1. From the Section of Immunology, Department of Developmental Therapeutics, University of Texas M.D. Anderson Hospital and Tumor Institute, Houston, Tex. (address reprint requests to Dr. Hersh at the Section of Immunology, Department of Developmental Therapeutics, Room RI-427, University of Texas M.D. Anderson Hospital and Tumor Institute at Houston, Texas Medical Center, Houston, Tex. 77025).