The biology of acute transplant rejection

Boosting regulatory T cell-dependent immune tolerance by activation of p53

Regulatory T cells (Tregs) have critical roles in maintaining immune hemostasis and have important anti-inflammatory functions in diseases. Recently, we identified that CX-5461 (a selective RNA polymerase I inhibitor and p53 activator) acted as a potent immunosuppressive agent, which prevented allogeneic acute rejection in animal models via a molecular mechanism distinct from all those of conventional immunosuppressive drugs. Unexpectedly, we discovered that CX-5461 could promote Treg differentiation. In this review, we have summarized the evidence for a potential role of p53 in mediating Treg differentiation and its possible mechanisms, including regulation of FoxP3 transcription, regulation of the expression of PTEN (phosphatase and tensin homolog), as well as protein-protein interaction with the transcription factor STAT5 (signal transducer and activator of transcription 5). Evidence also suggests that pharmacological p53 activators may potentially be used to boost Treg-mediated immune tolerance. Based on these data, we argue that novel p53 activators such as CX-5461 may represent a distinct class of immunosuppressants that repress conventional T cell-mediated alloimmunity with concomitant boosting of Treg-dependent immune tolerance.

Steroidal Alkaloids as an Emerging Therapeutic Alternative for Investigation of Their Immunosuppressive and Hepatoprotective Potential

The compounds, sarcovagine-D, alkaloid-C, and holaphylline isolated from Sarcococca saligna were found to possess immunosuppressive activities. These compounds were characterized for in vitro inhibition on human T-cells proliferation and IL-2 production. The compounds showed significant immunosuppressive effect on IL-2 production as well as on phytohemagglutinin stimulated T-cell proliferation in a dose dependent manner. Of all the tested compounds holaphylline was found to be less toxic and safe. These compounds were then evaluated for their in vivo hepatoprotective potential against CCl₄, in which alkaloid-C and holaphylline showed markedly reduced liver inflammation and biochemical parameter (ALT, AST, and ALP) of liver injury. The decrease in the activity of hepatic antioxidant enzyme (SOD) was significantly prevented by holaphylline, likewise gradually the levels of MDA and GSH were also normalized compared to silymarin. The CCl₄ induced inflammation and necrosis around the central vein of liver was reduced by sarcovagine-D, alkaloid-C and holaphylline, to 8%, 4% to 1% respectively as assessed by histopathology, thus having better hepatoprotective effect compared to positive control. Steroidal alkaloids attenuated the inflammation of liver around the injured central vein region by down regulating the CCl₄ induced activation of hepatic macrophages as well as their number respectively. Therefore, the in vitro and in vivo results suggest that steroidal alkaloids from S. saligna could be excellent immunosuppressive and hepatoprotective agents.

Deazaadenosine prevents leukozyte evasion during acute cardiac allograft rejection by suppression of adhesion molecule expression

BACKGROUND

In the initial phase after cardiac transplantation, mononuclear cells infiltrate the graft initiating a relevant impulse for rejection. 3-Deazaadenosin (c3Ado), an analog of adenosine, has demonstrated in vitro anti-inflammatory properties. Furthermore, in vivo studies on arteriosclerosis development and septic myocardial dysfunction c3Ado revealed reduced cellular infiltration. In addition ischemia and reperfusion injury could be diminished in a pulmonary animal model. The aim of our study was to investigate the properties of c3Ado to reduce adhesion molecule expression and cellular infiltration in a fully allogeneic cardiac transplant model.

METHODS AND RESULTS

Lewis rats were challenged with Wistar-Furth cardiac allografts. Untreated grafts were rejected within 7 days (group 1). In group 2, animals received 2 x 5 mg c3Ado SC per day. Grafts were harvested on days 1, 3, and 6 after transplantation for further examination (n = 4 per group and time point). Immunohistochemical examination revealed significant reduction of graft-infiltrating MHC II positive cells, T-cell receptor positive cells (R73), as well as ED1-positive monocytes and macrophages (P < .01) at days 3 and 6 after transplantation. Adhesion molecule (ICAM-1, VCAM-1) expression on days 1 and 3 after transplantation was almost completely diminished in c3Ado-treated grafts.

