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After deparaffinization, rehydration and washing of the sections, microwave antigen retrieval was carried out in Tris‐EDTA (pH 9.0). Sections were first incubated with blocking serum at room temperature for 30 minutes and with the mouse anti‐IDO1 mAb (4.16H1 Ab, 1:1000; a kind gift from Benoit J. Van den Eynde), combined with a rabbit anti‐CD34 mAb (EP373Y Ab 1:100; #ab81289, Abcam), a rabbit anti‐LAMP3 mAb (104G4 Ab, 1:50; #DDX0190A546‐100, Novus Biologicals), or a rabbit anti‐CD68 polyclonal Ab (1:100; #25747‐1‐AP, ProteinTech Group) at 4°C overnight. The second incubation was undertaken using DyLight 488 AffiniPure goat anti‐mouse IgG (1:100; #E032210, EarthOx, Millbrae, CA, USA) and DyLight 594 AffiniPure goat anti‐rabbit IgG (1:100; E032420, EarthOx). Following counterstaining with DAPI after serially rinsing with 1× PBST, images were acquired in a microscopic field at 600×. The observation and images acquisition of these sections were carried out using a confocal laser scanning microscope (Olympus Fluoview FV1000; Olympus, Tokyo, Japan).

After deparaffinization, rehydration, and washing of the 5‐μm sections, endogenous peroxidase was blocked (3% H₂O₂ for 10 minutes), and microwave antigen retrieval was undertaken in Tris‐EDTA (pH 9.0). The sections were first incubated with blocking serum at room temperature for 30 minutes and with a mouse anti‐IDO1 mAb (4.16H1 Ab, 1:1000; a kind gift from Benoit J. Van den Eynde), a rabbit anti‐CD8 Ab (SP16 Ab, 1:100; #ZA‐0508, ZSGB‐BIO, Beijing, China), a rabbit anti‐CD34 mAb (EP373Y Ab, 1:100; #ab81289, Abcam, Cambridge, UK), a mouse anti‐DC‐LAMP mAb (104G4 Ab, 1:50; #DDX0190A546‐100, Novus Biologicals, Littleton, CO, USA), a rabbit anti‐CD68 polyclonal Ab (1:100; #25747‐1‐AP, ProteinTech Group), a mouse anti‐CD4 Ab (UMAB64 Ab; #ZA‐0418, ZSGB‐BIO, Beijing, China), or a rabbit anti‐NCAM1/CD56 polyclonal Ab (1:400; #14255‐1‐AP, ProteinTech Group) at 4°C overnight. The second incubation was carried out using a goat anti‐mouse/rabbit Ab and visualized with DAB, following counterstaining with hematoxylin after serial rinsing. The observation and images acquisition of these sections were carried out by advanced research microscope (Nikon Eclipse 80i; Nikon, Tokyo, Japan).