@article {3715, title = {Efficient and error-free correction of sickle mutation in human erythroid cells using prime editor-2.}, journal = {Front Genome Ed}, volume = {4}, year = {2022}, month = {2022}, pages = {1085111}, abstract = {

Sickle cell anaemia (SCA) is one of the common autosomal recessive monogenic disorders, caused by a transverse point mutation (GAG \> GTG) at the sixth codon of the beta-globin gene, which results in haemolytic anaemia due to the fragile RBCs. Recent progress in genome editing has gained attention for the therapeutic cure for SCA. Direct correction of SCA mutation by homology-directed repair relies on a double-strand break (DSB) at the target site and carries the risk of generating beta-thalassaemic mutations if the editing is not error-free. On the other hand, base editors cannot correct the pathogenic SCA mutation resulting from A \> T base transversion. Prime editor (PE), the recently described CRISPR/Cas 9 based gene editing tool that enables precise gene manipulations without DSB and unintended nucleotide changes, is a viable approach for the treatment of SCA. However, the major limitation with the use of prime editing is the lower efficiency especially in human erythroid cell lines and primary cells. To overcome these limitations, we developed a modular lenti-viral based prime editor system and demonstrated its use for the precise modelling of SCA mutation and its subsequent correction in human erythroid cell lines. We achieved highly efficient installation of SCA mutation (up to 72\%) and its subsequent correction in human erythroid cells. For the first time, we demonstrated the functional restoration of adult haemoglobin without any unintended nucleotide changes or indel formations using the PE2 system. We also validated that the off-target effects mediated by the PE2 system is very minimal even with very efficient on-target conversion, making it a safe therapeutic option. Taken together, the modular lenti-viral prime editor system developed in this study not only expands the range of cell lines targetable by prime editor but also improves the efficiency considerably, enabling the use of prime editor for myriad molecular, genetic, and translational studies.

}, issn = {2673-3439}, doi = {10.3389/fgeed.2022.1085111}, author = {George, Anila and Ravi, Nithin Sam and Prasad, Kirti and Panigrahi, Lokesh and Koikkara, Sanya and Rajendiran, Vignesh and Devaraju, Nivedhitha and Paul, Joshua and Pai, Aswin Anand and Nakamura, Yukio and Kurita, Ryo and Balasubramanian, Poonkuzhali and Thangavel, Saravanabhavan and Marepally, Srujan and Velayudhan, Shaji R and Srivastava, Alok and Mohankumar, Kumarasamypet M} } @article {3341, title = {Erythroid lineage-specific lentiviral RNAi vectors suitable for molecular functional studies and therapeutic applications.}, journal = {Sci Rep}, volume = {12}, year = {2022}, month = {2022 08 18}, pages = {14033}, abstract = {

Numerous genes exert multifaceted roles in hematopoiesis. Therefore, we generated novel\ lineage-specific RNA interference\ (RNAi) lentiviral\ vectors, H23B-Ery-Lin-shRNA\ and H234B-Ery-Lin-shRNA, to probe the functions of these genes in erythroid cells\ without affecting other hematopoietic lineages. The lineage specificity of these vectors was confirmed by\ transducing multiple hematopoietic cells to express a fluorescent protein. Unlike the previously reported erythroid lineage RNAi vector, our vectors were designed for cloning the short hairpin RNAs (shRNAs) for\ any gene, and they also provide superior knockdown of the target gene expression with a\ single shRNA integration per cell. High-level lineage-specific downregulation of BCL11A and ZBTB7A,\ two\ well-characterized transcriptional repressors of HBG in adult erythroid cells, was achieved with substantial induction of fetal hemoglobin with a single-copy lentiviral vector integration. Transduction of primary healthy donor CD34 cells with these vectors resulted in\ \>80\% reduction in the target\ protein levels and up to 40\% elevation in the γ-chain levels in the differentiated erythroid cells. Xenotransplantation of the human CD34 cells transduced with H23B-Ery-Lin-shBCL11A\ LV in immunocompromised mice showed ~ 60\% reduction in BCL11A protein expression with ~\ 40\% elevation of γ-chain levels in the erythroid cells derived from the transduced CD34 cells. Overall, the novel erythroid lineage-specific lentiviral RNAi vectors described in this study provide a\ high-level knockdown of target gene expression in the erythroid cells, making them suitable for their use in gene therapy for hemoglobinopathies. Additionally, the design of these vectors also makes them ideal for high-throughput RNAi screening for studying normal and pathological erythropoiesis.

