Long-Term Follow-Up of Hematopoietic Stem-Cell Gene Therapy for Cerebral Adrenoleukodystrophy

Ligand-modified rAAV6 vectors with nanoblades allow high-level gene knockin in HSPCs without compromising cell survival

Nanoblades are viral particles loaded with the Cas9 protein complexed with gRNA, which allowed efficient gene editing in hematopoietic stem and progenitor cells (HSPCs). Combined with recombinant adeno-associated vector (rAAV) 6 containing two homologous arms to a gene locus resulted in 50% of expression cassette knockin into HSPCs. However, high effective doses of rAAV6 induced HSPC cell death. Here, we demonstrated that, at high doses, rAAV2 was much less toxic for template DNA delivery and allowed transduction levels in HSPCs equivalent to rAAV6. To improve donor template delivery, rAAV2 and rAAV6 were chemically bio-conjugated with a mannose ligand, via the lysine or tyrosine amino acid residues exposed at the adeno-associated vector (AAV) capsid surface. High-level transduction of HSPCs with mannose-coupled rAAV6 vectors accompanied by a remarkable lower toxicity was achieved as compared to control rAAV6 in correlation with highly reduced p53 pathway activation. Mannose-conjugated rAAV6 combined with nanoblades allowed efficient gene knockin and increased survival of HSPCs from 10% to 80% as compared to the unmodified rAAV6 even in the most immature CD34+CD38lowCD90+ hematopoietic stem cell (HSC) population. Summarizing, mannose-conjugated rAAV6 maintained high-level donor mediated gene knockin when combined with nanoblades without inducing significant toxicity for the HSPCs, an important feature for clinical translation of HSPC gene-editing strategies.

Revisiting the Pathogenesis of X-Linked Adrenoleukodystrophy

BACKGROUND

X-ALD is a white matter (WM) disease caused by mutations in the ABCD1 gene encoding the transporter of very-long-chain fatty acids (VLCFAs) into peroxisomes. Strikingly, the same ABCD1 mutation causes either devastating brain inflammatory demyelination during childhood or, more often, progressive spinal cord axonopathy starting in middle-aged adults. The accumulation of undegraded VLCFA in glial cell membranes and myelin has long been thought to be the central mechanism of X-ALD.

METHODS

This review discusses studies in mouse and drosophila models that have modified our views of X-ALD pathogenesis.

RESULTS

In the Abcd1 knockout (KO) mouse that mimics the spinal cord disease, the late manifestations of axonopathy are rapidly reversed by ABCD1 gene transfer into spinal cord oligodendrocytes (OLs). In a peroxin-5 KO mouse model, the selective impairment of peroxisomal biogenesis in OLs achieves an almost perfect phenocopy of cerebral ALD. A drosophila knockout model revealed that VLCFA accumulation in glial myelinating cells causes the production of a toxic lipid able to poison axons and activate inflammatory cells. Other mouse models showed the critical role of OLs in providing energy substrates to axons. In addition, studies on microglial changing substates have improved our understanding of neuroinflammation.

CONCLUSIONS

Animal models supporting a primary role of OLs and axonal pathology and a secondary role of microglia allow us to revisit of X-ALD mechanisms. Beyond ABCD1 mutations, pathogenesis depends on unidentified contributors, such as genetic background, cell-specific epigenomics, potential environmental triggers, and stochasticity of crosstalk between multiple cell types among billions of glial cells and neurons.

Development of a rabbit model for adrenoleukodystrophy: A pilot study on gene therapy using rAAV9

X-linked adrenoleukodystrophy (X-ALD) is a common peroxisomal disorder caused by mutations in the ABCD1 gene, leading to the accumulation of very long-chain fatty acids (VLCFAs). This progressive neurodegenerative disease manifests in three primary forms: childhood-acquired cerebral demyelination (CALD), adult myelopathy (AMN), and primary adrenal cortical insufficiency. Bone marrow transplantation effectively halts disease progression only in the early stages of CALD. A thorough investigation of the pathophysiology of X-ALD has been hampered by the lack of a reliable animal model. Valid animal models of X-ALD are urgently needed. To address this, we used CRISPR-Cas9 technology to knock out the ABCD1 gene and established a novel rabbit model of X-ALD. The mutants exhibited elevated serum levels of hexacosanoic acid (C26:0), lignoceric acid (C24:0), and an increased C26:0/C22:0 ratio, as well as significant white matter demyelination in the brain and spinal cord. We also investigated rAAV9-based gene therapy in this model and found a significant reduction in VLCFAs. This study introduces CRISPR-Cas9-mediated ABCD1 gene knockout rabbits as a novel animal model. It comprehensively evaluates the short-term outcomes and safety of rAAV-based gene therapy for X-ALD, providing a promising approach to explore the molecular and pharmacological mechanisms of the disease.

