Investigators placing pig organs in other animal species have stemmed endothelial cell activation and the resulting hyperacute rejection
by depleting a prospective recipient's store of alpha-gal antibodies before the xenotransplant.
Cozzi, "Incidence of hyperacute rejection
in pig-to-primate transplantation using organs from hDAF-transgenic donors," Transplantation, vol.
The basis of this protocol is that the antibodies that would lead to hyperacute rejection
or acute antibody-mediated rejection must be removed from the body, and the immune system must be modulated to reduce the production of the antibody in the future or dampen the immune response to the foreign antigen.
(2008) observed that no hyperacute rejection
developed and one graft survived up to 6 months after transplantation.
"Because both copies of the gene have been inactivated, tissues from these pigs have been shown to be completely devoid of the pig sugar that cause the pig sugar that caused the hyperacute rejection
to take place."
Once the hyperacute rejection
is overcome, another immunological obstacle to long-term xenograft survival may be the human [CD8.sup.+] cytotoxic T lymphocytes (CTL)mediated killing of xenograft cells in xenograft recipients.
No hyperacute rejection
occurred, and the incidence of acute rejections did not differ based on whether a pretransplant crossmatch was performed or not.
The stimulus of the immune system is exponentially more intense with the transplantation of genetically unmodified xenografts; hyperacute rejection
and graft thrombosis would occur immediately due to the presence of discordant species-specific antibodies.
The central problem with transplanting animal organs into humans is hyperacute rejection
, which can destroy an organ's function within an hour.
There are also a number of reports of a combined transplant enabling successful kidney grafts, despite a positive crossmatch between donor and recipient, which usually results in hyperacute rejection
of the kidney [64-67].
The authors identified five biologic hurdles: hyperacute rejection
, acute vascular rejection, accommodation, cellular rejection, and chronic rejection.
Due to the immaturity of the babies' immune systems, the researchers said none experienced hyperacute rejection
, and no morbidity was attributable to ABO incompatibility.