MSB2311 is an investigational humanized PD-L1 with pH dependent binding property. PD-L1 is involved in inhibiting the immune system's response to fight cancer. MSB2311 blocks the interaction between PD-L1 and PD-1, which reactivates the suppressed or exhausted anti-tumor effector T cell function in the tumor microenvironment. MSB2311 employs engineered IgG1 which lacks FcR binding. In addition, the binding of MSB2311 to PD-L1 results in internalization of MSB2311 and MSB2311 can dissociate from bound PD-L1 in endosome with pH level lower than 5.5. This allows MSB2311 to be recycled to plasma membrane and be reused to bind with PD-L1 on another tumor cell or immune cell. Results from preclinical studies demonstrate that MSB2311 can inhibit tumor growth of PD-L1 expressing tumor cells in syngeneic mouse-model. Two Phase 1 studies of MSB2311 have been completed in the US and China. MSB2311 is currently to be tested in Phase 2 trial in patients with solid tumors expressing selected biomarker in China.