What is the defining characteristic of a fully human monoclonal antibody?

A fully human monoclonal antibody is characterized by being composed entirely of human components. This means that all parts of the antibody, from its variable regions that recognize specific antigens to its constant regions, are derived from human proteins. This characteristic offers several advantages in therapeutic applications, such as reducing the likelihood of immune responses that may occur when a non-human (murine) component is present. Consequently, fully human monoclonal antibodies are less likely to provoke an adverse reaction in patients, making them safer and more effective in treating various conditions like cancer and autoimmune diseases.

In contrast, the other options indicate varying percentages of mouse components, which would classify those antibodies as chimeric or partially humanized, rather than fully human. The presence of even small amounts of non-human material can influence the antibody's behavior in the immune system and its overall effectiveness.