Hematopoietic stem cell transplantation for infantile osteopetrosis

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.].

One Disease, Many Genes: Implications for the Treatment of Osteopetroses

Osteopetrosis is a condition characterized by increased bone mass due to defects in osteoclast function or formation. In the last decades, the molecular dissection of osteopetrosis has unveiled a plethora of molecular players responsible for different forms of the disease, some of which present also primary neurodegeneration that severely limits the therapy. Hematopoietic stem cell transplantation can cure the majority of them when performed in the first months of life, highlighting the relevance of an early molecular diagnosis. However, clinical management of these patients is constrained by the severity of the disease and lack of a bone marrow niche that may delay immune reconstitution. Based on osteopetrosis genetic heterogeneity and disease severity, personalized therapies are required for patients that are not candidate to bone marrow transplantation. This review briefly describes the genetics of osteopetrosis, its clinical heterogeneity, current therapy and innovative approaches undergoing preclinical evaluation.

Impact of low-dose irradiation and in vivo T-cell depletion on hematopoietic stem cell transplantation for non-malignant diseases using fludarabine-based reduced-intensity conditioning

Reduced-intensity conditioning is widely used with hematopoietic stem cell transplantation for non-malignant diseases: however, the optimal conditioning to ensure stable engraftment has not been established. In this study, we retrospectively compared the impact of low-dose (1-6 Gy) irradiation and in vivo T-cell depletion on the clinical outcome of 523 patients with non-malignant disease who underwent a first allogeneic hematopoietic stem cell transplantation using fludarabine-based reduced-intensity conditioning. Use of low-dose irradiation, but not of anti-thymocyte globulin/anti-lymphocyte globulin, showed a beneficial effect on overall survival (adjusted hazard ratio: 0.56; 95% confidence interval: 0.35-0.91, P = 0.018). Furthermore, use of low-dose irradiation was strongly associated with lower transplant-related mortality (adjusted hazard ratio: 0.55; 95% confidence interval: 0.32-0.96, P = 0.034). The addition of low-dose irradiation to the conditioning regimen was beneficial, at least to the short-term clinical outcome. A large prospective study with long-term follow-up is now required to extend these findings and establish the optimal hematopoietic stem cell transplant conditioning for patients with at least some subgroups of non-malignant diseases.

MiT family translocation renal cell carcinoma after malignant infantile osteopetrosis in childhood: a case report

Malignant infantile osteopetrosis (MIOP) is a rare inherited bone metabolism disorder characterized by increased bone mineral density (BMD) and abnormal hematopoiesis. Hematopoietic stem cell transplantation (HSCT) is currently the only curative therapy for MIOP. However, a higher risk of secondary malignancy occurs in children previously exposed to cytotoxic drugs. Here we report a rare case of a 3-year-old female patient with MiT family translocation renal cell carcinoma (MiTF tRCC), who is a survivor of HSCT for MIOP 2 years earlier. The patient had a complete resection of the tumor. Microscopically, we detected diffusely and papillary-like arranged tumor cells whose cytoplasm was bright and clear. Immunohistochemistry showed tumor cells diffusely expressed TFE3, and fluorescence in situ hybridization (FISH) demonstrated disruption of the TFE3 locus, confirming the diagnosis of Xp11 translocation RCC, the subtype of MiTF tRCC. This case supports the view that chemotherapy exposure is a risk factor for MiTF tRCC and indicates the possible association of HSCT with MiTF tRCC.

Successful hematopoietic stem cell transplantation for osteopetrosis using reduced intensity conditioning

BACKGROUND

Infantile malignant osteopetrosis (IMO) is an autosomal recessive condition characterized by defective osteoclast activity, with hematopoietic bone marrow transplant being the only available cure. Over the past several years, new conditioning regimes and donor options have emerged, thus extending the possibility of cure to a greater number of patients and improving the outcomes of bone marrow transplant. Here we detail the outcomes of bone marrow transplant in a cohort of 31 patients treated with a combination of fludarabine, treosulphan, thiotepa, and antithymocyte globulin.

