Nucleofection-mediated α1,3-galactosyltransferase gene inactivation and membrane cofactor protein expression for pig-to-primate xenotransplantation

Long-term efficacy of encapsulated xenogeneic islet transplantation: Impact of encapsulation techniques and donor genetic traits

AIMS/INTRODUCTION

To investigate the long-term efficacy of various encapsulated xenogeneic islet transplantation, and to explore the impact of different donor porcine genetic traits on islet transplantation outcomes.

MATERIALS AND METHODS

Donor porcine islets were obtained from wild-type, α1,3-galactosyltransferase knockout (GTKO) and GTKO with overexpression of membrane cofactor protein genotype. Naked, alginate, alginate-chitosan (AC), alginate-perfluorodecalin (A-PFD) and AC-perfluorodecalin (AC-PFD) encapsulated porcine islets were transplanted into diabetic mice.

RESULTS

In vitro assessments showed no differences in the viability and function of islets across encapsulation types and donor porcine islet genotypes. Xenogeneic encapsulated islet transplantation with AC-PFD capsules showed the most favorable long-term outcomes, maintaining normal blood glucose levels for 180 days. A-PFD capsules showed comparable results to AC-PFD capsules, followed by AC capsules and alginate capsules. Conversely, blood glucose levels in naked islet transplantation increased to >300 mg/dL within a week after transplantation. Naked islet transplantation outcomes showed no improvement based on donor islet genotype. However, alginate or AC capsules showed delayed increases in blood glucose levels for GTKO and GTKO with overexpression of membrane cofactor protein porcine islets compared with wild-type porcine islets.

CONCLUSION

The AC-PFD capsule, designed to ameliorate both hypoxia and inflammation, showed the highest long-term efficacy in xenogeneic islet transplantation. Genetic modifications of porcine islets with GTKO or GTKO with overexpression of membrane cofactor protein did not influence naked islet transplantation outcomes, but did delay graft failure when encapsulated.

Current Status of Genetically Engineered Pig to Monkey Kidney Xenotransplantation in Korea

BACKGROUND

In South Korea, pig-to-nonhuman primate trials of solid organs have only been performed recently, and the results are not sufficiently satisfactory to initiate clinical trials. Since November 2011, we have performed 30 kidney pig-to-nonhuman primate xenotransplantations at Konkuk University Hospital.

METHODS

Donor αGal-knockout-based transgenic pigs were obtained from 3 institutes. The knock-in genes were CD39, CD46, CD55, CD73, and thrombomodulin, and 2-4 transgenic modifications with GTKO were done. The recipient animal was the cynomolgus monkey. We used the immunosuppressants anti-CD154, rituximab, anti-thymocyte globulin, tacrolimus, mycophenolate mofetil, and steroids.

RESULTS

The mean survival duration of the recipients was 39 days. Except for a few cases for which survival durations were <2 days because of technical failure, 24 grafts survived for >7 days, with an average survival duration of 50 days. Long-term survival was observed 115 days after the removal of the contralateral kidney, which is currently the longest-recorded graft survival in Korea. We confirmed functioning grafts for the surviving transplanted kidneys after the second-look operation, and no signs of hyperacute rejection were observed.

CONCLUSIONS

Although our survival results are relatively poor, they are the best-recorded results in South Korea, and the ongoing results are improving. With the support of government funds and the volunteering activities of clinical experts, we aim to further improve our experiments and contribute to the commencement of clinical trials of kidney xenotransplantation in Korea.

Comparison of Graft Survival Between Full-Thickness and Lamellar Pig-to-Monkey Corneal Xenotransplantation from the Same Genetically Engineered Pig Model with Minimal Immunosuppression

BACKGROUND

The graft survival rate of full-thickness corneal xenotransplantation (XTP) with minimal immunosuppression in genetically engineered pigs is unknown, whereas lamellar corneal XTP shows satisfactory results. We compared graft survival between full-thickness and lamellar transplantations in the same genetically engineered pig.

METHODS

Six pig-to-monkey corneal transplantations were performed on 3 transgenic pigs. Two corneas harvested from 1 pig were transplanted into 2 monkeys using full-thickness and lamellar corneal xenotransplantation. The transgenic donor pigs used were α1,3-galactosyltransferase gene-knockout + membrane cofactor protein (GTKO+CD46) in one recipient and GTKO+CD46+ thrombomodulin (TBM) in the other.

