Faculty Bibliography

RATIONALE/BACKGROUND:Lower airway enrichment with oral commensals has been previously associated with grade 3 severe primary graft dysfunction (PGD) after lung transplantation (LT). We aimed to determine whether this dysbiotic signature is present across all PGD severity grades, including milder forms, and whether it is associated with a distinct host inflammatory endotype. METHODS:Lower airway samples from 96 LT recipients with varying degrees of PGD were used to evaluate the lung allograft microbiota via 16S rRNA gene sequencing. Bronchoalveolar lavage (BAL) cytokine concentrations and cell differential percentages were compared across PGD grades. In a subset of samples, we evaluated the lower airway host transcriptome using RNA sequencing methods. RESULTS:Differential analyses demonstrated lower airway enrichment with supraglottic-predominant taxa (SPT) in both moderate and severe PGD. Dirichlet Multinomial Mixtures (DMM) modeling identified two distinct microbial clusters. A greater percentage of subjects with moderate-severe PGD were identified within the dysbiotic cluster (C-SPT) than within the no PGD group (48 and 29%, respectively) though this difference did not reach statistical significance (p=0.06). PGD severity associated with increased BAL neutrophil concentration (p=0.03) and correlated with BAL concentrations of MCP-1/CCL2, IP-10/CXCL10, IL-10, and TNF-α (p<0.05). Furthermore, microbial signatures of dysbiosis correlated with neutrophils, MCP-1/CCL-2, IL-10, and TNF-α (p<0.05). C-SPT exhibited differential expression of TNF, SERPINE1 (PAI-1), MPO, and MMP1 genes and upregulation of MAPK pathways, suggesting that dysbiosis regulates host signaling to promote neutrophilic inflammation. CONCLUSIONS:Lower airway dysbiosis within the lung allograft is associated with a neutrophilic inflammatory endotype, an immune profile commonly recognized as the hallmark for PGD pathogenesis. This data highlights a putative role for lower airway microbial dysbiosis in the pathogenesis of this syndrome.

INTRODUCTION/UNASSIGNED:Mounting evidence indicates that an individual's humoral adaptive immune response plays a critical role in the setting of SARS-CoV-2 infection, and that the efficiency of the response correlates with disease severity. The relationship between the adaptive immune dynamics in the lower airways with those in the systemic circulation, and how these relate to an individual's clinical response to SARS-CoV-2 infection, are less understood and are the focus of this study. MATERIAL AND METHODS/UNASSIGNED:We investigated the adaptive immune response to SARS-CoV-2 in paired samples from the lower airways and blood from 27 critically ill patients during the first wave of the pandemic (median time from symptom onset to intubation 11 days). Measurements included clinical outcomes (mortality), bronchoalveolar lavage fluid (BALF) and blood specimen antibody levels, and BALF viral load. RESULTS/UNASSIGNED:While there was heterogeneity in the levels of the SARS-CoV-2-specific antibodies, we unexpectedly found that some BALF specimens displayed higher levels than the paired concurrent plasma samples, despite the known dilutional effects common in BALF samples. We found that survivors had higher levels of anti-spike, anti-spike-N-terminal domain and anti-spike-receptor-binding domain IgG antibodies in their BALF (p<0.05), while there was no such association with antibody levels in the systemic circulation. DISCUSSION/UNASSIGNED:Our data highlight the critical role of local adaptive immunity in the airways as a key defence mechanism against primary SARS-CoV-2 infection.

