Human Cells Grown In Animals

Scientists have successfully transplanted human stem cells into pigs that were especially genetically modified for the purpose. Once implanted, the cells thrived, leading the researchers to believe they are one step closer to finding treatments for a number of incapacitating human diseases.

Stem cells are undifferentiated biological cells that can differentiate into specialized cells and can divide (through mitosis) to produce more stem cells.

In mammals, there are two broad types of stem cells: embryonic stem cells, which are isolated from the inner cell mass of blastocysts, and adult stem cells, which are found in various tissues. 

In adult organisms, stem cells and progenitor cells act as a repair system for the body, replenishing adult tissues.

In a developing embryo, stem cells can differentiate into all the specialized cells—ectoderm, endoderm and mesoderm (see induced pluripotent stem cells)—but also maintain the normal turnover of regenerative organs, such as blood, skin, or intestinal tissues.

Stem cells can also be taken from umbilical cord blood just after birth. Of all stem cell types, autologous harvesting involves the least risk. By definition, autologous cells are obtained from one's own body, just as one may bank his or her own blood for elective surgical procedures.

One of the major hurdles in stem cell research is the rejection of transplanted cells by the hosts. The ability to ensure that pigs will accept human transplants is a major leap forward for research into stem cell therapy, and could aid in developing treatments for patients suffering from severe immune deficiency.

Research into the possibilities of regenerative medicine has previously relied heavily on rodents as test animals. However, significant differences between the immune systems of mice and those of humans has limited the applicability of the findings.

“Many medical researchers prefer conducting studies with pigs because they are more anatomically similar to humans than other animals, such as mice and rats,” according to Randall Prather, one of the authors of the study and Curators Professor of reproductive physiology at the University of Missouri.

“Physically, pigs are much closer to the size and scale of humans than other animals, and they respond to health threats similarly. This means that research in pigs is more likely to have results similar to those in humans for many different tests and treatments.”

Prather led the development of the special line of genetically modified pigs used in the study. The animals have a compromised immune system which mimics that of human patients with immune deficiency problems and ensures that the transplanted cells are not rejected. 

Provided the pigs can be protected from exposure to pathogens, they could be used to trial stem cell therapies as well as whole-organ transplants.