The antigens of the galactose induce a "hyperacute rejection response" which must somehow be controlled. But even if this hurdle is cleared, there are still potential problems of acute or chronic rejection, caused by vascular coagulation and the cell-mediated immune system. The PRIT is currently trying to create a transgenic pig which could overcome acute and chronic rejection.
養豬研究所目前培育出攜帶「人類白血球表面抗原基因」的仔豬，可以同時克服異種移植時的Ｔ淋巴球排斥反應，並抑制補體反應之超急性排斥反應。