In this study we aimed to characterize immune infiltrates and expression of programmed death 1 (PD-1) and programmed death ligand 1 (PD-L1) in a series of melanoma BM to provide a basis for experimental therapy using immune checkpoint inhibitors.Methods and results:
We investigated expression of PD-1, PD-L1, CD3, CD8, CD45RO, forkhead box protein 3 (FoxP3), CD20 and BRAF V600E by immunohistochemistry in melanoma BM samples. Forty-three specimens [27 of which (62.8%) were BRAF V600E-positive] were available. CD3+ tumour-infiltrating lymphocytes (TILs) were evident in 33 specimens (76.7%), CD8+ in 39 (90.7%), CD45RO+ in 32 (74.4%), PD-1+ in 27 (62.8%), FoxP3+ in 21 (48.8%) and CD20+ TILs in 19 (44.2%). Tumour PD-L1 expression was observed in 22 specimens (51.1%), and in nine of these (40.9%) expression was observed in more than 5% of tumour cells. PD-L1 expression was associated with higher density of PD-1+ (P < 0.001), CD3+ (P = 0.014) and FoxP3+ (P < 0.001) TIL infiltration. Density of CD3+ TILs was associated with density of CD8+ (P < 0.001), PD-1+ (P < 0.001) and CD45RO+ (P < 0.001) TILs. PD-L1 expression or PD-1+, CD3+, CD8+ or CD45RO+ TILs density did not correlate with BRAF V600E status, previous systemic therapy or survival (P > 0.05).Conclusions:
Melanoma BM showed considerable lymphocytic infiltrates and expression of PD-L1 in the majority of investigated specimens, with high PD-L1 expression found predominantly in regions of abundant inflammation. Our data indicate that clinical studies should investigate the value of checkpoint inhibitors in patients with melanoma BMs.