Abstract: Disclosed are compositions and methods for mediating immunosuppressive myelopoiesis. Additionally, disclosed herein are combination therapies for treating cancers and methods of using the same.

Abstract: The present invention provides methods and compositions for modulating an immune response by controlling the level of arginase available to a cell, tissue or system. An immune response can be enhanced or depressed by altering the amount of arginine available to a cell, tissue or system through the manipulation of localized or systemic arginine levels using substances which provide arginine to the body and enzymes which break down arginine, such as arginase and nitric oxide synthase. Increasing or decreasing an immune response according to the present invention provides therapeutic treatments for a variety of conditions and diseases. The present invention also provides clinical methods and kits which can measure the strength or resistance to an immune response in a cell, tissue or system based upon the amount of available arginine and enzymes which break down arginine.