Transplantation Tolerance Induction: Cell Therapies and Their Mechanisms

Cell-Based Therapies Induce Tolerance of Vascularized Composite Allotransplants: A Systematic Review

INTRODUCTION

Vascularized composite allotransplantation (VCA) is the transplantation of multiple tissue types as a solution for devastating injuries. Despite the highly encouraging functional outcomes of VCA, the consequences of long-term immunosuppression remain the main obstacle in its application. In this review, we provide researchers and surgeons with a summary of the latest advances in the field of cell-based therapies for VCA tolerance.

METHODS

Four electronic databases were searched: PubMed, Scopus, Cumulative Index to Nursing and Allied Health Literature , and Web of Science. We used the Preferred Reporting Items for Systematic Reviews and Meta-Analysis as the basis of our organization.

RESULTS

Hematopoietic stem cells prolonged VCA survival. A combination of immature dendritic cells and tacrolimus was superior to tacrolimus alone. T cell Ig domain and mucin domain modified mature dendritic cells increased VCA tolerance. Bone marrow-derived mesenchymal stem cells prolonged survival of VCAs. A combination of adipose-derived mesenchymal stem cells, cytotoxic T-lymphocyte antigen 4 immunoglobulin, and antilymphocyte serum significantly improved VCA tolerance. Ex-vivo allotransplant perfusion with recipient's bone marrow-derived mesenchymal stem cells increased VCA survival. Recipient's adipose-derived mesenchymal stem cells and systemic immunosuppression prolonged VCA survival more than any of those agents alone. Additionally, a combination of peripheral blood mononuclear cells shortly incubated in mitomycin and cyclosporine significantly improved VCA survival. Finally, a combination of donor recipient chimeric cells, anti-αβ-T cell receptor (TCR), and cyclosporine significantly prolonged VCA tolerance.

CONCLUSIONS

Evidence from animal studies shows that cell-based therapies can prolong survival of VCAs. However, there remain many obstacles for these therapies, and they require rigorous clinical research given the rarity of the subjects and the complexity of the therapies. The major limitations of cell-based therapies include the need for conditioning with immunosuppressive drugs and radiation, causing significant toxicity. Safety concerns also persist as most research is on animal models. While completely replacing traditional immunosuppression with cell-based methods is unlikely soon, these therapies could reduce the need for high doses of immunosuppressants and improve VCA tolerance.

Effect of Mammalian Target of Rapamycin Inhibition on Activated Regulatory T-Cell Expansion in Kidney Transplantation

BACKGROUND

The mammalian target of rapamycin (mTOR) plays a critical role in the host immune response in organ transplantation. This study evaluates the regulatory benefits of mTOR inhibitors in kidney transplant recipients (KTRs).

METHODS

The mTOR-dependent immune-regulating effects in KTRs were evaluated by examining T-cell subsets among peripheral blood mononuclear cells from 79 KTRs. Recipients included an early introduction of everolimus (EVR) and reduced-exposure tacrolimus group (n = 46) and a standard tacrolimus-based without EVR (non-EVR) group (n = 33).

RESULTS

Trough concentrations of tacrolimus at 3 months and 1 year were significantly lower in the EVR group than the non-EVR group (both P < .001). In addition, the respective proportions of patients without estimated glomerular filtration rate < 20% in the EVR and non-EVR groups were 100% and 93.3% at 1 year, 96.3% and 89.7% at 2 years, and 96.3% and 89.7% at 3 years after blood collection, respectively (P = .079). The frequencies of CD3⁺ T cells and CD4⁺ T cells among peripheral blood mononuclear cells were comparable between groups. Total CD25^highCD127^-CD4⁺ regulatory T (Treg) cells were similar in the EVR and non-EVR groups. In contrast, circulating CD45RA^-CD25^highCD127^-CD4⁺ activated Treg cells were significantly higher in the EVR group (P= .008).

CONCLUSION

These results suggest that the early introduction of mTOR benefits long-term kidney graft function and circulating activated Treg-cell expansion in KTRs.

Aging Affects the Role of Myeloid-Derived Suppressor Cells in Alloimmunity

Myeloid-derived suppressor cells (MDSC) are defined as a group of myeloid cells with potent immunoregulatory functions that have been shown to be involved in a variety of immune-related diseases including infections, autoimmune disorders, and cancer. In organ transplantation, MDSC promote tolerance by modifying adaptive immune responses. With aging, however, substantial changes occur that affect immune functions and impact alloimmunity. Since the vast majority of transplant patients are elderly, age-specific modifications of MDSC are of relevance. Furthermore, understanding age-associated changes in MDSC may lead to improved therapeutic strategies. Here, we provide a comprehensive update on the effects of aging on MDSC and discuss potential consequences on alloimmunity.

Xenogeneic Sertoli cells modulate immune response in an evolutionary distant mouse model through the production of interleukin-10 and PD-1 ligands expression

BACKGROUND

Immunomodulatory mechanisms of Sertoli cells (SCs) during phylogeny have not been described previously. This study attempted to reveal mechanisms of SC immune modulation in an evolutionary distant host.

