Transmural Flow Upregulates PD-L1 Expression in Microvascular Networks.

Area of Science:

• Biophysics
• Immunology
• Cancer Biology

Background:

• Endothelial programmed death-ligand 1 (PD-L1) expression is elevated in tumors.
• Tumoral vasculature exhibits increased leakiness and transmural fluid flow compared to normal vessels.
• The direct impact of transmural flow on endothelial PD-L1 expression remains unclear.

Purpose of the Study:

• To investigate the relationship between transmural flow and endothelial PD-L1 expression.
• To elucidate the mechanisms underlying PD-L1 regulation by fluid flow in microvascular networks.
• To determine the role of transmural flow in modulating immune cell activity within the tumor microenvironment.

Main Methods:

• Development of a novel microfluidic device to model microvascular networks (MVNs).
• Application of controlled transmural flow to MVNs for 24 hours.
• Assessment of PD-L1 expression using cellular assays.
• Evaluation of CD8 T cell activation in response to transmural flow-conditioned MVNs.
• Investigation of the role of integrin αVβ3 using blocking antibodies and knock-out assays.

Main Results:

• Transmural flow significantly upregulates PD-L1 expression in endothelial cells within MVNs.
• Pre-conditioning MVNs with transmural flow suppresses CD8 T cell activation.
• Transmural flow further enhances PD-L1 expression in tumor microenvironment-derived vessels.
• Integrin αVβ3 was identified as the key mediator of transmural flow-induced PD-L1 upregulation.

Conclusions:

• Transmural fluid flow is a significant biophysical factor controlling endothelial PD-L1 expression.
• This mechanism contributes to the elevated PD-L1 observed in tumoral vasculatures.
• Understanding this flow-PD-L1-integrin axis offers new insights into tumor immune evasion and potential therapeutic strategies.