PD-L1 Overexpression During Endotoxin Tolerance Impairs the Adaptive Immune Response in Septic Patients via HIF1α

Abstract

Sepsis, among other pathologies, is an endotoxin tolerance (ET)-related disease. On admission, we classified 48 patients with sepsis into 3 subgroups according to the ex vivo response to lipopolysaccharide. This response correlates with the Acute Physiology and Chronic Health Evaluation (APACHE) II score and the ET degree. Moreover, the ET-related classification determines the outcome of these patients. Programmed cell death-ligand 1 (PD-L1) expression on septic monocytes is also linked with ET status. In addition to the regulation of cytokine production, one of the hallmarks of ET that significantly affects patients with sepsis is T-cell proliferation impairment or a poor switch to the adaptive response. PD-L1/programmed cell death-1 (PD-1) blocking and knockdown assays on tolerant monocytes from both patients with sepsis and the in vitro model reverted the impaired adaptive response. Mechanistically, the transcription factor hypoxia-inducible factor-1α (HIF1α) has been translocated into the nucleus and drives PD-L1 expression during ET in human monocytes. This fact, together with patient classification according to the ex vivo lipopolysaccharide response, opens an interesting field of study and potential personalized clinical applications, not only for sepsis but also for all ET-associated pathologies.

Oxygen Saturation on Admission Is a Predictive Biomarker for PD-L1 Expression on Circulating Monocytes and Impaired Immune Response in Patients With Sepsis

“…In accordance with our previous data, the biological activities described above are controlled by hypoxia-inducible factor-1α (HIF1α) expression ( 13 , 15 ). In this regard, HIF1α is the most important pathway for oxygen homeostasis in mammals ( 16 ).…”

“…The discovery and characterisation of immune checkpoints (ICs) adds a new parallel window of study in which cell-to-cell interaction could have an important role beyond cancer pathologies ( 9 ). In this regard, we and others have already reported programmed death-ligand 1 (PD-L1) overexpression on sepsis monocytes ( 10 – 13 ), which was associated with risk stratification and mortality in these patients ( 14 ).…”

“…The peripheral blood mononuclear cells (PBMCs) were isolated using Ficoll-Plus gradient (GE Healthcare Bio-Sciences) as reported previously ( 4 , 13 ).…”

“…Proliferation was analyzed by flow cytometry of CFSE-labeled cells, as reported previously ( 13 ). Briefly, PBMCs from patients were labeled with CFSE and 10 5 PBMCs per well were seeded in a round bottom p96 plate (Corning costar, USA) and stimulated with 2.5 μg/mL of PWD and treated or not with 5 μg/ml of fully human IgG4 (S228P) anti-PD-1 monoclonal antibody (Bristol-Myers Squibb) during 5 days.…”

Monocytes Undergo Functional Reprogramming to Generate Immunosuppression through HIF-1α Signaling Pathway in the Late Phase of Sepsis

“…The monocytes, a kind of antigen-presenting cells (APC), acted as instigators of T cell suppression in adaptive response by mediating the expression of inhibitory coreceptors such as programmed cell death protein 1 (PD-1) and cytotoxic T lymphocyte-associated protein 4 (CTLA4) [10,11]. The researches of Avendano-Ortiz et al [12] and Shalova et al [13] showed that hypoxia-inducible factor-1α (HIF-1α) regulated functional reprogramming of monocytes in sepsis to suppress T cells with inhibitory coreceptors, cytokines, and chemokines. It was also shown by Tsukamoto et al [14] that the myeloid-derived suppressor cells (MDSCs) were more suppressive in nature by upregulating the expression of PD-L1 to impair antigen-specific T cell priming and IgG production in sepsis.…”