Neutralizing antibodies (NAbs) to adeno-associated virus (AAV) vectors are highly prevalent in humans 1,2 , block liver transduction 3-5 and vector readministration 6 , thus representing a major limitation to in vivo gene therapy. Strategies aimed at overcoming anti-AAV antibodies are being studied 7 , which often involve immunosuppression and are not efficient in removing pre-existing antibodies. Imlifidase (IdeS) is an endopeptidase able to degrade circulating IgG that is currently being tested in transplant patients 8 . Here we studied if IdeS can eliminate anti-AAV antibodies in the context of gene therapy. We showed efficient cleavage of pooled human IgG (IVIg) in vitro upon endopeptidase treatment. In mice passively immunized with IVIg, IdeS administration decreased anti-AAV antibodies and enabled efficient liver gene transfer.The approach was scaled up to non-human primates, a natural host for wild type AAV.IdeS treatment prior to AAV vector infusion was safe and resulted in enhanced liver transduction, even in the setting of vector readministration. Finally, IdeS reduced anti-AAV antibody levels from human plasma samples in vitro, including plasma from prospective gene therapy trial participants. These results provide a potential solution to overcome pre-existing antibodies to AAV-based gene therapy.

Non-syndromic cleft lip with or without cleft palate (CL/P) is a common birth defect with substantial clinical and social impact and whose causes include both genetic and environmental factors. Folate and homocysteine (Hcy) metabolism have been indicated to play a role in the etiology of CL/P, and polymorphisms in folate and Hcy genes may act as susceptibility factors. We investigated a common polymorphism in the cystathionine beta-synthase (CBS) gene (c.844ins68) in 134 Italian CL/P cases and their parents using the transmission disequilibrium test (TDT). Although no overall linkage disequilibrium was observed, considering the parent-of-origin transmission of the CBS 68 bp insertion a significant (P = 0.002) transmission distortion was detected. When children receive the c.844ins68 allele from the mother compared to the father, they show a 18.7-fold increase in risk for CL/P. This evidence suggests CBS as a candidate gene for CL/P and supports a role of maternal-embryo interactions in the etiology of CL/P.

Targeted genome editing has a great therapeutic potential to treat disorders that require protein replacement therapy. To develop a platform independent of specific patient mutations, therapeutic transgenes can be inserted in a safe and highly transcribed locus to maximize protein expression. Here, we describe an ex vivo editing approach to achieve efficient gene targeting in human hematopoietic stem/progenitor cells (HSPCs) and robust expression of clinically relevant proteins by the erythroid lineage. Using CRISPR-Cas9, we integrate different transgenes under the transcriptional control of the endogenous α-globin promoter, recapitulating its high and erythroid-specific expression. Erythroblasts derived from targeted HSPCs secrete different therapeutic proteins, which retain enzymatic activity and cross-correct patients' cells. Moreover, modified HSPCs maintain long-term repopulation and multilineage differentiation potential in transplanted mice. Overall, we establish a safe and versatile CRISPR-Cas9-based HSPC platform for different therapeutic applications, including hemophilia and inherited metabolic disorders.

β-thalassemias (β-thal) are a group of blood disorders caused by mutations in the β-globin gene (HBB) cluster. β-globin associates with α-globin to form adult hemoglobin (HbA, α2β2), the main oxygen-carrier in erythrocytes. When β-globin chains are absent or limiting, free α-globins precipitate and damage cell membranes, causing hemolysis and ineffective erythropoiesis. Clinical data show that severity of β-thal correlates with the number of inherited α-globin genes (HBA1 and HBA2), with α-globin gene deletions having a beneficial effect for patients. Here, we describe a novel strategy to treat β-thal based on genome editing of the α-globin locus in human hematopoietic stem/progenitor cells (HSPCs). Using CRISPR/Cas9, we combined 2 therapeutic approaches: (1) α-globin downregulation, by deleting the HBA2 gene to recreate an α-thalassemia trait, and (2) β-globin expression, by targeted integration of a β-globin transgene downstream the HBA2 promoter. First, we optimized the CRISPR/Cas9 strategy and corrected the pathological phenotype in a cellular model of β-thalassemia (human erythroid progenitor cell [HUDEP-2] β0). Then, we edited healthy donor HSPCs and demonstrated that they maintained long-term repopulation capacity and multipotency in xenotransplanted mice. To assess the clinical potential of this approach, we next edited β-thal HSPCs and achieved correction of α/β globin imbalance in HSPC-derived erythroblasts. As a safer option for clinical translation, we performed editing in HSPCs using Cas9 nickase showing precise editing with no InDels. Overall, we described an innovative CRISPR/Cas9 approach to improve α/β globin imbalance in thalassemic HSPCs, paving the way for novel therapeutic strategies for β-thal.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The liver is a central organ for metabolism and hepatocytes are the main cell type responsible for most of its functions. Several previous studies investigated the cell types involved in tissue homeostasis and regeneration1–4, however the mechanisms underlying post-natal liver growth and establishment of the mature hepatocyte phenotypes remain to be fully understood. Here we investigate liver tissue dynamics in mice during growth and adulthood, by spatial transcriptomics5, clonal analysis, and lineage tracing. We observe progressive establishment of metabolic zonation of hepatocytes following weaning, with specification of the centrilobular identity only in adults. We report that only a fraction of hepatocytes proliferates in the newborn liver, generating most of the adult tissue and that preferential genetic modification (either gene transfer or gene editing) of the more proliferating hepatocytes allows expansion of the genetically engineered liver area, stably maintained throughout tissue homeostasis. We also describe age-dependent differences in the efficiency and distribution of lentiviral in vivo gene delivery, with higher efficiency of gene transfer in young compared to adult animals and a skewed localization within the liver lobule. We identify high proteasome activity in the peri-central lobular area as the major determinant of the observed outcome and successfully revert it by proteasomal inhibition before gene transfer. Overall, our findings provide new insights into the spatio-temporal dynamics of the liver during post-natal growth and hepatocyte heterogeneity, which extends our understanding of liver biology and have important implications for therapeutic applications.

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