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

Mesenchymal stem cells: immune evasive, not immune privileged

The diverse immunomodulatory properties of mesenchymal stem/stromal cells (MSCs) may be exploited for treatment of a multitude of inflammatory conditions. MSCs have long been reported to be hypoimmunogenic or 'immune privileged'; this property is thought to enable MSC transplantation across major histocompatibility barriers and the creation of off-the-shelf therapies consisting of MSCs grown in culture. However, recent studies describing generation of antibodies against and immune rejection of allogeneic donor MSCs suggest that MSCs may not actually be immune privileged. Nevertheless, whether rejection of donor MSCs influences the efficacy of allogeneic MSC therapies is not known, and no definitive clinical advantage of autologous MSCs over allogeneic MSCs has been demonstrated to date. Although MSCs may exert therapeutic function through a brief 'hit and run' mechanism, protecting MSCs from immune detection and prolonging their persistence in vivo may improve clinical outcomes and prevent patient sensitization toward donor antigens.

Expression of common gamma chain signalling cytokines and their receptors distinguishes rejection from tolerance in a rat organ transplant model

BACKGROUND

Signalling through the cytokine common γ chain (γc) is crucial for survival of activated T cells. In its absence, severe combined immunodeficiency ensues and transplanted tissues are not rejected.

METHODS

To determine whether differences in the availability of γc signalling cytokines correlate with rejection or acceptance, we examined expression of all γc signalling components in organs transplanted between PVG donors and DA recipients. In this combination hearts or kidneys are rejected in <10 days while livers survive >100 days. Expression of the γc cytokines IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21 and their receptors γc, IL-2Rα, IL-2Rβ/IL-15Rβ, IL-4Rα, IL-7Rα, IL-9Rα, IL-15Rα and IL-21Rα was determined by real-time PCR pre-transplant and on days 3, 5 and 7 after transplantation.

RESULTS

Most increased after transplantation, although there were significantly lower levels of IL-2, IL-2Rα, IL-4 and IL-15Rα in tolerant livers compared to rejecting hearts or kidneys. IL-9 was only expressed in normal kidneys and decreased during rejection. IL-15 was constitutively expressed and did not change after transplantation. IL-21 and IL-21R increased in all transplanted organs to a similar extent. IL-7Rα in liver was considerably increased compared with heart or kidney, consistent with its known inverse relationship to global levels of γc signalling.

CONCLUSIONS

In transplanted livers, acceptance is associated with low levels of all γc cytokines or receptors except IL-21. This is consistent with "dilution" of γc cytokines from a finite clone size of alloreactive T cells in livers, which are ten times larger than kidneys or hearts.

Tolerance in liver transplantation

Operational tolerance (OT) in liver transplant patients occurs much more frequently than OT of other transplanted organs; however the rate of OT varies considerably with the centre and patient population. Rates of OT range from 15% of the total liver transplant (LTX) patient population down to less than 5%. This review examines the reports of liver OT and compares the factors that could contribute to this variation. Multiple factors were examined, including the time from transplantation when weaning of immunosuppression (IS) was commenced, the rapidity of weaning, the contribution of maintenance and induction IS and the patient population transplanted. The approaches that might be used to increase the likelihood of OT are discussed and the approaches to monitoring OT in LTX patients are reviewed.

Cyclic AMP prolongs graft survival by suppressing apoptosis and inflammatory gene expression in acute cardiac allograft rejection

This study was designed to investigate the effects of cAMP on immune regulation and apoptosis during acute rat cardiac allograft rejection. We found that the production of immune markers such as inflammatory cytokines (IL-1beta, IL-6, and TNF-alpha), iNOS expression, and nitric oxide (NO) production, was significantly increased in the blood and transplanted hearts of allograft recipients, but not of isograft controls. These increases were effectively suppressed by the administration of the membrane permeable cAMP analog dibutyryl cAMP (db-cAMP). Administration of db-cAMP reduced allograft-induced elevation of several biochemical markers, such as adhesion molecule expression, iron-nitrosyl complex formation, caspase-3 activation, and apoptotic DNA fragmentation in an animal model. Furthermore, treatment of allograft recipients with db-cAMP prolonged median graft survival to 11 days compared with a median graft survival time of 8 days in saline-treated allograft recipients. These results suggest that db-cAMP exerts a beneficial effect on murine cardiac allograft survival by modulating allogeneic immune response and cytotoxicity.

