New frontiers in immunosuppression

The search for peripheral tolerance in lung transplantation

PURPOSE OF REVIEW

Median survival after lung transplantation is 5.7 years, which lags behind other solid organ transplants, such as heart, liver, and kidney. The major barrier to long-term survival in lung transplant recipients is chronic lung allograft dysfunction (CLAD). This review discusses the challenge of CLAD as a barrier to tolerance and identifies key areas in the field that require further development.

RECENT FINDINGS

CLAD is a heterogenous disease in its kinetics of onset and severity and remains a clinical diagnosis of exclusion, based on a decline in allograft function. While acute cellular rejection and antibody-mediated rejection are major risk-factors for CLAD, other barriers to long-term allograft acceptance are aspiration and primary graft dysfunction. However infections, particularly respiratory viral infections and Cytomegalovirus (CMV) remain the most significant risks for CLAD. Additionally, the lung transplant field is limited by a lack of molecular diagnostic assays for CLAD. Further, new targets are needed for precision immunosuppression, and more studies are needed to develop novel interventions to extend allograft acceptance.

SUMMARY

This review discusses new lines of study to address important unmet needs necessary to extend lung allograft acceptance. Other studies, such as tandem lung transplant and bone marrow transplant in select patients with primary immunodeficiency may provide additional lessons on how to potentially establish tolerance. However, tolerance in lung transplant is extremely rare, and further studies are needed to pursue this ultimate goal.

The role of induction therapy in lung transplantation

Induction immunosuppression in solid organ transplantation involves a short course of potent immunosuppression in the perioperative period, with the goal of preventing early acute rejection and delaying initiation or reducing the dose of calcineurin inhibitors to minimize kidney injury. The use of induction immunosuppression in lung transplantation has increased over time, with over 80% of adult lung transplant recipients receiving some form of induction therapy. Currently, more than 70% of lung transplant recipients receive induction with an interleukin-2 receptor antagonist, and basiliximab is the most used agent. Despite this now common practice, the evidence to support and guide induction immunosuppression following lung transplantation is limited, making the use of induction somewhat controversial. Here, we review the available literature addressing the use of induction immunosuppression in lung transplant recipients.

The Association Between Cytomegalovirus Infection and Kidney Damage in the Liver Transplant Setting

INTRODUCTION

The development of chronic kidney disease (CKD) is a common and significant complication, contributing to morbidity after liver transplantation (LT). Cytomegalovirus (CMV) infection is common in the overall population, and relevant reinfection after LT may occur. CMV-associated kidney damage has been discussed, but the clinical significance on CKD development after LT remains unclear.

METHODS

A total of 745 patients who underwent LT between 2006 and 2017 were included in this retrospective analysis. Clinical data, as well as laboratory parameters, were analyzed. Univariate and multivariate analysis were performed.

RESULTS

The univariate analysis revealed significantly impaired estimated glomerular filtration rates (eGFRs) in patients with histories of CMV infection (81.4 (8-137) mL/min vs. 90.0 (5-147) mL/min; p = 0.004). This effect was confirmed in the multivariate analysis. Post-LT, eGFR was impaired in patients with CMV (re)infection at 6, 12, 36, and 60 months, 10 years, and 15 years after LT. Immunosuppressive levels were comparable between groups. Overall survival was negatively affected by CMV infection (p = 0.001).

DISCUSSION

A clinically significant detrimental impact of CMV infection on renal function was observed, that could individualize clinical risk evaluation prior and after LT further. However, the pathophysiological mechanisms behind this observation are not yet understood.

Alternative Therapies in Transplantology as a Promising Perspective in Medicine

Despite continuous and rapid progress in the transplantation of cells, tissues, and organs, many patients die before receiving them. This is because of an insufficient number of donors, which leads to a significant disproportion between the need for donors and their availability. This review aims to present the possibilities offered by alternative therapies. We use the term "functional transplantology" to describe such alternative methods of transplantation that could help change the current state of transplantation medicine. Its purpose is not to replace a defective or removed organ with another but to replace its functions using complementary biological, mechanical, or biomechanical structures or devices. Implementation of many innovative solutions shown in the work for clinical applications is already a fact. In the case of others, it should be considered a future vision. We hope that the role of a defective or damaged tissue or a group of tissues will be taken over by different structures that are functionally complementary with the organ being substituted. Undoubtedly, developing the described methods based on functional transplantology will change the face of transplantation medicine. Thus, we show current trends and new directions of thinking and actions in transplantation medicine that combine technology and transplantology. The review considers the latest technologies, including 3D bioprinting, nanotechnology, cell encapsulation, and organoids. We discuss not only the advantages of new approaches but also the limitations and challenges that must be overcome to achieve significant progress in transplantation. That is the only option to provide a safe and efficient way of improving the quality of life of many patients.

