Immunoregulatory profiles in liver transplant recipients on different immunosuppressive agents

Involvement of circulating soluble HLA-G after liver transplantation in the low immunogenicity of hepatic allograft

Graft rejection is a critical risk in solid-organ transplantation. To decrease such risk, an understanding of the factors involved in low immunogenicity of liver allografts could potentially make it possible to transfer this tolerogenic property to other transplanted organs. HLA-G, a natural physiological molecule belonging to the Human Leukocyte Antigen class (HLA) Ib family that induces tolerance, is associated with fewer rejections in solid-organ transplantation. In contrast to HLA-G, HLA antigen incompatibilities between donor and recipient can lead to rejection, except in liver transplantation. We compared HLA-G plasma levels and the presence of anti-HLA antibodies before and after LT to understand the low immunogenicity of the liver. We conducted a large prospective study that included 118 patients on HLA-G plasma levels during a 12-month follow-up and compared them to the status of anti-HLA antibodies. HLA-G plasma levels were evaluated by ELISA at seven defined pre- and post-LT time points. HLA-G plasma levels were stable over time pre-LT and were not associated with patient characteristics. The level increased until the third month post-LT, before decreasing to a level comparable to that of the pre-LT period at one year of follow-up. Such evolution was independent of biological markers and immunosuppressive treatment, except with glucocorticoids. An HLA-G plasma level ≤ 50 ng/ml on day 8 after LT was significantly associated with a higher rejection risk. We also observed a higher percentage of rejection in the presence of donor specific anti-HLA antibodies (DSA) and an association between the increase in HLA-G plasma levels at three months and the absence of DSA. The low immunogenicity of liver allografts could be related to early elevated levels of HLA-G, which lead, in turn, to a decrease in anti-HLA antibodies, opening potential new therapeutic strategies using synthetic HLA-G proteins.

Biological Characteristics of HLA-G and Its Role in Solid Organ Transplantation

Organ transplantation is a lifesaving option for patients with advanced diseases. Rejection is regarded as one of the most severe risk factors post-transplantation. A molecule that contributes to immune tolerance and resisting rejection is human leukocyte antigen (HLA)-G, which belongs to the non-classical major histocompatibility complex class (MHC) I family. HLA-G was originally found to play a role during pregnancy to maintain immune tolerance between mother and child. It is expressed in the placenta and detected in several body fluids as soluble factor as well as different membrane isoforms on cells. Recent findings on HLA-G show that it can also play multifaceted roles during transplantation. This review will explain the general characteristics and biological function of HLA-G and summarize the views supporting the tolerogenic and other roles of HLA-G to better understand its role in solid organ transplantation (SOT) and its complications. Finally, we will discuss potential future research on the role of HLA-G in prevention, diagnosis, and treatment in SOT.

Ex vivo generation of regulatory T cells from liver transplant recipients using costimulation blockade

The potential of adoptive cell therapy with regulatory T cells (Tregs) to promote transplant tolerance is under active exploration. However, the impact of specific transplant settings and protocols on Treg manufacturing is not well-delineated. Here, we compared the use of peripheral blood mononuclear cells (PBMCs) from patients before or after liver transplantation to the use of healthy control PBMCs to determine their suitability for Treg manufacture using ex vivo costimulatory blockade with belatacept. Despite liver failure or immunosuppressive therapy, the capacity for Treg expansion during the manufacturing process was preserved. These experiments did not identify performance or quality issues that disqualified the use of posttransplant PBMCs-the currently favored protocol design. However, as Treg input correlated with output, significant CD4-lymphopenia in both pre- and posttransplant patients limited Treg yield. We therefore turned to leukapheresis posttransplant to improve absolute yield. To make deceased donor use feasible, we also developed protocols to substitute splenocytes for PBMCs as allostimulators. In addition to demonstrating that this Treg expansion strategy works in a liver transplant context, this preclinical study illustrates how characterizing cellular input populations and their performance can both inform and respond to clinical trial design and Treg manufacturing requirements.

