Xenotransplantation

Defining aging in cyborgs: a bio-techno-social definition of aging

Initially the aim of this article was to discuss and define aging at the intersection point between biology and sociology. However, recent biomedical and technological advances are changing the discourse on aging, and against this background the author of this article argues that current definitions of aging should be improved. The author emphasizes that there is a need to update current definitions of aging, or to formulate new multidisciplinary ones. The author suggests that (besides biology, psychology and sociology) the technological discipline should be included in the integrative gerontology model. Finally, in this article a new definition of aging is put forward. According to the author of this article, human bio-techno-social aging is characterized by: (a) a time-bound process of change including, (b) both reversible and irreversible biological processes, (c) social processes forming an irreversible chain of events, and (d) an increasing use of technological artifacts whose purpose is to support or replace damaged biological functions; and/or an increasing use of technological artifacts whose purpose is to facilitate or enable interaction.

Restrictive model of compensated carbon tetrachloride-induced cirrhosis in rats

AIM: To develop a simplified and quick protocol to induce cirrhosis and standardize models of partial liver resection in rats.

METHODS: In Fischer F344 rats two modified protocols of phenobarbital-carbon tetrachloride (CCl₄) (dilution 50%) gavage to induce cirrhosis (frequency adjusted according to weight, but each subsequent dose was systematically administered) were tested, i.e. the rapid and slow protocols. Prothrombin time (PT) and total bilirubin (TB) were also evaluated. Animals from the rapid group underwent 15% hepatectomy and animals from the slow group underwent 70% hepatectomy.

RESULTS: Rapid protocol: This corresponded to 1 gavage/4 d over 6 wk (mortality 30%). Mean PT was 35.2 ± 2.8 s (normal: 14.5 s), and mean TB was 1.8 ± 0.2 mg/dL (normal: 0.1 mg/dL). Slow protocol: This corresponded to 1 gavage/6 d over 9 wk (mortality 10%). Mean PT was 11.8 ± 0.2 s (normal: 14.5 s), and mean TB was 0.4 ± 0.04 mg/dL (normal: 0.1 mg/dL). Pathological analyses were performed in both protocols which showed persistent cirrhosis at 3 mo. Rat mortality in the rapid gavage group who underwent 15% hepatectomy and in the slow gavage group who underwent 70% hepatectomy was 50% and 70%, respectively.

CONCLUSION: Our modified model is a simplified method to induce cirrhosis which is rapid (6 to 9 wk), efficient and stable up to 3 mo. Using this method, “Child Pugh A” or “Child Pugh BC” cirrhotic rats were obtained. Our models of cirrhosis and hepatectomy can be used in various situations focusing on postoperative survival.

Liver repopulation trial using bone marrow cells in a retrorsine-induced chronic hepatocellular injury model

OBJECTIVES

The aim of this study was to determine the potential of bone marrow derived cells to participate in liver repopulation. In this model, the injected cells had a "selective growth advantage" compared to the native hepatocytes whose proliferation was blocked by retrorsine.

METHODS

Total bone marrow cells were isolated from male Fisher 344 rats not deficient in dipeptidyl peptidase activity (F344, DPP IV+). The animals were given an injection of retrorsine and were divided in 2 groups: 1/group R (N=13): female F344 rats received 4.106 male cells at day 0 (labeled by chromosome Y). 2/group RH (N=19): Male F344 DPP IV- rats received 4.106 male DPP IV+ cells after hepatectomy at day 0 (labelled by DPP IV activity).

RESULTS

Group R: no male cell was detected by PCR at day 14, 28, 56 and 84. Group RH: isolated DPP IV+ transplanted cells were observed at days 14 and 28 in the periportal areas. Later, these cells were no longer visible. Liver regeneration occurred by proliferation of small clusters of hepatocytes.

CONCLUSIONS

In this experimental model the capacity of transplanted bone marrow cells to repopulate the liver was tested against the same capacity of native liver stem cells. Liver regeneration occurred via native liver cells seen as small hepatocytes. In this model the small hepatocytes may be considered as hepatic stem cells.

