Effective Gene Therapy for Metachromatic Leukodystrophy Achieved with Minimal Lentiviral Genomic Integrations.

Metachromatic leukodystrophy (MLD) is a fatal lysosomal storage disease (LSD) characterized by the deficient enzymatic activity of arylsulfatase A (ARSA). Combined autologous hematopoietic stem cell transplant (HSCT) with lentiviral (LV) based gene therapy has great potential to treat MLD. However, if enzyme production is inadequate, this could result in continued loss of motor function, implying a high vector copy number (VCN) requirement for optimal enzymatic output. This may place children at increased risk for genomic toxicity due to higher VCN. We increased the expression of ARSA cDNA at single integration by generating novel LVs, optimizing ARSA expression, and enhancing safety. In addition, our vectors achieved optimal transduction in mouse and human HSC with minimal multiplicity of infection (MOI). Our top-performing vector (EA1) showed at least 4X more ARSA activity than the currently EU-approved vector and a superior ability to secrete vesicle-associated ARSA, a critical modality to transfer functional enzymes from microglia to oligodendrocytes. Three-month-old Arsa -KO MLD mice transplanted with Arsa -KO BM cells transduced with 0.6 VCN of EA1 demonstrated behavior and CNS histology matching WT mice. Our novel vector boosts efficacy while improving safety as a robust approach for treating early symptomatic MLD patients.

Combination of a TGF-ß ligand trap (RAP-GRL) and TMPRSS6-ASO is superior for correcting ß-thalassemia.

A recently approved drug that induces erythroid cell maturation (luspatercept) has been shown to improve anemia and reduce the need for blood transfusion in non-transfusion-dependent as well as transfusion-dependent ß-thalassemia (BT) patients. Although these results were predominantly positive, not all the patients showed the expected increase in hemoglobin (Hb) levels or transfusion burden reduction. Additional studies indicated that administration of luspatercept in transfusion-dependent BT was associated with increased erythropoietic markers, decreased hepcidin levels, and increased liver iron content. Altogether, these studies suggest that luspatercept may necessitate additional drugs for improved erythroid and iron management. As luspatercept does not appear to directly affect iron metabolism, we hypothesized that TMPRSS6-ASO could improve iron parameters and iron overload when co-administered with luspatercept. We used an agent analogous to murine luspatercept (RAP-GRL) and another novel therapeutic, IONIS TMPRSS6-LRx (TMPRSS6-ASO), a hepcidin inducer, to treat non-transfusion-dependent BT-intermedia mice. Our study shows that RAP-GRL alone improved red blood cell (RBC) production, with no or limited effect on splenomegaly and iron parameters. In contrast, TMPRSS6-ASO improved RBC measurements, ameliorated splenomegaly, and improved iron overload most effectively. Our results provide pre-clinical support for combining TMPRSS6-ASO and luspatercept in treating BT, as these drugs together show potential for simultaneously improving both erythroid and iron parameters in BT patients.

Novel potential therapeutics to modify iron metabolism and red cell synthesis in diseases associated with defective erythropoiesis.

Under normal conditions, iron metabolism is carefully regulated to sustain normal cellular functions and the production of hemoglobin in erythroid cells. Perturbation to the erythropoiesis-iron metabolism axis can result in iron imbalances and cause anemia or organ toxicity. Various congenital and acquired diseases associated with abnormal red cell production are characterized by aberrant iron absorption. Several recent studies have shown that improvements in red blood cell production also ameliorate iron metabolism and vice versa. Many therapeutics are now under development with the potential to improve a variety of hematologic diseases, from ß-thalassemia and iron-refractory iron deficiency anemia to anemia of inflammation and polycythemia vera. This review summarizes selected mechanisms related to red cell production and iron metabolism and describes potential therapeutics and their current uses. We also consider the potential application of the discussed therapeutics on various diseases, alone or in combination. The vast repertoire of drugs under development offers new opportunities to improve the clinical care of patients suffering from congenital or acquired red blood cell disorders with limited or no treatment options.

Voices on diversity: Making the scientific community more inclusive.

As part of our commitment to amplifying the voices of underrepresented scientists, we are publishing the insights and experiences of a panel of underrepresented scientists. In this piece, they discuss ways to make science more inclusive-from key points they wish their colleagues understood to actions those in the scientific community can take. These are the personal opinions of the authors and may not reflect the views of their institutions.

Voices on diversity: overcoming our own racial biases.

As part of our commitment to amplifying the voices of underrepresented scientists, we are publishing the insights and experiences of a panel of underrepresented scientists. Here they discuss ways that individuals in the scientific community can begin to recognize and overcome their own racial biases. These are the personal opinions of the authors and may not reflect the views of their institutions.

Voices on diversity: support systems that work.

As part of our commitment to amplifying the voices of underrepresented scientists, we are publishing the insights and experiences of a panel of underrepresented scientists. In this segment, we asked about support systems-the types of support that are most helpful (and less helpful), how to find a supportive network, and how institutions can better support underrepresented scientists. These are the personal opinions of the authors and may not reflect the views of their institutions.

