Anti-CD4 monoclonal antibody-induced allograft tolerance in rats despite persistence of donor-reactive T cells

A novel MyD88 inhibitor attenuates allograft rejection after heterotopic tracheal transplantation in mice

BACKGROUND

After lung transplantation, the major complication limiting the long-term survival of allografts is obliterative bronchiolitis (OB), characterized by chronic rejection. Innate immune responses contribute to the development of OB. In this study, we used a murine heterotopic tracheal transplantation mouse model to examine the effects of a newtype of innate immune inhibitor, TJ-M2010-5.

METHODS

Syngeneic tracheal grafts were transplanted heterotopically from C57BL/6 mice to C57BL/6 mice. Allografts from BALB/c mice were transplanted to C57BL/6 mice. The allograft recipients were treated with TJ-M2010-5, and anti-mouse CD154 (MR-1). The grafts were harvested at 7, 14, and 28 days and evaluated by histological and real-time RT-PCR analyses.

RESULTS

In untreated allografts, almost all epithelial cells fell off at 7 days and tracheal occlusion reached a peak at 28 days. However, the loss of the epithelium and airway obstruction were significantly improved in mice treated with TJ-M2010-5 combined with MR-1. The relative mRNA expression levels of pro-inflammatory cytokines were upregulated in allogeneic tracheal grafts, and treatment with the two drugs reduced the production of pro-inflammatory cytokines and infiltration of inflammatory cells.

CONCLUSIONS

In heterotopic tracheal transplantation models, TJ-M2010-5 combined with MR-1 could ameliorate the development of OB.

Mechanisms and rescue strategies of calcineurin inhibitor mediated tolerance abrogation induced by anti-CD4 mAb treatment

To ensure safety tolerance induction protocols are accompanied by conventional immunosuppressive drugs (IS). But IS such as calcineurin inhibitors (CNI), for example, cyclosporin A (CsA), can interfere with tolerance induction. We investigated the effect of an additional transient CsA treatment on anti-CD4mAb-induced tolerance induction upon rat kidney transplantation. Additional CsA treatment induced deteriorated graft function, resulting in chronic rejection characterized by glomerulosclerosis, interstitial fibrosis, tubular atrophy and vascular changes. Microarray analysis revealed enhanced intragraft expression of the B cell attracting chemokine CXCL13 early during CsA treatment. Increase in CXCL13 expression is accompanied by enhanced B cell infiltration with local and systemic IgG production and C3d deposition as early as 5 days upon CsA withdrawal. Adding different CNIs to cultures of primary mesangial cells isolated from glomeruli resulted in a concentration-dependent increase in CXCL13 transcription. CsA in synergy with TNF-α can enhance the B cell attracting and activating potential of mesangial cells. Transient B cell depletion or transfer of splenocytes from tolerant recipients 3 weeks after transplantation could rescue tolerance induction and did inhibit intragraft B cell accumulation, alloantibody production and ameliorate chronic rejection.

Permanent CNI treatment for prevention of renal allograft rejection in sensitized hosts can be replaced by regulatory T cells

Recent data suggest that donor-specific memory T cells (T(mem)) are an independent risk factor for rejection and poor graft function in patients and a major challenge for immunosuppression minimizing strategies. Many tolerance induction protocols successfully proven in small animal models e.g. costimulatory blockade, T cell depletion failed in patients. Consequently, there is a need for more predictive transplant models to evaluate novel promising strategies, such as adoptive transfer of regulatory T cells (Treg). We established a clinically more relevant, life-supporting rat kidney transplant model using a high responder (DA to LEW) recipients that received donor-specific CD4(+)/ 8(+) GFP(+) T(mem) before transplantation to achieve similar pre-transplant frequencies of donor-specific T(mem) as seen in many patients. T cell depletion alone induced long-term graft survival in naïve recipients but could not prevent acute rejection in T(mem)(+) rats, like in patients. Only if T cell depletion was combined with permanent CNI-treatment, the intragraft inflammation, and acute/chronic allograft rejection could be controlled long-term. Remarkably, combining 10 days CNI treatment and adoptive transfer of Tregs (day 3) but not Treg alone also induced long-term graft survival and an intragraft tolerance profile (e.g. high TOAG-1) in T(mem)(+) rats. Our model allows evaluation of novel therapies under clinically relevant conditions.

Interleukin-33 prolongs allograft survival during chronic cardiac rejection

Interleukin-33 (IL-33) stimulates the generation of cells and cytokines characteristic of a Th2 immune response. We examined the effects of IL-33 on allografted heart tissue in a chronic cardiac rejection model, including analysis of the peripheral myeloid and lymphoid compartments. B6.C-H2bm12/KhEg hearts were transplanted into MHC class II-mismatched C57Bl/6J mice; IL-33 was administered daily. Cells from allografts and spleens were isolated for flow cytometry and cultured for cytokine production; some tissues were used for immunohistochemistry. Animals treated with IL-33 showed significantly longer allograft survival, which was associated with a distinct cytokine profile produced by graft-infiltrating cells. Proinflammatory IL-17A production was decreased with IL-33 treatment, while increased levels of IL-5, IL-10, and IL-13 were observed. After IL-33 therapy, flow cytometry showed a direct induction of CD4(+) Foxp3(+) Treg, whereas the number of B220(+) CD19(+) B cells, and circulating, as well as allograft deposited, alloantibodies was reduced. Following IL-33 treatment, a significant decrease in graft-infiltrating CD11b(high) Gr1(high) granulocytes coincided with a significant increase in CD11b(high) Gr1(intermediate) myeloid-derived suppressor cells (MDSC). In conclusion, IL-33 treatment in the setting of chronic rejection promotes the development of a Th2-type immune response that favors MDSC and Treg expansion, reduces antibody-mediated rejection (AMR), and ultimately, prolongs allograft survival.

Innate and adaptive immune responses in obliterative airway disease in rat tracheal allografts

BACKGROUND

We assessed cellular innate and adaptive immune responses in a rat heterotopic tracheal allograft model during the development of obliterative airway disease.

METHODS

Syngeneic tracheal grafts were transplanted heterotopically from DA to DA rats and fully MHC-mismatched allografts from DA to WF rats. The recipients received either no immunosuppression or two different doses of cyclosporine and were euthanized at 3, 10 and 30 days. Non-transplanted DA tracheas served as controls. Histologic, immunohistochemical and real-time RT-PCR analyses were performed.

RESULTS

The syngrafts had normal epithelium at 10 days and no tracheal occlusion was seen at 30 days. In non-immunosuppressed allografts, almost total loss of epithelium was observed at 10 days, culminating in tracheal occlusion at 30 days. The activation of innate immune response was observed during the ischemic period at 3 days in both groups. Influx of the infiltrating inflammatory cells was more prominent in the allografts. In syngrafts, mRNA expression of pro-inflammatory, but also tolerogenic, cytokines was significantly upregulated, whereas Th1 and Th17 priming factors were significantly downregulated. In allografts, prominent mRNA expression of pro-inflammatory cytokines was seen and adaptive Th1 and Th17 alloresponses were increased. Cyclosporine treatment reduced tracheal occlusion and inhibited both tolerogenic and pro-inflammatory T-cell responses in allografts.

CONCLUSIONS

Ischemia induced a self-limiting, alloantigen-independent innate immune response in syngrafts. In allografts, the predominant pro-inflammatory milieu and alloantigen-dependent Th1 and Th17 responses were linked to the development of obliterative airway disease and were inhibited by cyclosporine treatment.

