Immune-checkpoint inhibitors PD-L1/2 are upregulated on both MyD88- and CARD11-mutant Eµ-myc lymphomas. (A) PD-L1 (top) and PD-L2 (bottom) RNA-seq transcript levels (relative to vector cohort) in B220-isolated NDM-carrying lymphoma cells. Sample numbers as indicated; error bars denote the standard error, and red color bar indicates significance (P < .05) as compared with the respective vector control cohorts. (B) PD-L1/2 surface expression on B220/GFP double-positive lymphoma cells by flow cytometry. Representative cases of n ≥ 3 independent experiments are shown. (C) Flow cytometric surface PD-L1/2 expression on individual GFP⁺ Eµ-myc lymphomas (n = 6) that were stably transduced in vitro with the MyD88-L265P or CARD11-L244P moiety vs an empty vector as a control (with error bars denoting the standard deviation). Gray dots represent mean fluorescence intensity (M.F.I.) of isotype controls. (D) PD-L1/2 expression measured as in panel B on F4/80⁺;B220⁻;GFP⁻ tumor-infiltrating macrophages isolated from bulk MyD88-L265P– and CARD11-L244P–mutant Eµ-myc lymphomas in n ≥ 3 individual cases per genotype (with error bars denoting the standard deviation). Gray dots represent M.F.I. of isotype controls. (E) Fraction of PD1⁺ T cells within the CD3⁺ cell population of bulk lymphomas as in panel D. (F) Costaining for the proliferation marker Ki67 and surface PD-L1 or PD-L2 in viable GFP⁺;B220⁺ MyD88-mutant lymphomas as in panel D. Gray dots represent M.F.I. of isotype controls. (G) Flow cytometric surface PD-L1/2 expression on individual GFP⁺ senescence-incapable INK4a/ARF-deficient (n ≥ 3) Eµ-myc lymphomas that were stably transduced in vitro with the MyD88-L265P or CARD11-L244P moiety vs an empty vector as a control (with error bars denoting the standard deviation). Gray dots represent M.F.I. of isotype controls. Asterisks indicate significance (P < .05); n.s., not significant.