CONCLUSION

Thus, c3Ado is able to reduce graft infiltration by preventing leukocyte evasion through the suppression of adhesion molecule expression. This may be a novel strategy to protect transplanted organs from early damage after transplantation and extend organ survival after transplantation.

Trafficking of Donor-Derived Bone Marrow Correlates With Chimerism and Extension of Composite Allograft Survival Across MHC Barrier

We proposed to evaluate differences between recipient's immune response to vascularized skin and combined vascularized skin/bone allografts, under a 7-day alphabeta-TCR plus cyclosporine (CsA) treatment protocol. Thirty-six transplantations were performed in six groups: group I (isograft control-vascularized skin graft; n=6); group II (isograft control-combined vascularized skin/bone graft; n=6); group III (allograft rejection control group-vascularized skin graft; n=6); group IV (allograft rejection control-combined vascularized skin/bone graft; n=6); group V (allograft treatment-vascularized skin graft; n=6); and group VI (allograft treatment-combined vascularized skin/bone graft; n=6). Isograft transplantations were performed between Lewis rats and allografts were transplanted across the MHC barrier from Brown Norway to Lewis rats. In the allograft treatment group, a combined alphabeta-TCR+CsA protocol was applied for 7 days. All groups were compared clinically, immunologically and histologically. Statistical significance was determined with two-tailed Student's t test. Indefinite graft survival was achieved in the isograft control group (>300 days). Allograft rejection controls rejected within 5 to 9 days posttransplant; chimerism levels were undetectable (<.5%). Allografts under the alphabeta-TCR+CsA protocol had significantly extended survival when skin was combined with bone (61-125 days) compared to vascularized skin allografts (43-61 days). Lymphoid macrochimerism was significantly higher in group VI than group V. Histology confirmed skin and bone viability. Combined vascularized skin/bone allografts had higher and sustained levels of donor-specific chimerism and extended allograft survival.

Association of CD20+ infiltrates with poorer clinical outcomes in acute cellular rejection of renal allografts

We undertook a study to ascertain the relationship between the presence of CD20-positive B-lymphocytes in renal allografts undergoing acute cellular rejection and graft survival. We identified 27 patients transplanted between January 1, 1998 and December 31, 2001, with biopsy-proven Banff 1-A or Banff 1-B rejection in the first year after transplantation, and stained the specimens for CD20 and C4d. At least 4 years of follow-up data were available for each patient studied. Six patients had CD20-positive B-cell clusters in the interstitium, and 21 patients were negative for CD20 infiltrates. The CD20-positive group was significantly more likely to have steroid-resistant rejection and reduced graft survival compared to CD20-negative controls. This study supports prospective identification of CD20-positive B-cell clusters in biopsy-proven rejection and offers a therapeutic rationale for a trial of monoclonal anti-CD20 antibody in such patients.

3-Deazaadenosine prevents leukocyte invasion by suppression of adhesion molecule expression during acute cardiac allograft rejection: Involvement of apoptotic cell death

BACKGROUND

In the initial phase after cardiac transplantation, mononuclear cells infiltrate the graft, initiating a relevant impulse for rejection. 3-Deazaadenosine (c3Ado), an analog of adenosine, has proven anti-inflammatory properties both in vitro and in vivo. We hypothesized that c3Ado can serve as a therapeutic tool to reduce cellular infiltration in cardiac allograft transplantation.

METHODS

Using the Wistar-Furth-to-Lewis rat cardiac allograft model, animals were treated with 5 mg c3Ado subcutaneously twice per day. Allografts of untreated animals served as controls. Grafts were harvested on Days 1, 3 and 6 after transplantation for further examination (n = 4 per group and timepoint).

RESULTS

Immunohistochemical examination of c3Ado-treated grafts revealed up to 80% reduction of infiltrating major histocompatability complex (MHC) II-positive cells and T-cell-receptor-positive cells (R73) as well as ED1-positive monocytes and macrophages at Days 3 and 6 after transplantation. Adhesion molecule (ICAM-1 and VCAM-1) expression at Days 1 and 3 was almost completely abolished in c3Ado-treated grafts. However, c3Ado treatment did not prevent apoptotic cell death (TUNEL assay, DNA laddering) at Day 6, nor did it prolong allograft survival. As in controls, grafts were rejected at Day 7.