Immune and gene expression profiling during tacrolimus to everolimus conversion early after liver transplantation

Early elimination of tacrolimus in favor of everolimus can improve renal function in liver transplant recipients. However, as this approach increases the risk of acute rejection, it may benefit from predictive biomarkers guiding weaning. We enrolled 20 recipients on stable tacrolimus + everolimus to undergo tacrolimus withdrawal early post-liver transplant. Blood samples were collected at month 3 (withdrawal initiation), 4 (withdrawal completion), 4.5 and 6 (both everolimus alone). 15 patients did not reject and 5 had mild rejection responding to tacrolimus resumption. Before tacrolimus withdrawal, eventual rejecters had higher percentages of CD56⁺ NK cells and CD19⁺CD27⁺CD24⁺ memory B cells, and lower levels of T cells expressing the exhaustion marker PD-1. Over time, memory B cells, Ki-67⁺CD3⁺ (proliferating) cells and CD4⁺CD127^-CD25^HIGH FOXP3⁺ Tregs increased in rejecters. Tregs also increased in non-rejecters over time. The number of differentially expressed genes progressively increased in rejecters, particularly in mTOR, Eukaryotic Initiation Factor 2, and Neuroinflammation signaling pathways. There was no difference in anti-HLA antibodies between the groups. In summary, blood mononuclear cell and gene expression may predict successful vs. failed early tacrolimus withdrawal in liver transplant recipients. While needing validation, these preliminary findings highlight the potential for cellular and molecular biomarkers to guide decision-making during tacrolimus weaning.

Immunosuppression Withdrawal in Liver Transplant Recipients on Sirolimus

BACKGROUND AND AIMS

As conversion from calcineurin inhibitor to sirolimus (SRL), a mechanistic target of rapamycin inhibitor (mTOR-I), has been shown to enhance immunoregulatory profiles in liver transplant (LT) recipients (LTRs), mTOR-I therapy might allow for increased success of immunosuppression (IS) withdrawal. Our aim was to determine if operational tolerance could be observed in LTRs withdrawn from SRL and if blood/graft tolerance biomarkers were predictive of successful withdrawal.

APPROACH AND RESULTS

We performed a prospective trial of SRL monotherapy withdrawal in nonimmune, nonviremic LTRs > 3 years post-LT. SRL was weaned over ~6 months, and biopsies were performed 12 months postweaning or at concern for acute rejection. Twenty-one LTRs consented; 6 were excluded due to subclinical acute rejection on baseline biopsy or other reasons, and 15 underwent weaning (age 61.3 ± 8.8 years; LT to SRL weaning 6.7 ± 3 years). Eight (53%) achieved operational tolerance (TOL). Of the 7 who were nontolerant (non-TOL), 6 had mild acute rejection on biopsy near the end of weaning or at study end; 1 was removed from the trial due to liver cancer recurrence. At baseline preweaning, there were statistically increased blood tolerogenic dendritic cells and cell phenotypes correlating with chronic antigen presentation in the TOL versus non-TOL groups. A previously identified biopsy gene signature accurately predicted TOL versus non-TOL in 12/14 LTRs before weaning. At study end, biopsy staining revealed statistically significant increases in antigen-presenting cell:leukocyte pairings, FOXP3⁺ /CD4⁺ T cells, Tbet⁺ /CD8⁺ T cells, and lobular dendritic cells in the non-TOL group.

CONCLUSIONS

This study evaluated IS withdrawal directly from mTOR-I therapy in LTRs and achieved > 50% operational tolerance. Preweaning gene expression and peripheral blood mononuclear cell profiling may be useful as predictors of successful mTOR-I therapy withdrawal. NCT02062944.

Dissecting the Multiplicity of Immune Effects of Immunosuppressive Drugs to Better Predict the Risk of de novo Malignancies in Solid Organ Transplant Patients

De novo malignancies constitute an emerging cause of morbidity after solid organ transplant (SOT), significantly affecting the long-term survival of transplant recipients. Pharmacologic immunosuppression may functionally impair the immunosurveillance in these patients, thereby increasing the risk of cancer development. Nevertheless, the multiplicity and heterogeneity of the immune effects induced by immunosuppressive drugs limit the current possibilities to reliably predict the risk of de novo malignancy in SOT patients. Therefore, there is the pressing need to better characterize the immune dysfunctions induced by the different immunosuppressive regimens administered to prevent allograft rejection to tailor more precisely the therapeutic schedule and decrease the risk of de novo malignancies. We herein highlight the impact exerted by different classes of immunosuppressants on the most relevant immune cells, with a particular focus on the effects on dendritic cells (DCs), the main regulators of the balance between immunosurveillance and tolerance.

