Similar levels of granzyme A and perforin mRNA expression in rejected and tolerated heart allografts in donor-specific tolerance in rats

Functional compartmentalization following induction of long-term graft survival with pregraft donor-specific transfusion

Long-term survival is achieved in rat recipients by pre-graft donor-specific blood transfusion. We characterized the immune compartments in long-term survivors and analyzed them for capacity to transfer tolerance and protect against chronic rejection. Splenocytes and spleen T cells from treated recipients transferred long-term graft survival to 100% of secondary recipients. In contrast, blood transferred graft survival to only 50% of recipients whereas blood T cells had no effect. An unaltered TCR repertoire, an increase in suppressive CD4+CD25+ T cells, a decrease in antidonor T-cell proliferative response and normal perforin-granzyme levels were the hallmarks of the spleen T cells. Blood T cells were characterized by a strongly altered CD8+ repertoire, normal CD4+CD25+ T cell number with unchanged antidonor T-cell proliferative response, an activated T-cell phenotype and an increase in perforin-granzyme levels. However, following the transfer of blood or spleen cells into secondary recipients, all grafts displayed chronic rejection. These findings provide evidence that distinct compartments play critical roles in DST recipients. Regulatory cells do not accumulate in blood, which appears to be a reservoir for cytotoxic T cells. Spleen T cells, which display a regulatory-like profile and transfer graft survival, are not able to prevent chronic rejection.

Combination Treatment with Donor-Specific Transfusions and Cyclosporine A Induces Long-Term Survival of Cardiac Allografts in Miniature Swine

BACKGROUND

To evaluate whether pretransplant donor-specific transfusions (DST) can induce tolerance to cardiac allografts in large animals, heterotopic cardiac transplants were performed across a class I MHC barrier in inbred miniature swine.

METHODS

Experimental animals received two DSTs, each containing 1.4x10 viable peripheral blood mononuclear cells, 14 and 7 days prior to transplantation together with a 12-day course of cyclosporine (CyA) (13 mg/kg IV) starting on postoperative day (POD) 0.

RESULTS

Untreated (n=2) and DST-only (n=2) treated control animals rejected between POD 6 and 8. Animals treated with CyA alone (n=3) exhibited graft survival to 53, 52 and 59 days. In contrast, the combination of DST and CyA (n=3) led to stable graft function for >200 days. Long-term survivors maintained peripheral CML response against donor antigen. Following DSTs, the donor-specific proliferative response of CD8+ recipient T cells was significantly increased (P=0.011), and a significant number of CD8+ T cells underwent apoptosis (10.1% on POD 0; 5.2% on POD -14; P=0.04). None of the DST-treated animals developed donor-specific antibodies.

CONCLUSIONS

These results are the first to demonstrate the ability of DST to induce operational tolerance to cardiac allografts in large animals, and they suggest that peripheral mechanisms of tolerance mediate this effect.

Different qualitative and quantitative regulation of V beta TCR transcripts during early acute allograft rejection and tolerance induction

Recently, using a global method of T cell repertoire analysis, we showed that purified naive T cells confronted in vitro with allogeneic APCs in a direct pathway-restricted MLR up-regulate their Vbeta mRNAs without exhibiting skewing of complementarity-determining region 3 (CDR3) length distribution. In this report, using this approach, we show in vivo that Vbeta transcript regulation and CDR3 length distribution follow the same pattern during acute rejection of MHC-incompatible heart allografts. In contrast, in tolerance induction by priming of recipients with donor cells, the vigorous Vbeta mRNA accumulation with Gaussian CDR3 length distribution is abolished, providing a possible explanation for the down-regulation of activated T cells in tolerant animals. In addition, tolerated grafts harbor T cells with a highly altered repertoire, suggestive of self-restricted presentation with some patterns corresponding to previously identified regulatory cells.

