Conflicts of interest: J.K.H.: consultant to AstraZeneca, Genentech, Inc., GlaxoSmithKline, Novartis, Regeneron, Sanofi Genzyme. B.Y., R.S., L.A.M.: employees of Genentech, Inc., a member of the Roche Group. J.B.: employee of Roche. S.E.L.: consultant to AstraZeneca, Genentech, Inc., GlaxoSmithKline, Novartis, Regeneron, Sanofi Genzyme.