A novel IgG4 isotype anti-KIR antibody, novel formulations of this and other IgG4 anti-KIR antibodies, and methods of using such formulations are provided. Also described are compositions, formulations, dosages, and administration regimens suitable for NK cell activation and therapeutic applications of anti-KIR antibodies, as well as kits comprising one or more anti-KIR antibodies with instructions for use in treating cancer.