Whole genomic analysis reveals atypical non-homologous off-target large structural variants induced by CRISPR-Cas9-mediated genome editing

Advances in T Cell-Based Cancer Immunotherapy: From Fundamental Mechanisms to Clinical Prospects

T cells and their T cell receptors (TCRs) play crucial roles in the adaptive immune system's response against pathogens and tumors. However, immunosenescence, characterized by declining T cell function and quantity with age, significantly impairs antitumor immunity. Recent years have witnessed remarkable progress in T cell-based cancer treatments, driven by a deeper understanding of T cell biology and innovative screening technologies. This review comprehensively examines T cell maturation mechanisms, T cell-mediated antitumor responses, and the implications of thymic involution on T cell diversity and cancer prognosis. We discuss recent advances in adoptive T cell therapies, including tumor-infiltrating lymphocyte (TIL) therapy, engineered T cell receptor (TCR-T) therapy, and chimeric antigen receptor T cell (CAR-T) therapy. Notably, we highlight emerging DNA-encoded library technologies in mammalian cells for high-throughput screening of TCR-antigen interactions, which are revolutionizing the discovery of novel tumor antigens and optimization of TCR affinity. The review also explores strategies to overcome challenges in the solid tumor microenvironment and emerging approaches to enhance the efficacy of T cell therapy. As our understanding of T cell biology deepens and screening technologies advances, T cell-based immunotherapies show increasing promise for delivering durable clinical benefits to a broader patient population.

Value of Optical Genome Mapping (OGM) for Diagnostics of Rare Diseases: A Family Case Report

Optical genome mapping (OGM) is a novel method enabling the detection of structural genomic variants. The method is based on the laser image acquisition of single, labeled, high-molecular-weight DNA molecules and can detect structural genomic variants such as translocations, inversions, insertions, deletions, duplications, and complex structural rearrangements. We aim to present our experience with OGM at the Clinical Institute of Genomic Medicine, University Medical Centre Ljubljana, Slovenia. Since its introduction in 2021, we have used OGM for the testing of facioscapulohumeral muscular dystrophy 1, characterization and resolution of variants identified by other technologies such as microarrays, exome and genome next-generation sequencing, karyotyping, as well as testing of rare disease patients in whom no genetic cause could be identified using these methods. We present an example family case of two previously undiagnosed male siblings with an overlapping clinical presentation of thrombocytopenia, obesity, and presacral teratoma. After karyotyping, microarray analysis and next-generation sequencing, by using OGM, a maternally inherited cryptic translocation t(X;18)(q27.1;q12.2) was identified in both brothers. Despite an extended segregation analysis, based on strictly applied ACMG criteria and ClinGen guidelines, the identified translocation remains a variant of unknown significance. Despite the remaining limitations of OGM, which will hopefully be resolved by improvements in databases of known benign SV variation and the establishment of official guidelines on the clinical interpretation of OGM variants, our work highlights the complexity of the diagnostic journey, including this novel method, in rare disease cases.

Effects, methods and limits of the cryopreservation on mesenchymal stem cells

Mesenchymal stem cells (MSCs) are a type of cell capable of regulating the immune system, as well as exhibiting self-renewal and multi-lineage differentiation potential. Mesenchymal stem cells have emerged as an essential source of seed cells for therapeutic cell therapy. It is crucial to cryopreserve MSCs in liquid nitrogen prior to clinical application while preserving their functionality. Furthermore, efficient cryopreservation greatly enhances MSCs' potential in a range of biological domains. Nevertheless, there are several limits on the MSC cryopreservation methods now in use, necessitating thorough biosafety assessments before utilizing cryopreserved MSCs. Therefore, in order to improve the effectiveness of cryopreserved MSCs in clinical stem cell treatment procedures, new technological techniques must be developed immediately. The study offers an exhaustive analysis of the state-of-the-art MSC cryopreservation techniques, their effects on MSCs, and the difficulties encountered when using cryopreserved MSCs in clinical applications.

The Central Role of Cytogenetics in Radiation Biology

Radiation cytogenetics has a rich history seldom appreciated by those outside the field. Early radiobiology was dominated by physics and biophysical concepts that borrowed heavily from the study of radiation-induced chromosome aberrations. From such studies, quantitative relationships between biological effect and changes in absorbed dose, dose rate and ionization density were codified into key concepts of radiobiological theory that have persisted for nearly a century. This review aims to provide a historical perspective of some of these concepts, including evidence supporting the contention that chromosome aberrations underlie development of many, if not most, of the biological effects of concern for humans exposed to ionizing radiations including cancer induction, on the one hand, and tumor eradication on the other. The significance of discoveries originating from these studies has widened and extended far beyond their original scope. Chromosome structural rearrangements viewed in mitotic cells were first attributed to the production of breaks by the radiations during interphase, followed by the rejoining or mis-rejoining among ends of other nearby breaks. These relatively modest beginnings eventually led to the discovery and characterization of DNA repair of double-strand breaks by non-homologous end joining, whose importance to various biological processes is now widely appreciated. Two examples, among many, are V(D)J recombination and speciation. Rapid technological advancements in cytogenetics, the burgeoning fields of molecular radiobiology and third-generation sequencing served as a point of confluence between the old and new. As a result, the emergent field of "cytogenomics" now becomes uniquely positioned for the purpose of more fully understanding mechanisms underlying the biological effects of ionizing radiation exposure.