Voices on diversity: confronting racial bias.

As part of our commitment to amplifying the voices of underrepresented scientists, we are publishing the insights and experiences of a panel of underrepresented scientists. Here, they discuss the impact of racial bias and share strategies for addressing it. These are the personal opinions of the authors and may not reflect the views of their institutions.

Voices on Diversity: Creating a Sense of Belonging.

As part of our commitment to amplifying the voices of underrepresented scientists, we are publishing the insights and experiences of a panel of underrepresented scientists. Here they tell us about behaviors that can lead underrepresented scientists to feel that they do not belong and what the scientific community can do to provide better support. These are the personal opinions of the authors and may not reflect the views of their institutions.

Voices on Diversity: Combating Racial Inequality to Increase Diversity.

As part of our commitment to amplifying the voices of underrepresented scientists, we are publishing the insights and experiences of a panel of underrepresented scientists in a series of questions and answers. Here, they discuss ways that the scientific community can combat racial inequality and increase diversity. These are the personal opinions of the authors and may not reflect the views of their institutions.

The Role of Iron in Benign and Malignant Hematopoiesis.

Significance: Iron is an essential element required for sustaining a normal healthy life. However, an excess amount of iron in the bloodstream and tissue generates toxic hydroxyl radicals through Fenton reactions. Henceforth, a balance in iron concentration is extremely important to maintain cellular homeostasis in both normal hematopoiesis and erythropoiesis. Iron deficiency or iron overload can impact hematopoiesis and is associated with many hematological diseases. Recent Advances: The mechanisms of action of key iron regulators such as erythroferrone and the discovery of new drugs, such as ACE-536/luspatercept, are of potential interest to treat hematological disorders, such as ß-thalassemia. New therapies targeting inflammation-induced ineffective erythropoiesis are also in progress. Furthermore, emerging evidences support differential interactions between iron and its cellular antioxidant responses of hematopoietic and neighboring stromal cells. Both iron and its systemic regulator, such as hepcidin, play a significant role in regulating erythropoiesis. Critical Issues: Significant pre-clinical studies are on the way and new drugs targeting iron metabolism have been recently approved or are undergoing clinical trials to treat pathological conditions with impaired erythropoiesis such as myelodysplastic syndromes or ß-thalassemia. Future Directions: Future studies should explore how iron regulates hematopoiesis in both benign and malignant conditions. Antioxid. Redox Signal. 35, 415-432.

Voices on Diversity: Overcoming Barriers to Pursuing a Career in Science.

As part of our commitment to amplifying the voices of underrepresented scientists, we are publishing the insights and experiences of a panel of underrepresented scientists in a series of questions and answers. Here, they tell us about barriers they faced in pursuing a scientific career. These are the personal opinions of the authors and may not reflect the views of their institutions.

Voices on Diversity: Multiple Paths to Becoming a Scientist.

As part of our commitment to amplifying the voices of underrepresented scientists, we will be publishing the insights and experiences of a panel of underrepresented scientists. To kick off this series, they introduce themselves, tell us what sparked their interest in science, and describe their scientific journeys. These are the personal opinions of the authors and may not reflect the views of their institutions.

Lobe specificity of iron binding to transferrin modulates murine erythropoiesis and iron homeostasis.

Transferrin, the major plasma iron-binding molecule, interacts with cell-surface receptors to deliver iron, modulates hepcidin expression, and regulates erythropoiesis. Transferrin binds and releases iron via either or both of 2 homologous lobes (N and C). To test the hypothesis that the specificity of iron occupancy in the N vs C lobe influences transferrin function, we generated mice with mutations to abrogate iron binding in either lobe (TfN-bl or TfC-bl). Mice homozygous for either mutation had hepatocellular iron loading and decreased liver hepcidin expression (relative to iron concentration), although to different magnitudes. Both mouse models demonstrated some aspects of iron-restricted erythropoiesis, including increased zinc protoporphyrin levels, decreased hemoglobin levels, and microcytosis. Moreover, the TfN-bl/N-bl mice demonstrated the anticipated effect of iron restriction on red cell production (ie, no increase in red blood cell [RBC] count despite elevated erythropoietin levels), along with a poor response to exogenous erythropoietin. In contrast, the TfC-bl/C-bl mice had elevated RBC counts and an exaggerated response to exogenous erythropoietin sufficient to ameliorate the anemia. Observations in heterozygous mice further support a role for relative N vs C lobe iron occupancy in transferrin-mediated regulation of iron homeostasis and erythropoiesis.

Emerging Therapies.

At present, the only definitive cure for ß-thalassemia is a bone marrow transplant (BMT); however, HLA-blood-matched donors are scarcely available. Current therapies undergoing clinical investigation with most potential for therapeutic benefit are the ß-globin gene transfer of patient-specific hematopoietic stem cells followed by autologous BMT. Other emerging therapies deliver exogenous regulators of several key modulators of erythropoiesis or iron homeostasis. This review focuses on current approaches for the treatment of hemoglobinopathies caused by disruptions of ß-globin.