The search for "magic bullets" capable of hunting down a cancer in the human body, attacking a disease virus or repairing a defective organ has gone on for years.
For a time, monoclonal antibodies, disease-recognizing molecules made by hybrid mouse blood cells, seemed the answer.
There was success, to be sure. Antibodies cloned in the laboratories showed strengthened abilities to zero in on disease agents, especially cancers, that had eluded traditional medical or surgical attack. After much experimentation, however, doctors found they hadn't anticipated all the problems.
Allergic reactions proved a major hurdle. Because the antibody came from a mouse and not a human, patients' immune systems recognized it as alien, stimulating reactions. Moreover, the relatively large antibody molecule couldn't penetrate tissues to get at disease-causing organisms or the interior of tumors. Antibodies work best in tissue areas with good blood flow. Finally, the cell-splitting and combining process is time-consuming and tricky. So far, only two cloned antibodies have received federal approval for human use, with a couple more likely soon.