Treatment with a MEK inhibitor or anti-PD-1 antibody decreases disease burden in a mouse model of LCH. (A) Treatment and evaluation schema for intervention with PD-L1 or PD-1 blocking antibodies and anti-MEKi. (B-D) Organ weight of lung (B), liver (C), and spleen (D) from BRAFV600E^CD11c mice treated with MEKi, vehicle control, isotype control, anti-PD-L1, or anti-PD-1. Data are the mean ± SD. ***P < .001, ****P < .0001, ns, not significant (P > .05), by WMW test. (E, F) Disease burden significantly decreased in lung (E) and liver (F) of BRAFV600E^CD11c mice treated with MEKi or anti-PD-1, but not anti-PD-L1 antibody, compared with isotype control. Data are the mean ± SD. ***P < .001, ****P < .0001, ns, not significant (P > .05), by 1-way ANOVA with Tukey’s post hoc test. (G, H) Hematoxylin and eosin–stained lung (G) and liver (H) specimens from BRAFV600E^CD11c mice after treatment with MEKi or anti-PD-1, but not anti-PD-L1, compared with the corresponding isotype control groups. Bars represent 100 µm. For panels B-F, n = 9 mice per group.