Approaching the promise of operational tolerance in clinical transplantation. Transplantation. 2011;91:1065-1074. [PMID: 21544029 DOI: 10.1097/tp.0b013e318215e742]

Combined Organ Transplantation in Patients with Advanced Liver Disease

Transplantation of the liver in combination with other organs is an increasingly performed procedure. Over the years, continuous improvement in survival could be realized through careful patient selection and refined organ preservation techniques, in spite of the challenges posed by aging recipients and donors, as well as the increased use of steatotic liver grafts. Herein, we revisit the epidemiology, allocation policies in different transplant zones, indications, and outcomes with regard to simultaneous organ transplants involving the liver, that is combined heart-liver, liver-lung, liver-kidney, and multivisceral transplantation. We address challenges surrounding combined organ transplantation such as equity, utility, and logistics of dual organ implantation, but also advantages that come along with combined transplantation, thereby focusing on molecular mechanisms underlying immunoprotection provided by the liver to the other allografts. In addition, the current standing and knowledge of machine perfusion in combined organ transplantation, mostly based on center experience, will be reviewed. Notwithstanding all the technical advances, shortage of organs, and the lack of universal eligibility criteria for certain multi-organ combinations are hurdles that need to be tackled in the future.

Leveraging the lymphohematopoietic graft-versus-host reaction (LGVHR) to achieve allograft tolerance and restore self tolerance with minimal toxicity

Mixed allogeneic chimerism has considerable potential to advance the achievement of immune tolerance to alloantigens for transplantation and the restoration of self-tolerance in patients with autoimmune disease. In this article, I review evidence that graft-versus-host (GVH) alloreactivity without graft-vs-host disease (GVHD), termed a lymphohematopoietic graft-vs-host reaction (LGVHR), can promote the induction of mixed chimerism with minimal toxicity. LGVHR was originally shown to occur in an animal model when non-tolerant donor lymphocytes were administered to mixed chimeras in the absence of inflammatory stimuli and was found to mediate powerful graft-vs-leukemia/lymphoma effects without GVHD. Recent large animal studies suggest a role for LGVHR in promoting durable mixed chimerism and the demonstration that LGVHR promotes chimerism in human intestinal allograft recipients has led to a pilot study aiming to achieve durable mixed chimerism.

Interleukin-5 (IL-5) Therapy Prevents Allograft Rejection by Promoting CD4+CD25+ Ts2 Regulatory Cells That Are Antigen-Specific and Express IL-5 Receptor

CD4⁺CD25⁺Foxp3⁺T cell population is heterogenous and contains three major sub-groups. First, thymus derived T regulatory cells (tTreg) that are naïve/resting. Second, activated/memory Treg that are produced by activation of tTreg by antigen and cytokines. Third, effector lineage CD4⁺CD25⁺T cells generated from CD4⁺CD25^- T cells' activation by antigen to transiently express CD25 and Foxp3. We have shown that freshly isolated CD4⁺CD25⁺T cells are activated by specific alloantigen and IL-4, not IL-2, to Ts2 cells that express the IL-5 receptor alpha. Ts2 cells are more potent than naïve/resting tTreg in suppressing specific alloimmunity. Here, we showed rIL-5 promoted further activation of Ts2 cells to Th2-like Treg, that expressed foxp3, irf4, gata3 and il5. In vivo, we studied the effects of rIL-5 treatment on Lewis heart allograft survival in F344 rats. Host CD4⁺CD25⁺T cells were assessed by FACS, in mixed lymphocyte culture and by RT-PCR to examine mRNA of Ts2 or Th2-like Treg markers. rIL-5 treatment given 7 days after transplantation reduced the severity of rejection and all grafts survived ≥60d whereas sham treated rats fully rejected by day 31 (p<0.01). Treatment with anti-CD25 or anti-IL-4 monoclonal antibody abolished the benefits of treatment with rIL-5 and accelerated rejection. After 10d treatment with rIL-5, hosts' CD4⁺CD25⁺ cells expressed more Il5ra and responded to specific donor Lewis but not self. Enriched CD4⁺CD25⁺ cells from rIL-5 treated rats with allografts surviving >60 days proliferated to specific donor only when rIL-5 was present and did not proliferate to self or third party. These cells had more mRNA for molecules expressed by Th2-like Treg including Irf4, gata3 and Il5. These findings were consistent with IL-5 treatment preventing rejection by activation of Ts2 cells and Th2-like Treg.

