The cult which claims to have cloned five babies says it has discovered a way of reversing the ageing process.
The Raelian sect believes it can use stem cells to turn back the clock on any part of the body.
It says it has already carried out experiments which involve shortening ageing human DNA, which stretches over time.
Cult chief Dr Brigitte Boisselier, 47, had been set to reveal the details of the work at a conference in London next week. However, organisers, who say the cult used a false name to book their facilities, have now cancelled it.
"As far as I am concerned, this is just not science until they prove it," said Professor Christopher Higgins, director of the Medical Research Council's Clinical Sciences Centre at Hammersmith Hospital, reports London Evening Standard.
Dr Boisselier said the cult had set up a new company, Stemaid, which is using stem cells. At least two patients are being treated; one has a brain tumour and the other is paralysed after a spinal cord injury.
"We have found a way to cure so many diseases and a way to look like you are 17 years old. There will be six to nine months demonstrating and then we will be showing everything," she said.
Dr Boisselier says the real significance of her work is the promise of eternal youth. She said: "A generation is coming that will never die. People can expect to stretch their lives for 50 or 70 years."