Here, we undertake deep immunophenotyping of circulating B cell and antibody immune states in patients with advanced stage III/IV melanoma in the context of anti-PD-1 CPI therapy, by mass cytometry (cytometry by time of flight, CyTOF), antibody isotyping and proteome-wide autoantigen discovery using immuno-mass spectrometry (IMS). Here, PDCD1 is linked to melanoma.