Generation and characterization of severe combined immunodeficiency rats

Can Humanized Immune System Mouse and Rat Models Accelerate the Development of Cytomegalovirus-Based Vaccines Against Infectious Diseases and Cancers?

Over the past three decades, immunodeficient mouse models carrying human immune cells, with or without human lymphoid tissues, termed humanized immune system (HIS) rodent models, have been developed to recapitulate the human immune system and associated immune responses. HIS mouse models have successfully modeled many human-restricted viral infections, including those caused by human cytomegalovirus (HCMV) and human immunodeficiency virus (HIV). HIS mouse models have also been used to model human cancer immunobiology, which exhibits differences from murine cancers in traditional mouse models. Variants of HIS mouse models that carry human liver cells, lung tissue, skin tissue, or human patient-derived tumor xenografts and human hematopoietic stem cells-derived-human immune cells with or without lymphoid tissue xenografts have been developed to probe human immune responses to infections and human tumors. HCMV-based vaccines are human-restricted, which poses limitations for mechanistic and efficacy studies using traditional animal models. The HCMV-based vaccine approach is a promising vaccine strategy as it induces robust effector memory T cell responses that may be critical in preventing and rapidly controlling persistent viral infections and cancers. Here, we review novel HIS mouse models with robust human immune cell development and primary and secondary lymphoid tissues that could address many of the limitations of HIS mice in their use as animal models for HCMV-based vaccine research. We also reviewed novel HIS rat models, which could allow long-term (greater than one year) vaccinology studies and better recapitulate human pathophysiology. Translating laboratory research findings to clinical application is a significant bottleneck in vaccine development; HIS rodents and related variants that more accurately model human immunology and diseases could increase the translatability of research findings.

DNA-PKcs governs LAT-dependent signaling in CD4 + and CD8 + T cells

Formation of the immune synapse (IS) following T cell antigen recognition includes recruitment of the Linker for Activation of T cells (LAT). Once at the IS, LAT tyrosines are phosphorylated allowing it to serve as a scaffold for formation of the "signalosome", a multiprotein complex that drives TCR signaling. Here, we show that upon T cell activation, DNA dependent protein kinase catalytic subunit (DNA-PKcs) interacts with LAT and localizes to the IS. Inhibition of DNA-PKcs diminishes LAT localization at the IS. We identified two LAT serines phosphorylated by DNA-PKcs, S224 and S241, that impact LAT tyrosine phosphorylation, protein binding, and cytokine production. Using our mouse model designed to delete DNA-PKcs expression within mature CD4 + or CD8 + T cells, we show loss of DNA-PKcs results in T cells unable to control tumor growth or induce allogeneic graft rejection. These data bring to the forefront DNA-PKcs as a pivotal protein in T cell function.

Immune deficiency phenotypes of Il2rg, Rag2 or Il2rg/Rag2 double knockout rats; establishment of human leukemia xenograft models

BACKGROUND

Genetically immunodeficient mice lacking Il2rg and Rag2 genes have been widely utilized in the field of biomedical research. However, immunodeficient rats, which offer the advantage of larger size, have not been as extensively used to date. Recently, Severe Combined Immunodeficiency (SCID) rats were generated using CRISPR/Cas9 system, targeting Il2rg and Rag2 in National BioResource Project in Japan. We imported and investigated more detailed phenotypes of wild-type (WT) Il2rg knockout (KO), Rag2 KO and Il2rg/Rag2 KO rats for 20 weeks.

RESULTS

During experiments, Il2rg KO, Rag2 KO and Il2rg/Rag2 KO rats showed decreased white blood cells and systemic lymphopenia, with reduced CD4+, CD8+ T cells and CD161+ NK cells. Additionally, all KO strains exhibited reduced relative spleen weights, hypoplasia of the germinal center in the white pulp, and atrophy with the disappearance of the boundary between the cortex and medulla in the thymus, compared to WT rats. Furthermore, we established human acute lymphoblastic leukemia xenograft rat model by intravenously injecting 5.0 × 106 cells/kg of NALM6 cells into Il2rg/Rag2 KO rats.

CONCLUSIONS

These findings indicate that Il2rg KO, Rag2 KO, and Il2rg/Rag2 KO rats exhibited SCID phenotypes, suggesting their potential application as immunodeficient animal models for tumor xenograft studies.

Efficient generation of human immune system rats using human CD34+ cells

Human immune system (HIS) mice generated using human CD34+ hematopoietic stem cells serve as a pivotal model for the in vivo evaluation of immunotherapies for humans. Yet, HIS mice possess certain limitations. Rats, due to their size and comprehensive immune system, hold promise for translational experiments. Here, we describe an efficacious method for long-term immune humanization, through intrahepatic injection of hCD34+ cells in newborn immunodeficient rats expressing human SIRPα. In contrast to HIS mice and similar to humans, HIS rats showed in blood a predominance of T cells, followed by B cells. Immune humanization was also high in central and secondary lymphoid organs. HIS rats treated with the anti-human CD3 antibody were depleted of human T cells, and human cytokines were detected in sera. We describe for the first time a method to efficiently generate HIS rats. HIS rats have the potential to be a useful model for translational immunology.

Genome editing using type I-E CRISPR-Cas3 in mice and rat zygotes

The type I CRISPR system has recently emerged as a promising tool, especially for large-scale genomic modification, but its application to generate model animals by editing zygotes had not been established. In this study, we demonstrate genome editing in zygotes using the type I-E CRISPR-Cas3 system, which efficiently generates deletions of several thousand base pairs at targeted loci in mice with 40%-70% editing efficiency without off-target mutations. To overcome the difficulties associated with detecting the variable deletions, we used a newly long-read sequencing-based multiplex genotyping approach. Demonstrating remarkable versatility, our Cas3-based technique was successfully extended to rats as well as mice, even by zygote electroporation methods. Knockin for SNP exchange and genomic replacement with a donor plasmid were also achieved in mice. This pioneering work with the type I CRISPR zygote editing system offers increased flexibility and broader applications in genetic engineering across different species.

The multifaceted functions of DNA-PKcs: implications for the therapy of human diseases

The DNA-dependent protein kinase (DNA-PK), catalytic subunit, also known as DNA-PKcs, is complexed with the heterodimer Ku70/Ku80 to form DNA-PK holoenzyme, which is well recognized as initiator in the nonhomologous end joining (NHEJ) repair after double strand break (DSB). During NHEJ, DNA-PKcs is essential for both DNA end processing and end joining. Besides its classical function in DSB repair, DNA-PKcs also shows multifaceted functions in various biological activities such as class switch recombination (CSR) and variable (V) diversity (D) joining (J) recombination in B/T lymphocytes development, innate immunity through cGAS-STING pathway, transcription, alternative splicing, and so on, which are dependent on its function in NHEJ or not. Moreover, DNA-PKcs deficiency has been proven to be related with human diseases such as neurological pathogenesis, cancer, immunological disorder, and so on through different mechanisms. Therefore, it is imperative to summarize the latest findings about DNA-PKcs and diseases for better targeting DNA-PKcs, which have shown efficacy in cancer treatment in preclinical models. Here, we discuss the multifaceted roles of DNA-PKcs in human diseases, meanwhile, we discuss the progresses of DNA-PKcs inhibitors and their potential in clinical trials. The most updated review about DNA-PKcs will hopefully provide insights and ideas to understand DNA-PKcs associated diseases.

