The global effort by scientists to find a way to grow human replacement organs in other animals may have been nudged forward by researchers at the Salk Institute for Biological Studies in La Jolla.

A team led by the Salk’s Juan Carlos Izpisúa Belmonte says it has combined a newly identified type of human stem cell with a mouse embryo allowed to partially develop. This resulted in growth that, at least in theory, could have produced distinct human tissues if the process had been allowed to proceed further.

The human stem cells grew in harmony with the mouse embryo cells, integrating in a way that previous human-animal combinations, or “chimeras”, failed to do.

The ultimate goal is to produce adult animals with human organs that can be transplanted. Since mice are too small for this purpose, the process – if the research bears fruit — would be done in larger animals.

The Salk published its findings Wednesday in the journal Nature, two days after Synthetic Genomics Inc., a biotech located a half-mile away, said it had made progress toward genetically engineering pigs to produce organs that the human immune system will accept.

The Salk and Synthetic Genomics — like institutions worldwide — are trying to find a solution to the critical lack of lungs, livers, hearts and other organs that are available for transplant. Patients needing transplant may wait years before a suitable organ is available, and some die on the waiting list. Most of the organs are unsuitable because they don’t match the patients’ immune system.

Izpisúa Belmonte told U-T San Diego that producing the harmonious merger of human and animal cells in a single organism is a significant advance toward that goal. Previous attempts had created animals with isolated patches of human cells that didn’t function as part of the animals.

“Using this new type of stem cell, we were able, for the first time, to truly seamlessly integrate the human cells into non-viable mouse embryos that had been partially dissected,” Izpisúa Belmonte said.

“The human cells began to generate cell types that are theoretically capable of producing all of the cells, tissues and organs of the body. This is a critical step for studying early human development and evolution and for potentially developing regenerative medicine techniques for growing human organs.”

Izpisúa Belmonte also said that similar technique might work in pigs, which are large enough to grow organs that could be used in humans.

The newly discovered stem cells, called region-selective pluripotent stem cells (rsPSCs), preferentially colonizes specific regions of the embryo. Matching human stem cells of this type with corresponding mouse embryo regions resulted in unified growth of the combined cell types.

Pluripotent stem cells can be derived from embryonic stem cells or artificially created from adult cells derived from skin tissue or other organs, called induced pluripotent stem cells. Their potential to create virtually any tissue type makes them attractive as the raw material from which to produce new organs and tissues.

MORE INFO: (5/5/2015)