CRISPR can be used in several ways to develop pigs for human transplant organs. In – , CRISPR can be used to allow pig organs to be transplanted. CRISPR must be used to mutate – genes and to manipulate production of – system proteins to avoid rejection. Another method uses CRISPR to grow human organs in pigs by first deleting genes that normally stimulate – and then inserting human – into the resulting pig embryo, allowing a pig to grow a human organ.