Timeline for Key Advances in Therapeutic Oligonucleotides. The various substitutions and the advances of chemical modifications are shown in yellow, main discoveries and technological achievements are noted in blue, and clinical studies are highlighted in green. Adapted from Lundin, K. E., Gissberg, O., and Smith, C. I. E. (2015) Oligonucleotide Therapies: The Past and the Present. Hum. Gene Ther. 26, 475–485.159 Copyright 2015, Mary Ann Liebert, Inc.