Alternatively Expressed Genes Identified in the CD4+ T Cells of Allograft Rejection Mice

Allograft rejection is a leading cause for the failure of allotransplantation. CD4+ T cells play critical roles in this process. The identification of genes that alternatively expressed in CD4+ T cells during allograft rejection will provide critical information for studying the mechanism of allograft rejection, finding specific gene markers for monitoring, predicting allograft rejection, and opening new ways to regulate and prevent allograft rejection. Here, we established allograft and isograft transplantation models by adoptively transferring wild-type BALB/c mouse CD4+ T cells into severe combined immunodeficient (SCID) mice with a C57BL/6 or BALB/c mouse skin graft. Using the whole transcriptome sequencing-based serial analysis of gene expression (SAGE) technology, we identified 97 increasingly and 88 decreasingly expressed genes that may play important roles in allograft rejection and tolerance. Functional classification of these genes shows that apoptosis, transcription regulation, cell growth and maintenance, and signal transduction are among the frequently changed functional groups. This study provides a genome-wide view for the candidate genes of CD4+ T cells related to allotransplantation, and this report is a good resource for further microarray studies and for identifying the specific markers that are associated with clinical organ transplantations.

Increased Th17 rather than Th1 alloimmune response is associated with cardiac allograft vasculopathy after hypothermic preservation in the rat

BACKGROUND

Preservation injury decreases patient survival and promotes the development of cardiac allograft vasculopathy. We investigated the sequential effects of hypothermic preservation on ischemia-reperfusion injury (IRI), subsequent innate immune activation, and adaptive immune response in rat cardiac allografts.

METHODS

Allografts were transplanted from fully major histocompatibility complex-mismatched Dark Agouti to Wistar Furth rats without pre-operative hypothermia or after 4 hours of hypothermic preservation. Recipients received cyclosporine A immunosuppression. The allografts were recovered at 6 hours (n = 6, 7), 24 hours (n = 6), 10 days (n = 5), and 8 weeks (n = 5). Immunohistochemical, histologic, and reverse-transcription polymerase chain reaction analysis was performed.

RESULTS

In IRI, significantly increased messenger RNA (mRNA) levels for Toll-like receptor 4, hyaluronan synthases (HAS)1-2 (p = 0.03), high-mobility group box 1 (p = 0.05), CD80/83 (p = 0.01, p = 0.048), and the cytokines tumor necrosis factor-alpha (p = 0.004), interferon-gamma (p = 0.012), and interleukin (IL)-6 (p = 0.019) were seen in allografts subjected to hypothermic preservation. During established alloimmune response, allografts subjected to hypothermic preservation expressed prominent infiltration of CD4+ T cells (p = 0.043) and dendritic cells (p = 0.029) and significantly up-regulated mRNA levels of CD80 (p = 0.036), chemokine (C-C motif) ligand 21 (p = 0.008), C-C chemokine receptor type 7 (p = 0.003), vascular endothelial growth factor-C (p = 0.016), and vascular endothelial growth factor receptor-3 (p = 0.02). These allografts also showed prominent mRNA upregulation of Foxp3 (p = 0.014), IL-17 (p = 0.038), and IL-23 (p = 0.043). Preservation significantly increased the incidence and intensity of allograft arteriosclerosis (p < 0.05) and cardiac fibrosis (p = 0.003) at 8 weeks.

CONCLUSION

Our results demonstrate that preservation injury induced a cascade leading to an innate immune response that modulated the adaptive immune response towards Th17 rather than Th1 T-cell response in rat cardiac allografts and ultimately enhanced cardiac fibrosis and arterial occlusion. Our results also suggest that this immune response was not regulated by the calcineurin inhibitor cyclosporine A.

Prolonged survival of renal allograft in rats by methotrexate-albumin conjugates as immunosuppressive therapy

Methothrexate (MTX) causes unwanted adverse events by affecting gastrointestinal and bone marrow cells when used as an immunosuppressant. Our aim was to reduce those side effects by covalent binding of methothrexate to human serum albumin (HSA) targeting rapidly proliferating lymphocytes, which are known to ingest albumin as an energy source. Twenty-one rats received a kidney transplant. Group A (n = 5) received standard immunosupression (free MTX); group B (n = 9), albumin-MTX conjugates; and group C (n = 7) albumin control. The primary endpoint of this animal study was transplant survival, which was evaluated as death due to uremia. The study was terminated on day 100. Placebo-treated rat recipients (group C) rejected their grafts at a median of 8 days, which was prolonged to 17 days in standard immunosuppressed rats (group A), resulting in doubling transplant survival compared to nonimmunosuppressed animals. However, the same dose given as HSA-conjugated MTX prolonged the median survival time to 43 days. (group B). Hence, the administration of conjugated methotrexate appeared to result in a doubling of transplant survival compared with standard immunosuppression. Moreover, two animals receiving MTX-HSA became long-term survivors without additional immunosuppression. Further studies should be performed to evaluate the significance of these findings in larger animals and possibly in clinical studies.

Donor brain death significantly interferes with tolerance induction protocols

Studies in rodents showed that antibodies are able to induce tolerance of allografts. As clinical results are unsatisfactory and deceased donors are still the main source of organ transplants, we investigated whether donor brain-death impacts on tolerance induction after experimental kidney transplantation. Anti-CD4 monoclonal antibodies (RIB 5/2; 2.5 mg/kg x 5 days) treated and untreated recipients of brain-dead donor grafts were compared with RIB 5/2 treated and untreated recipients of living donor grafts (F344-to-Lewis). All recipients received low-dose CsA (1.5 mg/kg x 10 days). Kidneys were recovered 4, 16 and 40 weeks after transplantation and examined by morphology, immunohistology and flow cytometry. Renal function was monitored monthly. RIB 5/2 treatment significantly decreased proteinuria in recipients of living donor allografts when compared with living donor controls. After 40 weeks, inflammatory cell infiltration and MHC class II expression were reduced while morphologic alterations were minimal. In contrast, treatment of brain-dead graft recipients had no impact on graft function. Structural changes and graft infiltration were comparable to brain-dead donor controls at all time points. RIB 5/2 treatment significantly improved graft function in recipients of living donor grafts; however, it was not effective in recipients of brain-dead donor organs.

Short-Term Anti-CD4 Plus Anti-TNF-α Receptor Treatment in Allogeneic Small Bowel Transplantation Results in Long-Term Survival

BACKGROUND

Despite improved immunosuppression, intestinal transplantation is still complicated by severe rejection episodes. To further improve immunosuppressive concepts, we evaluated an anti-CD4 antibody and an anti-tumor necrosis factor (TNF)-alpha monoclonal antibody for their immunosuppressive efficacy in the standard rat model of intestinal transplantation.

METHODS

Intestinal transplantation was performed in the DA to Lewis combination, and recipients were treated perioperatively with either the anti-CD4 antibody RIB5/2 (day -1, 0, postoperative days 1, 2, 4, 7, 10, 14, 17, and 21), the anti-TNF antibody etanercept (60 min before reperfusion, postoperative days 3, 6, and 9) or a combination of both. Survival, histology and expression of immunologic mediator genes on days 3 and 4 after transplantation were investigated.

RESULTS

Treatment with anti-CD4 antibody alone (19.71+/-5.94) and the antibody combination (171.58+/-122.76) prolonged survival. The chemokine MIP-1alpha was significantly decreased in both anti-CD4 antibody treatment groups, possibly indicating an additional effect of the TNF-alpha blockade on the immune modulation by RIB5/2.

