Human allograft acceptance is associated with immune regulation

Effects of Immunosuppressants on Induction of Regulatory Cells After Intratracheal Delivery of Alloantigen

BACKGROUND

We previously reported that intratracheal delivery (ITD) of alloantigen generated regulatory cells in mice. Here, we examined the effect of various doses of conventional immunosuppressants (FK506, cyclosporine A, azathioprine, mycophenolate mofetil, and rapamycin) on inducing regulatory cells in our model.

METHODS

CBA mice (primary recipients) were given C57BL/6 splenocytes by ITD and either no additional treatment or various doses of an immunosuppressant. Seven days later, splenocytes from these mice were adoptively transferred into naive secondary CBA recipients that underwent C57BL/6 cardiac grafting the same day.

RESULTS

Adoptive transfer from primary recipients given ITD of splenocytes alone induced prolonged allograft survival in secondary recipients (median survival time [MST], 50 days), suggesting that regulatory cells were generated. When ITD of alloantigen was combined with daily administration of 0.1 mg/kg FK506 or 0.2 mg/kg rapamycin, graft survival was similarly prolonged (MST 55 and 50 days, respectively). When combined with 20 or 40 mg/kg MMF or 0.4 mg/kg rapamycin, the majority of recipients demonstrated indefinite survival (MST, >100 days in all groups). When ITD of alloantigen was combined with 0.3, 0.5, or 1.0 mg/kg FK506; 5, 10, or 25 mg/kg cyclosporine A; or 1.0 or 2.0 mg/kg azathioprine, allografts were rejected acutely (MST 7-13 days).

CONCLUSION

Generation of regulatory cells by ITD of alloantigen was facilitated by mycophenolate mofetil and high doses of rapamycin but abrogated by cyclosporine A, azathioprine, and high doses of FK506. Low doses of rapamycin and of FK506 did not interfere with generation of regulatory cells.

CMV-infected allogeneic endothelial cells initiate responder and bystander donor HLA class I release via the metalloproteinase cleavage pathway

Although cytomegalovirus (CMV) interferes with major histocompatibility expression in infected cells, both host and donor soluble human leukocyte antigen class I (sHLA-I) are often released into the serum of transplant recipients during CMV infection and may contribute to anti-HLA antibody production and graft rejection. We hypothesized that CMV infection of endothelial cells (EC) induces host T cells to release interferon (IFN)-gamma, which in turn drives the metalloproteinase (MPase)-cleavage pathway of sHLA-I generation in "bystander" uninfected ECs. To test this hypothesis, cultures of peripheral blood mononuclear cells (PBMCs) and either uninfected ECs or CMV-infected ECs (EC/CMV) were established and supernatants were tested in enzyme-linked immunosorbent assay for sHLA-I. Responder PBMC became activated and released sHLA-I via the MPase pathway when stimulated with allogeneic EC/CMV; the sHLA-I release was contact dependent and cytokine independent. In transwell cultures, IFN-gamma released by PBMCs in response to EC/CMV stimulated a release of sHLA-I from uninfected allogeneic ECs across the transwell; this release was also MPase dependent. This implies that CMV infection within the transplanted allograft will not only stimulate the release of self HLA from responding PBMCs, but will also stimulate the release of donor sHLA-I from uninfected bystander ECs, both via the class I MPase-pathway.

Donor bone marrow transplantation: chimerism and tolerance

Infusion of donor bone marrow (DBM)-derived cells continue to be tested in clinical protocols intended to induce specific immunologic tolerance. Central clonal deletion of donor-specific alloreactive cells associated with mixed chimerism reliably produced long-term graft tolerance. In this setting, depletion of recipient T cells by antilymphocyte antibodies and subsequent repopulation by donor hematopoietic cells after donor bone marrow infusion (DBMI) are prerequisites for tolerance induction. Major advances have been made in animal models and in pilot clinical trials and the key questions with the future perspectives are presented in this article.

Operationally tolerant and minimally immunosuppressed kidney recipients display strongly altered blood T-cell clonal regulation

Most kidney transplant recipients who discontinue immunosuppression reject their graft. Nevertheless, a small number do not, suggesting that allogeneic tolerance state (referred to operational tolerance) is achievable in humans. So far, however, the rarity of such patients has limited their study. Because operational tolerance could be linked to anergy, ignorance or to an active regulatory mechanism, we analyzed the blood T-cell repertoire usage of these patients. We report on comparison of T-cell selection in drug-free operationally tolerant kidney recipients (or with minimal immunosuppression), recipients with stable graft function, chronic rejection and healthy individuals. The blood T cells of operationally tolerant patients display two major characteristics: an unexpected strongly altered T-cell receptor (TCR) Vbeta usage and high TCR transcript accumulation in selected T cells. The cytokine transcriptional patterns of sorted T cells with altered TCR usage show no accumulation of cytokine transcripts (IL10, IL2, IL13, IFN-gamma), suggesting a state of hyporesponsiveness in these patients. Identification of such a potential surrogate pattern of operational tolerance in transplant recipients under life-long immunosuppression may provide a new basis and rationale for exploration of tolerance state. However, these data obtained in a limited number of patients require further confirmation on larger series.

Ureteral necrosis after kidney transplantation: risk factors and impact on graft and patient survival

BACKGROUND

Ischemia, the main cause of ureteral necrosis in renal transplantation, cannot alone explain the late occurrence of some fistulas beyond the first postoperative month. The aim of this study, performed on a cohort of 1,629 consecutive kidney transplantations, was to analyze the risk factors implicated in the occurrence of ureteral necrosis and its impact on graft and patient survival.

METHODS

Between January 1990 and December 2001, 1,629 renal transplantations were performed in the authors' center. All biologic and clinical data were computerized in a cross-audited and validated data bank (Données Informatisées et Validées en Transplantation). The parameters studied were donor age, gender, cause of death and serum creatinine before procurement; and recipient age, gender, initial disease, panel reactive antibody, retransplantation, cold ischemia time, delayed graft function, human leukocyte antigen incompatibilities, induction and maintenance immunosuppression, right or left kidney, number of arteries, site of transplantation and the presence or not of a double-J stent. The follow-up parameters were the number and timing of acute rejection episodes, cytomegalovirus (CMV) infection (viremia, polymerase chain reaction), and acute pyelonephritis. Ureteral histologic analysis was performed in 25 cases (necrosis, leukocyte infiltration, and CMV or BK virus inclusions). Uni- and multivariate statistical tests were used (alpha risk at 5%). All of the patients with ureteral necrosis had undergone neoureterocystostomy or ureteral anastomosis with the native ureter but with a systematic double-J stent.

