CD4 and neoplasm: Recent profiling of tumour-infiltrating T cells using mass cytometry revealed distinct mechanisms of action of PD-1 and CTLA-4 blockade, demonstrating that PD-1 blockade reinvigorates CD8+ T-cell responses, and CTLA-4 blockade results in the expansion of Th1-like CD4+ cells expressing the co-stimulatory ligand ICOS (Wei et al, 2017).