Differential gene expression in non-adherent heart transplant survivors: Implications for regulatory T-cell expression

Survival despite prolonged non-adherence with immunosuppression is rare but has been reported in kidney, lung, and liver transplantation. Its occurrence in heart transplantation is quite rare. Our study was prompted by an index patient who survived despite prolonged medication non-adherence. Prospective consent and blood collection were conducted for seven additional patients who presented in a similar fashion. The blood of patients who were diagnosed with rejection, stable early post-transplant, and stable more than 5 years post-transplant were all compared with a custom gene array focusing on T-regulatory cell processes. The two genes that were differentially expressed in every comparison were TGF beta and RNASEN with very low expression in the rejector group. The prolonged non-adherent group had the maximum expression for TGF beta but average RNASEN expression as compared to the low expression for rejectors and high for post-5 years patients. The patients presented survived for varying lengths of time without immunosuppression. The gene array analysis showed intriguing differences between these rare patients and important patient cohorts. Further efforts should be directed to finding and studying more patients who survive despite lack of prescribed immunosuppression. The mechanisms underlying this phenomenon may inform future advances in transplant immunosuppression.

Alloactivation of Naïve CD4+CD8-CD25+T Regulatory Cells: Expression of CD8α Identifies Potent Suppressor Cells That Can Promote Transplant Tolerance Induction

Therapy with alloantigen-specific CD4⁺CD25⁺ T regulatory cells (Treg) for induction of transplant tolerance is desirable, as naïve thymic Treg (tTreg) are not alloantigen-specific and are weak suppressor cells. Naïve tTreg from DA rats cultured with fully allogeneic PVG stimulator cells in the presence of rIL-2 express IFN-gamma receptor (IFNGR) and IL-12 receptor beta2 (IL-12Rβ2) and are more potent alloantigen-specific regulators that we call Ts1 cells. This study examined additional markers that could identify the activated alloantigen-specific Treg as a subpopulation within the CD4⁺CD25⁺Foxp3⁺Treg. After culture of naïve DA CD4⁺CD8⁻CD25⁺T cells with rIL-2 and PVG alloantigen, or rIL-2 without alloantigen, CD8α was expressed on 10–20% and CD8β on <5% of these cells. These cells expressed ifngr and Il12rb2. CD8α⁺ cells had increased Ifngr that characterizes Ts1 cells as well was Irf4, a transcription factor induced by TCR activation. Proliferation induced by re-culture with rIL-12 and alloantigen was greater with CD4⁺CD8α⁺CD25⁺Treg consistent with the CD8α⁺ cells expressing IL-12R. In MLC, the CD8α⁺ fraction suppressed responses against allogeneic stimulators more than the mixed Ts1 population, whereas the CD4⁺CD8⁻CD25⁺T cells were less potent. In an adoptive transfer assay, rIL-2 and alloantigen activated Treg suppress rejection at a ratio of 1:10 with naïve effector cells, whereas alloantigen and rIL-2 activated tTreg depleted of the CD8α⁺ cells were much less effective. This study demonstrated that expression of CD8α by rIL-2 and alloantigen activation of CD4⁺CD8⁻CD25⁺Foxp3⁺T cells was a marker of activated and potent Treg that included alloantigen-specific Treg.

Revisiting the liver’s role in transplant alloimmunity

The transplanted liver can modulate the recipient immune system to induce tolerance after transplantation. This phenomenon was observed nearly five decades ago. Subsequently, the liver’s role in multivisceral transplantation was recognized, as it has a protective role in preventing rejection of simultaneously transplanted solid organs such as kidney and heart. The liver has a unique architecture and is home to many cells involved in immunity and inflammation. After transplantation, these cells migrate from the liver into the recipient. Early studies identified chimerism as an important mechanism by which the liver modulates the human immune system. Recent studies on human T-cell subtypes, cytokine expression, and gene expression in the allograft have expanded our knowledge on the potential mechanisms underlying immunomodulation. In this article, we discuss the privileged state of liver transplantation compared to other solid organ transplantation, the liver allograft’s role in multivisceral transplantation, various cells in the liver involved in immune responses, and the potential mechanisms underlying immunomodulation of host alloresponses.

