Doctors have been slow to use pigs as organ-donor alternatives for at least two reasons: first, the pig genome has a number of endogenous retroviruses that are harmless to pigs, but that could infect humans; second, the human immune system will target pig-specific proteins in the cell membranes, trying to reject the foreign bodies.
Church and his colleagues used CRISPR/Cas9 to inactivate 62 of the pig’s endogenous retroviruses in embryos. In a separate set of pig embryos, the team modified genes coding for the cell membrane proteins that would trigger a human immune response. Pigs intended as organ donors in the future will require both sets of gene edits, which amount to ten times more than previous edits in other animals.
CRISPR pioneer Jennifer Doudna, a biochemist at University of California, Berkeley, told Nature she was impressed by the number of edited genes.
Because the work is unpublished, Church and his colleagues didn’t reveal the exact genes that they targeted. But, according to Nature, Church said that both sets of edited pig embryos are almost ready to implant into mother pigs. “This is something I’ve been wanting to do for almost a decade,” he told Nature.