CONCLUSION

c3Ado significantly reduces graft infiltration by preventing leukocyte invasion, most likely through suppression of adhesion molecule expression. Although graft survival was not prolonged, treatment with c3Ado may still serve as a strategy to protect hearts from early damage after transplantation. Further studies will show whether peri-operative use of c3Ado can bridge the critical phase after transplantation when standard immunosuppression is not yet completely efficacious.

Are preformed antibodies to biliary epithelial cells of clinical importance in liver transplantation?

During acute liver allograft rejection, most of the tissue damage to bile duct epithelium is thought to occur as a consequence of direct immunologic injury by T-cell-mediated immune effector mechanisms. However, the role of antibodies to biliary epithelial cells (BECs) in liver transplant rejection is not known. We therefore investigated cross-match sera obtained immediately before liver transplantation from 95 patients for the presence of BEC-reactive antibodies to determine their association with acute rejection. BECs were isolated from one normal healthy liver. Antibody binding was detected by using flow cytometric analysis. Donor lymphocyte-specific cross-matches using complement-dependent cytotoxicity (CDC) and flow cytometric assays also were performed. The 2-year patient survival rate in this study was 86.3%. Eleven patients were positive for either CDC or flow cytometric cross-matches. BEC antibodies were detected in 41 serum samples (43.2%). Patients with BEC antibodies experienced acute rejection more frequently (65.9%) compared with 42.5% without antibodies (P <.03). HLA specificity determinations indicated that in 5 of 41 cases, anti-BEC reactivity was caused by HLA antibodies. No correlations between the presence of BEC antibodies and patient survival and the occurrence of cholangitis and nonsurgical bile duct strictures were found within 2 years of follow-up. In conclusion, preformed antibodies to BECs are associated with acute rejection. Thus, the presence of these antibodies before transplantation may facilitate acute liver graft rejection.

Leukemia inhibitory factor gene improves skin allograft survival in the mouse model

BACKGROUND

Leukemia inhibitory factor (LIF) is a widely expressed cytokine involved in both local and systemic immune response. Furthermore, it has been implicated in various immunological processes including thymic T cell maturation and embryo implantation. We investigated implication of various modalities in the application of prolonged and viable allograft to the wound, using cytokines and growth factors.

MATERIALS

BALB/c and B6D2F1 strains of mice were used either as a skin graft donor or host. LIF cDNA inserted in plasmid vector or the vector alone was injected intradermally in graft skin and observed up to 21 days. LIF, LIF-receptor, gp130, as well as type 1 and 2 T helper cytokine expressions were investigated by reverse transcription polymerasse chain reaction, in situ hybridization, and histological studies.

RESULTS

LIF cDNA-treated groups showed significantly improved graft survival compared to the vector-treated control in 21 days postoperatively for grafting from B6D2F1 to BALB/c and BALB/c to B6D2F1. LIF and LIF receptor mRNA expressions were observed 24 hr and 21 days posttransplantation. The gp130 expression was only observed in LIF-treated B6D2F1 to BALB/c allografting on day 21 posttransplantation. LIF transcripts were strongly present in the epidermal, dermal, and subdermal tissues as determined by an in situ hybridization of LIF-treated grafting.

CONCLUSIONS

These results suggest that LIF cDNA treatment is an effective and beneficial adjuvant for the skin allograft survival. Improved skin allograft modulation by cytokine gene transfer is a potentially promising therapy for temporary large skin coverage.

Early increased chemokine expression and production in murine allogeneic skin grafts is mediated by natural killer cells

BACKGROUND

Increased expression of chemokine mRNA is observed in allogeneic but not syngeneic skin grafts 3-4 days after transplantation. The recipient cells mediating this early inflammatory response in allografts remain unidentified.