Interleukin-10 produced by recombinant adenovirus prolongs survival of cardiac allografts in rats

Interleukin-10 (IL-10) and interleukin-4 (IL-4), two Th2-derived cytokines, are molecules with anti-inflammatory and immunodeviating properties whose direct expression in allografts may prolong graft survival. Recombinant adenoviruses represent efficient vectors for gene transfer in quiescent cells in vivo. Adenoviral vectors encoding rat IL-10 (AdIL-10), rat IL-4 (AdIL-4) or beta-galactosidase (AdlacZ) or without transgene (Addl324) were injected directly into rat hearts at the time of transplantation in order to test their potential to prolong heart allograft survival. Expression of vectorized sequences was confirmed in heart biopsies, and kinetic analysis of beta-galactosidase showed transient expression. Cardiac allograft survival was significantly prolonged after administration of 10(9) p.f.u. of AdIL-10 (16.6 +/- 3.2 days, P < 0.05), but not AdIL-4 (9.8 +/- 1.6 days), compared with Addl324-treated (9.3 +/- 3.3 days) or untreated groups (7.8 +/- 1.5 days). Immunohistochemical analysis of allografts after gene transfer of IL-10 showed that leukocyte infiltration was quantitatively equivalent to that seen in control groups but with a strong tendency towards lower levels of CD8+ cells. Importantly, adenovirus-derived IL-10 modified the functional status of leukocytes by inducing a significant decrease in IFN-gamma production but significantly increased transforming-growth factor beta 1 (TGF-beta 1) expression within the grafts compared with those treated with Addl324. These results show that expression of IL-10 by rat hearts after gene transfer mediated by an adenoviral vector decreases allogeneic immune responses and allows prolongation of allograft survival.

Tolerance and latent cellular rejection in long-term liver transplant recipients

Tolerance develops in a proportion of long-term liver transplant recipients but currently cannot be identified before an attempt at withdrawal from immunosuppression therapy. In the present study, we have examined the immunophenotypic characteristics of the cellular infiltrate in portal tracts and lobules as observed in liver biopsy specimens in relation to the outcome of subsequent withdrawal from immunosuppression therapy. Cryostat biopsy specimens from 27 long-term recipients before drug withdrawal, and from 10 patients with recent transplants who were having acute rejection, were analyzed. Immunohistochemical staining was performed for CD3+ (pan T cell), CD8+ (cytotoxic), CD4+ (helper), CD45RO+ (memory), CD45RA+ (naive), CD56+ (natural killer), CD68+ (macrophage), and CD8+ perforin+ cells. Fewer CD8+ and CD3+ cells were present in the lobular areas of biopsy specimens from patients who were successfully withdrawn from immunosuppression therapy (n = 6) compared with biopsy specimens from patients with nontolerant grafts (n = 9; 15 vs. 23 cells/high-power field [hpf] [P < .01] and 16 vs. 26 cells/hpf [P < .03], respectively) or biopsy specimens obtained during acute rejection (15 vs. 31 cells/hpf [P < .01] and 16 vs. 32 cells/hpf [P < .01]). Cell frequencies in the biopsy specimens of nontolerant long-term patients were similar to those found with acute rejection. Immunophenotyping the lobular inflammation within long-term liver allografts assists in identifying those patients in whom drug withdrawal is likely to be unsuccessful and in whom it is postulated a form of inactive, latent cellular rejection exists.

Tolerance in a rat cardiac allograft model after short-term treatment with LF 08-0299. Absence of clonal deletion and evidence of CD4+ suppressor cells

LF 08-0299 is a new immunosuppressive compound. In a fully mismatched rat cardiac allograft model (Dark Agouti [DA]-->Lewis [LEW]), long-term unresponsiveness was observed after LF 08-0299 short-term treatment (20 days). Survival of additional cardiac and skin DA allografts, and rejection of third-party (Brown Norway [BN]) skin allografts demonstrated induction of a donor-specific tolerance state. The aim of this study was to investigate mechanisms of cardiac acceptance in this model. LEW rats with long-term surviving heart grafts (LTS LEW) were examined for their immune proliferative and cytotoxic responses toward donors (DA) and third-party (BN) antigens. Normal proliferative responses were observed and limiting dilution analysis did not reveal a reduction of T cytotoxic cell precursors. In our model, tolerance exists despite the presence of cells reactive with donor alloantigens. In vivo adoptive transfer of serum from LTS LEW failed to transfer unresponsiveness, indicating that serum factors do not seem to be involved in tolerance maintenance. Transfer of spleen cells, obtained from LTS LEW, showed specific prolongation of DA cardiac allografts in syngeneic hosts. Moreover, these cells were able to induce the rejection of third-party BN grafts. These results suggest that although LTS LEW possessed suppressor cells, they remained immunocompetent in recognizing and responding to third-party alloantigens. Purified CD4+ cells transferred unresponsiveness to secondary hosts, but CD8+ cells did not. Taken together, these results suggest that tolerance to donor alloantigens after treatment with LF 08-0299 in the rat cardiac allograft model is most likely due to induction of specific CD4+ suppressor cell activity, rather than induction of suppressive serum factor and selective elimination of antidonor helper or cytotoxic cell precursors (clonal deletion).