History of xenotransplantation

The present historical review reports the clinical experiences of transplantations from animal to human. The first transplantation attempts were made without any knowledge of the species barrier. The pioneers of xenotransplantation realized xenotransfusions as early as the 16th century, then cell and tissue xenotransplantations in the 19th century. At the beginning of the 20th century, xenotransplantation of testicles became the latest craze. At the same time, and later in the 1960s, organ xenotransplantations were attempted, with disappointing results. Mathieu Jaboulay, Serge Voronoff, Keith Reemtsma, James Hardy, Denton Cooley, Thomas Starzl, Christiaan Barnard and Leonard Bailey were among the pionneers of xenotransplantation. Recent trials concerned above all tissue and cell xenotransplantations. Nowadays, with encapsulation, transgenesis, and cloning, great advances have been made for controlling xenograft rejection, but ethical questions linked to the risk of infections have become a major pre-occupation within the scientific community and the general population.

Comparison of in vivo lymphocyte proliferation between allogeneic and xenogeneic heart transplantation in mice

There are controversial in vitro data comparing the strength of the cellular immune response between allogeneic and xenogeneic stimulator/responder combinations. The present study therefore compares in vivo lymphocyte proliferation using heart transplantation (HTx) models in mice. Heterotopic HTx into BALB/c mice was performed using donor organs from mice (BALB/c and C57BL/6) or Lewis rats. Intraperitoneally given bromodeoxyuridine (BrdU) was incorporated into the DNA and was subsequently analyzed by flow cytometry. On postoperative days 3 and 5, proliferation of splenocytes, CD4(+) T-lymphocytes, and CD19(+) B-lymphocytes was significantly higher after xenogeneic than after allogeneic and isogeneic HTx. No significant difference was observed when proliferation of CD8(+) lymphocytes was determined. The increased in vivo proliferation after xenotransplantation may reflect an earlier and probably stronger cellular immune response compared to allogeneic transplantation. The higher CD4(+) lymphocyte proliferation underscores the importance of this cell population in xenograft rejection.

Expression and characterization of a recombinant novel reverse transcriptase of a porcine endogenous retrovirus

The study of porcine endogenous retroviruses (PERVs) becomes increasingly important due to the potential use of pig cells, tissues, and organs as a source for xenogenic cell therapy and xenotransplantation into humans. Consequently, we have constructed a plasmid that induces in bacteria the synthesis of a soluble and highly active reverse transcriptase (RT) of PERV-B. The purified PERV RT was studied biochemically in comparison with the RT of murine leukemia virus (MLV), because of the high-sequence homology between these two RTs. The data show that in several properties the two enzymes are similar, particularly regarding the monomeric subunit composition of the proteins in solution, the high resistance to deoxynucleoside analogues, and the pattern of RNA cleavage by the ribonuclease H activity (RNase H) of the RTs. However, in several cases there are apparent differences between the two RTs, most notable the divalent cation preference (Mn(+2) versus Mg(+2)) in the DNA polymerase reactions. As already shown for viral PERV RT, the novel recombinant PERV RT exhibits a relatively high resistance to several deoxynucleoside analogue inhibitors, suggesting that they might not be very efficient in inhibiting the replication of PERV virions. Therefore, the availability of large amounts of the recombinant RT can be useful for a wide screening of novel drugs against infectious PERV.

[A new model of isolated perfused heart. Study of hypodermin A in hyperacute xenograft rejection]

AIMS OF THE STUDY

Isolated perfused heart (IPH) system and heart transplantation in the guinea-pig/rat combination represent a good model for the study of hyperacute xenograft rejection (HAR) in which the component plays a central role. Hypodermin A (HA), a protease cleaving the component, could be used to delay the HAR.

METHODS

Creation of an original IPH working with rat serum (30 mL) and ex vivo study of HAR and I'HA.

RESULTS

Study of HAR is possible with this IPH system. The mean guinea-pig heart survival after perfusion by normal rat serum was 38 +/- 7 min and was lower than survival observed after perfusion by guinea-pig serum (210 +/- 34 min) (p < 0.001), by decomplemented rat serum (177 +/- 45 min) (p < 0.001), and by rat serum with 20 micrograms/mL of HA (154 +/- 71 min) (p < 0.001).

