A discovery whose time has come: transfer factor It's pushing 20 years now since H. Sherwood Lawrence, MD, discovered the substance called transfer factor. For most of those years, transfer factor has remained something of a curiosity, with only a few laboratories (including, of course, Dr. Lawrence's) trying to find out what it is and how it works. For a long time, all anyone knew was that transfer factor is a leukocyte extract that transfers what appears to be sensitivity to specific antigens (bacterial, fungal, viral and tissue) from one person to another. It seemed to have promise, but investigations were stymied by the lack of any animal models and by the fact that the only means of telling whether transfer factor was present or had transferred sensitivity was a skin test for delayed hypersensitivity. Those days appear to be over. Despite the many unknowns, transfer factor is off and