RESULTS

Ureteral necrosis occurred in 52 of the 1,629 patients (3.2%) and was significantly and independently correlated with donor age (P=0.041) and delayed graft function (P=0.016). CMV infections were also higher in the necrosis group (P=0.001), but donor CMV status was not statistically different between the two groups (36.2% vs. 36.7%). Ureteral histologic studies showed CMV and BK virus inclusions in 4 and 2 cases, respectively, and arterial and venous thrombosis in 4 and 16 cases, respectively. No pattern of ureteral rejection was observed. Ureteral necrosis did not affect the 10-year patient and graft survival, which were 87% and 66%, respectively, for the necrosis group and 86% and 58%, respectively, for the control group (P=not significant).

CONCLUSIONS

The authors' data provide new information concerning a classic surgical complication after kidney transplantation. The link they have identified between the occurrence of ureteral necrosis, donor age, and delayed graft function reemphasizes the interdependence between surgical and medical complications in kidney transplantation.

IFN-gamma gene polymorphisms associate with development of EBV+ lymphoproliferative disease in hu PBL-SCID mice

Posttransplantation lymphoproliferative disorder (PTLD) is a devastating post-transplantation complication often associated with Epstein-Barr virus (EBV). Although the type and length of immunosuppression are risk factors, a patient's inherent immune capacity also likely contributes to this disorder. This report uses severe-combined immunodeficient mice given injections of human peripheral blood leukocytes (hu PBL-SCID [Severe Combined Immunodeficient] mice) to test the hypothesis that cytokine genotype associates with the development of EBV-associated lymphoproliferative disease (LPD). We observed that the A/A (adenosine/adenosine) genotype for base + 874 of the interferon gamma (IFN-gamma) gene was significantly more prevalent in PBLs producing rapid, high-penetrance LPD in hu PBL-SCID mice, compared to PBLs producing late, low-penetrance LPD or no LPD. In examining the relationship between genotype and cytolytic T-lymphocyte (CTL) function, transforming growth factor beta (TGF-beta) inhibited restimulation of CTLs in PBLs with adenosine at IFNG base + 874, but not in PBLs homozygous for thymidine. Importantly, neutralization of TGF-beta in hu PBL-SCID mice injected with A/A genotype PBLs resulted in reduced LPD development and expanded human CD8(+) cells. Thus, our data show that TGF-beta may promote tumor development by inhibiting CTL restimulation and expansion. Further, our data indicate that IFNG genotype may provide valuable information for both identifying transplant recipients at greater risk for PTLD and developing preventive and curative strategies.

Minor H antigen HA-1-specific regulator and effector CD8+ T cells, and HA-1 microchimerism, in allograft tolerance

The role of the hematopoietic lineage-restricted minor histocompatibility (H) antigen HA-1 in renal allograft tolerance was explored. We obtained peripheral blood samples from three recipients of histocompatibility leukocyte antigen (HLA)–matched, HA-1–mismatched renal transplants, one of which had discontinued immunosuppression >30 yr ago while sustaining normal kidney function. Peripheral blood mononuclear cells (PBMCs) were injected into the footpads of severe combined immunodeficiency mice to measure human delayed type hypersensitivity (DTH) responses. All three patients manifested regulated DTH responses to HA-1^H peptide. By differential tetramer staining intensities, we observed two distinct minor H antigen HA-1–specific CD8⁺ T cell subsets. The one that stained dimly had the characteristics of a T regulatory (T_R) cell and produced interleukin (IL) 10 and/or transforming growth factor (TGF) β. These HA-1–specific T_R cells coexisted with bright tetramer-binding CD8⁺ T effector (T_E) cells. The CD8⁺ T_E cells mediated HA-1–specific DTH and produced interferon-γ. Suppression of these T_E functions by T_R cells was TGFβ, IL-10, and cytotoxic T lymphocyte–associated antigen 4 dependent. In addition, HA-1 microchimerism was detected in two recipients, primarily in the dendritic cell fraction of the PBMCs. This is the first demonstration of coexisting CD8⁺ memory T_R and T_E cells, both specific for the same HA-1 antigen, in the context of renal allograft tolerance.

Metastable tolerance to rhesus monkey renal transplants is correlated with allograft TGF-beta 1+CD4+ T regulatory cell infiltrates

Approaches that prevent acute rejection of renal transplants in a rhesus monkey model were studied to determine a common mechanism of acceptance. After withdrawal of immunosuppression, all 14 monkeys retained normal allograft function for >6 mo. Of these, nine rejected their renal allograft during the study, and five maintained normal function throughout the study period. The appearance of TGF-beta 1(+) interstitial mononuclear cells in the graft coincided with a nonrejection histology, whereas the absence/disappearance of these cells was observed with the onset of rejection. Analysis with a variety of TGF-beta 1-reactive Abs indicated that the tolerance-associated infiltrates expressed the large latent complex form of TGF-beta 1. Peripheral leukocytes from rejecting monkeys lacking TGF-beta 1(+) allograft infiltrates responded strongly to donor Ags in delayed-type hypersensitivity trans-vivo assays. In contrast, allograft acceptors with TGF-beta 1(+) infiltrates demonstrated a much weaker peripheral delayed-type hypersensitivity response to donor alloantigens (p < 0.01 vs rejectors), which could be restored by Abs that either neutralized active TGF-beta 1 or blocked its conversion from latent to active form. Anti-IL-10 Abs had no restorative effect. Accepted allografts had CD8(+) and CD4(+) interstitial T cell infiltrates, but only the CD4(+) subset included cells costaining for TGF-beta 1. Our data support the hypothesis that the recruitment of CD4(+) T regulatory cells to the allograft interstitium is a final common pathway for metastable renal transplant tolerance in a non-human primate model.

Regulating the immune system: the induction of regulatory T cells in the periphery

The immune system has evolved a variety of mechanisms to achieve and maintain tolerance both centrally and in the periphery. Central tolerance is achieved through negative selection of autoreactive T cells, while peripheral tolerance is achieved primarily via three mechanisms: activation-induced cell death, anergy, and the induction of regulatory T cells. Three forms of these regulatory T cells have been described: those that function via the production of the cytokine IL-10 (T regulatory 1 cells), transforming growth factor beta (Th3 cells), and a population of T cells that suppresses proliferation via a cell-contact-dependent mechanism (CD4+CD25+ TR cells). The present review focuses on the third form of peripheral tolerance - the induction of regulatory T cells. The review will address the induction of the three types of regulatory T cells, the mechanisms by which they suppress T-cell responses in the periphery, the role they play in immune homeostasis, and the potential these cells have as therapeutic agents in immune-mediated disease.

