The experiments made with human-animal hybrids were the subject of a great controversy in U.K., where scientists were granted permission to use animal eggs in human cloning process in 2007.

Although human clones appear similar to human-to-animal clones, the process of reprogramming the donor human cells is different. The research was based on the idea that cloned animal eggs could be used to create human embryonic stem cells, which have the ability to develop into any tissue of the body and therefore could be used to replace damaged tissues.

 

For their research, scientists have transferred human DNA into human, cow and rabbit eggs and grew them into early embryos. The scientists observed major differences in patterns between embryos from human eggs and embryos taken from animals. The findings lead to a discouraging conclusion: production of patient-specific stem cells using animal embryos is impracticable.

Lanza’s study was published online by the journal Cloning and Stem Cells. Researchers not involved in the study described the results as “very disappointing.”

 

The creation of human animal hybrid embryos has become legal in the U.K. under the Human Fertilisation and Embryology Act released last year.  

Many stem cell studies are based on the idea of inserting a person’s DNA into an egg and growing an embryo in order to obtain stem cell lines that could be used to create transplant tissue that avoids the risk of rejection. Scientists use human embryos in their studies, but their use has been controversial since 1978, when religious groups and the Catholic Church said it is immoral to “produce human embryos destined to be exploited as disposable ‘biological material.’”

 

Given this situation, many scientists work with IPS cells, which are stem cells derived from skin. Induced pluripotent stem cells have all the qualities of embryonic stem cells, but they are produced from adult cells, an alternative to the technique which involves taking human embryos. They can be cultured into any desired tissue, from heart muscle cells and blood cells to brain cells. But these cells are created using harmful viruses, which can integrate into the genome and pose a risk of cancer. Scientists at Massachusetts General Hospital and Harvard Medical School have managed to use a harmless virus called adenovirus, which doesn’t integrate the DNA into the cells, but the method has been tested only on animals. If the new method works with human cells as well, the discovery could lead to advances in cell therapy and treatments of incurable human diseases, including heart problems, Alzheimer’s or Parkinson’s.