Monocarboxylate transporter 4 deficiency enhances high-intensity interval training-induced metabolic adaptations in skeletal muscle

High-intensity exercise stimulates glycolysis, subsequently leading to elevated lactate production within skeletal muscle. While lactate produced within the muscle is predominantly released into the circulation via the monocarboxylate transporter 4 (MCT4), recent research underscores lactate's function as an intercellular and intertissue signalling molecule. However, its specific intracellular roles within muscle cells remains less defined. In this study, our objective was to elucidate the effects of increased intramuscular lactate accumulation on skeletal muscle adaptation to training. To achieve this, we developed MCT4 knockout mice and confirmed that a lack of MCT4 indeed results in pronounced lactate accumulation in skeletal muscle during high-intensity exercise. A key finding was the significant enhancement in endurance exercise capacity at high intensities when MCT4 deficiency was paired with high-intensity interval training (HIIT). Furthermore, metabolic adaptations supportive of this enhanced exercise capacity were evident with the combination of MCT4 deficiency and HIIT. Specifically, we observed a substantial uptick in the activity of glycolytic enzymes, notably hexokinase, glycogen phosphorylase and pyruvate kinase. The mitochondria also exhibited heightened pyruvate oxidation capabilities, as evidenced by an increase in oxygen consumption when pyruvate served as the substrate. This mitochondrial adaptation was further substantiated by elevated pyruvate dehydrogenase activity, increased activity of isocitrate dehydrogenase - the rate-limiting enzyme in the TCA cycle - and enhanced function of cytochrome c oxidase, pivotal to the electron transport chain. Our findings provide new insights into the physiological consequences of lactate accumulation in skeletal muscle during high-intensity exercises, deepening our grasp of the molecular intricacies underpinning exercise adaptation. KEY POINTS: We pioneered a unique line of monocarboxylate transporter 4 (MCT4) knockout mice specifically tailored to the ICR strain, an optimal background for high-intensity exercise studies. A deficiency in MCT4 exacerbates the accumulation of lactate in skeletal muscle during high-intensity exercise. Pairing MCT4 deficiency with high-intensity interval training (HIIT) results in a synergistic boost in high-intensity exercise capacity, observable both at the organismal level (via a treadmill running test) and at the muscle tissue level (through an ex vivo muscle contractile function test). Coordinating MCT4 deficiency with HIIT enhances both the glycolytic enzyme activities and mitochondrial capacity to oxidize pyruvate.

Comparative Study of Immunodeficient Rat Strains in Engraftment of Human-Induced Pluripotent Stem Cell-Derived Airway Epithelia

The airway epithelia (AE) play a role in the clearance of foreign substances through ciliary motility and mucus secreted. We developed an artificial trachea that is made of collagen sponges and polypropylene mesh for the regeneration of the tracheal defect, and it was used for a clinical study. Then, a model in which the luminal surface of an artificial trachea was covered with a human-induced pluripotent stem cell-derived AE (hiPSC-AE) was transplanted into the tracheal defect of nude rats to promote epithelialization. In the future, this model was expected to be applied to research on infectious diseases and drug discovery as a trachea-humanized rat model. However, at present, sufficient engraftment has not been achieved to evaluate functional recovery in transplanted cells. Therefore, this study focused on immunosuppression in recipient rats. Nude rats lack T cell function and are widely used for transplantation experiments; however, more severe immunosuppressed recipients are preferred for xenotransplantation. Several strains of immunodeficient rats were created as rats that exhibit more severe immunodeficiency until now. In this study, to establish a trachea-humanized rat model in which human AE function can be analyzed to improve engraftment efficiency, engraftment efficiency in nude rats and X-linked severe combined immunodeficiency (X-SCID) rats following hiPSC-AE transplantation was compared. In the analysis of the proportion of engrafted cells in total cells at the graft site, the engraftment efficiency of epithelial cells tended to be high in X-SCID rats, although no statistical difference was found between the two groups, whereas the engraftment efficiency of mesenchymal cells was higher in X-SCID rats. Furthermore, the number of immune cells that accumulated in the grafts showed that a pan T cell marker, that is, CD3-positive cells, did not differ between the two strains; however, CD45-positive cells and major histocompatibility complex (MHC) class II-positive cells significantly decreased in X-SCID rats. These results indicate that X-SCID rats are more useful for the transplantation of hiPSC-AE into the tracheae to generate trachea-humanized rat models.

A Novel Approach to Orthotopic Hepatocyte Transplantation Engineered With Liver Hydrogel for Fibrotic Livers, Enhancing Cell-Cell Interaction and Angiogenesis

Hepatocyte transplantation (HCT) is a potential bridging therapy or an alternative to liver transplantation. Conventionally, single-cell hepatocytes are injected via the portal vein. This strategy, however, has yet to overcome poor cell engraftment and function. Therefore, we developed an orthotopic HCT method using a liver-derived extracellular matrix (L-ECM) gel. PXB cells (flesh mature human hepatocytes) were dispersed into the hydrogel solution in vitro, and the gel solution was immediately gelated in 37°C incubators to investigate the affinity between mature human hepatocyte and the L-ECM gel. During the 3-day cultivation in hepatocyte medium, PXB cells formed cell aggregates via cell-cell interactions. Quantitative analysis revealed human albumin production in culture supernatants. For the in vivo assay, PXB cells were encapsulated in the L-ECM gel and transplanted between the liver lobes of normal rats. Pathologically, the L-ECM gel was localized at the transplant site and retained PXB cells. Cell survival and hepatic function marker expression were verified in another rat model wherein thioacetamide was administered to induce liver fibrosis. Moreover, cell-cell interactions and angiogenesis were enhanced in the L-ECM gel compared with that in the collagen gel. Our results indicate that L-ECM gels can help engraft transplanted hepatocytes and express hepatic function as a scaffold for cell transplantation.

Production of large, defined genome modifications in rats by targeting rat embryonic stem cells

Rats were more frequently used than mice to model human disease before mouse embryonic stem cells (mESCs) revolutionized genetic engineering in mice. Rat ESCs (rESCs) were first reported over 10 years ago, yet they are not as frequently used as mESCs. CRISPR-based gene editing in zygotes is widely used in rats but is limited by the difficulty of inserting or replacing DNA sequences larger than about 10 kb. We report here the generation of germline-competent rESC lines from several rat strains. These rESC lines maintain their potential for germline transmission after serial targeting with bacterial artificial chromosome (BAC)-based targeting vectors, and CRISPR-Cas9 cutting can increase targeting efficiency. Using these methods, we have successfully replaced entire rat genes spanning up to 101 kb with the human ortholog.

Long-term correction of hemophilia B through CRISPR/Cas9 induced homology-independent targeted integration

CRISPR/Cas9-mediated site-specific insertion of exogenous genes holds potential for clinical applications. However, it is still infeasible because homologous recombination (HR) is inefficient, especially for non-dividing cells. To overcome the challenge, we report that a homology-independent targeted integration (HITI) strategy is used for permanent integration of high-specificity-activity Factor IX variant (F9 Padua, R338L) at the albumin (Alb) locus in a novel hemophilia B (HB) rat model. The knock-in efficiency reaches 3.66%, as determined by droplet digital PCR (ddPCR). The clotting time is reduced to a normal level four weeks after treatment, and the circulating factor IX (FIX) level is gradually increased up to 52% of the normal level over nine months even after partial hepatectomy, demonstrating the amelioration of hemophilia. Through primer-extension-mediated sequencing (PEM-seq), no significant off-target effect is detected. This study not only provides a novel model for HB but also identifies a promising therapeutic approach for rare inherited diseases.

Efficient engraftment and viral transduction of human hepatocytes in an FRG rat liver humanization model

Humanized liver rodent models, in which the host liver parenchyma is repopulated by human hepatocytes, have been increasingly used for drug development and disease research. Unlike the leading humanized liver mouse model in which Fumarylacetoacetate Hydrolase (Fah), Recombination Activating Gene (Rag)-2 and Interleukin-2 Receptor Gamma (Il2rg) genes were inactivated simultaneously, generation of similar recipient rats has been challenging. Here, using Velocigene and 1-cell-embryo-targeting technologies, we generated a rat model deficient in Fah, Rag1/2 and Il2rg genes, similar to humanized liver mice. These rats were efficiently engrafted with Fah-expressing hepatocytes from rat, mouse and human. Humanized liver rats expressed human albumin and complement proteins in serum and showed a normal liver zonation pattern. Further, approaches were developed for gene delivery through viral transduction of human hepatocytes either in vivo, or in vitro prior to engraftment, providing a novel platform to study liver disease and hepatocyte-targeted therapies.

