PDCD1 and neoplasm: Multiple waves of newer therapeutic approaches are in developmentnow, with the total number of prospective IO therapeutics growingexponentially; by 2020, both PD-1 and PD-L1 were the intended therapeutictargets of over 100 distinct IO agents at various stages of development.One of the key themes with the coming iterations may indeed be toincrease the efficacy or therapeutic index of such agents with respectto on/off-tumor activity.