Gtx104763

FFPE full-face tissue sections from available tumors were dual IHC stained as detailed in supplementary text. All antibodies were initially tested on positive and negative control tissues with the Abs chosen for IHC detailed in the supplementary text file. Dual IHC stains were employed to examine the proximity of different lymphocyte subpopulations using the following markers: CD3 for total T cells, CD4⁺ and CD8⁺ for T-cell subsets, CD20 for total B cells (chosen for IHC instead of CD19 (used in flow cytometry experiments) because it has been shown to be more sensitive and specific for B cells in FFPE tissues⁵⁸ (link)), CD23 for follicular dendritic cells and GC B cells, PD-1 and PD-L1. IHC staining for PD-L1 (B7-H1) was compared between several different Abs (polyclonal Abs Ab58810 (Abcam) and GTX104763 (GeneTex) and monoclonal Ab E1L3N (Cell Signaling Technology)) and a non-commercial reference Ab kindly provided by Dr Lieping Chen's lab (murine IgG1, clone 5H1⁵⁹ (link)) with the best results achieved using E1L3N (control tissue staining shown in Fig. S1). Tumors with PD-L1 positivity on infiltrating immune cells were stained with CD68 (macrophage lineage marker).