The First Reciprocal Activities of Chiral Peptide Pharmaceuticals: Thymogen and Thymodepressin, as Examples

Peptides show high promise in the targeting and intracellular delivery of next-generation biotherapeutics. The main limitation is peptides' susceptibility to proteolysis in biological systems. Numerous strategies have been developed to overcome this challenge by chemically enhancing the resistance to proteolysis. In nature, amino acids, except glycine, are found in L- and D-enantiomers. The change from one form to the other will change the primary structure of polypeptides and proteins and may affect their function and biological activity. Given the inherent chiral nature of biological systems and their high enantiomeric selectivity, there is rising interest in manipulating the chirality of polypeptides to enhance their biomolecular interactions. In this review, we discuss the first examples of up-and-down homeostasis regulation by two enantiomeric drugs: immunostimulant Thymogen (L-Glu-L-Trp) and immunosuppressor Thymodepressin (D-Glu(D-Trp)). This study shows the perspective of exploring chirality to remove the chiral wall between L- and D-biomolecules. The selected clinical result will be discussed.

Detrimental impact of immunosuppressive burden on clinical course in patients with Cytomegalovirus infection after liver transplantation

INTRODUCTION

Cytomegalovirus (CMV)-infection and reactivation remain a relevant complication after liver transplantation (LT). The recipient and donor serum CMV-IgG-status has been established for risk stratification when choosing various pharmaceutical regimens for CMV-prophylaxis in the last two decades. However, factors influencing course of CMV-infection in LT remain largely unknown. In this study, the impact of immunosuppressive regimen was examined in a large cohort of patients.

METHODS

All patients that underwent primary LT between 2006 and 2018 at the Charité-Universitaetsmedizin, Berlin, were included. Clinical course as well as histological and laboratory findings of patients were analyzed our prospectively maintained database. Univariate and multivariate regression analysis for impact of variables on CMV-occurrence was conducted, and survival was examined using Kaplan-Meier analysis.

RESULTS

Overall, 867 patients were included in the final analysis. CMV-infection was diagnosed in 325 (37.5%) patients after transplantation. Significantly improved overall survival was observed in these patients (Log rank = 0.03). As shown by correlation and regression tree classification and regression tree analysis, the recipient/donor CMV-IgG-status with either positivity had the largest influence on CMV-occurrence. Analysis of immunosuppressive burden did not reveal statistical impact on CMV-infection, but statistically significant inverse correlation of cumulative tacrolimus trough levels and survival was found (Log rank < .001). Multivariate analysis confirmed these findings (p = .02).

DISCUSSION

CMV-infection remains of clinical importance after LT. Undergone CMV-infection of either recipient or donor requires prophylactic treatment. Additionally, we found a highly significant, dosage-dependent impact of immunosuppression (IS) on long-term outcomes for these patients, underlying the importance of minimization of IS in liver transplant recipients.

Classic and Current Opinions in Human Organ and Tissue Transplantation

Graft tolerance is a pathophysiological condition heavily reliant on the dynamic interaction of the innate and adaptive immune systems. Genetic polymorphism determines immune responses to tissue/organ transplantation, and intricate humoral and cell-mediated mechanisms control these responses. In transplantation, the clinician's goal is to achieve a delicate equilibrium between the allogeneic immune response, undesired effects of the immunosuppressive drugs, and the existing morbidities that are potentially life-threatening. Transplant immunopathology involves sensitization, effector, and apoptosis phases which recruit and engages immunological cells like natural killer cells, lymphocytes, neutrophils, and monocytes. Similarly, these cells are involved in the transfer of normal or genetically engineered T cells. Advances in tissue transplantation would involve a profound knowledge of the molecular mechanisms that underpin the respective immunopathology involved and the design of precision medicines that are safe and effective.

MTOR Signaling and Metabolism in Early T Cell Development

The mechanistic target of rapamycin (mTOR) controls cell fate and responses via its functions in regulating metabolism. Its role in controlling immunity was unraveled by early studies on the immunosuppressive properties of rapamycin. Recent studies have provided insights on how metabolic reprogramming and mTOR signaling impact peripheral T cell activation and fate. The contribution of mTOR and metabolism during early T-cell development in the thymus is also emerging and is the subject of this review. Two major T lineages with distinct immune functions and peripheral homing organs diverge during early thymic development; the αβ- and γδ-T cells, which are defined by their respective TCR subunits. Thymic T-regulatory cells, which have immunosuppressive functions, also develop in the thymus from positively selected αβ-T cells. Here, we review recent findings on how the two mTOR protein complexes, mTORC1 and mTORC2, and the signaling molecules involved in the mTOR pathway are involved in thymocyte differentiation. We discuss emerging views on how metabolic remodeling impacts early T cell development and how this can be mediated via mTOR signaling.