METHODS

The interaction of the SC cell line derived from Xenopus tropicalis (XtSC) with murine immune cells was studied in vivo and in vitro. The changes in the cytokine production, the intracellular and surface molecules expression on murine immune cells were evaluated after co-culturing with XtSCs. Migration of XtSCs in mouse recipients after intravenous application and subsequent changes in spleen and the testicular immune environment were determined by flow cytometry.

RESULTS

The in vitro co-culture model was established, allowing the study of XtSCs interaction with murine immune cells. Intracellular staining of interleukin (IL-)10 revealed a significant increase in its expression in macrophages and B cells co-cultured with XtSCs, compared to both unstimulated cells and xenogeneic control. On the contrary, a significant decrease in Th lymphocytes expressing interferon-gamma was observed. The expression of both PD-1 ligands (PD-L1 and PD-L2) was upregulated on the macrophage surfaces after co-culture with XtSCs, but not with the controls. XtSCs migrated specifically to testes when administered intravenously and modulated systemic and local testicular microenvironment; this was detected by the expression of molecules associated with suppressive phenotype by CD45⁺ cells in both spleen and testes.

CONCLUSION

We have demonstrated for the first time that SCs can migrate and modulate immune response in a phylogenetically distant host. It was further observed that SCs induce expression of molecules associated with immunosuppression, such as IL-10 and PD-1 ligands.

Macrophages in Transplantation: A Matter of Plasticity, Polarization, and Diversity

Macrophages have emerged at the forefront of research in immunology and transplantation because of recent advances in basic science. New findings have illuminated macrophage populations not identified previously, expanded upon traditional macrophage phenotypes, and overhauled macrophage ontogeny. These advances have major implications for the field of transplant immunology. Macrophages are known to prime adaptive immune responses, perpetuate T-cell-mediated rejection and antibody-mediated rejection, and promote allograft fibrosis. In this review, macrophage phenotypes and their role in allograft injury of solid organ transplants will be discussed with an emphasis on kidney transplantation. Additionally, consideration will be given to the prospect of manipulating macrophage phenotypes as cell-based therapy. Innate immunity and macrophages represent important players in allograft injury and a promising target to improve transplant outcomes.

Morphofunctional characteristics of animals in the detection of embryonic antigens in the prenatal and postnatal periods

Diseases in newborn animals cause significant damage to animal husbandry. This is a complex problem, in which, along with such factors as the environment and the pathogen, an important role is played by the reaction of the body of newborns and their close connection with the mother's body. The study of enzyme relationships in the functional system «mother-fetus-newborn» can make a significant contribution to solving the problem of improving the safety of the population of newborn animals. Newborn animals have different degrees of functional maturity. Functional capacity of some organs and the system of the newborn, in comparison with the parent individuals, can be determined both genetically and by the conditions of intrauterine development. Currently, a sufficient number of facts have been accumulated that any deviations or violations of homeostasis parameters the mother's body affects the fetus and Vice versa. The main role in compensating for impaired functions belongs to the mother's body, but the fetus is also able to participate in these reactions to a certain extent. Functional integration of fetal and maternal homologous systems when performing homeostatic functions concerns the activity of the blood enzyme component. The aim of our research was to study quantitative and qualitative changes in the activity of blood enzymes in non-pregnant sows, in the first and second half of pregnancy and the postpartum period.

Expansion of CD45RA-FOXP3++ regulatory T cells is associated with immune tolerance in patients with combined kidney and bone marrow transplantation

Objectives

Simultaneous transplantation of a solid organ and bone marrow from the same donor is a possible means of achieving transplant tolerance. Here, we attempted to identify biomarkers that indicate transplant tolerance for discontinuation of immunosuppressants in combined kidney and bone marrow transplantation (CKBMT).

Methods

Conventional kidney transplant (KT) recipients (n = 20) and CKBMT recipients (n = 6) were included in this study. We examined various immunological parameters by flow cytometry using peripheral blood mononuclear cells (PBMCs), including the frequency and phenotype of regulatory T (Treg) cell subpopulations. We also examined the suppressive activity of the Treg cell population in the setting of mixed lymphocyte reaction (MLR) with or without Treg cell depletion.

Results

Among six CKBMT recipients, three successfully discontinued immunosuppressants (tolerant group) and three could not (non‐tolerant group). The CD45RA⁻FOXP3⁺⁺ Treg cell subpopulation was expanded in CKBMT recipients compared to conventional kidney transplant patients, and this was more obvious in the tolerant group than the non‐tolerant group. In addition, high suppressive activity of the Treg cell population was observed in the tolerant group. The ratio of CD45RA⁻FOXP3⁺⁺ Treg cells to CD45RA⁻FOXP3⁺ cells indicated good discrimination between the tolerant and non‐tolerant groups.

Conclusion

Thus, our findings propose a biomarker that can distinguish CKBMT patients who achieve transplant tolerance and are eligible for discontinuation of immunosuppressants and may provide insight into tolerance mechanisms in CKBMT.

