mice is sufficient to rescue bone development in early-onset autosomal recessive osteopetrosis. We also found that the postnatal maintenance of osteoclasts, bone mass and the bone marrow cavity involve iterative fusion of circulating blood monocytic cells with long-lived osteoclast syncytia. As a consequence, parabiosis or transfusion of monocytic cells results in long-term gene transfer in osteoclasts in the absence of haematopoietic-stem-cell chimerism, and can rescue an adult-onset osteopetrotic phenotype caused by cathepsin K deficiency^23,24. In sum, our results identify the developmental origin of osteoclasts and a mechanism that controls their maintenance in bones after birth. These data suggest strategies to rescue osteoclast deficiency in osteopetrosis and to modulate osteoclast activity in vivo.

Indications for haematopoietic stem cell transplantation for haematological diseases, solid tumours and immune disorders: current practice in Europe, 2019

This is the seventh special EBMT report on the indications for haematopoietic stem cell transplantation for haematological diseases, solid tumours and immune disorders. Our aim is to provide general guidance on transplant indications according to prevailing clinical practice in EBMT countries and centres. In order to inform patient decisions, these recommendations must be considered together with the risk of the disease, the risk of the transplant procedure and the results of non-transplant strategies. In over two decades since the first report, the EBMT indications manuscripts have incorporated changes in transplant practice coming from scientific and technical developments in the field. In this same period, the establishment of JACIE accreditation has promoted high quality and led to improved outcomes of patient and donor care and laboratory performance in transplantation and cellular therapy. An updated report with operating definitions, revised indications and an additional set of data with overall survival at 1 year and non-relapse mortality at day 100 after transplant in the commonest standard-of-care indications is presented. Additional efforts are currently underway to enable EBMT member centres to benchmark their risk-adapted outcomes as part of the Registry upgrade Project 2020 against national and/or international outcome data.

Bone Marrow Transplantation for Treatment of the Col1a2+/G610C Osteogenesis Imperfecta Mouse Model

Bone marrow transplantation (BMT) of healthy donor cells has been postulated as a strategy for treating osteogenesis imperfecta (OI) and other bone fragility disorders. The effect of engraftment by tail vein injection and/or marrow ablation by 6 Gy whole body irradiation were tested in Col1a2^+/G610C (OI) mice as a model of mild-moderate OI. Dual-emission X-ray absorptiometry, microCT, and 4-point bending were used to measure bone volume (BV), bone mineral density (BMD), and biomechanical strength. BV, BMD, and mechanical strength were reduced in OI mice compared to wild type (WT) controls. BMT with and without irradiation yielded no difference in BV and BMD outcomes for both OI and WT mice, at 3 weeks. Transplantation of OI cells into OI mice to test for paracrine effects of BMT also showed no difference with non-transplanted OI mice. In a parallel cell tracking study, donor marrow was taken from transgenic mice constitutively expressing tdTomato and transplanted into WT mice. Lineage tracking demonstrated that irradiation considerably enhanced engraftment of tdTomato+ cells. However, tdTomato+ cells predominantly expressed TRAP and not AP, indicating engrafted donor cells were chiefly from the hematopoietic lineages. These data show that whole marrow transplantation fails to rescue the bone phenotype of Col1a2^+/G610C (OI) mice and that osteopoietic engraftment is not significantly enhanced by irradiation. These findings are highly relevant to modern approaches focused on the gene repair of patient cells ex vivo and their subsequent reintroduction into the osteopoietic compartment via the circulation.

Haploidentical Hematopoietic Stem Cell Transplantation with Post-Transplant Cyclophosphamide for Primary Immunodeficiencies and Inherited Disorders in Children

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative treatment for some inherited disorders, including selected primary immunodeficiencies (PIDs). In the absence of a well-matched donor, HSCT from a haploidentical family donor (HIFD) may be considered. In adult recipients high-dose post-transplant cyclophosphamide (PTCY) is increasingly used to mitigate the risks of graft failure and graft-versus-host disease (GVHD). However, data on the use of PTCY in children (and especially those with inherited disorders) are scarce. We reviewed the outcomes of 27 children transplanted with an HIFD and PTCY for a PID (n = 22) or osteopetrosis (n = 5) in a single center. The median age was 1.5 years (range, .2 to 17). HSCT with PTCY was a primary procedure (n = 21) or a rescue procedure after graft failure (n = 6). The conditioning regimen was myeloablative in most primary HSCTs and nonmyeloablative in rescue procedures. After a median follow-up of 25.6 months, 24 of 27 patients had engrafted. Twenty-one patients are alive and have been cured of the underlying disease. The 2-year overall survival rate was 77.7%. The cumulative incidences of acute GVHD grade ≥ II, chronic GVHD, and autoimmune disease were 45.8%, 24.2%, and 29.6%, respectively. There were 2 cases of grade III acute GVHD and no extensive cGVHD. The cumulative incidences of blood viral replication and life-threatening viral events were 58% and 15.6%, respectively. There was evidence of early T cell immune reconstitution. In the absence of an HLA-identical donor, HIFD HSCT with PTCY is a viable option for patients with life-threatening inherited disorders.

Comparison of Optic Canal Diameter in Children With Malignant Infantile Osteopetrosis and Normal Children and the Effects of Hematopoietic Stem Cell Transplantation on the Optic Canal Diameter

PURPOSE

To investigate the difference in the optic canal diameter between children with autosomal recessive malignant infantile osteopetrosis and normal children, and to assess the influence of hematopoietic stem cell transplantation on the optic canal diameter.

METHODS

Twenty pediatric patients with malignant infantile osteopetrosis and 22 normal control children were included in this study. Eleven patients with malignant infantile osteopetrosis underwent hematopoietic stem cell transplantation. The measurements included optical canal diameter and flash visual evoked potential. Comparisons of these measurements between patients with malignant infantile osteopetrosis and normal controls as well as before and after hematopoietic stem cell transplantation were performed. The correlation between age and optic canal diameter was analyzed using Pearson correlation analysis.

RESULTS

The mean optic canal diameter before hematopoietic stem cell transplantation was 1.65 ± 0.54 mm in patients with malignant infantile osteopetrosis and 3.38 ± 0.60 mm in the control group (P < .001). The mean optic canal diameter after hematopoietic stem cell transplantation was 2.72 ± 0.66 mm, which was significantly different from the pre-transplantation measurement (P < .001). The P2 latency for the flash visual evoked potential after hematopoietic stem cell transplantation (152.3 ± 36.4 ms) was significantly less than that before transplantation (165.5 ± 27.7 ms; P = .051). Pearson correlation analysis revealed a significant correlation between age and optic canal diameter (r = 0.722, P < .001).

CONCLUSIONS

The optic canal was narrower in pediatric patients with malignant infantile osteopetrosis than in age-matched normal controls. This condition can be relieved through hematopoietic stem cell transplantation and the impaired conductibility of the optic nerve can be improved in some cases. [J Pediatr Ophthalmol Strabismus. 2019;56(1):35-42.].