21.   The molecule had been acting as a magnet for human antibodies, betraying the fact that the transplanted tissue was not human.

22.   They gave the mice human antibody genes, and showed the mice produced human antibodies.

23.   The vaccines, given orally and for free over several doses, contain a weak dose of the virus to stimulate the production of human antibodies against the disease.

24.   The vaccines, given orally and for free over several doses, contain weakened virus to stimulate the production of human antibodies against the disease.