PROCEDURES

Thirty-one patients with IMO who underwent hematopoietic stem cell transplantation with fludarabine, treosulphan, thiotepa, and antithymocyte globulin at our center from 2012 to 2017 are retrospectively reviewed in this study. Twenty-six patients were transplanted from 10/10 matched donors (13 from siblings, 11 from unrelated, and two from extended family donors), four from 9/10 matched unrelated donors, and one from a 9/10 matched family donor.

RESULTS

Overall survival was 100% with a median follow-up of 363 days (range 74-1891). There were 12 cases of acute graft versus host disease (GvHD) (38.7%), no cases of veno-occlusive disease, and eight cases of hypercalcemia (25.8%). Almost 80% of patients suffered viral reactivations with two cases of Epstein-Barr-virus-driven post-transplant lymphoproliferative disease. All cases of GvHD and viral reactivation were successfully treated.

CONCLUSIONS

We conclude that transplantation in children with IMO using fludarabine, treosulphan, thiotepa, and antithymocyte globulin is safe and effective and should be performed as early as possible following diagnosis, prior to the development of severe disease sequelae.

Genetics of Osteopetrosis

PURPOSE OF REVIEW

The term osteopetrosis refers to a group of rare skeletal diseases sharing the hallmark of a generalized increase in bone density owing to a defect in bone resorption. Osteopetrosis is clinically and genetically heterogeneous, and a precise molecular classification is relevant for prognosis and treatment. Here, we review recent data on the pathogenesis of this disorder.

RECENT FINDINGS

Novel mutations in known genes as well as defects in new genes have been recently reported, further expanding the spectrum of molecular defects leading to osteopetrosis. Exploitation of next-generation sequencing tools is ever spreading, facilitating differential diagnosis. Some complex phenotypes in which osteopetrosis is accompanied by additional clinical features have received a molecular classification, also involving new genes. Moreover, novel types of mutations have been recognized, which for their nature or genomic location are at high risk being neglected. Yet, the causative mutation is unknown in some patients, indicating that the genetics of osteopetrosis still deserves intense research efforts.

Diagnosis and Management of Osteopetrosis: Consensus Guidelines From the Osteopetrosis Working Group

BACKGROUND

Osteopetrosis encompasses a group of rare metabolic bone diseases characterized by impaired osteoclast activity or development, resulting in high bone mineral density. Existing guidelines focus on treatment of the severe infantile forms with hematopoietic cell transplantation (HCT) but do not address the management of patients with less severe forms for whom HCT is not the standard of care. Therefore, our objective was to develop expert consensus guidelines for the management of these patients.

METHODS

A modified Delphi method was used to build consensus among participants of the Osteopetrosis Working Group, with responses to an anonymous online survey used to identify areas of agreement and conflict and develop a follow-up survey. The strength of recommendations and quality of evidence was graded using the Grading of Recommendations Assessment, Development and Evaluation system.

RESULTS

Consensus was found in the areas of diagnosis, monitoring, and treatment. We recommend relying on characteristic radiographic findings to make the diagnosis and found that genetic testing adds important information by identifying mutations associated with unique disease complications. We recommend ongoing monitoring for changes in mineral metabolism and other complications, including cranial nerve impingement, anemia, leukopenia, and dental disease. We suggest that calcitriol should not be used in high doses and instead recommend symptom-based supportive therapy for disease complications because noninfantile osteopetrosis has no effective treatment.

CONCLUSIONS

Scarcity of published studies on osteopetrosis reduce the ability to develop evidence-based guidelines for the management of these patients. Expert opinion-based guidelines for this rare condition are nevertheless important to enable improved care.

Allele-level HLA matching for umbilical cord blood transplantation for non-malignant diseases in children: a retrospective analysis

BACKGROUND

The standard for selecting unrelated umbilical cord blood units for transplantation for non-malignant diseases relies on antigen-level (lower resolution) HLA typing for HLA-A and HLA-B, and allele-level for HLA-DRB1. We aimed to study the effects of allele-level matching at a higher resolution-HLA-A, HLA-B, HLA-C, and HLA-DRB1, which is the standard used for adult unrelated volunteer donor transplantation for non-malignant diseases-for umbilical cord blood transplantation.