Targeting age-specific changes in CD4+ T cell metabolism ameliorates alloimmune responses and prolongs graft survival

Age impacts alloimmunity. Effects of aging on T-cell metabolism and the potential to interfere with immunosuppressants have not been explored yet. Here, we dissected metabolic pathways of CD4⁺ and CD8⁺ T cells in aging and offer novel immunosuppressive targets. Upon activation, CD4⁺ T cells from old mice failed to exhibit adequate metabolic reprogramming resulting into compromised metabolic pathways, including oxidative phosphorylation (OXPHOS) and glycolysis. Comparable results were also observed in elderly human patients. Although glutaminolysis remained the dominant and age-independent source of mitochondria for activated CD4⁺ T cells, old but not young CD4⁺ T cells relied heavily on glutaminolysis. Treating young and old murine and human CD4⁺ T cells with 6-diazo-5-oxo-l-norleucine (DON), a glutaminolysis inhibitor resulted in significantly reduced IFN-γ production and compromised proliferative capacities specifically of old CD4⁺ T cells. Of translational relevance, old and young mice that had been transplanted with fully mismatched skin grafts and treated with DON demonstrated dampened Th1- and Th17-driven alloimmune responses. Moreover, DON diminished cytokine production and proliferation of old CD4⁺ T cells in vivo leading to a significantly prolonged allograft survival specifically in old recipients. Graft prolongation in young animals, in contrast, was only achieved when DON was applied in combination with an inhibition of glycolysis (2-deoxy-d-glucose, 2-DG) and OXPHOS (metformin), two alternative metabolic pathways. Notably, metabolic treatment had not been linked to toxicities. Remarkably, immunosuppressive capacities of DON were specific to CD4⁺ T cells as adoptively transferred young CD4⁺ T cells prevented immunosuppressive capacities of DON on allograft survival in old recipients. Depletion of CD8⁺ T cells did not alter transplant outcomes in either young or old recipients. Taken together, our data introduce an age-specific metabolic reprogramming of CD4⁺ T cells. Targeting those pathways offers novel and age-specific approaches for immunosuppression.

Detection and Monitoring of Regulatory Immune Cells Following Their Adoptive Transfer in Organ Transplantation

Application of cell-based immunotherapy in organ transplantation to minimize the burden of immunosuppressive medication and promote allograft tolerance has expanded significantly over the past decade. Adoptively transferred regulatory immune cells prolong allograft survival and transplant tolerance in pre-clinical models. Many cell products are currently under investigation in early phase human clinical trials designed to assess feasibility and safety. Despite rapid advances in manufacturing practices, defining the appropriate protocol that will optimize in vivo conditions for tolerance induction remains a major challenge and depends heavily on understanding the fate, biodistribution, functional stability and longevity of the cell product after administration. This review focuses on in vivo detection and monitoring of various regulatory immune cell types administered for allograft tolerance induction in both pre-clinical animal models and early human clinical trials. We discuss the current status of various non-invasive methods for tracking regulatory cell products in the context of organ transplantation and implications for enhanced understanding of the therapeutic potential of cell-based therapy in the broad context of control of immune-mediated inflammatory disorders.

High-risk Corneal Transplantation: Recent Developments and Future Possibilities

Human corneal transplantation (keratoplasty) is typically considered to have superior short- and long-term outcomes and lower requirement for immunosuppression compared to solid organ transplants because of the inherent immune privilege and tolerogenic mechanisms associated with the anterior segment of the eye. However, in a substantial proportion of corneal transplants, the rates of acute rejection and/or graft failure are comparable to or greater than those of the commonly transplanted solid organs. Critically, while registry data and observational studies have helped to identify factors that are associated with increased risk of corneal transplant failure, the extent to which these risk factors operate through enhancing immune-mediated rejection is less clear. In this overview, we summarize a range of important recent clinical and basic insights related to high-risk corneal transplantation, the factors associated with graft failure, and the immunological basis of corneal allograft rejection. We highlight critical research areas from which continued progress is likely to drive improvements in the long-term survival of high-risk corneal transplants. These include further development and clinical testing of predictive risk scores and assays; greater use of multicenter clinical trials to optimize immunosuppressive therapy in high-risk recipients and robust clinical translation of novel, mechanistically-targeted immunomodulatory and regenerative therapies that are emerging from basic science laboratories. We also emphasize the relative lack of knowledge regarding transplant outcomes for infection-related corneal diseases that are common in the developing world and the potential for greater cross-pollination and synergy between corneal and solid organ transplant research communities.

Toll-Like Receptor 3 Activator Preconditioning Enhances Modulatory Function of Adipose‑Derived Mesenchymal Stem Cells in a Fully MHC-Mismatched Murine Model of Heterotopic Heart Transplantation

Background

Donor-specific tolerance is the ultimate goal in organ transplantation. Diverse approaches, including the use of mesenchymal stem cells (MSCs), have been investigated to induce graft tolerance. Non-stimulated MSCs showed limited regulatory functions through interaction with multiple immune-regulatory cells, such as regulatory T cells (Tregs). To augment their functions, MSCs have been preconditioned with toll-like receptor (TLR3/4) agonist in autoimmune disease models, but results were conflicting.

