Abstract Rationale Lymphangioleiomyomatosis (LAM) is a rare, slow growing metastasising neoplasm, predominantly presenting in women. Lung parenchyma infiltration by LAM cells is characteristic of this disease, with host immune cell interactions in the LAM lung microenvironment poorly understood. Evidence supports LAM cells evading immune detection via pathways dependant on mechanistic target of rapamycin (mTOR), with current treatment targeting mTOR inhibition. The aim of this study is to characterise LAM immune cell populations in peripheral blood samples by flow cytometry, examine potential treatment effects and correlate with markers of clinical decline. Methods Serum samples were obtained from LAM cases and healthy controls, for analysis by flow cytometry. An antibody panel consisting of CD45, Siglec8, CD14, CD15, CD19, CD3 and CD56 antibodies was developed to identify immune cell populations. LAM case data was collected, including pulmonary function, vascular endothelial growth factor D (VEGF-D) serum levels, treatment status and clinical features. FlowJo software was used to define cell populations via application of a gating strategy, with statistical analysis performed using GraphPad Prism. Results Analysis of immune populations in LAM patients (n = 17) versus healthy controls (n = 14) revealed a significant increase in neutrophils (p = 0.047) and significant reductions in monocytes (p = 0.036), B cells (p = 0.037), T cells (p = 0.031), natural killer (NK) T cells (p = 0.001) and NK cells (p = 0.049) in LAM. Clinical correlation in LAM revealed associations with elevated eosinophil counts and lower DLCO% (r2=0.322), mTOR inhibitor treatment (p = 0.028), and Tuberous Sclerosis Complex (TSC) (p = 0.038), while elevated neutrophil counts were associated with angiomyolipomas (AMLs) (p = 0.029). Treated LAM patients (n = 7) revealed significantly reduced NK T cells (p = 0.022) alone, while untreated LAM patients (n = 10) displayed reduced B cells (p = 0.045), T cells (p = 0.031) and NK T Cells (p = 0.0014). Treated patients revealed associations with reduced T cells and premenopausal status (p = 0.038) and reduced NK cells with reduced VEGF-D levels (r2=0.878) and preserved FEV1% (r2=0.672). Untreated patients revealed associations with elevated eosinophils and loss of FEV1% over time (r2=0.829); higher neutrophils with increased patient age (r2=0.618) and presence of AMLs (p = 0.029); reduced monocytes and FEV1/ml decline over time (r2=0.627) and reduced T cells with postmenopausal status (p = 0.005). Conclusions The results from our study reveal that immune cell populations are dysregulated within LAM patients versus controls, with signals towards normalisation on inhibition of mTOR pathways. Untreated patients particularly reveal reduced cell counts across lymphocyte populations, indicating a possible role in LAM pathophysiology. Clinical correlation reveals association between various immune cell populations and markers of clinical severity. This abstract is funded by: None
O’Malley et al. (Fri,) studied this question.