METHODS

We retrospectively studied 1199 paediatric donor-recipient pairs with allele-level HLA matching who received a single unit umbilical cord blood transplantation for non-malignant diseases reported to the Center for International Blood and Marrow Transplant Research or Eurocord and European Group for Blood and Marrow Transplant. Transplantations occurred between Jan 1, 2000, and Dec 31, 2012. The primary outcome was overall survival. The effect of HLA matching on survival was studied using a Cox regression model.

FINDINGS

Compared with HLA-matched transplantations, mortality was higher with transplantations mismatched at two (hazard ratio [HR] 1·55, 95% CI 1·08-2·21, p=0·018), three (2·04, 1·44-2·89, p=0·0001), and four or more alleles (3·15, 2·16-4·58, p<0·0001). There were no significant differences in mortality between transplantations that were matched and mismatched at one allele (HR 1·18, 95% CI 0·80-1·72, p=0·39). Other factors associated with higher mortality included recipient cytomegalovirus seropositivity (HR 1·40, 95% CI 1·13-1·74, p=0·0020), reduced intensity compared with myeloablative conditioning regimens (HR 1·36, 1·10-1·68, p=0·0041), transplantation of units with total nucleated cell dose of more than 21 × 10⁷ cells per kg compared with 21 × 10⁷ cells per kg or less (HR 1·47, 1·11-1·95, p=0·0076), and transplantations done in 2000-05 compared with those done in 2006-12 (HR 1·64, 1·31-2·04, p<0·0001). The 5-year overall survival adjusted for recipient cytomegalovirus serostatus, conditioning regimen intensity, total nucleated cell dose, and transplantation period was 79% (95% CI 74-85) after HLA matched, 76% (71-81) after one allele mismatched, 70% (65-75) after two alleles mismatched, 62% (57-68) after three alleles mismatched, and 49% (41-57) after four or more alleles mismatched transplantations. Graft failure was the predominant cause of mortality.

INTERPRETATION

These data support a change from current practice in that selection of unrelated umbilical cord blood units for transplantation for non-malignant diseases should consider allele-level HLA matching at HLA-A, HLA-B, HLA-C, and HLA-DRB1.

FUNDING

National Cancer Institute; National Heart, Lung, and Blood Institute; National Institute for Allergy and Infectious Diseases; US Department of Health and Human Services-Health Resources and Services Administration; and US Department of Navy.

Homozygous deletion of RAG1, RAG2 and 5' region TRAF6 causes severe immune suppression and atypical osteopetrosis

Mutations of several genes have been implicated in autosomal recessive osteopetrosis (OP), a disease caused by impaired function and differentiation of osteoclasts. Severe combined immune deficiencies (SCID) can likewise result from different genetic mutations. We report two siblings with SCID and an atypical phenotype of OP. A biallelic microdeletion encompassing the 5' region of TRAF6, RAG1 and RAG2 genes was identified. TRAF6, a tumor necrosis factor receptor-associated family member, plays an important role in T cell signaling and in RANKL-dependent osteoclast differentiation and activation but its role in human OP has not been previously reported. The RAG proteins are essential for recombination of B and T cell receptors, and for the survival and differentiation of these cells. This is the first study to report a homozygous deletion of TRAF6 as a cause of human disease.

Transplantation of Haploidentical TcRaß-Depleted Hematopoietic Cells Allows for Optimal Timing and Sustained Correction of the Metabolic Defect in Children With Infantile Osteopetrosis

In osteopetrosis, osteoclast dysfunction can lead to deafness, blindness, bone marrow failure, and death. Hematopoietic cell transplantation (HCT) is currently the only curative treatment, but outcome remains disappointing. Although a rapid progression toward HCT is detrimental to prevent further progress of disease manifestations, 70% of cases lack an HLA-matched sibling and require alternative stem cell sources. We present two cases of osteopetrosis that successfully received an HCT with haploidentical TcRαβ-depleted cells from one of the parents. These cases showed no further disease progression, had restoration of functional osteoclasts, and illustrate this approach to enable prompt HCT with ready available parental donors and rapid and sustained hematological, including osteoclast, recovery. © 2016 American Society for Bone and Mineral Research.

