Data from Immune Cell PD-L1 Colocalizes with Macrophages and Is Associated with Outcome in PD-1 Pathway Blockade Therapy

Abstract

<div>AbstractPurpose:<p>Programmed death ligand 1 (PD-L1) is expressed in tumor cells and immune cells, and both have been associated with response to anti-PD-1 axis immunotherapy. Here, we examine the expression of PD-L1 to determine which cell type carries the predictive value of the test.</p>Experimental Design:<p>We measured the expression of PD-L1 in multiple immune cells with two platforms and confocal microscopy on three retrospective Yale NSCLC cohorts (425 nonimmunotherapy-treated cases and 62 pembrolizumab/nivolumab/atezolizumab-treated cases). The PD-L1 level was selectively measured in different immune cell subsets using two multiplexed quantitative immunofluorescence panels, including CD56 for natural killer cells, CD68 for macrophages, and CD8 for cytotoxic T cells.</p>Results:<p>PD-L1 was significantly higher in macrophages in both tumor and stromal compartment compared with other immune cells. Elevated PD-L1 in macrophages was correlated with high PD-L1 level in tumor as well as CD8 and CD68 level (<i>P</i> < 0.0001). High PD-L1 expression in macrophages was correlated with better overall survival (OS; <i>P</i> = 0.036 by cell count/<i>P</i> = 0.019 by molecular colocalization), while high PD-L1 expression in tumor cells was not.</p>Conclusions:<p>In nearly 500 non–small cell lung cancer (NSCLC) cases, the predominant immune cell type that expresses PD-L1 is CD68<sup>+</sup> macrophages. The level of PD-L1 in macrophages is significantly associated with the level of PD-L1 in tumor cells and infiltration by CD8<sup>+</sup> T cells, suggesting a connection between high PD-L1 and “hot” tumors. In anti-PD-1 axis therapy–treated patients, high levels of PD-L1 expression in macrophages are associated with longer OS and may be responsible for the predictive effect of the marker.</p></div>