Your insurance will probably deny it, and you'll get a bill. ;-)

My guess is possibly not much, but it could vary greatly from one antibody to another. If the antibody isn't specific to any human protein, then it'll probably end up in your pee eventually. On the other hand, there are therapeutic proteins that are given by injection, so I could hardly suggest that it's intrinsically safe. And antibodies made for medicinal research stand a good chance of existing because of possible human interaction.