Distinct molecular and immunological properties of circulating exosomes isolated from pediatric lung transplant recipients with bronchiolitis obliterans syndrome - a retrospective study

Biomarkers for Chronic Lung Allograft Dysfunction: Ready for Prime Time?

Chronic lung allograft dysfunction (CLAD) remains a major hurdle impairing lung transplant outcome. Parallel to the better clinical identification and characterization of CLAD and CLAD phenotypes, there is an increasing urge to find adequate biomarkers that could assist in the earlier detection and differential diagnosis of CLAD phenotypes, as well as disease prognostication. The current status and state-of-the-art of biomarker research in CLAD will be discussed with a particular focus on radiological biomarkers or biomarkers found in peripheral tissue, bronchoalveolar lavage' and circulating blood' in which significant progress has been made over the last years. Ultimately, although a growing number of biomarkers are currently being embedded in the follow-up of lung transplant patients, it is clear that one size does not fit all. The future of biomarker research probably lies in the rigorous combination of clinical information with findings in tissue, bronchoalveolar lavage' or blood. Only by doing so, the ultimate goal of biomarker research can be achieved, which is the earlier identification of CLAD before its clinical manifestation. This is desperately needed to improve the prognosis of patients with CLAD after lung transplantation.

Morbidity of antireflux surgery in lung transplant and matched nontransplant cohorts is comparable

BACKGROUND

Safety data on perioperative outcomes of laparoscopic antireflux surgery (LARS) after lung transplantation (LT) are lacking. We compared the 30-day readmission rate and short-term morbidity after LARS between LT recipients and matched nontransplant (NT) controls.

METHODS

Adult patients who underwent LARS between January 1, 2015, and October 31, 2021, were included. The participants were divided into two groups: LT recipients and NT controls. First, we compared 30-day readmission rates after LARS between the LT and NT cohorts. Next, we compared 30-day morbidity after LARS between the LT cohort and a 1-to-2 propensity score-matched NT cohort.

RESULTS

A total of 1328 patients (55 LT recipients and 1273 NT controls) were included. The post-LARS 30-day readmission rate was higher in LT recipients than in the overall NT controls (14.5% vs. 2.8%, p < 0.001). Compared to matched NT controls, LT recipients had a lower prevalence of paraesophageal hernia, a smaller median hernia size, and higher peristaltic vigor. Also compared to the matched NT controls, the LT recipients had a lower median operative time but a longer median length of hospital stay. The proportion of patients with a post-LARS event within 30 postoperative days was comparable between the LT and matched NT cohorts (21.8% vs 14.5%, p = 0.24).

CONCLUSIONS

Despite a higher perceived risk of comorbidity burden, LT recipients and matched NT controls had similar rates of post-LARS 30-day morbidity at our large-volume center with expertise in transplant and foregut surgery. LARS after LT is safe.

Immune processes in the pathogenesis of chronic lung allograft dysfunction: identifying the missing pieces of the puzzle

Lung transplantation is the optimal treatment for selected patients with end-stage chronic lung diseases. However, chronic lung allograft dysfunction remains the leading obstacle to improved long-term outcomes. Traditionally, lung allograft rejection has been considered primarily as a manifestation of cellular immune responses. However, in reality, an array of complex, interacting and multifactorial mechanisms contribute to its emergence. Alloimmune-dependent mechanisms, including T-cell-mediated rejection and antibody-mediated rejection, as well as non-alloimmune injuries, have been implicated. Moreover, a role has emerged for autoimmune responses to lung self-antigens in the development of chronic graft injury. The aim of this review is to summarise the immune processes involved in the pathogenesis of chronic lung allograft dysfunction, with advanced insights into the role of innate immune pathways and crosstalk between innate and adaptive immunity, and to identify gaps in current knowledge.

Small Extracellular Vesicles in Transplant Rejection

Small extracellular vesicles (sEV), which are released to body fluids (e.g., serum, urine) by all types of human cells, may stimulate or inhibit the innate and adaptive immune response through multiple mechanisms. Exosomes or sEV have on their surface many key receptors of immune response, including major histocompatibility complex (MHC) components, identical to their cellular origin. They also exhibit an ability to carry antigen and target leukocytes either via interaction with cell surface receptors or intracellular delivery of inflammatory mediators, receptors, enzymes, mRNAs, and noncoding RNAs. By the transfer of donor MHC antigens to recipient antigen presenting cells sEV may also contribute to T cell allorecognition and alloresponse. Here, we review the influence of sEV on the development of rejection or tolerance in the setting of solid organ and tissue allotransplantation. We also summarize and discuss potential applications of plasma and urinary sEV as biomarkers in the context of transplantation. We focus on the attempts to use sEV as a noninvasive approach to detecting allograft rejection. Preliminary studies show that both sEV total levels and a set of specific molecules included in their cargo may be an evidence of ongoing allograft rejection.

The emerging field of non-human leukocyte antigen antibodies in transplant medicine and beyond

The major medical advances in our knowledge of the human leukocyte antigen (HLA) system have allowed us to uncover several gaps in our understanding of alloimmunity. Although the non-HLA system has long sparked the interest of the transplant community, recognition of the role of immunity to non-HLA antigenic targets has only emerged recently. In this review, we will provide a comprehensive summary of the paradigm-changing concept of immunity to the non-HLA angiotensin II type 1 receptor (AT1R), discovered by Duška Dragun et al., that began from careful bedside clinical observations, to validated detection of anti-AT1R antibodies and lead to clinical intervention. This scientific approach has also allowed the recognition of broader pathogenicity of anti-AT1R antibodies across multiple organ transplants and in other human diseases, the integration of both non-HLA and HLA systems to understand their immunologic effects on organ allografts, and the identification of future directions for therapeutic intervention to modulate immunity to AT1R. Rationally designed successful interventions to target AT1R system provide an exemplar for other non-HLA antibodies to cross borders between medical specialties, will generate new avenues in translational research beyond transplantation, and will foster the development of new and reliable tools to improve our understanding of non-HLA immunity and ultimately allow us to improve patient care.

Community-Acquired Respiratory Viruses Post-Lung Transplant

Survival in lung transplant recipients (LTRs) lags behind heart, liver, and kidney transplant, in part due to the direct and indirect effects of infection. LTRs have increased susceptibility to infection due to the combination of a graft continually exposed to the outside world, multiple mechanisms for impaired mucus clearance, and immunosuppression. Community-acquired respiratory viral infections (CARVs) are common in LTRs. Picornaviruses have roughly 40% cumulative incidence followed by respiratory syncytial virus and coronaviruses. Although single-center retrospective and prospective series implicate CARV in rejection and mortality, conclusive evidence for and well-defined mechanistic links to long-term outcome are lacking. Treatment of viral infections can be challenging except for influenza. Future studies are needed to develop better treatments and clarify the links between CARV and long-term outcomes.

Acute Rejection in the Modern Lung Transplant Era

Acute cellular rejection (ACR) remains a common complication after lung transplantation. Mortality directly related to ACR is low and most patients respond to first-line immunosuppressive treatment. However, a subset of patients may develop refractory or recurrent ACR leading to an accelerated lung function decline and ultimately chronic lung allograft dysfunction. Infectious complications associated with the intensification of immunosuppression can also negatively impact long-term survival. In this review, we summarize the most recent evidence on the mechanisms, risk factors, diagnosis, treatment, and prognosis of ACR. We specifically focus on novel, promising biomarkers which are under investigation for their potential to improve the diagnostic performance of transbronchial biopsies. Finally, for each topic, we highlight current gaps in knowledge and areas for future research.