Rapamycin Does Not Induce Anergy but Inhibits Expansion and Differentiation of Alloreactive Human T Cells

Regulatory T cells as metabolic sensors

Compelling experimental evidence links immunity and metabolism. In this perspective, we propose forkhead-box-P3 (FoxP3)⁺CD4⁺CD25⁺ regulatory T (Treg) cells as key metabolic sensors controlling the immunological state in response to their intrinsic capacity to perceive nutritional changes. Treg cell high anabolic state in vivo, residency in metabolically crucial districts, and recirculation between lymphoid and non-lymphoid sites enable them to recognize the metabolic cues and adapt their intracellular metabolism and anti-inflammatory function at the paracrine and systemic levels. As privileged regulators at the interface between neuroendocrine and immune systems, the role of Treg cells in maintaining metabolic homeostasis makes these cells promising targets of therapeutic strategies aimed at restoring organismal homeostasis not only in autoimmune but also metabolic disorders.

Comparing the Effects of the mTOR Inhibitors Azithromycin and Rapamycin on In Vitro Expanded Regulatory T Cells

Adoptive transfer of autologous polyclonal regulatory T cells (Tregs) is a promising option for reducing graft rejection in allogeneic transplantation. To gain therapeutic levels of Tregs there is a need to expand obtained cells ex vivo, usually in the presence of the mTOR inhibitor Rapamycin due to its ability to suppress proliferation of non-Treg T cells, thus promoting a purer Treg yield. Azithromycin is a bacteriostatic macrolide with mTOR inhibitory activity that has been shown to exert immunomodulatory effects on several types of immune cells. In this study we investigated the effects of Azithromycin, compared with Rapamycin, on Treg phenotype, growth, and function when expanding bulk, naïve, and memory Tregs. Furthermore, the intracellular concentration of Rapamycin in CD4+ T cells as well as in the culture medium was measured for up to 48 h after supplemented. Treg phenotype was assessed by flow cytometry and Treg function was measured as inhibition of responder T-cell expansion in a suppression assay. The concentration of Rapamycin was quantified with liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Azithromycin and Rapamycin both promoted a FoxP3-positive Treg phenotype in bulk Tregs, while Rapamycin also increased FoxP3 and FoxP3+Helios positivity in naïve and memory Tregs. Furthermore, Rapamycin inhibited the expansion of naïve Tregs, but also increased their suppressive effect. Rapamycin was quickly degraded in 37°C medium, yet was retained intracellularly. While both compounds may benefit expansion of FoxP3+ Tregs in vitro, further studies elucidating the effects of Azithromycin treatment on Tregs are needed to determine its potential use.

IL-2-Mediated In Vivo Expansion of Regulatory T Cells Combined with CD154-CD40 Co-Stimulation Blockade but Not CTLA-4 Ig Prolongs Allograft Survival in Naive and Sensitized Mice

In recent years, regulatory T cells (Treg)-based immunotherapy has emerged as a promising strategy to promote operational tolerance after solid organ transplantation (SOT). However, a main hurdle for the therapeutic use of Treg in transplantation is their low frequency, particularly in non-lymphopenic hosts. We aimed to expand Treg directly in vivo and determine their efficacy in promoting donor-specific tolerance, using a stringent experimental model. Administration of the IL-2/JES6-1 immune complex at the time of transplantation resulted in significant expansion of donor-specific Treg, which suppressed alloreactive T cells. IL-2-mediated Treg expansion in combination with short-term CD154–CD40 co-stimulation blockade, but not CTLA-4 Ig or rapamycin, led to tolerance to MHC-mismatched skin grafts in non-lymphopenic mice, mainly by hindering alloreactive CD8⁺ effector T cells and the production of alloantibodies. Importantly, this treatment also allowed prolonged survival of allografts in the presence of either donor-specific or cross-reactive memory cells. However, late rejection occurred in sensitized hosts, partly mediated by activated B cells. Overall, these data illustrate the potential but also some important limitations of Treg-based therapy in clinical SOT as well as the importance of concomitant immunomodulatory strategies in particular in sensitized hosts.

Ex vivo Akt inhibition promotes the generation of potent CD19CAR T cells for adoptive immunotherapy

Background

Insufficient persistence and effector function of chimeric antigen receptor (CAR)-redirected T cells have been challenging issues for adoptive T cell therapy. Generating potent CAR T cells is of increasing importance in the field. Studies have demonstrated the importance of the Akt pathway in the regulation of T cell differentiation and memory formation. We now investigate whether inhibition of Akt signaling during ex vivo expansion of CAR T cells can promote the generation of CAR T cells with enhanced antitumor activity following adoptive therapy in a murine leukemia xenograft model.

Methods

Various T cell subsets including CD8+ T cells, bulk T cells, central memory T cells and naïve/memory T cells were isolated from PBMC of healthy donors, activated with CD3/CD28 beads, and transduced with a lentiviral vector encoding a second-generation CD19CAR containing a CD28 co-stimulatory domain. The transduced CD19CAR T cells were expanded in the presence of IL-2 (50U/mL) and Akt inhibitor (Akti) (1 μM) that were supplemented every other day. Proliferative/expansion potential, phenotypical characteristics and functionality of the propagated CD19CAR T cells were analyzed in vitro and in vivo after 17-21 day ex vivo expansion. Anti-tumor activity was evaluated after adoptive transfer of the CD19CAR T cells into CD19+ tumor-bearing immunodeficient mice. Tumor signals were monitored with biophotonic imaging, and survival rates were analyzed by the end of the experiments.

Results

We found that Akt inhibition did not compromise CD19CAR T cell proliferation and expansion in vitro, independent of the T cell subsets, as comparable CD19CAR T cell expansion was observed after culturing in the presence or absence of Akt inhibitor. Functionally, Akt inhibition did not dampen cell-mediated effector function, while Th1 cytokine production increased. With respect to phenotype, Akti-treated CD19CAR T cells expressed higher levels of CD62L and CD28 as compared to untreated CD19CAR T cells. Once adoptively transferred into CD19+ tumor-bearing mice, Akti treated CD19CAR T cells exhibited more antitumor activity than did untreated CD19CAR T cells.

Conclusions

Inhibition of Akt signaling during ex vivo priming and expansion gives rise to CD19CAR T cell populations that display comparatively higher antitumor activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s40425-017-0227-4) contains supplementary material, which is available to authorized users.