Tolerance in clinical liver transplantation

While advances in immunosuppressive therapy have lowered the rate of acute rejection following liver transplantation, the consequence has been an increase in morbidity and mortality related to the lifelong need for maintenance immunosuppression. These complications include an increased risk of malignancy, infection, metabolic disorders, and chronic kidney disease, as well as high health care costs associated with these therapies and the required drug monitoring. Given these issues, most clinicians attempt trial and error dose minimization with variable success rates, and there has been significant interest in full drug withdrawal in select patients through research protocols. These strategies would be more successful if immunomodulatory therapies early after transplantation could be developed and if immune activation biomarkers guiding drug tapering were available to personalize these approaches. This review will review the mechanisms of liver transplant tolerance and potential strategies to achieve immunosuppression withdrawal.

Immunoregulatory Effects of Everolimus on In Vitro Alloimmune Responses

Everolimus (EVL) is a novel mTOR-inhibitor similar to sirolimus (SRL) that is used in organ transplant recipients, often in combination with tacrolimus (TAC) or mycophenolate (MPA). The current study aims to determine its effects on regulatory T cells. Increasing concentrations of EVL, MPA and TAC alone or in combination were added to MLRs of healthy volunteers. Lymphoproliferation by 3H-TdR incorporation and the percentage of newly generated CD4+CD127-CD25+FOXP3+ (total Treg) and CD4+CD127-CD25HighFOXP3+ (natural Treg) in CFSE labeled responder cells were assessed by flow cytometry. In comparison to medium controls, EVL and other agents dose-dependently inhibited 3H-TdR incorporation in HLA-2DR-matched and HLA-mismatched MLRs (n = 3-10). However, EVL significantly amplified newly generated total and natural Tregs in CFSE labeled responder cells (p<0.05) at all concentrations, while MPA and SRL did this only at sub-therapeutic concentrations and inhibited at therapeutic levels. In contrast, TAC inhibited newly generated Tregs at all concentrations. When tested in combination with TAC, EVL failed to reverse TAC inhibition of Treg generation. Combinations of EVL and low concentrations of MPA inhibited proliferation and amplified Treg generation in an additive manner when compared to medium controls or each drug tested alone (p<0.05). The relative tolerogenic effect from high to low was EVL > SRL> MPA > TAC. If the results from these in vitro studies are extrapolated to clinical transplantation, it would suggest EVL plus low concentrations of MPA may be the most tolerogenic combination.

Biology of the immunomodulatory molecule HLA-G in human liver diseases

The non-classical human leukocyte antigen-G (HLA-G), plays an important role in inducing tolerance, through its immunosuppressive effects on all types of immune cells. Immune tolerance is a key issue in the liver, both in liver homeostasis and in the response to liver injury or cancer. It would therefore appear likely that HLA-G plays an important role in liver diseases. Indeed, this molecule was recently shown to be produced by mast cells in the livers of patients infected with hepatitis C virus (HCV). Furthermore, the number of HLA-G-positive mast cells was significantly associated with fibrosis progression. The generation of immune tolerance is a role common to both HLA-G, as a molecule, and the liver, as an organ. This review provides a summary of the evidence implicating HLA-G in liver diseases. In the normal liver, HLA-G transcripts can be detected, but there is no HLA-G protein. However, HLA-G protein is detectable in the liver tissues and/or plasma of patients suffering from hepatocellular carcinoma, hepatitis B or C, or visceral leishmaniasis and in liver transplant recipients. The cells responsible for producing HLA-G differ between diseases. HLA-G expression is probably induced by microenvironmental factors, such as cytokines. The expression of HLA-G receptors, such as ILT2, ILT4, and KIRD2L4, on liver cells has yet to be investigated, but these receptors have been detected on all types of immune cells, and such cells are present in liver. The tolerogenic properties of HLA-G explain its deleterious effects in cancers and its beneficial effects in transplantation. Given the key role of HLA-G in immune tolerance, new therapeutic agents targeting HLA-G could be tested for the treatment of these diseases in the future.

