Persistence of stable intragraft cell chimerism in rat liver allografts after drug-induced tolerance

Should microchimerism turn into rejection prophylactics?

Non-self cells can circulate in the body of an individual after any sort of contact with an allogeneic source of cells, thus creating a situation of chimerism that can be transient or prolonged over time. This situation may appear after stem cell transplantation, pregnancy, transfusion or transplantation. Concerning transplantation, many hypotheses have been formulated regarding the existence, persistence and role of these circulating cells in the host. We will review the principal hypotheses that have been formulated for years since the first description of non-self circulating cells in mammals to the utilization of artificially induced chimerism protocols for the achievement of tolerance.

Prolonged survival of rat hepatic allograft after pretransplant intraportal infusion of recipient blood to the donor

AIM: To investigate the effect of pretransplant intraportal administration of recipient blood into the donor on the survival of rat hepatic allograft.

METHODS: Male LEW (RT1) and ACI (RT1^a) rats were used as liver transplant recipients and donors, respectively. In experimental group, 7 d prior to transplantation, ACI donors were anesthetized with ether and transfused with freshly heparinized LEW recipient blood (1 mL) via the portal vein. In control group, the rats only received 1 mL normal saline 7 d before transplantation. The serum levels of interferon-γ (IFN-γ) were determined after transplantation. Immunocompetent cells from the donors were identified with anti-donor classⅡ MHC (RT1B^a) (OX-76) antibodies. The number of donor-derived CD4⁺ and CD8⁺ T cells in hepatic allograft or recipient spleen was examined. Reverse transcription-polymerase chain reaction was used to detect the mRNA expression of cytokines in the allograft.

RESULTS: LEW rats transplanted with hepatic allograft from ACI rats survived a mean of 11.1 ± 2.1 d. Intraportal preadministration of recipient LEW blood significantly increased the survival of LEW recipients with ACI livers to 31.7 ± 7.6 d (P < 0.05). The serum level of IFN-γ was significantly increased in the experimental group as compared with that in the control group. Cellular infiltration of the hepatic allograft in experimental group was significantly lower than that in the control group. The ratio of OX76⁺CD4⁺ or OX76⁺CD8⁺ T cells to CD4⁺ or CD8⁺ cells was significantly greater in hepatic allograft pretreated with LEW recipient blood than that in the controls (OX76⁺CD4⁺ cells: 25.6% vs 6.2%, P < 0.05; OX76⁺CD8⁺ cells: 26.6% vs 7.4%, P < 0.05), but not in recipient spleen. OX76⁺CD8⁺ T cells from hepatic allograft in the experimental group expressed IFN-γ and interleukin-10 mRNA, but not interleukin-2 mRNA.

CONCLUSION: Pretransplant intraportal infusion of recipient blood to the donor rats prolonged the survival of hepatic allograft, which may be associated with the regional graft-versus-host reaction.

The difficulty of eliminating donor leukocyte microchimerism in rat recipients bearing established organ allografts

BACKGROUND

Unequivocal eradication of donor leukocyte microchimerism from recipients of long-surviving organ transplants has never been reported. Here we describe a drastic attempt to accomplish this objective.

METHODS

In control experiments, a rank order of microchimerism and of associated donor specific nonreactivity was produced in Brown-Norway (BN) rats by transplantation of Lewis (LEW) liver, bone marrow cell (BMC) and heart allografts under a brief course of tacrolimus. The degree of microchimerism at 60 and 110 days was estimated with semiquanitative immunocytochemical and PCR techniques. Tolerance at 110 days was assessed in the different control groups by challenge transplantation of naïve LEW hearts. In parallel experimental groups, an attempt was made to eliminate microchimerism from the BN recipients. The animals were submitted at 60 days to 9.5-Gy total body irradiation (TBI), reconstituted immediately with naïve BN BMC, and tested for donor specific nonreactivity by LEW heart transplantation at 110 days.

RESULTS

After the TBI-reconstitution at 60 days, microchimerism was undetectable in BMC recipients at 110 days, significantly reduced in heart recipients, and least affected in liver recipients. Except in liver recipients, abrogation of LEW-specific nonreactivity was demonstrated by rejection of the priming grafts, or by rejection of the challenge heart grafts, and by in vitro immune assay.

CONCLUSIONS

It is difficult to eliminate microchimerism in organ recipients once the donor cells have settled into tissue niches.

Prolonged survival of mouse skin allografts after transplantation of fetal liver cells transduced with hIL-10 gene

INTRODUCTION

Interleukin-10 (IL-10) is a cytokine with a moleculary weight of 18 kDa, that was first identified as being produced by Th2 cells. It appears to have anti-inflammatory action by diminishing the production of pro-inflammatory cytokines produced by Th1 cells. IL-10 also regulates the differentiation and proliferation of several immune cells such as T cells, B cells, natural killer cells, antigen-presenting cells, mast cells and granulocytes. Recent data suggest, however, that IL-10 also has immunostimulatory properties with important consequences on the prognosis of disease. In this study, we demonstrate the importance of injection of hematopoietic fetal liver cells transduced with the human IL-10 (hIL-10) gene into an allogenic recipient subsequently transplanted with allogenic skin grafts. The immaturity of stem cells and precursor cells from fetal liver and their transient survival in the host, due to the production of hIL-10, may afford 'prope' tolerance. It also explains the lack of graft-vs.-host reaction (GvHR) and the delay in rejection of the specific donor skin grafts after virtual disappearance of donor hematopoietic cells.

