bi·o·ther·a·py (b???-th?r??-p?)n. pl. bi·o·ther·a·pies Treatment of disease with biologics, such as certain drugs, vaccines, or antitoxins.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.biotherapythe treatment of illness and disease with substances derived from living organisms, as vaccines and serums.See also: Remedies-Ologies & -Isms. Copyright 2008 The Gale Group, Inc. All rights reserved.