Relatlimab is a lymphocyte-activation gene 3 (LAG-3)-blocking antibody that is being investigated with other agents in a variety of tumor types. LAG-3 is a cell-surface molecule found on effector T cells and regulatory T cells, and it works to control T cell response, activation, and growth. Preclinical studies suggest that inhibiting LAG-3 could restore effector function of exhausted T cells and could potentially promote an anti-tumor response. LAG-3 is a component of an immune checkpoint pathway that inhibits T-cell activity. Relatlimab, a human IgG4 LAG-3-blocking antibody, restores the effector function of exhausted T cells, reinvigorating T cells to attack cancer.Relatlimab and the anti-PD-1 agent nivolumab modulate potentially synergistic immune checkpoint pathways and can enhance antitumor immune responses. The two-drug combination has a generally manageable safety profile and can trigger durable tumor regressions in patients with melanoma whose disease has progressed after anti-PD-1 monotherapy.