Pilocytic astrocytoma in a child with spinal muscular atrophy treated with onasemnogene abeparvovec

Spinal muscular atrophy (SMA) is a severe neuromuscular disease, leading to progressive muscle weakness and potentially early mortality if untreated. Onasemnogene abeparvovec is a recombinant adeno-associated virus serotype 9 (rAAV9)-based gene therapy that has demonstrated improvements in survival and motor function for SMA patients. Here, we present a case of a patient diagnosed with a grade 1 pilocytic astrocytoma at the age of 2 years, approximately 8 months after onasemnogene abeparvovec treatment. Although vector genomes delivered by rAAVs persist primarily as episomes, rare integration events have been linked to tumor formation in neonate murine models. Therefore, we investigated the presence and possible integration of onasemnogene abeparvovec in formalin-fixed paraffin embedded (FFPE) and frozen tumor samples. In situ hybridization demonstrated variable transduction levels in individual tumor cells, while droplet digital PCR measured an average vector copy number ranging from 0.7 to 4.9 vector genomes/diploid genome. Integration site analysis identified a low number of integration sites that were not conserved between technical replicates, nor between FFPE and frozen samples, indicating that cells hosting integrating vector genomes represented a minority in the overall cell population. Thus, molecular analysis of the tumor tissue suggests that tumorigenesis was causally independent of the administration of onasemnogene abeparvovec.

Long-term tracking of haematopoietic clonal dynamics and mutations in non-human primate undergoing transplantation of lentivirally barcoded haematopoietic stem and progenitor cells

Haematopoietic stem and progenitor cell (HSPC) autologous gene therapies are promising treatment for a variety of blood disorders. Investigation of the long-term HSPC clonal dynamics and other measures of safety and durability following lentiviral-mediated gene therapies in predictive models are crucial for assessing risks and benefits in order to inform decisions regarding wider utilization. We established an autologous lentivirally barcoded HSPC transplantation model in rhesus macaque (RM), a model offering insights into haematopoiesis and gene therapies with direct relevance to human. Healthy young adult RMs underwent total body irradiation, followed by transplantation of autologous HSPCs transduced with a lentiviral vector containing a diverse genetic barcode library, uniquely labelling individual HSPCs and their progeny. With up to 131 months of follow-up, we now report quantitative clonal dynamics, characterizing the number, diversity, stability and lineage bias of hundreds of thousands of HSPC clones tracked in five RMs. We documented long-term stable and multi-lineage output from a highly polyclonal pool of HSPCs. Clonal succession after stable haematopoietic reconstitution was minimal. There was no evidence for accelerated acquisition of acquired somatic mutations following autologous lentivirally transduced HSPC transplantation. Our results provide relevant insights into long-term HSPC behaviours in vivo following transplantation and gene therapies.

Oligodendrocytes, the Forgotten Target of Gene Therapy

If the billions of oligodendrocytes (OLs) populating the central nervous system (CNS) of patients could express their feelings, they would undoubtedly tell gene therapists about their frustration with the other neural cell populations, neurons, microglia, or astrocytes, which have been the favorite targets of gene transfer experiments. This review questions why OLs have been left out of most gene therapy attempts. The first explanation is that the pathogenic role of OLs is still discussed in most CNS diseases. Another reason is that the so-called ubiquitous CAG, CBA, CBh, or CMV promoters-widely used in gene therapy studies-are unable or poorly able to activate the transcription of episomal transgene copies brought by adeno-associated virus (AAV) vectors in OLs. Accordingly, transgene expression in OLs has either not been found or not been evaluated in most gene therapy studies in rodents or non-human primates. The aims of the current review are to give OLs their rightful place among the neural cells that future gene therapy could target and to encourage researchers to test the effect of OL transduction in various CNS diseases.

From gene to therapy: a review of deciphering the role of ABCD1 in combating X-Linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is a severe genetic disorder caused by ABCD1 mutations, resulting in the buildup of very-long-chain fatty acids, leading to significant neurological decline and adrenal insufficiency. Despite advancements in understanding the mechanisms of X-ALD, its pathophysiology remains incompletely understood, complicating the development of effective treatments. This review provides a comprehensive overview of X-ALD, with a focus on the genetic and biochemical roles of ABCD1 and the impacts of its mutations. Current therapeutic approaches are evaluated, discussing their limitations, and emphasizing the need to fully elucidate the pathogenesis of X-ALD. Additionally, this review highlights the importance of international collaboration to enhance systematic data collection and advance biomarker discovery, ultimately improving patient outcomes with X-ALD.

