This study will test the safety and effectiveness of a drug called interleukin-12 (IL-12) in fighting severe infectious (other than tuberculosis) caused by a group of bacteria called mycobacteria. IL-12 is similar to a substance the body produces naturally to strengthen immune function (infection-fighting ability). It works by stimulating white blood cells to increase production of a chemical called interferon gamma, which can improve or cure mycobacterial infections in some patients.