BB serves as a consultant for Novartis, Sanofi-Genzyme, Biogen-IDEC, and Roche pharmaceuticals on work unrelated to this Comment. AB-O has received personal fees for advisory board participation and/or consulting fees from Abata, Accure, Atara Biotherapeutics, Biogen, BMS/Celgene/Receptos, GlaxoSmithKline, Gossamer, Horizon Therapeutics, Immunic, Janssen/Actelion, Medimmune, Merck/EMD Serono, Novartis, Roche/Genentech, Sangamo, and Sanofi-Genzyme, Viracta; and grant support to the University of Pennsylvania from Biogen Idec, Roche/Genentech, Merck/EMD Serono, and Novartis, all for work unrelated to this Comment. ST declares no competing interests.