Effector mechanisms in transplant rejection

Antigens, provided by the allograft, trigger the activation and proliferation of allospecific T cells. As a consequence of this response, effector elements are generated that mediate graft injury and are responsible for the clinical manifestations of allograft rejection. Donor-specific CD8+ cytotoxic T lymphocytes play a major role in this process. Likewise, CD4+ T cells mediate delayed-type hypersensitivity responses via the production of soluble mediators that function to further activate and guide immune cells to the site of injury. In addition, these mediators may directly alter graft function by modulating vascular tone and permeability or by promoting platelet aggregation. Allospecific CD4+ T cells also promote B-cell maturation and differentiation into antibody-secreting plasma cells via CD40-CD40 ligand interactions. Alloantibodies that are produced by these B cells exert most of their detrimental effects on the graft by activating the complement cascade. Alternatively, antibodies can bind Fc receptors on natural killer cells or macrophages and cause target cell lysis via antibody-dependent cell-mediated cytotoxicity. In this review, we discuss these major effector pathways, focusing on their role in the pathogenesis of allograft rejection.

Clinical transplantation tolerance: The promise and challenges

Organ transplantation is now well established as a preferred option for the treatment of end-stage organ failure. However, there is a severe shortage of donor organs and continued loss of a significant number of organ grafts due to chronic allograft dysfunction. Induction of tolerance of a transplant recipient toward their foreign organ graft, therefore, remains the "Holy Grail" of transplantation immunobiologists. Recently, clinical trials to explore pilot tolerance protocols in humans have been initiated. Defining the ideal strategy(ies) and the role of immunosuppressive drugs, developing tolerance assay(s), and enhancing cooperation between transplant professionals, industry, and the government are some of the challenges to achieving clinical transplantation tolerance. This article reviews the promise and the challenges of achieving clinical transplantation tolerance in human organ transplant recipients.

DEMONSTRATION THAT DONOR-SPECIFIC NONRESPONSIVENESS IN HUMAN LIVER ALLOGRAFT RECIPIENTS IS BOTH RARE AND TRANSIENT

BACKGROUND

The side effects of lifetime immunosuppression are a major cause of morbidity and mortality; however, in the absence of prospective monitoring, immunosuppression withdrawal may lead to graft loss from rejection. To detect and monitor suitable recipients for immunosuppression withdrawal, the authors used an in vitro assay of T-cell function to study 71 long-term liver allograft recipients.

METHODS

Interleukin-2 secretion by blood mononuclear cells was measured in response to recall antigens, alloantigen (donor and third-party), and phytohemagglutinin.

RESULTS

Forty-four recipients were studied at a single time point at least 1 month after transplantation. The majority reacted to all antigens (n=33), whereas four showed globally reduced or absent responses (n=4) and six had markedly reduced or absent responses to donor alloantigen in the presence of preserved responses to third-party alloantigen and recall antigens. Four of these donor-nonresponsive recipients were retested 6 to 12 months later, by which time all had redeveloped responses to donor alloantigen. Serial measurements for up to 2 years in a prospective cohort of 27 liver allograft recipients showed only two patients to be consistently donor-nonresponsive posttransplant.

CONCLUSIONS

Most patients rapidly reacquire vigorous immune responses after liver transplantation, and only a minority are hyporesponsive to donor alloantigen. Donor-specific nonresponsiveness is transient in most patients, and serial monitoring is required to define sustained periods of donor-specific nonresponsiveness. Whether such patients are suitable for immunosuppressive withdrawal is unclear.

In vivo IL-10 and TGF-beta production by PBMC from long-term kidney transplant recipients with excellent graft function: a possible feedback mechanism participating in immunological stability

BACKGROUND

Interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta) are Th2-derived multifunctional cytokines that exhibit potent immunoregulatory and anti-inflammatory properties which might prolong graft survival. The aim of this study was to explore whether spontaneous production of IL-10 and TGF-beta by blood mononuclear cells correlates with excellent long-term graft function.

METHODS

A cross-sectional study was carried out in 32 kidney transplant recipients, without albuminuria, treated with azathioprine and prednisone. Spontaneous IL-10 and TGF-beta were measured by enzyme-linked immunosorbent assay in supernatants from 24 h cultured unstimulated peripheral blood mononuclear cells. Both cytokines were also determined in 10 healthy kidney donors.

RESULTS

There was no correlation between IL-10 or TGF-beta with any variable tested, namely age, SCr, histocompatibility, and post-transplant follow-up. In vivo IL-10 production displayed a statistical trend to be higher in transplant recipients than in controls (362.3 +/- 465, range 12.5-1929.3 pg/ml, and 189 +/- 170, range 4.17-485.7 pg/ml, respectively; p = 0.08), whereas no difference was observed in TGF-beta among the same groups (134.7 +/- 79.2, range 68-421 pg/ml, and 121.4 +/- 25.8, range 75-151 pg/ml, respectively). Interestingly, a statistically significant inverse correlation was observed between IL-10 and TGF-beta in kidney transplant recipients (p = 0.03).

CONCLUSIONS

The higher IL-10 production observed in long-term kidney transplant recipients supports the notion that this cytokine contributes in decreasing allogenic immune responses and allows prolongation of allograft survival. The balance between TGF-beta and IL-10 may be of paramount importance in graft acceptance.

Immune regulation and graft survival in kidney transplant recipients are both enhanced by human leukocyte antigen matching

We hypothesized that donor/recipient sharing of the human leukocyte antigen (HLA) involved in allopeptide presentation to the T regulatory cell increases the incidence of immune regulation, thus contributing to long-term graft survival. Peripheral blood mononuclear cells (PBMC) were obtained from 40 living related donor (LRD) and 31 cadaver renal transplant recipients. The trans vivo delayed type hypersensitivity (DTH) assay was used to assign patients to regulator, nonregulator, and sensitized categories. In a large cohort (n=1934 patients), primary graft survival and rejection episodes were analyzed using a log rank test for comparison with the DTH results. The highest incidence of regulated anti-donor DTH was observed in the LRD HLA-identical group (6/6; 100%) followed by the LRD HLA 1 haplotype matched group (18/27; 67%). Within the cadaver population, two DR-matched recipients had a higher frequency of regulated anti-donor DTH (6/11; 55%) than 1 & 0 DR-matched recipients (3/18; 17%). In a multivariate model, matching for HLA-DR alone, or for DR plus DQ was significantly (p=0.045, p=0.041) correlated with DTH regulation. The better HLA-matched groups showed the highest incidence of DTH regulation and, in a larger retrospective analysis, displayed better graft survival and freedom from acute rejection (p<0.0001). HLA matching, and HLA-DR matching in particular, correlates with the incidence of immune regulation after kidney transplantation.