CTLA4-Ig plus bone marrow induces long-term allograft survival and donor specific unresponsiveness in the murine model. Evidence for hematopoietic chimerism

Allograft rejection is dependent on T cell activation, which requires both the engagement of the T cell receptor by antigen in the context of the MHC molecules and costimulatory signals delivered by cell surface molecules such as B7-CD28/CTLA4 pathway. CTLA4-Ig is a fusion protein that blocks this pathway and has previously been shown to prolong both allograft and xenograft survival. The current study demonstrates markedly prolonged murine cardiac allograft survival and specific prolongation of secondary skin grafts using a combination of CTLA4-Ig plus donor bone marrow. A role for hematopoietic chimerism in the establishment of CTLA4-Ig-induced transplantation tolerance was investigated using reverse transcriptase polymerase chain reaction analysis of recipient tissues. Expression of donor-specific MHC class II transcripts in both peripheral and lymphoid tissues was demonstrated at greater than 200 days after transplant. To investigate the functional significance of this observation, heart donors, and donor bone marrow were irradiated before transplantation in CTLA4-Ig-treated recipients. A reduction in allograft survival was associated with irradiation of both the donor heart and the bone marrow. These results suggest that there may be a donor-derived radiosensitive element that enhances allograft survival in this model. Reverse transcriptase polymerase chain reaction analysis of allografts of tolerant and control animals at days 5, 8, and 12 after transplantation failed to demonstrate a dramatic difference in the expression of interleukin (IL)-2, IL-4, IL-10, and interferon-gamma message. Cytotoxicity effector transcripts were largely intact in CTLA4-Ig + bone marrow-treated recipients as they showed no decrease in intragraft granzyme, perforin, Fas, or Fas ligand transcripts during thr first 8 days after transplant. These results imply that complex mechanisms may be important for the induction and maintenance of transplantation tolerance in the CTLA4-Ig plus bone marrow murine cardiac allograft model.

Perforin expression in peripheral blood lymphocytes in rejecting and tolerant kidney transplant recipients

Perforin (P) is a cytolytic molecule expressed in the granules of cytolytic T cells and natural killer cells. Although cytotoxic cells have been implicated in graft rejection, no prospective clinical study has been published that examines the dynamics of perforin expressing cells in peripheral blood lymphocytes of transplanted patients. The cytofluorimetric assay developed in our laboratory previously for the simultaneous detection of intracellular perforin together with cell surface molecules was used for posttransplantation monitoring of patients, for the assessment of the efficiency of immunosuppressive treatment, and for the prediction of acute kidney transplant rejection and the stability of tolerance to long lived kidney transplants. Immunosuppression for the purpose of allotransplantation causes a decline in the number of perforin-expressing cells in peripheral blood. In contrast, in patients with clinical signs of acute rejection, the total number of perforin-expressing lymphocytes was increased in comparison with nonrejecting patients. Analyzing perforin-expressing subsets, rejection crises were accompanied by a relative decrease of perforin expression in the CD4+ subpopulation while increasing in the CD8+ subset. In the CD56+ and CD16+ NK subpopulations changes in perforin expression were mixed. In nonrejecting patients the ratio of perforin expression in CD4+ cells was high compared with CD8+ cells. Intensive therapy of acute rejection episodes with high doses of corticosteroids (methylprednisolonet [Solumedrol] bolus) strongly and significantly decreased the percentage of both, the subpopulations of perforin-positive T cells and the subpopulation of CD56+P+ NK cells. The lowest level of perforin expression, including low frequencies of perforin among CD8+ and CD4+ cells, was found in the group of patients tolerating transplanted kidneys for several years. These changes in perforin protein expression in peripheral blood can be used to discriminate between immunosuppressed patients who are immunologically quiescent and those who undergo transplant rejection. Our results confirm the hypothesis that cytotoxicity mediated by perforin may be an important effector mechanism in the rejection of allografted kidneys.