Material/Methods

We evaluated the immunomodulatory effects of mouse adipose-derived mesenchymal stem cells (ADSCs) preconditioned with various combinations of TLR3/4 agonist and antagonists, including polyinosinic-polycytidylic acid poly(I:C)-TLR3 agonist, lipopolysaccharide (LPS) -TLR4 agonist, and TAK242-TLR4 antagonist. In vitro and in vivo experiments including mixed lymphocyte reaction, cytokines measurement, Tregs analysis, and a fully mismatched MHC heterotopic heart transplantation in mice (BALB/c to C57BL/6) were conducted.

Results

ADSCs preconditioned with poly(I:C) showed the highest efficiency in inhibiting lymphocyte proliferation, which was correlated with the upregulation of fibrinogen-like protein 2 (FGL2), an effector molecule of Tregs. The mean survival of cardiac allografts was extended from 8 to 12 days by intravenous injection of a single dose of ADSCs preconditioned with TLR3 agonist. The proportion of Tregs in the recipient’s spleen was significantly increased by injecting the poly(I:C)-stimulated ADSCs.

Conclusions

These results show that short-term TLR3 agonist preconditioning enhances the immunomodulatory efficacy of ADSCs, which can induce the generation of Tregs and upregulate the expression of FGL2, thereby improving the outcome of patients receiving organ transplantation.

Iodine-124 Based Dual Positron Emission Tomography and Fluorescent Labeling Reagents for In Vivo Cell Tracking

Understanding the in vivo behavior of experimental therapeutic cells is fundamental to their successful development and clinical translation. Iodine-124 has the longest half-life (4.2 days) among the clinically used positron emitters. Consequently, this isotope offers the longest possible tracking time for directly labeled cells using positron emission tomography (PET). Herein, we have radiosynthesized and evaluated two iodine-124/fluorescein-based dual PET and fluorescent labeling reagents, namely ¹²⁴I-FIT-Mal and ¹²⁴I-FIT-(PhS)₂Mal for cell surface thiol bioconjugation. ¹²⁴I-FIT-(PhS)₂Mal labeled cells significantly more effectively than ¹²⁴I-FIT-Mal. It conjugated to various cell lines in 22%-62% labeling efficiencies with prolonged iodine-124 retention. ¹²⁴I-FIT-(PhS)₂Mal mainly conjugated on the cell membrane, which was confirmed by high-resolution fluorescence imaging. The migration of ¹²⁴I-FIT-(PhS)₂Mal labeled Jurkat cells was visualized in NSG mice with excellent target-to-background contrast using PET/CT over 7 days. These data demonstrate that ¹²⁴I-FIT-(PhS)₂Mal can dynamically track cell migration in vivo using PET/CT over a clinically relevant time frame.

Inducción de tolerancia por vía oral en trasplante de órganos y tejidos. Revisión de la Literatura

Introducción. La tolerancia oral es la supresión de la respuesta inmune a antígenos administrados con anterioridad por vía oral; su inducción tiene el propósito de evitar el uso de fármacos inmunosupresores, los cuales, dado que son poco específicos a antígenos, vuelven al huésped más susceptible de contraer infecciones y desarrollar neoplasias.Objetivos. Realizar una revisión de la literatura sobre los referentes teóricos más relevantes de la inducción de a tolerancia oral en lo que respecta al trasplante de órganos y tejidos para demostrar que el uso de esta alternativa terapéutica es viable en pacientes trasplantados.Materiales y métodos. Se realizó una revisión de la literatura en PubMed, MEDLINE, LILACS y Embase mediante la siguiente estrategia de búsqueda: periodo de publicación: sin límites; idiomas: Inglés y Español; tipo de artículos: estudios caso-control, revisiones sistemáticas y de la literatura; términos de búsqueda: “T-Lymphocytes, Regulatory”, “Autoimmunity”, Immunosuppression”, “Immune system” and “Immune Tolerance”, y sus equivalentes en español.Resultados. La búsqueda inicial arrojó 719 registros, sin embargo solo 99 abordaban la inducción de la tolerancia oral. Una vez los registros duplicados y los artículos sin acceso a texto completo fueron removidos, se incluyeron 72 estudios en la revisión.Conclusiones. La administración oral de antígenos es una opción efectiva para inducir tolerancia inmunológica en pacientes trasplantados (modelos murinos), pues elimina los efectos adversos que conlleva la terapia inmunosupresora actualmente utilizada.

Pancreatic islet cell tumors in adolescents and young adults

BACKGROUND

Pancreatic islet cell tumors are rare in adolescents, and most studies published to date focus on older patients. We utilized a national database to describe the histology and clinical pattern of pancreatic islet cell tumors in adolescent and young adult (AYA) patients, and to compare AYAs to older adults. We hypothesized that AYAs with pancreatic islet cell tumors would have better overall survival.

