Porcine endogenous retrovirus encodes xenoantigens involved in porcine cellular xenograft rejection by mice

Instant Hepatic Differentiation of Human Embryonic Stem Cells Using Activin a and a Deleted Variant of HGF

Human embryonic stem (hES) cells have the ability to differentiate into a variety of different cell lineages and potentially provide a source of differentiated cells for many therapeutic uses. Here we investigated an efficient method of hepatic differentiation from hES cells. A human ES cell line, KhES-1, was used and maintained by a nonfeeder method. KhES-1 cells were cultured for 5 days in the presence of human activin A (50 ng/ml) and then treated with a deleted variant of hepatocyte growth factor (dHGF) at 0, 100, or 500 ng/ml for 7 days. The resultant cells were biologically analyzed. The expression of the endodermal genes SOX17 and FOXA2 increased in KhES-1 cells after activin A treatment. In contrast, Oct4, a self-renewal undifferentiated marker, decreased in a time-dependent manner in KhES-1 cells. Following a 7-day treatment of the resultant cells with dHGF, especially at 500 ng/ml, KhES-1 cells showed an expression of the hepatic makers albumin, AFP, and CK18. Transitional electron microscopy showed well-developed glycogen rosettes and a gap junction in KhES-1 cells treated with 500 ng/ml of dHGF. We developed an efficient method to differentiate KhES-1 cells into hepatocyte-like cells in vitro using 50 ng/ml of activin A and 500 ng/ml of dHGF.

Xenotransplantation, xenogeneic infections, biotechnology, and public health

Xenotransplantation is the attempt to use living biological material from nonhuman animal species in humans for therapeutic purposes. Clinical trials and preclinical studies have suggested that living cells and tissue from other species have the potential to be used in humans to ameliorate disease. However, the potential for successful xenotransplantation to cure human disease is coupled with the risk that therapeutic use of living nonhuman cells in humans may also serve to introduce xenogeneic infections of unpredictable significance. Animal husbandry practices and xenotransplantation product preparation may eliminate most exogenous infectious agents prior to transplantation. However, endogenous retroviruses are present in the genomes of all mammalian cells, have an inadequately defined ability to infect human cells, and have generated public health concern. The history of xenotransplantation, the implications for public health, the global consensus on public safeguards necessary to accompany clinical trials, and the future direction of xenotransplantation are discussed in the context of public health. Mt Sinai J Med 76:435-441, 2009. (c) 2009 Mount Sinai School of Medicine.

No in vivo infection of triple immunosuppressed non-human primates after inoculation with high titers of porcine endogenous retroviruses

Porcine endogenous retroviruses (PERVs) released from pig tissue can infect selected human cells in vitro and therefore represent a safety risk for xenotransplantation using pig cells, tissues, or organs. Although PERVs infect cells of numerous species in vitro, attempts to establish reliable animal models failed until now. Absence of PERV transmission has been shown in first experimental and clinical xenotransplantations; however, these trials suffered from the absence of long-term exposure (transplant survival) and profound immunosuppression.

METHODS

We conducted infectivity studies in rhesus monkeys, pig-tailed monkeys, and baboons under chronic immunosuppression with cyclosporine A, methylprednisolone, and the rapamycin derivative. These species were selected because they are close to the human species and PERVs can be transmitted in vitro to cells of these species. In addition, the animals received twice, a C1 esterase inhibitor to block complement activation before inoculation of PERV. In order to overcome the complications of microchimerism, animals were inoculated with high titers of cell-free PERV. In addition, to enable transmission via cell-cell contact, some animals also received virus-producing cells. For inoculation the primate cell-adapted strain PERV/5 degrees was used which is characterized by a high infectious titer. Produced on human cells, this virus does not express alpha 1,3 Gal epitopes, does not contain porcine antigens on the viral surface and is therefore less immunogenic in non-human primates compared with pig cell-derived virus. Finally, we present evidence that PERV/5 degrees productively infects cells from baboons and rhesus monkeys.

RESULTS

In a follow-up period of 11 months, no antibody production against PERV and no integration of proviral DNA in blood cells was observed. Furthermore, no PERV sequences were detected in the DNA of different organs taken after necropsy.

CONCLUSION

These results indicate that in a primate model, in the presence of chronic immunosuppression, neither the inoculation of cell-free nor cell-associated PERV using a virus already adapted to primate cells results in an infection; this is despite the fact that peripheral blood mononuclear cells of the same animals are infectible in vitro.

Transmissible infection of human 293T cells with porcine endogenous retroviruses subgroup a from NIH-miniature pig

In pig-to-human xenotransplantation, zoonotic infections have been an important barrier. The risk of zoonosis has been emphasized in xenotransplantation after finding that porcine endogenous retroviruses (PERVs) can infect human cells in vitro. Until now, transmissions of PERVs from PK15 cells have been studied in vitro and in vivo, but transmission of PERVs originating from miniature pigs have not been extensively reported. Peripheral blood mononuclear cells from miniature swine showed PERV transmission to human cells. In contrast, specific pathogen-free (SPF) pig islet cells showed no PERV transmission when co-incubated with 293T cells. To evaluate the risk of zoonosis with our experimental mini pigs, we tested the infectivity of PERVs from NIH-miniature pig primary ear cells for human 293T cells. As a result, all subgroups of infectious PERV virion (PERV-A, -B, and -C) were detected in the primary cell culture media. Unlike PERV-C, PERV-A and -B infected human 293T cells. Interestingly, only proviral PERV-A replicated in 293T cells to produce virions after infection. Our results suggested that a prevention study of PERV xenotransmission from experimental miniature pigs should concentrate on PERV-A control.