CONCLUSIONS

Our study demonstrated long-term graft survival in short-term treatment with a combination of an anti-CD4 antibody and a TNF-alpha antibody in more than 50% of the recipients of intestinal grafts. Such a combined approach could also be useful in clinical small bowel transplantation.

Infectious tolerance to ADP/ATP carrier peptides induced by anti-L3T4 monoclonal antibody in dilated cardiomyopathy mice

CD4 T cells are suspected to play an important role in the pathogenesis of dilated cardiomyopathy (DCM). This study sought to evaluate whether anti-L3T4 monoclonal antibody (McAb) could induce the infectious tolerance to the adenosine diphosphate (ADP)/adenosine triphosphate (ATP) carrier peptides to protect mice from DCM. BALB/c mice (n = 16) were immunized with the peptides derived from human ADP/ATP carrier on the 1st, 14th, 28th, 49th, and 79th days, and some of them (n = 6) were also injected with anti-L3T4 McAb on the -1st, 0, and 1st days. On the 180th day, the splenocytes (SC) from the McAb-treated group were transferred into the syngeneic recipients (n = 6) who were also immunized with the peptides in the same manner. The sham-immunized mice were taken as the controls (n = 10). Results showed that the serum antibody against the ADP/ATP carrier examined with ELISA was positive in all mice only immunized with the peptides (DCM group), while negative in the McAb-treated, the SC-transferred, and the Control groups. The mRNA expression of IFN-gamma, IL-2, and IL-4, especially IL-4 in T cells investigated using real-time quantitative PCR and the percentages of T helper 1 (Th1) and Th2 subsets, especially Th2 subset detected with Flow Cytometry were all increased in DCM group, accompanied by the cardiac histopathological changes like those in DCM. Such findings were not seen in the other three groups. It concluded that anti-L3T4 McAb could inhibit the occurrence of DCM induced by the ADP/ATP carrier peptides in mice, and this immune tolerance could be transferred to the syngeneic recipients.

Identification of gene markers for the prediction of allograft rejection or permanent acceptance

The clinical success of new treatment strategies aiming on inducing permanent graft acceptance will rely on the ability to determine whether specific unresponsiveness to donor alloantigens has developed and for how long it is maintained. To identify markers for such posttransplant monitoring, genes differentially expressed by graft infiltrating leukocytes during tolerance induction or rejection after kidney transplantation in rats were compared. A subsequently performed full kinetic analysis in two different transplant models, kidney and heart, in two species, rat and mouse identified two markers (TOAG-1, alpha-1,2-mannosidase) with high specificity and reproducibility, which are highly expressed during induction and maintenance of acceptance, and downregulated during rejection. Expression level of these markers showed a strong positive correlation with graft function. In addition, expression of both genes was downregulated in the peripheral blood and the graft prior to rejection, suggesting that these markers may be useful for monitoring in clinical transplantation where peripheral blood is the most easily accessible patient sample. Interestingly, downregulation of TOAG-1 and alpha-1,2-mannosidase expression occurred in graft infiltrating cells and expression of both genes was also downregulated after T-cell activation in vitro.

Transplant Tolerance Associated With a Th1 Response and Not Broken by IL-4, IL-5, and TGF-β Blockade or Th1 Cytokine Administration

BACKGROUND

Specific transplant tolerance is mediated by CD4 T cells that die unless supported by T-cell derived cytokines and donor antigen. This study examined the role of Th1 and Th2 cytokines in the maintenance of tolerance.

METHODS

Tolerance to fully allogeneic PVG cardiac allografts in DA rats was induced by short-term anti-CD3 monoclonal antibody therapy. Responses of tolerant cells to donor and third party antigen were assessed in vivo by examination of the infiltrate in the heart and application of skin grafts, and in vitro in mixed lymphocyte culture. Cell subsets were stained, induction of cytokine mRNA assayed by reverse-transcriptase polymerase chain reaction and the role of cytokines determined by treating with blocking monoclonal antibody to cytokines or cytokine administration.

RESULTS

Tolerated grafts had a T cell and macrophage infiltrate with increased mRNA for Th1 cytokines, interleukin (IL)-2, and interferon (IFN)-gamma but not Th2 cytokines. Peripheral lymphocytes proliferated in mixed lymphocyte culture and expressed Th1 cytokine mRNA. Tolerant hosts accepted PVG and rejected Lewis skin allografts and the lymph nodes draining both these grafts had similar induction of Th1 and Th2 cytokine mRNA. Treatment of tolerant rats with Th1 cytokines IL-2, IFN-gamma, and IL-12p70 or monoclonal antibody that blocked IL-4, IL-5, and transforming growth factor-beta did not prevent acceptance of PVG skin grafts.

CONCLUSIONS

These studies in a model of tolerance regulated by CD4CD25 T cells demonstrated there was no defect in Th1 responses. Tolerance was due to regulation that was not solely dependent on IL-4, IL-5, or transforming growth factor-beta and was not inactivated or overwhelmed by administration of Th1 cytokines, IL-2, IFN-gamma or IL-12p70.

Rat cytomegalovirus infection interferes with anti-CD4 mAb-(RIB 5/2) mediated tolerance and induces chronic allograft damage

In order to assess the role of heterologous immunity on tolerance induction (TI) by signal 1 modification, the influence of rat cytomegalovirus infection (RCMVI) on TI by a non-depleting monoclonal anti-CD4 mAb (monoclonal antibody) (RIB 5/2) in a rat kidney transplant (KTx) model was investigated. Orthotopic rat KTx (Dark Agouty (DA)-->Lewis (LEW)) was performed after TI with RIB 5/2 [10 mg/kg body weight (BW); day -1, 0, 1, 2, 3; i.p. (intraperitoneal route)]. RCMVI (5x10E5 Plaque forming units [PFU] i.p.) was simultaneously conducted to KTx, 50 days after KTx, and 14 days before and after KTx. RIB 5/2 induced robust allograft tolerance even across the high-responder strain barrier. RCMVI broke RIB 5/2-induced tolerance regardless of the time of RCMVI but did not induce acute graft failure during the 120 days follow-up. RCMVI induced a significant chronic deterioration of allograft function (p<0.01) and enhanced morphological signs of chronic allograft damage (p<0.05). Cellular infiltrates and major histo-compatibility complex (MHC)-expression were more pronounced (p<0.05) in the infected groups. RCMVI induced not only RCMV-specific T-cell response but also enhanced the frequency of alloreactive T cells. RCMV interferes with anti-CD4 mAb-induced tolerance and leads to chronic allograft damage. The data we presented suggest a potentially important role of viral infections and their prophylaxis in clinical TI protocols.

Biological and Biomaterial Approaches for Improved Islet Transplantation

Islet transplantation may be used to treat type I diabetes. Despite tremendous progress in islet isolation, culture, and preservation, the clinical use of this modality of treatment is limited due to post-transplantation challenges to the islets such as the failure to revascularize and immune destruction of the islet graft. In addition, the need for lifelong strong immunosuppressing agents restricts the use of this option to a limited subset of patients, which is further restricted by the unmet need for large numbers of islets. Inadequate islet supply issues are being addressed by regeneration therapy and xenotransplantation. Various strategies are being tried to prevent beta-cell death, including immunoisolation using semipermeable biocompatible polymeric capsules and induction of immune tolerance. Genetic modification of islets promises to complement all these strategies toward the success of islet transplantation. Furthermore, synergistic application of more than one strategy is required for improving the success of islet transplantation. This review will critically address various insights developed in each individual strategy and for multipronged approaches, which will be helpful in achieving better outcomes.