METHODS

The National Cancer Data Base (NCDB, 1998-2012) was queried for AYA patients (15-39 years) with a pancreatic islet cell tumor diagnosis. Demographics, tumor characteristics, treatment modalities, and outcomes were abstracted and compared to adults (≥40 years).

RESULTS

383 patients (56.4% female, 65% non-Hispanic Whites) were identified, with a median age of 27 (IQR 16-34) years. Islet cell carcinoma was the most common histology. Of patients with known stage of disease, 49% presented with early stage (I or II). Seventy percent of patients underwent surgical resection, including local excision 44%, Whipple procedure 37.5%, or total pancreatectomy 19%. Chemotherapy was utilized in 27% and radiotherapy in 7%. All-cause mortality was 36%. AYA patients underwent more extensive resections (p = 0.001) and had lower mortality rates (p < 0.001), with no differences in tumor stage or use of adjuvant therapies, when compared to adults.

CONCLUSIONS

AYA patients with pancreatic islet cell tumors had comparable utilization of adjuvant therapies but underwent more extensive resections and demonstrated a higher overall survival rate than adult counterparts. Further investigation into approaches to earlier diagnosis and tailoring of multimodality therapy of these neoplasms in the AYA population is needed.

LEVELS OF EVIDENCE

Prognostic Study, Level II - retrospective study.

Long-term tolerance of islet allografts in nonhuman primates induced by apoptotic donor leukocytes

Immune tolerance to allografts has been pursued for decades as an important goal in transplantation. Administration of apoptotic donor splenocytes effectively induces antigen-specific tolerance to allografts in murine studies. Here we show that two peritransplant infusions of apoptotic donor leukocytes under short-term immunotherapy with antagonistic anti-CD40 antibody 2C10R4, rapamycin, soluble tumor necrosis factor receptor and anti-interleukin 6 receptor antibody induce long-term (≥1 year) tolerance to islet allografts in 5 of 5 nonsensitized, MHC class I-disparate, and one MHC class II DRB allele-matched rhesus macaques. Tolerance in our preclinical model is associated with a regulatory network, involving antigen-specific Tr1 cells exhibiting a distinct transcriptome and indirect specificity for matched MHC class II and mismatched class I peptides. Apoptotic donor leukocyte infusions warrant continued investigation as a cellular, nonchimeric and translatable method for inducing antigen-specific tolerance in transplantation.

Injection of donor apoptotic cells induces graft tolerance in mice. Here the authors combine this approach with short immunosuppressive therapy to achieve long-term tolerance to allogeneic islets and restoration of normoglycemia in diabetic nonhuman primates, and delineate cellular and molecular correlates of tolerance induction.

Delivery of Rapamycin Using In Situ Forming Implants Promotes Immunoregulation and Vascularized Composite Allograft Survival

Vascularized composite allotransplantation (VCA), such as hand and face transplantation, is emerging as a potential solution in patients that suffered severe injuries. However, adverse effects of chronic high-dose immunosuppression regimens strongly limit the access to these procedures. In this study, we developed an in situ forming implant (ISFI) loaded with rapamycin to promote VCA acceptance. We hypothesized that the sustained delivery of low-dose rapamycin in proximity to the graft may promote graft survival and induce an immunoregulatory microenvironment, boosting the expansion of T regulatory cells (T_reg). In vitro and in vivo analysis of rapamycin-loaded ISFI (Rapa-ISFI) showed sustained drug release with subtherapeutic systemic levels and persistent tissue levels. A single injection of Rapa-ISFI in the groin on the same side as a transplanted limb significantly prolonged VCA survival. Moreover, treatment with Rapa-ISFI increased the levels of multilineage mixed chimerism and the frequency of T_reg both in the circulation and VCA-skin. Our study shows that Rapa-ISFI therapy represents a promising approach for minimizing immunosuppression, decreasing toxicity and increasing patient compliance. Importantly, the use of such a delivery system may favor the reprogramming of allogeneic responses towards a regulatory function in VCA and, potentially, in other transplants and inflammatory conditions.

The Evolving Roles of Macrophages in Organ Transplantation

Organ transplantation is a life-saving strategy for patients with end-stage organ failure. Over the past few decades, organ transplantation has achieved an excellent success in short-term survival but only a marginal improvement in long-term graft outcomes. The pathophysiology of graft loss is multifactorial and remains incompletely defined. However, emerging evidence suggests macrophages as crucial mediators of acute and chronic allograft immunopathology. In this process, macrophage-mediated mobilization of first-line defenses, particularly phagocytosis and the release of acute inflammatory mediators, is important, but macrophages also launch adaptive alloimmune reactions against grafts through antigen processing and presentation, as well as providing costimulation. Additionally, crosstalk with other immune cells and graft endothelial cells causes tissue damage or fibrosis in transplanted organs, contributing to graft loss or tolerance resistance. However, some macrophages function as regulatory cells that are capable of suppressing allogeneic T cells, inhibiting DC maturation, inducing the differentiation of Tregs, and subsequently promoting transplant tolerance. This functional diversity of macrophages in organ transplantation is consistent with their heterogeneity. Although our knowledge of the detrimental or beneficial effects of macrophages on transplants has exponentially increased, the exact mechanisms controlling macrophage functions are not yet completely understood. Here, we review recent advances in our understanding of the multifaceted nature of macrophages, focusing on their evolving roles in organ transplantation and the mechanisms involved in their activation and function in allograft transplantation. We also discuss potential therapeutic options and opportunities to target macrophage to improve the outcomes of transplant recipients.

