The majority of patients with mutations in CRB1 develop either early-onset retinitis pigmentosa as young children or Leber congenital amaurosis as newborns. The cause for the pheno-typic... Show moreThe majority of patients with mutations in CRB1 develop either early-onset retinitis pigmentosa as young children or Leber congenital amaurosis as newborns. The cause for the pheno-typic variability in CRB1-associated retinopathies is unknown, but might be linked to differences in CRB1 and CRB2 protein levels in Muller glial cells and photoreceptor cells. Here, CRB1KO and CRB1KOCRB2+/-differentiation day 210 retinal organoids showed a significant decrease in the number of photoreceptor nuclei in a row and a significant increase in the number of photoreceptor cell nuclei above the outer limiting membrane. This phenotype with outer retinal abnormalities is similar to CRB1 patient-derived retinal organoids and Crb1 or Crb2 mutant mouse retinal disease models. The CRB1KO and CRB1KOCRB2+/-retinal organoids develop an additional inner retinal phenotype due to the complete loss of CRB1 from Muller glial cells, suggesting an essential role for CRB1 in proper local-ization of neuronal cell types. Adeno-associated viral (AAV) transduction was explored at early and late stages of organoid development. Moreover, AAV-mediated gene augmentation therapy with AAV.hCRB2 improved the outer retinal pheno-type in CRB1KO retinal organoids. Altogether, these data pro -vide essential information for future gene therapy approaches for patients with CRB1-associated retinal dystrophies. Show less
Mucopolysaccharidosis type II (OMIM 309900) is a lysosomal storage disorder caused by iduronate 2-sulfatase (IDS) deficiency and accumulation of glycosaminoglycans, leading to progressive... Show moreMucopolysaccharidosis 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. Show less
The balance between safety and efficacy of T cell therapies re-mains challenging and T cell mediated toxicities have occurred. The stringent selection of tumor-specific targets and careful se... Show moreThe balance between safety and efficacy of T cell therapies re-mains challenging and T cell mediated toxicities have occurred. The stringent selection of tumor-specific targets and careful se-lection of tumor-specific T cells using T cell toxicity screenings are essential. In vitro screening options against vital organs or specialized cell subsets would be preferably included in preclin-ical pipelines, but options remain limited. Here, we set up preclinical models with human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes, epicardial cells, and kid-ney organoids to investigate toxicity risks of tumor-specific T cells more thoroughly. CD8+T cells reactive against PRAME, HA-1H, CD20, or WT1, currently used or planned to be used in phase I/II clinical studies, were included. Using these hiPSC-derived preclinical models, we demonstrated that WT1-specific T cells caused on-target toxicity that correlated with target gene expression. Multiple measures of T cell reac-tivity demonstrated this toxicity on the level of T cells and hiPSC-derived target cells. In addition, phenotypic analysis illustrated interaction and crosstalk between infiltrated T cells and kidney organoids. In summary, we demonstrated the benefit of hiPSC-derived models in determining toxicity risks of tumor-specific T cells. Furthermore, our data empha-sizes the additional value of other measures of T cell reactivity on top of the commonly used cytokine levels. Show less
Gaucher disease type 1 (GD1) is an inherited lysosomal disorder with multisystemic effects in patients. Hallmark symptoms include hepatosplenomegaly, cytopenias, and bone disease with varying... Show moreGaucher disease type 1 (GD1) is an inherited lysosomal disorder with multisystemic effects in patients. Hallmark symptoms include hepatosplenomegaly, cytopenias, and bone disease with varying degrees of severity. Mutations in a single gene, glucosidase beta acid 1 (GBA1), are the underlying cause for the disorder, resulting in insufficient activity of the enzyme glucocerebrosidase, which in turn leads to a progressive accumulation of the lipid