PDCD1LG2 and melanoma: Although αPD-1 and αPD-L1 block a receptor (PD-1)/ligand (PD-L1) signal axis, we previously showed that in B16F10 melanoma, young mice responded to αPD-1 and αPD-L1 ICI, whereas αPD-L1 was ineffective in aged mice despite αPD-1 efficacy.10 We hypothesized that this unexpected, dichotomous outcome reflected differential, age-related IC (PD-1, PD-L1, PD-L2, CD80) expression, among other considerations as IC other than PD-1 and PD-L1 are largely not considered in IC efficacy (or age) studies.