A high-quality severe combined immunodeficiency (SCID) rat bioresource

Immunodeficient animals are valuable models for the engraftment of exogenous tissues; they are widely used in many fields, including the creation of humanized animal models, as well as regenerative medicine and oncology. Compared with mice, laboratory rats have a larger body size and can more easily undergo transplantation of various tissues and organs. Considering the absence of high-quality resources of immunodeficient rats, we used the CRISPR/Cas9 genome editing system to knock out the interleukin-2 receptor gamma chain gene (Il2rg) in F344/Jcl rats—alone or together with recombination activating gene 2 (Rag2)—to create a high-quality bioresource that researchers can freely use: severe combined immunodeficiency (SCID) rats. We selected one founder rat with frame-shift mutations in both Il2rg (5-bp del) and Rag2 ([1-bp del+2-bp ins]/[7-bp del+2-bp ins]), then conducted mating to establish a line of immunodeficient rats. The immunodeficiency phenotype was preliminarily confirmed by the presence of severe thymic hypoplasia in Il2rg-single knockout (sKO) and Il2rg/Rag2-double knockout (dKO) rats. Assessment of blood cell counts in peripheral blood showed that the white blood cell count was significantly decreased in sKO and dKO rats, while the red blood cell count was unaffected. The decrease in white blood cell count was mainly caused by a decrease in lymphocytes. Furthermore, analyses of lymphocyte populations via flow cytometry showed that the numbers of B cells (CD3^- CD45⁺) and natural killer cells (CD3^- CD161⁺) were markedly reduced in both knockout rats. In contrast, T cells were markedly reduced but showed slightly different results between sKO and dKO rats. Notably, our immunodeficient rats do not exhibit growth retardation or gametogenesis defects. This high-quality SCID rat resource is now managed by the National BioResource Project in Japan. Our SCID rat model has been used in various research fields, demonstrating its importance as a bioresource.

In Vivo Modeling of Human Breast Cancer Using Cell Line and Patient-Derived Xenografts

Historically, human breast cancer has been modeled largely in vitro using long-established cell lines primarily in two-dimensional culture, but also in three-dimensional cultures of varying cellular and molecular complexities. A subset of cell line models has also been used in vivo as cell line-derived xenografts (CDX). While outstanding for conducting detailed molecular analysis of regulatory mechanisms that may function in vivo, results of drug response studies using long-established cell lines have largely failed to translate clinically. In an attempt to address this shortcoming, many laboratories have succeeded in developing clinically annotated patient-derived xenograft (PDX) models of human cancers, including breast, in a variety of host systems. While immunocompromised mice are the predominant host, the immunocompromised rat and pig, zebrafish, as well as the chicken egg chorioallantoic membrane (CAM) have also emerged as potential host platforms to help address perceived shortcomings of immunocompromised mice. With any modeling platform, the two main issues to be resolved are criteria for "credentialing" the models as valid models to represent human cancer, and utility with respect to the ability to generate clinically relevant translational research data. Such data are beginning to emerge, particularly with the activities of PDX consortia such as the NCI PDXNet Program, EuroPDX, and the International Breast Cancer Consortium, as well as a host of pharmaceutical companies and contract research organizations (CRO). This review focuses primarily on these important aspects of PDX-related research, with a focus on breast cancer.

Recent Advances in the Production of Genome-Edited Rats

The rat is an important animal model for understanding gene function and developing human disease models. Knocking out a gene function in rats was difficult until recently, when a series of genome editing (GE) technologies, including zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and the type II bacterial clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated Cas9 (CRISPR/Cas9) systems were successfully applied for gene modification (as exemplified by gene-specific knockout and knock-in) in the endogenous target genes of various organisms including rats. Owing to its simple application for gene modification and its ease of use, the CRISPR/Cas9 system is now commonly used worldwide. The most important aspect of this process is the selection of the method used to deliver GE components to rat embryos. In earlier stages, the microinjection (MI) of GE components into the cytoplasm and/or nuclei of a zygote was frequently employed. However, this method is associated with the use of an expensive manipulator system, the skills required to operate it, and the egg transfer (ET) of MI-treated embryos to recipient females for further development. In vitro electroporation (EP) of zygotes is next recognized as a simple and rapid method to introduce GE components to produce GE animals. Furthermore, in vitro transduction of rat embryos with adeno-associated viruses is potentially effective for obtaining GE rats. However, these two approaches also require ET. The use of gene-engineered embryonic stem cells or spermatogonial stem cells appears to be of interest to obtain GE rats; however, the procedure itself is difficult and laborious. Genome-editing via oviductal nucleic acids delivery (GONAD) (or improved GONAD (i-GONAD)) is a novel method allowing for the in situ production of GE zygotes existing within the oviductal lumen. This can be performed by the simple intraoviductal injection of GE components and subsequent in vivo EP toward the injected oviducts and does not require ET. In this review, we describe the development of various approaches for producing GE rats together with an assessment of their technical advantages and limitations, and present new GE-related technologies and current achievements using those rats in relation to human diseases.

Human Organoid and Supporting Technologies for Cancer and Toxicological Research

Recent progress in the field of organoid-based cell culture systems has enabled the use of patient-derived cells in conditions that resemble those in cancer tissue, which are better than two-dimensional (2D) cultured cell lines. In particular, organoids allow human cancer cells to be handled in conditions that resemble those in cancer tissue, resulting in more efficient establishment of cells compared with 2D cultured cell lines, thus enabling the use of multiple patient-derived cells with cells from different genetic background, in keeping with the heterogeneity of the cells. One of the most valuable points of using organoids is that human cells from either healthy or cancerous tissue can be used. Using genome editing technology such as clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein, organoid genomes can be modified to, for example, cancer-prone genomes. The normal, cancer, or genome-modified organoids can be used to evaluate whether chemicals have genotoxic or non-genotoxic carcinogenic activity by evaluating the cancer incidence, cancer progression, and cancer metastasis. In this review, the organoid technology and the accompanying technologies were summarized and the advantages of organoid-based toxicology and its application to pancreatic cancer study were discussed.

Survival-Assured Liver Injury Preconditioning (SALIC) Enables Robust Expansion of Human Hepatocytes in Fah-/- Rag2-/- IL2rg-/- Rats

Although liver-humanized animals are desirable tools for drug development and expansion of human hepatocytes in large quantities, their development is restricted to mice. In animals larger than mice, a precondition for efficient liver humanization remains preliminary because of different xeno-repopulation kinetics in livers of larger sizes. Since rats are ten times larger than mice and widely used in pharmacological studies, liver-humanized rats are more preferable. Here, Fah-/- Rag2-/- IL2rg-/- (FRG) rats are generated by CRISPR/Cas9, showing accelerated liver failure and lagged liver xeno-repopulation compared to FRG mice. A survival-assured liver injury preconditioning (SALIC) protocol, which consists of retrorsine pretreatment and cycling 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) administration by defined concentrations and time intervals, is developed to reduce the mortality of FRG rats and induce a regenerative microenvironment for xeno-repopulation. Human hepatocyte repopulation is boosted to 31 ± 4% in rat livers at 7 months after transplantation, equivalent to approximately a 1200-fold expansion. Human liver features of transcriptome and zonation are reproduced in humanized rats. Remarkably, they provide sufficient samples for the pharmacokinetic profiling of human-specific metabolites. This model is thus preferred for pharmacological studies and human hepatocyte production. SALIC may also be informative to hepatocyte transplantation in other large-sized species.

Establishment of an Experimental System for Intraperitoneal Chemotherapy in a Rat Model

AIM

To establish an experimental system for comparing different methods of intraperitoneal chemotherapy in a rat model.

MATERIALS AND METHODS

We used six-week-old Sprague-Dawley rats, and created an early postoperative intraperitoneal chemotherapy (EPIC) system using 18-gauge syringes and evacuators, and a hyperthermic intraperitoneal chemotherapy (HIPEC) system using two peristaltic pumps which controlled the flow rate and temperature. Pressurized intraperitoneal aerosol chemotherapy (PIPAC) was achieved using a nozzle for dispersing aerosols at a flow rate up to 41.5 ml/min. The distribution and intensity of 0.2% trypan blue dye was compared among three methods.