Donor IL-4-treatment induces alternatively activated liver macrophages and IDO-expressing NK cells and promotes rat liver allograft acceptance

Most approaches to transplant tolerance involve treatment of the recipient to prevent rejection. This study investigates donor treatment with IL-4 for its effect on subsequent rat liver allograft survival. Rat orthotopic liver transplants were performed in rejecting (PVG donor to Lewis recipient) or spontaneously tolerant (PVG to DA) strain combinations. Donors were untreated or injected intraperitoneally with IL-4 (30,000U/day) for 5days. Tissue infiltrates and gene expression were examined by immunohistochemistry and real-time quantitative PCR. IL-4 induced a marked leukocyte infiltrate in donor livers prior to transplant. Macrophages comprised the major population, although B cells, T cells and natural killer (NK) cells also increased. IL-4-induced liver macrophages had an alternatively activated phenotype with increased expression of mannose receptor but not inducible nitric oxide synthase (NOS2). IL-4 also induced IDO and IFN-gamma expression by NK cells. Donor IL-4-treatment converted rejection to acceptance in the majority of Lewis recipients (median survival time >96days) and did not prevent acceptance in DA recipients. Acceptance in Lewis recipients was associated with increased donor cell migration to recipient spleens and increased splenic IL-2, IFN-gamma and IDO expression 24h after transplantation. Donor IL-4-treatment increased leukocytes in the donor liver including potentially immunosuppressive populations of alternatively activated macrophages and IDO-expressing NK cells. Donor treatment led to long-term acceptance of most livers in association with early immune activation in recipient lymphoid tissues.

Neutralizing antibodies to therapeutic enzymes: considerations for testing, prevention and treatment

Lysosomal storage diseases are characterized by deficiencies in lysosomal enzymes, allowing accumulation of target substrate in cells and eventually causing cell death. Enzyme replacement therapy is the principal treatment for most of these diseases. However, these therapies are often complicated by immune responses to the enzymes, blocking efficacy and causing severe adverse outcomes by neutralizing product activity. It is thus crucial to understand the relationships between genetic mutations, endogenous residual enzyme proteins (cross-reactive immunologic material), development of neutralizing antibodies and their impact on clinical outcomes of lysosomal storage diseases. For patients in whom neutralizing antibodies may cause severe adverse clinical outcomes, it is paramount to develop tolerance inducing protocols to preclude, where predictable, or treat such life-threatening responses.

Blocking indoleamine dioxygenase activity early after rat liver transplantation prevents long-term survival but does not cause acute rejection

In a well-characterized rat model of liver transplantation, Piebald Virol Glaxo strain livers are accepted long term in fully mismatched Dark Agouti recipients (tolerance; TOL), but rejected in Lewis recipients (rejection; REJ). Spontaneous tolerance induction is associated with increased interferon-gamma expression, and we examined the role of the interferon-gamma-inducible immunomodulatory enzyme indoleamine dioxygenase (IDO) in this model. On day 3 after transplantation, IDO expression in the spleen of TOL recipients was significantly greater than in REJ. The B-cell population accounted for this early IDO increase. Intragraft expression of IDO increased to the same extent in both TOL and REJ. IDO inhibition for 7 days after transplantation reduced survival, but did not cause acute rejection of the liver in the TOL model. In conclusion, the differential IDO expression by B lymphocytes in the spleen of TOL recipients is not critical for preventing acute rejection.

Transplant tolerance: models, concepts and facts

Despite extensive research, our understanding of immunological tolerance to self-antigens is incomplete, and the goal of achieving tolerance to allogeneic transplanted tissue remains elusive. Currently, it is generally believed that the blockade of T cell co-stimulation offers considerable potential for achieving tolerance in the clinical setting. However, the recent finding that CD154-specific antibody may act through the depletion of activated T cells rather than co-stimulation blockade alone highlights the need for a re-evaluation of published data and the role of co-stimulation blockade in transplant tolerance. Activated T cells are programmed to die unless they receive sufficient survival signals in the form of inflammatory and lymphotropic cytokines produced by activated antigen-presenting cells or the T cells themselves. In conditions where the threshold for surviving activation is not reached, for example when a small number of responder T cells are activated in the absence of substantial injury or inflammation, the ensuing death of all activated T cells can result in deletional tolerance. Therefore, we propose that tolerance represents a failure of T cells to survive activation and develop into memory cells. This concept is likely to apply in the transplant setting, where the strength of the alloresponse depends on both the number/phenotype of the recipients' alloreactive T cells and immunogenicity of the transplanted tissue. Hence, in some rodent donor-recipient strain combinations that instigate a weak alloresponse, many treatments that only modestly decrease the alloresponse can achieve tolerance. In contrast, clinical transplantation is characterised by a strong alloresponse and highly immunogenic allografts, and thus, most treatments fail to control allograft rejection, and tolerance is difficult to achieve.

