EnGraft: a multicentre, open-label, randomised, two-arm, superiority study protocol to assess bioavailability and practicability of Envarsus® versus Advagraf™ in liver transplant recipients

BACKGROUND

Graft rejection and chronic CNI toxicity remain obstacles to organ transplant success. Current formulations of tacrolimus, such as Prograf® and Advagraf™, exhibit limitations in terms of pharmacokinetics and tolerability, related in part to suboptimal bioavailability. As dosing non-compliance can result in graft rejection, the once daily formulation of tacrolimus, Advagraf™, was developed (vs 2x/day Prograf®). Benefits of Advagraf™ are counterbalanced by delayed achievement of therapeutic trough levels and need for up to 50% higher doses to maintain Prograf®-equivalent troughs. Envarsus® is also a prolonged-release once-daily tacrolimus formulation, developed using MeltDose™ drug-delivery technology to increase drug bioavailability; improved bioavailability results in low patient drug absorption variability and less pronounced peak-to-trough fluctuations. In phase III de novo kidney transplant studies, Envarsus® proved non-inferior to twice-daily tacrolimus; however, no phase IV studies show superiority of Envarsus® vs Advagraf™ in de novo liver transplant (LTx) recipients.

METHODS

The EnGraft compares bioavailability and tests superiority of Envarsus® (test arm) versus Advagraf™ (comparator arm) in de novo LTx recipients. A total of 268 patients from 15 German transplant centres will be randomised 1:1 within 14 days post-LTx. The primary endpoint is dose-normalised trough level (C/D ratio) measured 12 weeks after randomisation. Secondary endpoints include the number of dose adjustments, time to reach first defined trough level and incidence of graft rejections. Additionally, clinical and laboratory parameters will be assessed over a 3-year period.

DISCUSSION

C/D ratio is an estimate for tacrolimus bioavailability. Improving bioavailability and increasing C/D ratio using Envarsus could reduce renal dysfunction and other tacrolimus-related toxicities; previous trials have shown that a higher C/D ratio (i.e. slower tacrolimus metabolism) is not only associated with improved renal function but also linked to reduced neurotoxic side effects. A higher C/D ratio could improve clinical outcomes for LTx recipients; EnGraft has begun, with one third of patients recruited by January 2022.

TRIAL REGISTRATION

This trial has been registered (4 May 2020) in the EU Clinical Trials Register, EudraCT-Nummer: 2020-000796-20. Additionally, this trial has been registered (22 January 2021) at ClinicalTrials.gov: NCT04720326. The trial received a favourable opinion from the concerned lead ethics committee at the University of Regensburg, under the reference 20-1842-112.

Hepatocellular carcinoma progression during bridging before liver transplantation

Background

Recipient selection for liver transplantation in hepatocellular carcinoma (HCC) is based primarily on criteria affecting the chance of long-term success. Here, the relationship between pretransplant bridging therapy and long-term survival was investigated in a subgroup analysis of the SiLVER Study.

Methods

Response to bridging, as defined by comparison of imaging at the time of listing and post-transplant pathology report, was categorized into controlled versus progressive disease (more than 20 per cent tumour growth or development of new lesions).

Results

Of 525 patients with HCC who had liver transplantation, 350 recipients underwent pretransplant bridging therapy. Tumour progression despite bridging was an independent risk factor affecting overall survival (hazard ratio 1.80; P = 0.005). For patients within the Milan criteria (MC) at listing, mean overall survival was longer for those with controlled versus progressive disease (6.8 versus 5.8 years; P < 0.001). Importantly, patients with HCCs outside the MC that were downsized to within the MC before liver transplantation had poor outcomes compared with patients who never exceeded the MC (mean overall survival 6.2 versus 6.6 years respectively; P = 0.030).

Conclusion

Patients with HCCs within the MC that did not show tumour progression under locoregional therapy had the best outcomes after liver transplantation. Downstaging into the limits of the MC did not improve the probability of survival.

Prognostic factors determining the long-term success of liver transplantation in patients with hepatocellular carcinoma are still under discussion. A subgroup analysis of the SiLVER trial showed that disease control under bridging therapy is strongly associated with improved prognosis in terms of overall survival. However, in tumours exceeding the limits of the Milan criteria, downstaging did not restore the probability of survival compared with that of patients within the Milan criteria.

Extracellular Citrate in Health and Disease

Citrate is one of the major substrates for intracellular metabolism. The extracellular level of citrate is stable in blood but varies locally, with slightly increased levels in brain and high levels in prostate. Recent metabolomics research suggests that citrate level is a potential harbinger of different pathophysiological states; its decrease has been correlated with male infertility, brain diseases and metastatic cancer. In this review we discuss the role of citrate as an energy substrate for sperm. We also review the function of citrate released by astrocytes in the normal operation of neurons, and consequently we suggest a potential role of neuronal plasma membrane citrate transporters in mental disorders. Finally, we review recent relevant publications studying blood, urine and tissue citrate levels in cancer patients and hypothesize that extracellular citrate supports cancer cell metabolism critical for metastasis. Despite the importance of extracellular citrate in physiological and pathophysiological processes, surprisingly little is known about citrate synthesis in specialized cells, or about citrate transporters controlling citrate movement across various membranes. Determination of the molecular origin of citrate transporters in astrocytes, sperm and cancer cells could offer novel therapeutic targets and the possibility to pharmacologically regulate citrate release and uptake for preventing male infertility, treating mental diseases and targeting cancer.

Basophils Trigger Fibroblast Activation in Cardiac Allograft Fibrosis Development

Fibrosis is a major component of chronic cardiac allograft rejection. Although several cell types are able to produce collagen, resident (donor-derived) fibroblasts are mainly responsible for excessive production of extracellular matrix proteins. It is currently unclear which cells regulate production of connective tissue elements in allograft fibrosis and how basophils, as potential producers of profibrotic cytokines, are involved this process. We studied this question in a fully MHC-mismatched model of heart transplantation with transient depletion of CD4(+) T cells to largely prevent acute rejection. The model is characterized by myocardial infiltration of leukocytes and development of interstitial fibrosis and allograft vasculopathy. Using depletion of basophils, IL-4-deficient recipients and IL-4 receptor-deficient grafts, we showed that basophils and IL-4 play crucial roles in activation of fibroblasts and development of fibrotic organ remodeling. In the absence of CD4(+) T cells, basophils are the predominant source of IL-4 in the graft and contribute to expansion of myofibroblasts, interstitial deposition of collagen and development of allograft vasculopathy. Our results indicated that basophils trigger the production of various connective tissue elements by myofibroblasts. Basophil-derived IL-4 may be an attractive target for treatment of chronic allograft rejection.