Regulation and Function of Lentiviral Vector-Mediated TCIRG1 Expression in Osteoclasts from Patients with Infantile Malignant Osteopetrosis: Implications for Gene Therapy

Infantile malignant osteopetrosis (IMO) is a rare, recessive disorder characterized by increased bone mass caused by dysfunctional osteoclasts. The disease is most often caused by mutations in the TCIRG1 gene encoding a subunit of the V-ATPase involved in the osteoclasts capacity to resorb bone. We previously showed that osteoclast function can be restored by lentiviral vector-mediated expression of TCIRG1, but the exact threshold for restoration of resorption as well as the cellular response to vector-mediated TCIRG1 expression is unknown. Here we show that expression of TCIRG1 protein from a bicistronic TCIRG1/GFP lentiviral vector was only observed in mature osteoclasts, and not in their precursors or macrophages, in contrast to GFP expression, which was observed under all conditions. Thus, vector-mediated TCIRG1 expression appears to be post-transcriptionally regulated, preventing overexpression and/or ectopic expression and ensuring protein expression similar to that of wild-type osteoclasts. Codon optimization of TCIRG1 led to increased expression of mRNA but lower levels of protein and functional rescue. When assessing the functional rescue threshold in vitro, addition of 30 % CB CD34⁺ cells to IMO CD34⁺ patient cells was sufficient to completely normalize resorptive function after osteoclast differentiation. From both an efficacy and a safety perspective, these findings will clearly be of benefit during further development of gene therapy for osteopetrosis.

Extending the Spectrum of Radiological Findings in Patients With Severe Osteopetrosis and Different Genetic Backgrounds

PURPOSE

To evaluate radiological findings in a cohort of 22 patients with infantile malignant osteopetrosis in order to establish the correlation between radiological findings and different genetic backgrounds.

MATERIALS AND METHODS

Clinical files, genetic analysis results, and radiological examinations of children treated for osteopetrosis with bone marrow transplantation in a referral center in the last 5 years were retrospectively evaluated. The study received institutional review board (IRB) approval.

RESULTS

Twenty-two patients were included in the study: 18 males, four females, ages 1 month-9 years 10 months, and the median age was 11 months (mean 23 months). There were 12 patients with different mutations in the TCIRG1 gene, five with mutations in the SNX10 gene, four children harbored RANK mutations, and one patient had a CLCN7 mutation. We noted more severe radiological findings in patients with TCIRG1 and RANK mutations, including fractures, osteopetrorickets, hydrocephalus, and hepatomegaly. Varus deformity of the femoral neck was seen exclusively in patients with a TCIRG1 mutation.

CONCLUSIONS

The variable genetic spectrum of osteopetrosis is associated with a variable radiological presentation. These correlations may be helpful for priorities in genetic analysis.

Therapeutic Approaches to Genetic Ion Channelopathies and Perspectives in Drug Discovery

In the human genome more than 400 genes encode ion channels, which are transmembrane proteins mediating ion fluxes across membranes. Being expressed in all cell types, they are involved in almost all physiological processes, including sense perception, neurotransmission, muscle contraction, secretion, immune response, cell proliferation, and differentiation. Due to the widespread tissue distribution of ion channels and their physiological functions, mutations in genes encoding ion channel subunits, or their interacting proteins, are responsible for inherited ion channelopathies. These diseases can range from common to very rare disorders and their severity can be mild, disabling, or life-threatening. In spite of this, ion channels are the primary target of only about 5% of the marketed drugs suggesting their potential in drug discovery. The current review summarizes the therapeutic management of the principal ion channelopathies of central and peripheral nervous system, heart, kidney, bone, skeletal muscle and pancreas, resulting from mutations in calcium, sodium, potassium, and chloride ion channels. For most channelopathies the therapy is mainly empirical and symptomatic, often limited by lack of efficacy and tolerability for a significant number of patients. Other channelopathies can exploit ion channel targeted drugs, such as marketed sodium channel blockers. Developing new and more specific therapeutic approaches is therefore required. To this aim, a major advancement in the pharmacotherapy of channelopathies has been the discovery that ion channel mutations lead to change in biophysics that can in turn specifically modify the sensitivity to drugs: this opens the way to a pharmacogenetics strategy, allowing the development of a personalized therapy with increased efficacy and reduced side effects. In addition, the identification of disease modifiers in ion channelopathies appears an alternative strategy to discover novel druggable targets.