CONCLUSION

We developed an original system of isolated perfused heart allowing ex vivo study of HAR. HA delayed the occurrence of the HAR and confirmed the central role of the component in the HAR.

Porcine endogenous retroviruses (PERVs): generation of specific antibodies, development of an immunoperoxidase assay (IPA) and inhibition by AZT

Xenotransplantation may be associated with the risk of transmission of microorganisms. In particular, the porcine endogenous retroviruses (PERV) have raised concerns as in vitro experiments show susceptibility of human cells for PERV infection. However, it remains unclear whether PERVs are able to infect transplant recipients in vivo and whether they are pathogenic. It is therefore essential that the risks are evaluated and for this purpose specific and sensitive screening methods for PERVs have to be developed. We generated specific antibodies against all major structural proteins of PERV and developed several assays which allow antibodies against PERV to be detected as indirect evidence of infection. For direct detection of PERV production, reverse transcriptase (RT) assays were used. PCR methods were used to detect provirus integration and the presence of viral mRNA. Here we present an immunoperoxidase assay (IPA), which would allow the detection of viral proteins in infected cells as well as antibodies against PERV in the serum of an infected host. The specificity of the sera used in the assay was determined by several methods, including immunoelectron microscopy, and the sensitivity of the assay was compared with other methods. This IPA was used to detect PERV infection in in vitro experiments for evaluation of the virus host range, for titrating the virus and for testing anti-viral properties of AZT. Using this method it was shown that AZT inhibits replication of PERV. This IPA may be very useful for the surveillance of preclinical and clinical xenotransplantations.

A case-control comparison of the results of renal transplantation from heart-beating and non-heart-beating donors

INTRODUCTION

The decline in heart-beating brainstem dead organ donors has necessitated the search for other organ sources. In the field of renal transplantation one alternative source currently available, but little used, is that of kidneys from non-heart-beating donors (NHBD). Reticence to use NHBD kidneys is in part due to concerns over the effect that warm ischemic may have subsequent graft function. Presented here are the results of the NHBD renal transplants at the Leicester transplant unit, and compared with matched heart-beating donor transplants as a case control analysis.

METHODS

In order to analyze any differences in graft performance between the two organ sources, the confounding effect of other variables known to influence the outcome of renal transplantation was minimized by matching NHBD and HBD transplants for the following criteria: donor age and sex, first or re-transplant, anastomosis and cold times, tissue match and PRA sensitisation. Transplant performance was assessed primarily by graft survival, the statistical evaluation of which was by log rank analysis of Kaplan-Meier curves.

RESULTS

72 NHBD and 192 HBD transplants were performed over an eight year period. Of the 192 HBD transplants, 105 matched one or more of the NHBD by the criteria outlined above, and thus constituted the control group for comparison. There was no significant difference in overall graft survival between the two groups. The 5 year survival for the NHBD was 73% compared with 65% for HBD kidneys. When death with a functioning graft is treated as censored data, then these figures become 75% and 81% respectively, again without statistical significance.

CONCLUSION

NHBD kidneys are a valuable additional source of organs for transplantation, with long-term survival, comparable to transplants from HBD.

Lewis rat pancreas, but not cardiac xenografts, are resistant to anti-gal antibody mediated hyperacute rejection

BACKGROUND

The objective of this study was to evaluate the role of anti-Gal Abs and non-anti-Gal Abs in hyperacute rejection (HAR) of concordant pancreas xenografts compared with heart xenografts. In addition, we tested whether rejection of Lewis rat pancreas grafts was T-cell dependent and could be prevented by anti-T-cell treatment.

METHODS

To determine the role of anti-Gal Abs in the induction of HAR, Lewis rat pancreas and heart xenografts were transplanted into alpha1,3Galactosyltransferase knockout (GT-Ko) mice treated with normal human serum (NHS) or hyperimmune serum, or into presensitized GT-Ko mice. To investigate whether rejection of pancreas xenograft was mediated by a T-cell dependent response, Lewis rat pancreas grafts were transplanted into streptozotocin (STZ)-induced diabetic GT-Ko mice treated with FK506, anti-CD4 mAbs (GK1.5), and thymectomy. Antidonor-specific IgM and IgG and anti-Gal Abs were analyzed by flow cytometry. Rejected and long-term surviving pancreas xenografts were assessed by functional (blood glucose) and histopathological examination.