Cyclosporine A Inhibits the T-bet-Dependent Antitumor Response of CD8(+) T Cells

Transplant recipients face an increased risk of cancer compared with the healthy population. Although several studies have examined the direct effects of immunosuppressive drugs on cancer cells, little is known about the interactions between pharmacological immunosuppression and cancer immunosurveillance. We investigated the different effects of rapamycin (Rapa) versus cyclosporine A (CsA) on tumor-reactive CD8(+) T cells. After adoptive transfer of CD8(+) T cell receptor-transgenic OTI T cells, recipient mice received either skin grafts expressing ovalbumin (OVA) or OVA-expressing B16F10 melanoma cells. Animals were treated daily with Rapa or CsA. Skin graft rejection and tumor growth as well as molecular and cellular analyses of skin- and tumor-infiltrating lymphocytes were performed. Both Rapa and CsA were equally efficient in prolonging skin graft survival when applied at clinically relevant doses. In contrast to Rapa-treated animals, CsA led to accelerated tumor growth in the presence of adoptively transferred tumor-reactive CD8(+) OTI T cells. Further analyses showed that T-bet was downregulated by CsA (but not Rapa) in CD8(+) T cells and that cancer cytotoxicity was profoundly inhibited in the absence of T-bet. CsA reduces T-bet-dependent cancer immunosurveillance by CD8(+) T cells. This may contribute to the increased cancer risk in transplant recipients receiving calcineurin inhibitors.

mTOR inhibition improves fibroblast growth factor receptor targeting in hepatocellular carcinoma

BACKGROUND

Systemic therapy has proven only marginal effects in hepatocellular carcinoma (HCC) so far. The aim of this study was to evaluate the effect of targeting fibroblast growth factor receptor (FGFR) on tumour and stromal cells in HCC models.

METHODS

Human and murine HCC cells, endothelial cells (ECs), vascular smooth muscle cells (VSMCs), hepatic stellate cells (HSCs), human HCC samples, FGFR inhibitor BGJ398 and mammalian target of rapamycin (mTOR) inhibitor rapamycin were used. Effects on growth, motility, signalling and angiogenic markers were determined. In vivo subcutaneous and syngeneic orthotopic tumour models were used.

RESULTS

In tumour cells and ECs, targeting FGFR showed significant inhibitory effects on signalling and motility. Minor effects of FGFR inhibition were observed on VSMCs and HSCs, which were significantly enhanced by combining FGFR and mTOR blockade. In vivo daily (5 mg kg(-1)) treatment with BGJ398 led to a significant growth inhibition in subcutaneous tumour models, but only a combination of FGFR and mTOR blockade impaired tumour growth in the orthotopic model. This was paralleled by reduced tumour cell proliferation, vascularisation, pericytes and increased apoptosis.

CONCLUSIONS

Targeting FGFR with BGJ398 affects tumour cells and ECs, whereas only a combination with mTOR inhibition impairs recruitment of VSMCs and HSCs. Therefore, this study provides evidence for combined FGFR/mTOR inhibition in HCC.

Inhibition of innate co-receptor TREM-1 signaling reduces CD4(+) T cell activation and prolongs cardiac allograft survival

The innate receptor "triggering-receptor-expressed-on-myeloid-cells-1" (TREM-1) enhances downstream signaling of "pattern recognition receptor" (PRR) molecules implicated in inflammatory responses. However the mechanistic role of TREM-1 in chronic heart rejection has yet to be elucidated. We examined the effect of TREM-1(+) antigen-presenting cells (APC) on alloreactive CD4(+) lymphocytes. Bm12 donor hearts were transplanted into wild-type MHC-class-II-mismatched C57BL/6J recipient mice. Progressive allograft rejection of bm12-donor hearts with decreased organ function, severe vasculopathy and allograft fibrosis was evident within 4 weeks. TREM-1(+) CD11b(+) MHC-II(+) F4/80(+) CCR2(+) APC and IFNγ-producing CD4(+) cells were detected during chronic rejection. Peptide inhibition of TREM-1 attenuated graft vasculopathy, reduced graft-infiltrating leukocytes and prolonged allograft survival, while being accompanied by sustained low levels of CD4(+) and CD8(+) cell infiltration. Remarkably, temporary inhibition of TREM-1 during early immune activation was sufficient for long-term allograft survival. Mechanistically, TREM-1 inhibition leads to reduced differentiation and proliferation of IFNγ-producing Th1 cells. In conclusion, TREM-1 influences chronic heart rejection by regulating the infiltration and differentiation of CD4(+) lymphocytes.

Mesenchymal stem cells are short-lived and do not migrate beyond the lungs after intravenous infusion

Mesenchymal stem cells (MSC) are under investigation as a therapy for a variety of disorders. Although animal models show long term regenerative and immunomodulatory effects of MSC, the fate of MSC after infusion remains to be elucidated. In the present study the localization and viability of MSC was examined by isolation and re-culture of intravenously infused MSC. C57BL/6 MSC (500,000) constitutively expressing DsRed-fluorescent protein and radioactively labeled with Cr-51 were infused via the tail vein in wild-type C57BL/6 mice. After 5 min, 1, 24, or 72 h, mice were sacrificed and blood, lungs, liver, spleen, kidneys, and bone marrow removed. One hour after MSC infusion the majority of Cr-51 was found in the lungs, whereas after 24 h Cr-51 was mainly found in the liver. Tissue cultures demonstrated that viable donor MSC were present in the lungs up to 24 h after infusion, after which they disappeared. No viable MSC were found in the other organs examined at any time. The induction of ischemia-reperfusion injury in the liver did not trigger the migration of viable MSC to the liver. These results demonstrate that MSC are short-lived after i.v. infusion and that viable MSC do not pass the lungs. Cell debris may be transported to the liver. Long term immunomodulatory and regenerative effects of infused MSC must therefore be mediated via other cell types.

Relevance of maintenance triple-drug immunosuppression to bridle the amplification of rat cytomegalovirus infection after experimental lung transplantation

Immunosuppressive therapy required to treat rejection after lung transplantation (LTx) contributes significantly to the pathogenesis of cytomegalovirus (CMV) infection and disease. In a weak allogeneic left LTx model in the rat (Fisher 344 [F344] to Wistar Kyoto [WKY] rats) we analyzed the influence of acute CMV infection on postoperative day (POD) 3, with application of standard triple-drug immunosuppression (TD-IS) (cyclosporin A, azathioprine, prednisolone) on late outcome after LTx. Native right lungs and syngeneic grafts (WKY to WKY) served as controls. Rats were sacrificed on POD 15, 30, 60, and 100. TD-IS completely prevented acute and chronic rejection in non-infected rats. Allografts of CMV-infected rats treated with TD-IS showed only mild perivascular infiltrations in 6/10 rats (POD 15 and 30), which persisted up to POD 100 in 4/10 rats. In the long-term course, mild isolated interstitial and alveolar changes were found in 40% of these animals. In conclusion, rat CMV infection partially neutralized the immunosuppressive effect of TD-IS. However, an amplification of CMV infection under TD-IS can be controlled and does not result in fatal outcome.