Effect of mTORC1/mTORC2 inhibition on T cell function: potential role in graft-versus-host disease control

The mechanistic target of rapamycin (mTOR) pathway is crucial for the activation and function of T cells, which play an essential role in the development of graft-versus-host disease (GvHD). Despite its partial ability to block mTOR pathway, the mTORC1 inhibitor rapamycin has shown encouraging results in the control of GvHD. Therefore, we considered that simultaneous targeting of both mTORC1 and mTORC2 complexes could exert a more potent inhibition of T cell activation and, thus, could have utility in GvHD control. To assess this assumption, we have used the dual mTORC1/mTORC2 inhibitors CC214-1 and CC214-2. In vitro studies confirmed the superior ability of CC214-1 versus rapamycin to block mTORC1 and mTORC2 activity and to reduce T cell proliferation. Both drugs induced a similar decrease in Th1/Th2 cytokine secretion, but CC214-1 was more efficient in inhibiting naïve T cell activation and the expression of T-cell activation markers. In addition, CC214-1 induced specific tolerance against alloantigens, while preserving anti-cytomegalovirus response. Finally, in a mouse model of GvHD, the administration of CC214-2 significantly improved mice survival and decreased GvHD-induced damages. In conclusion, the current study shows, for the first time, the immunosuppressive ability of CC214-1 on T lymphocytes and illustrates the role of CC214-2 in the allogeneic transplantation setting as a possible GvHD prophylaxis agent.

Signals and pathways controlling regulatory T cells

Induction of specific immune tolerance to grafts remains the sought-after standard following transplantation. Defined by expression of the Foxp3 (forkhead box protein 3) transcription factor, the regulatory T-cell (Treg) lineage has been noted to exert potent immunoregulatory functions that contribute to specific graft tolerance. In this review, we discuss the known signals and pathways which govern Treg development, both in the thymus and in peripheral sites, as well as lineage maintenance and homeostasis. In particular, we highlight the roles of T-cell receptor signaling, CD28 costimulation, and signals through phosphatidyl inositol 3-kinase (PI3K) and related metabolic pathways in multiple aspects of Treg biology.

Inhibition of Akt signaling promotes the generation of superior tumor-reactive T cells for adoptive immunotherapy

Effective T-cell therapy against cancer is dependent on the formation of long-lived, stem cell-like T cells with the ability to self-renew and differentiate into potent effector cells. Here, we investigated the in vivo existence of stem cell-like antigen-specific T cells in allogeneic stem cell transplantation (allo-SCT) patients and their ex vivo generation for additive treatment posttransplant. Early after allo-SCT, CD8+ stem cell memory T cells targeting minor histocompatibility antigens (MiHAs) expressed by recipient tumor cells were not detectable, emphasizing the need for improved additive MiHA-specific T-cell therapy. Importantly, MiHA-specific CD8+ T cells with an early CCR7+CD62L+CD45RO+CD27+CD28+CD95+ memory-like phenotype and gene signature could be expanded from naive precursors by inhibiting Akt signaling during ex vivo priming and expansion. This resulted in a MiHA-specific CD8+ T-cell population containing a high proportion of stem cell-like T cells compared with terminal differentiated effector T cells in control cultures. Importantly, these Akt-inhibited MiHA-specific CD8+ T cells showed a superior expansion capacity in vitro and in immunodeficient mice and induced a superior antitumor effect in intrafemural multiple myeloma-bearing mice. These findings provide a rationale for clinical exploitation of ex vivo-generated Akt-inhibited MiHA-specific CD8+ T cells in additive immunotherapy to prevent or treat relapse in allo-SCT patients.

Current and prospective pharmacotherapy for autoimmune hepatitis

INTRODUCTION

Corticosteroids alone or in combination with azathioprine are the mainstay therapies of autoimmune hepatitis. Suboptimal responses (treatment failure, partial response, drug toxicity), frequent relapse after drug withdrawal, and the emergence of alternative immunosuppressive medications have fueled the pursuit of new treatments. The goals of this review are to present current management strategies and evolving interventions.

AREAS COVERED

PubMed searches from 1970 - 2014 provide the bases for this review. Corticosteroid regimens should be administered until resolution of symptoms, laboratory tests, and liver tissue abnormalities. Treatment failure warrants high doses of the original regimen, and relapse warrants re-treatment followed by long-term maintenance with azathioprine. The calcineurin inhibitors, budesonide, and mycophenolate mofetil are evolving as frontline therapies, and they may be considered as salvage therapies with the exception of budesonide. Rapamycin, rituximab, and infliximab have also rescued refractory patients but experiences are limited. Anti-oxidants, recombinant molecules, mAbs, and modulators of critical cell populations are key prospects.

EXPERT OPINION

Autoimmune hepatitis must be managed by multiple medications that supplement or supplant current regimens depending on the clinical situation. Rescue therapies will emerge as adjunctive interventions to minimize tissue damage (prevent fibrosis and hepatocyte apoptosis) and improve immune tolerance (regulatory T cell manipulations).

Inhibitory effects of belatacept on allospecific regulatory T-cell generation in humans

BACKGROUND

It is unclear if new costimulatory blockade agents, such as the cytotoxic T lymphocyte-associated antigen 4-Ig molecule belatacept (BEL), promote or inhibit the potential for immunologic tolerance in transplantation. We therefore tested the in vitro effects of BEL on human regulatory T cells (Tregs) in mixed lymphocyte reactions (MLR) alone and in combination with maintenance agents used in transplant recipients.

METHODS

BEL, mycophenolic acid (MPA), and sirolimus, either alone or in combination, were added to healthy volunteer Treg-MLR, testing (a) H-TdR incorporation for inhibition of lymphoproliferation and (b) flow cytometry to analyze for newly generated CD4+ CD25(high) FOXP3+ Tregs in carboxyfluorescein succinimidyl ester-labeled MLR responders. In addition, the modulatory effects of putative Tregs generated in the presence of these drugs were also tested using the lymphoproliferation and flow cytometric assays.

RESULTS

In comparison with medium controls, BEL dose-dependently inhibited both lymphoproliferation and Treg generation in human leukocyte antigen DR matched and mismatched MLRs either alone or in combination with MPA or sirolimus. However, MPA alone inhibited lymphoproliferation but significantly enhanced Treg generation at subtherapeutic concentrations (P<0.01). In addition, purified CD4+ CD127- cells generated in MLR in the presence of MPA and added as third component modulators in fresh MLRs significantly enhanced newly developed Tregs in the proliferating responder cells compared with those generated with BEL or medium controls.

CONCLUSIONS

BEL alone and in combination with agents used in transplant recipients inhibits the in vitro generation of human Tregs. BEL might therefore be a less optimal agent for tolerance induction in human organ transplantation.

Review article: autoimmune hepatitis -- current management and challenges

BACKGROUND

Autoimmune hepatitis (AIH) is a disease of unknown aetiology characterised by interface hepatitis, hypergammaglobulinaemia, circulating autoantibodies and a favourable response to immunosuppression.

AIM

To review recent advancements in understanding aetiopathogenesis, clinical, serological and histological features, diagnostic criteria and treatment strategies of AIH.

