Prevention Of Allograft Rejection Research Articles

Donor IL-6 deficiency evidently reduces memory T cell responses in sensitized transplant recipients

BackgroundResistance of tolerance induction in sensitized transplantation is mainly caused by generation of memory T cells. It is unknown whether alteration of graft niche such as level of pro-inflammatory cytokines can affect generation of memory T cells. MethodsIL-6 deficient or wild-type (WT) C57BL/6 heart grafts were transplanted into pre-sensitized wild-type BALB/c recipients. Frequencies of memory T cells in the peripheral blood, grafts, and spleen were evaluated. ResultsWe revealed that deficiency of donor IL-6 could significant prolong sensitized allograft survival. Compared with counterpart of WT group, frequency of effector memory CD4 + T cells (CD4 + CD44 + CD62L-) in the peripheral blood was significantly lower in the IL-6 KO group (p = .026) at day 3 post-transplantation. Frequency of effector memory CD8 + T cells (CD8 + CD44 + CD62L-) in the peripheral blood was significantly lower in the IL-6 KO group (p < .0001) at day 3 post-transplant in comparison to that of WT group. No significant difference of central memory T cells was found between these groups. Histology demonstrated that deficiency of donor pro-inflammatory cytokine IL-6 (IL-6 KO group) preserved cardiac architecture with a mild infiltration of lymphocytes, whereas wild-type donor (control group) caused an evident lymphocytic infiltration within myocardial fibers of grafts and destruction of cardiac structure. ConclusionDeficiency of pro-inflammatory IL-6 of donor graft could effectively prolong sensitized allograft survival, which was caused by a remarkable decrease of peripheral memory T cells rather than central memory T cells. This unveiled mechanism of targeting IL-6 signaling pathway might provide a novel insight into preventing allograft rejection for sensitized transplant recipients.

A novel 2,4-diaminopyrimidine derivative as selective inhibitor of protein kinase C theta prevents allograft rejection in a rat heart transplant model

Protein kinase C theta (PKCθ) plays a critical role in T cell signaling and is an attractive target for the treatment of T cell-mediated diseases such as transplant rejection and autoimmune disease. To identify PKCθ inhibitors, we focused on the 2,6-diamino-3-carbamoyl-5-cyanopyrazine derivative 2, which exhibited moderate PKCθ inhibitory activity. Optimization of 2 identified the 2,4-diamino-5-cyanopyrimidine derivative 16c, which exhibited potent PKCθ inhibitory activity and showed good selectivity against other PKC isozymes. Compound 16c prolonged graft survival in an in vivo rat heterotopic cardiac transplant model.

Advances in T follicular helper and T follicular regulatory cells in transplantation immunity.

B cells play a crucial role in alloreactivity of organ transplant rejection and graft versus host diseases (GVHD). Over the past decade, it has been well recognized that B-cell infiltration in allografts and de novo donor-specific antibodies (DSA) were strongly associated with severe graft rejection and loss, as well as glucocorticoid resistance. Emerging evidence has demonstrated that Follicular T helper (Tfh) cells are key effectors to promote the proliferation and differentiation of B cells into antibody-producing plasmablasts and memory B cells. T-follicular regulatory (Tfr) cells are a recently recognized cell population that has a negative regulatory role on Tfh cells in the follicle, preventing incessant antibody production. It is still less clear how those humoral immunoreactive cells affect transplant rejection and allograft loss. This review focuses on the production and function of Tfr/Tfh cells in the transplant environment. Better understanding of the functions and mechanisms of Tfr/Tfh cells will help to design new strategies to prevent allograft rejection and prolong graft survival.

Quantification of Torque Teno Virus Viremia as a Prospective Biomarker for Infectious Disease in Kidney Allograft Recipients.

