Transplant immunology for non-immunologist

Immunopathology of lung transplantation: from infection to rejection and vice versa

Lung transplantation offers a lifesaving option for patients with end-stage lung disease, but it is marred by a high risk of post-transplant infections, particularly involving multidrug-resistant bacteria, Cytomegalovirus, and fungal pathogens. This elevated infection rate, the highest among solid organ transplants, poses a significant challenge for clinicians, particularly within the first year post-transplantation, where infections are the leading cause of mortality. The direct exposure of lung allografts to the external environment exacerbates this vulnerability leading to constant immune stimulation and consequently to an elevated risk of triggering alloimmune responses to the lung allograft. The necessity of prolonged immunosuppression to prevent allograft rejection further complicates patient management by increasing susceptibility to infections and neoplasms, and complicating the differentiation between rejection and infection, which require diametrically opposed management strategies. This review explores the intricate balance between preventing allograft rejection and managing the heightened infection risk in lung transplant recipients.

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

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

Challenges of Cellular Therapy During the COVID-19 Pandemic

Currently, coronavirus disease 2019 (COVID-19) has spread worldwide and continues to rise. There remains a significant unmet need for patients with hematological malignancies requiring specialized procedures and treatments, like cellular therapy to treat or cure their disease. For instance, chimeric antigen receptor T (CAR-T) cell therapy is approved for relapsed/refractory (after two or more lines of therapy) diffuse large B cell lymphoma and B cell acute lymphoblastic leukemia that is refractory or in the second relapse in patients younger than 25 years of age. Similarly, hematopoietic stem cell transplantation (HSCT) can be a lifesaving procedure for many patients, such as those with acute myeloid leukemia with high-risk cytogenetics. Unfortunately, the COVID-19 pandemic has thrust upon the hematologists and transplant specialists' unique challenges with the implementation and management of cellular therapy. One of the significant concerns regarding this immunocompromised patient population is the significant risk of acquiring SARS-CoV-2 infection due to its highly contagious nature. Experts have recommended that if medically indicated, especially in high-risk disease (where chemotherapy is unlikely to work), these lifesaving procedures should not be delayed even during the COVID-19 pandemic. However, proceeding with CAR-T cell therapy and HSCT during the pandemic is a considerable task and requires dedication from the transplant team and buy-in from the patients and their family or support system. Open conversations should be held with the patients about the risks involved in undergoing cellular therapies during current times and the associated future uncertainties.

Effect of donor-specific antibodies and panel reactive antibodies in living donor liver transplant recipients

Purpose

Preformed circulating donor-specific antibodies (DSAs) immunologically challenge vascular endothelium and the bile duct. However, the liver is an immune-tolerant organ and can avoid immunological challenges. This study was undertaken to analyze the effects of DSAs after adult living donor liver transplantation (LDLT).

Methods

We retrospectively reviewed 219 LDLT patients' records treated at our center.

Results

Of the 219 patients, 32 (14.6%) were DSA (+) and 187 (85.4%) were DSA (-). Class I DSAs were present in 18 patients, class II in seven patients, and both in seven patients. Seven patients (3.2%) showed DSA to HLA-A, four (1.8%) to HLA-B, seven (3.2%) to HLA-DR, and 14 (6.4%) to two or more HLAs. More DSAs were observed in female recipients than male recipients in the DSA (+) group. The DSA (+) group showed significantly higher levels of class I and II panel reactive antibody (PRA) than did the DSA (-) group. No significant intergroup differences were found between incidences of primary nonfunction, acute rejection, vascular complication, or biliary complication. There were no significant differences in graft survival rates between the two groups. However, the recipients with multiple DSAs tended to have more acute rejection episodes and events of biliary stricture and lower graft survival rates than did patients in the DSA (-) group.

Conclusion

In LDLT, the presence of multiple DSAs and high PRA seemed to be associated with poor graft outcomes, although our results did not reach statistical significance. Large cohort studies are necessary to clarify the impact of DSA and PRA in LDLT.