Click editing enables programmable genome writing using DNA polymerases and HUH endonucleases

Genome editing technologies based on DNA-dependent polymerases (DDPs) could offer several benefits compared with other types of editors to install diverse edits. Here, we develop click editing, a genome writing platform that couples the advantageous properties of DDPs with RNA-programmable nickases to permit the installation of a range of edits, including substitutions, insertions and deletions. Click editors (CEs) leverage the 'click'-like bioconjugation ability of HUH endonucleases with single-stranded DNA substrates to covalently tether 'click DNA' (clkDNA) templates encoding user-specifiable edits at targeted genomic loci. Through iterative optimization of the modular components of CEs and their clkDNAs, we demonstrate the ability to install precise genome edits with minimal indels in diverse immortalized human cell types and primary fibroblasts with precise editing efficiencies of up to ~30%. Editing efficiency can be improved by rapidly screening clkDNA oligonucleotides with various modifications, including repair-evading substitutions. Click editing is a precise and versatile genome editing approach for diverse biological applications.

Novel off-Targeting Events Identified after Genome Wide Analysis of CRISPR-Cas Edited Pigs

CRISPR-Cas technology has transformed our ability to introduce targeted modifications, allowing unconventional animal models such as pigs to model human diseases and improve its value for food production. The main concern with using the technology is the possibility of introducing unwanted modifications in the genome. In this study, we illustrate a pipeline to comprehensively identify off-targeting events on a global scale in the genome of three different gene-edited pig models. Whole genome sequencing paired with an off-targeting prediction software tool filtered off-targeting events amongst natural variations present in gene-edited pigs. This pipeline confirmed two known off-targeting events in IGH knockout pigs, AR and RBFOX1, and identified other presumably off-targeted loci. Independent validation of the off-targeting events using other gene-edited DNA confirmed two novel off-targeting events in RAG2/IL2RG knockout pig models. This unique strategy offers a novel tool to detect off-targeting events in genetically heterogeneous species after genome editing.

Deciphering the Substrate Specificity Reveals that CRISPR-Cas12a Is a Bifunctional Enzyme with Both Endo- and Exonuclease Activities

The class 2 CRISPR-Cas9 and CRISPR-Cas12a systems, originally described as adaptive immune systems of bacteria and archaea, have emerged as versatile tools for genome-editing, with applications in biotechnology and medicine. However, significantly less is known about their substrate specificity, but such knowledge may provide instructive insights into their off-target cleavage and previously unrecognized mechanism of action. Here, we document that the Acidaminococcus sp. Cas12a (AsCas12a) binds preferentially, and independently of crRNA, to a suite of branched DNA structures, such as the Holliday junction (HJ), replication fork and D-loops, compared with single- or double-stranded DNA, and promotes their degradation. Further, our study revealed that AsCas12a binds to the HJ, specifically at the crossover region, protects it from DNase I cleavage and renders a pair of thymine residues in the HJ homologous core hypersensitive to KMnO4 oxidation, suggesting DNA melting and/or distortion. Notably, these structural changes enabled AsCas12a to resolve HJ into nonligatable intermediates, and subsequently their complete degradation. We further demonstrate that crRNA impedes HJ cleavage by AsCas12a, and that of Lachnospiraceae bacterium Cas12a, without affecting their DNA-binding ability. We identified a separation-of-function variant, which uncouples DNA-binding and DNA cleavage activities of AsCas12a. Importantly, we found robust evidence that AsCas12a endonuclease also has 3'-to-5' and 5'-to-3' exonuclease activity, and that these two activities synergistically promote degradation of DNA, yielding di- and mononucleotides. Collectively, this study significantly advances knowledge about the substrate specificity of AsCas12a and provides important insights into the degradation of different types of DNA substrates.