Lentiviral Gene Therapy for Cerebral Adrenoleukodystrophy

BACKGROUND

Cerebral adrenoleukodystrophy is a severe form of X-linked adrenoleukodystrophy characterized by white-matter disease, loss of neurologic function, and early death. Elivaldogene autotemcel (eli-cel) gene therapy, which consists of autologous CD34+ cells transduced with Lenti-D lentiviral vector containing ABCD1 complementary DNA, is being tested in persons with cerebral adrenoleukodystrophy.

METHODS

In a phase 2-3 study, we evaluated the efficacy and safety of eli-cel therapy in boys with early-stage cerebral adrenoleukodystrophy and evidence of active inflammation on magnetic resonance imaging (MRI). The primary efficacy end point was survival without any of six major functional disabilities at month 24. The secondary end points included overall survival at month 24 and the change from baseline to month 24 in the total neurologic function score.

RESULTS

A total of 32 patients received eli-cel; 29 patients (91%) completed the 24-month study and are being monitored in the long-term follow-up study. At month 24, none of these 29 patients had major functional disabilities; overall survival was 94%. At the most recent assessment (median follow-up, 6 years), the neurologic function score was stable as compared with the baseline score in 30 of 32 patients (94%); 26 patients (81%) had no major functional disabilities. Four patients had adverse events that were directly related to eli-cel. Myelodysplastic syndrome (MDS) with excess blasts developed in 1 patient at month 92; the patient underwent allogeneic hematopoietic stem-cell transplantation and did not have MDS at the most recent follow-up.

CONCLUSIONS

At a median follow-up of 6 years after lentiviral gene therapy, most patients with early cerebral adrenoleukodystrophy and MRI abnormalities had no major functional disabilities. However, insertional oncogenesis is an ongoing risk associated with the integration of viral vectors. (Funded by Bluebird Bio; ALD-102 and LTF-304 ClinicalTrials.gov numbers NCT01896102 and NCT02698579, respectively.).

Phase I clinical trial of intracerebral injection of lentiviral-ABCD1 for the treatment of cerebral adrenoleukodystrophy

This was a single-arm, multicenter, open-label phase I trial. Lentiviral vectors (LV) carrying the ABCD1 gene (LV-ABCD1) was directly injected into the brain of patients with childhood cerebral adrenoleukodystrophy (CCALD), and multi-site injection was performed. The injection dose increased from 200 to 1600 μL (vector titer: 1×109 transduction units per mL (TU/mL)), and the average dose per kilogram body weight ranges from 8 to 63.6 μL/kg. The primary endpoint was safety, dose-exploration and immunogenicity and the secondary endpoint was initial evaluation of efficacy and the expression of ABCD1 protein. A total of 7 patients participated in this phase I study and were followed for 1 year. No injection-related serious adverse event or death occurred. Common adverse events associated with the injection were irritability (71%, 5/7) and fever (37.2-38.5 ℃, 57%, 4/7). Adverse events were mild and self-limited, or resolved within 3 d of symptomatic treatment. The maximal tolerable dose is 1600 μL. In 5 cases (83.3%, 5/6), no lentivirus associated antibodies were detected. The overall survival at 1-year was 100%. The ABCD1 protein expression was detected in neutrophils, monocytes and lymphocytes. This study suggests that the intracerebral injection of LV-ABCD1 for CCALD is safe and can achieve successful LV transduction in vivo; even the maximal dose did not increase the risk of adverse events. Furthermore, the direct LV-ABCD1 injection displayed low immunogenicity. In addition, the effectiveness of intracerebral LV-ABCD1 injection has been preliminarily demonstrated while further investigation is needed. This study has been registered in the Chinese Clinical Trial Registry (https://www.chictr.org.cn/, registration number: ChiCTR1900026649).

Gene therapy for ultrarare diseases: a geneticist's perspective

Gene therapy has made considerable strides in recent years. More than 4000 protein-coding genes have been implicated in more than 6000 genetic diseases; next-generation sequencing has dramatically revolutionized the diagnosis of genetic diseases. Most genetic diseases are considered very rare or ultrarare, defined here as having fewer than 1:100,000 cases, but only one of the 12 approved gene therapies (excluding RNA therapies) targets an ultrarare disease. This article explores three gene supplementation therapy approaches suitable for various rare genetic diseases: lentiviral vector-modified autologous CD34+ hematopoietic stem cell transplantation, systemic delivery of adeno-associated virus (AAV) vectors to the liver, and local AAV delivery to the cerebrospinal fluid and brain. Together with RNA therapies, we propose a potential business model for these gene therapies.