Emerging targeted drug therapies in skeletal dysplasias

Quantum advances have occurred in the field of human genetics in the six decades since Watson and Crick expressed their "wish to suggest a structure for the salt of deoxyribose nucleic acid." These culminated with the human genome project, which has opened up myriad possibilities, including that of individualized genetic medicine, the ability to deliver medical advice, management, and therapy tailored to an individual's genetic blueprint. Advances in genetic diagnostic capabilities have been rapid, to the point where the genome can be sequenced for several thousand dollars. Crucially, it has facilitated the identification of targets for "precision" treatments to combat genetic diseases at their source. This manuscript will review the innovative, pathogenesis-based therapies that are revolutionizing management of skeletal dysplasias, giving patients and families new options and outcomes. © 2016 Wiley Periodicals, Inc.

Improved Outcomes of Hematopoietic Stem Cell Transplantation in Patients With Infantile Malignant Osteopetrosis Using Fludarabine-Based Conditioning

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is the only curative treatment for infantile malignant osteopetrosis (IMO), but is associated with a high incidence of adverse outcomes. In this study, we present our experience with HSCT for IMO patients comparing different types of conditioning regimens.

METHODS

Thirty-eight patients with IMO (aged from 1 month to 6 years, median 0.66 years) who underwent allogeneic HSCT from 1983 in our hospital were included in this retrospective study. Fludarabine-based conditioning regimens were used in 26 patients and 12 patients were transplanted using other conditioning regimens.

RESULTS

The overall survival after conditioning with fludarabine was 96% (25/26) versus 58% (7/12) for the alternative regimens (P = 0.004), with significantly fewer adverse effects including hypercalcemia and veno-occlusive disease of liver. All patients who survive are clinically well.

CONCLUSIONS

We conclude that fludarabine-based conditioning regimens are safe and effective in patients with IMO, improving morbidity and mortality related to HSCT.

Targeted Gene Correction in Osteopetrotic-Induced Pluripotent Stem Cells for the Generation of Functional Osteoclasts

Autosomal recessive osteopetrosis is a human bone disease mainly caused by TCIRG1 gene mutations that prevent osteoclasts resorbing activity, recapitulated by the oc/oc mouse model. Bone marrow transplantation is the only available treatment, limited by the need for a matched donor. The use of induced pluripotent stem cells (iPSCs) as an unlimited source of autologous cells to generate gene corrected osteoclasts might represent a powerful alternative. We generated iPSCs from oc/oc mice, corrected the mutation using a BAC carrying the entire Tcirg1 gene locus as a template for homologous recombination, and induced hematopoietic differentiation. Similarly to physiologic fetal hematopoiesis, iPSC-derived CD41⁺ cells gradually gave rise to CD45⁺ cells, which comprised both mature myeloid cells and high proliferative potential colony-forming cells. Finally, we differentiated the gene corrected iPSC-derived myeloid cells into osteoclasts with rescued bone resorbing activity. These results are promising for a future translation into the human clinical setting.

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iPSCs from oc/oc mice bearing Tcirg1 gene mutation were generated for the first time

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A BAC-based approach corrects the Tcirg1 gene mutation

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iPSCs differentiate similarly to physiologic fetal hematopoiesis

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The osteopetrotic phenotype in osteoclasts from BAC-corrected iPSCs was rescued