Fc-Receptor Interactions Regulate Both Cytotoxic and Immunomodulatory Therapeutic Antibody Effector Functions.

Antibodies are now recognized as key therapeutic tools to combat most forms of malignancy. Although the first wave of therapeutic antibodies that emerged over two decades ago directly target tumor cells for killing, a new class of antibody therapies targeting immunoregulatory pathways to boost antitumor immune responses by activating the immune system is poised for clinical success. A notable common characteristic of both classes of therapeutic antibodies is the importance of the IgG Fc domain, which connects the fine specificity of an antibody with immune cells that mediate antibody-triggered effector functions through their engagement of Fc receptor (FcR) family members. It is now clear that multiple variables, including the nature of the target molecules, the local presence of effector cells, and the expression patterns of FcRs, will dictate whether and how an antibody will necessitate interactions with FcRs to mediate optimal therapeutic effects. Thus, through careful in vivo mechanistic analyses of individual therapeutic antibodies, Fc domains engineered for optimal engagement of the appropriate cellular FcRs must be designed to maximize clinical success.