METHODS

Isogeneic and allogeneic skin grafts were transplanted to euthymic and athymic nude mice. mRNA expression and protein production of macrophage inflammatory protein-1alpha (MIP-1alpha), MIP-1beta, and the murine homolog of Gro(alpha), i.e. KC, from graft homogenates retrieved 3-4 days posttransplantation was tested by Northern blot hybridization and ELISA. To deplete NK cells, recipients were treated with antiasialo GM1 (ASGM1) antisera or with anti-NK1.1 mAb before transplantation.

RESULTS

Expression of KC, MIP-1alpha, and MIP-1beta mRNA was equivalent in C57BL/6 allogeneic skin grafts and BALB/c isografts at day 2 posttransplant. At day 3 posttransplant, chemokine mRNA levels decreased in isografts but were maintained at high levels in the allografts. Increased early chemokine mRNA was also observed in C57BL/6, but not BALB/c++ grafts on BALB/c athymi(nu/nu) recipients. Treatment of allograft recipients with ASGM1 or with anti-NK1.1 antibody eliminated NK cells from the spleen and allograft infiltrating cell populations and decreased early chemokine mRNA levels in allografts 60-70%. Analyses of allograft homogenates indicated increased levels of KC, MIP-1alpha, and MIP-1beta protein at day 4 posttransplant that were decreased in recipients depleted of NK cells. Early chemokine mRNA levels were equivalent in isogeneic and semiallogeneic F1 grafts.

CONCLUSIONS

Early chemokine mRNA expression and protein production in allogeneic skin grafts is amplified by recipient natural killer (NK) cells. These results indicate a novel function for infiltrating NK cells in mediating early increased intra-allograft chemokine production and inflammation during the initiation of acute rejection.

Rat allotransplantation of epigastric microsurgical flaps: a study of rejection and the immunosuppressive effect of cyclosporin A

The rejection of allotransplantation of epigastric microsurgical flaps and the effect of immunosuppression have been studied in 58 rats. Three sets of experiments were planned: (1) Wistar Furth isogenic donors and receptors (control set); (2) Brown Norway donors and Wistar Furth receptors (rejection set); and (3) Brown Norway donors and Wistar Furth immunosuppressed receptors (cyclosporin A set). Cyclosporin A (10 mg/kg/d) treated rats had a transplantation survival rate of up to 30 days: 83.3% among isogenic animals and 60% among allogeneic. There was 100% rejection by the 9th day after the transplantation in allogeneic non-immunosuppressed rats. Biopsies embedded with historesin were taken from the flap and normal contralateral skin (used as control) on the 3rd, 7th, 15th, and 30th days after the surgery. A quantitative study of infiltrating lymphocytes in the flaps, with and without cyclosporin A, was done by evaluating the local inflammatory infiltrate. A significant increase in the number of lymphocytes among the rejection and immunosuppressed groups was seen, as compared to the isogenic set. Local lymphocytosis in allogeneic non-immunosuppressed transplantations reached its highest level on the 3rd day after surgery, before gross findings of rejection, which could only be seen by naked eye on the 5th or 6th day. Therefore, we conclude that cyclosporin A is effective in preserving allogenic transplantation in rats. Biopsies of transplanted areas may contribute to earlier diagnosis of the need for immunosuppressive therapy.

Acute pulmonary allograft rejection. Mechanisms, diagnosis, and management

Rejection is a common complication following lung transplantation, and can lead to considerable short- and long-term morbidity. As numbers and survival rates of lung transplant recipients increase, it is apparent that acute rejection can occur months or years after transplantation, and may be resistant to standard therapies. Mechanisms of acute rejection have been well studied in other solid organ transplant recipients, and are beginning to be addressed in the lung recipient. This article addresses some of the common issues of diagnosis and management of acute rejection which arise frequently during the care of lung transplant recipients.