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.

Influence of pharmacological immunomodulatory agents on CD4(+)CD25(high)FoxP3(+) T regulatory cells in humans

T regulatory cells (Tregs) play a critical role in the immunologic tolerance to the graft in transplantation. Thus, due to their immunosuppressive capability, ex vivo expanded Tregs may be used as a cellular therapy and an attractive novel strategy to control chronic rejection and eliminate need for lifelong pharmacological immunosuppression. Since Treg therapy is still in its infancy, initially Tregs still need to be applied in combination with pharmacological agents to prevent rejection. Fortunately, some of the medications have been shown to enhance the function and number of Tregs. In the clinic, different immunosuppressive regimens are used for individual patients for different types of organ transplantation. In this review, we present the most commonly used pharmacological agents for immunosuppression and discuss how they affect the Treg population. It is extremely difficult to dissect the effect of single agent on Tregs population in clinical settings since usually the combination of several medications is applied at the same time for graft protection. Nevertheless, experimental and clinical data indicate that thymoglobulin as immunosuppressive induction and mTOR inhibitors as immunosuppressive maintenance agents have the most beneficial effect on Treg population in the blood. Among supplemental agents promoting Tregs, anti-TNFα preparations have been in clinical use (in autoimmune diseases) for many years, so they are optimal candidates for testing in transplant settings in combination with Treg based cellular therapy.

Clinical operational tolerance in liver transplantation: state-of-the-art perspective and future prospects

BACKGROUND

Liver transplantation is the definite treatment for end-stage liver diseases with satisfactory results. However, untoward effects of life-long immunosuppression prevent the development of alternative strategies to achieve better long-term outcome. Achieving clinical operational tolerance is the ultimate goal.

DATA SOURCES

A PubMed and Google Scholar search using terms: "immune tolerance", "liver transplantation", "clinical trial", "operational tolerance" and "immunosuppression withdrawal" was performed, and relevant articles published in English in the past decade were reviewed. Full-text publications relevant to the field were selected and relevant articles from reference lists were also included. Priority was given to those articles which are relevant to the review.

RESULTS

Because of the inherent tolerogenic property, around 20%-30% of liver transplantation recipients develop spontaneous operational tolerance after immunosuppression withdrawal, and the percentage may be even higher in pediatric living donor liver transplantation recipients. Several natural killer and gammadeltaT cell related markers have been identified to be associated with the tolerant state in liver transplantation patients. Despite the progress, clinical operational tolerance is still rare in liver transplantation. Reprogramming the recipient immune system by creating chimerism and regulatory cell therapies is among newer promising means to achieve clinical liver transplantation tolerance in the future.

CONCLUSION

Although clinical operational tolerance is still rare in liver transplantation recipients, ongoing basic research and collaborative clinical trials may help to decipher the mystery of transplantation tolerance and extend the potential benefits of drug withdrawal to an increasing number of patients in a more predictable fashion.

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.

Successful resolution of inflammation and increased regulatory T cells in sirolimus-treated post-transplant allograft hepatitis

This retrospective case series reviews our center's experience with sirolimus and a CNI as alternative therapy for the treatment of PTAH. It also characterizes regulatory T cells (Tregs) in PTAH. LT recipients with PTAH who had received or were receiving treatment with sirolimus were retrospectively identified (n = 12). Liver enzymes, immunohistochemistry, and histology were compared in all 12 patients. Immunophenotyping for Tregs in peripheral blood mononuclear cells was performed on LT recipients with PTAH on conventional therapy with CNI, azathioprine ± prednisone (CT) (n = 11), recipients with PTAH on sirolimus, CNI ± prednisone (n = 8), recipients without PTAH (n = 25), and pre-transplant patients (n = 5). Severity of necro-inflammatory changes markedly improved with sirolimus. Treg frequency and number were significantly lower in recipients with PTAH on CT compared to (i) those on sirolimus (p = 0.002 and p = 0.01, respectively), and (ii) recipients without PTAH (p = 0.07 and p = 0.009, respectively). Treg frequency was significantly higher in recipients with PTAH on sirolimus compared to recipients without PTAH under CNI therapy (p = 0.027). Sirolimus in addition to a CNI is successful in reversing inflammation in LT recipients with PTAH. This is associated with significantly higher circulating Tregs.