Metastable tolerance in nonhuman primates and humans

It is clear that both humans and nonhuman primates can do without immunosuppression for long periods of time before rejecting their allogeneic organ transplants. Immune cell depletion, particularly lymphocyte depletion, is an effective clinical strategy for achieving a tolerant state. Based on nonhuman primate and human studies, evidence suggests that metastable tolerance develops over time in a donor-specific manner and is mediated at least in part by donor antigen-specific regulatory T cells. Suppression of effector T cells by CD8+ and CD4+ T-regulatory cells is mediated by transforming growth factor (TGF)-beta or interleukin 10, and the presence of CD4+ TGF beta(latent) T-cell infiltrates may be a useful diagnostic marker for metastable tolerance. Loss of these cells has been shown to correlate with loss of tolerance. Future efforts to withdraw immunosuppressive drugs and establish a tolerant state will depend importantly on development of such diagnostic immunologic monitoring tools. Some of the reasons that tolerance remains such a challenging goal in clinical transplantation are discussed herein.

Tolerance to noninherited maternal MHC antigens in mice

The phenomenon of tolerance to noninherited maternal Ags (NIMA) is poorly understood. To analyze the NIMA effect C57BL/6 (H-2(b/b)) males were mated with B6D2F(1) (H-2(b/d)) females, whereby 50% of the offspring are H-2(b/b) mice that have been exposed to maternal H-2(d) alloantigens. Controls were H-2(b/b) offspring of C57BL/6 mothers, either inbred C57BL/6 mice or F(1) backcross mice from breedings with H-2(b/d) fathers. We found that 57% of the H-2(b/b) offspring of semiallogeneic (H-2(b/d)) mothers accepted fully allogeneic DBA/2 (H-2(d/d)) heart grafts for >180 days, while similar transplants were all rejected by day 11 in controls (p < 0.0004). Foster nursing studies showed that both oral and in utero exposure to NIMA are required for this tolerogenic effect. An effect of NIMA was also found to extend the survival of skin grafts from a semiallogeneic donor (p < 0.02). Pretransplant analysis of splenocytes showed a 40-90% reduction of IL-2-, IL-5-, and IFN-gamma-producing T cells responding to H-2(d)-expressing APC in NIMA(d)-exposed vs control mice. Injection of pregnant BALB/c-dm2 (H-2L(d)-negative) female mice i.v. with H-2L(d)(61-80) peptide profoundly suppressed the offspring's indirect pathway alloreactive CD4(+) T cell response to H-2L(d). These results suggest that the natural exposure of the fetus and newborn to maternal cells and/or soluble MHC Ags suppresses NIMA-allospecific T cells of the offspring, predisposing to organ transplant tolerance in adult mice.

The role of cytokines (and not only) in inducing and expanding T regulatory type 1 cells

T regulatory (Tr) type 1 cells are one of the most studied of CD4+ Tr cell subsets. They are distinct from other T-cell subsets in their cytokine production profile and in their ability to suppress immune responses both in vitro and in vivo. Human and murine Tr1 cells share many properties, but signals regarding their in vitro induction are different. Although culture of murine naive CD4+ cells in the presence of high doses of interleukin (IL)-10 is sufficient for Tr1 induction, human naive CD4+ T cells can give rise to Tr1 cells when cultured with IL-10 and interferon-alpha. Tr1 cells can also be induced in vivo, although the mere administration of IL-10 is not sufficient to generate Tr1 cells in a context of murine allogenic transplant. IL-10 needs to be combined with immunosuppressive compounds, which are permissive for tolerance induction, to generate or expand Tr1 cells in vivo and mediate antigen-specific tolerance. Whether this combined treatment can also be used in humans is still an open question.

Immunologic monitoring

The development of reliable in vitro assays that could allow the quantitation and characterization of anti-donor alloimmune responses has always been a goal in clinical transplantation, both to predict presensitization to the transplanted tissue and to be able to identify rejection without resorting to more invasive tests. With recent development in our understanding of transplantation biology and therapeutics, there is a real expectation that these tests may be used to identify tolerance as much as to predict rejection. The traditional limiting dilution assays still have a contribution to make and are being complemented by an array of tools, such as ELISpot, flow cytometry-based techniques, and microarray analysis. The assays that have been informative, to date, are discussed in this review. This information will lead, at least, to a better understanding of how and when the rejection process occurs. More interestingly, the objective is to apply this information to evaluate tolerance-inducing strategies or to identify patients that have become tolerant to their graft and can be weaned of immunosuppression. Of course sensitive, accurate and specific immunologic monitoring has applications well beyond the field of transplantation.

Regulatory CD25+ T cells in human kidney transplant recipients

Recent evidence suggests that a population of professional regulatory cells, which limit immune responsiveness, exist in rodents and healthy human subjects. However, their role in disease states remains unclear. A proportion of renal transplant recipients do not demonstrate in vitro reactivity toward their mismatched donor-derived HLA-DR antigens; it was therefore hypothesized that this may be due to such regulatory cells. A cohort of 23 renal transplant recipients was studied at a single institution. In patients with no history of acute rejection, 6 (40%) of 15 demonstrated regulation toward the mismatched HLA-DR allopeptides by CD25(+) cells. By contrast, only one (12.5%) in eight of those with a history of acute rejection demonstrated regulation. Interestingly, if the patient assays were stratified according to initial in vitro immune responsiveness toward the mismatched allopeptides, 8 (47.1%) of 17 of patient assays with low allopeptide responsiveness (alloreactive T cell frequencies less than 60/million) demonstrated regulation of indirect pathway alloresponses by CD25(+) cells, whereas 0 of 8 with higher responses (frequencies greater than 60/million) demonstrated no such regulation (P < 0.05 by chi(2) test). The regulatory cells are present in the circulation as early as 3 mo after transplantation and persist for a number of years, despite conventional immunosuppression. Furthermore, induction treatment with anti-IL-2R mAb did not prevent the development of these regulatory CD25(+) cells. Data from two patients suggest that these cells may also play a role in preventing epitope shifting, implicated in the ongoing immune activation contributing to chronic rejection, and that loss of regulation in a given patient may precede an episode of rejection.

The vasculopathy of Raynaud's phenomenon and scleroderma

The scleroderma (SSc) disease process involves dramatic dysfunction in acute and chronic vascular regulatory mechanisms; it presents initially with heightened vasoconstrictor or vasospastic activity and progresses to structural derangement or vasculopathy of the microcirculation. This article discusses the regulatory mechanisms that contribute to this dysfunction and the vascular changes in the context of the other aspects of the SSc disease process in a novel attempt to integrate the individual pathologies of the disease process.

Immunobiology and long-term graft function in a transplant heterotopic renal rat model

BACKGROUND

The Th1-Th2 paradigm proposes clonal expansion of Th2 lymphocytes as the basis of allograft tolerance. The Th2 cells have been found to be present in recipients with long-term allograft survival. However, the presence of Th2 cells and tolerance is not a uniform finding. Previously we have shown that pre-engraftment single dose rapamycin and a 7-d course of cyclosporin induce transplantation tolerance to 120 d. In the present study, we investigated the immunobiology of grafts in a long-term follow-up (>350 d).