Drug-induced immunosuppression following kidney transplantation is crucial to prevent allograft rejection, but increases risk for infectious disease. Tailoring of drug dosing to prevent both rejection and infection is greatly desirable. The apathogenic and ubiquitous torque teno virus (TTV) reflects immunocompetence of the host and might be a potential candidate for immunologic monitoring. To assess TTV as an infection biomarker, virus load was prospectively quantified in peripheral blood of 169 consecutive renal allograft recipients at the Medical University Vienna. Patients with infection showed higher TTV levels compared to patients without infection (4.2 × 108 copies/mL [interquartile range, IQR, 2.7 × 107-1.9 × 109] vs 2.9 × 107 [IQR 1.0 × 106-7.2 × 108]; P = .006). Differences in TTV load became evident almost 3 months before infection (median 77 days, IQR 19-98). Each log level of TTV copies/mL increased the odds ratio for infection by 23% (95% confidence interval 1.04-1.45; P = .014). TTV >3.1 × 109 copies/mL corresponded to 90% sensitivity to predict infections. Logistic regression demonstrated independent association between TTV levels and infection. TTV quantification predicts infection after kidney transplantation and might be a potential tool to tailor immunosuppressive drug therapy.

Review of Major Drug-Drug Interactions in Thoracic Transplantation

The first human lung transplant surgery in the world was done in 1963, followed by the first heart transplant in 1967, making this year its 50th anniversary. Since then, there has been great advancement in immunotherapy, with the adoption of calcineurin inhibitors (CNI), mycophenolate mofetil, and proliferation signal inhibitors (PSI). However, while these medications are crucial to maintenance of allograft function and prevention of allograft rejection, they have many toxicities and side effects, which make therapeutic dose monitoring and recognition of drug-drug interactions of critical importance. Most of drug-drug interactions in transplant medicine can be explained through the mechanism of CYP3A4 and P-glycoprotein. A large component of the medical management of post-transplant care is in the appropriate utilization of immunosuppression drugs while minimizing side effects and drug-drug interactions.

315 - Multipotent Adult Progenitor Cells suppress homeostatic driven activation of T cells in vivo

In the setting of transplantation, T cells are deliberately depleted to prevent allograft rejection. However, this IL-7 activates the accelerated proliferation of effector memory T cells, which are the predominant mediators of graft rejection. Multipotent adult progenitor cells (MAPC) have been previously shown to modulate the response of T cells to IL-7, in vitro but not in vivo. Here, for the first time, we demonstrate that MAPC suppress IL-7 and anti-thymocyte (ATG) driven pro-inflammatory cytokine production by both CD4+ and CD8+ T cells in the spleen. While, MAPC significantly suppressed T cell proliferation in the IL-7 driven model, MAPC did not suppress T cell proliferation in the ATG model when administered on day 4. The effects of routes of administration on the bio-distribution of MAPC in our model of homeostatic proliferation was further clarified using novel 3D whole animal Cryo-imaging technology. MAPC administered i.v. were observed in the spleen 48 hours post injection. However, following i.p. administration, MAPC do not gain access to the spleen but reside in the omentum tissue suggesting that MAPC mediate their effects in the spleen through trophic signalling. Importantly, we demonstrate that MAPC mediate their suppression of pro-inflammatory cytokine production in a PGE-2 dependent manner. Given the importance of successful reconstitution of the immune cell compartment to provide a functional immune system, the fact that MAPC do not suppress this reconstitution but dampen pathogenic cytokine production is a very positive finding. Together this data supports the idea that MAPC may be useful in controlling immune dysregulation via suppression of T cell cytokine production while sparing T cell reconstitution in lymphodepleted patients. (Less)

Multipotent Adult Progenitor Cells Suppress T Cell Activation in In Vivo Models of Homeostatic Proliferation in a Prostaglandin E2-Dependent Manner.