Imbalance of regulatory T cells in human autoimmune diseases

The breakdown of mechanisms assuring the recognition of self and non-self is a hallmark feature of autoimmune diseases. In the past 10 years, there has been a steadily increasing interest in a subpopulation of regulatory T cells, which exert their suppressive function in vitro in a contact-dependent manner and preferentially express high levels of CD25 and forkhead and winged-helix family transcription factor forkhead box P3 (FOXP3) (TREGs). Recent findings of changed prevalences and functional efficiencies indicate that these TREGs play a unique role in autoimmune diseases. Clinical findings in patients with mutated FOXP3 genes and a specific polymorphism in the promotor region of FOXP3 also support the role of FOXP3 as a 'master control gene' in the development and functioning of TREGs. Both altered generation of TREGs and insufficient suppression of inflammation in autoimmune diseases are considered to be crucial for the initiation and perpetuation of disease. TREG-related somatic cell therapy is considered as an intriguing new intervention to approach autoimmune diseases.

Induction of transplantation tolerance in non-human primate preclinical models

Short-term outcomes following organ transplantation have improved considerably since the availability of cyclosporine ushered in the modern era of immunosuppression. In spite of this, many of the current limitations to progress in the field are directly related to the existing practice of relatively non-specific immunosuppression. These include increased risks of opportunistic infection and cancer, and toxicity associated with long-term immunosuppressive drug exposure. In addition, long-term graft loss continues to result in part from a failure to adequately control the anti-donor immune response. The development of a safe and reliable means of inducing tolerance would ameliorate these issues and improve the lives of transplant recipients, yet given the improving clinical standard of care, the translation of new therapies has become appropriately more cautious and dependent on increasingly predictive preclinical models. While convenient and easy to use, rodent tolerance models have not to date been reliably capable of predicting a therapy's potential efficacy in humans. Non-human primates possess an immune system that more closely approximates that found in humans, and have served as a more rigorous preclinical testing ground for novel therapies. Prior to clinical adaptation therefore, tolerance regimens should be vetted in non-human primates to ensure that there is sufficient potential for efficacy to justify the risk of its application.

Infectious tolerance develops after intrathymic alloantigen-induced acceptance of rat heart allografts can be adoptively transferred

BACKGROUND

We have shown that intrathymic (IT) injection of alloantigen with antirat lymphocyte serum (ALS) treatment can induce donor-specific allograft acceptance. The purpose of this study was to investigate whether T-regulatory (T-reg) cells play a role in the maintenance of donor-specific heart graft tolerance that develops after IT injection of Lewis (LEW, RT1(l)) alloantigen into a Dark Agouti (DA, RT1(a)).

METHODS

Naïve DA rats were injected IT with 2.5 x10(7) LEW donor splenocytes and injected intraperitoneally with 1 mL ALS. Twenty-one days after pretreatment, a LEW or Brown Norway (BN, RT1(n)) heart was transplanted into a treated DA recipient. Splenocytes (1 x 10(8) or 5 x 10(7)) from a LEW heart-tolerant long-term survivor (LTS; >60 days) DA recipient were harvested and adoptively transferred (AT) into an irradiated (450 rad) naïve DA rat 24 hours before transplanting a LEW heart.

RESULTS

All LEW heart allografts were rejected by untreated DA rats in a mean survival time (MST) of 7.4 +/- 1.7 days (n=7). In contrast, 66.7% of LEW heart grafts into IT+ALS-pretreated DA recipients were accepted indefinitely (n=24). When either 1 x 10(8) (n=5) or 5 x 10(7) (n=5) splenocytes from a LEW heart graft-tolerant LTS (>60 days) DA recipient were AT into a new naïve DA rat, all new LEW heart grafts were accepted indefinitely.

CONCLUSIONS

The donor-specific tolerance that develops after IT+ALS-induced LEW heart acceptance by DA recipients can be transferred adoptively to new naïve DA recipients, thus indicating that it is infectious tolerance.

Development of Donor-Specific Immunoregulatory T-Cells After Local CTLA4Ig Gene Transfer to Pancreatic Allograft

BACKGROUND

CTLA4Ig gene transfer directly to graft tissue might have the potential to avoid the need for systemic immunosuppression. In our previous studies of bio-breeding (BB) rats, local adenovirus-mediated CTLA4Ig gene transfer protected the pancreas from autoimmune and alloimmune responses. This study investigated the potency of local CD28/B7 costimulatory blockade for induction of donor-specific tolerance and further examined the existing mechanisms.

METHODS

Brown Norway (BN; RT1)-pancreaticoduodenal grafts transfected with Ad.CTLA4Ig via intraarterial ex vivo perfusion were transplanted into streptozotocin-induced diabetic Lewis (LEW; RT1) rats.

RESULTS

Ad.CTLA4Ig transduced grafts combined with a short course of FK506 resulted in indefinitely prolonged survival (>156 days vs. 19.5 days with FK506 alone). CTLA4Ig was predominantly expressed in grafts on day 4. The expression was gradually diminished and was only slightly detectable at day >100. The proliferative responses against BN antigen were remarkably enhanced among recipients with rejected grafts, but the T-cells from tolerant recipients (>100 days) showed poor cytotoxic responses. On adoptive transfer assay, the splenic T-cells of tolerant recipients were able to suppress the rejection of BN, but not third-party Wistar Furth (WF; RT1) hearts in irradiated (480 cGy) LEW recipients. The percentage of CD4CD25 splenic T-cells was significantly increased in tolerant recipients (13.53 +/- 4.06% vs. 6.06 +/- 0.56% in naive rats).

CONCLUSION

CTLA4Ig gene transfer to the pancreaticoduodenal allograft combined with a short course of FK506 induces donor-specific tolerance. The mechanism of maintaining tolerance could be explained by development of splenic T suppressor cells.

FTY720 prevents anti-CD4 mAb-induced tolerance but cannot reverse established tolerance in a rat kidney transplantation model

FTY720 is highly effective in various models of transplantation and autoimmunity. In order to find drugs that act synergistically with a tolerance-inducing nondepleting anti-CD4 mAb we studied this combination in a strong DA to LEW kidney transplantation model. Rats were treated with 0.3 mg/kg of FTY720 for 14 days and anti-CD4 mAb RIB5/2, alone or in combination. After kidney transplantation serum creatinine and blood lymphocyte counts were monitored. Immunohistology, ELISPOT and TaqMan trade mark -PCR analysis of biopsies were performed. Short-term application of RIB5/2 but not FTY720 induced long-term survival of kidney transplants. Moreover, the combination of FTY720 + RIB5/2 prevented tolerance induction. In the combination group serum creatinine levels increased 1 week after cessation of therapy and all rats died from uremia within 72 days. Intragraft immunohistology, ELISPOT and real-time RT-PCR analysis at day 21 demonstrated an enhanced T-cell infiltration and activation but a diminished up-regulation of protective genes in the grafts from recipients receiving the combination therapy. In contrast, delayed application of FTY720 to RIB5/2-treated rats did not interact with RIB5/2-induced tolerance. In summary, FTY720 is powerful in preventing intragraft infiltration by naive T cells but this might also affect the early development of graft-protecting regulatory T cells and tolerance induction.

Evaluating the validity of animal models for research into therapies for immune-based disorders

The last few decades of the 20th century have shown an intensified search for safer and more effective medications against chronic diseases that burden ageing societies of the western world. The impressive development of biotechnological production techniques has greatly facilitated the pharmaceutical development of relatively non-toxic biological molecules. However, despite the huge investments, only a few effective therapies for immune-based diseases have reached the clinic. In this article we use examples from monoclonal antibody trials to discuss the validity and predictive strength of the animal models currently used for the development of effective therapies.

