Although the concept of immunotherapy has been around for more than a century, it only gained prominence as a method of targeted cancer therapy in the early 2000s. In 2015, Merck’s Keytruda® (pembrolizumab), a checkpoint inhibitor drug, made headlines as a breakthrough therapy for melanoma after former U.S. president Jimmy Carter was treated with it. Keytruda had just received approval from the U.S. Food and Drug Administration (FDA) as the first anti-PD-1 therapy, and its highly-publicized success created a frenzy in the media; followed by the initiation of scores of immuno-oncology (I-O) clinical trials.