Lymphodepletion strategies are used in the setting of transplantation (including bone marrow, hematopoietic cell, and solid organ) to create space or to prevent allograft rejection and graft versus host disease. Following lymphodepletion, there is an excess of IL-7 available, and T cells that escape depletion respond to this cytokine undergoing accelerated proliferation. Moreover, this environment promotes the skew of T cells to a Th1 pro-inflammatory phenotype. Existing immunosuppressive regimens fail to control this homeostatic proliferative (HP) response, and thus the development of strategies to successfully control HP while sparing T cell reconstitution (providing a functioning immune system) represents a significant unmet need in patients requiring lymphodepletion. Multipotent adult progenitor cells (MAPC®) have the capacity to control T cell proliferation and Th1 cytokine production. Herein, this study shows that MAPC cells suppressed anti-thymocyte globulin-induced cytokine production but spared T cell reconstitution in a pre-clinical model of lymphodepletion. Importantly, MAPC cells administered intraperitoneally were efficacious in suppressing interferon-γ production and in promoting the expansion of regulatory T cells in the lymph nodes. MAPC cells administered intraperitoneally accumulated in the omentum but were not present in the spleen suggesting a role for soluble factors. MAPC cells suppressed lymphopenia-induced cytokine production in a prostaglandin E2-dependent manner. This study suggests that MAPC cell therapy may be useful as a novel strategy to target lymphopenia-induced pathogenic T cell responses in lymphodepleted patients.

Cell Therapy in Organ Transplantation: Our Experience on the Clinical Translation of Regulatory T Cells.

Solid organ transplantation is the treatment of choice for patients with end-stage organ dysfunction. Despite improvements in short-term outcome, long-term outcome is suboptimal due to the increased morbidity and mortality associated with the toxicity of immunosuppressive regimens and chronic rejection (1–5). As such, the attention of the transplant community has focused on the development of novel therapeutic strategies to achieve allograft tolerance, a state whereby the immune system of the recipient can be re-educated to accept the allograft, averting the need for long-term immunosuppression. Indeed, reports of “operational” tolerance, whereby the recipient is off all immunosuppressive drugs and maintaining good graft function, is well documented in the literature for both liver and kidney transplantations (6–8). However, this phenomenon is rare and in the setting of liver transplantation has been shown to occur late after transplantation, with the majority of patients maintained on life-long immunosupression to prevent allograft rejection (9). As such, significant research has focused on immune regulation in the context of organ transplantation with regulatory T cells (Tregs) identified as cells holding considerable promise in this endeavor. This review will provide a brief introduction to human Tregs, their phenotypic and functional characterization and focuses on our experience to date at the clinical translation of Treg immunotherapy in the setting of solid organ transplantation.

Ex vivo allotransplantation engineering: Delivery of mesenchymal stem cells prolongs rejection-free allograft survival.

Current pharmacologic regimens in transplantation prevent allograft rejection through systemic recipient immunosuppression but are associated with severe morbidity and mortality. The ultimate goal of transplantation is the prevention of allograft rejection while maintaining recipient immunocompetence. We hypothesized that allografts could be engineered ex vivo (after allotransplant procurement but before transplantation) by using mesenchymal stem cell-based therapy to generate localized immunomodulation without affecting systemic recipient immunocompetence. To this end, we evaluated the therapeutic efficacy of bone marrow-derived mesenchymal stem cells in vitro and activated them toward an immunomodulatory fate by priming in inflammatory or hypoxic microenvironments. Using an established rat hindlimb model for allotransplantation, we were able to significantly prolong rejection-free allograft survival with a single perioperative ex vivo infusion of bone marrow-derived mesenchymal stem cells through the allograft vasculature, in the absence of long-term pharmacologic immunosuppression. Critically, transplanted rats rejected a second, nonengineered skin graft from the same donor species to the contralateral limb at a later date, demonstrating that recipient systemic immunocompetence remained intact. This study represents a novel approach in transplant immunology and highlights the significant therapeutic opportunity of the ex vivo period in transplant engineering.

RNA expression profiling of nonhuman primate renal allograft rejection identifies tolerance.