Gene therapy for the leukodystrophies: From preclinical animal studies to clinical trials

Leukodystrophies are progressive single gene disorders affecting the white matter of the brain. Several gene therapy trials are in progress to address the urgent unmet need for this patient population. We performed a comprehensive literature review of all gene therapy clinical trials listed in www.clinicaltrials.gov through August 2024, and the relevant preclinical studies that enabled clinical translation. Of the approximately 50 leukodystrophies described to date, only eight have existing gene therapy clinical trials: metachromatic leukodystrophy, X-linked adrenoleukodystrophy, globoid cell leukodystrophy, Canavan disease, giant axonal neuropathy, GM2 gangliosidoses, Alexander disease and Pelizaeus-Merzbacher disease. What led to the emergence of gene therapy trials for these specific disorders? What preclinical data or disease context was enabling? For each of these eight disorders, we first describe its pathophysiology and clinical presentation. We discuss the impact of gene therapy delivery route, targeted cell type, delivery modality, dosage, and timing on therapeutic efficacy. We note that use of allogeneic hematopoietic stem cell transplantation in some leukodystrophies allowed for an accelerated path to clinic even in the absence of available animal models. In other leukodystrophies, small and large animal model studies enabled clinical translation of experimental gene therapies. Human clinical trials for the leukodystrophies include ex vivo lentiviral gene delivery, in vivo AAV-mediated gene delivery, and intrathecal antisense oligonucleotide approaches. We outline adverse events associated with each modality focusing specifically on genotoxicity and immunotoxicity. We review monitoring and management of events related to insertional mutagenesis and immune responses. The data presented in this review show that gene therapy, while promising, requires systematic monitoring to account for the precarious disease biology and the adverse events associated with new technology.

Viral-mediated gene therapy in pediatric neurological disorders

BACKGROUND

Due to the broad application of next-generation sequencing, the molecular diagnosis of genetic disorders in pediatric neurology is no longer an unachievable goal. However, treatments for neurological genetic disorders in children remain primarily symptomatic. On the other hand, with the continuous evolution of therapeutic viral vectors, gene therapy is becoming a clinical reality. From this perspective, we wrote this review to illustrate the current state regarding viral-mediated gene therapy in childhood neurological disorders.

DATA SOURCES

We searched databases, including PubMed and Google Scholar, using the keywords "adenovirus vector," "lentivirus vector," and "AAV" for gene therapy, and "immunoreaction induced by gene therapy vectors," "administration routes of gene therapy vectors," and "gene therapy" with "NCL," "SMA," "DMD," "congenital myopathy," "MPS" "leukodystrophy," or "pediatric metabolic disorders". We also screened the database of ClinicalTrials.gov using the keywords "gene therapy for children" and then filtered the results with the ones aimed at neurological disorders. The time range of the search procedure was from the inception of the databases to the present.

RESULTS

We presented the characteristics of commonly used viral vectors for gene therapy for pediatric neurological disorders and summarized their merits and drawbacks, the administration routes of each vector, the research progress, and the clinical application status of viral-mediated gene therapy on pediatric neurological disorders.

CONCLUSIONS

Viral-mediated gene therapy is on the brink of broad clinical application. Viral-mediated gene therapy will dramatically change the treatment pattern of childhood neurological disorders, and many children with incurable diseases will meet the dawn of a cure. Nevertheless, the vectors must be optimized for better safety and efficacy.

Combining CRISPR-Cas9 and TCR exchange to generate a safe and efficient cord blood-derived T cell product for pediatric relapsed AML

BACKGROUND

Hematopoietic cell transplantation (HCT) is an effective treatment for pediatric patients with high-risk, refractory, or relapsed acute myeloid leukemia (AML). However, a large proportion of transplanted patients eventually die due to relapse. To improve overall survival, we propose a combined strategy based on cord blood (CB)-HCT with the application of AML-specific T cell receptor (TCR)-engineered T cell therapy derived from the same CB graft.

METHODS

We produced CB-CD8+ T cells expressing a recombinant TCR (rTCR) against Wilms tumor 1 (WT1) while lacking endogenous TCR (eTCR) expression to avoid mispairing and competition. CRISPR-Cas9 multiplexing was used to target the constant region of the endogenous TCRα (TRAC) and TCRβ (TRBC) chains. Next, an optimized method for lentiviral transduction was used to introduce recombinant WT1-TCR. The cytotoxic and migration capacity of the product was evaluated in coculture assays for both cell lines and primary pediatric AML blasts.

