Macrophage and CD8 T cell discordance are associated with acute lung allograft dysfunction progression

Persistent and progressive acute lung allograft dysfunction is linked to cell compositional and transcriptional changes in small airways

BACKGROUND

Acute lung allograft dysfunction (ALAD) is a clinical syndrome of forced expiratory volume in 1-second (FEV1) decline concerning for chronic lung allograft dysfunction (CLAD) onset. Novel diagnostic tools are needed to identify those with ALAD who will progress to CLAD and to target appropriate therapies. We hypothesized that progressive ALAD would be associated with changes in small airway cell composition and cell-specific transcription.

METHODS

We prospectively identified recipients with undifferentiated ALAD and controls with stable allograft function for small airway brushing and single-cell RNA sequencing analysis. ALAD outcome group was categorized as (1) control (n = 8), or ALAD with (2) recovered (n = 4), (3) persistent (n = 5), or (4) progressive (n = 3) FEV1 decline. Cell compositional changes, pseudobulk Reactome pathways, and the AI2 score, previously linked to CLAD in airway brush transcriptomes, were assessed as a function of ALAD outcome group.

RESULTS

Across 68,140 cells, the distribution of cell composition was linked to ALAD outcome group (PERMANOVA, p = 0.004). Worse ALAD outcomes correlated with loss of basal cells, changes in club and ciliated subsets, a loss of macrophages, and expansion of cytotoxic T cells. The AI2 gene score was positively associated with ALAD outcome group, particularly in epithelial cell subsets (p < 0.001). Pathway analysis showed increased interferon signaling and inhibition of cell proliferation in epithelial cells.

CONCLUSIONS

In this pilot study, persistent and progressive ALAD was associated with changes in bronchiolar cell composition and transcriptional programs. Molecular phenotyping may help identify and characterize individuals with ALAD at increased risk for progression.

The ABC of transplant: ALAD, BLAD, and CLAD: definition and significance

PURPOSE OF REVIEW

Chronic lung allograft dysfunction (CLAD) is a recognized complication after lung transplantation, with a clear definition, although some pitfalls in phenotyping still exist. Recently, new terminologies, such as acute lung allograft dysfunction (ALAD) and baseline lung allograft dysfunction (BLAD) were introduced, but their definitions and real significance are not yet fully established.

RECENT FINDINGS

Based on the existing literature and ongoing discussions within two expert groups of the Advanced Lung Failure & Transplantation Interdisciplinary Network (ALFTx IDN) of the International Society for Heart and Lung Transplantation (ISHLT), we will describe current definitions, prevalence and outcome of these rather new entities, keeping in mind that a lot of uncertainties still exist.

SUMMARY

ALAD and BLAD will be defined, and the currently accepted outcome of these conditions will be summarized. Existing pitfalls in the phenotyping of CLAD will also be discussed.

The prognostic value of single and repeated ≥10% FEV1 declines for chronic lung allograft dysfunction

There is a paucity of data reporting the positive and negative predictive values (PPV, NPV) of acute declines in lung function on chronic lung allograft dysfunction (CLAD). We sought to define the predictive ability of single or repeated forced expiratory volume in the first second (FEV1) declines for at least 3 weeks on the development of CLAD or death by 1-year. We analyzed 340 subjects with at least 3 years of follow-up data from two lung transplant centers. A single ≥10% FEV1 decline had a PPV of 35% and NPV of 63%, and a repeated ≥10% FEV1 decline for at least 3 weeks had a PPV of 44% and NPV of 65%. Notably, the proportion of individuals with incipient CLAD at the time of a single or repeated ≥20% FEV1 decline was 50% and 71%, respectively. These estimates could inform the development of acute lung allograft dysfunction FEV1 thresholds as enrollment criteria or surrogate outcome measures.

Lung allograft dysbiosis associates with immune response and primary graft dysfunction

BACKGROUND

Lower airway enrichment with oral commensals has been previously associated with severe primary graft dysfunction (PGD) after lung transplantation (LT). We aimed to determine whether this dysbiotic signature is present across all PGD severity grades and whether it is associated with a distinct host inflammatory endotype.

METHODS

Lower airway samples from 96 LT recipients 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 moderate and severe PGD. Dirichlet multinomial mixtures modeling identified 2 distinct microbial clusters. A greater percentage of subjects with moderate-severe PGD than no PGD were identified within the dysbiotic cluster (C-SPT, 48% and 29%, respectively) though this 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, 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, MPO, and MMP1 genes and upregulation of MAPK pathways, host signling associated with 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. These data highlight a putative role of lower airway microbial dysbiosis in the pathogenesis of this syndrome.

Chronic Lung Allograft Dysfunction: Clinical Manifestations and Immunologic Mechanisms

The term "chronic lung allograft dysfunction" has emerged to describe the clinical syndrome of progressive, largely irreversible dysfunction of pulmonary allografts. This umbrella term comprises 2 major clinical phenotypes: bronchiolitis obliterans syndrome and restrictive allograft syndrome. Here, we discuss the clinical manifestations, diagnostic challenges, and potential therapeutic avenues to address this major barrier to improved long-term outcomes. In addition, we review the immunologic mechanisms thought to propagate each phenotype of chronic lung allograft dysfunction, discuss the various models used to study this process, describe potential therapeutic targets, and identify key unknowns that must be evaluated by future research strategies.

Update on the immunological mechanisms of primary graft dysfunction and chronic lung allograft dysfunction

PURPOSE OF REVIEW

Primary graft dysfunction (PGD) and chronic lung allograft dysfunction (CLAD) are the leading causes of graft loss in lung transplant recipients. The development of mouse lung transplant models has allowed for the genetic dissection of cellular and molecular pathways that prevent graft survival. This review provides an overview into recent mechanistic insights into PGD and CLAD.

RECENT FINDINGS

Mouse orthotopic lung transplant models and investigations of human lung transplant recipeints have revealed new molecular and cellular targets that promote PGD and CLAD. Donor and recipient-derived innate immune cells promote PGD and CLAD. PGD is driven by communication between classical monocytes and tissue-resident nonclassical monocytes activating alveolar macrophages to release chemokines that recruit neutrophils. Products of cell damage trigger neutrophil NET release, which together with NK cells, antibodies and complement, that further promote PGD. The development of CLAD involves circuits that activate B cells, CD8 + T cells, classical monocytes, and eosinophils.

SUMMARY

Effective targeted management of PGD and CLAD in lung transplant recipient to improve their long-term outcome remains a critical unmet need. Current mechanistic studies and therapeutic studies in mouse models and humans identify new possibilities for prevention and treatment.