component glucocerebroside. In this study, we treat mice with signs consistent with GD1, with hematopoietic stem/progenitor cells transduced with a lentiviral vector containing an RNA transcript that, after reverse transcription, results in codon-optimized cDNA that, upon its integration into the genome encodes for functional human glucocerebrosidase. Five months after gene transfer, a highly significant reduction in glucocerebroside accumulation with subsequent reversal of hepatosplenomegaly, restoration of blood parameters, and a tendency of increased bone mass and density was evident in vector-treated mice compared to non-treated controls. Furthermore, histopathology revealed a prominent reduction of Gaucher cell infiltration after gene therapy. The vector displayed an oligoclonal distribution pattern but with no sign of vector-induced clonal dominance and a typical lentiviral vector integration profile. Cumulatively, our findings support the initiation of the first clinical trial for GD1 using the lentiviral vector described here. Show less
Buck, T.M.; Vos, R.M.; Alves, C.H.; Wijnholds, J. 2021
Loss of Crumbs homolog 1 (CRB1) or CRB2 proteins in Muller cells or photoreceptors in the mouse retina results in a CRB dose-dependent retinal phenotype. In this study, we present a novel Muller... Show moreLoss of Crumbs homolog 1 (CRB1) or CRB2 proteins in Muller cells or photoreceptors in the mouse retina results in a CRB dose-dependent retinal phenotype. In this study, we present a novel Muller cell-specific Crb1(KO)Crb2(LowMGC) retinitis pigmentosa mouse model (complete loss of CRB1 and reduced levels of CRB2 specifically in Muller cells). The Crb double mutant mice showed deficits in electroretinography, optokinetic head tracking, and retinal morphology. Exposure of retinas to low levels of DL-alpha-aminoadipate acid induced gliosis and retinal disorganization in Crb1(KO)Crb2(LowMGC) retinas but not in wild-type or Crb1-deficient retinas. Crb1(KO)Crb2(LowMGC) mice showed a substantial decrease in inner/outer photoreceptor segment length and optokinetic head-tracking response. Intravitreal application of rAAV vectors expressing human CRB2 (hCRB2) in Muller cells of Crb1(KO)Crb2(LowMGC) mice subsequently exposed to low levels of DL-alpha-aminoadipate acid prevented loss of vision, whereas recombinant adeno-associated viral (rAAV) vectors expressing human CRB1 (hCRB1) did not. Both rAAV vectors partially protected the morphology of the retina. The results suggest that hCRB expression in Muller cells is vital for control of retinal cell adhesion at the outer limiting membrane, and that the rAAV-cytomegalovirus (CMV)-hCRB2 vector is more potent than rAAV-minimal CMV (CMVmin)-hCRB1 in protection against loss of vision. Show less
The development of gene therapies for central nervous system disorders is challenging because it is difficult to translate preclinical data from current in vitro and in vivo models to the clinic.... Show moreThe development of gene therapies for central nervous system disorders is challenging because it is difficult to translate preclinical data from current in vitro and in vivo models to the clinic. Therefore, we developed induced pluripotent stem cell (iPSC)-derived cerebral organoids as a model for recombinant adeno-associated virus (rAAV) capsid selection and for testing efficacy of AAV-based gene therapy in a human context. Cerebral organoids are physiological 3D structures that better recapitulate the human brain compared with 2D cell lines. To validate the model, we compared the transduction efficiency and distribution of two commonly used AAV serotypes (rAAV5 and rAAV9). In cerebral organoids, transduction with rAAV5 led to higher levels of vector DNA, transgenic mRNA, and protein expression as compared with rAAV9. The superior transduction of rAAV5 was replicated in iPSC-derived neuronal cells. Furthermore, rAAV5-mediated delivery of a human sequence-specific engineered microRNA to cerebral organoids led to a lower expression of its target ataxin-3. Our studies provide a new tool for selecting and deselecting AAV serotypes, and for demonstrating therapeutic efficacy of transgenes in a human context. Implementing cerebral organoids during gene therapy development could reduce the usage of animal models and improve translation to the clinic. Show less