Favorable effects of alemtuzumab on allospecific regulatory T-cell generation

We studied the effects of alemtuzumab on T-regulatory cells (Tregs) during alloactivation, first by differences in depletion of various naive versus alloactivated cell subsets in peripheral blood of healthy volunteers, then by adding serial concentrations to human leukocyte antigen (HLA)-DR-matched and -mismatched responding and stimulating cells in mixed lymphocyte reaction (MLR). Lymphoproliferation inhibition and the development of proliferating carboxyfluorescein succinimidyl ester (CFSE)-diluted CD4(+)CD25(high)CD127(-)FOXP3(+) (phenotypic) Tregs by flow cytometry were measured. Also, the ability of alemtuzumab-treated versus nontreated MLR generated CD4(+)CD127(-) cells to allospecifically inhibit MLRs and recruit additional responding Tregs was tested. We found a more pronounced refractoriness of alloactivated versus naive CD4(+)CD25(high) cells to alemtuzumab induced lymphodepletion. Alemtuzumab dose dependently inhibited lymphoproliferation while amplifying percentages of MLR-generated Tregs. This was somewhat augmented by human complement addition. CD127(-)CD4(+) cells immunoselected after 7 days from alemtuzumab-treated MLRs allospecifically inhibited lymphoproliferation and recruited additional Tregs in fresh MLR-responding cells, similar to modulators derived from MLRs without drug addition (media). Addition of tacrolimus and sirolimus to alemtuzumab further inhibited MLR proliferation. However, Treg percentages were markedly higher with sirolimus. These results support the notion that alemtuzumab induces immunoregulation in naïve T cells undergoing alloactivation absent presensitization, especially used in conjunction with maintenance SRL.

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.

Human leukocyte antigen-G expression on dendritic cells induced by transforming growth factor-beta1 and CD4+ T cells proliferation

BACKGROUND

During antigen capture and processing, mature dendritic cells (DC) express large amounts of peptide-MHC complexes and accessory molecules on their surface. DC are antigen-presenting cells that have an important role in tolerance and autoimmunity. The transforming growth factor-beta1 (TGF-Beta1) cytokine has a regulatory role on the immune and non-immune cells. The aim of this study is to evaluate the effect of TGF-Beta1 on the induction of human leukocyte antigen-G (HLA-G) expression on the DC which is derived from monocyte.

METHODS

In this study, we evaluated the effect of TGF-Beta1 in induction HLA-G expression on the monocyte-derived DC by flowcytometry and then CD4+ T cell proliferative responses in the presence of DC-treated TGF-Beta1 was studied.

RESULTS

The results of this study showed that DC bearing HLA-G down-regulated activation of CD4+ T cells and production of IL-6 and IL-17 in comparison with control (P<0.05).

CONCLUSION

It is concluded that TGF-Beta1 has an important regulatory role in CD4+ T cell proliferation by increasing HLA-G on DC and these cells can probably prevent unexpected immune responses in vivo.

Expression of soluble HLA-G identifies favorable outcomes in liver transplant recipients

BACKGROUND

Human leukocyte antigen (HLA)-G displays immunotolerogenic properties toward the main effector cells involved in graft rejection through inhibition of natural killer cell- and cytotoxic T-lymphocyte-mediated cytolysis, and CD4 T-cell alloproliferation. An increase in serum and graft levels of HLA-G has been noted in transplant patients with improved allograft survival. However, the clinical relevance of soluble serum HLA-G molecules in tolerant pediatric and young adult liver transplant patients remains to be studied.

METHODS

We examined the serum HLA-G levels in 42 pediatric and young adult liver transplant patients with a mean age of 15 years; 13 patients had operational tolerance (TOL), with complete immunosuppression withdrawal for 2.3 to 13.2 years.

