Generation by somatic cell nuclear transfer of GGTA1 knockout pigs expressing soluble human TNFRI-Fc and human HO-1

A brief review of the current status of pig islet xenotransplantation

An estimated 1.5 million Americans suffer from Type I diabetes mellitus, and its incidence is increasing worldwide. Islet allotransplantation offers a treatment, but the availability of deceased human donor pancreases is limited. The transplantation of islets from gene-edited pigs, if successful, would resolve this problem. Pigs are now available in which the expression of the three known xenoantigens against which humans have natural (preformed) antibodies has been deleted, and in which several human 'protective' genes have been introduced. The transplantation of neonatal pig islets has some advantages over that of adult pig islets. Transplantation into the portal vein of the recipient results in loss of many islets from the instant blood-mediated inflammatory reaction (IBMIR) and so the search for an alternative site continues. The adaptive immune response can be largely suppressed by an immunosuppressive regimen based on blockade of the CD40/CD154 T cell co-stimulation pathway, whereas conventional therapy (e.g., based on tacrolimus) is less successful. We suggest that, despite the need for effective immunosuppressive therapy, the transplantation of 'free' islets will prove more successful than that of encapsulated islets. There are data to suggest that, in the absence of rejection, the function of pig islets, though less efficient than human islets, will be sufficient to maintain normoglycemia in diabetic recipients. Pig islets transplanted into immunosuppressed nonhuman primates have maintained normoglycemia for periods extending more than two years, illustrating the potential of this novel form of therapy.

Effects of klotho protein or klotho knockdown in porcine oocytes at different stages

Klotho is a protein that plays different functions in female fertility. We have previously reported that klotho protein supplementation during in vitro maturation improves porcine embryo development, while klotho knockout for somatic cell cloning completely blocks full-term pregnancy in vivo. However, the effects of the microinjection of klotho protein or klotho knockdown dual vector in porcine embryos at different time points and the specific molecular mechanisms remain largely unknown. In this study, we injected the preassembled cas9 + sgRNA dual vector, for klotho knockdown, into the cytoplasm of the germinal vesicle stage of oocytes and into porcine embryos after 6-h parthenogenetic activation. Similarly, the klotho protein was inserted into the cytoplasm of germinal vesicle stage oocytes and porcine embryos after 6-h parthenogenetic activation. Compared with the controls, the microinjection of klotho dual vector markedly decreased the blastocyst formation rates in germinal vesicle stage oocytes and activated embryos. However, the efficiency of blastocyst formation when klotho protein was inserted before in vitro maturation was significantly higher than that after klotho protein insertion into parthenogenetically activated embryos. These results indicated that klotho knockdown may impair embryo development into blastocyst irrespective of injection timing. In addition, klotho protein injection timing in pig embryos may be an important factor for regulating embryo development.

Current Topics of Relevance to the Xenotransplantation of Free Pig Islets

Pig islet xenotransplantation is a potential treatment for patients with type 1 diabetes. Current efforts are focused on identifying the optimal pig islet source and overcoming the immunological barrier. The optimal age of the pig donors remains controversial since both adult and neonatal pig islets have advantages. Isolation of adult islets using GMP grade collagenase has significantly improved the quantity and quality of adult islets, but neonatal islets can be isolated at a much lower cost. Certain culture media and coculture with mesenchymal stromal cells facilitate neonatal islet maturation and function. Genetic modification in pigs affords a promising strategy to prevent rejection. Deletion of expression of the three known carbohydrate xenoantigens (Gal, Neu5Gc, Sda) will certainly be beneficial in pig organ transplantation in humans, but this is not yet proven in islet transplantation, though the challenge of the '4th xenoantigen' may prove problematic in nonhuman primate models. Blockade of the CD40/CD154 costimulation pathway leads to long-term islet graft survival (of up to 965 days). Anti-CD40mAbs have already been applied in phase II clinical trials of islet allotransplantation. Fc region-modified anti-CD154mAbs successfully prevent the thrombotic complications reported previously. In this review, we discuss (I) the optimal age of the islet-source pig, (ii) progress in genetic modification of pigs, (iii) the immunosuppressive regimen for pig islet xenotransplantation, and (iv) the reduction in the instant blood-mediated inflammatory reaction.