Tolerance induction to prevent allograft rejection is a long-standing clinical goal. However, convincing and dependable tolerance identification remains elusive. Hypothesizing that intragraft RNA expression is informative in both rejection and tolerance, we profile intrarenal allograft RNA expression in a mixed chimerism renal allograft model of cynomolgus monkeys and identify biologically significant tolerance. Analysis of 67 genes identified 3 dominant factors, each with a different pattern of gene expressions, relating to T cell-mediated rejection (TCMR), chronic antibody-mediated rejection (CAMR), or Tolerance. Clustering these 3 factors created 9 groups. One of the 9 clustered groups, the Tolerance cluster, showed the lowest probability of terminal rejection, the longest duration of allograft survival, and the lowest relative risk of terminal rejection. The Tolerance factor consists of a novel set of gene expressions including cytokine and immunoregulatory genes adding mechanistic insights into tolerance. The Tolerance factor could not be identified within current pathologic diagnostic categories. The TCMR and CAMR factors are dominant to the Tolerance factor, causing rejection even if the Tolerance factor is present. These 3 factors determine the probability of terminal rejection or tolerance. This novel a posteriori approach permits identification of pathways of rejection, including tolerance.

Immunosuppression by a subconjunctival implant releasing dexamethasone in a rabbit model of penetrating keratoplasty

AimsTo evaluate the efficacy of a subconjunctival dexamethasone-releasing implant in preventing rejection of penetrating keratoplasty (PK) in an animal model.MethodsTwenty-two rabbits underwent allogenic PK. After randomisation, they received either a...

Pilot Study of Delayed ICOS/ICOS-L Blockade With αCD40 to Modulate Pathogenic Alloimmunity in a Primate Cardiac Allograft Model.

Inducible costimulator (ICOS) is rapidly upregulated with T-cell stimulation and may represent an escape pathway for T-cell costimulation in the setting of CD40/CD154 costimulation blockade. Induction treatment exhibited no efficacy in a primate renal allograft model, but rodent transplant models suggest that the addition of delayed ICOS/ICOS-L blockade may prolong allograft survival and prevent chronic rejection. Here, we ask whether ICOS-Ig treatment, timed to anticipate ICOS upregulation, prolongs NHP cardiac allograft survival or attenuates pathogenic alloimmunity. Cynomolgus monkey heterotopic cardiac allograft recipients were treated with αCD40 (2C10R4, d0-90) either alone or with the addition of delayed ICOS-Ig (d63-110). Median allograft survival was similar between ICOS-Ig + αCD40 (120 days, 120-125 days) and αCD40 (124 days, 89-178 days) treated animals, and delayed ICOS-Ig treatment did not prevent allograft rejection in animals with complete CD40 receptor coverage. Although CD4+ TEM cells were decreased in peripheral blood (115 ± 24) and mLNs (49 ± 1.9%) during ICOS-Ig treatment compared with monotherapy (214 ± 27%, P = 0.01; 72 ± 9.9%, P = 0.01, respectively), acute and chronic rejection scores and kinetics of alloAb elaboration were similar between groups. Delayed ICOS-Ig treatment with the reagent tested is probably ineffective in modulating pathogenic primate alloimmunity in this model.

Cyclosporin A inhibits mitochondrial biogenesis in Hep G2 cells

Dysregulation of mitochondrial biogenesis is associated with pathogenesis in many diseases, including liver diseases. Cyclosporine A (CsA), one of the most commonly used drug to treat many autoimmune diseases and to prevent allograft rejection after organ transplantation, has been reported to cause mitochondrial dysfunction. However, the cellular mechanisms underlying CsA on mitochondrial dysfunction remain at present not completely elucidated. In this study, we found that CsA reduced the expression of PGC-1α at both the mRNA and protein levels in HepG2 cells. Correspondingly, the expressions of its target genes NRF 1 and TFAM were reduced in response to CsA treatment. In addition, mtDNA/nDNA, mitochondria mass, ATP production, and cytochrome C oxidase activity were significantly reduced by treatment with CsA. Over-expression of PGC-1α was found to rescue the negative effect of CsA administration on mitochondrial biogenesis. Mechanistically, CREB was involved in the inhibitory effects of CsA in mitochondrial biogenesis.