Sequential cellular and molecular kinetics in acutely rejecting renal allografts in rats

The initial (0-24 hr), early (3-5 days), and late (7-14 days) events occurring in LBNF1 renal allografts transplanted into Lew recipients were examined to define precisely the sequential cellular and molecular kinetics during acute rejection. Grafts and spleens were harvested at 3, 6, 12, and 24 hr, and at 3, 5, 7, and 14 days and processed for morphology, immunohistology, and reverse transcriptase-polymerase chain reaction. Various factors (mRNA) were up-regulated sequentially in the allografts over time. In the initial phase, E-selectin and complement (C1 and C3) expression was noted within 6 hr, peaking by 24 hr. RANTES (regulated upon activation, normal T cell expressed and secreted) increased within 6 hr, and then again between 3 and 6 days. By immunohistology, MHC class II was up-regulated consistently after day 1. Intercellular adhesion molecule-1 expression increased after day 3; lymphocyte function-associated antigen-1+ infiltrating leukocytes peaked at day 5. Infiltrating CD8+ T lymphocytes increased strikingly between days 1 and 3, peaking at day 5; CD4+ cells infiltrated more slowly until day 5. The kinetics of ED1+ macrophages were similar to those of lymphocyte function-associated antigen-1+ cells. The CD4+ T cell-derived product, interleukin (IL)-2, peaked at 7 days. Interferon-gamma increased progressively up to 14 days. By 3 days, the macrophage-associated factor, transforming growth factor-beta, peaked; this was followed by increased IL-6 expression by day 5. IL-1, tumor necrosis factor-alpha, and inducible nitric oxide synthase increased slowly until day 7, declining thereafter. Endothelin increased progressively over the 14-day follow-up period. Cytokine dynamics occurring in host spleen were similar to those noted in the allografts. Although acute rejection is primarily T cell mediated, adhesion molecules, macrophages, and their associated products may influence initial and later changes. The brisk expression of complement, E-selectin, and RANTES within the first few hours after engraftment may occur secondary to ischemic injury and trigger subsequent immunological events. Macrophages and their products may play a larger role in the process than hitherto appreciated.

T cell-dependent acceleration of chemoattractant cytokine gene expression during secondary rejection of allogeneic skin grafts

Chemoattractant cytokines, chemokines, are likely to play a critical role in directing leukocytes to graft sites and in amplifying intragraft inflammation during rejection. Since second-set graft rejection occurs at an accelerated rate, we hypothesized that chemokine genes would be expressed earlier during secondary allograft rejection than during rejection of primary allografts. We have tested this hypothesis by using Northern blot analysis to compare intragraft expression levels of genes encoding interleukin (IL) 1beta and six chemokines during rejection of C57BL/6 skin grafts on naive and C57BL/6-sensitized BALB/c recipients. Expression levels of IL-1beta, interferon-gamma inducible protein, macrophage inflammatory protein-1 (MIP-1) alpha, and MIP-1beta genes were 10- to 17-fold higher on day 5 after transplantation in C57BL/6 grafts on C57BL/6-presensitized recipients than in C57BL/6 grafts on unprimed recipients. Intragraft expression of the chemokines regulated upon activation, normal T cell expressed and secreted (RANTES), during primary C57BL/6 graft rejection was virtually undetectable at day 7 after primary transplantation, but was expressed at high levels by day 5 after secondary transplantation. In third-party CBA/Ca allografts on unsensitized and C57BL/6-presensitized BALB/c mice, similar levels of IL-1beta, MIP-1alpha, and MIP-1beta expression were observed. High levels of RANTES and interferon-gamma inducible protein expression, however, were observed at day 5 after transplantation in CBA/Ca grafts on C57BL/6-presensitized recipients and correlated with accelerated rejection of the third-party grafts. Although T cells from C57BL/6-presensitized recipients did not express increased reactivity to CBA/Ca stimulator cells in vitro, serum antibodies from these recipients demonstrated reactivity to cells from CBA/Ca and A/J mice. When compared with transfer of unprimed cells, transfer of C57BL/6-primed lymphoid cells to sublethally irradiated BALB/c mice engrafted with C57BL/6 grafts resulted in increased intragraft proinflammatory cytokine gene expression. Deletion of T cells before transfer abrogated the increased intragraft expression of proinflammatory cytokine genes. Collectively, these results indicate that the accelerated expression of chemokine genes during second-set rejection of allogeneic skin grafts is mediated by immune T cells.

