Nonetheless, the most frequently used mAbs for cancer therapy are pembrolizumab, nivolumab, bevacizumab, trastuzumab and rituximab, which target proteins involved in tumorigenesis including PD-1, vascular endothelial growth factor A (VEGF-A), human epidermal growth factor receptor 2 (HER2) and CD20, respectively (Table 1) [15]. Here, PDCD1 is linked to cancer.