METHODS

Published studies on AIH extracted mainly from PubMed during the last 15 years.

RESULTS

Autoimmune hepatitis has a global distribution affecting any age, both sexes and all ethnic groups. Clinical manifestations are variable ranging from no symptoms to severe acute hepatitis and only seldom to fulminant hepatic failure. Autoimmune attack is perpetuated, possibly via molecular mimicry mechanisms, and favoured by the impaired control of regulatory T-cells. A typical laboratory finding is hypergammaglobulinaemia with selective elevation of IgG, although in 15-25% of patients - particularly children, elderly and acute cases - IgG levels are normal. Liver histology and autoantibodies, although not pathognomonic, still remain the hallmark for diagnosis. Immunosuppressive treatment is mandatory and life-saving; however, to meet strict response criteria, the conventional therapy with prednisolone with or without azathioprine is far from ideal.

CONCLUSIONS

Autoimmune hepatitis remains a major diagnostic and therapeutic challenge. The clinician, the hepato-pathologist and the laboratory personnel need to become more familiar with different expressions of the disease, interpretation of liver histology and autoimmune serology. According to the strict definition of treatment response issued by the 2010 AASLD guidelines, many patients are nonresponders to conventional treatment. Newer immunosuppressive agents targeting pathogenetic mechanisms can improve patient management, which needs to be tailored on a case-by-case basis.

First clinical experience with polysol solution: pilot study in living kidney transplantation

In this study, we assessed the safety of the new organ preservation solution polysol solution in the clinical setting of living kidney transplantation. We conducted a prospective pilot study in nine adult donor-recipient couples using polysol solution for washout and cold storage of kidney grafts. Adverse reactions possibly related to the use of polysol solution as well as renal function at 1, 6, and 12 months after transplantation were monitored. All living kidney transplantation performed in adults in our center within 2002 to 2008 using the University of Winconsin solution served as controls (n = 190). The use of polysol solution was associated with a higher acute rejection rate compared to University of Wisconsin solution at all time points. Also, antibody-mediated rejection occurred more frequently in the polysol group. Renal function at all time points was also comparable between the groups. This pilot study in living kidney transplantation is the first clinical study on the use of polysol solution. Although the study was not powered on the endpoint rejection, we observed a high number of acute rejection and antibody-mediated rejection episodes in recipients of polysol solution preserved grafts as compared to University of Wisconsin solution controls. As a consequence the study was terminated prematurely.

Targeting the trimolecular complex: the pathway towards type 1 diabetes prevention

George Eisenbarth devoted his life to understanding the basic immunology of the autoimmune polyglandular syndromes and type 1 diabetes, while providing exceptional clinical care to individuals afflicted with these disorders. Over the last 5 years, I was privileged to know George Eisenbarth as a mentor, colleague, and friend. His enthusiasm for science and specifically understanding the basic immunology of type 1 diabetes was infectious. George was the first to initially hypothesize that type 1 diabetes is a chronic autoimmune disorder. He made diabetes a predictable disease by developing biochemical assays to measure islet autoantibodies and provided this technology worldwide to researchers and the medical community. His work identifying and detecting islet autoantibodies allowed for clinical intervention trials aimed at preventing type 1 diabetes. George worked fervently to prevent the disease. During my time as a fellow in George's laboratory and faculty member at the Barbara Davis Center for Diabetes, we focused our efforts for diabetes prevention at the trimolecular complex (human leukocyte antigen molecule, self-peptide, and T cell receptor), which plays a pivotal role in diabetes pathogenesis. It is our belief that targeting this complex with safe and specific therapies will lead to the prevention of type 1 diabetes and an improved understanding as to why diabetes develops.

Systemic immunoregulatory and proteogenomic effects of tacrolimus to sirolimus conversion in liver transplant recipients

Immunosuppression (IS) withdrawal from calcineurin inhibitors is only possible in ≈ 20% of liver transplant recipients. However, mammalian target of rapamycin inhibitors (e.g., sirolimus; SRL) appear to be more immunoregulatory and might promote a tolerant state for withdrawal. Our aim was to determine whether systemic (i.e., blood, marrow, and allograft) signatures of immunoregulation are promoted by conversion from tacrolimus (TAC) to SRL. We therefore performed the following serial assays before and after SRL conversion in liver transplant recipients to test for enhanced markers of immunoregulation: (1) flow-cytometry immunophenotyping of peripheral blood mononuclear cells (PBMCs) and bone marrow aspirates for regulatory T cells (Tregs) (e.g., CD4(+) CD25(+++) FOXP3(+) ) and regulatory dendritic cells (DCregs) (immunoglobulin-like transcript 3(+) /4(+) ); (2) liver biopsy immunohistochemical staining (e.g., FOXP3:CD3 and CD4:CD8 ratios) and immunophenotyping of biopsy-derived Tregs after growth in culture; (3) effects of pre- versus postconversion sera on Treg generation in mixed lymphocyte reactions; (4) peripheral blood nonspecific CD4 responses; and (5) peripheral blood gene transcripts and proteomic profiles. We successfully converted 20 nonimmune, nonviremic recipients (age, 57.2 ± 8.0; 3.5 ± 2.1 years post-liver transplantation) from TAC to SRL for renal dysfunction. Our results demonstrated significant increases in Tregs in PBMCs and marrow and DCregs in PBMCs (P < 0.01) after conversion. In biopsy staining, FOXP3:CD3 and CD4:CD8 ratios were significantly higher after conversion and a number of biopsy cultures developed new or higher FOXP3(+) cell growth. Nonspecific CD4 responses did not change. Both pre- and postconversion sera inhibited mixed lymphocyte reactions, although only TAC sera suppressed Treg generation. Finally, 289 novel genes and 22 proteins, several important in immunoregulatory pathways, were expressed after conversion.

CONCLUSIONS

TAC to SRL conversion increases systemic Tregs, DCregs, and immunoregulatory proteogenomic signatures in liver transplant recipients and may therefore facilitate IS minimization or withdrawal.

Systematic review: managing suboptimal treatment responses in autoimmune hepatitis with conventional and nonstandard drugs

BACKGROUND

Corticosteroid treatment for autoimmune hepatitis has been shown by randomised controlled clinical trials to ameliorate symptoms, normalise liver tests, improve histological findings and extend survival. Nevertheless, suboptimal responses to corticosteroid treatment still occur.

AIM

To describe the current definitions, frequencies, clinical relevance and treatment options for suboptimal responses, and to discuss alternative medications that have been used off-label for these occurrences.

METHODS

Literature search was made for full-text papers published in English using the keyword 'autoimmune hepatitis'. Authors' personal experience and investigational studies also helped to identify important contributions to the literature.