Garcia Perez, L.; Eggermond, M. van; Roon, L. van; Vloemans, S.A.; Cordes, M.; Schambach, A.; ... ; Pike-Overzet, K. 2020
Recombinase-activating gene-1 (RAG1)-deficient severe combined immunodeficiency (SCID) patients lack B and T lymphocytes due to the inability to rearrange immunoglobulin and T cell receptor genes.... Show moreRecombinase-activating gene-1 (RAG1)-deficient severe combined immunodeficiency (SCID) patients lack B and T lymphocytes due to the inability to rearrange immunoglobulin and T cell receptor genes. Gene therapy is an alternative for those RAG1-SCID patients who lack a suitable bone marrow donor. We designed lentiviral vectors with different internal promoters driving codon-optimized RAG1 to ensure optimal expression. We used Rag1(-/-) mice as a preclinical model for RAG1-SCID to assess the efficacy of the various vectors. We observed that B and T cell reconstitution directly correlated with RAG1 expression. Mice with low RAG1 expression showed poor immune reconstitution; however, higher expression resulted in phenotypic and functional lymphocyte reconstitution comparable to mice receiving wild-type stem cells. No signs of genotoxicity were found. Additionally, RAG1-SCID patient CD34(+) cells transduced with our clinical RAG1 vector and transplanted into NSG mice led to improved human B and T cell development. Considering this efficacy outcome, together with favorable safety data, these results substantiate the need for a clinical trial for RAG1-SCID. Show less
Gene therapy for severe hemophilia B is advancing and offers sustained disease amelioration with a single treatment. We have reported the efficacy and safety of AMT-060, an investigational gene... Show moreGene therapy for severe hemophilia B is advancing and offers sustained disease amelioration with a single treatment. We have reported the efficacy and safety of AMT-060, an investigational gene therapy comprising an adeno-associated virus serotype 5 capsid encapsidating the codon-optimized wild-type human factor IX (WT hFIX) gene with a liver-specific promoter, in patients with severe hemophilia B. Treatment with 2 x 10(13) gc/kg AMT-060 showed sustained and durable FIX activity of 3%-13% and a substantial reduction in spontaneous bleeds without T cell-mediated hepatoxicity. To achieve higher FIX activity, we modified AMT-060 to encode the R338L "Padua" FIX variant that has increased specific activity (AMT-061). We report the safety and increased FIX activity ofAMT-061 in non-human primates. Animals (n = 3/group) received intravenous AMT-060 (5 x 10(12) gc/kg), AMT-061 (ranging from 5 x 10(11) to 9 x 10(13) gc/kg), or vehicle. Human FIX protein expression, FIX activity, and coagulation markers including D-dimer and thrombin-antithrombin complexes were measured. At equal doses, AMT-060 and AMT-061 resulted in similar human FIX protein expression, but FIX activity was 6.5-fold enhanced using AMT-061. Both vectors show similar safety and transduction profiles. Thus, AMT-061 holds great promise as a more potent FIX replacement gene therapy with a favorable safety profile. Show less
Huntington disease (HD) is a fatal neurodegenerative genetic disorder, thought to reflect a toxic gain of function in huntingtin (Htt) protein. Adeno-associated viral vector serotype 5 (AAV5)-... Show moreHuntington disease (HD) is a fatal neurodegenerative genetic disorder, thought to reflect a toxic gain of function in huntingtin (Htt) protein. Adeno-associated viral vector serotype 5 (AAV5)- microRNA targeting huntingtin (miHTT) is a HD gene-therapy candidate that efficiently lowers HTT using RNAi. This study analyzed the efficacy and potential for offtarget effects with AAV5-miHTT in neuronal and astrocyte cell cultures differentiated from induced pluripotent stem cells (iPSCs) from two individuals with HD (HD71 and HD180). One-time AAV5-miHTT treatment significantly reduced human HTT mRNA by 57% and Htt protein by 68% in neurons. Small RNA sequencing showed that mature miHTT was processed correctly without off-target