The Calcineurin Inhibitor FK506 Prevents Cognitive Impairment by Inhibiting Reactive Astrogliosis in Pilocarpine-Induced Status Epilepticus Rats.

Status epilepticus (SE) is a severe clinical manifestation of epilepsy accompanying with cognitive impairment and brain damage. Astrocyte activation occurs following seizures and plays an important role in epilepsy-induced pathological injury, including cognitive impairment. FK506, an immunosuppressant used in clinical settings to prevent allograft rejection, has been shown to exhibit neuroprotective effects in central nervous system diseases. The present study was designed to investigate the effect of FK506 on cognitive impairment in a lithium-pilocarpine-induced SE rat model. It's found that FK506 treatment significantly increased the latency period to seizures and decreased the maximal intensity of seizures. FK506 treatment also markedly increased the surviving cells and reduced the neuron apoptosis after seizures. Meanwhile, FK506 treatment reduced the escape latency and prolonged the swimming distance in the Morris water maze test. In addition, FK506 treatment down-regulated the expression level of GFAP, a specific marker of astrocytes. In conclusion, FK506 could prevent and recover cognitive impairment by inhibiting reactive astrogliosis in pilocarpine-induced status epilepticus rats, suggesting that FK506 may be a promising agent for the treatment of epilepsy.

Immunosuppressive therapy after solid organ transplantation

Solid organ transplantation is often life-saving. Transplanting a different genetic graft determines the immune response of the recipient, which detects the graft as a non-self, and tries to eliminate it. Immunosuppressive therapy is essential to prevent allograft rejection. Immunosuppression begins with induction therapy, followed by maintenance therapy. If hyperacute or acute rejections occur, they are reversed with certain immunosuppressive intensive care regimens. Immunosuppression is realized with glucocorticosteroids and other drugs that diminish T lymphocytes response or interfere with other stages of the immune response to the graft. Marked toxicity of individual immunosuppressants, as well as the risks associated with immunosuppression make it imperious to use minimal effective doses of immunosuppressants to maintain graft maintenance. Therefore, synergic drug combinations are commonly used, which allow for the smaller doses of each drug. Immunosuppressants are frequently involved in drug interactions and drug-food interactions, making treatment surveillance more challenging.

Nanoparticle-Based Modulation and Monitoring of Antigen-Presenting Cells in Organ Transplantation.

Donor-specific unresponsiveness while preserving an intact immune function remains difficult to achieve in organ transplantation. Induction of tolerance requires a fine modulation of the interconnected innate and adaptive immune systems. Antigen-presenting cells (APCs) predominate during allograft rejection and create a highly inflammatory context where allospecific T cells are primed. Currently, the available protocols to prevent allograft rejection include a cocktail of drugs that are efficient in the short-term, but with severe long-term side effects and considerable toxicity. Consequently, better and less burdensome strategies are needed to promote indefinite allograft survival. Targeted delivery of immunosuppressive drugs that prevent the alloimmune response may address some of these problems. Nanoparticle-based approaches represent a promising strategy to negatively modulate the alloresponse by specifically delivering small compounds to APCs in vivo. Nanoparticles are also used as integrating imaging moieties to monitor inflammation for diagnostic purposes. Therefore, nanotechnology approaches represent an attractive strategy to deliver and monitor the efficacy of immunosuppressive therapy in organ transplantation with the potential to improve the clinical treatment of transplant patients.