RESULTS

The graft survival time for GTKO+CD46 XTP was 28 days. With the addition of TBM, the survival differences between lamellar and full-thickness XTP were 98 days versus 14 days and >463 days (ongoing) versus 21 days, respectively. An excessive number of inflammatory cells was observed in failed grafts, but none were in the recipient's stromal bed.

CONCLUSIONS

Unlike full-thickness corneal XTP, lamellar xenocorneal transplantation does not exhibit surgical complications, such as retrocorneal membrane or anterior synechia. The graft survival of lamellar XTP in this study was not as good as in our previous experiments, although the survival period was superior to that of full-thickness XTP. The difference in graft survival based on transgenic type is not definitive. Further studies using transgenic pigs and minimal immunosuppression need to focus on improving graft survival of lamellar XTP and using a larger sample size to determine the potential of full-thickness corneal XTP.

Nucleic acid direct delivery to fibroblasts: a review of nucleofection and applications

The fibroblast is one of the ideal target cell candidates for cell-based gene therapy approaches to promote tissue repair. Gene delivery to fibroblasts by viral transfection has been confirmed to have high transfection efficiency. However, in addition to immunogenic effects of viruses, the random integration of viral genes may damage the genome, affect the cell phenotype or even cause cancerous mutations in the transfected cells. Due to these potential biohazards and unknown long-term risks, the clinical use of viral transfection has been very limited. In contrast, initial non-viral transfection methods have been simple and safe to implement, with low immunogenicity, insertional mutagenesis, and risk of carcinogenesis, but their transfection efficiency has been relatively low. Nucleofection, a more recent non-viral transfection method, now combines the advantages of high transfection efficiency and direct nucleic acid delivery to the nucleus with a high safety.Here, we reviewed recent articles on fibroblast nucleofection, summarized different research points, improved methods and application scopes, and opened up ideas for promoting the further improvement and development of fibroblast nucleofection to meet the needs of a variety of disease research and clinical applications.

Codon optimized membrane cofactor protein expression in α 1, 3 galactosyltransferase knockout pig cells improve protection against cytotoxicity of monkey serum

In this study, we attempted to upgrade GT ^-MCP/-MCP pig genetically to express MCP at a higher level and additionally thrombomodulin (TBM), which have respective roles as a complement regulatory protein and a coagulation inhibitor. We constructed a dicistronic cassette consisting of codon-optimized MCP (mMCP) and TBM (m-pI2), designed for ubiquitous expression of MCP and endothelium specific expression of TBM. The cassette was confirmed to allow extremely increased MCP expression compared with non-modified MCP, and an endothelial-specific TBM expression. We thus transfected m-pI2 into ear-skin fibroblasts isolated from a GT ^-MCP/-MCP pig. By twice selection using magnetically activated cell sorting (MACS), and single-cell culture, we were able to obtain clones over 90% expressing MCP. The cells of a clone were provided as a donor for nuclear transfer resulting in the generation of a GT ^-MCP/-MCP /mMCP/TBM pig, which was confirmed to be carrying cells expressing MCP and functioning as an inhibitor against the cytotoxic effect of normal monkey serum, comparable with donor cells. Collectively, these results demonstrated an effective approach for upgrading transgenic pig, and we assumed that upgraded pig would increase graft survival.

Stable Regulation of Senescence-Related Genes in Galactose-alpha1,3-galactose Epitope Knockout and Human Membrane Cofactor Protein hCD46 Pig

BACKGROUND

Pigs are considered suitable animal donor models for xenotransplantation. For successful organ transplantation, immune rejection must be overcome. Xenotransplantation has recently been successfully performed using galactose-alpha1,3-galactose epitopes knockout (GalTKO) and a human membrane cofactor protein (hCD46) in a pig model. However, the growth and lifespan of the grafted organ have not been evaluated. Therefore, in the present study we evaluated aging and 84 senescence-related genes using the RT² Profiler PCR array and whole blood samples from GalTKO/hCD46 Massachusetts General Hospital (MGH) pigs.

METHODS

Experimental groups were double GalTKO/hCD46 (5-month-old), single GalTKO/hCD46 (2-year-old), and non-genetically modified (>3.5-year-old; control group within the same strain). Age-matched white hairless Yucatan (WHY) miniature pig groups were used as controls.