RESULTS

The distribution was limited and the intensity was weak after EPIC, and the dye stained moderately in gravity-dependent regions after HIPEC. On the other hand, the distribution was the most comprehensive, and the intensity was the greatest after PIPAC.

CONCLUSION

This experimental system in a rat model may reflect the comparative effect among EPIC, HIPEC and PIPAC in humans.

DNA-Dependent Protein Kinase Catalytic Subunit: The Sensor for DNA Double-Strand Breaks Structurally and Functionally Related to Ataxia Telangiectasia Mutated

The DNA-dependent protein kinase (DNA-PK) is composed of a DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and Ku70/Ku80 heterodimer. DNA-PK is thought to act as the “sensor” for DNA double-stranded breaks (DSB), which are considered the most deleterious type of DNA damage. In particular, DNA-PKcs and Ku are shown to be essential for DSB repair through nonhomologous end joining (NHEJ). The phenotypes of animals and human individuals with defective DNA-PKcs or Ku functions indicate their essential roles in these developments, especially in neuronal and immune systems. DNA-PKcs are structurally related to Ataxia–telangiectasia mutated (ATM), which is also implicated in the cellular responses to DSBs. DNA-PKcs and ATM constitute the phosphatidylinositol 3-kinase-like kinases (PIKKs) family with several other molecules. Here, we review the accumulated knowledge on the functions of DNA-PKcs, mainly based on the phenotypes of DNA-PKcs-deficient cells in animals and human individuals, and also discuss its relationship with ATM in the maintenance of genomic stability.

The Mononuclear Phagocyte System of the Rat

The laboratory rat continues to be the model of choice for many studies of physiology, behavior, and complex human diseases. Cells of the mononuclear phagocyte system (MPS; monocytes, macrophages, and dendritic cells) are abundant residents in every tissue in the body and regulate postnatal development, homeostasis, and innate and acquired immunity. Recruitment and proliferation of MPS cells is an essential component of both initiation and resolution of inflammation. The large majority of current knowledge of MPS biology is derived from studies of inbred mice, but advances in technology and resources have eliminated many of the advantages of the mouse as a model. In this article, we review the tools available and the current state of knowledge of development, homeostasis, regulation, and diversity within the MPS of the rat.

Patient-derived xenograft: a developing tool for screening biomarkers and potential therapeutic targets for human esophageal cancers

Esophageal cancer (EC) represents a human malignancy, diagnosed often at the advanced stage of cancer and resulting in high morbidity and mortality. The development of precision medicine allows for the identification of more personalized therapeutic strategies to improve cancer treatment. By implanting primary cancer tissues into immunodeficient mice for expansion, patient-derived xenograft (PDX) models largely maintain similar histological and genetic representations naturally found in patients' tumor cells. PDX models of EC (EC-PDX) provide fine platforms to investigate the tumor microenvironment, tumor genomic heterogeneity, and tumor response to chemoradiotherapy, which are necessary for new drug discovery to combat EC in addition to optimization of current therapeutic strategies for EC. In this review, we summarize the methods used for establishing EC-PDX models and investigate the utilities of EC-PDX in screening predictive biomarkers and potential therapeutic targets. The challenge of this promising research tool is also discussed.

Advances in Genome Editing and Application to the Generation of Genetically Modified Rat Models

The rat has been extensively used as a small animal model. Many genetically engineered rat models have emerged in the last two decades, and the advent of gene-specific nucleases has accelerated their generation in recent years. This review covers the techniques and advances used to generate genetically engineered rat lines and their application to the development of rat models more broadly, such as conditional knockouts and reporter gene strains. In addition, genome-editing techniques that remain to be explored in the rat are discussed. The review also focuses more particularly on two areas in which extensive work has been done: human genetic diseases and immune system analysis. Models are thoroughly described in these two areas and highlight the competitive advantages of rat models over available corresponding mouse versions. The objective of this review is to provide a comprehensive description of the advantages and potential of rat models for addressing specific scientific questions and to characterize the best genome-engineering tools for developing new projects.

Humanization of Immunodeficient Animals for the Modeling of Transplantation, Graft Versus Host Disease, and Regenerative Medicine

The humanization of animals is a powerful tool for the exploration of human disease pathogenesis in biomedical research, as well as for the development of therapeutic interventions with enhanced translational potential. Humanized models enable us to overcome biologic differences that exist between humans and other species, while giving us a platform to study human processes in vivo. To become humanized, an immune-deficient recipient is engrafted with cells, tissues, or organoids. The mouse is the most well studied of these hosts, with a variety of immunodeficient strains available for various specific uses. More recently, efforts have turned to the humanization of other animal species such as the rat, which offers some technical and immunologic advantages over mice. These advances, together with ongoing developments in the incorporation of human transgenes and additional mutations in humanized mouse models, have expanded our opportunities to replicate aspects of human allotransplantation and to assist in the development of immunotherapies. In this review, the immune and tissue humanization of various species is presented with an emphasis on their potential for use as models for allotransplantation, graft versus host disease, and regenerative medicine.

Deficiency of the RIβ subunit of protein kinase A causes body tremor and impaired fear conditioning memory in rats

The RIβ subunit of cAMP-dependent protein kinase (PKA), encoded by Prkar1b, is a neuronal isoform of the type I regulatory subunit of PKA. Mice lacking the RIβ subunit exhibit normal long-term potentiation (LTP) in the Schaffer collateral pathway of the hippocampus and normal behavior in the open-field and fear conditioning tests. Here, we combined genetic, electrophysiological, and behavioral approaches to demonstrate that the RIβ subunit was involved in body tremor, LTP in the Schaffer collateral pathway, and fear conditioning memory in rats. Genetic analysis of WTC-furue, a mutant strain with spontaneous tremors, revealed a deletion in the Prkar1b gene of the WTC-furue genome. Prkar1b-deficient rats created by the CRISPR/Cas9 system exhibited body tremor. Hippocampal slices from mutant rats showed deficient LTP in the Schaffer collateral-CA1 synapse. Mutant rats also exhibited decreased freezing time following contextual and cued fear conditioning, as well as increased exploratory behavior in the open field. These findings indicate the roles of the RIβ subunit in tremor pathogenesis and contextual and cued fear memory, and suggest that the hippocampal and amygdala roles of this subunit differ between mice and rats and that rats are therefore beneficial for exploring RIβ function.

The SRG rat, a Sprague-Dawley Rag2/Il2rg double-knockout validated for human tumor oncology studies

We have created the immunodeficient SRG rat, a Sprague-Dawley Rag2/Il2rg double knockout that lacks mature B cells, T cells, and circulating NK cells. This model has been tested and validated for use in oncology (SRG OncoRat®). The SRG rat demonstrates efficient tumor take rates and growth kinetics with different human cancer cell lines and PDXs. Although multiple immunodeficient rodent strains are available, some important human cancer cell lines exhibit poor tumor growth and high variability in those models. The VCaP prostate cancer model is one such cell line that engrafts unreliably and grows irregularly in existing models but displays over 90% engraftment rate in the SRG rat with uniform growth kinetics. Since rats can support much larger tumors than mice, the SRG rat is an attractive host for PDX establishment. Surgically resected NSCLC tissue from nine patients were implanted in SRG rats, seven of which engrafted and grew for an overall success rate of 78%. These developed into a large tumor volume, over 20,000 mm3 in the first passage, which would provide an ample source of tissue for characterization and/or subsequent passage into NSG mice for drug efficacy studies. Molecular characterization and histological analyses were performed for three PDX lines and showed high concordance between passages 1, 2 and 3 (P1, P2, P3), and the original patient sample. Our data suggest the SRG OncoRat is a valuable tool for establishing PDX banks and thus serves as an alternative to current PDX mouse models hindered by low engraftment rates, slow tumor growth kinetics, and multiple passages to develop adequate tissue banks.