Early post-operative intravenous tacrolimus in pediatric liver transplant recipients is not superior to oral tacrolimus

We aimed to compare the early results of i.v. with p.o. TAC as a primary immunosuppressant in pediatric patients undergoing LT. This retrospective study enrolled 75 children who underwent LT and received TAC-steroid regimens as a primary immunosuppressant between September 2011 and October 2015 at our institution. Thirty-five recipients received TAC i.v. and 40 received TAC p.o. Early results were evaluated and compared, including ACR, EBV, or CMV infection; renal adverse effects; and hospital stay. Comparisons of 90-day post-transplant results showed that the rates of overall viral (74% vs 40% P < 0.002), EBV (46% vs 17.5% P < 0.008), and CMV (51% vs 30% P = 0.05) infections were significantly higher in the i.v. than in the p.o. group. Neither regimen has any adverse effects on renal function. There were no between-group differences in ACR incidence and severity, serum creatinine concentration, and hospital stay. Patient and graft survival rates at 3 months and 1 year did not differ significantly between the two groups. Compared with p.o. treatment, i.v. administration of high TAC concentration did not have beneficial post-transplant effects on ACR incidence and severity, while increasing the incidence of viral infections in pediatric LT.

Lower tacrolimus trough levels in the late period after living donor liver transplantation contribute to improvements in long-term clinical outcomes

BACKGROUND

Previous studies have emphasized the need to reduce tacrolimus (TAC) trough levels in the early post-liver transplantation (LT) period. However, whether late-period TAC trough levels influence the long-term outcomes of liver recipients is not clear.

METHODS

We enrolled 155 adult liver recipients survived more than 3 years after living donor liver transplantation because of non-malignant liver diseases. The maintenance immunosuppressive regimens were TAC monotherapy and combined therapy with mycophenolate mofetil. Patients were divided into three groups according to their late-period TAC trough levels: < 3 ng/mL group, 3-5 ng/mL group, and  >5 ng/mL group. The complications and adverse effects of TAC were analyzed.

RESULTS

Each group showed similar rejection, graft loss and mortality. Patients achieved the < 5 ng/mL state in less than 4 years had fewer new-onset diabetes, hyperlipidemia, de novo malignancies, and hepatitis B virus recurrence; the complications of renal dysfunction and hypertension rates were the same among these 3 groups.

CONCLUSIONS

Collectively, our findings indicated that lower TAC trough levels in the late period of liver transplantation are safe, improve the long-term outcomes.

Regulatory T cells in renal disease

The kidney is vulnerable to injury, both acute and chronic from a variety of immune and metabolic insults, all of which at least to some degree involve inflammation. Regulatory T cells modulate systemic autoimmune and allogenic responses in glomerulonephritis and transplantation. Intrarenal regulatory T cells (Tregs), including those recruited to the kidney, have suppressive effects on both adaptive and innate immune cells, and probably also intrinsic kidney cells. Evidence from autoimmune glomerulonephritis implicates antigen-specific Tregs in HLA-mediated dominant protection, while in several human renal diseases Tregs are abnormal in number or phenotype. Experimentally, Tregs can protect the kidney from injury in a variety of renal diseases. Mechanisms of Treg recruitment to the kidney include via the chemokine receptors CCR6 and CXCR3 and potentially, at least in innate injury TLR9. The effects of Tregs may be context dependent, with evidence for roles for immunoregulatory roles both for endogenous Tbet-expressing Tregs and STAT-3-expressing Tregs in experimental glomerulonephritis. Most experimental work and some of the ongoing human trials in renal transplantation have focussed on unfractionated thymically derived Tregs (tTregs). However, induced Tregs (iTregs), type 1 regulatory T (Tr1) cells and in particular antigen-specific Tregs also have therapeutic potential not only in renal transplantation, but also in other kidney diseases.