Myeloid-Derived Suppressor Cells and Their Potential Application in Transplantation

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immunosuppressive cells of the myeloid lineage upregulated by mediators of inflammation, such as IL-2, granulocyte colony-stimulating factor, and S100A8/A9. These cells have been studied extensively by tumor biologists. Because of their robust immunosuppressive potential, MDSCs have stirred recent interest among transplant immunologists as well. MDSCs inhibit T-cell responses through, among other mechanisms, the activity of arginase-1 and inducible nitric oxide synthase, and the expansion of T regulatory cells. In the context of transplantation, MDSCs have been studied in several animal models, and to a lesser degree in humans. Here, we will review the immunosuppressive qualities of this important cell type and discuss the relevant studies of MDSCs in transplantation. It may be possible to exploit the immunosuppressive capacity of MDSCs for the benefit of transplant patients.

Relationship of Transforming Growth Factor-βl and Arginase-1 Levels with Long-term Survival after Kidney Transplantation

In this study, we compared the serum levels of transforming growth factor-pi (TGF-β1), interleukin-10 (IL-10), and arginase-1 in long-term survival kidney transplant recipients (LTSKTRs) with those in short-term survival kidney transplant recipients (STSKTRs). We then evaluated the relationship between these levels and graft function. Blood samples were collected from 50 adult LTSKTRs and 20 STSKTRs (graft survival approximately 1-3 years post-transplantation). All patients had stable kidney function. The samples were collected at our institution during the patients' follow-up examinations between March 2017 and September 2017. The plasma levels of TGF-β1, IL-10, and arginase-1 were analyzed using enzyme-linked immunosorbent assays (ELIS A). The levels of TGF-β1 and arginase-1 were significantly higher in the LTSKTRs than in the STSKTRs. The time elapsed since transplantation was positively correlated with the levels of TGF-β1 and arginase-1 in the LTSKTRs. The estimated glomerular filtration rate was positively correlated with the TGF-β1 level, and the serum creatinine level was negatively correlated with the TGF-β1 level. Higher serum levels of TGF-pi and arginase-1 were found in LTSKTRs than in STSKTRs, and we found that TGF-β1 was positively correlated with long-term graft survival and function. Additionally, TGF-β1 and arginase-1 levels were positively correlated with the time elapsed since transplantation. On the basis of these findings, TGF-β1 and arginase-1 may play important roles in determining long-term graft survival. Thus, we propose that TGF-pi and arginase-1 may potentially be used as predictive markers for evaluating long-term graft survival.

Cell Membrane Bioconjugation and Membrane-Derived Nanomaterials for Immunotherapy

Cell membrane engineering, including live cell membrane bioconjugation and cell membrane-derived nanomaterials is a highly promising strategy to modulate immune responses for treating diseases. Many cell membrane engineering methods have potential for translation for human clinical use in the near future. In this Topical Review, we summarize the cell membrane conjugation strategies that have been investigated for cancer immunotherapy, the prevention of immune rejection to donor cells and tissues, and the induction of antigen-specific tolerance in autoimmune diseases. Additionally, cell membrane-derived or membrane-coated nanomaterials are an emerging class of nanomaterials that is attracting significant attention in the field of nanomedicine. Some of these nanomaterials have been employed to elicit immune responses against cancer, toxins, and bacteria, although their application in establishing immune tolerance has not been explored. In addition to discussing potential problems, we provide our perspectives for promising future directions.

Mechanisms and biomarkers of immune quiescence in kidney transplantation

This review discusses the current understanding of biomarkers of immune quiescence based on reviews of published literature in kidney transplant operational tolerance and mechanistic studies based on a better characterization of the stable, well-functioning renal allograft.

Immunomodulatory plasticity of mesenchymal stem cells: a potential key to successful solid organ transplantation

Organ transplantation remains to be a treatment of choice for patients suffering from irreversible organ failure. Immunosuppressive (IS) drugs employed to maintain the allograft have shown excellent short-term graft survival, but, their long-term use could contribute to immunological and non-immunological risk factors, resulting in graft dysfunctionalities. Upcoming IS regimes have highlighted the use of cell-based therapies, which can eliminate the risk of drug-borne toxicities while maintaining efficacy of the treatment. Mesenchymal stem cells (MSCs) have been considered as an invaluable cell type, owing to their unique immunomodulatory properties, which makes them desirable for application in transplant settings, where hyper-activation of the immune system is evident. The immunoregulatory potential of MSCs holds true for preclinical studies while achieving it in clinical studies continues to be a challenge. Understanding the biological factors responsible for subdued responses of MSCs in vivo would allow uninhibited use of this therapy for countless conditions. In this review, we summarize the variations in the preclinical and clinical studies utilizing MSCs, discuss the factors which might be responsible for variability in outcome and propose the advancements likely to occur in future for using this as a "boutique/personalised therapy" for patient care.