METHODS

Kidney allografts (n = 7), isografts (n = 5) and single nephrectomy (n = 3) groups were followed for 350 +/- 87 d. Heterotopic kidney transplant was performed by the same surgeon in the allograft group (ACI-Lewis) and the isograft group (Lewis-Lewis). The left kidney was removed in the single nephrectomy group. The allograft group was treated with pre-engraftment single dose rapamycin and a 7-d course of cyclosporin. A kidney biopsy was performed at midpoint time for histological study and tissue was frozen for measuring intragraft cytokine expression (IL-4, IL-10) in all animals. Prior to biopsy, serum blood urea nitrogen (BUN) and creatinine (Cr) levels were studied. Serum BUN, Cr levels, plus 24-h urinary protein (PRO) were measured prior to sacrifice. Randomly, four allograft rats received skin grafts (ACI, Lewis and Buffalo skin donors) after kidney biopsy. Skin grafts were studied for a mean of 6 weeks for signs of acceptance or rejection. Analysis of variance (ANOVA) with Tukey's test was used; p < 0.05 was considered statistically significant.

RESULTS

The mean follow up was 352 +/- 87 d. BUN and Cr levels at biopsy time (mean 214 d) were not statistically different between the three groups (p = 0.19 and p = 0.66). At sacrifice (mean 352 d), BUN, Cr and PRO were statistically different between allograft and isograft groups (p = 0.013), and between allograft and single nephrectomy groups (p = 0.027). Functional and histological signs of graft loss occurred in three of seven (42.8%) of the allografts at 352 d. Using BANFF criteria, three allografts at biopsy time and seven allografts (100%) and four isografts (80%) at sacrifice time developed chronic histologic changes. Intragraft overexpression of IL-4 and IL-10 was seen at biopsy and sacrifice time in six of seven allografts and one of five isografts. All donor specific skin grafts (ACI-Lewis) on allografts were accepted and third party (Buffalo) donor skin grafts were rejected in all animals (>95% skin necrosis).

CONCLUSIONS

This highly stringent, functional, renal transplant model yields 100% normal renal function as compared with isografts at 120 d follow-up. With the follow-up extended to 350 d, 43% of the allografts loose function and develop a chronic allograft histology despite a demonstrated intragraft Th2 cytokine dominance and donor specific skin graft acceptance.

IFN-gamma production is specifically regulated by IL-10 in mice made tolerant with anti-CD40 ligand antibody and intact active bone

We have developed a strategy to induce tolerance to allografts, involving cotransplantation of allogeneic intact active bone and transient anti-CD40 ligand mAb therapy. Tolerance induced by this approach in C57BL/6 mice receiving BALB/c hearts is not mediated by deletional mechanisms, but by peripheral regulatory mechanisms. Tolerance is associated with diminished ex vivo IFN-gamma production that is donor specific, and a reduction in the frequency of IFN-gamma-producing cells. Splenocytes from mice tolerant to BALB/c grafts, but sensitized to third-party C3H skin grafts, demonstrated normally primed ex vivo IFN-gamma responses to C3H stimulators. Neutralizing anti-IL-10 and anti-IL-10R, but not anti-TGF-beta, anti-IL-4, or anti-CTLA-4, Abs restored the ex vivo IFN-gamma response to BALB/c stimulators. There was no significant difference in IL-2 or IL-4 production between tolerant and rejecting mice, and anti-IL-10 mAbs had no effect on IL-2 or IL-4 production. The Cincinnati cytokine capture assay was used to test whether suppression of IFN-gamma production in vivo was also a marker of tolerance. In naive mice, we observed a dramatic increase in serum IFN-gamma levels following challenge with allogeneic BALB/c splenocytes or hearts. Tolerant mice challenged with allogeneic BALB/c splenocytes or hearts made significantly less or undetectable amounts of IFN-gamma. No IL-4 or IL-10 production was detected in tolerant or rejecting mice. Collectively, our studies suggest that active suppression of IFN-gamma production by IL-10 is correlated with, and may contribute to, tolerance induced with intact active bone and anti-CD40 ligand mAbs.

Allograft acceptance despite differential strain-specific induction of TGF-beta/IL-10-mediated immunoregulation

We examined the immune approaches that C57BI/6 and BALB/c mice take when treated to accept cardiac allografts. C57BI/6 mice accept DBA/2 cardiac allografts when treated with gallium nitrate (GN) or anti-CD40L mAb (MR1). These allograft acceptor mice fail to mount donor-reactive delayed type hypersensitivity (DTH) responses, and develop a donor-induced immunoregulatory mechanism that inhibits DTH responses. In contrast, BALB/c mice accept C57BI/6 cardiac allografts when treated with MR1 but not with GN. These allograft acceptor mice display modest donor-reactive DTH responses, and do not develop donor-induced immune regulation of DTH responses. Real-time PCR analysis of rejecting graft tissues demonstrated no strain-related skewing in the production of cytokines mRNAs. In related studies, C57BI/6 recipients of cytokine and alloantigen educated syngeneic peritoneal exudate cells (PECs) failed to mount DTH responses to the alloantigens unless neutralizing antibodies to transforming growth factor-beta (TGF-p were present at the DTH site demonstrating regulation of cell-mediated alloimmune responses. In contrast, BALB/c recipients of cytokine-and alloantigen-educated PECs expressed strong DTH responses to alloantigens demonstrating a lack of regulated alloimmunity. In conclusion, C57BI/6 mice respond to immunosuppression by accepting cardiac allografts and generating TGF-beta-related regulation of donor-reactive T cell responses, unlike BALB/c mice that do not generate these regulatory responses yet still can accept cardiac allografts.

Interferon-gamma drives the metalloproteinase-dependent cleavage of HLA class I soluble forms from primary human bronchial epithelial cells

Activation of bronchial epithelial cells (BEC) and disruption of an intact epithelial barrier in a lung transplant recipient can lead to acute or chronic rejection, events that are associated with release of soluble human leukocyte antigen (sHLA) class I. Although we know that HLA is released from mitogen-activated lymphocytes in a metalloproteinase (MPase)-dependent fashion, the mechanism of release from nonlymphoid tissue is not well understood. To this end, we stimulated primary BEC with increasing amounts of the T-helper cell-1 cytokines, interferon gamma (IFNgamma), and/or tumor necrosis factor alpha (TNFalpha) and measured the quantity and forms of HLA class I release. We found that IFNgamma, but not TNFalpha, was able to stimulate a time- and concentration-dependent release of HLA/beta(2)m and beta(2)m-free heavy chain (HC) from the BEC. A portion (50%) of the HLA/beta(2)m release and >90% of the beta(2)m-free HC release was mediated by a MPase. Western blot analysis supported the conclusion that a MPase-sensitive pathway produced 36 and 37 kDa cleaved forms, whereas the secreted 39 kDa form of beta(2)m-associated soluble HLA class I (sHLA/beta(2)m) was MPase-resistant. This adds to the growing understanding of the extracellular processing pathways of major histocompatibility complex class I that may be critical for both chronic rejection as well as immune regulation.