Cytokines affecting CD4+T regulatory cells in transplant tolerance. III. Interleukin-5 (IL-5) promotes survival of alloantigen-specific CD4+ T regulatory cells

CD4⁺T cells mediate antigen-specific allograft tolerance, but die in culture without activated lymphocyte derived cytokines. Supplementation of the media with cytokine rich supernatant, from ConA activated spleen cells, preserves the capacity of tolerant cells to transfer tolerance and suppress rejection. rIL-2 or rIL-4 alone are insufficient to maintain these cells, however. We observed that activation of naïve CD4⁺CD25⁺FOXP3⁺Treg with alloantigen and the Th2 cytokine rIL-4 induces them to express interleukin-5 specific receptor alpha (IL-5Rα) suggesting that IL-5, a Th2 cytokine that is produced later in the immune response may promote tolerance mediating Treg. This study examined if recombinant IL-5(rIL-5) promoted survival of tolerant CD4⁺, especially CD4⁺CD25⁺T cells. CD4⁺T cells, from DA rats tolerant to fully allogeneic PVG heart allografts surviving over 100days without on-going immunosuppression, were cultured with PVG alloantigen and rIL-5. The ability of these cells to adoptively transfer tolerance to specific-donor allograft and suppress normal CD4⁺T cell mediated rejection in adoptive DA hosts was examined. Tolerant CD4⁺CD25⁺T cells' response to rIL-5 and expression of IL-5Rα was also assessed. rIL-5 was sufficient to promote transplant tolerance mediating CD4⁺T cells' survival in culture with specific-donor alloantigen. Tolerant CD4⁺T cells cultured with rIL-5 retained the capacity to transfer alloantigen-specific tolerance and inhibited naïve CD4⁺T cells' capacity to effect specific-donor graft rejection. rIL-5 promoted tolerant CD4⁺CD25⁺T cells' proliferation in vitro when stimulated with specific-donor but not third-party stimulator cells. Tolerant CD4⁺CD25⁺T cells expressed IL-5Rα. This study demonstrated that IL-5 promoted the survival of alloantigen-specific CD4⁺CD25⁺T cells that mediate transplant tolerance.

Regulatory T cells in kidney disease and transplantation

Regulatory T cells (Tregs) have been shown to be important in maintaining immune homeostasis and preventing autoimmune disease, including autoimmune kidney disease. It is also likely that they play a role in limiting kidney transplant rejection and potentially in promoting transplant tolerance. Although other subsets of Tregs exist, the most potent and well-defined Tregs are the Foxp3 expressing CD4(+) Tregs derived from the thymus or generated peripherally. These CD4(+)Foxp3(+) Tregs limit autoimmune renal disease in animal models, especially chronic kidney disease, and kidney transplantation. Furthermore, other subsets of Tregs, including CD8 Tregs, may play a role in immunosuppression in kidney disease. The development and protective mechanisms of Tregs in kidney disease and kidney transplantation involve multiple mechanisms of suppression. Here we review the development and function of CD4(+)Foxp3(+) Tregs. We discuss the specific application of Tregs as a therapeutic strategy to prevent kidney disease and to limit kidney transplant rejection and detail clinical trials in this area of transplantation.

Functional Immune Anatomy of the Liver-As an Allograft

The liver is an immunoregulatory organ in which a tolerogenic microenvironment mitigates the relative "strength" of local immune responses. Paradoxically, necro-inflammatory diseases create the need for most liver transplants. Treatment of hepatitis B virus, hepatitis C virus, and acute T cell-mediated rejection have redirected focus on long-term allograft structural integrity. Understanding of insults should enable decades of morbidity-free survival after liver replacement because of these tolerogenic properties. Studies of long-term survivors show low-grade chronic inflammatory, fibrotic, and microvascular lesions, likely related to some combination of environment insults (i.e. abnormal physiology), donor-specific antibodies, and T cell-mediated immunity. The resultant conundrum is familiar in transplantation: adequate immunosuppression produces chronic toxicities, while lightened immunosuppression leads to sensitization, immunological injury, and structural deterioration. The "balance" is more favorable for liver than other solid organ allografts. This occurs because of unique hepatic immune physiology and provides unintended benefits for allografts by modulating various afferent and efferent limbs of allogenic immune responses. This review is intended to provide a better understanding of liver immune microanatomy and physiology and thereby (a) the potential structural consequences of low-level, including allo-antibody-mediated injury; and (b) how liver allografts modulate immune reactions. Special attention is given to the microvasculature and hepatic mononuclear phagocytic system.