The immunosuppressive potential of misoprostol--efficacy and variability

Existing evidence on the immunosuppressive efficacy of prostaglandin E (PGE) and its analogues in vivo is conflicting. We investigated the effect of misoprostol, an orally available PGE1 analogue, on T-cell proliferation, Th cell-derived cytokine production, and phagocytosis in healthy volunteers. All participants (n=20) received increasing doses of misoprostol (0-400 microg). Blood was drawn before and after intake. Misoprostol intake caused a time- and dose-dependent reduction of anti-CD3-stimulated cell proliferation. Whereas the synthesis of Th1 cytokines (IL-2 and IFN-gamma) was dose-dependently reduced, IL-10 expression was increased at lower misoprostol doses. Concerning IL-4 expression, we observed an increased IL-4 production in males, but a decreased IL-4 production in females. Misoprostol intake also reduced phagocytosis activity in a dose-dependent manner. At least in part our results explain the immunosuppressive effects of misoprostol observed in vivo. The considerable interindividual variability as well as gender-specific differences seem to account for the variability of clinical study results.

New rat model of Pneumocystis pneumonia induced by anti-CD4(+) T-lymphocyte antibodies

The CD4(+) T lymphocyte plays a central role in host defense against Pneumocystis pneumonia but has received only limited attention in rats. CD4(+) T-cell-depleting (OX-38) and nondepleting (W3/25) monoclonal antibodies, which recognize an identical or adjacent epitope, were administered for up to 14 weeks to Lewis rats that had been exposed to PNEUMOCYSTIS: While OX-38 produced a greater decrease in circulating CD4(+) cells than W3/25, both antibody treatments resulted in similar effects on the health of the rats and the levels of Pneumocystis pneumonia, which were milder than those found with corticosteroids. W3/25 also did not enhance the severity of Pneumocystis pneumonia achieved with corticosteroids alone. We conclude that CD4(+) cell function is more important than CD4(+) cell number in host defense against Pneumocystis in the rat and that this new model permits study of opportunistic infections in the rat without the confounding effects of corticosteroids.

Down regulation of CD45 expression on CD4 T cells during acute renal allograft rejection: evidence of a decline in T suppressor/inducer activity

Acute rejection is associated with the activation of helper and cytotoxic cells. A shifting balance between the suppressor/inducer CD45+ CD4+ and T helper/inducer (CD4+CD45-) cells may be responsible for the transition from quiescence to overt rejection. We examined the kinetics of CD45 expression on CD4+ T cells in renal allograft recipients from pretransplant values to acute rejection and after reversal of rejection, searching for a shift in balance between helper/inducer and suppressor/inducer cell subsets. Using two color flow cytometry, the peripheral blood levels of CD4+, CD4+CD45- [T helper/inducer (Thi)], CD4+CD45+ [T suppressor/inducer (Tsi)], CD3+, and CD8+ T cells subsets and their interrelationships, were determined in 49 patients prior to transplantation, and in 10 of them, during acute rejection and after its reversal. Results were analyzed and compared to data obtained from 10 healthy blood donors. Acute rejection was associated with a significant decline in CD45+ CD4+ expression compared to quiescent phase (22% +/- 3.7% vs. 26.5% +/- 3.2%, p = 0.05) and controls (29.5% +/- 6.2%, p = 0.01). No difference was observed compared to pretransplant levels (19.9% +/- 3.2%, p = ns). CD45-/CD45+ (Thi/Tsi) ratio was lowest during quiescence (0.75) compared to rejection (0.97, p = 0.05), in controls (0.98, p = 0.05) and pretransplant values (1.4, p = 0.01). Acute rejection was characterized by higher Thi/CD8+ and lower Tsi/CD8+ ratio (103 and 88 respectively, p = 0.045), compared to clinical quiescence (104 and 116 respectively, p = 0.039). These data suggest that acute rejection is associated with down regulation of CD4+CD45+ suppressor/inducer subset. This shift may account for the transition from quiescence to overt rejection, concurring with reports on CD4+CD45 regulatory function.

Dominant transplantation tolerance

Long-term allograft survival in the absence of continuous immunosuppression can be induced following a short treatment of nondepleting antibodies, such as those that target CD4 or CD154 (CD40 ligand). It is now established that this may involve dominant tolerance mechanisms that are maintained by CD4+ regulatory T cells present within the lymphoid tissue and the tolerated graft. The phenotype of these cells, their relationship to CD4+CD25+ T cells, and the mechanism of action are still controversial.

Regulatory cell-mediated tolerance does not protect against chronic rejection

BACKGROUND

Regulatory cells prevent graft loss to acute rejection and induce tolerance, possibly by promoting Th2 deviation. Th2 cytokines stimulate B cells, which cause alloantibody-mediated chronic rejection. We searched to determine whether regulatory cell-mediated tolerance protects or not against chronic rejection.

METHODS

Heart transplantation (Htx) was performed using RA (RT1P) and PVG (RT1c) rats as donor and recipients. Donor-specific blood transfusion (DSBT) was given on preTx day 12. Secondary grafts were implanted at day 100. Splenocytes were transferred from tolerant rats (and controls) into lightly irradiated (450 rad) naive PVG, which received RA Htx. Primary Htx were investigated for the development of vascular occlusion (VO), the production of Th1/Th2 intragraft cytokines, and for the nature of graft infiltrate as well as for endothelial deposition of immunoglobulin (Ig)G isotypes and complement (C3) binding. Results were compared with rejecting controls (no DSBT) and syngeneic Htx.

RESULTS

RA Htx were rejected within 10 days (8, 9, 10x4). PreTx DSBT prolonged primary Htx survival indefinitely (>140 days) with acceptance of secondary donor-specific (but not third-party) grafts (P<0.001). Naive irradiated PVG rats given splenocytes from tolerant rats but not from controls accepted RA Htx, showing the existence of regulatory cells in allograft acceptors. Despite being tolerant, DSBT-treated rats displayed typical features of chronic rejection at day 90 (VO=77%; P<0.001 vs. VO=4% in syngeneic rats). An overt Th2 deviation, particularly intragraft production of interleukin (IL)-4, was observed at day 30. Simultaneously to this Th2 deviation, B cells emerged in the grafts and endothelial deposition of IgG1 (Th2 dependent) and C3 binding were observed.

CONCLUSIONS

Regulatory cells that prevent graft loss to acute rejection in primary and secondary grafts do not protect against the development of chronic rejection.

Development of infectious tolerance after donor-specific transfusion and rat heart transplantation

Regulatory cells developed after donor-specific transfusion (DST)-induced acceptance of a LEW heart transplanted into a DA rat. Both DST and the cardiac transplant were necessary to generate the regulatory cells. This donor-specific tolerance can then be transferred into a new DA recipient by adoptive transfer of lymphocytes from the DST-treated long term survivor (LTS) in a dose-dependent manner. The effectiveness of tolerance did not diminish over five generations of adoptive transfer, thus supporting its infectious nature. Although both spleen and lymph node cells were equally effective, graft-infiltrating lymphocytes were more potent. A high level of indirect CTL activity and MLC proliferation were observed in lymphocytes from LTS. In vivo tracking of adoptively transferred CFSE-labeled splenocytes from LTS showed equivalent FACS proliferation and a higher percentage of graft-infiltrating lymphocytes 7 days after heart transplantation, compared with adoptively transferred naive splenocytes. Adoptive transfer of CD8(+)-depleted LTS splenocytes resulted in 100% subsequent LEW allograft acceptance; whereas CD4(+) depletion decreased acceptance to 40%, and depletion of both CD4 and CD8 resulted in 0% acceptance. When positively selected CD4(+) or CD8(+) cells were adoptively transferred, 100% or 62.5% of LEW cardiac allografts survived, respectively. In conclusion, DST alone promotes a donor-specific infectious tolerance of a heart graft that can be adoptively transferred to subsequent naive allograft recipients despite the undiminished in vitro immunological response to donor Ag. Although both CD4(+) and CD8(+) populations are responsible for the regulatory mechanism in DST-induced tolerance, the CD4(+) population appears to dominate.