Effects of ASA404, a vascular disrupting agent, on tumor growth of gastric cancer in an experimental model

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Background: A functional vascular system is essential for growth of solid malignancies including gastric cancer. For establishment and maintenance of such a vascular system endothelial cells (ECs) and pericytes (e.g. vascular smooth muscle cells, VSMC) are required. We hypothesized that targeting tumor vasculature with the vascular disrupting agent (VDA) ASA404 (Novartis Oncology) reduces tumor growth in a model of gastric cancer.

Methods: Gastric cancer (GC) cell lines, ECs and VSMCs were used for experiments. Effects of ASA404 on growth of GC, EC and VSMC were assessed by MTT assays. Impact of ASA404 (20 mg/kg on day 1, 5, 9) in combination with paclitaxel (10 mg/kg on day 1 and 7) on tumor growth was assessed in a subcutaneous tumor model. Treatment was started when tumors reached a size of approximately 200 mm3. Tumors were measured and harvested on day 23 for IHC analyses. Effect of ASA404 on blood perfusion of tumors during therapy was monitored by contrast-enhanced ultrasound (CEUS).

Results: In vitro ASA404 impaired growth of ECs and VSMCs upon stimulation with condition media from gastric cancer cells. No direct effect on tumor cells was observed. In vivo, treatment with ASA404 led to marked decrease of tumor perfusion and an increase of necrosis as determined by CEUS. Furthermore, combination of ASA404 with paclitaxel showed significant reduction of tumor growth compared to controls (p < 0.05). In addition, tumor vascularisation and tumor cell proliferation were significantly reduced as determined by CD31-positive vessel area and BrdU-positive cells (p < 0.05).

Conclusions: Combination of the VDA ASA404 with paclitaxel impairs tumor growth and perfusion of gastric cancer in an experimental model. Hence, targeting tumor vasculature with ASA404 appears to be a promising strategy for therapy of gastric cancer.

No significant financial relationships to disclose.

Signal transducer and activator of transcription 5b (STAT5b) as a novel target for anti-neoplastic therapy in human pancreatic cancer

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Background: Activation of signal transducer and activator of transcription 5b (STAT5b) has been associated with tumor growth and metastases in various tumor entities. A number of cytokines, growth factors, and oncogenes that can induce STAT5b activity are also implicated in pancreatic cancer growth and metastases. Hence, we sought to determine STAT5b expression in human pancreatic cancer specimen and effects of selective STAT5b inhibition on pancreatic cancer cells.

Methods: Expression of STAT5b in human pancreatic adenocarcinomas was determined by immunohistochemistry. For in vitro experiments, human pancreatic cancer cell lines (BxPC-3, HPAF-II, L3.6pl) were used. Cancer cells were transfected with STAT5b shRNA plasmid to create stable STAT5b knock-down. Effects of STAT5b inhibition on growth and motility of tumor cells was investigated by MTT and modified Boyden chamber assays. In vivo effects of STAT5b blockade were determined in subcutaneous mouse model.

Results: Nuclear expression of STAT5b was detected in 42/80 human pancreatic adenocarcinomas. In human cancer cell lines, stable knock-down of STAT5b had no effect on growth of tumor cells in vitro. However, tumor cell motility was significantly reduced upon STAT5b blockade (p<0.05). Moreover, expression of various signaling intermediates and transcription factors including c-myc was impaired upon STAT5b knock-down. In a subcutaneous tumor model, inhibition of STAT5b led to significantly reduced tumor growth (p<0.05) which was also reflected by final tumor weights (p<0.05). Furthermore, as revealed by immunohistochemistry, blockade of STAT5b significantly reduced tumor vascularization in vivo (p<0.05).

Conclusions: STAT5b is expressed in human pancreatic adenocarcinomas. Blockade of STAT5b impairs cancer cell motility in vitro, suggesting antimetastatic potential. Moreover, inhibition of STAT5b significantly reduces tumor growth and tumor vascularization in vivo. Hence, STAT5b might be an interesting target for antineoplastic therapy in human pancreatic cancer.

No significant financial relationships to disclose.

Mesenchymal stem cells together with mycophenolate mofetil inhibit antigen presenting cell and T cell infiltration into allogeneic heart grafts

Donor-derived mesenchymal stem cells (MSC) can induce long-term acceptance in a rat heart transplantation model when injected prior to transplantation in combination with mycophenolate mofetil (MMF). In contrast, MSC alone cause accelerated graft rejection. To better understand these conflicting data we studied the effects of MSC and MMF on lymphocyte populations in heart allografts and secondary lymphatic organs. Allogeneic MSC injected prior to transplantation are immunogenic in this model because activated CD4+ and CD8+ cells emerged earlier in secondary lymphatic organs of MSC- and MSC/MMF-treated animals, compared to animals not treated with MSC. Consequently T cells infiltrated the grafts of MSC-only treated animals promptly causing accelerated graft rejection. However, few T cells or antigen-presenting cells (APC) infiltrated the grafts of animals treated with MSC and MMF. Consistent with this finding, intercellular adhesion molecule 1 (ICAM-1) and E-selectin was down-regulated exclusively in MSC/MMF-treated grafts, indicating that MSC together with MMF interfere with endothelial activation. Additionally, the presence of interferon-gamma (IFN-γ) enhanced MSC capabilities to suppress T cell proliferation in vitro. Interestingly, MMF did not influence serum IFN-γ levels in vivo. Together, our data indicate that MSC pre-activate T cells, but co-treatment with MMF eliminates these T cells, decreases intragraft APC and T cell trafficking by inhibiting endothelial activation, and allows IFN-γ stimulation of suppressive MSC.

