Anti-PD-1 therapy

Anti-PD-1 therapy is a class of cancer immunotherapy in which monoclonal antibodies — nivolumab and pembrolizumab among them — block the Programmed cell death 1 (PD-1) receptor on T cells, interrupting its engagement by the ligand CD274 molecule. PD-1 is an inhibitory checkpoint that normally restrains T-cell activation to limit autoimmunity, and many tumors exploit it to escape attack; blocking PD-1/PD-L1 signaling restores cytotoxic effector function in T cells that have already recognized the tumor. This is the crucial condition — the drugs release a brake rather than supply a signal, so they work only where tumor-reactive T cells are present. Anti-PD-1 belongs to the broader checkpoint inhibitor family alongside anti-PD-L1 antibodies and blockade of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), and is used across many solid tumors including melanoma, hepatocellular carcinoma and cervical cancer, as well as in the tissue-agnostic setting of mismatch repair–deficient or microsatellite instability–high disease, where the indication follows a molecular feature rather than an organ.

Because the mechanism is release of a physiological restraint, the characteristic toxicities are immune-related adverse events — colitis, hepatitis, pneumonitis, dermatitis and endocrinopathies affecting the pituitary, thyroid and adrenal axes. Their management inverts the therapeutic logic, requiring corticosteroids or further immunosuppression, and endocrine damage is often permanent even when the inflammation resolves.

Response depends heavily on the tumor microenvironment. Tumors that respond tend to carry pre-existing CD8+ T-cell infiltrates and active interferon gamma signaling, while resistance is associated with T-cell exhaustion, immunosuppressive macrophage and myeloid states, cancer-associated fibroblasts including fibroblast activation protein alpha (FAP)-positive populations, and tumor-derived extracellular vesicles that propagate suppression. Alternative checkpoints such as TIGIT with its ligand CD155 can sustain inhibition even when PD-1 is blocked, and loss of interferon signaling or of antigen presentation removes the pathway the drug depends on. Current work therefore centers on converting immunologically cold tumors into responsive ones, through combinations and through mechanisms spanning CD28 costimulatory signaling that supports T-cell activation, Spp1-mediated myeloid recruitment, proprotein convertase subtilisin/kexin type 9 (PCSK9), Sting-dependent innate sensing, oncolytic viruses and tumor metabolic pathways such as fatty acid uptake.