In Vivo Analysis of Human Immune Responses in Immunodeficient Rats

Supplemental Digital Content is available in the text.

Background.

Humanized immune system immunodeficient mice have been extremely useful for the in vivo analyses of immune responses in a variety of models, including organ transplantation and graft versus host disease (GVHD) but they have limitations. Rat models are interesting complementary alternatives presenting advantages over mice, such as their size and their active complement compartment. Immunodeficient rats have been generated but human immune responses have not yet been described.

Methods.

We generated immunodeficient Rat Rag−/− Gamma chain−/− human signal regulatory protein alpha-positive (RRGS) rats combining Rag1 and Il2rg deficiency with the expression of human signal regulatory protein alpha, a negative regulator of macrophage phagocytosis allowing repression of rat macrophages by human CD47-positive cells. We then immune humanized RRGS animals with human peripheral blood mononuclear cells (hPBMCs) to set up a human acute GVHD model. Treatment of GVHD was done with a new porcine antihuman lymphocyte serum active through complement-dependent cytotoxicity. We also established a tumor xenograft rejection model in these hPBMCs immune system RRGS animals by subcutaneous implantation of a human tumor cell line.

Results.

RRGS animals receiving hPBMCs showed robust and reproducible reconstitution, mainly by T and B cells. A dose-dependent acute GVHD process was observed with progressive weight loss, tissue damage, and death censoring. Antihuman lymphocyte serum (L1S1) antibody completely prevented acute GVHD. In the human tumor xenograft model, detectable tumors were rejected upon hPBMCs injection.

Conclusions.

hPBMC can be implanted in RRGS animals and elicit acute GVHD or rejection of human tumor cells and these are useful models to test new immunotherapies.

Rat models of human diseases and related phenotypes: a systematic inventory of the causative genes

The laboratory rat has been used for a long time as the model of choice in several biomedical disciplines. Numerous inbred strains have been isolated, displaying a wide range of phenotypes and providing many models of human traits and diseases. Rat genome mapping and genomics was considerably developed in the last decades. The availability of these resources has stimulated numerous studies aimed at discovering causal disease genes by positional identification. Numerous rat genes have now been identified that underlie monogenic or complex diseases and remarkably, these results have been translated to the human in a significant proportion of cases, leading to the identification of novel human disease susceptibility genes, helping in studying the mechanisms underlying the pathological abnormalities and also suggesting new therapeutic approaches. In addition, reverse genetic tools have been developed. Several genome-editing methods were introduced to generate targeted mutations in genes the function of which could be clarified in this manner [generally these are knockout mutations]. Furthermore, even when the human gene causing a disease had been identified without resorting to a rat model, mutated rat strains (in particular KO strains) were created to analyze the gene function and the disease pathogenesis. Today, over 350 rat genes have been identified as underlying diseases or playing a key role in critical biological processes that are altered in diseases, thereby providing a rich resource of disease models. This article is an update of the progress made in this research and provides the reader with an inventory of these disease genes, a significant number of which have similar effects in rat and humans.

Pathological characteristics of Ccdc85c knockout rats: a rat model of genetic hydrocephalus

Spontaneous hhy mice show hydrocephalus and subcortical heterotopia, and a mutation in the Ccdc85c gene has been identified. To contribute to the comparison of the role of Ccdc85c in different species, we established a Ccdc85c KO rat and investigated its pathological phenotypes. Ccdc85c KO rats were produced by genomic engineering using transcription activator-like effector nuclease (TALEN). The KO rats had an approximately 350-bp deletion in Ccdc85c and lacked CCDC85C protein expression. The KO rats showed non-obstructive hydrocephalus, subcortical heterotopia, and intracranial hemorrhage. The KO rats had many pathological characteristics similar to those in hhy mice. These results indicate that CCDC85C plays an important role in cerebral development in rats, and the function of CCDC85C in the cerebrum are similar in rats and mice.

Establishment of a rat ovarian peritoneal metastasis model to study pressurized intraperitoneal aerosol chemotherapy (PIPAC)

BACKGROUND

pressurized intraperitoneal aerosol chemotherapy (PIPAC), with or without electrostatic precipitation (ePIPAC), was recently introduced in the treatment of peritoneal metastases (PM) from ovarian cancer (OC). Preliminary clinical data are promising, but several methodological issues as well the anticancer efficacy of PIPAC remain unaddressed. Here, we propose a rat ePIPAC model that allows to study these issues in a clinically relevant, reproducible, and high throughput model.

METHODS

laparoscopy and PIPAC were established in healthy Wistar rats. Aerosol properties were measured using laser diffraction spectrometry based granulometric analyses. Electrostatic precipitation was accomplished using a commercially available generator (Ultravision™). A xenograft model of ovarian PM was created in athymic rats using intraperitoneal (IP) injection of SKOV-3 luciferase positive cells. Tumor growth was monitored weekly by in vivo bioluminescence imaging.

RESULTS

PIPAC and electrostatic precipitation were well tolerated using a capnoperitoneum of 8 mmHg. All rats survived the (e)PIPAC procedure and no gas or aerosol leakage was observed over the entire procedure. With an injection pressure of 20 bar, granulometry showed a mean droplet diameter (D(v,0.5)) of 47 μm with a flow rate of 0.5 mL/s, and a significantly lower diameter (30 μm) when a flow rate of 0.8 mL/s was used. Experiments using IP injection of SKOV-3 luciferase positive cells showed that after IP injection of 20 × 10⁶ cells, miliary PM was observed in all animals. PIPAC was feasible and well supported in these tumor bearing animals.

CONCLUSIONS

we propose a reproducible and efficient rodent model to study PIPAC and ePIPAC in OC xenografts with widespread PM. This model allows to characterize and optimize pharmacokinetic and biophysical parameters, and to evaluate the anti-cancer efficacy of (e)PIPAC treatment.

Severe-combined immunodeficient rats can be used to generate a model of perinatal hypoxic-ischemic brain injury to facilitate studies of engrafted human neural stem cells

Cerebral palsy (CP) encompasses a group of non-progressive brain disorders that are often acquired through perinatal hypoxic-ischemic (HI) brain injury. Injury leads to a cascade of cell death events, resulting in lifetime motor and cognitive deficits. There are currently no treatments that can repair the resulting brain damage and improve functional outcomes. To date, preclinical research using neural precursor cell (NPC) transplantation as a therapy for HI brain injury has shown promise. To translate this treatment to the clinic, it is essential that human-derived NPCs also be tested in animal models, however, a major limitation is the high risk of xenograft rejection. A solution is to transplant the cells into immune-deficient rodents, but there are currently no models of HI brain injury established in such a cohort of animals. Here, we demonstrate that a model of HI brain injury can be generated in immune-deficient Prkdc knockout (KO) rats. Long-term deficits in sensorimotor function were similar between KO and wildtype (WT) rats. Interestingly, some aspects of the injury were more severe in KO rats. Additionally, human induced pluripotent stem cell derived (hiPSC)-NPCs had higher survival at 10 weeks post-transplant in KO rats when compared to their WT counterparts. This work establishes a reliable model of neonatal HI brain injury in Prkdc KO rats that will allow for future transplantation, survival, and long-term evaluation of the safety and efficacy of hiPSC-NPCs for neonatal brain damage. This model will enable critical preclinical translational research using human NPCs.