Early and late effects of the immunosuppressants rapamycin and mycophenolate mofetil on UV carcinogenesis

Increased skin cancer risk in organ transplant recipients has been experimentally emulated with enhanced UV carcinogenesis from administering conventional immunosuppressants. However, newer generation immunosuppressive drugs, rapamycin (Rapa) and mycophenolate mofetil (MMF), have been shown to impair angiogenesis and outgrowth of tumor implants. To ascertain the overall effect on UV carcinogenesis, Rapa and MMF were admixed into the food pellets of hairless SKH1 mice receiving daily sub-sunburn UV dosages. With immunosuppressive blood levels neither of the drugs affected onset of tumors (<2 mm), but in contrast to MMF, Rapa significantly increased latency of large tumors (>or=4 mm, medians of 190 vs 125 days) and reduced their multiplicity (1.6 vs 4.5 tumors per mouse at 200 days). Interestingly, tumors (>2 mm) from the Rapa-fed group showed a reduction in UV-signature p53 mutations (39% vs 90%) in favor of mutations from putative base oxidation. This shift in mutation spectrum was not essentially linked to the reduction in large tumors because it was absent in large tumors similarly reduced in number when feeding Rapa in combination with MMF, possibly owing to an antioxidant effect of MMF. Significantly fewer tumor cells were Vegf-positive in the Rapa-fed groups, but a correspondingly reduced expression of Hif1alpha target genes (Vegf, Ldha, Glut1, Pdk1) that would indicate altered glucose metabolism with increased oxidative stress was not found. Remarkably, we observed no effect of the immunosuppressants on UV-induced tumor onset, and with impaired tumor outgrowth Rapa could therefore strongly reduce skin carcinoma morbidity and mortality rates in organ transplant recipients.

Mesenchymal stem cells require a sufficient, ongoing immune response to exert their immunosuppressive function

Mesenchymal stem cells (MSC) have emerged to be one of the most promising candidates for cellular immunotherapy in solid organ transplantation because the reduction of conventional immunosuppression is highly desirable. However, little is known about the details of MSC-mediated immunomodulation and their clinical relevance. To address conflicting studies about the ability of MSC to suppress or augment T-cell proliferation, we introduce a transplantation-related rat model that allows studying the influence of MSC on alloproliferation. Hearts transplanted in a fully allogeneic transplantation model (LEW to ACI) were rejected earlier when recipients were pretreated with donor MSC, indicating activation of T cells in vivo. In additional co-culture experiments, T cells were differently affected by allogeneic MSC depending on the extent of previous activation: When conditions were rendered proinflammatory by adding high concanavalin A (ConA) concentrations or proinflammatory cytokines (interferon-gamma, interleukin-2, or tumor necrosis factor-alpha), MSC inhibited proliferation. Application of low doses of ConA or anti-inflammatory cytokines like IL-10 abrogated the suppressive effect of MSC. For application of MSC in solid organ transplantation, it will be important to further describe this switch effect of MSC function.

VEGF: a surrogate marker for peripheral vascular disease

This study aims to evaluate the value of VEGF as a surrogate marker for peripheral vascular disease (PVD). Prior to treatment, serum VEGF levels were evaluated by enzyme-linked immunosorbent assay (ELISA) in 293 PVD patients. Risk factors and clinical parameters of PVD were documented. Twenty-six age-matched healthy volunteers served as controls. Serum VEGF values strongly correlated with Fontaine stages (p<0.006, stage IV vs. controls). High VEGF values prior to treatment were associated with poor outcome. Serum VEGF appears to indicate the severity of PVD and might serve as a surrogate indicator of disease severity.

Fighting malignancy in organ transplant recipients

The development of malignancy in immunosuppressed organ transplant recipients has recently gained increasing attention. Increased awareness of this problem has come from recent data indicating that vascular disease and cancer are the leading causes of death in transplant recipients. Despite the realization of this fact, few efforts have been made to thwart deaths due to cancer in transplant recipients. However, now that many transplant recipients maintain their organ allografts for decades, the risk for cancer is increasing even more, exposing a need for possible solutions. Fundamentally, transplant recipients are at a high risk for cancer because the immunosuppressive drugs used in their treatment regimen suppress immune reactivity against arising cancer cells. Some of these drugs directly impede DNA repair, induce cancer cell aggressiveness, and promote tumor angiogenesis. In situations where cancer has developed in transplant recipients, one potential action is to reduce their daily immunosuppression. In some cases immunosuppression minimization can reduce tumor growth or even result in tumor regression, but the threat of rejection increases substantially. Another possible solution is to move toward mammalian target of rapamycin (mTOR)-based immunosuppression, use of which has been experimentally demonstrated to have both immunosuppressive and potent anticancer effects. Clinical studies are presently underway to test this idea, which could help to alleviate the problem of cancer in transplant recipients. In this overview, the topic of cancer in transplant recipients will be addressed, as well as new approaches to reduce this increasingly recognized problem in transplantation.

Immunosuppression for liver transplantation

In the last few decades liver transplantation (LTx) has become a reliable life-saving procedure for patients with chronic end-stage liver diseases. LTx has an outstanding success rate in the first few years after allografting, especially considering that many patients are on the brink of survival at the time of transplantation. The success of LTx is owed to the pioneers who developed the surgical procedures and to researchers who discovered the medications to help prevent immunological rejection of allografts. However, several problems continue to impose serious limits on LTx today, including a shortage of donor livers, recurrence of disease (eg, hepatitis, hepatocellular cancer), preservation of long-term allograft function and the side effects of anti-rejection drugs. While the dilemma of organ shortage is not a focus of this review, we will address the latter issues as they relate to the "oldest" and "newest" approaches to immunosuppression, and discuss the prospect that recipients could potentially be made immunologically tolerant to liver transplants. Due to the critical shortage of organs, new strategies to preserve transplanted liver allografts for the longest possible time are of paramount importance.

Mesenchymal stem cells can induce long-term acceptance of solid organ allografts in synergy with low-dose mycophenolate

The induction of tolerance towards allogeneic solid organ grafts is one of the major goals in transplantation medicine. Mesenchymal stem cells (MSC) inhibit the immune response in vitro, and thus are promising candidate cells to promote acceptance of transplanted organs in vivo. Such novel approaches of tolerance induction are needed since, to date, graft acceptance can only be maintained through life-long treatment with unspecific immunosuppressants that are associated with toxic injury, opportunistic infections and malignancies. We demonstrate that donor-derived MSC induce long-term allograft acceptance in a rat heart transplantation model, when concurrently applied with a short course of low-dose mycophenolate. This tolerogenic effect of MSC is at least partially mediated by the expression of indoleamine 2,3-dioxygenase (IDO), demonstrated by the fact that blocking of IDO with 1-methyl tryptophan (1-MT) abrogates graft acceptance. Moreover we hypothesize that MSC interact with dendritic cells (DC) in vivo, because allogeneic MSC are rejected in the long-term but DC acquire a tolerogenic phenotype after applying MSC. In summary, we demonstrate that MSC constitute a promising tool for induction of non-responsiveness in solid organ transplantation that warrants further investigation in clinical trials.

