Antibody-Dependent Cellular Cytotoxicity Activity of a Novel Anti–PD-L1 Antibody Avelumab (MSB0010718C) on Human Tumor Cells

Several anti-PD1/PD-L1 monoclonal antibodies (MAbs) are currently providing evidence of clinical benefit in subsets of cancer patients. The mode of action of these MAbs is to inhibit PD1 on immune cells interacting with PD-L1 on tumor cells. These MAbs are either designed or engineered to eliminate antibody-dependent cell-mediated cytotoxicity (ADCC). ADCC, however, has been implicated as an important mechanism in several highly effective MAb-mediated cancer therapies. A fully human anti-PD-L1 MAb would potentially be able to block PD-L1/PD1 interactions and also mediate the ADCC lysis of tumor cells. MSB0010718C (designated avelumab) is a fully human IgG1 anti-PD-L1 MAb. The studies reported here demonstrate (a) the ability of avelumab to lyse a range of human tumor cells in the presence of PBMC or NK effectors; (b) IFN-γ can enhance tumor cell PD-L1 expression and in some cases enhance ADCC tumor cell lysis; (c) purified NK cells are potent effectors for avelumab; (d) similar levels of avelumab-mediated ADCC lysis of tumor cells are seen using purified NK as effectors from either healthy donors or cancer patients; (e) very low levels of avelumab-mediated lysis are seen using whole PBMC as targets; this finding complements results seen in analyses of PBMC subsets of patients receiving avelumab; and (f) the addition of IL-12 to NK cells greatly enhances avelumab-mediated ADCC. These studies thus provide an additional mode of action for an anti-PD-L1 MAb and provide the rationale for further studies to enhance avelumab-mediated ADCC activity.