RESULTS

Suboptimal responses to standard therapy include treatment failure (7%), incomplete response (14%), drug toxicity (13%) and relapse after drug withdrawal (50-86%). The probability of a suboptimal response prior to treatment is higher in young patients and in patients with a severe presentation, jaundice, high MELD score at diagnosis, multilobular necrosis or cirrhosis, antibodies to soluble liver antigen, or inability to improve by clinical indices within two weeks or by MELD score within 7 days of conventional corticosteroid treatment. Management strategies have been developed for the adverse responses and nonstandard drugs, including mycophenolate mofetil, budesonide, ciclosporin, tacrolimus, sirolimus and rituximab, are emerging as rescue therapies or alternative frontline agents.

CONCLUSIONS

Once diagnosed, the suboptimal response should be treated by a highly individualised and well-monitored regimen, preferentially using first-line therapy. Nonstandard drugs warrant consideration as salvage or second-line therapies.

Drug choices in autoimmune hepatitis: part B--Nonsteroids

Nonsteroidal medications, previously unfamiliar in the management of autoimmune hepatitis, can supplement or replace conventional corticosteroid regimens, especially in problematic patients. Mycophenolate mofetil is a next-generation purine antagonist that has been useful in treating patients with azathioprine intolerance. It has been less effective in salvaging patients with steroid-refractory disease. Azathioprine is the choice as a corticosteroid-sparing agent in treatment-naive patients and in individuals with corticosteroid intolerance, incomplete response and relapse after drug withdrawal. Tacrolimus is preferred over cyclosporine for recalcitrant disease because of its established preference in organ transplantation, but replacement with cyclosporine should be considered if the disease worsens on treatment. Rapamycin has antiproliferative and proapoptotic actions that warrant further study in autoimmune hepatitis. The nonstandard, nonsteroidal medications are mainly salvage therapies with off-label indications that must be used in highly individualized and well-monitored clinical situations.

Diagnosis, pathogenesis, and treatment of autoimmune hepatitis after liver transplantation

Autoimmune hepatitis can recur or appear de novo after liver transplantation, and it can result in hepatic fibrosis, graft loss, and re-transplantation. The goals of this review are to describe the prevalence, manifestations, putative pathogenic mechanisms, outcomes, and management of these occurrences. Autoimmune hepatitis recurs in 8-12 % of transplanted patients at 1 year and 36-68 % at 5 years. Recurrence may be asymptomatic and detected only by surveillance liver test abnormalities or protocol liver tissue examination. Autoantibodies that characterized the original disease, hypergammaglobulinemia, increased serum immunoglobulin G level, and histological findings of interface hepatitis, lymphoplasmacytic infiltration, perivenular hepatocyte necrosis, pseudo-rosetting, and acidophil bodies typify recurrence. Premature corticosteroid withdrawal and pre-transplant severity of the original disease are possible risk factors. De novo autoimmune hepatitis occurs in 1-7 % of patients 0.1-9 years after transplantation, especially in children. The appearance of autoantibodies may herald its emergence, and antibodies to glutathione-S-transferase T1 have been predictive of the disease. Recurrent disease may reflect recruitment of residual memory T lymphocytes and host-specific genetic predispositions, whereas de novo disease may reflect an allo-antigenic immune response and molecular mimicries that override self-tolerance. Treatment should be appropriate for autoimmune hepatitis and not based on anti-rejection drugs. Corticosteroid therapy alone or combined with azathioprine is the essential treatment. The substitution of mycophenolate mofetil for azathioprine and switch of the calcineurin inhibitor or its replacement with rapamycin have also been used for refractory disease. Re-transplantation has been necessary in 8-23 %.

Advances in the current treatment of autoimmune hepatitis

Current treatment strategies for autoimmune hepatitis are complicated by frequent relapse after drug withdrawal, medication intolerance, and refractory disease. The objective of this review is to describe advances that have improved treatment outcomes by defining the optimum objectives of initial therapy, managing relapse more effectively, identifying problematic patients early, and incorporating the new pharmacological interventions that have emerged as frontline and salvage therapies. Initial corticosteroid treatment should be continued until serum aminotransferase, γ-globulin, and immunoglobulin G levels are normal, and maintenance of this improvement for 3-8 months before liver tissue assessment. Improvement to normal liver tissue is the ideal histological result that justifies drug withdrawal, but it is achievable in only 22 % of patients. Minimum portal hepatitis, inactive cirrhosis, or minimally active cirrhosis is the most common treatment end point. Relapse after drug withdrawal warrants institution of a long-term maintenance regimen, preferably with azathioprine. Mathematical models can identify problematic adult patients early, as also can clinical phenotype (age ≤ 30 years and HLA DRB1 03), rapidity of treatment response (≤ 24 months), presence of antibodies to soluble liver antigen, and non-white ethnicity. The calcineurin inhibitors (cyclosporine and tacrolimus) can be effective in steroid-refractory disease; mycophenolate mofetil can be corticosteroid-sparing and effective for azathioprine intolerance; budesonide combined with azathioprine can be effective for treatment-naïve, non-cirrhotic patients. Standard treatment regimens for autoimmune hepatitis can be upgraded without adjustments that require major new expertise.

Circulating lymphocyte subsets in different clinical situations after renal transplantation

Phenotypic characterization of T and B lymphocytes allows the discrimination of functionally different subsets. Here, we questioned whether changes in peripheral lymphocyte subset distribution reflect specific clinical and histopathological entities after renal transplantation. Sixty-five renal transplant recipients with either histologically proven (sub)clinical acute rejection or chronic allograft dysfunction, or without abnormalities were studied for their peripheral lymphocyte subset composition and compared with 15 healthy control individuals. Naive, memory and effector CD8(+) T-cell counts were measured by staining for CD27, CD28 and CD45RO/RA. In addition, we studied the CD25(+) CD4(+) T-cell population for its composition regarding regulatory Foxp3(+) CD45RO(+) CD127(-) cells and activated CD45RO(+) CD127(+) cells. Naive, non-switched and switched memory B cells were defined by staining for IgD and CD27. We found a severe decrease in circulating effector-type CD8(+) T cells in recipients with chronic allograft dysfunction at 5 years after transplantation. Percentages of circulating CD25(+) CD127(low) CD4(+) regulatory T cells after transplantation were reduced, but we could not detect any change in the percentage of CD127(+) CD45RO(+) CD4(+) activated T cells in patients at any time or condition after renal transplantation. Regardless of clinical events, all renal transplant recipients showed decreased total B-cell counts and a more differentiated circulating B-cell pool than healthy individuals. The changes in lymphocyte subset distribution probably reflect the chronic antigenic stimulation that occurs in these transplant recipients. To determine the usefulness of lymphocyte subset-typing in clinical practice, large cohort studies are necessary.