Sprague Dawley Rag2-Null Rats Created from Engineered Spermatogonial Stem Cells Are Immunodeficient and Permissive to Human Xenografts

The rat is the preferred model for toxicology studies, and it offers distinctive advantages over the mouse as a preclinical research model including larger sample size collection, lower rates of drug clearance, and relative ease of surgical manipulation. An immunodeficient rat would allow for larger tumor size development, prolonged dosing and drug efficacy studies, and preliminary toxicologic testing and pharmacokinetic/pharmacodynamic studies in the same model animal. Here, we created an immunodeficient rat with a functional deletion of the Recombination Activating Gene 2 (Rag2) gene, using genetically modified spermatogonial stem cells (SSC). We targeted the Rag2 gene in rat SSCs with TALENs and transplanted these Rag2-deficient SSCs into sterile recipients. Offspring were genotyped, and a founder with a 27 bp deletion mutation was identified and bred to homozygosity to produce the Sprague-Dawley Rag2 - Rag2 ^tm1Hera (SDR) knockout rat. We demonstrated that SDR rat lacks mature B and T cells. Furthermore, the SDR rat model was permissive to growth of human glioblastoma cell line subcutaneously resulting in successful growth of tumors. In addition, a human KRAS-mutant non-small cell lung cancer cell line (H358), a patient-derived high-grade serous ovarian cancer cell line (OV81), and a patient-derived recurrent endometrial cancer cell line (OV185) were transplanted subcutaneously to test the ability of the SDR rat to accommodate human xenografts from multiple tissue types. All human cancer cell lines showed efficient tumor uptake and growth kinetics indicating that the SDR rat is a viable host for a range of xenograft studies. Mol Cancer Ther; 17(11); 2481-9. ©2018 AACR.

An Immune System-Modified Rat Model for Human Stem Cell Transplantation Research

Due to its lack of both innate and acquired immune responses to human cells, the NODSCIDIl2rγ^−/− (NSG) mouse model has become an important tool for human stem cell research. When compared with the mouse, the rat is physiologically more similar to humans and offers advantages in preclinical efficacy studies on human stem cells, particularly in evaluating neural, hepatic, and cardiac functions. Therefore, we generated a human SIRPα⁺Prdkc^−/−Il2rγ^−/− rat model, denoted NSG-like (NSGL) rat, which expresses human SIRPα and is abolished in the development of B, T, and natural killer cells. When compared with Prdkc^−/−Il2rγ^−/− (SG) rats, NSGL rats allow more efficient engraftment of human cancer cells and human pluripotent stem cells. In addition, only NSGL rats, but not SG rats, can be engrafted with human hematopoietic stem cells to reconstitute the human immune system. Therefore, NSGL rats represent an improved xenotransplantation model for efficacy studies of human stem cells.

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Generation of human SIRPα⁺Prkdc^−/−Il2rγ^−/− NSG-like (NSGL) rat model

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NSGL rats lack B, T, and NK cells but express human SIRPα

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NSGL rats can be efficiently engrafted with human stem cells

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NSGL rats can be reconstituted by human HSCs to generate a human immune system

A novel immunodeficient rat model supports human lung cancer xenografts

Patient-derived xenograft (PDX) animal models allow the exogenous growth of human tumors, offering an irreplaceable preclinical tool for oncology research. Mice are the most commonly used host for human PDX models, however their small body size limits the xenograft growth, sample collection, and drug evaluation. Therefore, we sought to develop a novel rat model that could overcome many of these limitations. We knocked out Rag1, Rag2, and Il2rg in Sprague Dawley (SD) rats by clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 technology. The development of lymphoid organs is significantly impaired in Rag1^-/-Rag2^-/-Il2rg^-/Y (designated as SD-RG) rats. Consequently, SD-RG rats are severely immunodeficient with an absence of mature T, B, and NK cells in the immune system. After subcutaneous injection of tumor cell lines of different origin, such as NCI-H460, U-87MG, and MDA-MB-231, the tumors grow significantly faster and larger in SD-RG rats than in nonobese diabetic- Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ mice. Most important of all, we successfully established a PDX model of lung squamous cell carcinoma in which the grafts recapitulate the histopathologic features of the primary tumor for several passages. In conclusion, the severely immunodeficient SD-RG rats support fast growth of PDX compared with mice, thus holding great potential to serve as a new model for oncology research.-He, D., Zhang, J., Wu, W., Yi, N., He, W., Lu, P., Li, B., Yang, N., Wang, D., Xue, Z., Zhang, P., Fan, G., Zhu, X. A novel immunodeficient rat model supports human lung cancer xenografts.

Reproductive technologies for the generation and maintenance of valuable animal strains

Many types of mutant and genetically engineered strains have been produced in various animal species. Their numbers have dramatically increased in recent years, with new strains being rapidly produced using genome editing techniques. In the rat, it has been difficult to produce knockout and knock-in strains because the establishment of stem cells has been insufficient. However, a large number of knockout and knock-in strains can currently be produced using genome editing techniques, including zinc-finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN), and the clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 (Cas9) system. Microinjection technique has also contributed widely to the production of various kinds of genome edited animal strains. A novel electroporation method, the “Technique for Animal Knockout system by Electroporation (TAKE)” method, is a simple and highly efficient tool that has accelerated the production of new strains. Gamete preservation is extremely useful for maintaining large numbers of these valuable strains as genetic resources in the long term. These reproductive technologies, including microinjection, TAKE method, and gamete preservation, strongly support biomedical research and the bio-resource banking of animal models. In this review, we introduce the latest reproductive technologies used for the production of genetically engineered animals, especially rats, using genome editing techniques and the efficient maintenance of valuable strains as genetic resources. These technologies can also be applied to other laboratory animals, including mice, and domestic and wild animal species.

Rats deficient C-type natriuretic peptide suffer from impaired skeletal growth without early death

We have previously investigated the physiological role of C-type natriuretic peptide (CNP) on endochondral bone growth, mainly with mutant mouse models deficient in CNP, and reported that CNP is indispensable for physiological endochondral bone growth in mice. However, the survival rate of CNP knockout (KO) mice fell to as low as about 70% until 10 weeks after birth, and we could not sufficiently analyze the phenotype at the adult stage. Herein, we generated CNP KO rats by using zinc-finger nuclease-mediated genome editing technology. We established two lines of mutant rats completely deficient in CNP (CNP KO rats) that exhibited a phenotype identical to that observed in mice deficient in CNP, namely, a short stature with severely impaired endochondral bone growth. Histological analysis revealed that the width of the growth plate, especially that of the hypertrophic chondrocyte layer, was markedly lower and the proliferation of growth plate chondrocytes tended to be reduced in CNP KO rats. Notably, CNP KO rats did not have malocclusions and survived for over one year after birth. At 33 weeks of age, CNP KO rats persisted significantly shorter than wild-type rats, with closed growth plates of the femur in all samples, which were not observed in wild-type rats. Histologically, CNP deficiency affected only bones among all body tissues studied. Thus, CNP KO rats survive over one year, and exhibit a deficit in endochondral bone growth and growth retardation throughout life.

Creating a stem cell niche in the inner ear using self-assembling peptide amphiphiles

The use of human embryonic stem cells (hESCs) for regeneration of the spiral ganglion will require techniques for promoting otic neuronal progenitor (ONP) differentiation, anchoring of cells to anatomically appropriate and specific niches, and long-term cell survival after transplantation. In this study, we used self-assembling peptide amphiphile (PA) molecules that display an IKVAV epitope (IKVAV-PA) to create a niche for hESC-derived ONPs that supported neuronal differentiation and survival both in vitro and in vivo after transplantation into rodent inner ears. A feature of the IKVAV-PA gel is its ability to form organized nanofibers that promote directed neurite growth. Culture of hESC-derived ONPs in IKVAV-PA gels did not alter cell proliferation or viability. However, the presence of IKVAV-PA gels increased the number of cells expressing the neuronal marker beta-III tubulin and improved neurite extension. The self-assembly properties of the IKVAV-PA gel allowed it to be injected as a liquid into the inner ear to create a biophysical niche for transplanted cells after gelation in vivo. Injection of ONPs combined with IKVAV-PA into the modiolus of X-SCID rats increased survival and localization of the cells around the injection site compared to controls. Human cadaveric temporal bone studies demonstrated the technical feasibility of a transmastoid surgical approach for clinical intracochlear injection of the IKVAV-PA/ONP combination. Combining stem cell transplantation with injection of self-assembling PA gels to create a supportive niche may improve clinical approaches to spiral ganglion regeneration.