RESULTS

Among the 19 senescence-related genes selected from the 84 genes for further evaluation, 13 were upregulated in the double GalTKO/hCD46 MGH pigs compared to control MGH pigs; however, in WHY pigs, only 4 genes were up- or down-regulated among the 19 genes. Moreover, in double GalTKO/hCD46 MGH and WHY pigs, the expression of the 19 genes changed only 1- to 2-fold, suggesting that there were no significant differences in senescence signals between the 2 pig lines.

CONCLUSIONS

The present results indicate that the double GalTKO/hCD46 MGH pig might be a suitable model for human xenotransplantation studies. However, we used a limited number of experimental individuals, so further studies using larger experimental groups should be conducted to verify the present results.

Detection of Pig Cells Harboring Porcine Endogenous Retroviruses in Non-Human Primate Bladder After Renal Xenotransplantation

Pigs are used as potential donor animals for xenotransplantation. However, porcine endogenous retrovirus (PERV), shown to infect both human and non-human primate (NHP) cells in vitro, presents a risk of transmission to humans in xenotransplantation. In this study, we analyzed PERV transmission in various organs after pig-to-NHP xenotransplantation. We utilized pig-to-NHP xenotransplant tissue samples obtained using two types of transgenic pigs from the National Institute of Animal Science (NIAS, Republic of Korea), and examined them for the existence of PERV genes in different organs via PCR and RT-PCR with specific primers. To determine PERV insertion into chromosomes, inverse PCR using PERV long terminal repeat (LTR) region-specific primers was conducted. The PERV gene was not detected in NHP organs in cardiac xenotransplantation but detected in NHP bladders in renal xenotransplantation. The insertion experiment confirmed that PERVs originate from porcine donor cells rather than integrated provirus in the NHP chromosome. We also demonstrate the presence of pig cells in the NHP bladder after renal xenotransplantation using specific-porcine mitochondrial DNA gene PCR. The PERV sequence was detected in the bladder of NHPs after renal xenotransplantation by porcine cell-microchimerism but did not integrate into the NHP chromosome.

Improvement of cloning efficiency in minipigs using post-thawed donor cells treated with roscovitine

Massachusetts General Hospital miniature pigs (MGH minipigs) have been established for organ transplantation studies across the homozygous major histocompatibility complex, but cloning efficiency of MGH minipigs is extremely low. This study was designed to increase the productivity of MGH minipigs by nuclear transfer of post-thaw donor cells after 1 h co-incubation with roscovitine. The MGH minipig cells were genetically modified with GT KO (alpha1,3-galactosyltransferase knock-out) and hCD46 KI (human CD46 knock-in) and used as donor cells. The GT KO/hCD46 KI donor cells were cultured for either 3 days (control group) or 1 h after thawing with 15 μM roscovitine (experimental group) prior to the nuclear transfer. The relative percentage of the transgenic donor cells that entered into G0/G1 was 93.7 % (±2.54). This was different from the donor cells cultured for 1 h with the roscovitine-treated group (84.6 % ±4.6) (P < 0.05) and without roscovitine (78.6 % ±5.5) (P < 0.01), respectively. The pregnancy rate and delivery rate in the roscovitine group (8/12 and 6/8, respectively) were significantly higher (P < 0.01) than those in the control group (6/19 and 3/6, respectively). In the experimental group, 12 GT KO/hCD46 KI transgenic minipigs were successfully generated, and five minipigs among them survived for more than 6 months so far. The recipient-based individual cloning efficiency ranged from 0.74 to 2.54 %. In conclusion, gene-modified donor cells can be used for cloning of MGH minipigs if the cells are post-thawed and treated with roscovitine for 1 h prior to nuclear transfer.

Islet cell xenotransplantation: a serious look toward the clinic

Type I diabetes remains a significant clinical problem in need of a reliable, generally applicable solution. Both whole organ pancreas and islet allotransplantation have been shown to grant patients insulin independence, but organ availability has restricted these procedures to an exceptionally small subset of the diabetic population. Porcine islet xenotransplantation has been pursued as a potential means of overcoming the limits of allotransplantation, and several preclinical studies have achieved near-physiologic function and year-long survival in clinically relevant pig-to-primate model systems. These proof-of-concept studies have suggested that xenogeneic islets may be poised for use in clinical trials. In this review, we examine recent progress in islet xenotransplantation, with a critical eye toward the gaps between the current state of the art and the state required for appropriate clinical investigation.