Short-term treatment with anti-CD44v7 antibody, but not CD44v4, restores the gut mucosa in established chronic dextran sulphate sodium (DSS)-induced colitis in mice

Increased expression of CD44 variant isoforms have been shown on the inflammatory infiltrates in human and mouse colitis and blockade or deletion of CD44 isoforms inhibit experimental colitis. The objective of this study was to find out if short-term treatment of CD44 antibodies specific to CD44v7, but not to other variant isoforms, suppresses leucocyte-endothelial interaction in chronic dextran sodium sulphate (DSS)-induced colitis in mice. Chronic colitis was induced by oral administration of four cycles of 5% DSS in BALB/c mice. Expression of CD44 was investigated on isolated mononuclear cells of the gut immune system. In established colitis, mice were treated with antibodies against CD44v7 or CD44v4 three times in 7 days. Intravital microscopy was used to study leucocyte-endothelial interactions and leucocyte extravasation. As a marker of inflammatory infiltrates myeloperoxidase was quantified in gut tissue. CD44-induced apoptosis was determined by fluorescence staining of hypodiploidic cell nuclei. In chronic DSS-induced colitis both CD44 variant isoforms, v4 and v7 were significantly up-regulated on mononuclear cells. However, whereas anti-CD44v7 antibody treatment induced a marked restoration of the gut mucosa and significantly reduced endothelial sticking and extravasation of circulating leucocyte in vivo (P < 0.01), application of anti-CD44v4 or an isotype control antibody had no anti-inflammatory effect. A significant reduction of myeloperoxidase activity was detected after blockade of CD44v7, but not v4. Short-term treatment with anti-CD44v7 antibody blocks T cell extravasation and recruitment to the intestinal mucosa and cures established experimental colitis.

Preferential migration of CD62L cells into the appendix in mice with experimental chronic colitis

BACKGROUND

Clinical and experimental studies suggest that appendectomy can protect against development of ulcerative colitis and Crohn's disease. However, how T cells in the appendix affect the development of colitis has not been clarified.

AIM

To investigate the in vivo migration and activation of colitis-inducing CD62L+ cells during development of chronic colitis.

METHODS

CD62L+CD4+ cells were fluorescently labeled and transferred to severe combined immunodeficient (SCID) mice to induce colitis. In vivo migration of T cells into the mucosa of the appendix and colon was quantified by in vivo microscopy after 7 weeks. In a second experiment, unlabeled CD62L+CD4+ cells were transferred, reisolated after 7 weeks, and adhesion molecule (integrin alpha4beta7) and costimulatory molecule (CD154) expression was analyzed.

RESULTS

Six to eight weeks after CD62L+CD4+ cell transfer, SCID mice developed chronic colitis. In vivo microscopic analysis demonstrated a preferential migration of fluorescence-labeled CD62L+CD4+ cells into the mucosa of the appendix versus the colon. Re-isolation of lamina propria cells from mice with colitis confirmed that CD62L+CD4+ cell migration was significantly enhanced in the appendix, compared to the colon (3.5-fold). Furthermore, a higher proportion of CD62L+CD4+ cells re-isolated from the appendix expressed integrin alpha4beta7 and CD154 than from the colon.

CONCLUSION

This study demonstrates the preferential migration of CD62L+CD4+ cells into the appendix as compared to the colon. This migration pattern correlated with upregulation of integrin alpha4beta7 and CD154 (CD40 ligand) on T cells. Our results suggest an important role of the appendix in the pathogenesis of colitis.

Conditioning of liver grafts with prostaglandins improves bile acid transport

INTRODUCTION

Conditioning of liver grafts by bolus pretreatment with prostaglandins has been previously demonstrated to improve hepatic bile flow. However, the underlying mechanisms have not been investigated. To elucidate whether improved bile flow after prolonged ischemia is due to maintained bile acid secretion or due to increased paracellular permeability, we performed a study using increasing doses of the marker acid taurocholate in the isolated perfused rat liver system.

METHODS

Livers were harvested from adult Lewis rats and stored for 24 hours in UW solution. Pretreatment of livers was performed 1 minute before preservation. One group received prostaglandin I2, the second group received prostaglandin E1, and the control group was treated with saline. After 24 hours of cold storage the grafts were investigated in the isolated perfused rat liver system by perfusion with an oxygenated Krebs-Ringer-Henseleit buffer. Increasing doses of the radiolabeled marker bile acid taurocholate were infused to investigate bile acid transport.

RESULTS

Bile flow and bile acid output were increased by pretreatment of the livers with prostaglandin I2 and prostaglandin E1, as compared to the control group. More specifically, the maximum transport rate was tripled by prostaglandin I2 and by prostaglandin E1 preconditioning of liver grafts, in comparison to the control group (P < .01 vs prostaglanin I2 and E1).

CONCLUSION

The results clearly demonstrate that increased bile flow after conditioning of liver grafts with prostaglandins is not due to increased paracellular permeability but is based on markedly improved bile acid output.

Therapeutic success and efficacy of nonviral liposomal cDNA gene transfer to the skin in vivo is dose dependent

It is well documented that responses to growth factor treatment typically display bell-shaped dose responses that can significantly affect efficacy. Here we tested the hypothesis that nonviral liposomal gene delivery also displays this characteristic. We chose two different growth factors, keratinocyte growth factor (KGF) and insulin-like growth factor-I (IGF-I) CMV-driven transfecting constructs at three different concentrations and assessed efficacy on several physiological parameters that are descriptive of wound healing progress in a burn-wound healing model. Rats were given a 60% TBSA scald burn and randomly divided into one of seven groups to receive weekly subcutaneous injections of liposomes containing the cDNA for KGF (0.2 microg, 2.2 microg, or 22.2 microg), or liposomes containing the cDNA for IGF-I (0.2 microg, 2.2 microg, or 22.2 microg) at various concentrations, but constant liposome:DNA ratios and a LacZ gene (0.2 microg) CMV-driven construct for beta-galactosidase as vehicle and marker gene. Transfection was confirmed by histology for beta-galactosidase. Physiological efficacy was evaluated by measuring the wound healing parameters that define dermal and epidermal regeneration. Transfection products were found in the cytoplasm of rapidly dividing cells of the granulation tissue. Different doses of the nonviral cDNA gene transfer coding for KGF or IGF-I resulted in different outcomes for dermal and epidermal regeneration. There was a dose-dependent response to both growth factor gene transfers that was not dissimilar from that typically displayed by treatment with growth factor proteins. Both concentrations below and above the optimal concentration of DNA:liposomal preparations did not yield the results observed at the optimal concentration.