Operational tolerance: past lessons and future prospects

Every liver transplant (LT) center has had patients who either self-discontinue immunosuppressive (IS) therapy or are deliberately withdrawn due to a research protocol or clinical concern (ie, lymphoproliferative disorder [LPD], overwhelming infection). This is understandable because maintenance IS therapy, particularly calcineurin inhibitors (CNI), is associated with significant cost, side effects, and considerable long-term morbidity and mortality. Detrimental effects of IS therapy include increased risk of cardiovascular disease, metabolic syndrome, bone loss, opportunistic and community-acquired infections, and malignancy. In fact, LT recipients have among the highest rates of chronic kidney disease and associated mortality among all nonkidney solid organ recipients. This mortality is only ameliorated by undergoing a curative kidney transplant, usurping costs and valuable organ resources. The search for improved treatment algorithms includes trial and error CNI dose minimization, the use of alternative IS agents (antimetabolites, mammalian target of rapamycin [mTOR] inhibitors), or even complete CNI withdrawal. Yet those who are successful in achieving such operational tolerance (no immunosuppression and normal allograft function) are considered lucky. The vast majority of recipients will fail this approach, develop acute rejection or immune-mediated hepatitis, and require resumption of IS therapy. As such, withdrawal of IS following LT is not standard-of-care, leaving clinicians to currently maintain transplant patients on IS therapy for life. Nonetheless, the long-term complications of all IS therapies highlight the need for strategies to promote immunologic or operational tolerance. Clinically applicable biomarker assays signifying the potential for tolerance as well as tolerogenic IS conditioning are invariably needed if systematic, controlled rather than "hit or miss" approaches to withdrawal are considered. This review will provide an overview of the basic mechanisms of tolerance, particularly in relation to LT, data from previous IS withdrawal protocols and biomarker studies in tolerant recipients, and a discussion on the prospect of increasing the clinical feasibility and success of withdrawal.

Allospecific regulatory effects of sirolimus and tacrolimus in the human mixed lymphocyte reaction

BACKGROUND

Tacrolimus (TAC) and sirolimus (SRL), two commonly used immunosuppressive agents, have demonstrated contrasting immunoregulatory effects. We recently described factors affecting the generation of allospecific CD4CD25 forkhead/winged helix transcription factor P3 (FOXP3) T-regulatory (Treg) cells in mixed lymphocyte reaction (Treg MLR) and now report additional findings on the effects of TAC and SRL.

METHODS

TAC, SRL, or media without agents were added separately to MLRs using human leukocyte antigen two DR-matched and -mismatched healthy volunteers and prekidney transplant donor/recipient pairs. Concentrations correlated with subtherapeutic and therapeutic blood levels. Stimulation indices of H-TDR uptake, cell proliferation, and the generation of carboxy-fluorescein diacetate succinimidyl ester (CFSE) labeled CD4CD25FOXP3 cells by flow cytometry were initially compared. Each group of (non-CFSE labeled) MLR-generated cells were then added as third components to CFSE-labeled responding cells in freshly prepared primary MLRs, to determine allospecific and nonspecific inhibitory and Treg recruitment effects.

RESULTS

TAC inhibited stimulation indices and CD4CD25 FOXP3 cell generation in both human leukocyte antigen DR-matched and -mismatched pairs, particularly at therapeutic levels (≥5 ng/mL). SRL had an equivalent effect in matched pairs but was associated with a significantly higher %generation of CD4CD25FOXP3 cells than TAC. SRL-MLR-generated Tregs added as third components allospecifically inhibited MLR proliferation and recruited additional CFSE-labeled autologous Tregs compared with addition of TAC- or media-MLR-generated Tregs.

CONCLUSIONS

Calcineurin and mammalian target of rapamycin inhibitors have disparate effects on allospecific Treg generation using the Treg MLR. This assay can thereby be helpful in assessing allospecific regulatory effects of diverse immunosuppressive agents.

Generation of human regulatory T cells de novo with suppressive function prevent xenogeneic graft versus host disease

Treatment with rapamycin (RAPA) favorably affects regulatory T cells (Treg) in vivo, and RAPA induces the de novo expression of FOXP3 in murine alloantigen-specific T cells. Whether RAPA acts independently or with transforming growth factor beta (TGF-β) to produce ex vivo-induced Treg generation is unknown. Naïve CD4(+) T cells isolated from peripheral blood mononuclear cells were stimulated with anti-CD3/CD28 coated beads in the presence of IL-2 for 5 to 7 days. Ten ng/ml of TGF-β (1 to 100 ng/mL RAPA) was added to some of the cultures. The phenotypes were analyzed with flow cytometry. The conditioned cells were cocultured with CFSE-labeled T cells in different ratios for 5 days. CFSE dilution indicating T response cell proliferation was analyzed by flow cytometry. Xenogeneic graft-versus-host disease (x-GVHD) was induced by transplanting human peripheral blood mononuclear cells into RAG2(-/-) γc(-/-) mice exposed to total body irradiation, and various factors in the subjects were subsequently compared. CD4 cells induced by rapamycin and TGF-β (CD4(RAPA/TGF-β)) expressed the natural Treg phenotypes and trafficking receptors, and no significant cytotoxicity was observed. CD4(RAPA/TGF-β) was anergic and demonstrated potent suppressive activity in vitro. Although the transfer of human peripheral blood mononuclear cells into RAG2(-/-) γc(-/-) mice caused x-GVHD, the cotransfer of CD4(RAPA/TGF-β) decreased human cell engraftment and extended survival in mice. RAPA plus TGF-β induces human naïve T cells to become suppressor cells, a novel strategy for treating human autoimmune diseases and preventing allograft rejection.

Combined administration of a mutant TGF-beta1/Fc and rapamycin promotes induction of regulatory T cells and islet allograft tolerance

The critical roles of TGF-β in the reciprocal differentiation of tolerance-promoting CD4(+)Foxp3(+) regulatory T cells (Tregs) and proinflammatory Th17 effector cells affect alloimmune reactivity and transplant outcome. We reasoned that a strategy to harness TGF-β and block proinflammatory cytokines would inhibit the differentiation of Th17 cells and strengthen the cadre of Tregs to promote tolerance induction and long-term allograft survival. In this study, we report the development of a long-lasting autoactive human mutant TGF-β1/Fc fusion protein that acts in conjunction with rapamycin to inhibit T cell proliferation and induce the de novo generation of Foxp3(+) Treg in the periphery, while at the same time inhibiting IL-6-mediated Th17 cell differentiation. Short-term combined treatment with TGF-β1/Fc and rapamycin achieved long-term pancreatic islet allograft survival and donor-specific tolerance in a mouse model. This effect was accompanied by expansion of Foxp3(+) Tregs, enhanced alloantigen-specific Treg function, and modulation of transcript levels of Foxp3, IL-6, and IL-17. Our strategy of combined TGF-β1/Fc and rapamycin to target the IL-6-related Tregs and Th17 signaling pathways provides a promising approach for inducing transplant tolerance and its clinical application.