BACKGROUND:The effect of prolonged allograft ischemic time on lung transplant outcomes remains controversial, with most studies associating it with increased mortality, but this effect is partly mitigated by center volume. This study sought to evaluate the mechanism of these findings and clarify the impact of ischemic time on short-term outcomes in a national sample. METHODS:Data on lung transplants (January 2010-Janary 2017) were extracted from the Scientific Registry of Transplant Recipients database. Ischemic time was dichotomized as prolonged ischemic time (PIT) or no PIT (N-PIT) at 6 hours. High-volume centers were defined as the top quintile. The primary outcome was 30-day, 1-year, and 3-year mortality; secondary outcomes included in-hospital complications and 72-hour oxygenation. RESULTS:Among 11,809 records, there were significant differences between PIT and N-PIT recipients by demographics, lung allocation score, and donor organ metrics. In a 1:1 propensity score-matched cohort (n = 6422), PIT recipients had reduced survival compared with N-PIT at 3 years (66.5% vs 68.8%, P = .031). On multivariable analysis, this effect persisted among low-volume but not high-volume centers. PIT recipients were more likely to require reintubation, prolonged (>5 days) mechanical ventilation, hemodialysis, longer stay, and acute rejection (all P < .01). Except for reintubation, these disparities were present at both high- and low-volume centers independently. Ischemic time had no effect on 72-hour oxygenation. CONCLUSIONS:PIT remains associated with higher rates of postoperative complications and reduced short-term survival. While center volume ameliorated the survival impact, this was not achieved by reducing postoperative complications. Further research is warranted before broadening ischemic time thresholds among low-volume centers.

Rates of lung donation have increased over the past several years. This has been accomplished through the utilization of donors with extended criteria, the creation of donor hospitals or centers, and the optimization of lungs through the implementation of donor management protocols. These measures have resulted in augmenting the pool of available donors thereby decreasing the wait time for lung transplantation candidates. Although transplant programs vary significantly in their acceptance rates of these organs, studies have not shown any difference in the incidence of primary graft dysfunction or overall mortality for the recipient when higher match-run sequence organs are accepted. Yet, the level of comfort in accepting these donors varies among transplant programs. This deviation in practice results in these organs going to lower-priority candidates thereby increasing the waitlist time of other recipients and ultimately has a deleterious effect on an institution's waitlist mortality.

Xenotransplantation promises to alleviate the issue of donor organ shortages and to decrease waiting times for transplantation. Recent advances in genetic engineering have allowed for the creation of pigs with up to 16 genetic modifications. Several combinations of genetic modifications have been associated with extended graft survival and life-supporting function in experimental heart and kidney xenotransplants. Lung xenotransplantation carries specific challenges related to the large surface area of the lung vascular bed, its innate immune system's intrinsic hyperreactivity to perceived 'danger', and its anatomic vulnerability to airway flooding after even localized loss of alveolocapillary barrier function. This article discusses the current status of lung xenotransplantation, and challenges related to immunology, physiology, anatomy, and infection. Tissue engineering as a feasible alternative to develop a viable lung replacement solution is discussed.

OBJECTIVE:There is a shortage of donor lungs relative to need, but overall donor organ utilization remains low. The most common reason for refusal is organ quality, but the standards applied to selection vary. In this study we sought to characterize differences in lung utilization according to quality across several clinically distinct recipient pools. METHODS:Data on donor lungs recovered (April 2006 to September 2019) were extracted from the Scientific Registry of Transplant Recipients database. Organs were classified as ideal, standard, or extended quality according to their poorest metric among selected parameters. Subanalyses were performed on the basis of procedure type, age, lung allocation score, era, and alternative definitions of extended quality. Recipient traits and survival according to organ quality were assessed. RESULTS:Of 156,022 lungs analyzed during the study period, 25,777 (16.5%) were transplanted. There was no difference in quality distribution for single and bilateral transplants. Young candidates were more likely to receive ideal (14.7% vs 12.3%) or standard (9.5% vs 8.2%) lungs, but not extended lungs (75.9% vs 79.5%; all P < .01). Absolute differences in distribution according to lung allocation score quartile were small (<2%). Extended quality donor utilization increased over time. Survival according to donor category was similar at 1 and 3 years post transplant in unadjusted and Cox regression analyses. CONCLUSIONS:Extended quality lungs comprise an increasing share of transplants in a national sample. Organ selection varies according to recipient age and lung allocation score. However, absolute differences in quality distribution are small, and adverse effects on outcomes are limited to organs with multiple extended qualifying characteristics.