Requirement of MyD88 for macrophage-mediated islet xenograft rejection after adoptive transfer

BACKGROUND

Porcine antigen primed and CD4+ T-cell activated macrophages are able to migrate to and destroy porcine xenografts. However, the specific signaling mechanisms involved remain to be identified.

METHODS

In this study macrophages which lack the universal toll-like receptor (TLR) adaptor MyD88 were used to investigate the role of TLR in the recognition and activation of macrophages in islet xenograft rejection. Macrophages were isolated from rejecting MyD88(-/-) and wild-type C57BL/6 mice that were recipients of neonatal porcine pancreatic cell cluster (NPCC) xenografts, and were transferred to NPCC recipient NOD-SCID mice.

RESULTS

Both wild-type C57BL/6 and MyD88(-/-) mice rejected NPCC xenografts 8 and 10 days, respectively after transplantation, and the grafts were heavily infiltrated with CD4+ T cells and macrophages. However, graft infiltrating macrophages from rejecting MyD88(-/-) recipients demonstrated impaired up-regulation of TLR expression and impaired activation phenotype, when compared to those from rejecting C57BL/6 recipients. Transfer of NOD-SCID recipients with macrophages from rejecting C57BL/6 mice resulted in NPCC xenograft rejection along with massively infiltrated macrophages 8 days after transfer, whereas NPCC xenografts in NOD-SCID mice transferred with macrophages from rejecting MyD88(-/-) mice remained intact until the end of this study, 90 days after transfer, with insulin-positive islets and no infiltration by macrophages.

CONCLUSION

This study demonstrates that deletion of MyD88 causes impaired macrophage activation after pig islet xenotransplantation. However, graft survival is not prolonged and xenografts are rejected rapidly by alternate mechanisms.

Transient transmission of porcine endogenous retrovirus to fetal lambs after pig islet tissue xenotransplantation

Evidence for the in vivo transmission of porcine endogenous retrovirus (PERV) from porcine xenografts to various recipient animals has been inconsistent. To characterize the contribution of the host immune system to the potential for PERV transmission from pig islet tissue xenografts to host tissues, we examined two immunoincompetent animal models, thymectomizsed fetal lambs and NODscid mice. Pig proislets were grafted into fetal lambs or adult NODscid mice. Conventional, nested and real-time PCR/RT-PCR tests were used to search for PERV and pig cell-specific sequences (porcine mitochondrial cytochrome oxidase II (COII) or mitochondrial ribosomal 12S) in pig proislets, host liver and spleen at 5-84 days (lambs) or 96 days (mice) after transplantation. Xenografts were harvested at the same time points. The copy number of PERV sequences and host cell-specific nuclear (palmitoylcarnitine transferase) sequences was assessed by real-time PCR to estimate the proportion of PERV-infected host cells. Pig proislets were shown to be PERV+ve by PCR and immunohistochemistry (PERV B env protein p15E). PERV transmission (PERV A, B or C DNA in the absence of porcine COII or 12S sequences) was detected by nested PCR and real-time PCR in 4/12 fetal lamb liver samples 5-23 days after transplantation; the maximum copy number of PERV B env sequences was found at day 5 (700 copies/1 x 10(6) lamb cells). A total of 4/12 fetal lambs demonstrated both PERV and 12S porcine sequences in liver samples (days 5-84) by real-time PCR, suggesting that pig cells had migrated to those tissues and established microchimerism; nested PCR showed evidence for microchimerism (porcine COII sequences alone) in 2/12 lambs (day 5). The incidence of PERV transmission and frequency of microchimerism was similar in host spleen analysed by real-time PCR. Histological examination showed complete xenograft rejection by 23 days after transplantation to fetal lambs. In contrast, pig proislet xenografts survived long term (> or =day 96) in NODscid mice but no PERV transmission was found. Both nested and real-time PCR assays revealed that 2/3 mice had become microchimeric. Long-term expression of PERV A, B and C as well as porcine 12S or COII RNAs was found at the graft site (day 96) only, indicating that PERV transcription and possibly replication, continued in the donor pig islet tissue after transplantation. Overall, detection of PERV transmission and microchimerism was limited by the sensitivity of the PCR assay and the primers chosen. The absence of stable PERV transmission and microchimerism in fetal lambs and the rejection of pig proislet xenografts correlated in time with the establishment of host immunocompetence. We therefore suggest that the frequent failure to identify PERV transmission late after transplantation could be due to the immunological destruction of PERV-infected host cells. Recipient NODscid mice demonstrated long-term microchimerism and intragraft PERV expression, which was consistent with their stable immunoincompetence.