Role of micro-chimerism in inducing immunological tolerance by intraportal injection of donor spleen cells in rats

Role of the liver in determining alloimmune response in vitro following donor-specific spleen cell injection

The aim of our study was to investigate the allogeneic influence inside and outside the liver in vitro following donor-specific cell injection (DSI). DA rats (RT1a) were used as donors and WS rats (RT1k) as recipients. WS were sensitized with DA spleen cells, followed 24h later by total hepatectomy. The liver was transplanted into another WS (sensitized liver-grafted; SL-Grafted). The hepatectomized WS underwent liver transplantation from a naive WS (sensitized liver-removed; SL-Removed). Alloantigens accumulated in the liver in SL-Grafted and in the extrahepatic tissue/organ(s) in SL-Removed. DA hearts were transplanted 10days after antigen administration. To analyze the immune responses, we measured Th1/Th2 cytokine profiles, and perforin mRNA in various organs, allogeneic mixed lymphocyte reaction (MLR), and donor-specific immunoglobulin. Th1 cytokine levels in the liver of SL-Grafted and in spleen of SL-Removed were highly and rapidly upregulated but decreased thereafter. IFN-gamma and perforin mRNAs were significantly higher in SL-Grafted and lower in SL-Removed. MLR was significantly higher in SL-Grafted than SL-Removed and controls. There was no significant difference in the donor-specific immunoglobulin level. Our findings suggest that liver and other organs may behave differently to alloantigen, suggesting the importance of an early Th1 reaction in the liver and spleen.

Induction of long-term graft acceptance by a combination treatment of donor splenocytes and CTLA4Ig in a high responder rat liver transplantation model

The CTLA4Ig has led to an improved survival rate in various allograft transplantation models. We investigated in a high responder rat model (Dark Agouti to Lewis) of orthotopic liver transplantation (ORLT), whether an additional adoptive cell transfer can enhance the effect of CTLA4Ig. After transplantation, recipients (n = 13/group) were treated with donor or third-party splenocytes alone or in combination with CTLA4Ig. Administration of splenocytes alone had no significant effect on survival (median 13 days, range 9-14) compared with untreated controls (median 10 days, range 8-12). CTLA4Ig monotherapy prolonged survival to a median of 30 days (range 11-150) but resulted in long-term graft rejection. The additional administration of third-party splenocytes showed no significant improvement over CTLA4Ig monotherapy. Only the combination of donor splenocytes with CTLA4Ig led to long-term graft acceptance (>150 days) without clinical and/or histological signs of rejection. A higher rate of apoptosis could be detected in livers at early time-points in long-term survivors receiving CTLA4Ig and donor splenocytes. Analysis of cytokine mRNA expression revealed a decrease of interleukin-2 at early time-points in all groups receiving CTLA4Ig; whereas, interferon-gamma was increased in long-term survivors receiving CTLA4Ig and donor cells or donor cells alone. The combination of CTLA4Ig and donor derived splenocytes is potent to induce long-term survival and graft acceptance. The mechanisms appear to involve the induction of an early inflammatory impulse and apoptosis.

Liver sinusoidal endothelial cells are insufficient to activate T cells

Liver sinusoidal endothelial cells (LSEC) have been reported to express MHC class II, CD80, CD86, and CD11c and effectively stimulate naive T cells. Because dendritic cells (DC) are known to possess these characteristics, we sought to directly compare the phenotype and function of murine LSEC and DC. Nonparenchymal cells from C57BL/6 mice were obtained by collagenase digestion of the liver followed by density gradient centrifugation. From the enriched nonparenchymal cell fraction, LSEC (CD45(-)) were then isolated to 99% purity using immunomagnetic beads. Flow cytometric analysis of LSEC demonstrated high expression of CD31, von Willebrand factor, and FcgammaRs. However, unlike DC, LSEC had low or absent expression of MHC class II, CD86, and CD11c. LSEC demonstrated a high capacity for Ag uptake in vitro and in vivo. Although acetylated low-density lipoprotein uptake has been purported to be a specific function of LSEC, we found DC captured acetylated low-density lipoprotein to a similar extent in vivo. Consistent with their phenotype, LSEC were poor stimulators of allogeneic T cells. Furthermore, in the absence of exogenous costimulation, LSEC induced negligible proliferation of CD4(+) or CD8(+) TCR-transgenic T cells. Thus, contrary to previous reports, our data indicate that LSEC alone are insufficient to activate naive T cells.

Absence of a relationship between the increased survival of skin grafts provoked by additional spleen transplantation and the detection of donor chimeric cells in rats

The goal of this study was to examine the relationship between the effects of spleen transplantation on the acceptance of a skin allograft from the same donor and the detection of donor chimerism in recipient tissues. Male Sprague-Dawley rats and female Wistar rats were used as donors and recipients, respectively. Four experimental groups were established: group C: only skin grafting was performed; group S: recipients were splenectomized before skin grafting; group 1: skin grafts were performed immediately after splenectomy of recipients and spleen transplantation, and group 2: splenectomy of the recipients and spleen grafting were performed 48 h before skin grafting. All animals were sacrificed 14 weeks after surgery. The rate of acceptance of skin grafts was significantly higher in animals that received both skin and spleen transplantations than in group C (p = 0.03) or in group S (p = 0.04). Detection of donor chimeric cells was significantly more frequent in rats after spleen transplantation than in group C (p = 0.03). However, the detection of chimeric cells was not related to the acceptance of skin grafts. To conclude, the beneficial effect of spleen auxiliary transplantation on allograft survival was not related to the detection of long-term chimerism in the recipient's tissues.

Use of allogeneic bone marrow labeled with neomycin resistance gene to examine bone marrow-derived chimerism in experimental organ transplantation

Posttransplant infusion of viable donor bone marrow cells (DBMC) has been shown in our previous studies to promote acceptance of incompatible kidney allografts in rhesus monkeys after treatment with polyclonal antithymocyte globulin to deplete peripheral T-lymphocytes. In this nonhuman primate model, the infusion of the DBMC is requisite for the induction of functional graft tolerance and specific MLR and CTLp unresponsiveness, although the relevant role and fate of bone marrow-derived chimeric cells is uncertain. Standard immunological and molecular techniques applied to this monkey model are unable to differentiate between chimeric cells derived from the infused DBMC and those derived from allograft-borne passenger leukocyte emigrants. To distinguish chimerism due to infused DBMC, we transduced DBMC with a functional neomycin resistance gene (Neo(r)) using the retroviral vector pHSG-Neo.Neo(r)-transduced BMC were infused into recipients approximately 2 wk after kidney transplantation and treatment with rabbit antithymocyte globulin. No maintenance immunosuppressive drugs were given. Genomic DNA isolated from peripheral blood leukocytes was used to monitor the presence ofNeo(r)-positive cells. Tissue samples obtained at necropsy also were assessed forNeo(r)-positive chimeric cells. The presence of DBMC-derived chimerism was assessed by polymerase chain reaction usingNeo(r) sequence-specific primers (PCR-SSP). Chimerism was detectable in recipient tissues at various times for up to 6 mo after DBMC infusion. These studies using gene transduction methodology indicate that a stable genetic marker can provide capability to examine DBMC-derived chimerism for prolonged periods in a nonhuman primate model. This approach should facilitate future studies in preclinical models to study the role and type of chimeric cell lineages in relation to functional allograft tolerance.