Biopharmaceutical Reactor: Design, Sterility and GMP Compliance Answering the core question: What is a biopharmaceutical reactor? A biopharmaceutical reactor, or bioreactor, is a sterile vessel in which living cells, mammalian, microbial or viral, are grown under tightly controlled conditions to produce a biologic such as a monoclonal antibody, vaccine or recombinant protein. Unlike a chemical reactor, its product is made by biology rather than by mixing reagents, so the