Fig. 3From: Multidimensional, quantitative assessment of PD-1/PD-L1 expression in patients with Merkel cell carcinoma and association with response to pembrolizumabThe density of PD-1+ cells adjacent to a PD-L1+ cell correlates with clinical response to anti-PD-1. a Representative composite image depicting proximity analysis between PD-1+ and PD-L1+ cells performed using the HALO software Spatial Analysis module, Supplemental Methods. The distance between each PD-1+ cell and the nearest PD-L1+ cell (green circles) was calculated, and only those at a distance ≤20 μm (black lines) are quantified (red circles). b Responders (R) had significantly higher median densities (±IQR) of PD-1+, but not CD8+, cells interacting with PD-L1+ cells compared to non-responders (NR). *p < 0.05. The density of PD-L1+ cells within  20 μm of a PD-1+ or CD8+ cell was also calculated, and a similar association with response was observed, Additional file 1: Figure S6Back to article page