passenger strand. No cellular microRNAs were dysregulated, indicating that endogenous RNAi machinery was unaffected by miHTT overexpression. qPCR validation of in silico-predicted off-target transcripts, next-generation sequencing, and pathway analysis confirmed absence of dysregulated genes due to sequence homology or seed-sequence activity of miHTT. Minor effects on gene expression were observed in both AAV5-miHTT and AAV5-GFP-treated samples, suggesting that they were due to viral transduction rather than miHTT. This study confirms the efficacy of AAV5-miHTT in HD patient iPSC-derived neuronal cultures and lack of off-target effects in gene expression and regulation in neuronal cells and astrocytes. Show less
Spinocerebellar ataxia type 3 (SCA3) or Machado-Joseph disease (MJD) is a progressiveneurodegenerative disorder caused by a CAG expansion in the ATXN3 gene. The expanded CAGrepeat is translated... Show moreSpinocerebellar ataxia type 3 (SCA3) or Machado-Joseph disease (MJD) is a progressiveneurodegenerative disorder caused by a CAG expansion in the ATXN3 gene. The expanded CAGrepeat is translated into a prolonged polyglutamine repeat in the ataxin-3 protein and accumulateswithin inclusions, acquiring toxic properties, which results in degeneration of the cerebellum and brainstem.In the current study, a non-allele specific ATXN3 silencing approach was investigated using artificialmicroRNAs engineered to target various regions of the ATXN3 gene (miATXN3). The miATXN3candidates were screened in vitro based on their silencing efficacy on a luciferase reporter co-expressing ATXN3. The three best miATXN3 candidates were further tested for target engagement andpotential off-target activity in induced-pluripotent stem cells (iPSC) differentiated into frontal brain-like neurons and in a SCA3 knock-in mouse model. Besides a strong reduction of ATXN3 mRNA andprotein, small RNA sequencing revealed efficient guide strand processing without passenger strandsbeing produced. We used different methods to predict alteration of off-target genes upon AAV5-miATXN3 treatment and found no evidence for unwanted effects. Furthermore, we demonstrated in alarge animal model, the minipig, that intrathecal delivery of AAV5 can transduce the main areasaffected in SCA3 patients. These results proved a strong basis to move forward to investigatedistribution, efficacy and safety of AAV5-miATXN3 in large animals. Show less
Huntington disease (HD) is a fatal neurodegenerative disorder caused by an autosomal dominant CAG repeat expansion in the huntingtin (HTT) gene. The translated expanded polyglutamine repeat in the... Show moreHuntington disease (HD) is a fatal neurodegenerative disorder caused by an autosomal dominant CAG repeat expansion in the huntingtin (HTT) gene. The translated expanded polyglutamine repeat in the HTT protein is known to cause toxic gain of function. We showed previously that strong HTT lowering prevented neuronal dysfunction in HD rodents and minipigs after single intracranial injection of adeno-associated viral vector serotype 5 expressing a microRNA targeting human HTT (AAV5-miHTT). To evaluate long-term efficacy, AAV5-miHTT was injected into the striatum of knockin Q175 HD mice, and the mice were sacrificed 12 months post-injection. AAV5-miHTT caused a dose-dependent and sustained HTT protein reduction with subsequent suppression of mutant HTT aggregate formation in the striatum and cortex. Functional proof of concept was shown in transgenic R6/2 HD mice. Eight weeks after AAV5-miHTT treatment, a significant improvement in motor coordination on the rotarod was observed. Survival analysis showed that a single AAV5-miHTT treatment resulted in a significant 4-week increase in median survival compared with vehicle-treated R6/2 HD mice. The combination of long-term HTT lowering, reduction in aggregation, prevention of neuronal dysfunction, alleviation of HD-like symptoms, and beneficial survival observed in HD rodents treated with AAV5-miHTT supports the continued development of HTT-lowering gene therapies for HD. Show less
Aldi, S.; Matic, L.P.; Hamm, G.; Keulen, D. van; Tempel, D.; Holmstrom, K.; ... ; Hurt-Camejo, E. 2018