A Naturally Transmitted Epitheliotropic Polyomavirus Pathogenic in Immunodeficient Rats: Characterization, Transmission, and Preliminary Epidemiologic Studies

We report the identification, pathogenesis, and transmission of a novel polyomavirus in severe combined immunodeficient F344 rats with null Prkdc and interleukin 2 receptor gamma genes. Infected rats experienced weight loss, decreased fecundity, and mortality. Large basophilic intranuclear inclusions were observed in epithelium of the respiratory tract, salivary and lacrimal glands, uterus, and prostate gland. Unbiased viral metagenomic sequencing of lesioned tissues identified a novel polyomavirus, provisionally named Rattus norvegicus polyomavirus 2 (RatPyV2), which clustered with Washington University (WU) polyomavirus in the Wuki clade of the Betapolyomavirus genus. In situ hybridization analyses and quantitative polymerase chain reaction (PCR) results demonstrated viral nucleic acids in epithelium of respiratory, glandular, and reproductive tissues. Polyomaviral disease was reproduced in Foxn1^rnu nude rats cohoused with infected rats or experimentally inoculated with virus. After development of RatPyV2-specific diagnostic assays, a survey of immune-competent rats from North American research institutions revealed detection of RatPyV2 in 7 of 1,000 fecal samples by PCR and anti-RatPyV2 antibodies in 480 of 1,500 serum samples. These findings suggest widespread infection in laboratory rat populations, which may have profound implications for established models of respiratory injury. Additionally, RatPyV2 infection studies may provide an important system to investigate the pathogenesis of WU polyomavirus diseases of man.

Impaired Lymphocytes Development and Xenotransplantation of Gastrointestinal Tumor Cells in Prkdc-Null SCID Zebrafish Model

Severe combined immunodeficiency (SCID) mice have widely been used as hosts for human tumor cell xenograft study. This animal model, however, is labor intensive. As zebrafish is largely emerging as a promising model system for studying human diseases including cancer, developing efficient immunocompromised strains for tumor xenograft study are also demanded in zebrafish. Here, we have created the Prkdc-null SCID zebrafish model which provides the stable immune-deficient background required for xenotransplantation of tumor cell. In this study, the two transcription activator-like effector nucleases that specifically target the exon3 of the zebrafish Prkdc gene were used to induce a frame shift mutation, causing a complete knockout of the gene function. The SCID zebrafish showed susceptibility to spontaneous infection, a well-known phenotype found in the SCID mutation. Further characterization revealed that the SCID zebrafish contained no functional T and B lymphocytes which reflected the phenotypes identified in the mice SCID model. Intraperitoneal injection of human cancer cells into the adult SCID zebrafish clearly showed tumor cell growth forming into a solid mass. Our present data show the suitability of using the SCID zebrafish strain for xenotransplantation experiments, and in vivo monitoring of the tumor cell growth in the zebrafish demonstrates use of the animal model as a new platform of tumor xenograft study.

From engineering to editing the rat genome

Since its domestication over 100 years ago, the laboratory rat has been the preferred experimental animal in many areas of biomedical research (Lindsey and Baker The laboratory rat. Academic, New York, pp 1-52, 2006). Its physiology, size, genetics, reproductive cycle, cognitive and behavioural characteristics have made it a particularly useful animal model for studying many human disorders and diseases. Indeed, through selective breeding programmes numerous strains have been derived that are now the mainstay of research on hypertension, obesity and neurobiology (Okamoto and Aoki Jpn Circ J 27:282-293, 1963; Zucker and Zucker J Hered 52(6):275-278, 1961). Despite this wealth of genetic and phenotypic diversity, the ability to manipulate and interrogate the genetic basis of existing phenotypes in rat strains and the methodology to generate new rat models has lagged significantly behind the advances made with its close cousin, the laboratory mouse. However, recent technical developments in stem cell biology and genetic engineering have again brought the rat to the forefront of biomedical studies and enabled researchers to exploit the increasingly accessible wealth of genome sequence information. In this review, we will describe how a breakthrough in understanding the molecular basis of self-renewal of the pluripotent founder cells of the mammalian embryo, embryonic stem (ES) cells, enabled the derivation of rat ES cells and their application in transgenesis. We will also describe the remarkable progress that has been made in the development of gene editing enzymes that enable the generation of transgenic rats directly through targeted genetic modifications in the genomes of zygotes. The simplicity, efficiency and cost-effectiveness of the CRISPR/Cas gene editing system, in particular, mean that the ability to engineer the rat genome is no longer a limiting factor. The selection of suitable targets and gene modifications will now become a priority: a challenge where ES culture and gene editing technologies can play complementary roles in generating accurate bespoke rat models for studying biological processes and modelling human disease.

Comparative Analysis of piggyBac, CRISPR/Cas9 and TALEN Mediated BAC Transgenesis in the Zygote for the Generation of Humanized SIRPA Rats

BAC transgenic mammalian systems offer an important platform for recapitulating human gene expression and disease modeling. While the larger body mass, and greater genetic and physiologic similarity to humans render rats well suited for reproducing human immune diseases and evaluating therapeutic strategies, difficulties of generating BAC transgenic rats have hindered progress. Thus, an efficient method for BAC transgenesis in rats would be valuable. Immunodeficient mice carrying a human SIRPA transgene have previously been shown to support improved human cell hematopoiesis. Here, we have generated for the first time, human SIRPA BAC transgenic rats, for which the gene is faithfully expressed, functionally active, and germline transmissible. To do this, human SIRPA BAC was modified with elements to work in coordination with genome engineering technologies-piggyBac, CRISPR/Cas9 or TALEN. Our findings show that piggyBac transposition is a more efficient approach than the classical BAC transgenesis, resulting in complete BAC integration with predictable end sequences, thereby permitting precise assessment of the integration site. Neither CRISPR/Cas9 nor TALEN increased BAC transgenesis. Therefore, an efficient generation of human SIRPA transgenic rats using piggyBac opens opportunities for expansion of humanized transgenic rat models in the future to advance biomedical research and therapeutic applications.

Efficient liver repopulation of transplanted hepatocyte prevents cirrhosis in a rat model of hereditary tyrosinemia type I

Hereditary tyrosinemia type I (HT1) is caused by a deficiency in the enzyme fumarylacetoacetate hydrolase (Fah). Fah-deficient mice and pigs are phenotypically analogous to human HT1, but do not recapitulate all the chronic features of the human disorder, especially liver fibrosis and cirrhosis. Rats as an important model organism for biomedical research have many advantages over other animal models. Genome engineering in rats is limited till the availability of new gene editing technologies. Using the recently developed CRISPR/Cas9 technique, we generated Fah(-/-) rats. The Fah(-/-) rats faithfully represented major phenotypic and biochemical manifestations of human HT1, including hypertyrosinemia, liver failure, and renal tubular damage. More importantly, the Fah(-/-) rats developed remarkable liver fibrosis and cirrhosis, which have not been observed in Fah mutant mice or pigs. Transplantation of wild-type hepatocytes rescued the Fah(-/-) rats from impending death. Moreover, the highly efficient repopulation of hepatocytes in Fah(-/-) livers prevented the progression of liver fibrosis to cirrhosis and in turn restored liver architecture. These results indicate that Fah(-/-) rats may be used as an animal model of HT1 with liver cirrhosis. Furthermore, Fah(-/-) rats may be used as a tool in studying hepatocyte transplantation and a bioreactor for the expansion of hepatocytes.

Simple Genome Editing of Rodent Intact Embryos by Electroporation

The clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated (Cas) system is a powerful tool for genome editing in animals. Recently, new technology has been developed to genetically modify animals without using highly skilled techniques, such as pronuclear microinjection of endonucleases. Technique for animal knockout system by electroporation (TAKE) method is a simple and effective technology that produces knockout rats by introducing endonuclease mRNAs into intact embryos using electroporation. Using TAKE method and CRISPR/Cas system, the present study successfully produced knockout and knock-in mice and rats. The mice and rats derived from embryos electroporated with Cas9 mRNA, gRNA and single-stranded oligodeoxynucleotide (ssODN) comprised the edited targeted gene as a knockout (67% of mice and 88% of rats) or knock-in (both 33%). The TAKE method could be widely used as a powerful tool to produce genetically modified animals by genome editing.