Effect of Mycophenolate Mofetil Therapy on Recurrence of Hepatocellular Carcinoma after Liver Transplantation: A Population-Based Cohort Study

Hepatocellular carcinoma (HCC) recurrence after liver transplantation is associated with immunosuppressants. However, the appropriate immunosuppressant for HCC recipients is still debated. Data for this nationwide population-based cohort study were extracted from the National Health Insurance Research Database of Taiwan. A total of 1250 liver transplant recipients (LTRs) with HCC were included. We analyzed the risk factors for post-transplant HCC recurrences. Cumulative defined daily dose (cDDD) represented the exposure duration and was calculated as the amount of dispensed defined daily dose (DDD) of mycophenolate mofetil (MMF). The dosage effects of MMF on HCC recurrence and liver graft complication rates were investigated. A total of 155 LTRs, having experienced post-transplant HCC recurrence, exhibited low survival probability at 1-, 3-, 5-, and 10-year observations. Our results demonstrated increased HCC recurrence rate after liver transplantation (p = 0.0316) following MMF administration; however, no significant increase was demonstrated following cyclosporine, tacrolimus, or sirolimus administration. Notably, our data demonstrated significantly increased HCC recurrence rate following MMF administration with cDDD > 0.4893 compared with cDDD ≤ 0.4893 or no administration of MMF (p < 0.0001). MMF administration significantly increases the risk of HCC recurrence. Moreover, a MMF-minimizing strategy (cDDD ≤ 0.4893) is recommended for recurrence-free survival.

FAS-670A＞G gene polymorphism and the risk of allograft rejection after organ transplantation: a systematic review and meta-analysis

The association between the risk of allograft rejection after organ transplantation and FAS gene polymorphism has been evaluated previously. However, inconsistent results have been reported. Hence, we conducted the most up-to-date meta-analysis to evaluate this association. All eligible studies reporting the association between FAS-670A＞G polymorphism and the risk of allograft rejection published up to December 2019 were extracted using a comprehensive systematic database search in the Web of Science, Scopus, and PubMed. The pooled odds ratios (OR) and corresponding 95% confidence intervals (CI) were calculated to determine the association strength. This meta-analysis included six case-control studies with 277 patients who experienced allograft rejection and 1,001 patients who did not experience allograft rejection (controls) after organ transplantation. The overall results showed no significant association between FAS-670A＞G polymorphism and the risk of allograft rejection in five genetic models (dominant model: OR=0.81, 95% CI=0.58‒1.12; recessive model: OR=0.10, 95% CI=0.80‒1.53; allelic model: OR=0.96, 95% CI=0.79‒1.18; GG vs. AA: OR=0.92, 95% CI=0.62‒1.36; and AG vs. AA: OR=0.75, 95% CI=0.52‒1.08). Moreover, subgroup analysis according to ethnicity and age did not reveal statistically significant results. Our findings suggest that FAS-670A＞G polymorphism is not associated with the risk of allograft rejection after organ transplantation.

Drug Interactions between Antimicrobial and Immunosuppressive Agents in Solid Organ Transplant Recipients

The number of allogeneic solid organ and bone marrow transplants is increasing all over the world. To prevent transplant rejection and treat acute rejection of transplant, immunosuppressant drugs are used. The outcomes of solid organ transplants have dramatically improved over last 30 years, due to availability of multiple immunosuppressive agents, with varied mechanisms of action. The use of intense immunosuppression makes the individual having undergone solid organ transplant at the risk of several serious infections, which may prove fatal. To prevent and treat these infections (when they occur), patients are often given antimicrobial prophylaxis and therapy. The use of antimicrobials can interfere with the metabolism of the immunosuppressants, and may put the patient at risk of developing severe adverse effects due to unwanted increase or decrease in the serum levels of immunosuppressive agents. Knowledge of these interactions is essential for successful management of solid organ transplant patients. We therefore decided to review the literature and present the interactions that commonly occur between these two life-saving groups of drugs.

How to cite this article: Bhagat V, Pandit RA, Ambapurkar S, Sengar M, Kulkarni AP. Drug Interactions between Antimicrobial and Immunosuppressive Agents in Solid Organ Transplant Recipients. Indian J Crit Care Med 2021;25(1):67–76.