Donor Leukocytes Combined With Delayed Immunosupressive Drug Therapy Prolong Limb Allograft Survival

Donor leukocytes administered at the time of transplantation may prolong organ allograft survival. Delayed administration of calcineurin inhibitors, such as FK506 or cyclosporine, may enhance their efficacy. Herein the effectiveness of this strategy to promote limb transplant survival was investigated in the strong histocompatibility barrier of Brown-Norway donor to Lewis recipients. Donor leukocytes (6 x 10(7) intravenously) were injected on the day of transplantation followed on day 1 to 14 with mycophenolate mofetil (MMF; 15 mg/kg/d) and prednisone, (0.5 mg/kg/d) which were then tapered by 20% each week and stopped at week 7. Administration of of FK506 (2 mg/kg/d) was started on day 4 and continued for 8 weeks, then tapered for 4 weeks to a maintenance dose of 0.8 mg/kg/d, which was continued for 12 weeks (group A; n = 8). A control group (n = 8) underwent identical treatment save for donor leukocyte injection but rather commencement of FK506 on day 1. Rejection was common during FK506 tapering in both groups. However group A showed a significantly later onset, a shorter period for reversal of the first rejection, and a significantly lower dosage of FK506 at the time of rejection. After the completion of immunosuppression, rejection occurred significantly later in group A than the control group with one animal surviving without immunosuppression on day 344. This is the first trial of a donor leukocyte injection combined with delayed FK506 administration in limb transplantation, which suggested that it could produce a modest but significant improvement in outcome.

Posttransplant Interleukin-4 Treatment Converts Rat Liver Allograft Tolerance to Rejection

BACKGROUND

Previous studies showed that liver transplant rejection in the Piebald Virol Glaxo (PVG)-to-Lewis combination was associated with more intragraft interleukin (IL)-4 mRNA expression than in spontaneously tolerant grafts in the PVG-to-Dark Agouti (DA) combination. There was also immunoglobulin (Ig) G1 antibody deposition, suggesting an IL-4-induced IgG class switch in rejection. The aim of this study was to investigate whether IL-4 treatment converts PVG-->DA liver transplant tolerance to rejection.

METHODS

DA (RT1a) rats were recipients of orthotopic PVG (RT1c) liver transplants and DA liver transplants were syngeneic controls. Supernatant from IL-4-transfected Chinese hamster ovary cells (0.5 mL, 30,000 U) or from untransfected cells was injected intraperitoneally on days 3 through 7. Samples were taken for immunohistochemical staining of frozen tissue sections to analyze cellular infiltrate and antibody deposition.

RESULTS

IL-4 treatment significantly reduced survival of liver allografts from greater than 100 days in untreated animals to 9 days (P=0.004). Pathologic analysis of IL-4-treated animals showed that death was caused by liver transplant rejection, with a heavy infiltrate of mononuclear cells, disruption of portal tract areas, and infarction. Immunohistochemistry revealed an extensive infiltrate of T cells, CD25-expressing cells, and B cells that was similar to the level in PVG--> Lewis liver allograft recipients that reject the liver. There was also a more extensive monocyte-macrophage infiltrate and more major histocompatibility complex class II expression in IL-4-treated animals compared with untreated animals. There was moderate increase of IgM, little IgG1, and no IgE or IgG2a antibody deposition.

CONCLUSIONS

IL-4, a T-helper type 2 cytokine that has previously been shown to inhibit delayed-type hypersensitivity responses such as rejection, was found to promote rejection of liver allografts. There was only slight evidence of a graft-specific antibody response, showing that IL-4 induces liver allograft rejection in association with some, but not all, of the changes accompanying rejection in the PVG-->Lewis strain combination.

Combined donor leucocyte administration and immunosuppressive drug treatment for survival of rat heart allografts

BACKGROUND

Donor leucocytes (DL) play an important role in rat liver transplant tolerance and their postoperative administration can convert rejection to tolerance. They appear to induce early activation, altered patterns of infiltration and death of recipient alloreactive T cells. The ability of immunosuppressive drugs to combine with DL administration was examined in a rat heart transplant model.

