Federal health authorities are allowing the use of a rat virus as part of an experimental treatment of humans for melanoma, a devastating and often fatal skin cancer.

The decision Thursday by the National Institutes of Health and the Food and Drug Administration represents the first approval of a therapy using foreign genes transferred into human patients.The subjects in the experimental treatment will be 10 patients in advanced stages of melanoma.

The study is aimed at increasing an understanding of a promising new cancer treatment called tumor-infiltrating lymphocyte therapy, or TIL, that was pioneered by Dr. Steven A. Rosenberg, a National Cancer Institute researcher who will supervise the experiment.