LEICESTER, United Kingdom – The creation of a human-nonhuman interspecies embryo is “deeply unethical,” according to the UK’s leading Catholic bioethics institute.

The scientific journal Cell published the findings of a U.S.-Chinese team of scientists who placed human stem cells – which have the ability to turn into different types of tissue – into the embryo of a long-tailed macaque monkey, creating a chimera embryo with cells developing from the two different species.

The researchers said they were studying possible methods of creating human organs for transplant, and the embryos were destroyed after 19 days, at which time they claimed they were able to detect human cells still growing in the embryos.

“These experiments are deeply unethical,” said David Albert Jones, the director of the Oxford-based Anscombe Bioethics Centre.

“They cross a moral boundary because they mix human and nonhuman elements at a very early stage of development in a way that raises serious questions about moral status,” he said in a statement.

Jones points out that it is an open question on whether these embryos are human or not.

“It is not apparent what such human-nonhuman chimeras would be like if they were born. It is not clear how far they share the orientation to develop essential human characteristics,” he said.

“It is always wrong deliberately to create a being of uncertain and perplexing moral status. Even though these creatures were destroyed after 19 days, in their short life they raised questions about how we should regard them. Did these embryos have a share in human dignity?” Jones continued.

The lead researcher, Professor Juan Carlos Izpisua Belmonte of the Salk Institute, has made chimeric embryos before, including injecting human cells into a pig embryo, but that was a far smaller percentage of total material, due to the evolutionary distance between pigs and humans.

Jones noted that it is not always wrong to mix human and nonhuman cells, “where there is no ambiguity,” and where it is done for legitimate medical reasons.

“It can be morally acceptable to introduce human cells into experimental animals in medical research. It can be morally acceptable to transplant tissues from a nonhuman animal into a human being if this can be done safely,” he explained.

“What is wrong is to create real uncertainty or perplexity, as when scientists in the 1920s tried to cross human beings with nonhuman primates,” he said, referring the experiments of Soviet scientist Ivanovich Ivanov, who attempted to crossbreed humans and apes through artificial insemination.

“It is the closeness of the species and the early stage of development that creates the disturbing ambiguity,” Jones said.

Professor Julian Savulescu, the Director of the Oxford Uehiro Centre for Practical Ethics and Co-Director of the Wellcome Centre for Ethics and Humanities at the University of Oxford, said the most difficult issues arising from the experiment lie in the future.

“This research opens Pandora’s box to human-nonhuman chimeras. These embryos were destroyed at 20 days of development, but it is only a matter of time before human-nonhuman chimeras are successfully developed, perhaps as a source of organs for humans. That is one of the long-term goals of the research,” he said in a statement.

“The key ethical question is: What is the moral status of these novel creatures? Before any experiments are performed on live born chimeras, or their organs extracted, it is essential that their mental capacities and lives are properly assessed. What looks like a nonhuman animal may mentally be close to a human. We will need new ways to understand animals, their mental lives and relationships before they used for human benefit,” Savulescu said.

Dr. Alfonso Martinez Arias, an affiliated lecturer at the Department of Genetics of University of Cambridge, said he thought the Cell article overstated what the researchers said they achieved.

“I do not think that the conclusions are backed up by solid data. The results, in so far as they can be interpreted, show that these chimeras do not work and that all experimental animals are very sick,” he said.

Izpisua Belmonte defended his research, saying the goal is not to “generate any new organism, any monster.”

“We are trying to understand how cells from different organisms communicate with one another,” he told NPR.

“This knowledge will allow us to go back now and try to re-engineer these pathways that are successful for allowing appropriate development of human cells in these other animals,” he said.

Jones said there should be an “immediate moratorium” on the creating of embryos that mix human cells with those of nonhuman primates.

“Science requires clear ethical boundaries if it is to maintain public trust and an essential moral boundary is that between the human and the nonhuman,” he said.

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