METHODS

Immediately after PVG to DA heterotopic heart transplantation, 6 x 10(7) spleen DL were injected. Cyclosporine A (CsA), 1.5 mg/kg/day, or methotrexate (MTX), 0.1 or 0.2 mg/kg/day, were given from day (d) 0 to d4 (early) or from d3 to d7 (delayed). Castanospermine (CAST) was administered from d0 to d7 at 100 or 300 mg/kg/day. In a separate experiment, transplanted hearts and recipient spleens were collected from treatment groups for analysis of infiltrate and cytokine mRNA expression.

RESULTS

Delayed treatment with CsA or early treatment with MTX but not CAST combined with DL to result in prolonged graft survival. Recipients treated with DL and delayed CsA had a reduced level of intra-graft interleukin (IL)-2, interferon (IFN)-gamma, IL-4, and IL-4R mRNA expression and reduced infiltrate compared to DL alone. Early MTX plus DL led to almost complete inhibition of all markers of inflammation during treatment followed by a rapid increase after cessation. In combination with DL, CsA was more effective than MTX for induction of donor-specific tolerance at the dose and administration regimens tested.

CONCLUSIONS

Delayed CsA or early MTX combine with DL to prolong heart allograft survival. Early and extensive inhibition of rejection by MTX was less effective than delayed and partial inhibition of the response by CsA for induction of transplant tolerance.

Revisiting liver transplant immunology: from the concept of immune engagement to the dualistic pathway paradigm

Ever since the demonstration that allografts are rejected through immune reactions of the host, clinical therapies for organ allografts have relied on immune suppression to prevent these destructive events. A growing body of clinical and experimental data suggests that allografts elicit multiple, interactive immune responses. The result is not inevitably graft rejection, and "spontaneous" acceptance of fully allogeneic liver grafts occurs in rodents without immunosuppression. A spectrum of results range from spontaneous acceptance without immunosuppression to rejection with immunosuppression. The "dualistic pathway paradigm" aims to reconcile apparently conflicting observations in liver transplantation and proposes that: (1) immune engagement between the host and the allograft is instrumental in both rejection and acceptance; (2) there exist in all mammalian species congruent interactive pathways of immune activation whereby the fate of the allograft is determined by the quantitative results of these interactions; (3) the dualistic effect of immunosuppressive drugs on pathways of immune activation, conferring the capacity for favorable or unfavorable graft outcome should be investigated in experimental models in which organ allografts are spontaneously accepted. In conclusion the design of clinical strategies based on this research may contribute to protocols resulting in allograft acceptance without chronic immunosuppression.

A short course of mycophenolate immunosuppression inhibits rejection, but not tolerance, of rat liver allografts in association with inhibition of interleukin-4 and alloantibody responses

BACKGROUND

Some immunosuppressive drug therapies inhibit transplant tolerance in animal models, and we have shown that treatment of recipients with methylprednisolone, but not cyclosporine, inhibits spontaneous acceptance of liver transplants. This study investigates the effects of mycophenolate mofetil (MMF) on liver acceptance and rejection.

METHODS

Piebald Virol Glaxo rat livers were transplanted into Dark Agouti recipients, which spontaneously tolerate (TOL) the liver, or into Lewis recipients, which reject (REJ) the liver. MMF (40 mg/kg/day subcutaneously) was given for 5 days from days 0 to 4 (early) or from days 3 to 7 (late). In separate experiments, liver grafts were collected for assessment of infiltrate and of interleukin (IL)-2, IL-4, IL-10, and interferon-gamma mRNA expression.

RESULTS

TOL liver transplants had a median survival time (MST) of more than 100 days (n=6), and neither early nor late MMF treatment of TOL transplants reduced survival (MST 85 days, P=0.19 and 78 days, P=0.08, respectively). Liver failure in most of these animals was the result of biliary problems, not rejection. There were few consistent differences between treated and untreated TOL animals in infiltrate or liver cytokine expression, although there was a moderate reduction in T-cell infiltrate in MMF-treated TOL animals (P=0.003 on day 5 TOL). In contrast, REJ transplants had an MST of 13 days (n=10), and early MMF treatment led to five of six animals surviving more than 100 days (P=0.0002), whereas late treatment was much less effective, with one of six animals surviving more than 100 days. REJ livers had significantly more IL-4 mRNA expression and immunoglobulin G1 deposition in the graft than TOL livers, and this was inhibited by early, but not late, MMF treatment.

CONCLUSIONS

MMF treatment inhibited rejection but not acceptance of liver allografts. Early administration was more effective in preventing rejection and demonstrated a more marked effect on IL-4 expression and alloantibody deposition than on graft T-cell infiltrate and expression of other cytokines.