OBJECTIVES

Transduction of CBA hematopoietic fetal cells with the human IL-10 gene was used with the aim of inducing tolerance to donor antigen in recipient BALB/c mice. The observed effects were prolonged IL-10 production, donor cell chimerism in the host and delayed rejection of skin grafts from the specific donor strain.

MATERIALS AND METHODS

To prevent or delay rejection of highly incompatible skin allografts, we used IL-10 gene transfer to establish chimerism with donor hematopoietic cells. Fetal liver cells from CBA mice were transduced with the human IL-10 gene and injected into BALB/c mice.

RESULTS

Human IL-10, which is active in mice but does not cross-react with murine IL-10 in ELISA, was produced in vivo for 3 weeks. Donor cells were identified in the recipients during the same time period, on the basis of presence of the H-2 k gene and human IL-10 intracellular protein. Skin allografts from CBA or C57BL/6 mice survived for a mean of 9.5 days in recipient mice injected with non-transduced cells. In contrast, survival of CBA allograft was extended to 18.9+/-1.8 days in recipients injected with hIL-10-transduced fetal liver cells from CBA mice. Human IL-10 alone, without donor hematopoietic cell engraftment, did not prolong graft survival (9.6+/-1.2 days).

CONCLUSIONS

IL-10 transduction of donor hematopoietic stem cells resulted in production of IL-10, cell engraftment and chimerism. Although full tolerance was not obtained at this level of donor cell development in the host, a specific and highly significant (P<0.001) prolongation of the survival of donor skin allografts was observed.

Extensive chimerism in liver transplants: vascular endothelium, bile duct epithelium, and hepatocytes

The transplanted liver has been shown to be particularly capable of inducing tolerance. An explanation may be the presence of chimerism. Cells of donor origin have been found in recipient tissues after transplantation of any solid organ. Evidence for the presence of cells of recipient origin within the transplanted liver is very limited. We investigated whether nonlymphoid cells of recipient origin can be found within human liver allografts. Five male patients who received a liver transplant from a female donor and 11 patients who received an HLA-I mismatched liver transplant were studied. We confirmed our observations with two different techniques in combination with double-staining techniques. To identify male cells in female liver transplants, we used in situ hybridization for sex chromosomes. To identify specific HLA class I antigens of recipient origin, we used immunohistochemistry with HLA class I-specific antibodies. Double staining was performed to discriminate different cell lineages and inflammatory cells. Endothelial cells of recipient origin were found in 14 of 16 donor livers. Bile duct epithelial cells of recipient origin were found in 5 of 16 cases. Hepatocytes of recipient origin were seen in only 1 of the 5 studied sex-mismatched donor livers. Our study provides evidence that cells of recipient origin can replace biliary epithelial cells, endothelial cells, and hepatocytes within the human liver allograft. This is consistent with the concept that circulating pluripotent progenitor cells exist, capable of differentiating into endothelial cells, epithelial cells, and hepatocytes.

A short course of cyclosporine immunosuppression inhibits rejection but not tolerance of rat liver allografts

BACKGROUND

Orthotopic liver transplants in many animal models are spontaneously accepted without requiring immunosuppression. Liver transplant acceptance is associated with early immune activation, and immunosuppressive drugs such as methylprednisolone inhibit acceptance. We investigated whether cyclosporine (CsA) inhibits rat liver transplant acceptance. We also examined the effects of CsA on infiltration and cytokine gene expression.

METHODS

Orthotopic liver transplantation was performed in the PVG donor to Dark Agouti recipient rat strain combination, which accepts the graft (tolerance; TOL), and in the PVG-to-Lewis combination, which rejects the graft in 9 to 16 days (rejection; REJ). CsA (1.5 mg/kg per day subcutaneously) was given to recipients for 5 days, starting from the day of transplantation to day 4 or from day 3 to day 7. In a separate experiment, transplanted livers were collected at days 1, 3, 5, and 7 after transplantation and examined for infiltration by immunohistochemistry and for expression of interleukin (IL)-2, IL-4, IL-10, and interferon-gamma mRNA by quantitative reverse transcriptase-polymerase chain reaction.

RESULTS

Both early and delayed treatment with CsA significantly increased survival in the REJ strain combination, with a median survival time of 81 days and more than 100 days, respectively, compared with 13 days in the untreated group. Neither treatment affected survival of TOL animals, and all TOL groups had a median survival time of more than 100 days. Delayed treatment did not reduce survival; more animals survived for greater than 100 days after delayed treatment, although this did not reach significance ( P=0.08). T-cell infiltrate was inhibited in CsA-treated TOL animals compared with untreated animals at all times after treatment, whereas CD25 cells were only inhibited on day 3. CsA treatment of TOL grafts markedly reduced expression of IL-2, IL-4, and interferon-gamma compared with untreated recipients.

CONCLUSIONS

CsA did not significantly inhibit liver transplant acceptance and allowed some activation of T cells and CD25 expression but almost completely inhibited IL-2 and IL-4, which are required for survival of activated T cells.