Local secretion of TNF-alpha from the liver does not correlate with endotoxin, IL-6, or organ function in the early phase after orthotopic liver transplantation

Hepatic ischemia/reperfusion leads to an excessive release of proinflammatory cytokines, which promotes local and remote cell damage. The value of cytokine measurement in humans for predicting graft function after orthotopic liver transplantation (OLT) remains unclear. Therefore, in this study, tumor-necrosis-factor-alpha (TNF-alpha), interleukin-6 (IL-6), and endotoxin (ET) levels were determined in the blood taken from the hepatic veins of 31 patients who underwent OLT. Peak levels of TNF-alpha in hepatic venous blood were measured shortly after reperfusion and were significantly higher than concentrations in the systemic circulation. IL-6 concentrations, peaking 90 min after reperfusion, only correlated with postoperative pulmonary dysfunction. ET was detectable in 21 patients, but levels did not correlate with either IL-6 or TNF-alpha concentrations. Additionally, serum cytokine levels did not correlate with the duration of ischemia or with histological changes seen in liver biopsies. In general, our study suggests that local secretion of cytokines does not predict liver function in the early posttransplant phase.

A primary tumor promotes dormancy of solitary tumor cells before inhibiting angiogenesis

Mechanisms that regulate the transition of micrometastases from clinically undetectable and dormant to progressively growing are critically important but poorly understood in cancer biology. Here we examined the effect of a primary tumor on the growth of solitary tumor cells in the mouse liver, as well as on the development of tumor angiogenesis in a dorsal skin-fold chamber. s.c. placement of a CT-26 (BALB/c-derived mouse colon carcinoma) primary tumor markedly inhibited development of liver metastasis in BALB/c mice after subsequent intraportal injection of tumor cells. Dorsal skin-fold chamber experiments showed that this growth inhibition paralleled a strong antiangiogenic effect by the primary tumor. Furthermore, intravital microscopy of the liver after intraportal injection of green fluorescent protein-expressing tumor cells showed that primary tumors promoted dormancy of single tumor cells for up to 7 days. Immunohistological staining for Ki-67 confirmed that these solitary cells were indeed dormant. In contrast, in the absence of a primary tumor, GFP-expressing tumor cells quickly developed into micrometastases. Thus, primary CT-26 tumor implants nearly abrogated tumor metastasis by inhibition of angiogenesis and by promoting a state of single-cell dormancy. Knowledge of the mechanism underlying this dormancy state could result in the development of new therapeutic tools to fight cancer.

Soluble donor MHC class I gene transfer to thymus promotes allograft survival in a high-responder heart transplant model

Thymic selection of self and non-self-reactive lymphocytes is a process that may be targeted to induce donor-specific immunologic unresponsiveness in organ transplantation. In the present study, gene transfer was used to preexpose the recipient thymus to soluble donor-specific MHC class I molecules prior to heart transplantation in the high-responder ACI (RT1a) to Lewis (RT1l) rat strain combination. Specifically, cultured Lewis hepatocytes were transfected with DNA encoding a secreted form of the donor allo-MHC class I antigen, RT1.Aa. Seven days prior to ACI heart transplantation, genetically altered recipient-strain hepatocytes were injected into the thymus of Lewis recipients which also received a dose of antilymphocyte serum (ALS). Results showed that treatment with both ALS and soluble donor MHC-expressing hepatocytes prolonged transplant survival time by twofold, compared to injection of control hepatocytes and ALS. Therefore, intrathymic gene therapy delivery of soluble donor MHC molecules may be useful for promoting allograft survival in heart transplantation.

Immunologic considerations for therapeutic strategies utilizing allogeneic hepatocytes: hepatocyte-expressed membrane-bound major histocompatibility complex class I antigen sensitizes while soluble antigen suppresses the immune response in rats

Understanding the immunologic effects of hepatocytes is critical because of the potential to use these cells for bioartificial livers, as a vehicle for gene transfer, and as a means to induce donor-specific immunosuppression in organ transplantation. However, this understanding is complicated by the fact that hepatocytes express membrane-bound and soluble forms of major histocompatibility complex (MHC) class I antigen, each with the potential to induce different immune responses. In the present study we first determined the immunologic effect of normal donor-derived hepatocytes in a rat heart transplant model. We then used ex vivo hepatocyte gene transfer to examine the immunologic effects of different forms of hepatocyte-expressed MHC class I antigen. Results showed that intrasplenic injection of purified, donor-strain-specific hepatocytes into recipients primes alloimmunity, as evidenced by acceleration of heart allograft rejection. Interestingly, injection of autologous hepatocytes transfected ex vivo with DNA encoding only membrane-bound donor MHC class I antigen (RT1.A(a)) also accelerated allograft rejection. However, hepatocytes transfected to express only secreted donor MHC antigen prolonged transplant survival. Limiting-dilution analysis of lymphocytes from animals treated with hepatocytes producing only secreted alloantigen showed an antigen-specific reduction in cytotoxic T lymphocyte (CTL) and helper T lymphocyte (HTL) precursors. Further analysis of CTL populations by flow cytometry revealed a relatively high percentage of nonviable cells, implying that soluble antigen promotes allospecific CTL death. In summary, this study suggests that hepatocyte-expressed MHC class I molecules have opposing immunologic effects, with the membrane-bound antigen inducing immunologic sensitization, and the soluble antigen promoting donor-specific immunosuppression.

Effective use of donor MHC class I gene therapy in organ transplantation: prevention of antibody-mediated hyperacute heart allograft rejection in highly sensitized rat recipients

Immunologically sensitized recipients present one of the most critical problems in clinical organ transplantation today, since preformed antibodies rapidly destroy donor tissue expressing specific MHC class I antigens (Ag). Therefore, sensitized patients are either unable to receive a compatible organ, or experience a prolonged waiting period. In this study we examined the effectiveness of donor MHC class I gene therapy in preventing hyperacute rejection (HR) of rat heart allografts in passively sensitized recipients. Our gene therapy strategy to address this problem is based on the phenomenon that liver transplants, which resist antibody-mediated HR, produce soluble MHC class I Ag capable of neutralizing preformed antibodies and suppressing the immune response. To mimic this "liver effect," we used liposomes to transfect cultured recipient (Lewis-RT1.Al) hepatocytes with plasmid DNA encoding the soluble donor MHC class I Ag, RT1.Aa. Control or RT1.Aa-transfected hepatocytes were implanted intrasplenically into Lewis recipients 1 day prior to heterotopic ACI (RT1.Aa) heart transplantation and injection of 6 ml of anti-ACI hyperimmune serum (HIS). Results showed that nearly all recipients receiving ACI-specific HIS and control hepatocytes experienced HR, while none of the recipients receiving HIS and hepatocytes expressing soluble RT1.Aa developed HR. Furthermore, active immunosuppression by soluble RT1.Aa was evidenced by prolongation of allograft survival, compared with controls not receiving HIS. In summary, soluble donor-MHC class I Ag gene therapy can prevent antibody-mediated destruction associated with HR. Future development of a similar strategy in humans may significantly improve the results of clinical organ transplantation in immunologically sensitized recipients.

