Donor-specific transfusions enhance the immunosuppressive effects of single-dose cyclosporine A and CTLA4-Ig but do not result in long-term graft acceptance in a histoincompatible model of rat lung allograft rejection

Clinical islet transplant: current and future directions towards tolerance

The ultimate goal of islet transplantation is to completely correct the diabetic state from an unlimited donor source, without the need for chronic immunosuppressive drug therapy. Although islet transplantation provides an opportunity to develop innovative strategies for tolerance in the clinic, both alloimmune and autoimmune barriers must be controlled, if stable graft function is to be maintained long-term. After islet extraction from the pancreas, the cellular graft may be stored in tissue culture or cryopreserved for banking, providing an opportunity not only to optimally condition the recipient but also to allow in vitro immunologic manipulation of the graft before transplantation, unlike solid organ grafts. As such, islets may be considered a "special case." Remarkable progress has occurred in the last three years, with dramatic improvements in outcomes after clinical islet transplantation. The introduction of a steroid-free, sirolimus-based, anti-rejection protocol and islets prepared from two (or rarely three) donors led to high rates of insulin independence. The "Edmonton Protocol" has been successfully replicated by other centers in an international multicenter trial. A number of key refinements in pancreas transportation, processing, purification on non-ficoll-based media, storage of islets in culture for two days and newer immunological conditioning and induction therapies have led to continued advancement through extensive collaboration between key centers. This review outlines the historical development of islet transplantation over the past 30 years, provides an update on current clinical outcomes, and summarizes a series of unique opportunities for development and early testing of tolerance protocols in patients.

Synergistic effects of CTLA-4Ig and sirolimus on orthotopic lung-allograft survival and histology

BACKGROUND AND AIMS

The combination of CTLA-4Ig with sirolimus can promote indefinite survival in allograft models for which CTLA-4Ig monotherapy is ineffective. We sought to determine whether a limited course of CTLA-4Ig and sirolimus would alter survival of rat orthotopic single-lung transplantations.

METHODS

Left lungs of Brown Norway rats were transplanted into four groups of Lewis recipients (n=6 per group): group 1, no treatment; group 2, mCTLA-4Ig (250 microg/day for 4 days); group 3, sirolimus (3 mg/kg per day for 14 days); group 4, combined therapy with sirolimus and mCTLA-4Ig. Graft survival was determined by daily radiologic examination. Histologic grading of rejection and immunohistochemical staining for T and B lymphocytes were carried out at the time of radiologic graft loss.

RESULTS

Rejection of lung allografts in group 1 occurred at a median of 6.5 days. Neither sirolimus nor mCTLA-4Ig monotherapy resulted in significant prolongation of graft survival (median 9.5 and 8.0 days, respectively). Graft survival in group 4 was significantly prolonged compared with all other groups (median 29.5 days), and a significant reduction in histologic grade of rejection was observed following combination therapy compared with all other groups. Infiltration by CD8+ve T cells at the time of rejection was proportionately greater than CD4+ve T-cell infiltration for groups 1, 2, and 3 but not for the combined-therapy group.

CONCLUSIONS

A brief course of combined mCTLA-4Ig and sirolimus prolongs graft survival, reduces severity of rejection, and attenuates CD8+ve T-cell infiltration of fully major histocompatibility complex mismatched lung allografts.

Prevention of acute lung allograft rejection in rat by CTLA4Ig

CTLA4 immunoglobulin (CTLA4Ig), which binds with a high affinity to B7-1 and B7-2, interrupts T-cell activation by inhibiting costimulatory signal. CTLA4Ig has been used in hopes of achieving antigen-specific tolerance induction in several solid organ transplants. In lung allograft rejection, however, its use has been controversial in terms of its effect on prevention of rejection. In the present study, the effect of murine CTLA4Ig on rat-lung allograft rejection was investigated. Rat left-lung transplantation was performed in an RT1 incompatible donor (Brown Norway; BN)-recipient (F344) combination. All allografts (n = 12) without any treatment were rejected within 7 days after transplantation. A single injection of murine form CTLA41g at a dose of 100 microg intraperitoneally (ip) or intravenously (iv) on day 1 post-transplantation achieved long-term graft survival (>90days) in 2/5 (40%) and 3/8 (38%), respectively. Moreover, 6/7 (86%) allografts in rats that received iv injection of 500 microg CTLA4Ig survived more than 90days. Allograft survival in the CTLA4Ig 500 microg iv recipient group was significantly longer than that in the no-treatment control or control immunoglobulin group (p <0.01). Four out of seven recipients bearing functional allografts for more than 90 days with the CTLA4Ig treatment accepted donor-specific skin grafts, whereas all third-party skin grafts (n=3) were rejected. Prevention of rat-lung allograft rejection could be achieved by intravenous administration of CTLA4Ig, resulting in long-term allograft survival with acceptance of donor-specific skin grafts.

Hydrophobic extracts of a Chinese herb (CMX-13) exhibit potent immunosuppressive properties and prevent acute rejection in a highly histoincompatible model of rat lung transplantation

BACKGROUND

The potential of higher plants as sources for new immunosuppressive medications is well recognized. In our experiments we investigated the immunosuppressive effect of a highly refined and potent extract of a Chinese herbal preparation, CMX-13, on inhibiting acute allograft rejection (AR) in a highly histoincompatible rat lung transplant model, BN-->LEW, and on lymphocyte activation and cytokine gene expression in vitro.