Maintenance immunosuppressive therapy with everolimus preserves humoral immune responses

While the guidelines for vaccination in renal transplant recipients recommend the use of pneumococcal polysaccharide (PPS) and tetanus toxoid (TT), their efficacy in immunocompromised renal transplant recipients is not known. Here we tested the effect of everolimus on immune responses after vaccination by measuring the capacity of 36 stable renal transplant recipients to mount cellular and humoral responses after vaccination. Twelve patients in each treatment arm received immunosuppressive therapy consisting of prednisolone (P) plus cyclosporine (CsA), mycophenolate sodium (MPA), or everolimus. Patients were vaccinated with the T-cell-dependent antigens immunocyanin and TT, and the T-cell-independent PPS. Treatment with CsA partially inhibited and MPA completely abolished the capacity to mount a primary humoral response, whereas everolimus left this largely intact. Recall responses were inhibited by MPA only. All drug combinations inhibited cellular responses against TT. In patients treated with MPA, B-cell numbers were severely reduced. Thus, combined with P, treatment with MPA completely disturbed primary and secondary humoral responses. Everolimus or CsA allowed the boosting of T-cell-dependent and -independent secondary humoral responses. Treatment with everolimus allowed a primary response.

Transforming growth factor beta 1 (TGF-beta1) and rapamycin synergize to effectively suppress human T cell responses via upregulation of FoxP3+ Tregs

BACKGROUND

The major obstacle faced by patients with type 1 diabetes who undergo islet transplantation is a gradual decline in insulin independence. This decline may reflect alloimmune rejection, autoimmune recurrence and toxicity of drugs such as rapamycin to islet beta cells. Thus, there is a pressing need to refine immunosuppressive protocols in order to reduce toxicity to islet grafts and yet prevent rejection. Recent studies demonstrated that TGF-beta1 is a critical cytokine for the regulation of immune responses. In naive T cells, TGF-beta1 induces FoxP3(+) regulatory T cells and thus could promote transplant tolerance. In this study, in vitro experiments were performed to determine whether TGF-beta1 could synergize with low-dose rapamycin and inhibit T cell activation and production of inflammatory cytokines, as well as enhance FoxP3 expression for potential application in islet transplantation.

METHODS

Human peripheral blood mononuclear cells were stimulated with either anti-CD3/CD28 or anti-CD3 during TGF-beta1 and rapamycin treatment.

RESULTS

TGF-beta1 inhibited T cell proliferation induced with anti-CD3 stimulation, but not with anti-CD3/CD28 stimulation. The combination of these reagents produced a synergistic inhibition of T cell proliferation induced with both anti-CD3/CD28 and anti-CD3 stimulations. Moreover, TGF-beta1 and rapamycin significantly suppressed cytokine production and induced regulatory T cells by upregulating FoxP3 expression.

CONCLUSIONS

These results suggest that the combination of TGF-beta1 and low-dose rapamycin can potently inhibit T cell responses in vivo and would be beneficial in supporting islet graft survival by limiting toxicity and preventing immune rejection.

Regulatory T cells in transplantation: does extracellular adenosine triphosphate metabolism through CD39 play a crucial role?

Despite tremendous improvements in short-term renal allograft survival, many patients still have chronic rejection or side effects of nonspecific immunosuppression. The discovery of Foxp3(+) regulatory T cells (Tregs) has revolutionized the concepts in immunoregulation and offers perspectives for overcoming rejection. Recently, a subset of Foxp3(+)CD39(+) effector/memory-like Tregs (T(REM)) was identified. The role of CD39(+) Tregs in immunoregulation is supported by the occurrence of alopecia areata and experimental autoimmune encephalomyelitis in CD39-deficient mice and by the failure of CD39(-) Tregs to suppress contact hypersensitivity. In humans, CD39 polymorphisms have been associated with diabetes and nephropathy, and multiple sclerosis patients have reduced numbers of blood CD39(+) Tregs. Preliminary experiments in a murine transplantation model showed that CD39(+) Tregs can determine allograft outcome. CD39 degrades the extracellular adenosine triphosphate (ATP) released during tissue injury, which otherwise would trigger inflammation. Currently, our groups are assessing the role of CD39(+) Tregs and extracellular ATP metabolism in clinical transplantation and whether tolerogenic Treg profiles possess immunopredictive value, envisioning the development of clinical trials using CD39(+) Treg-based vaccination for autoimmunity or transplantation. This is a comprehensive review on the fundamentals of Treg biology, the potential role of ATP metabolism in immunoregulation, and the potential use of Treg-based immunotherapy in transplantation.

Induction of granzyme B expression in T-cell receptor/CD28-stimulated human regulatory T cells is suppressed by inhibitors of the PI3K-mTOR pathway

Background

Regulatory T cells (Tregs) can employ a cell contact- and granzyme B-dependent mechanism to mediate suppression of bystander T and B cells. Murine studies indicate that granzyme B is involved in the Treg-mediated suppression of anti-tumor immunity in the tumor microenvironment and in the Treg-mediated maintenance of allograft survival. In spite of its central importance, a detailed study of granzyme B expression patterns in human Tregs has not been performed.

Results

Our data demonstrated that natural Tregs freshly isolated from the peripheral blood of normal adults lacked granzyme B expression. Tregs subjected to prolonged TCR and CD28 triggering, in the presence of IL-2, expressed high levels of granzyme B but CD3 stimulation alone or IL-2 treatment alone failed to induce granzyme B. Treatment of Tregs with the mammalian target of rapamycin (mTOR) inhibitor, rapamycin or the PI3 kinase (PI3K) inhibitor LY294002 markedly suppressed granzyme B expression. However, neither rapamycin, as previously reported by others, nor LY294002 inhibited Treg proliferation or induced significant cell death in TCR/CD28/IL-2 stimulated cells. The proliferation rate of Tregs was markedly higher than that of CD4+ conventional T cells in the setting of rapamycin treatment. Tregs expanded by CD3/CD28/IL-2 stimulation without rapamycin demonstrated increased in vitro cytotoxic activity compared to Tregs expanded in the presence of rapamycin in both short term (6 hours) and long term (48 hours) cytotoxicity assays.

Conclusion

TCR/CD28 mediated activation of the PI3K-mTOR pathway is important for granyzme B expression but not proliferation in regulatory T cells. These findings may indicate that suppressive mechanisms other than granzyme B are utilized by rapamycin-expanded Tregs.

