He Jiankui, the Chinese scientist who sparked global outrage in 2018 when he revealed that he had created the first gene-edited children, has put forward a new proposal for modifying human embryos that he claims could help aid the "aging population."

He, who in 2019 was sentenced to three years in prison in China for "illegal medical practices," reemerged last year and surprised the global scientific community when he announced on social media that he was opening a research lab in Beijing.

Since that time, updates on his research posted on his Twitter account have focused on proposed plans to develop gene therapy for rare disease.

But on Thursday, he again courted controversy by posting a new research proposal that experts say is reminiscent of his earlier work, which scientists broadly decried as unethical and dangerous -- with the potential to impact human DNA across generations.

In a succinct, one page document, He proposed research that would involve gene-editing mouse embryos and then human fertilized egg cells, or zygotes, in order to test whether a mutation "confers protection against Alzheimer's disease."

"The aging population is of grave importance as both a socioeconomic issue and a strain on the medical system ... Currently, there is no effective drug for Alzheimer's disease," he wrote in an apparent nod to China's growing demographic burden due to a rising proportion of elderly.

Unlike the science that landed him in jail, this potential experiment involves a kind of abnormal fertilized egg cell generally considered not suitable to be implanted in a woman.

No human embryo would be implanted for pregnancy and "government permit and ethical approval" were required before experimentation, the proposal said.

It's not clear whether He would get approval for such work in China, even if the proposal he put forward were deemed to have merit -- and outside experts say the current proposal is not scientifically sound.

Authorities in China took multiple steps to tighten rules and ethical standards affecting human gene editing in the wake of the revelations about his previous research. They also banned He from engaging in work related to assisted reproductive technology services and placed limits on his work with human genetic resources, according to state media.

But the scientist's release of a new proposal involving gene editing of embryos has scientists and medical ethics experts concerned -- and confused.

"The whole thing is, to put it bluntly, insane," said Peter Dröge, an associate professor at the Nanyang Technological University in Singapore, who focuses on molecular and biochemical genetics.

The proposed research could be seen as a step to explore if such a method of genetic editing could be used in a viable embryo in future, according to Dröge.

Apart from ethical considerations, gene-editing an embryo to address a complex disease that affects people toward the end of their life and doesn't have a clear, single genetic cause is "highly questionable," he said.

"He basically wants to genetically modify the human species so they don't get Alzheimer's," he said. "I'm really surprised that he's coming forward with this again."

Joy Zhang, founding director of the Centre for Global Science and Epistemic Justice at the University of Kent in Britain, said the proposal seemed to be "more of a publicity stunt than a substantiated research agenda."

"However, we do need to take these public claims with vigilance, as it may nevertheless misguide patients and their families, and tint the reputations not just of science in China, but global research effort in this area," she said.

In response to questions from CNN, He said he was "collecting feedback from scientists and bioethicists now" and did not have a timeline for the study.

"I will make a revision to the Alzheimer's disease proposal later. I will not conduct any experiments until I get the government permit, and also get the approval by an international ethics committee with bioethicists from USA and Europe," he told CNN via email.

"I want to emphasize that this is a preclinical study, no embryo will be used for pregnancy in this study. The research will be open and transparent, and all experiment results and progress will be posted on Twitter," he said.

He did not address questions on whether he was limited from conducting certain work in China.

CNN also approached China's Ministry of Science and Technology and National Health Commission for comment.

Controversy and response

In 2018, He, formerly a researcher at the Southern University of Science and Technology in Shenzhen, claimed he had used a gene-editing tool called CRISPR to modify human embryos of twin girls in the hopes of protecting them from HIV. A third genetically edited baby was also born from He's experimentation, a court in Shenzhen later said.

The research sparked a fierce uproar over the ethics of using new and potentially dangerous technology in people and the risk of unintended mutations being passed on not only to the children but potentially any future offspring. It also raised concerns about cracking open the door to a potentially species-changing future of "designer children."

In recent media interviews, He has indicated he feels he acted "too quickly" in conducting the research and has given sparse details on the children, besides indicating they were living "normal" lives.

Genetic manipulation of human embryos -- both viable and nonviable ones -- is typically tightly controlled globally and some countries ban all such research, experts say.

But there is robust global debate around allowing genome editing of human embryos to treat serious genetic conditions or expanding research.

Scientists say genome editing, including in adults, shows promise for one day treating diseases that are currently difficult to treat or cure, like cystic fibrosis or sickle cell disease.

Chinese law does not allow gene-edited human embryos used in research to be implanted into humans, or developed for more than 14 days. All gene editing for reproductive purposes has also long been banned.

Since 2019, a broader raft of regulation of China's biosciences field has added more legal controls and ethical standards to such research, including a major update to national bioethics guidelines earlier this year.

There's also been sharp backlash against He within China's scientific community.

In March, over 200 Chinese scholars released a statement in response to his public activities, including what they said was He's "misleading marketing campaign" over his claimed research plans on rare disease.

They condemned He's "attitude and refusal to reflect on his criminal actions of violating ethics and regulations of gene editing," and called for regulatory authorities to launch a new investigation into He's "alleged re‐violation of scientific integrity, ethical norms, laws and regulations."

"The ethical boundaries shall not be crossed," they wrote.

As for the future of He's research, Canadian bioethicist Françoise Baylis of Dalhousie University said numerous questions should be considered, from whether He has the requisite scientific expertise to test the hypothesis, to whether he can be trusted to follow the rules for research involving humans.

"It is possible for people to learn from their mistakes and to change their behavior ... but many are concerned, however, that He Jiankui may not have learned from his past mistakes," Baylis said.