RESULTS

The gene editing and transduction procedures achieved high efficiency, with up to 95% of cells lacking eTCR and over 70% of T cells expressing rWT1-TCR. WT1-TCR-engineered T cells lacking the expression of their eTCR (eTCR-/- WT1-TCR) showed increased cell surface expression of the rTCR and production of cytotoxic cytokines, such as granzyme A and B, perforin, interferon-γ (IFNγ), and tumor necrosis factor-α (TNFα), on antigen recognition when compared with WT1-TCR-engineered T cells still expressing their eTCR (eTCR+/+ WT1-TCR). CRISPR-Cas9 editing did not affect immunophenotypic characteristics or T cell activation and did not induce increased expression of inhibitory molecules. eTCR-/- WT1-TCR CD8+ CB-T cells showed effective migratory and killing capacity in cocultures with neoplastic cell lines and primary AML blasts, but did not show toxicity toward healthy cells.

CONCLUSIONS

In summary, we show the feasibility of developing a potent CB-derived CD8+ T cell product targeting WT1, providing an option for post-transplant allogeneic immune cell therapy or as an off-the-shelf product, to prevent relapse and improve the clinical outcome of children with AML.

Tagged IDS causes efficient and engraftment-independent prevention of brain pathology during lentiviral gene therapy for Mucopolysaccharidosis type II

Mucopolysaccharidosis type II (OMIM 309900) is a lysosomal storage disorder caused by iduronate 2-sulfatase (IDS) deficiency and accumulation of glycosaminoglycans, leading to progressive neurodegeneration. As intravenously infused enzyme replacement therapy cannot cross the blood-brain barrier (BBB), it fails to treat brain pathology, highlighting the unmet medical need to develop alternative therapies. Here, we test modified versions of hematopoietic stem and progenitor cell (HSPC)-mediated lentiviral gene therapy (LVGT) using IDS tagging in combination with the ubiquitous MND promoter to optimize efficacy in brain and to investigate its mechanism of action. We find that IDS tagging with IGF2 or ApoE2, but not RAP12x2, improves correction of brain heparan sulfate and neuroinflammation at clinically relevant vector copy numbers. HSPC-derived cells engrafted in brain show efficiencies highest in perivascular areas, lower in choroid plexus and meninges, and lowest in parenchyma. Importantly, the efficacy of correction was independent of the number of brain-engrafted cells. These results indicate that tagged versions of IDS can outperform untagged IDS in HSPC-LVGT for the correction of brain pathology in MPS II, and they imply both cell-mediated and tag-mediated correction mechanisms, including passage across the BBB and increased uptake, highlighting their potential for clinical translation.

Evidence Synthesis of Gene Therapy and Gene Editing from Different Disorders-Implications for Individuals with Rett Syndrome: A Systematic Review

This systematic review and thematic analysis critically evaluated gene therapy trials in amyotrophic lateral sclerosis, haemoglobinopathies, immunodeficiencies, leukodystrophies, lysosomal storage disorders and retinal dystrophies and extrapolated the key clinical findings to individuals with Rett syndrome (RTT). The PRISMA guidelines were used to search six databases during the last decade, followed by a thematic analysis to identify the emerging themes. Thematic analysis across the different disorders revealed four themes: (I) Therapeutic time window of gene therapy; (II) Administration and dosing strategies for gene therapy; (III) Methods of gene therapeutics and (IV) Future areas of clinical interest. Our synthesis of information has further enriched the current clinical evidence base and can assist in optimising gene therapy and gene editing studies in individuals with RTT, but it would also benefit when applied to other disorders. The findings suggest that gene therapies have better outcomes when the brain is not the primary target. Across different disorders, early intervention appears to be more critical, and targeting the pre-symptomatic stage might prevent symptom pathology. Intervention at later stages of disease progression may benefit by helping to clinically stabilise patients and preventing disease-related symptoms from worsening. If gene therapy or editing has the desired outcome, older patients would need concerted rehabilitation efforts to reverse their impairments. The timing of intervention and the administration route would be critical parameters for successful outcomes of gene therapy/editing trials in individuals with RTT. Current approaches also need to overcome the challenges of MeCP2 dosing, genotoxicity, transduction efficiencies and biodistribution.

Genetic engineering meets hematopoietic stem cell biology for next-generation gene therapy

The growing clinical success of hematopoietic stem/progenitor cell (HSPC) gene therapy (GT) relies on the development of viral vectors as portable "Trojan horses" for safe and efficient gene transfer. The recent advent of novel technologies enabling site-specific gene editing is broadening the scope and means of GT, paving the way to more precise genetic engineering and expanding the spectrum of diseases amenable to HSPC-GT. Here, we provide an overview of state-of-the-art and prospective developments of the HSPC-GT field, highlighting how advances in biological characterization and manipulation of HSPCs will enable the design of the next generation of these transforming therapeutics.