Tolerance and the "Holy Grail" of transplantation

Advances in transplantation biology have greatly improved patient outcomes following transplant surgery. However, generalized immunosuppression remains the Achilles heel of modern transplantation surgery with its associated infectious and neoplastic morbidities. Tolerance remains the ultimate goal for the entire field. Although recent advances in transplant immunology suggest that tolerance may be achievable in the near future, the complex and redundant nature of the human immune system may not allow us to circumvent such a basic function as the recognition of nonself. In this paper, advances in transplant immunology are reviewed and their potential relevance to achieving the "Holy Grail" of transplantation are discussed.

Efficiency of cytokine gene transfer in corneal endothelial cells and organ-cultured corneas mediated by liposomal vehicles and recombinant adenovirus

PURPOSE

Gene transfer of immunoregulatory cytokines could contribute to reduce rejection of corneal grafts. The aim of our study was to examine the gene transfer efficiency of liposomal vehicles compared to adenoviral vectors for transferring the Epstein-Barr-virus-derived interleukin 10 homologue (viral IL-10, vIL-10) into corneal endothelial cells and organ-cultured human corneas (HC) in vitro.

METHOD

To test liposomal efficiency, 2 lipid formulations (SP-Chol/DOPE 20/80 and DDAB/DOPE 30/70 in various concentrations) were complexed with a plasmid containing the vIL-10 cDNA in an eukaryotic expression vector (pcDSRalpha-BCRF-I). The complexes were transferred to (1) subconfluent bovine corneal endothelial cells (BCEC) after 1 passage and to (2) HC stored in organ culture. In addition, BCEC and HC were transduced with the recombinant adenoviral vector encoding for vIL-10 (AdvIL-10). Secretion of vIL-10 in the supernatants from both transfected BCEC and HC was measured by specific ELISA.

RESULTS

For gene transfer in BCEC, both transfection methods (liposomes and adenovirus) led to high secretion of vIL-10 [>2 ng/ml (liposomes) and <150 ng/ml (adenovirus) per 5,000 initially planted BCEC]. Expression levels in BCEC were dependent on the concentration of applied liposomes. For gene transfer in HC, only the adenoviral transduction technique achieved a high production of vIL-10, whereas liposomal transfection led only to low vIL-10 secretion (4.8 microg/ml vs. 95 pg/ml per quarter of cornea).

CONCLUSION

For transfection of corneal endothelial cells in culture, liposomes can be considered as a safe and useful alternative method of gene transfer avoiding side-effects of viral vectors. However, for transfection of organ-cultured HC, adenoviral vectors are superior to liposomal vehicles.

Anti-human CD4 induces peripheral tolerance in a human CD4+, murine CD4-, HLA-DR+ advanced transgenic mouse model

Selection in vivo of potent mAbs to human CD4 useful for immunotherapy, e.g., for the induction of immunological tolerance, is restricted for ethical reasons. We therefore used multiple transgenic mice that lack murine CD4, but express human CD4 specifically on Th cells, and HLA-DR3 as its natural counterligand (CD4/DR3 mice). The injection of CD4/DR3 mice with anti-human CD4 (mAb Max.16H5) before immunization with tetanus toxoid (TT, day 0) totally blocked the formation of specific Abs. This state of unresponsiveness persisted a subsequent boost again performed in the presence of anti-human CD4. When these mice were left untreated for at least 40 days, and were then re-exposed with TT, but in the absence of anti-human CD4, they consistently failed to induce specific Abs (long-term unresponsiveness). Exposure to second party Ags (hen egg lysozyme, human acetylcholine receptor) induced specific Abs comparable with control mice, demonstrating that the anti-CD4-induced unresponsiveness was Ag specific (immunological tolerance). Importantly, the concurrent injection of TT and anti-human CD4 at day 0, followed by another two anti-CD4 treatments, also led to tolerant animals, indicating that tolerance was inducible at the same day as the Ag exposure is provided. We finally demonstrate a limited ability of spleen cells to respond to TT in vitro, indicating that T cells are essentially involved in the maintenance of TT-specific tolerance. These data show for the first time that the human CD4 coreceptor mediates tolerance-inducing signals when triggered by an appropriate ligand in vivo.

Interferon-gamma is not a universal requirement for islet allograft survival

BACKGROUND

Although many transplantation studies have implicated a graft-destructive role for T helper (Th)1 cytokines and a graft-protective role for Th2 cytokines, more recent studies have challenged this paradigm by showing that long-term allograft survival can actually require the presence of Th1 cytokines, such as interleukin 2 and interferon (IFN)-gamma. The purpose of this study was to examine the requirement for IFN-gamma in the induction of islet allograft acceptance after monoclonal antibody therapy targeting conceptually distinct molecular pathways: the costimulatory molecule CD154, the CD4 coreceptor, or the beta2 integrin lymphocyte function-associated antigen (LFA)-1 (CD11a).

METHODS

Diabetic C57Bl/6 (B6; H2b) mice were grafted with fully MHC mismatched BALB/c (H2d) islets, or reciprocally, diabetic BALB/c mice underwent transplantation with B6 islets and were treated with anti-CD154, anti-CD4, or anti-LFA-1.

RESULTS

When IFN-gamma gene knockout mice were used as graft recipients, the requirement for IFN-gamma in allograft survival was found to be highly conditional, depending on both the host strain and the induction therapy used. In both strain combinations studied, anti-CD154 was effective in the presence or absence of IFN-gamma, whereas anti-CD4 lost therapeutic potential in the absence of this cytokine. Alternatively, the requirement for IFN-gamma for allograft prolongation by anti-LFA-1 therapy was noted only in B6 transplant recipients.

CONCLUSIONS

IFN-gamma is not always requisite in islet allograft survival but rather varies according to the molecular target of induction therapy and the genetic background of the transplant recipient.

Transfer of "infectious" cardiac allograft tolerance induced by donor-specific transfusion

BACKGROUND

"Infectious tolerance" has been defined as the tolerance induced in a new recipient by the adoptive transfer of cells from a recipient accepting an allograft after anti-CD4 and anti-CD8 monoclonal antibody treatment. A clear understanding of the mechanisms responsible for graft acceptance after donor-specific blood transfusion (DST) has remained elusive. We examined the development and "infectious" nature of immunologic changes resulting in indefinite survival of LEW to DA rat cardiac allografts after DST alone without the need for antibody.

METHODS

One hundred x 10(6) LEW splenocytes (SC) as DST were injected intravenously into DA recipients 7 days before LEW cardiac transplantation. Subsequently, 100 x 10(6) SC harvested from a DA recipient 30, 60, or 100 days after graft acceptance were adoptively transferred into lightly gamma-irradiated (450 rad) naïve DA recipients 24 hours before a second LEW cardiac allograft. Subsequent graft function was determined.