Near-infrared fluorescence imaging of non-Hodgkin's lymphoma CD20 expression using Cy7-conjugated obinutuzumab

PURPOSE

Obinutuzumab is the first fully humanized and glycoengineered monoclonal antibody (mAb) directly targeting CD20 antigen, which is expressed on B cell lymphocytes and the majority of non-Hodgkin's lymphoma (NHL). This study aims to design a diagnostic molecular probe, Cy7-Obinutuzumab (Cy7-Obi), in which Cy7 is a near-infrared fluorescent dye. This probe is used to noninvasively image CD20 antigen expressed in NHL cells.

PROCEDURES

Cy7-Obi probe was synthesized through nucleophilic substitution reaction between NHS-Cy7 and obinutuzumab. After purification, the conjugate was fully characterized by a series of methods. The immunoreactivity and molecular specificity of the probe were confirmed using flow cytometry and in vitro microscopy on Raji (CD20-positive) cells. For in vivo imaging, Cy7-Obi probe (1 nmol) was injected intravenously in severe combined immunodeficiency (SCID) mice bearing Raji tumors which overexpress CD20 (n = 3) and was imaged with near-infrared fluorescence (NIRF) at 6, 9, 12, 24, 60, and 96 h post-probe injection. For pre-block, obinutuzumab (3.25 mg) was injected intravenously in tumor-bearing mice 6 h before the administration of Cy7-Obi probe.

RESULTS

The synthesized Cy7-Obi probe in this paper mimics obinutuzumab in both structure and function. Flow cytometry analysis of the probe and obinutuzumab on Raji cells showed minor difference in binding affinity/specificity with CD20. The probe showed significant fluorescence signal when it was examined on Raji cells using in vitro microscopy. The fluorescence signal can be blocked by pretreatment with obinutuzumab. The probe Cy7-Obi also showed high tumor uptake when it was examined by in vivo optical imaging on Raji tumor-bearing mice. The tumor uptake can be blocked by pretreatment with obinutuzumab (n = 3, p < 0.05). The in vivo imaging results were also confirmed by ex vivo imaging of dissected organs. Finally, the probe Cy7-Obi has shown excellent tumor targeting and specificity through immunofluorescence analysis.

CONCLUSIONS

We have shown that humanized Cy7-Obi probe can be used for NIRF imaging successfully. The probe may be an effective and noninvasive diagnostic molecular probe capable of tracking CD20 overexpression in NHL.

Oxidative/Nitrative Stress and Inflammation Drive Progression of Doxorubicin-Induced Renal Fibrosis in Rats as Revealed by Comparing a Normal and a Fibrosis-Resistant Rat Strain

Chronic renal fibrosis is the final common pathway of end stage renal disease caused by glomerular or tubular pathologies. Genetic background has a strong influence on the progression of chronic renal fibrosis. We recently found that Rowett black hooded rats were resistant to renal fibrosis. We aimed to investigate the role of sustained inflammation and oxidative/nitrative stress in renal fibrosis progression using this new model. Our previous data suggested the involvement of podocytes, thus we investigated renal fibrosis initiated by doxorubicin-induced (5 mg/kg) podocyte damage. Doxorubicin induced progressive glomerular sclerosis followed by increasing proteinuria and reduced bodyweight gain in fibrosis-sensitive, Charles Dawley rats during an 8-week long observation period. In comparison, the fibrosis-resistant, Rowett black hooded rats had longer survival, milder proteinuria and reduced tubular damage as assessed by neutrophil gelatinase-associated lipocalin (NGAL) excretion, reduced loss of the slit diaphragm protein, nephrin, less glomerulosclerosis, tubulointerstitial fibrosis and matrix deposition assessed by periodic acid-Schiff, Picro-Sirius-red staining and fibronectin immunostaining. Less fibrosis was associated with reduced profibrotic transforming growth factor-beta, (TGF-β1) connective tissue growth factor (CTGF), and collagen type I alpha 1 (COL-1a1) mRNA levels. Milder inflammation demonstrated by histology was confirmed by less monocyte chemotactic protein 1 (MCP-1) mRNA. As a consequence of less inflammation, less oxidative and nitrative stress was obvious by less neutrophil cytosolic factor 1 (p47phox) and NADPH oxidase-2 (p91phox) mRNA. Reduced oxidative enzyme expression was accompanied by less lipid peroxidation as demonstrated by 4-hydroxynonenal (HNE) and less protein nitrosylation demonstrated by nitrotyrosine (NT) immunohistochemistry and quantified by Western blot. Our results demonstrate that mediators of fibrosis, inflammation and oxidative/nitrative stress were suppressed in doxorubicin nephropathy in fibrosis-resistant Rowett black hooded rats underlying the importance of these pathomechanisms in the progression of renal fibrosis initiated by glomerular podocyte damage.

Genetically modified pigs to model human diseases

Genetically modified mice are powerful tools to investigate the molecular basis of many human diseases. Mice are, however, of limited value for preclinical studies, because they differ significantly from humans in size, general physiology, anatomy and lifespan. Considerable efforts are, thus, being made to develop alternative animal models for a range of human diseases. These promise powerful new resources that will aid the development of new diagnostics, medicines and medical procedures. Here, we provide a comprehensive review of genetically modified porcine models described in the scientific literature: various cancers, cystic fibrosis, Duchenne muscular dystrophy, autosomal polycystic kidney disease, Huntington’s disease, spinal muscular atrophy, haemophilia A, X-linked severe combined immunodeficiency, retinitis pigmentosa, Stargardt disease, Alzheimer’s disease, various forms of diabetes mellitus and cardiovascular diseases.

New humanized mouse model of bronchiolitis obliterans syndrome

Humanized animals are transplanted with human tissues and cells to study their behavior as they do in the human body. This commentary briefly summarizes the recent developments and discusses the limitations of these humanized animal models.

Exacerbation of intracranial aneurysm and aortic dissection in hypertensive rat treated with the prostaglandin F-receptor antagonist AS604872

Intracranial aneurysm (IA) and aortic dissection are both complications of hypertension and characterized by degeneration of the media. Given the involvement of prostaglandin F2α and its receptor, FP, in extracellular matrix remodeling in a mouse model of pulmonary fibrosis, here we induced hypertension and IA in rats by salt loading and hemi-lateral ligation of renal and carotid arteries and examined effects of a selective FP antagonist, AS604872, on these vascular events. AS604872 significantly accelerated degeneration of the media in both cerebral artery and aorta as evidenced by thinning of the media and disruption of the elastic lamina and promoted IA and aortic dissection. Notably, AS604872 induced expression of pro-inflammatory genes such as E-selectin in lesions and significantly enhanced macrophage infiltration. Suppression of surface expression of E-selectin with cimetidine prevented macrophage infiltration and aortic dissection. Thus, AS604872 exacerbates vascular inflammation in hypertensive rats and facilitates IA and aortic dissection. These results demonstrate that both IA and aortic dissection are caused by chronic inflammation of the arterial wall, which is worsened by AS604872, cautioning that other FP antagonists may share such deleterious actions in vascular homeostasis and suggesting that AS604872 can be used to make models of these vascular diseases with extensive degeneration.

Simple knockout by electroporation of engineered endonucleases into intact rat embryos

Engineered endonucleases, such as zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated (Cas) system, provide a powerful approach for genome editing in animals. However, the microinjection of endonucleases into embryos requires a high skill level, is time consuming, and may cause damage to embryos. Here, we demonstrate that the electroporation of endonuclease mRNAs into intact embryos can induce editing at targeted loci and efficiently produce knockout rats. It is noteworthy that the electroporation of ZFNs resulted in an embryonic survival rate (91%) and a genome-editing rate (73%) that were more than 2-fold higher than the corresponding rates from conventional microinjection. Electroporation technology provides a simple and effective method to produce knockout animals.