}, keywords = {Animals, Cell Line, Tumor, Cell Lineage, DNA-Binding Proteins, Genetic Vectors, Humans, Lentivirus, Mice, RNA Interference, RNA, Small Interfering, Transcription Factors, Transduction, Genetic}, issn = {2045-2322}, doi = {10.1038/s41598-022-13783-0}, author = {Bagchi, Abhirup and Devaraju, Nivedhitha and Chambayil, Karthik and Rajendiran, Vignesh and Venkatesan, Vigneshwaran and Sayed, Nilofer and Pai, Aswin Anand and Nath, Aneesha and David, Ernest and Nakamura, Yukio and Balasubramanian, Poonkuzhali and Srivastava, Alok and Thangavel, Saravanabhavan and Mohankumar, Kumarasamypet M and Velayudhan, Shaji R} } @article {2465, title = {Identification of novel HPFH-like mutations by CRISPR base editing that elevate the expression of fetal hemoglobin.}, journal = {Elife}, volume = {11}, year = {2022}, month = {2022 02 11}, abstract = {

Naturally occurring point mutations in the promoter switch hemoglobin synthesis from defective adult beta-globin to fetal gamma-globin in sickle cell patients with hereditary persistence of fetal hemoglobin (HPFH) and ameliorate the clinical severity. Inspired by this natural phenomenon, we tiled the highly homologous proximal promoters using adenine and cytosine base editors that avoid the generation of large deletions and identified novel regulatory regions including a cluster at the -123 region. Base editing at -123 and -124 bp of promoter induced fetal hemoglobin (HbF) to a higher level than disruption of well-known BCL11A binding site in erythroblasts derived from human CD34+ hematopoietic stem and progenitor cells (HSPC). We further demonstrated in vitro that the introduction of -123T \> C and -124T \> C HPFH-like mutations drives gamma-globin expression by creating a de novo binding site for KLF1. Overall, our findings shed light on so far unknown regulatory elements within the promoter and identified additional targets for therapeutic upregulation of fetal hemoglobin.

}, keywords = {Adenine, Anemia, Sickle Cell, beta-Globins, beta-Thalassemia, Cell Line, Clustered Regularly Interspaced Short Palindromic Repeats, CRISPR-Cas Systems, Cytosine, Fetal Hemoglobin, gamma-Globins, Gene Editing, Hematopoietic Stem Cells, Humans, Point Mutation, Promoter Regions, Genetic}, issn = {2050-084X}, doi = {10.7554/eLife.65421}, author = {Ravi, Nithin Sam and Wienert, Beeke and Wyman, Stacia K and Bell, Henry William and George, Anila and Mahalingam, Gokulnath and Vu, Jonathan T and Prasad, Kirti and Bandlamudi, Bhanu Prasad and Devaraju, Nivedhitha and Rajendiran, Vignesh and Syedbasha, Nazar and Pai, Aswin Anand and Nakamura, Yukio and Kurita, Ryo and Narayanasamy, Muthuraman and Balasubramanian, Poonkuzhali and Thangavel, Saravanabhavan and Marepally, Srujan and Velayudhan, Shaji R and Srivastava, Alok and DeWitt, Mark A and Crossley, Merlin and Corn, Jacob E and Mohankumar, Kumarasamypet M} } @article {2884, title = {Preferential Expansion of Human CD34CD133CD90 Hematopoietic Stem Cells Enhances Gene-Modified Cell Frequency for Gene Therapy.}, journal = {Hum Gene Ther}, volume = {33}, year = {2022}, month = {2022 02}, pages = {188-201}, abstract = {