Humanized skeletal muscle in MYF5/MYOD/MYF6-null pig embryos

Because post-mortem human skeletal muscle is not viable, autologous muscle grafts are typically required in tissue reconstruction after muscle loss due to disease or injury. However, the use of autologous tissue often leads to donor-site morbidity. Here, we show that intraspecies and interspecies chimaeric pig embryos lacking native skeletal muscle can be produced by deleting the MYF5, MYOD and MYF6 genes in the embryos via CRISPR, followed by somatic-cell nuclear transfer and the delivery of exogenous cells (porcine blastomeres or human induced pluripotent stem cells) via blastocyst complementation. The generated intraspecies chimaeras were viable and displayed normal histology, morphology and function. Human:pig chimaeras generated with TP53-null human induced pluripotent stem cells led to higher chimaerism efficiency, with embryos collected at embryonic days 20 and 27 containing humanized muscle, as confirmed by immunohistochemical and molecular analyses. Human:pig chimaeras may facilitate the production of exogenic organs for research and xenotransplantation.

Failure to maintain full-term pregnancies in pig carrying klotho monoallelic knockout fetuses

Background

Small animals that show a deficiency in klotho exhibit extremely shortened life span with multiple aging-like phenotypes. However, limited information is available on the function of klotho in large animals such as pigs.

Results

In an attempt to produce klotho knockout pigs, an sgRNA specific for klotho (targeting exon 3) was designed and Cas9-sgRNA ribonucleoproteins were transfected into porcine fibroblasts. Transfected fibroblasts were cultured for one to 2 days and then directly used for nuclear transfer without selection. The cloned embryos were cultured in vitro for 7 days and analyzed to detect modifications of the klotho gene by both T7E1 and deep sequencing analysis. Modification succeeded in 13 of 20 blastocysts (65%), 8 of which (40.0%) were monoallelic modifications and 5 (25.0%) were biallelic modifications. Based on high mutation rates in blastocysts, we transferred the cloned embryos to 5 recipient pigs; 1 recipient was pregnant and 16 fetuses were recovered at Day 28 post transfer. Of the 16 fetuses, 9 were resorbing and 7 were viable. Four of 9 (44.4%) resorbing fetuses and 3 of the 7 (42.9%) viable fetuses had monoallelic modifications. Thus, 3 klotho monoallelic knockout cell lines were established by primary culture. A total of 2088 cloned embryos reconstructed with 2 frame-shifted cell lines were transferred to 11 synchronized recipients. Of the recipients, 7 of 11 eleven (63.6%) became pregnant. However, none of the pregnancies was maintained to term. To discover why klotho monoallelic knockout fetuses were aborted, expression of aging- and apoptosis-related genes and klotho protein in placentas from klotho monoallelic knockout and wild-type fetuses was investigated. Placentas from klotho monoallelic knockout fetuses showed negatively changed expression of aging- and apoptosis-related genes with lower relative expression of klotho protein. These results indicated that the reason why klotho monoallelic knockout fetuses were not maintained to term was possibly due to decreased klotho expression in placentas, negatively affecting aging- and apoptosis-related genes.

Conclusions

Klotho monoallelic knockout porcine fetal fibroblasts were successfully established. However, pigs carrying klotho monoallelic knockout fetuses failed to maintain full-term pregnancy and a decrease in klotho expression in placenta likely leads to pregnancy loss.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-020-00660-9.

Efficient generation of GGTA1-deficient pigs by electroporation of the CRISPR/Cas9 system into in vitro-fertilized zygotes

BACKGROUND

Xenoantigens are a major source of concern with regard to the success of interspecific xenografts. GGTA1 encodes α1,3-galactosyltransferase, which is essential for the biosynthesis of galactosyl-alpha 1,3-galactose, the major xenoantigen causing hyperacute rejection. GGTA1-modified pigs, therefore, are promising donors for pig-to-human xenotransplantation. In this study, we developed a method for the introduction of the CRISPR/Cas9 system into in vitro-fertilized porcine zygotes via electroporation to generate GGTA1-modified pigs.

RESULTS

We designed five guide RNAs (gRNAs) targeting distinct sites in GGTA1. After the introduction of the Cas9 protein with each gRNA via electroporation, the gene editing efficiency in blastocysts developed from zygotes was evaluated. The gRNA with the highest gene editing efficiency was used to generate GGTA1-edited pigs. Six piglets were delivered from two recipient gilts after the transfer of electroporated zygotes with the Cas9/gRNA complex. Deep sequencing analysis revealed that five out of six piglets carried a biallelic mutation in the targeted region of GGTA1, with no off-target events. Furthermore, staining with isolectin B4 confirmed deficient GGTA1 function in GGTA1 biallelic mutant piglets.