Evolution of the enzyme-linked immunosorbent spot assay for post-transplant alloreactivity as a potentially useful immune monitoring tool

Post-transplant monitoring of cellular immunity has the potential to guide alterations in medical therapy. To this end, our laboratory has developed an enzyme-linked immunosorbent spot (ELISPOT) assay for detection of peripheral blood alloimmunity. Peripheral blood lymphocytes (PBLs) from normal volunteers and from renal allograft recipients were tested against donor stimulator cells for their ability to respond in 'one-way' cytokine ELISPOT assays. T cell depletion of donor spleen or PBLs eliminated donor cell cytokine secretion while preserving the ability of these cells to present allo-antigen to responding T cells. Alloreactive IFN-gamma-producing PBLs derive from the memory T cell pool and are readily detectable in recipients of renal allografts taking immunosuppressant medications. A significant expansion of IFN-gamma-producing donor-reactive memory PBLs was detectable at 4-6 months post-transplant in those who had experienced an acute rejection episode compared with those with a stable post-transplant course. The data demonstrate the feasibility of repeated post-transplant monitoring of allograft recipients, and provide the foundation for improving the care of human transplant recipients through rational clinical decision-making based on measures of immune function.

Human liver allograft acceptance and the "tolerance assay". II. Donor HLA-A, -B but not DR antigens are able to trigger regulation of DTH

In our initial study of liver transplant recipients using the trans vivo delayed-type hypersensitivity (DTH) assay, we found that in donor derived B-LCL or sonicates of donor leukocytes triggered linked suppression of the response to recall antigens tetanus toxoid (TT) or Epstein-Barr virus (EBV). Since both donor antigen sources contain HLA class I and class II proteins, we wished to determine which donor HLA proteins were responsible for the linked suppression effect. PBMC from four liver transplant recipients with donor-specific DTH regulation were studied. Surprisingly, we found that single donor HLA-A or B antigens (4/4 patients) but not single HLA-DR (0/4) donor antigens triggered linked suppression of DTH. A dose response study of two patients revealed that donor-type HLA-DR antigens (0.5-500ng) were not capable of triggering any linked suppression; however, as little as 500pg of donor-type HLA-class I protein triggered linked suppression of DTH response to a recall antigen. These findings may have implications for the differential impacts of class I vs class II mismatching in organ transplantation. On a practical level, they indicate that soluble HLA-A and B antigens are the proper choice for detection of DTH regulation as part of a "tolerance assay" in human liver transplant recipients.

Strategies for preclinical evaluation of dendritic cell subsets for promotion of transplant tolerance in the nonhuman primate

A role for dendritic cells (DC) as critical regulators of immune reactivity has become increasingly recognized. There is evidence in rodent models that donor-derived DC, particularly in the immature state, can prolong organ allograft survival and even induce donor-specific tolerance. To allow the potential tolerogenic properties of these cells to be evaluated more fully with a view to clinical testing, it is necessary to identify DC subsets in nonhuman primates. We have identified the putative rhesus monkey equivalents of circulating human DC subset precursors as lineage(-), HLA-DR(+), CD123(lo),CD11c(hi)(pDC1) and lineage(-), HLA-DR(+), CD123(hi),CD11c(lo)(pDC2). Testing of these DC populations both in vitro and in vivo, as well as in transplant models in combination with conventional or experimental immunosuppressive reagents, will aid the development of novel strategies for the promotion of allo-antigen specific tolerance in transplantation.

MHC-identical heart and hepatocyte allografts evoke opposite immune responses within the same host

BACKGROUND

Purified allogeneic hepatocytes are highly antigenic and elicit immune responses that are not easily controlled. However, it is not clear whether hepatocytes are not capable of protective immune mechanisms or whether they are not to protection by immune mechanisms that permit long-term survival of other allografts. The purpose of the current study was to determine whether donor-matched allogeneic hepatocytes are protected from rejection in mice that have been induced to accept heart allografts.

METHODS

Transient treatment with anti-CD4 monoclonal antibody (mAb) or gallium nitrate (GN) was used to induce acceptance of heterotopic FVB/N (H-2(q)) heart allografts by C57BL/6 (H-2(b)) mice. Transgenic hA1AT-FVB/N hepatocytes were sequentially transplanted into C57BL/6 mice that had accepted FVB/N heart allografts more than 60 days (heart acceptor mice), CD8 depleted C57BL/6 heart acceptor mice, or B-cell knockout (BCKO, H-2(b)) heart acceptor mice. Hepatocyte survival was determined by the detection of secreted transgenic product hA1AT by enzyme-linked immunosorbent assay (ELISA).

RESULTS

FVB/N hepatocytes were rejected by day 10-14 posttransplant, while FVB/N heart allografts continued to function in C57BL/6, BCKO, and CD8 depleted heart acceptor mice. When FVB/N hepatocytes and heart allografts were transplanted into C57BL/6 or BCKO mice under short-term cover of anti-CD4 mAb or GN, hepatocyte rejection occurred by day 10 posttransplant, while most heart allografts survived for more than 60 days.

CONCLUSIONS

Hepatocyte rejection does not appear to interfere with the of mechanisms that permit heart allograft acceptance. However, immune responses to allogeneic hepatocytes are not to regulation by mechanisms induced in heart acceptor mice. The simultaneous rejection of FVB/N allogeneic hepatocytes and continued acceptance of FVB/N-matched heart allografts is independent of host CD8+ T cells and humoral immunity.

Regulatory functions of alloreactive Th2 clones in human renal transplant recipients

BACKGROUND

Chronic allograft rejection is the major clinical problem in organ transplantation. There is evidence that indirect T cell recognition of donor-specific HLA peptides may play an important role in the immunopathogenesis of chronic allograft rejection. We have recently shown that HLA allopeptide-specific T cell clones generated from renal transplant recipients with chronic allograft nephropathy are of the Th1 phenotype, while those from stable patients are Th2. There is evidence in experimental animal models of autoimmunity and transplantation that Th2 cells may function to regulate immune responses, but the biological relevance of these observations in humans has not been reported.

METHODS

The purpose of this study was to investigate the putative regulatory functions of alloreactive human Th2 clones. HLA-DR allopeptide-specific Th1 and Th2 cell clones were generated from peripheral blood lymphocytes of human renal allograft recipients with chronic allograft nephropathy (CAN) or with stable renal function (SRF), respectively.

