1. Testing of retroviral vector-based human gene therapy products for replication competent retrovirus during product manufacture and patient follow-up Publication: Silver Spring, MD : Center for Biologics Evaluation and Research, January 2020 Subject(s): Drug ContaminationGenetic TherapyGenetic VectorsRetroviridaeVirus ReplicationUnited StatesUnited States. Department of Health and Human Services.United States. Food and Drug Administration.