Posted by Al Gordon on October 16, 1997 at 21:11:13:
In Reply to: Re: Porcine Virus posted by tom cavanagh on October 16, 1997 at 14:46:25:
Tom:
The risk of zoonotic transfection of islet xenotransplant recipients is a very theoretical risk that has never been demonstrated. I find it distressing that you can tolerate perpetuating the horrors of diabetes, a risk that is definitely NOT theoretical, to avoid a risk that has yet to be manifested.
Looking at some of the key issues:
1. You quoted the warning sent to the FDA regarding xenotransplantation. This letter was entitled "Draft Public Health Service Guidelines on Infectious Disease Issues in Xenotransplantation" headed by Jon Allan of the Southwest Foundation for Biomedical Research, dated December 20, 1996. In this letter, the scientists caution against the use of baboons and other non-human primates as sources of organs, while stating that "swine represent the future species of choice."
2. One of the biggest concerns in the above letter to FDA is the fact that the recipient is immunosuppressed for a whole organ transplant, while this is not be the case for islet transplants. Islet cell recipients retain an uncompromised immune system.
3. As for the Pig Endogenous Retrovirus (PERV), there are commercial herds in the United States (not even special SPF herds) in which PERV is not present. Hence, there can be no risk of transfection from a virus that is not present.
4. Even if PERV is present, the following questions need to be asked:
* Has this pathogen ever passed from a pig to a human? Humans and pigs have mixed for thousands of years. There have likely been millions of cases of pigs butchered by humans who had open wounds on their hands or other means of pathogen entry into their bodies. Yet transfection has never been a public health issue.
* Is PERV replication-competent?
* If it is replication-competent, can it cause disease in humans?
* If it can cause disease in humans, can this disease be spread to other humans, or will it merely injure the host?
Considering the chain of events needed before we even have a public health risk, and considering the KNOWN risks of diabetes, I believe the risk/reward ratio is highly favorable.
5. Consider the risks that we accept every day. For example, hospitals will treat people who are HIV-positive. This is no theoretical risk. If a healthcare worker contracts HIV from a patient, that worker can then spread this disease throughout his or her circle of intimate contacts. Should we refuse to provide medical care to people with AIDS? Of course not, just as we should not delay or prevent promising treatment for diabetes based on a purely theoretical and unproven risk. Remember, while we are "exercising caution" over an unsubstantiated risk, diabetes is crippling and killing thousands of people. This is not judicious caution, it is totally irresponsible.
6. We accept the risks of human-to-human organ transplants, yet almost every pathogen present in the donor can pass to the recipient, especially considering that the recipient is immunosuppressed. Yet we accept this risk in return for the life-saving reward of organ transplantation.
7. Donor pigs can be bred in a specific-pathogen-free (SPF) environment with the sole objective being the provision of clean islets for curing diabetes in humans. This option is obviously impossible in human-to-human organ transplants.
8. You mentioned in your message that "the relative dissimilarity between pigs and humans makes pigs a better choice for xenotransplantation, but not one which is guaranteed to be risk-free." If we are only willing to accept risk-free advances, we may as well close the United States to all further progress. I do not know of any advance that is "risk-free".
Tom, if I sound a little strident, please forgive me. However, I truly believe that no parent of a diabetic child would ever accept the arguments presented in your message. Please remember the enormous suffering that you are accepting when you counsel caution and patience in the face of an unproven and theoretical risk.
Al