Through the things they eat
The process of cloning effectively involves taking a cell from your body and turning it back into an embryo. The embryo would then either develop into a human being as has been proposed by various scientists around the world and which is currently banned, or it would be turned into a stem cell.
The bodies immune response includes all of those cells to help destroy pathogens that wish to bestow havoc on the beautiful homeostasis of the body.