RESULTS

Adoptive transfer of SC from the DST-treated DA rats 30 days after LEW heart transplant acceptance into naïve gamma-irradiated DA rats failed to transfer tolerance to LEW cardiac allografts. However, SC from DA rats bearing LEW hearts for more than 60 days induced indefinite tolerance to all LEW hearts. This infectious tolerance could be adoptively transferred again to a second DA recipient.

CONCLUSIONS

DST-generated regulatory cells can downregulate naïve lymphocytes to promote allograft acceptance. This tolerance can be expanded and serially transferred to a subsequent naïve cardiac recipient.

Bag-1 up-regulation in anti-CD4 mAb-treated allo-activated T cell confers resistance to activation-induced cell death (AICD)

The non-depleting anti-CD4 monoclonal antibody (mAb) RIB5/2 is a powerful inducer of tolerance to major histocompatibility complex (MHC)-incompatible allografts in rat recipients. The unresponsiveness induced is characterized by the persistence (over 300 days) of donor-reactive regulatory T cells within the graft. We applied differential-display reverse-transcription polymerase chain reaction (RT-PCR) to identify differences at the mRNA level between graft-infiltrating cells of anti-CD4 mAb-treated and non-treated control rats at day 5 after kidney transplantation. A 550-bp DNA fragment appearing only in anti-CD4 mAb-treated rats is identical with the anti-apoptotic protein Bag-1. A further investigation of Bag-1 expression during mixed lymphocyte reactions (MLR) revealed a three-four-fold up-regulation of Bag-1 mRNA expression in anti-CD4 mAb-treated allogeneic cultures. Bag-1 up-regulation is associated with higher protection against apoptosis of anti-CD4 mAb-treated cultures. Application of antisense oligonucleotides specific for Bag-1 leads to both a reduction in Bag-1 expression and sensibility against apoptosis. Thus, the expression of Bag-1 in anti-CD4 mAb-treated alloreactive T cells conferred resistance against apoptosis, which may contribute to the long-term survival of tolerance-mediating T cells in vivo.

Tolerance and pancreatic islet transplantation

Islet transplantation holds renewed promise as a cure for type I diabetes mellitus. Results of recent clinical trials have shown remarkable success, and have reignited universal optimism for this procedure. In spite of this success, the need for life-long immunosuppression of the recipient still limits islet transplantation to patients with poorly controlled diabetes or to those requiring kidney transplantation. It is obvious that the achievement of immunological tolerance would broaden the indication for islet transplantation to a much larger cohort of patients with type I diabetes mellitus, most likely preventing long-term complications and contributing to a much improved quality of life. Increased understanding of the basic mechanisms of tolerance induction has resulted in the implementation of numerous experimental approaches to achieve long-term survival of islet grafts in the absence of chronic immunosuppression. In this brief review we will attempt to summarize the current status of research and knowledge.

STAT5 pathway: target of anti-CD4 antibody in attenuation of IL-2 receptor signaling

BACKGROUND

Anti-CD4 antibodies induce long-term graft survival by incompletely understood mechanisms, and CD4-ligation with HIV gp120-derivatives attenuates interleukin (IL)-2 receptor signaling. We examined the latter in the context of the CD4-modulating antibody 16H5.

MATERIALS AND METHODS

We performed immunoblots to assess the IL-2-induced phosphorylation of signal transducer and activator of transcription (STAT)5 and Akt in the presence or absence of 16H5. Furthermore, we documented the effects of 16H5 on the induction of STAT5, activating protein (AP)-1, and myc by IL-2 in DNA-binding assays. 3H-thymidine incorporation of the human lymphoid cell line CMO, which exhibits constitutive activation of the STAT5 pathway and IL2-independent growth, was also measured during 16H5 treatment.

RESULTS

In human T lymphocytes, 16H5 attenuated both the tyrosine phosphorylation of STAT5 by IL-2 and the IL-2-induced DNA-binding of this transcription factor. In contrast, 16H5 had no effect on the serine phosphorylation of Akt by IL-2 or on the IL-2-induced DNA-binding of myc. Signal transduction involving AP-1 was unaffected by 16H5 and IL-2. 16H5 also attenuated CMO cell proliferation.

CONCLUSIONS

16H5 targets the STAT5 signaling pathway to attenuate IL-2 receptor signal transduction in human T cells. This observation provides a molecular explanation for the immunomodulatory actions of anti-CD4 antibodies.

Non-depleting anti-CD4, but not anti-CD8, antibody induces long-term survival of xenogeneic and allogeneic hearts in alpha1,3-galactosyltransferase knockout (GT-Ko) mice

The anti-galactose-alpha1,3-galactose (Gal) antibody (Ab) response following pig-to-human transplantation is vigorous and largely resistant to currently available immunosuppression. The recent generation of GT-Ko mice provides a unique opportunity to study the immunological basis of xenograft-elicited anti-Gal Ab response in vivo, and to test the efficacy of various strategies at controlling this Ab response [1]. In this study, we compared the ability of non-depleting anti-CD4 and anti-CD8 to control rejection and antibody production in GT-Ko mice following xenograft and allograft transplantation. Hearts from baby Lewis rat or C3H mice were transplanted heterotopically into GT-Ko. Non-depleting anti-CD4 (YTS177) and anti-CD8 (YTS105) Abs were used at 1 mg/mouse, and given as four doses daily from day -2 to 1 then q.o.d. till day 21. Xenograft rejection occurred at 3 to 5 days post-transplantation in untreated GT-Ko recipients, and was histologically characterized as vascular rejection. Anti-CD4, but not anti-CD8, Ab treatment prolonged xenograft survival to 68 to 74 days and inhibited anti-Gal Ab as well as xeno-Ab production. In four of the five hearts from anti-CD4 mAbs-treated GT-Ko mice, we observed classic signs of chronic rejection, namely, thickened intima in the lumen of vessels, significant IgM deposition, fibrosis and modest mononuclear cell infiltrate of Mac-1+ macrophages and scattered T cells (CD8>CD4). Xenograft rejection in untreated, as well as anti-CD4- and anti-CD8-treated, recipients was associated with increased intragraft IL-6, IFN-gamma and IL-10 mRNA. C3H allografts were rejected in 7 to 9 days by untreated GT-Ko mice and were histologically characterized as cellular rejection. Treatment with anti-CD4 and anti-CD8 mAb resulted in graft survivals of >94.8 and 11.8 days, respectively. Anti-CD4 mAb treatment resulted in a transient inhibition of alloreactive and anti-Gal Ab production. The presence of circulating alloreactive and anti-Gal Abs at >50 days post-transplant was associated with significant IgM and IgG deposition in the graft. Yet, in the anti-CD4 mAb-treated group, the allografts showed no signs of rejection at the time of sacrifice (>100 days post-transplantation). All rejected allografts had elevated levels of intragraft IL-6, IFN-gamma and IL-10 mRNA, while the long-surviving anti-CD4-treated allografts had reduced mRNA levels of these cytokines. Collectively, our studies suggest that the elicited xeno-antibody production and anti-Gal Ab production in GT-Ko mice are CD4+ T-cell dependent. The majority of xenografts succumbed to chronic rejection, while allografts survived with minimal histological change, despite elevated levels of circulating alloAbs. Thus, immunosuppression with anti-CD4 mAb therapy induces long-term survival of allografts more effectively than to xenografts.