Differences between buccal and lingual bone quality and quantity of peri-implant regions

The objective of the current study was to examine whether peri-implant bone tissue properties are different between the buccal and lingual regions treated by growth factors. Four dental implant groups were used: titanium (Ti) implants, alumina-blasted zirconia implants (ATZ-N), alumina-blasted zirconia implants with demineralized bone matrix (DBM) (ATZ-D), and alumina-blasted zirconia implants with rhBMP-2 (ATZ-B). These implants were placed in mandibles of six male dogs. Nanoindentation elastic modulus (E) and plastic hardness (H) were measured for the buccal and lingual bone tissues adjacent and away from the implants at 3 and 6 weeks post-implantation. A total of 2281 indentations were conducted for 48 placed implants. The peri-implant buccal region had less bone quantity resulting from lower height and narrower width of bone tissue than the lingual region. Buccal bone tissues had significant greater mean values of E and H than lingual bone tissues at each distance and healing period (p<0.007). Nearly all implant treatment groups displayed lower mean values of the E at the lingual bone tissues than at the buccal bone tissues (p<0.046) although the difference was not significant for the Ti implant group (p=0.758). The DBM and rhBMP-2 treatments stimulated more peri-implant bone remodeling at the lingual region, producing more immature new bone tissues with lower E than at the buccal region. This finding suggests that the growth factor treatments to the zirconia implant system may help balance the quantity and quality differences between the peri-implant bone tissues.

Withdrawal of immunosuppression in liver transplantation and the mechanism of tolerance

BACKGROUND

Immunosuppression reagents have side effects and cause considerable long-term morbidity and mortality in patients after liver transplantation. Sufficient evidences showed that minimization or withdrawal of immunosuppression reagents does not deteriorate the recipient's immune response and physiological function and therefore, is feasible in some recipients of liver transplantation. However, the mechanisms are not clear. The present review was to update the current status of immunosuppression in liver transplantation and the mechanism of minimization or withdrawal of immunosuppression in liver recipients.

DATA SOURCES

We searched articles in English on minimization or withdrawal of immunosuppression in liver transplantation in PubMed. We focused on the basic mechanisms of immune tolerance in liver transplantation. Studies on immunosuppression minimization or withdrawal protocols and biomarker in tolerant recipients were also analyzed.

RESULTS

Minimization or withdrawal of immunosuppression can be achieved by the induction of immune tolerance, which may not be permanent and can be affected by various factors. However, accurately evaluating immune status post-transplant is a prerequisite to achieve individualized immunosuppression. Numerous mechanisms for immune tolerance have been found, including immunophenotypic shift of memory CD8+ T cells and CD4+ T cell subsets. Activation of the inflammasome through apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC) in dendritic cells is associated with rejection after liver transplantation.

CONCLUSIONS

Minimization or withdrawal of immunosuppression can be achieved by the induction of immune tolerance via different mechanisms. This process could be affected by immunophenotypic shift of memory CD8+ T cells and CD4+ T cell subsets, which may be correlated with activation of the inflammasome through ASC in dendritic cells.

Inhibition of the purinergic pathway prolongs mouse lung allograft survival

Lung transplantation has limited survival with current immunosuppression. ATP is released from activated T cells, which act as costimulatory molecules through binding to the purinergic receptor P2XR7. We investigated the role of blocking the ATP/purinergic pathway, primarily P2XR7, using its inhibitor oxidized ATP (oATP) in modulating rejection of mouse lung allografts. Mouse lung transplants were performed using mice with major histocompatibility complex mismatch, BALB/c to C57BL6. Recipients received suramin or oATP, and lung allografts were evaluated 15 to ≥ 60 days after transplantation. Recipients were also treated with oATP after the onset of moderate to severe rejection to determine its ability to rescue lung allografts. Outcomes measures included lung function, histology, thoracic imaging, and allo-immune responses. Blocking purinergic receptors with the nonselective inhibitor suramin or with the P2XR7-selective inhibitor oATP reduced acute rejection and prolonged lung allograft survival for ≥ 60 days with no progression in severity. There were fewer inflammatory cells within lung allografts, less rejection, and improved lung function, which was maintained over time. CD4 and CD8 T cells were reduced within lung allografts with impaired activation with prolonged impairment of CD8 responses. In vitro, oATP reduced CD8 activation of Th1 inflammatory cytokines IFN-γ and TNF-α and cytolytic machinery, granzyme B. Cotreatment with immunosuppressive agents, cyclosporine, rapamycin, or CTLA-4Ig resulted in no additive benefits, and oATP alone resulted in better outcomes than cyclosporine alone. This study illustrates a potential new pathway to target in hopes of prolonging survival of lung transplant recipients.