The Immunocompromised Surgical Patient and Opportunistic Infections

Immunosuppressive medications used to prevent allograft rejection render solid-organ transplant recipients vulnerable to various opportunistic infections. These infections include bacteria, viruses, fungi, and parasites and occur either via reactivation of previously acquired latent infection or de novo acquisition from the donor organ itself or the environment after the transplantation. The type and clinical course of the infection depend on various factors, including the transplanted organ, nature of immunosuppressive regimens, timing of infection relative to the organ transplant, and type and duration of prophylaxis. Proper donor and recipient screening for preventable infections and posttransplantation prophylaxis are instrumental in preventing morbid infections. Posttransplantation infections may present with subtle findings and thus may cause a delay in diagnosis and treatment, resulting in a poor outcome. Appropriate pathogen-specific tests should be requested promptly for early diagnosis. Since these infections may have overlapping clinical and radiologic features, tissue biopsy, if feasible, should be done to establish a definitive diagnosis. Surgical excision or débridement should be attempted in patients presenting with abscesses or invasive fungal sinusitis along with antimicrobial therapy. After the completion of treatment, suppressive therapy may be required in certain infections to prevent a relapse as long as the patient remains immunosuppressed. This review contains 3 tables, and 82 references. Key words: allograft, donor, immunocompromised, infection, opportunistic, organ, transplant

Update on Dendritic Cell-Induced Immunological and Clinical Tolerance.

Dendritic cells (DCs) as highly efficient antigen-presenting cells are at the interface of innate and adaptive immunity. As such, they are key mediators of immunity and antigen-specific immune tolerance. Due to their functional specialization, research efforts have focused on the characterization of DCs subsets involved in the initiation of immunogenic responses and in the maintenance of tissue homeostasis. Tolerogenic DCs (tolDCs)-based therapies have been designed as promising strategies to prevent and control autoimmune diseases as well as allograft rejection after solid organ transplantation (SOT). Despite successful experimental studies and ongoing phase I/II clinical trials using autologous tolDCs in patients with type 1 diabetes, rheumatoid arthritis, multiple sclerosis, and in SOT recipients, additional basic research will be required to determine the optimal DC subset(s) and conditioning regimens for tolDCs-based treatments in vivo. In this review, we discuss the characteristics of human DCs and recent advances in their classification, as well as the role of DCs in immune regulation and their susceptibility to in vitro or in vivo manipulation for the development of tolerogenic therapies, with a focus on the potential of tolDCs for the treatment of autoimmune diseases and the prevention of allograft rejection after SOT.

Clinical Challenges of Tacrolimus for Maintenance Immunosuppression Post–Lung Transplantation

Lung transplantation (LTx) is a successful treatment option for end-stage lung disease, and immunosuppressant regimens, utilized to prevent rejection of the transplanted graft, are paramount to maintaining long-term graft survival. Immunosuppression can be classified as induction, maintenance, and antirejection therapy. This article focuses on maintenance immunosuppression that includes a combination of a calcineurin inhibitor (CNI), cell cycle inhibitor, and corticosteroid. CNIs remain the cornerstone of immunosuppression following LTx, and tacrolimus is now the preferred CNI, based on a better adverse effect profile and some limited evidence for enhanced efficacy. Tacrolimus is associated with a number of unique challenges post-LTx, with erratic and highly variable absorption making it difficult to achieve and maintain therapeutic levels. Current methods of therapeutic drug monitoring are extrapolated from models in liver and kidney transplants and are not validated in the LTx population. Alternative methods of delivering tacrolimus can address some of the issues associated with their use and can be utilized in particular clinical scenarios. Long-term toxicities attributed to tacrolimus, such as nephrotoxicity and neurotoxicity, can limit the long-term success of tacrolimus in preventing allograft rejection. This article emphasizes the current clinical challenges faced when managing LTx recipients with tacrolimus, offers strategies to manage these issues, and highlights the areas that need further research.

Opportunistic Pulmonary Infections in the Solid Organ Transplant Recipient: A Focus on Drug Therapy.

Immunosuppression required to prevent allograft rejection in the solid organ transplant recipient increases vulnerability to infections. Given continuous environmental exposure, the lungs are increasingly susceptible to bacterial, viral, and fungal opportunistic infections. Drug therapy options for the treatment of opportunistic pulmonary infections are used infrequently. These medications are often classified as high risk with specific administration instructions, as well as a multitude of toxicities. Therefore, in this article, we will discuss select pulmonary opportunistic infections and their associated drug therapies.