CD34CD133CD90 hematopoietic stem cells (HSCs) are responsible for long-term multilineage hematopoiesis, and the high frequency of gene-modified HSCs is crucial for the success of hematopoietic stem and progenitor cell (HSPC) gene therapy. However, the culture and gene manipulation steps of HSPC graft preparation significantly reduce the frequency of HSCs, thus necessitating large doses of HSPCs and reagents for the manipulation. In this study, we identified a combination of small molecules, Resveratrol, UM729, and SR1 that preferentially expands CD34CD133CD90 HSCs over other subpopulations of adult HSPCs in culture. The preferential expansion enriches the HSCs in culture, enhances the adhesion, and results in a sixfold increase in the long-term engraftment in NSG mice. Further, the culture-enriched HSCs are more responsive to gene modification by lentiviral transduction and gene editing, increasing the frequency of gene-modified HSCs up to 10-fold . The yield of gene-modified HSCs obtained by the culture enrichment is similar to the sort-purification of HSCs and superior to Cyclosporin-H treatment. Our study addresses a critical challenge of low frequency of gene modified HSCs in HSPC graft by developing and demonstrating a facile HSPC culture condition that increases the frequency of gene-modified cells . This strategy will improve the outcome of HSPC gene therapy and also simplify the gene manipulation process.

}, keywords = {Animals, Antigens, CD34, Fetal Blood, Genetic Therapy, Hematopoietic Stem Cell Transplantation, Hematopoietic Stem Cells, Humans, Mice, Mice, Inbred NOD, Mice, SCID}, issn = {1557-7422}, doi = {10.1089/hum.2021.089}, author = {Christopher, Abisha Crystal and Venkatesan, Vigneshwaran and Karuppusamy, Karthik V and Srinivasan, Saranya and Babu, Prathibha and Azhagiri, Manoj Kumar K and Chambayil, Karthik and Bagchi, Abhirup and Rajendiran, Vignesh and Ravi, Nithin Sam and Kumar, Sanjay and Marepally, Srujan Kumar and Mohankumar, Kumarasamypet Murugesan and Srivastava, Alok and Velayudhan, Shaji R and Thangavel, Saravanabhavan} } @article {2377, title = {Gene Editing in Human Induced Pluripotent Stem Cells Using Doxycycline-Inducible CRISPR-Cas9 System.}, journal = {Methods Mol Biol}, year = {2021}, month = {2021 Apr 09}, abstract = {

Induced pluripotent stem cells (iPSCs) generated from patients are a valuable tool for disease modelling, drug screening, and studying the functions of cell/tissue-specific genes. However, for this research, isogenic iPSC lines are important for comparison of phenotypes in the wild type and mutant differentiated cells generated from the iPSCs. The advent of gene editing technologies to correct or generate mutations helps in the generation of isogenic iPSC lines with the same genetic background. Due to the ease of programming, CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-Cas9-based gene editing tools have gained pace in gene manipulation studies, including investigating complex diseases like cancer. An iPSC line with drug inducible Cas9 expression from the Adeno-Associated Virus Integration Site 1 (AAVS1) safe harbor locus offers a controllable expression of Cas9 with robust gene editing. Here, we describe a stepwise protocol for the generation and characterization of such an iPSC line (AAVS1-PDi-Cas9 iPSC) with a doxycycline (dox)-inducible Cas9 expression cassette from the AAVS1 safe harbor site and efficient editing of target genes with lentiviral vectors expressing gRNAs. This approach with a tunable Cas9 expression that allows investigating gene functions in iPSCs or in the differentiated cells can serve as a versatile tool in disease modelling studies.

}, issn = {1940-6029}, doi = {10.1007/7651_2021_348}, author = {Thamodaran, Vasanth and Rani, Sonam and Velayudhan, Shaji R} }