Soluble donor MHC class I antigen inhibits immunologic priming in vitro and in vivo

Previous studies suggest liver transplants can protect other transplanted organs. This effect may be mediated by hepatocytes secreting large amounts of soluble MHC class I antigen. Here our aim was to determine whether immunologic priming by membrane-bound alloantigen could be inhibited by allospecific antigen produced in a secreted form. Cultured Lewis (RT1.A1) hepatocytes were transfected with plasmids encoding either a membrane-bound or secreted form of the alloantigen, RT1.Aa. Cytotoxic T-lymphocyte (CTL) precursor assays were performed on Lewis splenocytes cultured with transfected hepatocytes, or hepatocytes were injected into the portal vein of prospective Lewis recipients of an ACI (RT1.Aa) liver allograft. Results showed CTL priming by membrane-bound RT1.Aa was inhibited in vitro by soluble RT1.Aa. Similarly, acceleration of ACI allograft rejection induced by membrane-bound antigen was abrogated following co-injection of hepatocytes secreting donor alloantigen. In conclusion, production of soluble donor alloantigen by liver transplants may provide protection against the alloimmune response.

Immunologic suppression mediated by genetically modified hepatocytes expressing secreted allo-MHC class I molecules

Studies suggest that immunosuppression associated with liver transplantation may be related to the secretion of MHC class I antigen (Ag) by hepatocytes. To investigate this possibility, we developed a culture system whereby naive Lewis (RT1.A1) splenocytes were cocultured with autologous hepatocytes transfected with plasmids encoding either the membrane-bound or secreted allogeneic MHC class I Ag, RT1.Aa. Cytotoxic T lymphocyte (CTL) and helper T lymphocyte (HTL) limiting dilution assays were subsequently performed on preconditioned lymphocytes. Lymphocytes preconditioned with hepatocytes secreting RT1.Aa showed an alloantigen specific inhibition of CTL precursors (CTLp). In contrast, exposure of splenocytes to hepatocyte-expressed membrane-bound RT1.Aa resulted in Ag-specific CTLp priming. This CTLp priming effect by hepatocyte-expressed membrane-bound Ag could be effectively blocked when splenocytes were first preincubated with hepatocytes secreting RT1.Aa, before being exposed to hepatocytes expressing membrane-bound RT1.Aa. In contrast to CTLp, HTLp frequency, as determined by IL-2 production, was unaffected by either hepatocyte-expressed membrane-bound or secreted RT1.Aa. Further studies on splenocytes conditioned with hepatocytes expressing secreted allo-MHC Ag suggest the possibility of suppressor cell development. This was demonstrated by prolongation of ACI (RT1a) heart allograft survival in Lewis recipients following adoptive transfer of splenocytes that were preconditioned in vitro with hepatocytes secreting alloantigen.

[Prevention of early rejection by soluble MHC class I antigen after allogenic liver transplantation]

Recent evidence suggests that liver transplants may be immunologically protective for other simultaneously transplanted organs. One possible explanation is that the liver secretes MHC class I molecules. Here we show that these donor-specific secreted molecules can inhibit the priming effect of donor derived membrane-bound MHC antigen. Lewis rats were injected with syngeneic hepatocytes transfected with plasmids encoding either a membrane-bound or a secreted form of the RT1. A allo-MHC class I antigen of ACI rats. To test the immunologic effects of the different forms of alloantigen, ACI to Lewis liver transplants were performed 7 days after injection. As demonstrated previously, injection of hepatocytes expressing membrane-bound alloantigen sensitizes host immunity, leading to accelerated allograft rejection. However, after simultaneous injection of hepatocytes expressing the two different forms of the alloantigen, the accelerated liver allograft rejection caused by hepatocytes expressing membrane-bound molecules was no longer evident. Our results show that soluble allo-MHC class I antigen can inhibit the sensitizing effect of the same molecule in a membrane-bound form.

Secreted donor-MHC class I antigen prolongs liver allograft survival and inhibits recipient anti-donor cytotoxic T lymphocyte responses

BACKGROUND

Liver transplants may be less susceptible to rejection and may protect other transplanted organs from rejection, because the liver produces large amounts of soluble MHC class I antigen. Most studies supporting this hypothesis have used in vitro models. Here we tested the application of this theory in vivo in a rat transplant model.

METHODS

Primary cultured Lewis (RT1.A(l)) hepatocytes were transfected by lipofection with plasmids encoding allogeneic membrane-bound or secreted RT1.A(a). After portal vein injection of transfected hepatocytes into a Lewis rat, either an ACI (RT1.A(a)) liver transplant was performed or lymph nodes were removed for immunologic analysis.

RESULTS

Rats injected with hepatocytes secreting alloantigen showed extended liver allograft survival and decreased cytotoxic T lymphocyte activity. Recipients injected with hepatocytes expressing membrane-bound alloantigen demonstrated accelerated graft rejection and showed cytotoxic T lymphocyte sensitization.

CONCLUSIONS

Soluble donor-specific MHC class I molecules may have immunosuppressive effects that can be used to promote graft survival in an organ transplantation situation.

Direct MHC class I complementary DNA transfer to thymus induces donor-specific unresponsiveness, which involves multiple immunologic mechanisms

Our purposes were 1) to determine whether direct transfer of cDNA encoding allogeneic MHC class I Ag to the rat thymus would be capable of inducing donor-specific unresponsiveness and 2) to study the immunologic mechanism of this effect. Plasmid DNA encoding donor strain (ACI-RT1.Aa) MHC class I Ag was directly injected into Lewis (RT1(l)) rat recipient thymus 7 to 10 days before ACI liver transplantation. A single dose of anti-lymphocyte serum was given i.p. on the day of thymic injection. Rats injected intrathymically with plasmid DNA and treated with anti-lymphocyte serum demonstrated prolonged survival in 9 of 13 rats (&gt;100 days). PCR was used to demonstrate that RT1.Aa cDNA was expressed in thymus transiently and later appeared in spleen. CTL limiting dilution assays showed that CTL precursor frequency was decreased in tolerant liver recipients. To test the hypothesis of clonal deletion vs anergy, CTL limiting dilution assays cultures were restimulated with donor cells and IL-2 to reverse anergy. Restimulation caused CTL precursor frequency to return to near normal in only one of five tolerant rats, suggesting clonal deletion or a dense anergic state. Passive transfer of splenocytes from tolerant rats to naive recipients prolonged cardiac allograft survival, suggesting that suppressor-type cells may also contribute to thymic tolerance in our model. In summary, our data suggest that donor MHC class I Ag expressed in thymus by direct DNA injection, followed by liver allografting, results in donor-specific unresponsiveness. The mechanism of this effect is complex, involving multiple immunologic mechanisms.