RESULTS

An in vitro co-culture system showed that the proliferative responses of Th1 clones from patients with CAN were significantly inhibited by the Th2 clones in response to the donor-derived HLA allopeptides. In addition, co-culture of the Th2 clones inhibited cytokine production (IFN-gamma) by the Th1 clones in response to the donor-specific peptides. The regulatory functions of Th2 clones were antigen-specific since they only occurred when both the Th1 and Th2 clones were reactive to the same HLA-DR allopeptide, and were mediated by IL-4 and IL-10.

CONCLUSIONS

This is the first demonstration, to our knowledge, indicating that Th2 cells may function to regulate indirect Th1 alloimmune responses that are critical for the progression of CAN in humans.

Antigen-bearing immature dendritic cells induce peptide-specific CD8(+) regulatory T cells in vivo in humans

Regulatory T cells (T(R)s) can suppress the function of other effector T cells in the setting of autoimmunity, transplantation, and resistance to tumors. The mechanism for the induction of T(R)s has not been defined. We previously reported that an injection of immature dendritic cells (DCs) pulsed with influenza matrix peptide (MP) led 7 days later to antigen-specific silencing of effector T-cell function in the blood of 2 healthy human subjects. Here, we found that interferon-gamma-producing effectors return by 6 months. Importantly, in mixing experiments, CD8(+) T cells from the sample obtained 7 days after injection could suppress MP-specific effectors obtained before injection and those in recovery samples. This suppression or regulation was specific for the immunizing peptide (MP) and cell-dose dependent, and it required contact between the 2 samples. These data show the capacity of immature DCs to induce antigen-specific regulatory CD8(+) T cells in humans.

Evidence that a similar range of alloimmune responses can develop in murine and human allograft recipients

Based on discrepancies between various laboratory and clinical observations, skepticism has developed regarding the pre-clinical value of rodent immunologic studies. In this article, we review the progression of our murine and human studies over the last several years, which have demonstrated that humans and mice can make very similar types of immune responses in vivo to allografts. Early studies by ourselves and others, demonstrated that mice can make either pro-inflammatory (rejection) or anti-inflammatory (acceptance) immune responses to graft alloantigens. We demonstrated that donor-reactive DTH assays could be used to monitor which type of alloimmune response had been selected by the allograft recipient. To help determine if similar immune response options are available to humans and detectable by DTH assays, we first developed the transvivo DTH assay. In this system, mice are used as a receptacle in which DTH responses made by human PBMC can be induced and measured. These transvivo DTH studies revealed that human allograft recipients, like mice, commonly make either pro-inflammatory or anti-inflammatory immune responses to graft alloantigens. In transplant patients, this rarely correlates with the development of donor-reactive alloantibodies during the post-transplant period.

Acute graft pyelonephritis and long-term kidney allograft outcome

BACKGROUND

Long-term graft function is the result of multiple parameters, including both immune and non-immune components, which have a beneficial or detrimental potential. Among these, despite its frequency and theoretical interest (expression of "danger signals" in the graft itself), the effects of acute graft pyelonephritis (AGPN) on immediate and long-term outcome have not been studied in a large series. This article reviews a cohort of 1387 consecutive primary renal transplant recipients.

METHODS

The objective of the study was to define the risk factor for AGPN, the risk profile for recurrence, and the impact of AGPN on long-term graft survival. According to a higher risk for AGPN in females during their follow-up, statistical analyses (Cox model, and multiple regression analysis) were performed by recipient sex strata.

RESULTS

Multivariate analysis showed that CMV infection was the only risk factor for AGPN occurrence. AGPN occurred in 13% of the graft recipients during their follow-up. Taken as a whole, AGPN was not associated with a significantly poor long-term outcome. However, when assessed in more detail, the outcome of this population was found to be more complex and to depend on several factors. Early AGPN (during the first 3 months) was significantly detrimental for graft outcome, independently of acute rejection episodes. Moreover, E. coli involvement in a first episode was linked to an increased AGPN recurrence.

CONCLUSION

This analysis did not support the concept that with current immunosuppression, strong "danger signals" such as those derived from bacteria within an allograft, are instrumental in initiating acute or chronic rejection.

Long-term care of pediatric renal transplant patients: from bench to bedside

In this review, we discuss current and future issues in the management of pediatric renal transplant recipients, including the optimization of long-term graft function and the minimization of complications caused by immunosuppression. Long-term management involves not only the monitoring of graft function but also the identification of patients at risk for the development of complications. The identification of patients with immunoreactive or immunoregulatory responses can be performed molecular monitoring of the immune response. Also, the use of frequent surveillance kidney biopsies, surrogate markers of chronic rejection, and glomerular filtration rate will be a part of future management. Identifying high-risk patients enables the physician to optimize immunosuppression to limit acute rejection. Short-and long-term management of pediatric transplant patients also includes adequate monitoring of growth and the monitoring for post-transplant lymphoproliferative disease. Ongoing clinical trials are underway that focus on these novel approaches in caring for pediatric transplant recipients.

Cellular methods used to evaluate the immune response in transplantation

Cellular assays have been developed to test for various effector, cytotoxic, and regulatory functions of T cells and have been used throughout the history of clinical transplantation to assess the immune profile of solid organ and marrow recipients. One goal of these cellular studies has been to determine if posttransplant changes in the donor antigen-specific cellular response could predict good and poor graft outcome, thereby allowing for individualization of immunosuppression. This review outlines the use of established and newly developed cellular assays to assess the dynamic processes of the posttransplant immune response and to provide insights into the mechanisms involved and potential points for intervention.

Loss of direct and maintenance of indirect alloresponses in renal allograft recipients: implications for the pathogenesis of chronic allograft nephropathy

Chronic allograft nephropathy (CAN) is the principal cause of late renal allograft failure. This complex process is multifactorial in origin, and there is good evidence for immune-mediated effects. The immune contribution to this process is directed by CD4(+) T cells, which can be activated by either direct or indirect pathways of allorecognition. For the first time, these pathways have been simultaneously compared in a cohort of 22 longstanding renal allograft recipients (13 with good function and nine with CAN). CD4(+) T cells from all patients reveal donor-specific hyporesponsiveness by the direct pathway according to proliferation or the secretion of the cytokines IL-2, IL-5, and IFN-gamma. Donor-specific cytotoxic T cell responses were also attenuated. In contrast, the frequencies of indirectly alloreactive cells were maintained, patients with CAN having significantly higher frequencies of CD4(+) T cells indirectly activated by allogeneic peptides when compared with controls with good allograft function. An extensive search for alloantibodies has revealed significant titers in only a minority of patients, both with and without CAN. In summary, this study demonstrates widespread donor-specific hyporesponsiveness in directly activated CD4(+) T cells derived from longstanding recipients of renal allografts, whether they have CAN or not. However, patients with CAN have significantly higher frequencies of CD4(+) T cells activated by donor Ags in an indirect manner, a phenomenon resembling split tolerance. These findings provide an insight into the pathogenesis of CAN and also have implications for the development of a clinical tolerance assay.