Multivariate analysis and model building for classifying patients in the peroxisomal disorders X-linked adrenoleukodystrophy and Zellweger syndrome in Chinese pediatric patients

BACKGROUND

The peroxisome is a ubiquitous single membrane-enclosed organelle with an important metabolic role. Peroxisomal disorders represent a class of medical conditions caused by deficiencies in peroxisome function and are segmented into enzyme-and-transporter defects (defects in single peroxisomal proteins) and peroxisome biogenesis disorders (defects in the peroxin proteins, critical for normal peroxisome assembly and biogenesis). In this study, we employed multivariate supervised and non-supervised statistical methods and utilized mass spectrometry data of neurological patients, peroxisomal disorder patients (X-linked adrenoleukodystrophy and Zellweger syndrome), and healthy controls to analyze the role of common metabolites in peroxisomal disorders, to develop and refine a classification models of X-linked adrenoleukodystrophy and Zellweger syndrome, and to explore analytes with utility in rapid screening and diagnostics.

RESULTS

T-SNE, PCA, and (sparse) PLS-DA, operated on mass spectrometry data of patients and healthy controls were utilized in this study. The performance of exploratory PLS-DA models was assessed to determine a suitable number of latent components and variables to retain for sparse PLS-DA models. Reduced-features (sparse) PLS-DA models achieved excellent classification performance of X-linked adrenoleukodystrophy and Zellweger syndrome patients.

CONCLUSIONS

Our study demonstrated metabolic differences between healthy controls, neurological patients, and peroxisomal disorder (X-linked adrenoleukodystrophy and Zellweger syndrome) patients, refined classification models and showed the potential utility of hexacosanoylcarnitine (C26:0-carnitine) as a screening analyte for Chinese patients in the context of a multivariate discriminant model predictive of peroxisomal disorders.

Neurocognitive and mental health impact of adrenoleukodystrophy across the lifespan: Insights for the era of newborn screening

X-linked adrenoleukodystrophy (ALD) is a rare inherited neurological disorder that poses considerable challenges for clinical management throughout the lifespan. Although males are generally more severely affected than females, the time course and presentation of clinical symptoms are otherwise difficult to predict. Opportunities to improve outcomes for individuals with ALD are rapidly expanding due to the introduction of newborn screening programs for this condition and an evolving treatment landscape. The aim of this comprehensive review is to synthesize current knowledge regarding the neurocognitive and mental health effects of ALD. This review provides investigators and clinicians with context to improve case conceptualization, inform prognostic counseling, and optimize neuropsychological and mental health care for patients and their families. Results highlight key predictive factors and brain-behavior relationships associated with the diverse manifestations of ALD. The review also discusses considerations for endpoints within clinical trials and identifies gaps to address in future research.

An update on the diagnosis and treatment of adrenoleukodystrophy

PURPOSE OF REVIEW

The present review summarizes recent advances in the diagnosis and management of patients with X-linked adrenoleukodystrophy (ALD).

RECENT FINDINGS

Although ALD screening has been on the list of Recommended Uniform Screening Panel since 2016, only 30 states in the United States are currently testing their newborns for this disease. Hematopoietic stem cell transplant (HSCT) remains the only successful treatment option available for early cerebral ALD but does not reverse neurological changes or affect the course of adrenal insufficiency. There remains a significant knowledge gap in our understanding and treatment of this disease. Novel therapies such as gene therapy and gene editing have shown promising results in animal models and are exciting potential treatment options for the future.Recently, the American Academy of Neurologists released their consensus guidelines on the diagnosis, surveillance, and management of ALD.

SUMMARY

Early diagnosis and HSCT are key to improving the morbidity and mortality associated with ALD. The implementation of universal newborn screening for ALD and rigorous investigations of novel diagnostic and therapeutic agents is the need of the hour.

X-Linked intellectual disability update 2022

Genes that are involved in the transcription process, mitochondrial function, glycoprotein metabolism, and ubiquitination dominate the list of 21 new genes associated with X-linked intellectual disability since the last update in 2017. The new genes were identified by sequencing of candidate genes (2), the entire X-chromosome (2), the whole exome (15), or the whole genome (2). With these additions, 42 (21%) of the 199 named XLID syndromes and 27 (25%) of the 108 numbered nonsyndromic XLID families remain to be resolved at the molecular level. Although the pace of discovery of new XLID genes has slowed during the past 5 years, the density of genes on the X chromosome that cause intellectual disability still appears to be twice the density of intellectual disability genes on the autosomes.

