Programmed death 1 (PD-1) is an immune checkpoint molecule that negatively regulates T-cell immune function through the interaction with its ligand PD-L1. Blockage of this interaction unleashes the immune system to fight cancer. Immunotherapy using PD-1 blockade has led to a paradigm shift in the field of cancer drug discovery, owing to its durable effect against a wide variety of cancers with limited adverse effects. A brief history and development of PD-1 blockade, from the initial discovery of PD-1 to the recent clinical output of this therapy will be first summarized. Despite its tremendous clinical success rate over other cancer treatments, PD-1 blockade has its own pitfall; a significant fraction of patients remains unresponsive to this therapy. The key to improve the PD-1 blockade therapy is the development of combination therapies. Since this approach has garnered worldwide interest, here, I will overview the recent trends in the development of PD-1 blockade-based combination therapies and the ongoing clinical trials. These include combinations with checkpoint inhibitors, radiation therapy, chemotherapy, and several other existing cancer treatments. Energy metabolism has emerged as one of the important regulatory mechanisms for the function and differentiation of T cells. I will discuss here the recent results regarding the augmentation of PD-1 blockade efficacy by augmenting mitochondrial energy metabolism of T cell.