Analysis of transgene integration sites in transgenic pigs by fluorescence in situ hybridization

Serial cloning of pigs by somatic cell nuclear transfer: restoration of phenotypic normality during serial cloning

Somatic cell nuclear transfer (scNT) is a useful way to create cloned animals. However, scNT clones exhibit high levels of phenotypic instability. This instability may be due to epigenetic reprogramming and/or genomic damage in the donor cells. To test this, we produced transgenic pig fibroblasts harboring the truncated human thrombopoietin (hTPO) gene and used them as donor cells in scNT to produce first-generation (G1) cloned piglets. In this study, 2,818 scNT embryos were transferred to 11 recipients and five G1 piglets were obtained. Among them, a clone had a dimorphic facial appearance with severe hypertelorism and a broad prominent nasal bridge. The other clones looked normal. Second-generation (G2) scNT piglets were then produced using ear cells from a G1 piglet that had an abnormal nose phenotype. We reasoned that, if the phenotypic abnormality of the G1 clone was not present in the G2 and third-generation (G3) clones, or was absent in the G2 clones but reappeared in the G3 clones, the phenotypic instability of the G1 clone could be attributed to faulty epigenetic reprogramming rather than to inherent/accidental genomic damage to the donor cells. Blastocyst rates, cell numbers in blastocyst, pregnancy rates, term placenta weight and ponderal index, and birth weight between G1 and G2 clones did not differ, but were significantly (P < 0.05) lower than control age- and sex-matched piglets. Next, we analyzed global methylation changes during development of the preimplantation embryos reconstructed by donor cells used for the production of G1 and G2 clones and could not find any significant differences in the methylation patterns between G1 and G2 clones. Indeed, we failed to detect the phenotypic abnormality in the G2 and G3 clones. Thus, the phenotypic abnormality of the G1 clone is likely to be due to epigenetic dysregulation. Additional observations then suggested that expression of the hTPO gene in the transgenic clones did not appear to be the cause of the phenotypic abnormality in the G1 clones and that the abnormality was acquired by only a few of the G1 clone's cells during its gestational development.

Rapid detection of human HLA transgenes in pigs by fluorescence in situ hybridization (FISH) for adjuvant study of human xenotransplantation

OBJECTIVES

We have recently generated several lines of transgenic pigs for HLA-DP and -DQ to elucidate the role of HLA-II antigens in the modulation of cell-mediated rejection of xenotransplantation. Using fluorescence in situ hybridization (FISH) analysis, the aim of this study was to determine integration sites and to test zygosity of these transgenes in the piglets after cross mating.

METHODS

Blood lymphocytes of transgenic pigs for HLA-DP and -DQ were collected and cultured. Chromosome spreads were prepared by standard methodology. Gene constructs of HLA-DP A1+B1, -DQ A1 & B1 were labeled with fluorescein isothiocyanate or Texas Red by nick-translation. Hybridization was based on a standard FISH protocol.

RESULTS

FISH analysis revealed that the HLA-DP probe hybridized to porcine chromosome 6, while both HLA-DQ A1 and B1 probes hybridized to porcine chromosome 11 at the same site. There was no cross-hybridization of HLA transgenes to the swine leukocyte antigen complex. Mosaic integration of HLA-DQ transgenes in the genome of F0, but full penetrance in F1 after selective breeding was observed. Both HLA-DP and HLA-DQ lines were determined to be heterozygous at the integration site.

CONCLUSION

By FISH, we have detected specific integration sites of the HLA-DP and -DQ transgenes in pig genome and determined mosaic levels and zygosity types of these transgenes. We conclude that FISH is both sensitive and labor-efficient in confirming and differentiating transgenic pigs for multiple rejection-regulatory genes by visualizing individual integration sites in chromosomes or interphase nuclei.

Expression of complement regulatory proteins on islets of Langerhans: a comparison between human islets and islets isolated from normal and hDAF transgenic pigs

BACKGROUND

The expression of regulators of complement activity (RCAs) on islet cells may be of great importance for protecting them against complement-mediated lysis in the immediate posttransplant period after intraportal islet transplantation. We examined porcine and human islet cells for expression of RCA. We also examined to what extent human decay accelerating factor (hDAF) is expressed on adult and fetal islet cells isolated from hDAF transgenic (TG) pigs having a high transgene expression on endothelial cells. Moreover, the susceptibility of the various types of cells to lysis in human serum and blood was investigated.