Rapamycin prevents and breaks the anti-CD3-induced tolerance in NOD mice

OBJECTIVE

Non-Fc-binding anti-CD3-specific antibodies represent a promising therapy for preserving C-peptide production in subjects with recent-onset type 1 diabetes. However, the mechanisms by which anti-CD3 exerts its beneficial effect are still poorly understood, and it is questionable whether this therapeutic approach will prove durable with regard to its ability to impart metabolic preservation without additional actions designed to maintain immunological tolerance. We used the NOD mouse model to test whether rapamycin, a compound well-known for its immunomodulatory activity in mice and humans, could increase the therapeutic effectiveness of anti-CD3 treatment in type 1 diabetes.

RESEARCH DESIGN AND METHODS

Rapamycin was administered to diabetic NOD mice simultaneously with anti-CD3 or to NOD mice cured by anti-CD3 therapy. The ability of this combined therapy to revert type 1 diabetes and maintain a state of long-term tolerance was monitored and compared with that of anti-CD3 therapy alone.

RESULTS

Rapamycin inhibited the ability of anti-CD3 to revert disease without affecting the frequency/phenotype of T-cells. Rapamycin also reinstated diabetes in mice whose disease was previously reversed by anti-CD3. Withdrawal of rapamycin in these latter animals promptly restored a normoglycemic state.

CONCLUSIONS

Our findings indicate that, when combined with anti-CD3, rapamycin exerts a detrimental effect on the disease outcome in NOD mice for as long as it is administered. These results suggest strong caution with regard to combining these treatments in type 1 diabetic patients.

Immunoregulatory profiles in liver transplant recipients on different immunosuppressive agents

We compared peripheral blood immunophenotyping in 31 adult liver transplant recipients on differing long-term immunosuppressive (IS) monotherapy with and without peri-transplantation alemtuzumab (AL) induction. All patients had been stable on monotherapy with either sirolimus (SRL) (n = 10) or without SRL (tacrolimus (TAC) (n = 10), mycophenolate mofetil (MMF) (n = 11)) for more than 6 months. Five-color flow cytometry for putative "regulatory" T and dendritic cells as well as serum assays for soluble HLA-G (sHLA-G) were performed. The SRL monotherapy group had significantly higher percentages of CD4+CD25(high+)Foxp3+ T cells (1.3 +/- 1.0) compared with the non-SRL group (0.7 +/- 0.6) (p = 0.04). The SRL effect was even higher in a subset with prior AL induction and no prior hepatitis C or rejection (1.7 +/- 0.2) compared with all other subgroups (0.7 +/- 0.6) (p = 0.02). TAC patients showed significantly higher "regulatory" DC2:DC1 ratios (10 +/- 7.6) compared with non-TAC patients (4.1 +/- 2.3) (p = 0.04). Although sHLA-G levels appeared higher in TAC patients, the differences were not statistically significant. In conclusion, IS monotherapy provides an opportunity to investigate regulatory roles of individual agents. SRL maintenance and prior AL induction in subsets of patients appeared to show a regulatory T cell immunophenotype. However, TAC patients may have other regulatory characteristics, supporting the need for larger, prospective studies to clarify differences.

Mammalian target of rapamycin (mTOR) orchestrates the defense program of innate immune cells

The mammalian target of rapamycin (mTOR) can be viewed as cellular master complex scoring cellular vitality and stress. Whether mTOR controls also innate immune-defenses is currently unknown. Here we demonstrate that TLR activate mTOR via phosphoinositide 3-kinase/Akt. mTOR physically associates with the MyD88 scaffold protein to allow activation of interferon regulatory factor-5 and interferon regulatory factor-7, known as master transcription factors for pro-inflammatory cytokine- and type I IFN-genes. Unexpectedly, inactivation of mTOR did not prevent but increased lethality of endotoxin-mediated shock, which correlated with increased levels of IL-1beta. Mechanistically, mTOR suppresses caspase-1 activation, thus inhibits release of bioactive IL-1beta. We have identified mTOR as indispensable component of PRR signal pathways, which orchestrates the defense program of innate immune cells.

Defects in skin gamma delta T cell function contribute to delayed wound repair in rapamycin-treated mice

Disruptions in the normal program of tissue repair can result in poor wound healing, which perturbs the integrity of barrier tissues such as the skin. Such defects in wound repair occur in transplant recipients treated with the immunosuppressant drug rapamycin (sirolimus). Intraepithelial lymphocytes, such as gammadelta T cells in the skin, mediate tissue repair through the production of cytokines and growth factors. The capacity of skin-resident T cells to function during rapamycin treatment was analyzed in a mouse model of wound repair. Rapamycin treatment renders skin gammadelta T cells unable to proliferate, migrate, and produce normal levels of growth factors. The observed impairment of skin gammadelta T cell function is directly related to the inhibitory action of rapamycin on mammalian target of rapamycin. Skin gammadelta T cells treated with rapamycin are refractory to IL-2 stimulation and attempt to survive in the absence of cytokine and growth factor signaling by undergoing autophagy. Normal wound closure can be restored in rapamycin-treated mice by addition of the skin gammadelta T cell-produced factor, insulin-like growth factor-1. These studies not only reveal that mammalian target of rapamycin is a master regulator of gammadelta T cell function but also provide a novel mechanism for the increased susceptibility to nonhealing wounds that occurs during rapamycin administration.

Conferring indirect allospecificity on CD4+CD25+ Tregs by TCR gene transfer favors transplantation tolerance in mice

T cell responses to MHC-mismatched transplants can be mediated via direct recognition of allogeneic MHC molecules on the cells of the transplant or via recognition of allogeneic peptides presented on the surface of recipient APCs in recipient MHC molecules - a process known as indirect recognition. As CD4(+)CD25(+) Tregs play an important role in regulating alloresponses, we investigated whether mouse Tregs specific for allogeneic MHC molecules could be generated in vitro and could promote transplantation tolerance in immunocompetent recipient mice. Tregs able to directly recognize allogeneic MHC class II molecules (dTregs) were obtained by stimulating CD4(+)CD25(+) cells from C57BL/6 mice (H-2(b)) with allogeneic DCs from BALB/c mice (H-2(d)). To generate Tregs that indirectly recognized allogeneic MHC class II molecules, dTregs were retrovirally transduced with TCR genes conferring specificity for H-2K(d) presented by H-2A(b) MHC class II molecules. The dual direct and indirect allospecificity of the TCR-transduced Tregs was confirmed in vitro. In mice, TCR-transduced Tregs, but not dTregs, induced long-term survival of partially MHC-mismatched heart grafts when combined with short-term adjunctive immunosuppression. Further, although dTregs were only slightly less effective than TCR-transduced Tregs at inducing long-term survival of fully MHC-mismatched heart grafts, histologic analysis of long-surviving hearts demonstrated marked superiority of the TCR-transduced Tregs. Thus, Tregs specific for allogeneic MHC class II molecules are effective in promoting transplantation tolerance in mice, which suggests that such cells have clinical potential.

