collected peripheral blood samples from metastatic melanoma patients treated with anti–PD-1 monotherapy or combination ICIs of anti–PD-1 and anti–CTLA-4, and built a strong connection between severe irAEs within 3 months of treatment initiation and pre-treatment circulating activated CD4+ memory T-cell abundance as well as bulk TCR diversity (15). This evidence concerns the gene PDCD1 and metastatic melanoma.