Immunophenotype of a Rat Model of Duchenne's Disease and Demonstration of Improved Muscle Strength After Anti-CD45RC Antibody Treatment.

Corticosteroids (CS) are standard therapy for the treatment of Duchenne's muscular dystrophy (DMD). Even though they decrease inflammation, they have limited efficacy and are associated with significant side effects. There is therefore the need for new protolerogenic treatments to replace CS. Dystrophin-deficient rats (Dmdmdx ) closely resemble the pathological phenotype of DMD patients. We performed the first Immunophenotyping of Dmdmdx rats and showed leukocyte infiltration in skeletal and cardiac muscles, which consisted mostly of macrophages and T cells including CD45RChigh T cells. Muscles of DMD patients also contain elevated CD45RChigh T cells. We treated Dmdmdx rats with an anti-CD45RC MAb used in previous studies to deplete CD45RChigh T cells and induce immune tolerance in models of organ transplantation. Treatment of young Dmdmdx rats with anti-CD45RC MAb corrected skeletal muscle strength and was associated with depletion of CD45RChigh T cells with no side effects. Treatment of young Dmdmdx rats with prednisolone resulted in increase in skeletal muscle strength but also severe growth retardation. In conclusion, anti-CD45RC MAb treatment has potential in the treatment of DMD and might eventually result in reduction or elimination of CS use.

Generation of Immunodeficient Rats With Rag1 and Il2rg Gene Deletions and Human Tissue Grafting Models.

BACKGROUND: Immunodeficient mice are invaluable tools to analyze the long-term effects of potentially immunogenic molecules in the absence of adaptive immune responses. Nevertheless, there are models and experimental situations that would beneficiate of larger immunodeficient recipients. Rats are ideally suited to perform experiments in which larger size is needed and are still a small animal model suitable for rodent facilities. Additionally, rats reproduce certain human diseases better than mice, such as ankylosing spondylitis and Duchenne disease, and these disease models would greatly benefit from immunodeficient rats to test different immunogenic treatments. METHODS: We describe the generation of Il2rg-deficient rats and their crossing with previously described Rag1-deficient rats to generate double-mutant RRG animals. RESULTS: As compared with Rag1-deficient rats, Il2rg-deficient rats were more immunodeficient because they partially lacked not only T and B cells but also NK cells. RRG animals showed a more profound immunossuppressed phenotype because they displayed undetectable levels of T, B, and NK cells. Similarly, all immunoglobulin isotypes in sera were decreased in Rag1- or Il2rg-deficient rats and undetectable in Rats Rag1 and Il2rg (RRG) animals. Rag1- or Il2rg-deficient rats rejected allogeneic skin transplants and human tumors, whereas animals not only accepted allogeneic rat skin but also xenogeneic human tumors, skin, and hepatocytes. Immune humanization of RRG animals was unsuccessful. CONCLUSIONS: Thus, immunodeficient RRG animals are useful recipients for long-term studies in which immune responses could be an obstacle, including tissue humanization of different tissues.

Generation of gene-edited rats by delivery of CRISPR/Cas9 protein and donor DNA into intact zygotes using electroporation.

The generation of gene-edited animals using the CRISPRs/Cas9 system is based on microinjection into zygotes which is inefficient, time consuming and demands high technical skills. We report the optimization of an electroporation method for intact rat zygotes using sgRNAs and Cas9 protein in combination or not with ssODNs (~100 nt). This resulted in high frequency of knockouts, between 15 and 50% of analyzed animals. Importantly, using ssODNs as donor template resulted in precise knock-in mutations in 25-100% of analyzed animals, comparable to microinjection. Electroporation of long ssDNA or dsDNA donors successfully used in microinjection in the past did not allow generation of genome-edited animals despite dsDNA visualization within zygotes. Thus, simultaneous electroporation of a large number of intact rat zygotes is a rapid, simple, and efficient method for the generation of a variety of genome-edited rats.

Advances in transgenic animal models and techniques.

On May 11th and 12th 2017 was held in Nantes, France, the international meeting "Advances in transgenic animal models and techniques" ( http://www.trm.univ-nantes.fr/ ). This biennial meeting is the fifth one of its kind to be organized by the Transgenic Rats ImmunoPhenomic (TRIP) Nantes facility ( http://www.tgr.nantes.inserm.fr/ ). The meeting was supported by private companies (SONIDEL, Scionics computer innovation, New England Biolabs, MERCK, genOway, Journal Disease Models and Mechanisms) and by public institutions (International Society for Transgenic Technology, University of Nantes, INSERM UMR 1064, SFR François Bonamy, CNRS, Région Pays de la Loire, Biogenouest, TEFOR infrastructure, ITUN, IHU-CESTI and DHU-Oncogeffe and Labex IGO). Around 100 participants, from France but also from different European countries, Japan and USA, attended the meeting.

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.

A Rapid and Cost-Effective Method for Genotyping Genome-Edited Animals: A Heteroduplex Mobility Assay Using Microfluidic Capillary Electrophoresis.

The recent emergence and application of engineered endonucleases have led to the development of genome editing tools capable of rapidly implementing various targeted genome editions in a wide range of species. Moreover, these novel tools have become easier to use and have resulted in a great increase of applications. Whilst gene knockout (KO) or knockin (KI) animal models are relatively easy to achieve, there is a bottleneck in the detection and analysis of these mutations. Although several methods exist to detect these targeted mutations, we developed a heteroduplex mobility assay on an automated microfluidic capillary electrophoresis system named HMA-CE in order to accelerate the genotyping process. The HMA-CE method uses a simple PCR amplification of genomic DNA (gDNA) followed by an automated capillary electrophoresis step which reveals a heteroduplexes (HD) signature for each mutation. This allows efficient discrimination of wild-type and genome-edited animals down to the single base pair level.

Homology-directed repair in rodent zygotes using Cas9 and TALEN engineered proteins.

The generation of genetically-modified organisms has been revolutionized by the development of new genome editing technologies based on the use of gene-specific nucleases, such as meganucleases, ZFNs, TALENs and CRISPRs-Cas9 systems. The most rapid and cost-effective way to generate genetically-modified animals is by microinjection of the nucleic acids encoding gene-specific nucleases into zygotes. However, the efficiency of the procedure can still be improved. In this work we aim to increase the efficiency of CRISPRs-Cas9 and TALENs homology-directed repair by using TALENs and Cas9 proteins, instead of mRNA, microinjected into rat and mouse zygotes along with long or short donor DNAs. We observed that Cas9 protein was more efficient at homology-directed repair than mRNA, while TALEN protein was less efficient than mRNA at inducing homology-directed repair. Our results indicate that the use of Cas9 protein could represent a simple and practical methodological alternative to Cas9 mRNA in the generation of genetically-modified rats and mice as well as probably some other mammals.