Universal allogeneic CAR T cells engineered with Sleeping Beauty transposons and CRISPR-CAS9 for cancer immunotherapy

Allogeneic CD19-specific chimeric antigen receptor (CAR) T cells with inactivated donor T cell receptor (TCR) expression can be used as an "off-the-shelf" therapeutic modality for lymphoid malignancies, thus offering an attractive alternative to autologous, patient-derived T cells. Current approaches for T cell engineering mainly rely on the use of viral vectors. Here, we optimized and validated a non-viral genetic modification platform based on Sleeping Beauty (SB) transposons delivered with minicircles to express CD19-28z.CAR and CRISPR-Cas9 ribonucleoparticles to inactivate allogeneic TCRs. Efficient TCR gene disruption was achieved with minimal cytotoxicity and with attainment of robust and stable CD19-28z.CAR expression. The CAR T cells were responsive to CD19+ tumor cells with antitumor activities that induced complete tumor remission in NALM6 tumor-bearing mice while significantly reducing TCR alloreactivity and GvHD development. Single CAR signaling induced the similar T cell signaling signatures in TCR-disrupted CAR T cells and control CAR T cells. In contrast, TCR disruption inhibited T cell signaling/protein phosphorylation compared with the control CAR T cells during dual CAR/TCR signaling. This non-viral SB transposon-CRISPR-Cas9 combination strategy serves as an alternative for generating next-generation CD19-specific CAR T while reducing GvHD risk and easing potential manufacturing constraints intrinsic to viral vectors.

Haematopoietic stem cell gene therapy in inborn errors of metabolism

Over the last 30 years, allogeneic haematopoietic stem cell transplantation (allo-HSCT) has been adopted as a therapeutic strategy for many inborn errors of metabolism (IEM), due to the ability of donor-derived cells to provide life-long enzyme delivery to deficient tissues and organs. However, (a) the clinical benefit of allo-HSCT is limited to a small number of IEM, (b) patients are left with a substantial residual disease burden and (c) allo-HSCT is still associated with significant short- and long-term toxicities and transplant-related mortality. Haematopoietic stem/progenitor cell gene therapy (HSPC-GT) was established in the 1990s for the treatment of selected monogenic primary immunodeficiencies and over the past few years, its use has been extended to a number of IEM. HSPC-GT is particularly attractive in neurodegenerative IEM, as gene corrected haematopoietic progenitors can deliver supra-physiological enzyme levels to difficult-to-reach areas, such as the brain and the skeleton, with potential increased clinical benefit. Moreover, HSPC-GT is associated with reduced morbidity and mortality compared to allo-HSCT, although this needs to be balanced against the potential risk of insertional mutagenesis. The number of clinical trials in the IEM field is rapidly increasing and some HSPC-GT products recently received market approval. This review describes the development of ex vivo HSPC-GT in a number of IEM, with a focus on recent results from GT clinical trials and risks versus benefits considerations, when compared to established therapeutic strategies, such as allo-HSCT.

Long-term disease prevention with a gene therapy targeting oligodendrocytes in a mouse model of adrenomyeloneuropathy

Adrenomyeloneuropathy (AMN) is a late-onset axonopathy of spinal cord tracts caused by mutations of the ABCD1 gene that encodes ALDP, a peroxisomal transporter of very long chain fatty acids (VLCFA). Disturbed metabolic interaction between oligodendrocytes (OL) and axons is suspected to play a major role in AMN axonopathy. To develop a vector targeting OL, the human ABCD1 gene driven by a short 0.3 kb part of the human myelin-associated glycoprotein (MAG) promoter was packaged into an adeno-associated viral serotype 9 (rAAV9). An intravenous injection of this vector at postnatal day 10 (P10) in Abcd1-/- mice, a model of AMN, allowed a near normal motor performance to persist for 24 months, while age-matched untreated mice developed major defects of balance and motricity. Three weeks post vector, 50-54% of spinal cord white matter OL were expressing ALDP at the cervical level, and only 6-7% after 24 months. In addition, 29-32% of cervical spinal cord astrocytes at 3 weeks and 16-19% at 24 months also expressed ALDP. C26:0-lysoPC, a sensitive VLCFA marker of AMN, was lower by 41% and 50%, respectively in the spinal cord and brain of vector-treated compared with untreated mice. In a non-human primate (NHP), the intrathecal injection of the rAAV9-MAG vector induced abundant ALDP expression at 3 weeks in spinal cord OL (43%, 29%, 26% at cervical, thoracic and lumbar levels) and cerebellum OL (35%). In addition, 33-41 % of spinal cord astrocytes expressed hALDP, and 27% of cerebellar astrocytes. To our knowledge, OL targeting had not been obtained before in primates with other vectors or promoters. The current results thus provide a robust proof-of-concept not only for the gene therapy of AMN but for other CNS diseases where the targeting of OL with the rAAV9-MAG vector may be of interest.