Peripheral blood and intrahepatic subsets of T lymphocyte activation and function in liver allograft rejection and drug-induced tolerance in rats

T lymphocyte kinetics in liver allograft rejection were studied by measuring levels of activated (CD25+ and class II MHC+) T lymphocytes (CD5+) and T cell subsets (CD4 and CD8) in peripheral blood and the livers of allogeneic DA (RT1b) to LEW (RT1') and syngeneic LEW to LEW orthotopic rat liver transplants. Median survival was 10 days in untreated allogeneic rats (n = 17). Mean (+/- SEM) T lymphocyte class II MHC expression increased from 3.4 +/- 0.44% (day 2/3) to 4.9 +/- 1.1% (day 7) (p = 0.01). Complete sequential data were available for nine animals over the period of rejection confirming the increase in class II MHC expression (p = 0.05) and showing a decrease in CD25 expression (p = 0.05). There was a significant fall in CD4:CD8 ratio from day 2/3 to day 7 (p = 0.002). CD25 and class II MHC molecule expression and the CD4:CD8 ratio remained unchanged over the comparable period in the syngeneic LEW to LEW control model (n = 5, p > 0.3 for all comparisons). Cyclosporin A (5 mg/kg/day) was given orally for 17 days and then withdrawn to induce allograft tolerance in a further nine DA to LEW rats (median survival > 100 days). Samples taken at 2/3, 7, 17, 30, 40 and 100 days showed that T cell activation marker expression remained low during cyclosporin treatment (e.g. class II MHC expression 2.32 +/- 0.35%; CD25 expression 3.53 +/- 0.44% on day 7) but increased thereafter (e.g. class II MHC expression 8.19 +/- 0.65%. CD25 13.25 +/- 0.95% on day 100). There was a fall in CD4:CD8 ratio throughout (p < 0.001). Intrahepatic mononuclear cells were harvested from six normal livers, four allogeneic livers (at 10 days), five syngeneic livers (at 10 days) and five tolerant allografts (at 100 days). Rejecting grafts showed the highest proportion of T lymphocytes (66.8 +/- 4.0% vs 18.5 +/- 3.6% in controls, p = 0.01). T cell activation was higher in both rejecting and tolerant grafts versus normal control livers (p = 0.05 for CD25 and p < 0.01 for class II MHC expression). CD8+ lymphocytes predominated in the hepatic infiltrate in all models, although the majority of these cells were both CD5 and alpha beta T cell receptor negative. There was a higher proportion of T cells in tolerant allografts (44.5 +/- 5.2%, p < 0.01) compared with control animals. Serial changes in peripheral T lymphocyte subsets may be useful in monitoring experimental acute rejection. In peripheral blood, the increase in T cell activation and loss of CD4+ lymphocytes, along with evidence of increased intragraft infiltration by this subset implies that it has a primary role in the development of tolerance in this nodel.

Binding of lymphocytes to acutely rejecting rat kidney allografts in vitro is guided by events in the graft itself rather than by sensitization of host lymphocytes

Circulating host lymphocytes recognize, bind to, become activated by, and infiltrate engrafted allogeneic tissues. The mechanisms responsible for these early events which lead to acute immunological rejection have not been precisely defined. We have examined sequentially in vitro lymphocyte binding patterns in a kidney transplant model of acute rejection in rats and their relationship to the expression of two representative adhesion molecules, ICAM-1 and LFA-1. The extent of binding of naive, or allosensitized recipient strain LNL or PBL, or donor strain or third party cells to frozen sections of kidney allografts was not significantly different; adherence was dependent upon whether the graft was an allograft or an isograft. The pattern of lymphocyte adherence to various allograft compartments was distinct and varied with time. Within 3 days after transplantation only a few cells had bound to the frozen tissues, preferentially to vascular endothelium. By days 5 and 7, increasing numbers of cells bound primarily to tubules, as did the few cells adhering to isografts. Immunohistologically, ICAM-1 expression increased progressively during acute rejection, first on vascular endothelium, later on tubules. LFA-1+ infiltrating cells peaked more quickly. Lymphocyte binding could be inhibited (approx. 40%) by monoclonal antibodies directed against LFA-1 and ICAM-1. The results indicate that in vitro lymphocyte binding to acutely rejecting kidney transplants is directed by the allogenicity of the graft itself via upregulation of adhesion molecules rather than sensitization of the host cells.