Genetic variants of innate immune receptors and infections after liver transplantation

Infection is the leading cause of complication after liver transplantation, causing morbidity and mortality in the first months after surgery. Allograft rejection is mediated through adaptive immunological responses, and thus immunosuppressive therapy is necessary after transplantation. In this setting, the presence of genetic variants of innate immunity receptors may increase the risk of post-transplant infection, in comparison with patients carrying wild-type alleles. Numerous studies have investigated the role of genetic variants of innate immune receptors and the risk of complication after liver transplantation, but their results are discordant. Toll-like receptors and mannose-binding lectin are arguably the most important studied molecules; however, many other receptors could increase the risk of infection after transplantation. In this article, we review the published studies analyzing the impact of genetic variants in the innate immune system on the development of infectious complications after liver transplantation.

Local graft irradiation for kidney allograft rejection: a case series and review of the literature

Introduction:

Due to its immunosuppressive properties, local graft irradiation (LGI) has been proposed as a second line therapy for treatment of acute kidney rejection.

Case Presentation:

In this case-series we report 6 patients with biopsy proven acute kidney allograft rejection refractory to conventional antirejection therapy who underwent LGI for treatment of acute rejection at our center. Three of these patients had living donor transplants, 2 had deceased donor transplants, and one had received a simultaneous kidney/pancreas transplant. All patients were treated with anti thymocyte-globulin or muromonab-CD3, and intravenous steroids for initial treatment of rejection. Three patients also received intravenous immunoglobulin. LGI was tried as a last resort and was well tolerated and resulted in either improvement or stabilization of renal function in 5 patients. One patient could not be given the complete course of chemical immunosuppression for treatment of rejection due to concomitant cryptococcal meningitis and was switched to LGI with good short-term response.

Discussion:

Our results suggest that LGI could be considered a second line therapy to the conventional anti-rejection therapy for patients with refractory acute kidney allograft rejection, or for patients who cannot receive systemic immunosuppression due to severe infection.

Immunosuppression and allograft rejection following lung transplantation: evidence to date

The enduring success of lung transplantation is built on the use of immunosuppressive drugs to stop the immune system from rejecting the newly transplanted lung allograft. Most patients receive a triple-drug maintenance immunosuppressive regimen consisting of a calcineurin inhibitor, an antiproliferative and corticosteroids. Induction therapy with either an antilymphocyte monoclonal or an interleukin-2 receptor antagonist are prescribed by many centres aiming to achieve rapid inhibition of recently activated and potentially alloreactive T lymphocytes. Despite this generic approach acute rejection episodes remain common, mandating further fine-tuning and augmentation of the immunosuppressive regimen. While there has been a trend away from cyclosporine and azathioprine towards a preference for tacrolimus and mycophenolate mofetil, this has not translated into significant protection from the development of chronic lung allograft dysfunction, the main barrier to the long-term success of lung transplantation. This article reviews the problem of lung allograft rejection and the evidence for immunosuppressive regimens used both in the short- and long-term in patients undergoing lung transplantation.

Neopterin is associated with cardiovascular events and all-cause mortality in renal transplant patients

BACKGROUND

Inflammatory markers show significant associations with cardiovascular events and all-cause mortality after kidney transplantation. Neopterin, reflecting interferon-γ-release, may better reflect the proinflammatory state of recipients than less specific markers.

METHODS

Kidney transplant recipients in the Assessment of LEscol in Renal Transplant (ALERT) trial were examined and investigated for an association between serum neopterin and subsequent clinical events: graft loss, major cardiovascular events (MACE) and all-cause mortality.

RESULTS

After adjustment for established and emerging risk factors neopterin expressed as neopterin-to-creatinine ratio was significantly associated with MACE (p = 0.009) and all-cause mortality (p = 0.002). Endpoints were more frequent with increasing quartiles of neopterin-to-creatinine ratio. The incidence rates of MACE and all-cause mortality were significantly increased in the upper quartiles compared with the first.

CONCLUSIONS

This long-term prospective analysis in stable kidney allograft recipients suggests that neopterin is associated with long-term risk of cardiovascular events and all-cause mortality, but not renal outcomes.

A surgeons' guide to renal transplant immunopathology, immunology, and immunosuppression

The response to allografting involves adaptive and innate immune mechanisms. In the adaptive system, activated T cells differentiate to cytotoxic effectors that attack the graft and trigger B cells to differentiation to plasma cells that produce anti-HLA antibodies. The innate immune system recognizes antigens in a non-specific manner and recruits immune cells to the graft through the productions of chemotactic factors, and activation of cytokines and the complement cascade. In the kidney the tubules and the endothelium are the targets of the rejection response. Immune suppression is effective in modulating the adaptive immune system effect on graft histology.