Increased degradation of ATP is driven by memory regulatory T cells in kidney transplantation tolerance

Regulatory T cells were recently proposed as the central actor in operational tolerance after renal transplantation. Tolerant patients harbor increased FoxP3hi memory Treg frequency and increased demethylation in the Foxp3 Treg-specific demethylated region when compared to stable kidney recipients and exhibit greater memory Treg suppressive capacities and higher expression of the ectonucleotidase CD39. However, in this particular and unique situation the mechanisms of action of Tregs were not identified. Thus, we analyzed the ability of memory Tregs to degrade extracellular ATP in tolerant patients, healthy volunteers, and patients with stable graft function under immunosuppression and determined the role of immunosuppressive drugs on this process. The conserved proportion of memory Tregs leads to the establishment of a pro-tolerogenic balance in operationally tolerant patients. Memory Tregs in tolerant patients display normal capacity to degrade extracellular ATP/ADP. In contrast, memory Tregs from patients with stable graft function do not have this ability. Finally, in vitro, immunosuppressive drugs may favor the lower proportion of memory Tregs in stable patients, but they have no effect on CD39-dependent ATP degradation and do not explain memory Treg lack of extracellular ATP/ADP degradation ability. Thus, intrinsic active regulatory mechanisms may act long after immunosuppressive drug arrest in operationally tolerant patients and may contribute to kidney allograft tolerance via the maintenance of CD39 Treg function.

Adipose-derived cellular therapies in solid organ and vascularized-composite allotransplantation

PURPOSE OF REVIEW

Controlling acute allograft rejection following vascularized composite allotransplantation requires strict adherence to courses of systemic immunosuppression. Discovering new methods to modulate the alloreactive immune response is essential for widespread application of vascularized composite allotransplantation. Here, we discuss how adipose-derived cellular therapies represent novel treatment options for immune modulation and tolerance induction in vascularized composite allotransplantation.

RECENT FINDINGS

Adipose-derived mesenchymal stromal cells are cultured from autologous or allogeneic adipose tissue and possess immunomodulatory qualities capable of prolonging allograft survival in animal models of vascularized composite allotransplantation. Similar immunosuppressive and immunomodulatory effects have been observed with noncultured adipose stromal-vascular-fraction-derived therapies, albeit publication of in-vivo stromal vascular fraction cell modulation in transplantation models is lacking. However, both stromal vascular fraction and adipose derived mesenchymal stem cell therapies have the potential to effectively modulate acute allograft rejection via recruitment and induction of regulatory immune cells.

SUMMARY

To date, most reports focus on adipose derived mesenchymal stem cells for immune modulation in transplantation despite their phenotypic plasticity and reliance upon culture expansion. Along with the capacity for immune modulation, the supplemental wound healing and vasculogenic properties of stromal vascular fraction, which are not shared by adipose derived mesenchymal stem cells, hint at the profound therapeutic impact stromal vascular fraction-derived treatments could have on controlling acute allograft rejection and tolerance induction in vascularized composite allotransplantation. Ongoing projects in the next few years will help design the best applications of these well tolerated and effective treatments that should reduce the risk/benefit ratio and allow more patients access to vascularized composite allotransplantation therapy.

Murine models of transplantation tolerance through mixed chimerism: advances and roadblocks

Organ transplantation is the treatment of choice for patients with end-stage organ failure, but chronic immunosuppression is taking its toll in terms of morbidity and poor efficacy in preventing late graft loss. Therefore, a drug-free state would be desirable where the recipient permanently accepts a donor organ while remaining otherwise fully immunologically competent. Mouse studies unveiled mixed chimerism as an effective approach to induce such donor-specific tolerance deliberately and laid the foundation for a series of clinical pilot trials. Nevertheless, its widespread clinical implementation is currently prevented by cytotoxic conditioning and limited efficacy. Therefore, the use of mouse studies remains an indispensable tool for the development of novel concepts with potential for translation and for the delineation of underlying tolerance mechanisms. Recent innovations developed in mice include the use of pro-apoptotic drugs or regulatory T cell (Treg ) transfer for promoting bone marrow engraftment in the absence of myelosuppression and new insight gained in the role of innate immunity and the interplay between deletion and regulation in maintaining tolerance in chimeras. Here, we review these and other recent advances in murine studies inducing transplantation tolerance through mixed chimerism and discuss both the advances and roadblocks of this approach.

