This Pig is not a PERV: Major Xenotransplantation Advance

One of the most exciting fields of medicine which represents the integration of several disciplines is organ transplantation. The advances that have made such an innovative and life-enhancing feat possible were the result of breakthrough insights by heroic pioneers in the life sciences. However, despite the feasibility and almost routine nature of solid organ transplantation today, the full benefits have not been achieved. It is basically universally known that there are not enough organs procured per year to meet the needs of those on waiting lists. Several partial solutions have been proposed including more efficient allocation algorithms, increased public outreach campaigns to increase organ donation, and the use of "high risk" organs but even with all these initiatives combined demand is still outpacing supply. 

Using organs from animals closely related to humans -- such as pigs -- has been a proposed fix that has, unfortunately, not been able to reach fruition for several reasons. One reason xenotransplantation from pigs has been stalled is the presence of viruses integrated into the chromosomes of the pig. The fear is that porcine endogenous retroviruses (PERVs) could reactivate in the transplanted human, as several viruses can do in the presence of immunosuppression, and cause unknown effects which may be benign or not. A xenozoonosis would have major implications as it would virtually unprecedented, with no treatment protocol (though HIV drugs may work), and unknown contagiousness. To date, pig heart valves, pig skin, pig-derived insulin, and encapsulated pig islet cells are being used in humans with no evidence of PERV infection. 

A team from Harvard, which included the visionary George Church, recently harnessed the power of CRISPR to clean pig DNA of these viruses and allow PERV-free piglets to be borne. The study was published in Science. This is an unequivocally major achievement and has removed a major roadblock while illustrating the enormous value of CRISPR in furthering human life. 

Now that this hurdle has been cleared, it will be necessary to ensure that the human immune system is not too aggressive in rejecting the organ, which will need some further genetic modification in order to not tip off the immune system to its origin.

There is no timeline for how long it will be before pig xenotransplantation is adopted on a larger scale as protocols and regulations that govern these procedures will have to be rewritten, but each step forward should be applauded.