RESULTS

Median HLA-G level in patients with acute rejection (AR) was similar to the level in pediatric healthy volunteers (9.9 vs. 4.2 U/mL, P=0.13). HLA-G was higher in patients with stable liver function on immunosuppression (54.6 U/mL) than in patients with AR (P=0.01) and healthy volunteers (P=0.003), but almost 6-fold lower than in TOL patients (325.4 U/mL). HLA-G did not correlate with clinical confounders or a history of posttransplant lymphoproliferative disease or Epstein-Barr virus; although levels in the TOL group were negatively correlated with time after immunosuppression withdrawal (r=-0.75, P=0.003). In rejectors, HLA-G levels trended to negatively correlate with a higher number (r=-0.58) and greater severity of AR episodes (r=-0.56) after 1 year posttransplantation.

CONCLUSIONS

Increased serum HLA-G levels track with operational tolerance of liver grafts and support favorable outcomes in pediatric and young adult recipients.

JC virus T-Antigen DNA in gastrointestinal mucosa of immunosuppressed patients: a prospective, controlled study

BACKGROUND

JC virus (JCV), a polyoma virus, is the etiological agent of progressive multifocal leukoencephalopathy in immunosuppressed patients. JCV T-Ag has proven oncogenic potential and is expressed in colonic polyps and carcinomas. We proposed that the prevalence of JCV T-Ag DNA is higher in the normal gastrointestinal (GI) mucosa of immunosuppressed patients compared with their immunocompetent counterparts.

AIMS

To look for JCV T-Ag DNA in the normal gastrointestinal mucosa of immunosuppressed patients compared with immunocompetent controls.

METHODS

Macroscopically normal samples of upper and lower GI mucosa were obtained from 38 immunosuppressed patients. A control group included samples from 19 immunocompetent inflammatory bowel disease (IBD) and 29 non-IBD cases. DNA was extracted and polymerase chain reaction (PCR) was performed using primers specific for T-Ag.

RESULTS

JCV T-Ag DNA was found in nine of the immunosuppressed patients (23.7%) and in three of the controls (6.3%; P = 0.02). Transplant recipients had a particularly high prevalence of JCV T-Ag DNA (35.3%). Patients with IBD receiving immunosuppressive drugs had a higher prevalence of JCV T-Ag DNA in comparison with IBD patients who did not receive immunosuppression (22.2% versus 10.5%, respectively), but this difference was not statistically significant (P = 0.574).

CONCLUSION

JCV T-Ag DNA is more prevalent in the upper and lower GI mucosa of immunosuppressed patients, possibly indicating that the virus resides in these patients. This may account for the higher prevalence of GI carcinomas in immunosuppressed patients.

The effects of immunosuppressive drugs on CD4(+) CD25(+) regulatory T cells: a systematic review of clinical and basic research

OBJECTIVE

To review the effects of different immunosuppressive drugs on proliferation and function of regulatory T cells (Tregs).

METHODS

We searched MEDLINE, Embase (from inception to September 2009), and the Cochrane Library (Issue 4, 2009) for clinical and basic research about the effects of various immunosuppressive drugs on Tregs. Data were extracted and methodological quality was assessed by two independent reviewers. Outcome measures for clinical research included blood Tregs levels, acute rejection episodes, and graft function. Outcomes for basic research included percentage of Tregs proliferation, function, Tregs phenotype, and evidence for possible mechanisms. We analyzed data qualitatively.

RESULTS

Forty-two studies, including 19 clinical trials and 23 basic studies, were included. The immunosuppressive drugs studied were calcineurin inhibitors (CNIs), Rapa, anti-metabolism drugs, IL-2 receptor-blocking antibodies, T-cell depleting antibodies, and co-stimulation blockade antibodies. Most of the studies were on Rapa and CNIs. Eight basic studies on Rapa and CNIs showed that Rapa could promote the proliferation and function of Tregs, while CNIs could not. Five clinical trials involving a total of 158 patients showed that patients taking Rapa had higher blood concentration of Tregs than patients taking CNIs, but no difference was found in graft function (6-42 months follow-up).

CONCLUSION

There is substantial evidence that Rapa favors Tregs survival and function. However, the higher numbers of blood Tregs in patients treated with Rapa do not show any association with better graft function. Larger clinical studies with longer follow-up are needed to more thoroughly assess the efficacy of immunosuppressive drugs on Tregs, and reveal whether a relationship exists between Tregs and graft function.