Because transplanted cells and tissues are not immediately perfused with recipient blood after transplantation they are not hyperacutely rejected. Clinical trials using such transplants have therefore progressed further compared to clinical trials with solid organ transplants. Porcine pancreatic islets have been transplanted into a number of patients with diabetes(45) and foetal porcine neural cells have been injected into a significant number of patients (more than 50) suffering from Parkinson's Disease, Huntington's Disease or strokes.(⁴⁶) Only limited clinical benefit has been reported to date. A significant number of patients with acute liver failure have taken part in multicentre studies using pig hepatocytes in artificial devices (bioartificial liver) with promising initial results.(⁴⁷)

There are considerable differences of opinion as to how long a pig organ should survive in a non-human primate before one proceeds to clinical trials involving the transplantation of pig organs into humans. Some suggest that clinical trials on humans could begin only after routine survival periods of ninety days or more have been obtained for pig organs which are transplanted into nonhuman primates and which must perform life-supporting functions.(⁴⁸) At present, survival periods for this type of xenotransplants vary from a few weeks to about three months, and three-month survival is certainly not routine.(⁴⁹) Clearly, a significant improvement on current figures must be achieved before clinical trials using solid organ xenografts are warranted.

However, while survival of pig organs in non-human primates at present is not sufficiently long to consider transplanting such organs into humans as a permanent replacement organ, the option of using pig organs as "bridge' transplants may well be possible in a shorter time.