Direct MHC class I complementary DNA transfer to thymus induces donor-specific unresponsiveness, which involves multiple immunologic mechanisms

Our purposes were 1) to determine whether direct transfer of cDNA encoding allogeneic MHC class I Ag to the rat thymus would be capable of inducing donor-specific unresponsiveness and 2) to study the immunologic mechanism of this effect. Plasmid DNA encoding donor strain (ACI-RT1.Aa) MHC class I Ag was directly injected into Lewis (RT1(l)) rat recipient thymus 7 to 10 days before ACI liver transplantation. A single dose of anti-lymphocyte serum was given i.p. on the day of thymic injection. Rats injected intrathymically with plasmid DNA and treated with anti-lymphocyte serum demonstrated prolonged survival in 9 of 13 rats (>100 days). PCR was used to demonstrate that RT1.Aa cDNA was expressed in thymus transiently and later appeared in spleen. CTL limiting dilution assays showed that CTL precursor frequency was decreased in tolerant liver recipients. To test the hypothesis of clonal deletion vs anergy, CTL limiting dilution assays cultures were restimulated with donor cells and IL-2 to reverse anergy. Restimulation caused CTL precursor frequency to return to near normal in only one of five tolerant rats, suggesting clonal deletion or a dense anergic state. Passive transfer of splenocytes from tolerant rats to naive recipients prolonged cardiac allograft survival, suggesting that suppressor-type cells may also contribute to thymic tolerance in our model. In summary, our data suggest that donor MHC class I Ag expressed in thymus by direct DNA injection, followed by liver allografting, results in donor-specific unresponsiveness. The mechanism of this effect is complex, involving multiple immunologic mechanisms.

Split tolerance induced by immunotoxin in a rhesus kidney allograft model

BACKGROUND

Renal allografts were performed in rhesus monkeys using FN18-CRM9, a potent immunotoxin capable of depleting T cells to less than 1% of baseline levels in blood and lymph nodes, as a preparative agent. We have recently reported that animals pretreated with FN18-CRM9 1 week before transplantation without further immunosuppression had prolonged graft survival time compared with control animals, and frequently became tolerant.

METHODS

This report examines the alloimmune responses of recipient monkeys to the donor, including cytotoxic T lymphocyte precursor (CTLp) frequency, mixed lymphocyte response, and antidonor IgG response.

RESULTS

CTLp frequencies declined significantly (P<0.01) after FN18-CRM9 treatment and renal transplantation. This decline in CTLp was initially nonspecific, as CTLp frequencies against third-party animals also declined (P<0.01). The decrease in CTLp was maintained in five of five animals tested 6 months after transplant. However, unresponsiveness was limited to the CTL arm of the immune response as antidonor IgG was detected in four of four animals tested, and the 5-day mixed lymphocyte response stimulation index and relative response were not significantly different before and after transplant. In long-term survivors (>150 days), an increase in anti-third-party CTLp was detected 1 month after grafting with third-party skin. No change was seen in the antidonor CTLp frequency after donor skin grafting, indicating that a specific defect in the antidonor CTL response had developed.

CONCLUSIONS

These data suggest that FN18-CRM9 treatment of rhesus monkeys allows the development of specific down-regulation of antidonor CTL activity in renal allograft recipients.

Immunosuppressive effects of an HLA class I-derived peptide in a rat cardiac allograft model

B7.75-84, a 10-amino-acid peptide derived from the HLA-B7 molecule, prolongs rat heterotopic cardiac allograft survival time (GST) when used with cyclosporine in the Lewis-to-ACI strain combination. We evaluated the ability of B7.75-84 to prolong GST in other strain combinations without cyclosporine and studied the effect of B7.75-84 on the immune response in the Wistar-Furth (WF)-to-ACI strain combination. GST was markedly prolonged in most low-responder (ACI) recipients but only slightly prolonged in the high-responder (Lewis) recipient. Cytotoxic T lymphocyte (CTL) and helper T lymphocyte (HTL) limiting dilution assays (LDA) were performed 10 days after cardiac allografts from WF donors were placed in ACI recipients treated with B7.75-84. HTL-LDA assays at 10 days posttransplant showed a slight decrease in HTL precursor frequency and a decrease in their IL-2 production in B7.75-84 treated recipients with prolonged GST in response to donor antigen as well as third-party (Lewis) antigen. CTL-LDA assays at day 10 showed no difference in CTL precursor frequency among treated recipients but did show a significant decrease in CTL killing activity against donor cells in recipients with prolonged GST. No significant difference in CTL killing activity was seen against third- party cells. Antibody analysis was performed at day 8 in treated recipients. Serum from B7.75-84-treated recipients with prolonged graft survival generally showed no detectable IgG antibody response against donor MHC class I antigen. All B7.75-84 treated recipients showed a strong IgM response against donor antigen regardless of allograft outcome. Our results suggest that the immunosuppressive effect of B7.75-84 in rats is greater using a low-responder RT1 haplotype. Furthermore, B7.75-84 induces a nonspecific decrease in HTL function while producing a donor-specific decrease in CTL function and a diminished antidonor MHC class I IgG response.

Use of donor serum to prevent passive transfer of hyperacute rejection

Organ transplantation in presensitized recipients continues to be contraindicated for heart and kidney recipients due to the risk of hyperacute rejection, which has no known treatment at this time. We tested whether donor serum, which contains soluble MHC class I antigen, is able to neutralize the effect of anti-donor antibody in the recipient and prevent hyperacute or accelerated rejection. A rat model of passive immunization was used to test the role of anti-donor antibody in hyperacute rejection. Seven of 10 recipients of hyperimmune serum (HyS), derived from Lewis rats (RT1l) following 3 ACI (RT1a) skin grafts, developed hyperacute or accelerated rejection. Intravenous injection of ACI serum prior to the HyS administration prevented hyperacute rejection in all recipients tested. When third-party (Wistar-Furth, RT1u) serum was given to Lewis rats injected with HyS, hyperacute rejection was not abrogated. When examining the mechanism of this effect, a simple antibody blocking phenomenon was found to be unlikely since flow cytometry analysis showed that ACI serum needed to be present at > or = 256-fold excess compared to HyS to block anti-ACI antibody binding to RT1.Aa+cells by 50%. We tested whether the RT1.Aa class I antigen in ACI serum had other biologic properties that resulted in the prolonged graft survival. However, removal of RT1.Aa antigen from ACI serum prior to use in the passive transfer model did not abrogate the graft prolongation observed previously. These data suggest that components of donor serum other than MHC class I antigen may be useful for preventing the antibody-mediated component of hyperacute rejection.