The Food and Drug Administration has approved a new genetically engineered drug to boost the infection-fighting ability of patients who get transplants of their own bone marrow.

The drug, a protein called granulocyte macrophage colony stimulating factor or GM-CSF, promotes the growth of infection-fighting white blood cells that are formed in the bone marrow. Experts have said it could eventually be used in fighting AIDS.The drug will be sold by Immunex Corp. of Seattle, the developer, under the name Leukine and by Hoechst-Roussel Pharmaceuticals Inc. under the name Prokine.

Some forms of cancer treatment using radiation and chemotherapy kill the marrow, leaving the patient less able to fight infection.

Doctors sometimes take marrow from such patients, store it during treatment, then re-inject it. Some of these patients still die of infection in "failed" transplants, estimated at 10 percent to 15 percent of those undertaken.

The new drug, approved Monday, is given at re-injection to stimulate the marrow's production of white cells.