PDCD1 and cancer: In leukaemic cell lines it was found that in vitro, the combination of pembrolizumab – an anti‐PD‐1 therapy – and Zoledronate (ZOL) was only able to significantly increase the production of IFN‐γ against one out of the four cell lines tested, which was likely a result of variable expression of PD‐1 ligand by cancer cell lines.61