Optical Genome Mapping Reveals Genomic Alterations upon Gene Editing in hiPSCs: Implications for Neural Tissue Differentiation and Brain Organoid Research

Genome editing, notably CRISPR (cluster regularly interspaced short palindromic repeats)/Cas9 (CRISPR-associated protein 9), has revolutionized genetic engineering allowing for precise targeted modifications. This technique's combination with human induced pluripotent stem cells (hiPSCs) is a particularly valuable tool in cerebral organoid (CO) research. In this study, CRISPR/Cas9-generated fluorescently labeled hiPSCs exhibited no significant morphological or growth rate differences compared with unedited controls. However, genomic aberrations during gene editing necessitate efficient genome integrity assessment methods. Optical genome mapping, a high-resolution genome-wide technique, revealed genomic alterations, including chromosomal copy number gain and losses affecting numerous genes. Despite these genomic alterations, hiPSCs retain their pluripotency and capacity to generate COs without major phenotypic changes but one edited cell line showed potential neuroectodermal differentiation impairment. Thus, this study highlights optical genome mapping in assessing genome integrity in CRISPR/Cas9-edited hiPSCs emphasizing the need for comprehensive integration of genomic and morphological analysis to ensure the robustness of hiPSC-based models in cerebral organoid research.

Exonic knockout and knockin gene editing in hematopoietic stem and progenitor cells rescues RAG1 immunodeficiency

Recombination activating genes (RAGs) are tightly regulated during lymphoid differentiation, and their mutations cause a spectrum of severe immunological disorders. Hematopoietic stem and progenitor cell (HSPC) transplantation is the treatment of choice but is limited by donor availability and toxicity. To overcome these issues, we developed gene editing strategies targeting a corrective sequence into the human RAG1 gene by homology-directed repair (HDR) and validated them by tailored two-dimensional, three-dimensional, and in vivo xenotransplant platforms to assess rescue of expression and function. Whereas integration into intron 1 of RAG1 achieved suboptimal correction, in-frame insertion into exon 2 drove physiologic human RAG1 expression and activity, allowing disruption of the dominant-negative effects of unrepaired hypomorphic alleles. Enhanced HDR-mediated gene editing enabled the correction of human RAG1 in HSPCs from patients with hypomorphic RAG1 mutations to overcome T and B cell differentiation blocks. Gene correction efficiency exceeded the minimal proportion of functional HSPCs required to rescue immunodeficiency in Rag1-/- mice, supporting the clinical translation of HSPC gene editing for the treatment of RAG1 deficiency.

CRISPR/Cas-based gene editing in therapeutic strategies for beta-thalassemia

Beta-thalassemia (β-thalassemia) is an autosomal recessive disorder caused by point mutations, insertions, and deletions in the HBB gene cluster, resulting in the underproduction of β-globin chains. The most severe type may demonstrate complications including massive hepatosplenomegaly, bone deformities, and severe growth retardation in children. Treatments for β-thalassemia include blood transfusion, splenectomy, and allogeneic hematopoietic stem cell transplantation (HSCT). However, long-term blood transfusions require regular iron removal therapy. For allogeneic HSCT, human lymphocyte antigen (HLA)-matched donors are rarely available, and acute graft-versus-host disease (GVHD) may occur after the transplantation. Thus, these conventional treatments are facing significant challenges. In recent years, with the advent and advancement of CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 (CRISPR-associated protein 9) gene editing technology, precise genome editing has achieved encouraging successes in basic and clinical studies for treating various genetic disorders, including β-thalassemia. Target gene-edited autogeneic HSCT helps patients avoid graft rejection and GVHD, making it a promising curative therapy for transfusion-dependent β-thalassemia (TDT). In this review, we introduce the development and mechanisms of CRISPR/Cas9. Recent advances on feasible strategies of CRISPR/Cas9 targeting three globin genes (HBB, HBG, and HBA) and targeting cell selections for β-thalassemia therapy are highlighted. Current CRISPR-based clinical trials in the treatment of β-thalassemia are summarized, which are focused on γ-globin reactivation and fetal hemoglobin reproduction in hematopoietic stem cells. Lastly, the applications of other promising CRISPR-based technologies, such as base editing and prime editing, in treating β-thalassemia and the limitations of the CRISPR/Cas system in therapeutic applications are discussed.

Click editing enables programmable genome writing using DNA polymerases and HUH endonucleases

Genome editing technologies that install diverse edits can widely enable genetic studies and new therapeutics. Here we develop click editing, a genome writing platform that couples the advantageous properties of DNA-dependent DNA polymerases with RNA-programmable nickases (e.g. CRISPR-Cas) to permit the installation of a range of edits including substitutions, insertions, and deletions. Click editors (CEs) leverage the "click"-like bioconjugation ability of HUH endonucleases (HUHes) with single stranded DNA substrates to covalently tether "click DNA" (clkDNA) templates encoding user-specifiable edits at targeted genomic loci. Through iterative optimization of the modular components of CEs (DNA polymerase and HUHe orthologs, architectural modifications, etc.) and their clkDNAs (template configurations, repair evading substitutions, etc.), we demonstrate the ability to install precise genome edits with minimal indels and no unwanted byproduct insertions. Since clkDNAs can be ordered as simple DNA oligonucleotides for cents per base, it is possible to screen many different clkDNA parameters rapidly and inexpensively to maximize edit efficiency. Together, click editing is a precise and highly versatile platform for modifying genomes with a simple workflow and broad utility across diverse biological applications.