PERV was not detectable in any patient despite the presence of pig cells observed in 23 patients up to 8.5 years after the original procedure. These findings demonstrate that infection from PERV is either not occurring, is occurring and is being removed by the recipient's immune system, or is occurring at a very low level that is beyond the limits of our current detection techniques. PERV cannot be considered highly infectious and, if transmitted at all, cannot be highly aggressive as there was no detectable illness, side effects or other morbidity even in those patients that had received their therapy many years earlier. The possibility of a very low level of infection with a long latency to disease was not ruled out by this study and cannot be ruled out by any study excepting a monitored clinical trial of xenotransplantation. A thoughtful process of trial and error characterises the emergence of all complex fields of medicine with the full knowledge that failures and setbacks are bound to occur.
Xenotransplantation is no exception.
The first recipients of pig organs will need to submit to a high level of vigilance to assess retroviral infection. The implications for the individual and his or her intimate contacts will be profound but are likely to be preferred to years of waiting followed by almost certain death. The risk to broader society will be much more remote than that to the individual because, unlike those exposed to HIV, recipients of pig organs will be a known and already highly monitored section of the population. Both the FDA and British authorities are moving towards approval of small-scale human trials of xenotransplantation and their efforts need applause and encouragement. The alternative is to abandon xenotransplantation and forever deny a therapy that could save tens of thousands of lives.