Allogeneic hematopoietic stem cell transplantation in a prior lung transplant recipient

Hematological diseases after solid organ transplant (SOT) are an emerging issue as the number of long-term SOT survivors increases. Expertise in managing patients requiring allogeneic hematopoietic stem cell transplantation (HSCT) after SOT from independent donors is needed; however, clinical reports of HSCT after SOT are limited, and the feasibility and risk are not well understood. In particular, HSCT in prior lung transplant recipients is thought to be complicated as the lung is immunologically distinct and is constantly exposed to the surrounding environment. Herein, we describe a case of successful HSCT in a patient with myelodysplastic syndromes who had previously received a lung transplant from a deceased donor for bronchiolitis obliterans syndrome. Reports about cases of HSCT after lung transplant are quite rare; thus, we discuss the mechanisms of immune tolerance through the clinical course of our case. This case suggests that HSCT after SOT can be considered a therapeutic option in cases where the transplanted organ is functionally retained and the hematological disease is in remission.

Cyclosporine A promotes the therapeutic effect of mesenchymal stem cells on transplantation reaction

The successful application of mesenchymal stem cells (MSCs) remains a major challenge in stem cell therapy. Currently, several in vitro studies have indicated potentially beneficial interactions of MSCs with immunosuppressive drugs. These interactions can be even more complex in vivo, and it is in this setting that we investigate the effect of MSCs in combination with Cyclosporine A (CsA) on transplantation reaction and allogeneic cell survival. Using an in vivo mouse model, we found that CsA significantly promoted the survival of MSCs in various organs and tissues of the recipients. In addition, compared to treatment with CsA or MSCs alone, the survival of transplanted allogeneic cells was significantly improved after the combined application of MSCs with CsA. We further observed that the combinatory treatment suppressed immune response to the alloantigen challenge and modulated the immune balance by harnessing proinflammatory CD4+T-bet+ and CD4+RORγt+ cell subsets. These changes were accompanied by a significant decrease in IL-17 production along with an elevated level of IL-10. Co-cultivation of purified naive CD4+ cells with peritoneal macrophages isolated from mice treated with MSCs and CsA revealed that MSC-educated macrophages play an important role in the immunomodulatory effect observed on distinct T-cell subpopulations. Taken together, our findings suggest that CsA promotes MSC survival in vivo and that the therapeutic efficacy of the combination of MSCs with CsA is superior to each monotherapy. This combinatory treatment thus represents a promising approach to reducing immunosuppressant dosage while maintaining or even improving the outcome of therapy.

Cyclosporine-A-Based Immunosuppressive Therapy-Induced Neurotoxicity: A Case Report

Cyclosporine-A (CsA) and mycophenolate mofetil are immunosuppressive drugs used for the prevention of transplant rejection. Various clinical studies have been performed on different forms of CsA neurotoxicity, including tremor, paresthesia, confusion, ataxia, neuralgia, hemiplegia, occipital seizures, and transient cortical blindness. Mycophenolate is associated with several neurological side effects including headache, insomnia, dizziness, depression, confusion, hypertonia, and paresthesia. A 31-year-old male with a history of kidney transplantation was treated with CsA and mycophenolate mofetil, for 18 years. He had been referred to the emergency department with complaints of generalized tonic-clonic seizure for 1 minute and 15 minutes of the post-ictal phase. Almost all laboratory tests including cerebrospinal fluid analysis were within normal limits. Brain MRI findings were compatible with CsA-based neurotoxicity. The patient's symptoms and MRI findings improved on decreasing CsA to the minimum dose. CsA neurotoxicity is more common in intravenous therapy, early days of CsA administration, P450 inhibitors administration, and following liver transplantation. MRI findings in CsA neurotoxicity include signal changes in the cerebral cortex and juxtacortical white matter of the occipital lobes, temporal, parietal, and frontal lobes. Every year, many solid organ transplantations are performed. Many of these patients received CsA-based regimens for the prevention of rejection. Therefore, it is necessary to consider CsA neurotoxicity in suspected patients.

Immune cell diversity contributes to the pathogenesis of myocarditis

Myocarditis (MCD) is a type of inflammatory disease in which inflammatory cells infiltrate the myocardium, leading to cardiac dysfunction, myocardial necrosis, and fibrosis. Although it has been reported that MCD is mediated by T cells, the immune system is complex and includes many types of immune cells that interact with one another. Through investigations of the inflammatory responses in MCD including myocardial necrosis, fibrosis, and arrhythmia, we have gained further insight into the pathogenesis of MCD. This article aims to discuss the diversity and the roles of immune cells involved in the pathogenesis of MCD. Moreover, immunotherapy for the treatment of MCD remains controversial, and further investigation is required to identify accurate immunotherapies for special cell types.

Brief Overview of Lung, Heart, and Heart-Lung Transplantation

Lung transplantation, heart transplantation, and heart-lung transplantation are life-saving treatment options for patients with lung and/or cardiac failure. Evolution in these therapies over the past several decades has led to better outcomes with application to more patients. The complexity and severity of illness of patients in the pretransplant phase has steadily increased, making posttransplant intensive care unit management more difficult. Despite these factors and the pervasive complications of immunosuppressive therapy, outcomes continue to improve.