Gene Therapy Developments for Pompe Disease

Pompe disease is an inherited neuromuscular disorder caused by deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). The most severe form is infantile-onset Pompe disease, presenting shortly after birth with symptoms of cardiomyopathy, respiratory failure and skeletal muscle weakness. Late-onset Pompe disease is characterized by a slower disease progression, primarily affecting skeletal muscles. Despite recent advancements in enzyme replacement therapy management several limitations remain using this therapeutic approach, including risks of immunogenicity complications, inability to penetrate CNS tissue, and the need for life-long therapy. The next wave of promising single therapy interventions involves gene therapies, which are entering into a clinical translational stage. Both adeno-associated virus (AAV) vectors and lentiviral vector (LV)-mediated hematopoietic stem and progenitor (HSPC) gene therapy have the potential to provide effective therapy for this multisystemic disorder. Optimization of viral vector designs, providing tissue-specific expression and GAA protein modifications to enhance secretion and uptake has resulted in improved preclinical efficacy and safety data. In this review, we highlight gene therapy developments, in particular, AAV and LV HSPC-mediated gene therapy technologies, to potentially address all components of the neuromuscular associated Pompe disease pathology.

Low donor chimerism may be sufficient to prevent demyelination in adrenoleukodystrophy

Adrenoleukodystrophy (ALD) is a peroxisomal disorder characterized by white matter degeneration caused by adenosine triphosphate-binding cassette subfamily D member 1 (ABCD1) gene mutations, which lead to an accumulation of very-long-chain fatty acids (VLCFA). Hematopoietic stem cell transplantation (HSCT) is the most effective treatment; however, the ratio of donor-to-recipient cells required to prevent the progression of demyelination is unclear. The proband was diagnosed with the childhood cerebral form of ALD at 5 years of age based on the clinical phenotype, elevated plasma VLCFA levels, and pathogenic ABCD1 mutation c.293C>T (p.Ser98Leu). Soon after the diagnosis, he became bedridden. At 1 year of age, his younger brother was found to carry the same ABCD1 mutation; despite being asymptomatic, at 1 year and 9 months, head magnetic resonance imaging (MRI) showed high-signal-intensity lesions in the cerebral white matter. The patient underwent unrelated cord blood transplantation (UCBT) with a reduced conditioning regimen, which resulted in mixed chimerism. For 7 years after UCBT, the donor chimerism remained low (<10%) in peripheral blood and cerebrospinal fluid. However, even though a second HSCT was not performed, his neurological symptoms and brain MRI findings did not deteriorate. Our case suggests that even a small number of donor cells may prevent demyelination in ALD. This is an important case when considering the timing of a second HSCT.

Elivaldogene Autotemcel: First Approval

Elivaldogene autotemcel (SKYSONA™, eli-cel; Lenti-D™ gene therapy) is a gene therapy that has been developed by bluebird bio for the treatment of cerebral adrenoleukodystrophy (CALD), a rare, X-linked genetic disease that mainly affects the nervous system and adrenal glands. In July 2021, elivaldogene autotemcel received its first approval (in the EU) for the treatment of for the treatment of early CALD in patients < 18 years of age, with an ABCD1 genetic mutation, and for whom a human leukocyte antigen (HLA)-matched sibling haematopoietic stem cell (HSC) donor is not available. This article summarizes the milestones in the development of elivaldogene autotemcel leading to this first approval.

Skeletal muscle atrophy: From mechanisms to treatments

Skeletal muscle is a crucial tissue for movement, gestural assistance, metabolic homeostasis, and thermogenesis. It makes up approximately 40% of the total body weight and 50% of total protein. However, several pathological abnormalities (e.g., chronic diseases, cancer, long-term infection, aging) can induce an imbalance in skeletal muscle protein synthesis and degradation, which triggers muscle wasting and even leads to atrophy. Skeletal muscle atrophy is characterized by weakening, shrinking, and decreasing muscle mass and fiber cross-sectional area at the histological level. It manifests as a reduction in force production, easy fatigue and decreased exercise capability, along with a lower quality of life. Mechanistically, there are several pathophysiological processes involved in skeletal muscle atrophy, including oxidative stress and inflammation, which then activate signal transduction, such as the ubiquitin proteasome system, autophagy lysosome system, and mTOR. Considering the great economic and social burden that muscle atrophy can inflict, effective prevention and treatment strategies are essential but still limited. Exercise is widely acknowledged as the most effective therapy for skeletal muscle atrophy; unfortunately, it is not applicable for all patients. Several active substances for skeletal muscle atrophy have been discovered and evaluated in clinical trials, however, they have not been marketed to date. Knowledge is being gained on the underlying mechanisms, highlighting more promising treatment strategies in the future. In this paper, the mechanisms and treatment strategies for skeletal muscle atrophy are briefly reviewed.