In a recent interview with Scientific American, a Spanish biologist named Juan Carlos Izpisua Belmonte at the California-based Salk Institute claimed that Pope Francis had given an ethical thumbs-up to research on animal/human genetic hybrids.

After that report made the rounds, the Vatican issued a swift denial: “It’s absolutely unfounded that Pope Francis has pronounced himself with an encouragement for this type of research,” the Rev. Federico Lombardi told the Italian news outletIl Sismografo.

One of Catholicism’s leading experts on bioethics now says it was always implausible the pope would sign off on animal/human hybrids, called “chimeras,” in such a sweeping fashion, because “there’s no way to give blanket approval for something like this … it has to be looked at on a case-by-case, proposal-by-proposal basis.”

The Rev. Tad Pacholczyk, director of education for the Philadelphia-based National Catholic Bioethics Center, told Crux Thursday that when it comes to the ethics of mixing materials between humans and animals, “the devil is always in the details.”

The type of research Izpisua is proposing involves implanting human cells into embryonic pigs and other farm animals in order to grow human hearts, kidneys, and other organs, primarily to alleviate the donor shortage for organ transplants.

The aim is to induce one species to grow an organ of the other, not a combination of two species.

Initially, some Catholic observers wondered if such research might run afoul of a 2008 Vatican document called Dignitas Personae, which warned of an “offense against the dignity of human beings on account of the admixture of human and animal genetic elements capable of disrupting the specific identity of man.”

According to Pacholczyk, however, that’s not on-point, because the 2008 document was referring specifically to a procedure known as “nuclear transfer,” which was being explored at the time as an alternative way of obtaining human embryonic stem cells without having to persuade women to donate eggs.

Because the Catholic Church is convinced that life begins at conception, it has always opposed any form of research or medical therapy that involves the creation or destruction of human embryos.

“Dignitas Personae does not apply to what [Izpisua] is talking about,” Pacholczyk said.

In principle, he said, the research that biologists such as Izpisua are pursuing could pass ethical muster if three conditions are satisfied:

• The procedures must not involve the creation or destruction of human embryos.
• They must not involve the replication of major pillars of human identity in animals, such as the brain system.
• They must not involve the production of human gametes, meaning the basic building blocks of human reproduction.

Assuming that’s the case, he said, and that technical challenges can be worked out – for instance, avoiding the risk of transferring diseases from one species to the other – then in principle, the Church likely would not object.

“We use animals for a wide panoply of purposes,” Pacholczyk said. “We eat them, we use them to make clothing, we use them for basic scientific research … so if we can use them to produce organs to save people’s lives without crossing fundamental ethical lines, presumably it would be morally non-problematic.”

“Kidneys, for instance, are in tremendously short supply when it comes to transplants, and if we can have pigs producing human kidneys, it would be a great blessing for very many sick people,” he said.

At the same time, Pacholczyk insisted that the ethical boundaries of such research should be clearly identified in advance.

“It demands very careful ethical discernment, drawing lines that include barriers, meaning things we agree we will not do,” he said. “That’s where the Church often parts company with researchers, who say in principle there’s nothing you can’t do as long as the benefits are compelling enough.”

Some reporting of the pope’s alleged endorsement set it up in opposition to the US National Institutes of Health, which last September imposed a ban on funding of research into animal/human hybrids until ethical guidelines can be developed.

In truth, Pacholczyk said, the Church and the NIH seem to be on roughly the same page.

“Funding is not a question the Church would answer generically in terms of all chimeric research,” he said, “but it certainly would agree that ethical lines need to be demarcated prior to providing funding that would encourage further research.”

A priest of the Fall River, Massachusetts, diocese, Pacholczyk is also a neuroscientist. He said he’d love to have the chance to sit down with fellow scientists such as Izpisua to hash out those ethical lines.

“This is an area where a dialogue with the Church could be very fruitful,” he said. “I think many people in the Church and among the general public would love to see that kind of high-level dialogue occurring in a responsible way.”

“Otherwise, scientists often seek to become arbiters over ethics,” he said, “and that’s a little bit like the fox guarding the henhouse.”