RESULTS

HAR of Lewis rat pancreas xenografts could not be induced by NHS (0.4 ml), whereas NHS (0.2 ml) resulted in HAR of Lewis heart xenografts. Infusion of Lewis rat-specific hyperimmune serum (0.2 ml) resulted in HAR of Lewis rat pancreas xenografts. In addition, second Lewis rat pancreas grafts were hyperacutely rejected by presensitized GT-Ko mice. Immunohistochemical staining showed a low expression of Galalpha1,3Gal antigen in the endocrine tissue compared with that in the cardiac grafts. The levels of anti-Gal Abs in pancreas xenograft transplantation did not increase in GT-Ko mice after pancreas xenograft transplantation that was significantly increased after heart transplantation. FK506 treatment induced long-term survival of Lewis pancreas xenografts (mean survival time (MST) >90 days). Anti-CD4 treatment delayed rejection of Lewis rat pancreas xenografts with MST of 34.3 days, whereas anti-CD4, in combination with thymectomy, synergistically prolonged survival of pancreas xenograft (MST=70.4 days).

CONCLUSION

Pancreas xenograft is resistant to anti-Gal Abs-induced HAR but is susceptible to anti-donor specific Abs. Rejection of Lewis pancreas xenograft in STZ-induced, diabetic, GT-Ko mice is T-cell dependent.

Attitudes and behavior of young European adults towards the donation of organs--a call for better information

Public perception of organ donation critically affects the availability of organ transplantation in the Western world. To assess the attitude of young adults towards the donation of organs and to investigate potential factors influencing their knowledge and actual behavior regarding organ transplantation, we evaluated a handout questionnaire survey of all Swiss-Italian recruits during six of the years 1989-98 (n = 7272). The attitude of recruits towards organ donation did not change significantly within the 10-year survey period: 61% of young men would personally donate their organs in the case of brain death, 13% would refuse, and 26% had not made up their mind. If they had to decide for close relatives, 50% would consent; 60% of recruits neither knew their next of kin's attitude nor had informed them about their own opinion; 80% felt they were insufficiently informed about organ transplantation. A significantly more positive attitude towards organ donation was found among men who felt they were sufficiently informed, who had close next of kin who were aware of their personal attitude (p < 0.0001), who had contacts with transplanted persons (p < 0.015), or who believed in an existence after death (p < 0.001; chi2-test). Our results suggest that there is potentially large support towards organ donation in this population. To minimize the high rate of indecisiveness, young adults need more appropriate information on the subject and they ask for it.

Human islet cell transplantation--future prospects

BACKGROUND

Islet transplantation has the potential to cure diabetes mellitus. Nevertheless despite successful reversal of diabetes in many small animal models, the clinical situation has been far more challenging. The aim of this review is to discuss why insulin-independence after islet allotransplantation has been so difficult to achieve.

METHODS

A literature review was undertaken using Medline from 1975 to July 2000. Results reported to the International Islet Transplant Registry (ITR) up to December 1998 were also analysed.

RESULTS

Up to December 1998, 405 islet allotransplants have been reported the ITR. Of those accurately documented between 1990 and 1998 (n = 267) only 12% have achieved insulin-independence (greater than 7 days). However with refined peri-transplant protocols insulin independence at 1 year can reach 20%.

CONCLUSIONS

There are many factors which can explain the failure of achieving insulin-independence after islet allotransplantation. These include the use of diabetogenic immunosuppressive agents to abrogate both islet allo-immunity and auto-immunity, the critical islet mass to achieve insulin-independence and the detrimental effects of transplanting islets in an ectopic site. However recent evidence most notably from the Edmonton group demonstrates that islet allotransplantation still has great potential to become an established treatment option for diabetic patients.