Rapid tolerance induction by hematopoietic progenitor cells in the absence of donor-matched lymphoid cells

BACKGROUND

Donor specific hematopoietic cell transplantation has long been recognized for its potential in tolerance induction for subsequently transplanted organs. We have recently published that co-administration of Myeloid Progenitor (MP) and third party Hematopoietic Stem Cells (HSC) can induce MP-specific tolerance for subsequently transplanted organs [1].

METHODS

Mice received an allogeneic HSC and third party MP transplantation simultaneous with placement of a MP-matched skin graft. Variants tested include time of graft placement, MP genotype and source of cells.

RESULTS

Using B10;B6-Rag2(-/-)Il2rg(-/-) mice, we demonstrate that specific tolerance can be induced by MP given simultaneous with the skin graft in the complete absence of MP-donor-matched lymphoid cells. Ex vivo expanded MP function as well as sorted cells in inducing tolerance. In addition we demonstrate that tolerance can be induced by MP in the context of autologous HSC transplantation.

CONCLUSIONS

Our results demonstrate that the previously observed expansion of organ donor matched Treg is not essential for tolerance, and that MP tolerance protocols can be envisioned in most clinical settings, including those involving deceased donor organs.

Transplantation tolerance: from theory to clinic

Tolerance induction and alloreactivity can be applied to the clinic for the transplantation of solid organs and in the treatment of human cancers respectively. Hematopoietic chimerism, the stable coexistence of host and donor blood cells, guarantees that a solid organ from the same donor will be tolerated without a requirement for maintenance immunosuppression, and it also serves as a platform for the adoptive immunotherapy of hematologic malignancies using donor lymphocyte infusions. This review focuses on clinically relevant methods for inducing hematopoietic chimerism and transplantation tolerance, with a special emphasis on reduced intensity transplantation conditioning and high dose, post-transplantation cyclophosphamide to prevent graft rejection and graft-versus-host disease (GVHD). Reduced intensity transplantation regimens permit a transient cooperation between donor and host immune systems to eradicate malignancy without producing GVHD. Their favorable toxicity profile also enables the application of allogeneic stem cell transplantation to treat non-malignant disorders of hematopoiesis and to induce tolerance for solid organ transplantation.

Alloreactivity

The alloimmune response between individuals genetically disparate for antigens encoded within the major histocompatibility complex (MHC) remains a substantial barrier to transplantation of solid organs, tissues, and hematopoietic stem cells. Alloreactivity has been an immunological paradox because of its apparent contradiction to the requirement of MHC restriction for the induction of normal T lymphocyte mediated immune responses. Through crystallographic analyses and experimental systems utilizing murine CD8(+) cytolytic T cell clones, major advances have been achieved in understanding the molecular and structural basis of T cell receptor recognition of MHC-peptide complexes and the basis of T cell mediated alloreactivity. These studies have further provided an explanation for the relatively high frequencies of alloreactive T cells compared to the frequencies of T cells for microbial derived antigens.

Predicting operational tolerance in pediatric living-donor liver transplantation by absence of HLA antibodies

BACKGROUND

The role of anti-human leukocyte antigen (HLA) antibodies in operational tolerance (OT) after pediatric living-donor liver transplantation (LDLT) remains inconclusive. We investigated whether the presence of HLA antibodies impeded the development of OT.

METHODS

We retrospectively examined the prevalence of anti-HLA antibodies in pediatric LDLT recipients before transplantation and at 3 weeks after transplantation and analyzed the significance of those antibodies in relation to later OT. Forty pediatric LDLTs were performed between April 1996 and December 2000 and followed up through July 2011, with sera available for measurement of HLA antibodies. Seventeen patients achieved OT (mean follow-up, 4571.9±544.7 days) and 23 patients did not achieve OT (mean follow-up, 4532.0±425.4 days). Protocol liver biopsy was done for 14 OT patients and 16 non-OT patients. Their sera were tested for anti-HLA class I and II antibodies using the LABScreen single antigen beads test, in which a 1000 mean fluorescence value was considered positive.

RESULTS

The prevalence of antibodies after transplantation in non-OT patients was higher than in OT patients (95.2% vs. 73.3%; P<0.001). The highest mean fluorescence intensity of antibodies was significantly higher in non-OT patients than in OT patients. The prevalence of HLA-B, HLA-C, HLA-DQ, and HLA-DR antibodies was significantly higher in non-OT patients than in OT patients. The highest mean fluorescence intensity of HLA-A, HLA-B, and HLA-DQ observed in non-OT patients was significantly higher than those in OT patients.

