The team led by the Spanish scientist has managed human cells to survive and integrate in pig embryos during early stages of development.

These cells have also generated organs such as pancreas, eye or rat heart in healthy mice who develop and lead a normal life.

The group of scientists led by MD Juan Carlos Izpisua, professor of Gene Expression Laboratories at the Salk Institute for Biological Studies and PhD of Development Biology of the Catholic University San Antonio of Murcia (UCAM), have applied technologies of genetic edition and pluripotent cells to study the organism embryo development, the causes of the illnesses, develop new medicines and generate organs for transplantations.

Last scientific advances leading to the generation of cells, tissues and organs in organisms of different species offer an opportunity without precedent to solve serious problems concerning human health, particularly the need of organs and tissues for transplantations.

In the report published in Cell, Spanish researchers from the Catholic University San Antonio of Murcia (entity that promotes and finances this project), are involved in this multidisciplinary and international group. They together with Pedro Guillén Foundation, CEMTRO Clinic in Madrid, the University of Murcia and Clinic Hospital of Barcelona describe the progress achieved in the race to integrate pluripotent cells (iPSC) from a species of embryos to a different animal species.

These scientists have created mice with rat eyes, pancreas and heart, by means of the technique CRISPR/Cas9, and have demonstrated that functional organs of a species can develop in different species organisms. For the first time, these experts have been able to integrate human cells in pig and cow embryos, ushering in the beginning of the generation of transplantable human organ.

“Our discoveries in the generation of inter-specific  chimeras are a hope for the science and medicine advance, providing an unprecedented  opportunity to study the first stages of the embryo development and the organ formation as well as a new way to study medical therapies”, explains professor Juan Carlos Izpisua. “Our observations show that an organism of a species can develop and lead a normal life carrying an organ constituted by other species cells. These technologies provide a very powerful tool to study the species evolution, the development of diseases and can as a last resort lead to the possibility of generating human organs functional for transplantation”.

 An “inter-specific chimera” is an organism made up by cells from different species. The word ”chimera” originally described mythological creatures or deities in the polytheistic religions. In science, inter-specific chimeras are becoming powerful tools in basic research for the development of clinical implementations.

In one of the experiments performed in the article published in Cell, the researchers used CRISPR/Cas9 gene edition technology to deactivate the gene producing the pancreas in mouse embryos. Next, they inserted rat pluripotent mother cells, containing the intact gene for the pancreas generation in those embryos and they implanted them in a receptor female mouse to continue its growing. The embryos developed normally, except for the fact that in every mouse was growing a rat pancreas.

This initial experience led the team to generate other organs, such as eye and heart. Besides that, surprisingly, rat pluripotent mother cells were able to generate a gallbladder in the mouse, organ that is not present in rats. “This experiment revealed a great secret: the mouse embryo was able to unblock the route, inhibited in the rat evolution, for the formation of the gallbladder”, said Jun Wu, scientist in the research team of professor Izpisua laboratory. “These results show the relevance of the ambience or the receptor animal niche in organs development and the evolutionary specialization”. Wu also highlighted that the experiment with mice and rats showed that the growing of human organs in animals for the transplant could be possible. “The mice were healthy and led a normal life, which shows that their development took place correctly. Estrella Núñez, UCAM Research Vicerrector and also author of the article points out: “It has been hard work, in which each researcher from the different institutions involved has contributed with his/her skill and talent to develop the study involving different disciplines together with the most innovative techniques in order to try and give a response to current medicine needs”.

Nevertheless, to generate human organs in mice and/or rats has no sense, because rodents are too small and have a physiology very different from human’s one. Hence the research team decided to work with pigs, whose size and organs development times are more equivalent or similar to those of human beings. After generating several kinds of human induced pluripotent mother cells (iPSC), these were inserted in pig embryos, which later on were implanted in receptor mother pigs. The experiment was stopped at the fourth week of pregnancy to assess the efficacy and certainty up to that stage. Some of the embryos showed that the human cells had specialised and become  precursor of the different tissues, although the rate of success and the level of contribution of the human cells in pigs was much lower than in the case of rat and mice. These results are the proof of the concept of integration of human cells in a big animal species.

In this sense, Emilio Martinez, CATEDRÁTICO of the Medicine and Animal Surgery of the University of Murcia and also author of the article, considers that with the improvement of the protocols used, the efficiency of the human-pig system will increase highly and sooner than expected we could see the differentiation of iPS human cells inside pig’s organ previously deactivated, by using CRISPR/Cas9, as it has taken place in the rat-mouse system. Scientists warn the research is at its first stages and there are still lots of important challenges to face before developing medical therapies based in this technology.

The ultimate target of the research with chimeras is to know if we can use techniques of gene edition and pluripotent cells to generate tissues and human organs compatible, says Dr. Izpisua. “These studies open new perspectives in the knowledge filed of species evolution, human embryogenesis and diseases development; knowledge difficult to obtain with current methodologies”.

More information:

Magazine: Cell

Title: Interspecies chimerism with mammalian pluripotent stem cells

Autores: Jun Wu, Aida Platero-Luengo, Masahiro Sakurai, Atsushi Sugawara, María Antonia Gil, Takayoshi Yamauchi, Keiichiro Suzuki, Yanina Soledad Bogliotti, Cristina Cuello, Mariana Morales Valencia, Daiji Okumura, Jingping Luo, Marcela Vilariño, Inmaculada Parrilla, Delia Alba Soto, Cristina A. Martínez, Tomoaki Hishida, Sonia Sánchez-Bautista, M Llanos Martínez-Martínez, Huili Wang, Alicia Nohalez, Emi Aizawa, Paloma Martínez-Redondo, Alejandro Ocampo, Pradeep Reddy, Jordi Roca, Elizabeth A. Maga, Concepción Rodríguez Esteban, W. Travis Berggren, Estrella Núñez Delicado, Jerónimo Lajara, Isabel Guillén, Pedro Guillén, Josep M. Campistol, Emilio A. Martínez, Pablo Juan Ross, Juan Carlos Izpisua Belmonte.