Predominant IL-10 production in indirect alloreactivity is not associated with rejection

In a prospective study of indirect alloresponse in renal transplantation, we detected proliferation and cytokine production to donor and third-party HLA-DR peptides unrelated to rejection. Twenty of 28 patients (71%) presented proliferation, 29% before and 71% after transplantation. Half of the patients also presented proliferation to third-party peptides. Indirect alloresponse was also detected in 75% of healthy individuals (HI). Variability of response was observed in patients and HI for both proliferation and cytokine production. IL-10 predominance was observed in indirect alloresponses to donor peptides pre- and post-Tx, in contrast with more IFN-gamma and TGF-beta being detected in HI. IL-10 production was frequently detected without proliferation, in contrast with more frequent proliferation being found with IFN-gamma and TGF-beta production. The lack of association of either cytokine or proliferation with rejection, together with the predominance of IL-10 unrelated to proliferation, suggests that regulatory cells may be part of the T cell repertoire involved in indirect alloreactivity.

Murine renal allografts: spontaneous acceptance is associated with regulated T cell-mediated immunity

It was shown >20 yr ago that mice will spontaneously accept renal allografts in the absence of immunosuppression, but the mechanism responsible for this is not understood. We transplanted DBA/2 (H-2(d)) kidneys into nephrectomized C57BL/6 (H-2(b)) mice, and the allografts were spontaneously accepted for >60 days without immunosuppression. In contrast, nonimmunosuppressed cardiac and skin allografts in the same strain combination are rejected within approximately 10 days. The accepted renal allografts have a prominent leukocytic infiltrate, suggesting an ongoing, local immune response. At 60 days post-transplant, the recipients of accepted renal allografts display DBA/2-reactive alloantibodies. They also display DBA/2-reactive delayed-type hypersensitivity responses that are actively counter-regulated by DBA/2-induced TGF-beta production, but not by IL-10 production. These data suggest that a donor-reactive, cell-mediated immune mechanism involving TGF-beta is associated with the spontaneous acceptance of renal allografts in mice.

Human liver allograft acceptance and the "tolerance assay": in vitro anti-donor T cell assays show hyporeactivity to donor cells, but unlike DTH, fail to detect linked suppression

Human allograft acceptance is associated with immune regulation, characterized by donor-antigen-linked suppression of delayed-type hypersensitivity (DTH). We wished to determine if "classical" in vitro assays of alloreactivity could also detect linked suppression and thus be useful in the clinical diagnosis of active immune regulation. We analyzed peripheral blood mononuclear cells from a group of eight liver transplant recipients, one of whom had stopped all immunosuppression 4.5 years ago yet continues to have good graft function (graft acceptor). The regulator phenotype was defined as the ability to suppress a DTH response to a recall antigen in the presence of donor antigen. Using the trans vivo DTH test, we identified four regulators, and four nonregulators. When we tested two of the regulators for in vitro mixed lymphocyte culture (MLC) and cytotoxic T lymphocyte (CTL) responses to B-lymphoblastoid cell lines (B-LCL), we found both patients to be specifically hyporesponsive to donor compared with third-party B-LCL stimulators. However, in contrast to the linked suppression of DTH seen when a given B-LCL expressed donor-type HLA-B antigens, there was no evidence of linked suppression in vitro, either in CTL, proliferative, or interferon-gamma cytokine release assays. The primary CTL hyporesponsiveness to donor B-LCL could not be reversed by neutralizing antibodies to transforming growth factor beta or interleukin-10, which could restore a strong DTH response to donor B-LCL. We conclude that DTH analysis can readily detect donor antigen-linked suppression in liver transplant recipients. CTL and MLC tests failed to do so. These findings may be relevant to the development of a tolerance assay suitable for use in clinical trials.

Regulatory T cells induced by 1 alpha,25-dihydroxyvitamin D3 and mycophenolate mofetil treatment mediate transplantation tolerance

1alpha,25-dihydroxyvitamin D3, the active form of vitamin D3, and mycophenolate mofetil, a selective inhibitor of T and B cell proliferation, modulate APC function and induce dendritic cells (DCs) with a tolerogenic phenotype. Here we show that a short treatment with these agents induces tolerance to fully mismatched mouse islet allografts that is stable to challenge with donor-type spleen cells and allows acceptance of donor-type vascularized heart grafts. Peritransplant macrophages and DCs from tolerant mice express down-regulated CD40, CD80, and CD86 costimulatory molecules. In addition, DCs from the graft area of tolerant mice secrete, upon stimulation with CD4+ cells, 10-fold lower levels of IL-12 compared with DCs from acutely rejecting mice, and induce a CD4+ T cell response characterized by selective abrogation of IFN-gamma production. CD4+ but not CD8+ or class II+ cells from tolerant mice, transferred into naive syngeneic recipients, prevent rejection of donor-type islet grafts. Graft acceptance is associated with impaired development of IFN-gamma-producing type 1 CD4+ and CD8+ cells and an increased percentage of CD4+CD25+ regulatory cells expressing CD152 in the spleen and in the transplant-draining lymph node. Transfer of CD4+CD25+ cells from tolerant but not naive mice protects 100% of the syngeneic recipients from islet allograft rejection. These results demonstrate that a short treatment with immunosuppressive agents, such as 1alpha,25-dihydroxyvitamin D3/mycophenolate mofetil, induces tolerance to islet allografts associated with an increased frequency of CD4+CD25+ regulatory cells that can adoptively transfer transplantation tolerance.

IL-10 is required for regulatory T cells to mediate tolerance to alloantigens in vivo

We present evidence that donor-reactive CD4(+) T cells present in mice tolerant to donor alloantigens are phenotypically and functionally heterogeneous. CD4(+) T cells contained within the CD45RB(high) fraction remained capable of mediating graft rejection when transferred to donor alloantigen-grafted T cell-depleted mice. In contrast, the CD45RB(low) CD4(+) and CD25(+)CD4(+) populations failed to induce rejection, but rather, were able to inhibit rejection initiated by naive CD45RB(high) CD4(+) T cells. Analysis of the mechanism of immunoregulation transferred by CD45RB(low) CD4(+) T cells in vivo revealed that it was donor Ag specific and could be inhibited by neutralizing Abs reactive with IL-10, but not IL-4. CD45RB(low) CD4(+) T cells from tolerant mice were also immune suppressive in vitro, as coculture of these cells with naive CD45RB(high) CD4(+) T cells inhibited proliferation and Th1 cytokine production in response to donor alloantigens presented via the indirect pathway. These results demonstrate that alloantigen-specific regulatory T cells contained within the CD45RB(low) CD4(+) T cell population are responsible for the maintenance of tolerance to donor alloantigens in vivo and require IL-10 for functional activity.