CONCLUSIONS

In our study, posttransplantation HLA antibodies were associated with the future absence of OT. A prospective study with more patients is necessary to confirm the predictive value of HLA antibodies for OT.

How regenerative medicine and tissue engineering may complement the available armamentarium in gastroenterology?

The increasing shortage of donors and the adverse effects of immunosuppression have restricted the impact of solid organ transplantation. Despite the initial promising developments in xenotransplantation, roadblocks still need to be overcome and this form of organ support remains a long way from clinical practice. While hepatocyte transplantation may be effectively correct metabolic defects, it is far less effective in restoring liver function than liver transplantation. Tissue engineering, using extracellular matrix scaffolds with an intact but decellularized vascular network that is repopulated with autologous or allogeneic stem cells and/or adult cells, holds great promise for the treatment of failure of organs within gastrointestinal tract, such as end-stage liver disease, pancreatic insufficiency, bowel failure and type 1 diabetes. Particularly in the liver field, where there is a significant mortality of patients awaiting transplant, human bioengineering may offer a source of readily available organs for transplantation. The use of autologous cells will mitigate the need for long term immunosuppression thus removing a major hurdle in transplantation.

Tacrolimus trough levels, rejection and renal impairment in liver transplantation: a systematic review and meta-analysis

We hypothesized that current trough concentrations of tacrolimus after liver transplantation are set too high, considering that clinical consequences of rejection are not severe while side effects are increased.We systematically reviewed 64 studies (32 randomized controlled trials and 32 observational studies) to determine how lower tacrolimus trough concentrations than currently recommended affect acute rejection rates and renal impairment. Among randomized trials the mean of tacrolimus trough concentration during the first month was positively correlated with renal impairment within 1 year (r = 0.73; p = 0.003), but not with acute rejection, either defined using protocol biopsies (r = -0.37; p = 0.32) or not (r = 0.11; p = 0.49). A meta-analysis of randomized trials directly comparing tacrolimus trough concentrations (five trials for acute rejection [n = 957] and two trials for renal impairment [n = 712]) showed that "reduced tacrolimus" trough concentrations (<10 ng/mL) within the first month after liver transplantation were associated with less renal impairment at 1 year (RR = 0.51 [0.38-0.69]), with no significant influence on acute rejection (RR = 0.92 [0.65-1.31]) compared to "conventional tacrolimus" trough levels (>10 ng/mL). Lower trough concentrations of tacrolimus (6-10 ng/mL during the first month) would be more appropriate after liver transplantation. Regulatory authorities and the pharmaceutical industry should allow changes of regulatory drug information.

Emerging uses for pediatric hematopoietic stem cells

Many new therapies are emerging that use hematopoietic stem and progenitor cells. In this review, we focus on five promising emerging trends that are altering stem cell usage in pediatrics: (i) The use of hematopoietic stem cell (HSC) transplantation, autologous or allogeneic, in the treatment of autoimmune disorders is one. (ii) The use of cord blood transplantation in patients with inherited metabolic disorders such as Hurler syndrome shows great benefit, even more so than replacement enzyme therapy. (iii) Experience with the delivery of gene therapy through stem cells is increasing, redefining the potential and limitations of this therapy. (iv) It has recently been shown that human immunodeficiency virus (HIV) infection can be cured by the use of selected stem cells. (v) Finally, it has long been postulated that HSC-transplantation can be used to induce tolerance in solid-organ transplant recipients. A new approach to tolerance induction using myeloid progenitor cells will be described.

Tolerance in liver transplantation

Operational tolerance (OT) in liver transplant patients occurs much more frequently than OT of other transplanted organs; however the rate of OT varies considerably with the centre and patient population. Rates of OT range from 15% of the total liver transplant (LTX) patient population down to less than 5%. This review examines the reports of liver OT and compares the factors that could contribute to this variation. Multiple factors were examined, including the time from transplantation when weaning of immunosuppression (IS) was commenced, the rapidity of weaning, the contribution of maintenance and induction IS and the patient population transplanted. The approaches that might be used to increase the likelihood of OT are discussed and the approaches to monitoring OT in LTX patients are reviewed.