2. METHODS2.1. Search strategyThe systematic search of the published literature was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) guidelines. 16 Our search strategy was developed to identify studies in Medline, Embase, and Pubmed. The following terms: (hematopoietic stem cell transplantation) AND (transplantation) AND (bone marrow BM transplantation) AND (cord blood transplantation) AND (peripheral blood progenitor cell transplantation) AND (CRISPR) AND (gene editing) were used as part of our search strategy. Databases were searched from 1947 up to 20 October 2020. The complete electronic search strategy is presented in Supplementary Table 1 and was prepared with the assistance of an information specialist (Risa Shorr). The search strategy was peer reviewed by a second information specialist. Our research protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO; registration number CRD42020207607 registered 12 October 2020; https://www.crd.york.ac.uk/prospero/).2.2. Study selection and data extractionWe included all controlled interventional preclinical studies that tested the in vivo use of CRISPR‐Cas9 gene edited blood‐derived cells for transplantation. Review articles, editorials, preclinical in vitro or ex vivo studies, and conference abstracts were excluded. Studies that specifically addressed the treatment of cancer, including studies that reported the use of CRISPR/Cas9 gene editing as a means to manufacture chimeric antigen receptor T cells, were excluded from further analysis in this study since these studies were primarily focused on cancer‐related outcomes with less focus on persistence of gene‐edited cells following infusion and will be analyzed and reported separately. Studies that reported on blood‐derived cells for applications other than restoration of the blood system were also excluded 17 (ie, marrow‐derived mesenchymal stromal cells) as persistence of these cells after infusion may not have been a primary concern.All records from the search were imported into Rayyan (https://rayyan.qcri.org/; accessed October 12, 2020). Duplicates were excluded. Abstracts of all the identified studies were independently screened by three investigators (H. Maganti, A. Bailey, A. Kirkham), and all potentially relevant articles were retrieved for further review based on the eligibility criteria (see below). Data were extracted independently by H. Maganti and A. Bailey using standardized forms (created using Excel, Microsoft, Seattle, Washington). Consensus was achieved through discussion with a senior team member (D.S. Allan) as needed to resolve discrepancies. Data were estimated from published graphs using Digitizelt (Version 2.2; Braunschweig, Germany) when raw data were not reported.2.3. Data analysisFor the meta‐analysis involving preclinical in vivo studies, raw data relating to engraftment percentages and/or percentage edited cells within the BM at input and endpoint were abstracted from the manuscripts or from published supplementary data. In studies where the raw data were not presented, the data were estimated from the presented graphs using Digitizelt (Version 2.2). To minimize bias, raw data were extracted by two individuals (H. Maganti and A. Bailey) and all discrepancies were resolved through consensus. Control (unedited) and edited arms of individual pre‐clinical studies were compared using Student's t test. Bias and significance in pooled analysis was done using DerSimonian and Laird random effects model for long‐term persistence of gene‐edited cells and fixed effects model for cell engraftment. Key parameters such as the number of animals which contributed to specific results reported in the study, cells used for transplantation in mice, randomization, and reporting of investigator and/or lab personnel blinding were also noted and summarized. These key parameters have been previously identified as potential sources of bias in systematic reviews and their reporting is crucial in order to strengthen the conclusions of the review. 18 Potential sources of bias were examined in each study using the Systematic Review Centre for Laboratory Animal Experimental (SYRCLE) tool. 19
Article TitlePersistence ofCRISPR/Cas9gene edited hematopoietic stem cells following transplantation: A systematic review and meta‐analysis of preclinical studies
Data sharing is not applicable to this article as no new data were created or analyzed in this study.