METHODS

Adult human islets (n=5), normal adult and fetal porcine islets (n=9 and n=8, respectively), and islets from adult and fetal hDAF TG pigs (n=5 and n=6, respectively) were examined. With islet single-cell suspensions and flow cytometry, adult human islet cells were examined for expression of hDAF (CD55), hCD59, and human membrane cofactor protein (hMCP; CD46), while porcine islet cells were examined for expression of pCD59 and pMCP. Islet cells from hDAF TG pigs were also examined for hDAF expression. Porcine peripheral blood lymphocytes, normal and hDAF TG porcine endothelial cell lines, a human endothelial cell line, and the human cell line U937 served as controls. Islet cytotoxicity was assayed after incubation of the islet cells with fresh human serum. Furthermore, adult islets from normal control pigs and hDAF TG pigs were exposed to fresh human blood in vitro for 60 min, and the inflammatory reaction elicited was compared between the different types of islets.

RESULTS

All human islet cell preparations expressed hCD59, two of five expressed hMCP, but none expressed hDAF. Porcine islet cells expressed both pCD59 and pMCP. Normal adult porcine islet cells exposed to fresh human serum resulted in 74+/-5.4% cell lysis (mean+/-SEM, n=16). In comparison, only 1.3+/-2.8% (n=20, P<0.001) of human islet cells were lysed in the human serum. One islet cell preparation from an hDAF TG pig expressed small amounts of hDAF. This preparation from hDAF TG pigs bound significantly less C3c than did normal control islets (mean fluorescence ratio 16+/-2.2 and 58+/-4.3, respectively; P=0.046) and were partially protected from cell lysis in fresh human serum (47+/-10% and 78+/-18% cell lysis, respectively; P=0.046). The other four preparations from hDAF TG pigs were negative for hDAF and were equally susceptible to lysis as normal control islets. All fetal pancreatic islet cells from hDAF TG pigs analyzed were negative for hDAF expression. When exposed to fresh human blood in vitro, adult and fetal islets from hDAF TG pigs elicited equally strong inflammatory changes as did the normal control islets. The inflammatory changes were characterized by activation of the complement and coagulation systems, resulting in islet damage with "dumping" of insulin into the blood.

CONCLUSIONS

Porcine and human islet cells express species-restricted complement regulatory proteins, with the human islet cells expressing mainly hCD59. A low expression of hDAF was detected on islet cells from one of five hDAF TG pigs. These islet cells displayed reduced islet cell cytotoxicity in fresh human serum. We conclude that protection from complement-mediated lysis will be important in the context of intraportal pig-to-human islet transplantation, and expression of a human RCA on islet cells should be beneficial in this context.

Life-supporting pig-to-primate renal xenotransplantation using genetically modified donors

BACKGROUND

In order to circumvent the complement-mediated hyperacute rejection of discordant xenografts, a colony of pigs transgenic for the human regulator of complement activity, human decay-accelerating factor (hDAF), has been produced.

METHODS

Seven kidneys from hDAF transgenic pigs and six kidneys from nontransgenic control pigs were transplanted into cynomolgus monkeys; both native kidneys were removed during the same operation. The recipient animals were immunosuppressed with cyclosporine, steroids, and cyclophosphamide.

RESULTS

In the transgenic group, the median survival time was 13 days (range, 6-35 days); the median survival time in the control group was 6.5 days (range, 0.3-30 days). There were no cases of hyperacute rejection in the transgenic group, and the two longest-surviving kidneys in this group showed no evidence of rejection on histological examination. In contrast, all control kidneys underwent antibody-mediated rejection, one demonstrating hyperacute rejection and the others acute vascular rejection.

CONCLUSION

This study demonstrates that (i) a kidney from an hDAF transgenic pig can support the life of a primate for up to 35 days (and also shows the basic physiological compatibility between the pig and nonhuman primate); (ii) nontransgenic kidneys are not routinely hyperacutely rejected; and (iii) the presence of hDAF on the kidney confers some protection against acute vascular rejection. Improved immunosuppression and immunological monitoring may enable extended survival.