Prolongation of allograft survival by Nippostrongylus brasiliensis is associated with decreased allospecific cytotoxic T lymphocyte activity and development of T cytotoxic cell type 2 cells

BACKGROUND

We have demonstrated that infection with Nippostrongylus brasiliensis (Nb), which induces strong type 2 responses, prolongs kidney allograft survival in rats. Here, we confirm that this effect is not species-specific and address immune modulation in allospecific T-cell responses mediated by nematode infection.

METHODS

C57BL/6 mice were injected with Nb or phosphate-buffered saline. Four days later, mice were transplanted with BALB/c hearts and graft survival was assessed. In other experiments, Nb-infected mice were immunized with BALB/c spleen cells and allospecific T-cell responses were determined in vitro.

RESULTS

In this study, we show that Nb prolongs cardiac allograft survival in mice. Further, spleen T cells from Nb-infected, allo-immunized mice exhibit reduced allospecific cytotoxic T-lymphocyte activity. In contrast, allospecific proliferation of T cells in the mixed lymphocyte reaction was not reduced by Nb, ruling out immunosuppression as the mechanism of Nb-induced allograft survival. Nb infection induced IL-4 and IL-6 and inhibited IFN-gamma production by T cells in response to allo-antigen. Furthermore, anti-IL-4 treatment reduced allospecific T-cell proliferation from Nb-infected but not control mice, indicating that type 2 allospecific T cells develop in the presence of Nb. We also double-stained T cells for CD8 and IL-4 and showed that Nb induces an 8-fold increase in Tc2 cell numbers.

CONCLUSIONS

These results are consistent with a hypothesis that Nb mediates prolongation of allograft survival through induction of type 2 immunity, including the development of regulatory Tc2 cells, and subsequent inhibition of allospecific cytotoxic T-lymphocyte activity.

Anti-LFA-1 therapy induces long-term islet allograft acceptance in the absence of IFN-gamma or IL-4

mAb therapy directed against a variety of cell surface accessory molecules has been effectively utilized to prolong allograft acceptance in various models of tissue and organ transplantation. The purpose of this study was to determine whether transient therapy directed against the adhesion molecule LFA-1 (CD11a) was sufficient to induce donor-specific tolerance to pancreatic islet allografts. Anti-LFA-1 monotherapy was found to be efficacious in inducing long-term islet allograft acceptance in multiple donor-recipient strain combinations. Graft acceptance following anti-LFA-1 therapy was not simply due to clonal ignorance of donor Ags in that the majority of recipients bearing established islet allografts resisted rejection induced by immunization with donor-type APCs. Furthermore, donor-specific tolerance from anti-LFA-1-treated animals could be transferred to secondary immune-deficient animals. Taken together, these results indicated that transient anti-LFA-1 monotherapy resulted in donor-specific tolerance. In vitro, functionally tolerant animals retained normal anti-donor reactivity as assessed by proliferative, cytotoxic, and cytokine release assays that demonstrated that tolerance was not secondary to general clonal deletion or anergy of donor-reactive T cells. Finally, anti-LFA-1 treatment was effective in both IL-4-deficient and IFN-gamma-deficient recipients, indicating that neither of these cytokines are universally required for allograft acceptance. These results suggest that anti-adhesion-based therapy can induce a nondeletional form of tolerance that is not overtly dependent on the prototypic Th1 and Th2 cytokines, IFN-gamma and IL-4, respectively, in contrast to results in other transplantation models.

Intragraft overexpression of interleukin-4 is neither sufficient nor essential for tolerance induction to cardiac allografts in a high-responder strain combination

BACKGROUND

Recently we have demonstrated that the nondepleting anti-CD4 monoclonal antibody (mAb) RIB5/2 induces long-term acceptance of kidney and heart allografts in all rat strain combinations tested. Cytokine gene expression studies by reverse transcriptase-polymerase chain reaction revealed a reversed intragraft interleukin (IL)-4/interferon-gamma ratio. Whether IL-4 mediated immune deviation contributes to transplantation tolerance is not clear so far.

METHODS

To learn more about the functional relevance of the relative IL-4 up-regulation, IL-4 was overexpressed in rat heart allografts by using ex vivo adenoviral gene transfer. The efficiency of gene transfer was analyzed by reporter gene assays as well by reverse transcriptase-polymerase chain reaction analysis of IL-4 mRNA expression.

RESULTS

The intragraft overexpression of IL-4 did not prolong the allograft survival compared with controls. Moreover, neutralization of IL-4 by OX81 mAb did not prevent tolerance induction by RIB5/2 treatment.

CONCLUSIONS

Anti-CD4 mAb-induced tolerance is associated with an intragraft type1/type2 shift, however, the up-regulation of IL-4 alone is neither sufficient nor essential to induce tolerance to cardiac allografts in a high-responder strain combination.

What is the role of regulatory T cells in transplantation tolerance?

There has been considerable recent progress in the characterization of the regulatory T cells that mediate tolerance in a number of transplantation models. The conditions that facilitate the generation of regulatory T cells point to the thymus, the nature of immune suppression and the dose of immunosuppressive agent(s) being important. Putative mechanisms of immune regulation by regulatory T cells, particularly in the 'infectious' tolerance pathway, include Th2-type cytokines (IL-4, IL-10 and transforming growth factor beta) that may play a direct role as an indispensable requirement or may contribute indirectly as a favorable milieu for acquisition of tolerance. Anergic T cells may suppress immune responses via either cytokine competition or antigen-presenting cells. Models of autoimmune disease, in which regulatory T cells were shown to represent a distinct thymus-derived T cell subset, also suggest the role of antigen-presenting cells in mediating immune suppression. Progress has also been made in generating and characterizing regulatory T cells in vitro.

Recent advances in immunosuppressants

In recent years, a large number of structurally diverse immunosuppressants have been discovered that are effective for the treatment of organ transplantation. Some of them are undergoing clinical trials and may soon enter into routine clinical practice. These compounds are either chemical entities obtained from natural sources/synthetic means or biomaterials such as monoclonal antibodies/gene products/proteins. They have been found to interfere at different stages of T cell activation and proliferation, and can be identified as inhibitors of nucleotide synthesis, growth factor signal transduction and differentiation. Newer strategies involving combination of new agents with traditional immunosuppressants, monoclonal antibodies and gene therapy offer enormous potential, not only for the investigation of mechanisms pertaining to graft rejection, but also for its therapeutic prevention.

Interleukin-4 secretion by the allograft fails to affect the allograft-specific interleukin-4 response in vitro

BACKGROUND

The role of the cytokine, interleukin (IL)-4, in allograft rejection and protection is not clear. We have previously shown that IL-4 transgenically expressed in a pancreas allograft does not protect the allograft from rejection. Here, we analyze the effect of the transgenically expressed IL-4 on the cytokine profile of the allograft-specific immune response.

METHODS

C57BL/6SCID mice were infused with small numbers of spleen cells from C57BL/6 donors. The former received pancreas grafts from 1- to 2-day-old BALB/c donors which did or did not transgenically express IL-4 in the graft. Three weeks after the cell infusion, the spleens were removed and the splenocytes were restimulated in vitro with BALB/c APC, and third party BALB.K APC. IL-2 and IL-4 levels in the culture supernatants were measured.

RESULTS

The presence of a pancreatic allograft induced an increase in the levels of both IL-2 and IL-4 in culture supernatants from splenocytes of mice receiving grafts compared with mice not receiving grafts. The presence of IL-4 transgenically expressed in the pancreas allograft had no effect on the in vitro cytokine profile.

CONCLUSIONS

from these results we conclude that the failure of transgenically expressed IL-4 to protect the allograft was not associated with up-regulation of a graft antigen-specific IL-4 response.