rhIL-15 administration is associated with hypercellular marrow and a reduction in adipocytes. Shown is the impact of rhIL-15 on the bone marrow examination of animals receiving vehicle diluent control or rhIL-15 at 50 μg/kg/d for 12 days. Left panel is the vehicle control bone marrow at day 44. Center panel is the bone marrow of animals receiving 50 μg/kg/d for 12 days determined at necropsy at day 13 within 24 hours of the last rhIL-15 administration showing marrow hyperplasia with a reduction in adipocytes. Right panel is the bone marrow examination of rhesus macaques receiving 50 μg/kg/d for 12 days studied at necropsy at day 44, 32 days after the last rhIL-15 administration, showing a return to a normal marrow pattern.