Single-cell RNAseq (scRNAseq) of melanoma samples before and after pembrolizumab administration, an anti–PD-1 Abs, revealed that the majority of TFH cells were isolated from patients who had a positive response to pembrolizumab posttreatment and that these cells were present in the same patients pretreatment (Sade-Feldman et al., 2018; Strazza et al., 2021b). Here, PDCD1 is linked to melanoma.