METHODS

Left lung transplants: the control group (group 1) received only dimethylsulfoxide (DMSO) which is the solvent for CMX-13. Group 2 received intramuscular cyclosporin A (CsA, 25 mg/kg) on day 2 posttransplant. Group 3 and 4 received i.p. CMX-13 (0.5 mg/day, low dose and 5 mg/day, high dose, respectively) on day 1, 2, and 3 posttransplant. All animals were killed on day 6 posttransplant. Several pathological categories of inflammation were examined. In vitro experiments: rat spleen cells were incubated with Con A or irradiated stimulator cells with/without serial dilutions of CMX-13 or CsA. Cell proliferation was measured by 3H-thymidine incorporation. mRNA expression of interleukin-2 and interferon-gamma was examined by reverse transcriptase-polymerase chain reaction.

RESULTS

The severity of AR in animals receiving high dose CMX-13 was significantly reduced (stage II, P<0.05) compared with controls (stage IV). Significant differences were also seen when more specific parameters of inflammation were examined (necrosis, 0 vs. 1.7+/-1.0, P<0.05; interalveolar hemorrhage, 0 vs. 3.0+/-0.9, P<0.05). The responses seen in the animals treated with high dose CMX-13 were similar to those in the CsA group. CMX-13 inhibited T cell proliferative responses induced by Con A and alloantigen stimulation in a dose-dependent manner that were similar to CsA. Interleukin-2, and interferon-gamma mRNA expression in Con A-stimulated spleen cells was not inhibited by CMX-13 although CsA showed significant inhibition.

CONCLUSIONS

1) CMX-13 significantly reduces the stage of AR and parameters of inflammation in a highly histoincompatible rat lung transplant model. 2) CMX-13 has equal potency to CsA in the inhibition of Con A and alloantigen stimulated rat spleen cell proliferation. 3) CMX-13 showed no inhibitory effects on IL-2 and gamma-IFN mRNA expression, suggesting that its mechanism of action is different from CsA. 4) CMX-13 or derivatives may have potential utility as an immunosuppressive agent(s) in modulation of AR and management of other inflammatory and immunological disorders.

CTLA4-Ig: a novel immunosuppressive agent

Activation of naive T-cells requires two signals: one is antigen-specific and based on T-cell receptor (TCR) recognition of a peptide-MHC complex and the second is antigen-nonspecific and delivered by specific T-cell receptors after ligation with their ligands (costimulatory molecules) expressed by antigen-presenting cells (APCs). Engagement of the B7 family of molecules on APCs with their T-cell associated ligands, CD28 and CTLA-4 (CD152), provides a pivotal costimulatoty signal in T-cell activation. The lack of costimulation after engagement of the T-cell receptor by antigen, results in a state of antigen-specific unresponsiveness, termed anergy. Manipulation of CD28/B7 pathway has therefore been envisioned as a potential strategy for achieving therapeutically useful immunosuppression or tolerance. CTLA4-Ig has been initially developed by Bristol-Myers Squibb as a competitive inhibitor of CD28/B7 pathway (BMS-188667). Thereafter, CTLA4-Ig was produced by Repligen and also in some individual laboratories. In various animal models, discussed in this paper, CTLA4-Ig has been shown to inhibit T-cell-dependent antibody responses, significantly prolong transplanted organ survival, induce long-term donor-specific tolerance in some models, slow progression of autoimmune disease and to have immunomodulatory function in several other immunological disease models. Recently, CTLA4-Ig has entered Phase I clinical trials for the treatment of psoriasis, a T-cell mediated skin disease and treatment of graft-versus-host disease in allogeneic bone marrow transplantation. Large clinical randomised trials on the use of CTLA4-Ig are missing, nevertheless, its immunosuppressive effects coupled with features such as specificity of interaction and low toxicity, make CTLA4-Ig a promising new therapeutic agent for induction of donor-specific immunological tolerance, the ultimate goal of clinical immunosuppression.

Down-modulation of host reactivity by anti-CD44 in skin transplantation

BACKGROUND

A major goal in transplantation medicine is to achieve donor-specific tolerance while sustaining unaltered immunoreactivity toward donor-independent stimuli. Pretransplant immunization and concomitant blockade of costimulatory molecules may be one way to achieve this goal. We investigated whether transplant acceptance could be achieved by sensitization with semiallogeneic blood and blockade of CD44s (standard isoform) or CD44v6 (variant exon 6), since the adhesion molecule CD44 is known to function as a costimulatory molecule in T-cell activation.

METHODS

Immunoregulatory regimens were examined in BDX rats that had received full-thickness (DA x BDX)F1 skin grafts by controlling graft acceptance and immunoreactivity.

RESULTS

When BDX rats received full-thickness (DA x BDX)F1 skin grafts together with either anti-CD44s or anti-CD44v6, graft rejection was delayed, but none of the animals accepted the graft. An analysis of immunoreactivity revealed reduced numbers of infiltrating lymphocytes in anti-CD44s- as well as anti-CD44v6-treated rats. Expansion of donor-specific helper and cytotoxic T cells was particularly impaired in anti-CD44v6-treated rats. The effect of anti-CD44s could not be intensified by presensitization with donor-derived blood. However, when rats received anti-CD44v6 concomitantly with presensitization, 75% permanently accepted the graft and 50% accepted a second graft provided they were continuously treated with anti-CD44v6 and received a low dose of cyclosporine (CsA) during the first weeks after grafting. The frequency of graft-reactive helper T cells was reduced to less than 10% of the level in controls, and cytotoxic T cells could hardly be detected.

CONCLUSION

According to the in vivo and the vitro analyses of the graft and the draining lymph nodes, anti-CD44s blocked homing of activated lymphocytes into the graft, while anti-CD44v6 inhibited clonal expansion of donor-specific T cells. Suppression by anti-CD44v6 apparently functioned distinctly to cyclosporine and was most effective in combination with presensitization. Since expression of CD44v6 on lymphocytes is restricted to a short period during lymphocyte activation, anti-CD44v6 treatment could lead to a quite specific immunosuppression during a limited time period.