CONCLUSIONS

We established GGTA1-modified pigs with high efficiency by introducing a CRISPR/Cas9 system into zygotes via electroporation. Multiple gene modifications, including knock-ins of human genes, in porcine zygotes via electroporation may further improve the application of the technique in pig-to-human xenotransplantation.

Xeno-organ donor pigs with multiple genetic modifications - the more the better?

The number of donated human organs and tissues for patients with terminal organ failure falls far short of the need. Alternative sources, such as organs and tissues from animals, are therefore urgently required. During the past few years, major progress has been made in the development of genetically multi-modified donor pigs, and their organs have been shown to be safe and efficacious in life-supporting transplantation models into non-human primates, paving the way to clinical xenotransplantation studies. Here, we summarize recent developments in pig genome engineering and discuss efforts to develop the optimum donor pig for xenotransplantation. In addition, we speculate on how many genetic modifications may be required for initial xenotransplantation clinical trials.

CRISPR/Cas9-Mediated Biallelic Knockout of IRX3 Reduces the Production and Survival of Somatic Cell-Cloned Bama Minipigs

Bama minipigs are a local pig breed that is unique to China and has a high development and utilization value. However, its high fat content, low feed utilization rate, and slow growth rate have limited its popularity and utilization. Compared with the long breeding cycle and high cost of traditional genetic breeding of pigs, clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) endonuclease 9 system (CRISPR/Cas9)-mediated gene editing can cost-effectively implement targeted mutations in animal genomes, thereby providing a powerful tool for rapid improvement of the economic traits of Bama minipigs. The iroquois homeobox 3 (IRX3) gene has been implicated in human obesity. Mouse experiments have shown that knocking out IRX3 significantly enhances basal metabolism, reduces fat content, and controls body mass and composition. This study aimed to knock out IRX3 using the CRISPR/Cas9 gene editing method to breed Bama minipigs with significantly reduced fat content. First, the CRISPR/Cas9 gene editing method was used to efficiently obtain IRX3-/- cells. Then, the gene-edited cells were used as donor cells to produce surviving IRX3-/- Bama minipigs using somatic cell cloning. The results show that the use of IRX3-/- cells as donor cells for the production of somatic cell-cloned pigs results in a significant decrease in the average live litter size and a significant increase in the average number of stillbirths. Moreover, the birth weight of surviving IRX3-/- somatic cell-cloned pigs is significantly lower, and viability is poor such that all piglets die shortly after birth. Therefore, the preliminary results of this study suggest that IRX3 may have important biological functions in pigs, and IRX3 should not be used as a gene editing target to reduce fat content in Bama minipigs. Moreover, this study shows that knocking out IRX3 does not favor the survival of pigs, and whether targeted regulation of IRX3 in the treatment of human obesity will also induce severe adverse consequences requires further investigation.

Adipose-Tissue-Specific Expression of Pig ApoR Protects Mice from Diet-Induced Obesity

Fat deposition is one of the most important economic traits of pigs. Decreasing the subcutaneous fat and increasing the intramuscular fat are believed to be an effective way to improve pork quality, which is one of the main goals of pig breeding. Identifying key genes that control porcine lipid metabolism is essential for achieving this goal. Apolipoprotein R (apoR) was identified as the crucial molecule in the process of pig adipose reduction by clenbuterol. In this study, transgenic mice with adipose-tissue-specific overexpression of pig apoR (apoR mice) were constructed. The apoR mice gained less weight than wild-type (WT) mice after 18 weeks of feeding a high-fat diet. A comparison of organs between the two genotypes revealed that the weight of white adipose tissue, including inguinal and epididymal fat tissue, was significantly decreased and the weight of liver tissue was increased in apoR mice compared with WT mice. Glucose and insulin intolerance tests showed that the glucose metabolism of apoR mice was similar to that of WT mice. Histological staining proved that the adipocytes of apoR mice had a reduced average size, and gene expression analysis indicated that lipolysis in the adipose tissue of apoR mice was enhanced. Finally, the primary culture of inguinal adipocytes revealed that apoR promotes lipolysis via the Erk1/2 pathway. Taken together, the results indicate that adipose-tissue-specific expression of pig apoR protects mice from diet-induced obesity by enhancing lipolysis.