Expanding Diversity and Common Goal of Regulatory T and B Cells. II: In Allergy, Malignancy, and Transplantation

Regulation of immune response was found to play an important role in the course of many diseases such as autoimmune diseases, allergy, malignancy, organ transplantation. The studies on immune regulation focus on the role of regulatory cells (Tregs, Bregs, regulatory myeloid cells) in these disorders. The number and function of Tregs may serve as a marker of disease activity. As in allergy, the depletion of Tregs is observed and the results of allergen-specific immunotherapy could be measured by an increase in the population of IL-10⁺ regulatory cells. On the basis of the knowledge of anti-cancer immune response regulation, new directions in therapy of tumors are introduced. As the proportion of regulatory cells is increased in the course of neoplasm, the therapeutic action is directed at their inhibition. The depletion of Tregs may be also achieved by an anti-check-point blockade, anti-CD25 agents, and inhibition of regulatory cell recruitment to the tumor site by affecting chemokine pathways. However, the possible favorable role of Tregs in cancer development is considered and the plasticity of immune regulation should be taken into account. The new promising direction of the treatment based on regulatory cells is the prevention of transplant rejection. A different way of production and implementation of classic Tregs as well as other cell types such as double-negative cells, Bregs, CD4⁺ Tr1 cells are tested in ongoing trials. On the basis of the results of current studies, we could show in this review the significance of therapies based on regulatory cells in different disorders.

Targeting the Monocyte-Macrophage Lineage in Solid Organ Transplantation

There is an unmet clinical need for immunotherapeutic strategies that specifically target the active immune cells participating in the process of rejection after solid organ transplantation. The monocyte–macrophage cell lineage is increasingly recognized as a major player in acute and chronic allograft immunopathology. The dominant presence of cells of this lineage in rejecting allograft tissue is associated with worse graft function and survival. Monocytes and macrophages contribute to alloimmunity via diverse pathways: antigen processing and presentation, costimulation, pro-inflammatory cytokine production, and tissue repair. Cross talk with other recipient immune competent cells and donor endothelial cells leads to amplification of inflammation and a cytolytic response in the graft. Surprisingly, little is known about therapeutic manipulation of the function of cells of the monocyte–macrophage lineage in transplantation by immunosuppressive agents. Although not primarily designed to target monocyte–macrophage lineage cells, multiple categories of currently prescribed immunosuppressive drugs, such as mycophenolate mofetil, mammalian target of rapamycin inhibitors, and calcineurin inhibitors, do have limited inhibitory effects. These effects include diminishing the degree of cytokine production, thereby blocking costimulation and inhibiting the migration of monocytes to the site of rejection. Outside the field of transplantation, some clinical studies have shown that the monoclonal antibodies canakinumab, tocilizumab, and infliximab are effective in inhibiting monocyte functions. Indirect effects have also been shown for simvastatin, a lipid lowering drug, and bromodomain and extra-terminal motif inhibitors that reduce the cytokine production by monocytes–macrophages in patients with diabetes mellitus and rheumatoid arthritis. To date, detailed knowledge concerning the origin, the developmental requirements, and functions of diverse specialized monocyte–macrophage subsets justifies research for therapeutic manipulation. Here, we will discuss the effects of currently prescribed immunosuppressive drugs on monocyte/macrophage features and the future challenges.

Transplantology: Challenges for Today

Clinical transplantology in Poland had its 50th anniversary this year. With the early and long results comparable to the best achieved in the world leading centers, we face old and completely new challenges for this medical speciality. Main and growing challenge is insufficient number of available organs. With less than 15 donors/mln population/year Poland stay in the lower row of European countries in this measurement of transplant activity. Donation system is not efficient enough and we lose a big number of potential donors still. Living donation (with the exception for the fragments of the liver) remains low despite of different initiatives made so far on the national and local levels. Donation after cardiac death is possible from the point of Polish juridical regulations, but since last 3 years had not showed real impact on country donation rates (only three procedures done). Methods of tissue typing remain slow and cause relatively long times of cold ischemia for kidney programs. Second main challenge is chronic rejection causing loss of organs in the long-term follow-up and no efficient treatment employed. The emerging possibility of tolerance induction despite of plenty of new protocols proposition in the publications does not show up a clinical everyday practice in work. The same is with xenotransplantation promises; even we were informed recently that till 2030 such genetically modified porcine organs will be available. The next challenge is production of organs and tissues from own recipients cells installed on the different scaffolds or 3D printed. Other challenge is the personnel working in this field. We observe like in the other European countries lack of new candidates for work in this field together with serious problems of nursing staff, being a catastrophic perspective in country medical service in general, not only in transplant centers. The last but not least challenge is financial side of transplant programs.

Immunological characteristics of renal transplant tolerance in humans

Establishing allograft tolerance is a highly desirable therapeutic goal in kidney transplantation, from which recipients would greatly benefit by withdrawing or minimizing immunosuppression. Identifying biomarkers in predicting tolerance or early diagnosing rejection is essential to direct personalized management. Recent findings have revealed that multiple populations of immune cells have involved in promoting long-term graft function or inducing rejection in renal transplant recipients. Thus, roles of immune cells add another level to predict the renal tolerant state; tailoring their functional and/or phenotypic characteristics would provide insights into mechanism involved in transplant tolerance that may aid in designing new therapies. Here, we review these findings and discuss the current understanding immunological characteristics of renal transplant tolerance in humans, and their potential clinical translation to immune tolerance biomarkers.