Alloantigen-induced regulatory CD8+CD103+ T cells

Regulatory T cells (Tregs) appear of great importance in the balance between alloreactivity and tolerance and subsets of both CD4(+) and CD8(+) T cells have been recognized to function as regulatory T cells after allogenic transplantation. Among the CD8(+) T-cell subsets, the CD103(+) cells were most recently identified as regulatory. In this review, we describe their phenotypical and functional properties, as well as their relevance for the alloimmune response in vivo. These CD8(+)CD103(+) Tregs are generated within mixed lymphocyte cultures (MLCs) and are elevated by additional transforming growth factor-beta. Interestingly, myeloid dendritic cells are the responsible cell type for induction of CD103(+) Tregs. Allostimulated CD8(+)CD103(+) Tregs display an antigen-experienced effector phenotype with limited effector functions such as cytotoxicity and interferon-gamma production and show a reduced proliferation capacity after restimulation. Beside this anergic phenotype, CD8(+)CD103(+) Tregs are able to suppress alloreactive effector T cells. Through intracellular cytokine staining and transwell assays, we showed that the mechanism of suppression is cytokine independent, but close cell-cell contact is required for suppression.

Rapamycin monotherapy in patients with type 1 diabetes modifies CD4+CD25+FOXP3+ regulatory T-cells

OBJECTIVE

Rapamycin is an immunosuppressive drug currently used to prevent graft rejection in humans, which is considered permissive for tolerance induction. Rapamycin allows expansion of both murine and human naturally occurring CD4(+)CD25(+)FOXP3(+) T regulatory cells (nTregs), which are pivotal for the induction and maintenance of peripheral tolerance. Preclinical murine models have shown that rapamycin enhances nTreg proliferation and regulatory function also in vivo. Objective of this study was to assess whether rapamycin has in vivo effects on human nTregs.

RESEARCH DESIGN AND METHODS

nTreg numbers and function were examined in a unique set of patients with type 1 diabetes who underwent rapamycin monotherapy before islet transplantation.

RESULTS

We found that rapamycin monotherapy did not alter the frequency and functional features, namely proliferation and cytokine production, of circulating nTregs. However, nTregs isolated from type 1 diabetic patients under rapamycin treatment had an increased capability to suppress proliferation of CD4(+)CD25(-) effector T-cells compared with that before treatment.

CONCLUSIONS

These findings demonstrate that rapamycin directly affects human nTreg function in vivo, which consists of refitting their suppressive activity, whereas it does not directly change effector T-cell function.

Combination of rapamycin and IL-2 increases de novo induction of human CD4(+)CD25(+)FOXP3(+) T cells

The immune system protects itself from autoreactivity by maintaining a balance between effector and Treg responses. Peripheral induction of Treg is one mechanism by which this balance may be maintained. Thus, it is important to understand factors that influence de novo generation of CD4(+)CD25(+)FOXP3(+) Treg. Here, we focus on the effects of cytokines and the cell cycle inhibitor rapamycin. The cytokines IL-2 and IL-7, but not IL-4, increased initial activation induced FOXP3 expression, increased proliferation and sustained expression of FOXP3(+) cells throughout the culture. Addition of rapamycin to cultures containing IL-2 further increased the frequency and absolute number of functional CD4(+)CD25(+)FOXP3(+) Treg. This increase was not due to selective proliferation of FOXP3 cells, but was instead, the result of an increase in the frequency of FOXP3(+) cells induced in G0 through delayed activation while the addition of IL-2 promoted survival and proliferation of the FOXP3(+) population. Thus, combination of rapamycin and IL-2 may provide improved treatment options in transplantation and autoimmunity by promoting induction, survival, and expansion of functional iTreg from CD4(+)CD25(-) cells.

Rapamycin enhances the number of alloantigen-induced human CD103+CD8+ regulatory T cells in vitro

BACKGROUND

Regulatory T cells (T(reg) cells) may be operational in both the induction and maintenance of transplantation tolerance. We recently showed that alloantigen-induced CD103+ CD8+ T cells strongly suppressed T-cell proliferation in mixed lymphocyte culture (MLC) via a contact-dependent mechanism. CD103 directs T lymphocytes to their ligand E-cadherin, which is expressed on renal tubular epithelial cells, and CD103+ CD8+ T cells have been described to be present in late renal allograft rejection.

METHODS

We studied the influence of prednisolone, cyclosporin, tacrolimus, CD25 monoclonal antibodies, rapamycin, and mycophenolate mofetil (MMF) on the development and functional activity of alloantigen-activated CD103+ CD8+ T cells in MLC.

RESULTS

Calcineurin inhibitors, MMF, and CD25mAb did not influence the number of CD103 expressing CD8+ T cells. In contrast, corticosteroids diminished CD103 expression on alloactivated CD8+ T cells, which appeared to be caused by their inhibitory action on myeloid dendritic cells. Addition of rapamycin to allocultures led to an increased percentage of CD103+ CD8+ alloreactive T cells. Moreover, in the presence of rapamycin, these cells tended to show higher suppressive capacity.

CONCLUSIONS

Alloreactive CD103+ CD8+ T(reg) cells may expand and exert their suppressive function during immunosuppressive treatment with rapamycin. These data are relevant in the design of immunosuppressive drug regimens intended to induce and/or maintain transplantation tolerance.

Rapamycin promotes expansion of functional CD4+CD25+FOXP3+ regulatory T cells of both healthy subjects and type 1 diabetic patients

CD4+CD25+FOXP3+ T regulatory cells (Tregs) are pivotal for the induction and maintenance of peripheral tolerance in both mice and humans. Rapamycin has been shown to promote tolerance in experimental models and to favor CD4+CD25+ Treg-dependent suppression. We recently reported that rapamycin allows in vitro expansion of murine CD4+CD25+FoxP3+ Tregs, which preserve their suppressive function. In the current study, we show that activation of human CD4+ T cells from healthy subjects in the presence of rapamycin leads to growth of CD4+CD25+FOXP3+ Tregs and to selective depletion of CD4+CD25- T effector cells, which are highly sensitive to the antiproliferative effect of the compound. The rapamycin-expanded Tregs suppress proliferation of both syngeneic and allogeneic CD4+ and CD8+ T cells. Interestingly, rapamycin promotes expansion of functional CD4+CD25+FOXP3+ Tregs also in type 1 diabetic patients, in whom a defect in freshly isolated CD4+CD25+ Tregs has been reported. The capacity of rapamycin to allow growth of functional CD4+CD25+FOXP3+ Tregs, but also to deplete T effector cells, can be exploited for the design of novel and safe in vitro protocols for cellular immunotherapy in T cell-mediated diseases.