Source: Brian Wang 

Researchers injected D-ESCs (embryonic stem cells) into porcine blastocysts (pig pre-embyros) to obtain neonatal interspecies chimeras. The D-ESCs differentiated into all three germ layers in the pig fetuses, consistent with a previous study reporting human/pig chimeras. The human/pig fetuses survived only 28-days, and it was not possible to observe whether the chimeric human ESCs could develop into mature functional cells in pigs for ethical issues. In this study, they confirmed that monkey/pig chimeras can form functional hepatocytes and renal cells in neonatal pigs. These functional cells could be isolated for further research and future clinical application.

The findings could pave the way toward overcoming the obstacles in the re-engineering of heterogeneous organs and achieve the ultimate goal of human organ reconstruction in a large animal.

Interspecies chimerism has been most successful in rodents, and these studies typically achieve a high proportion of chimerism and generate xenogeneic organs. The pluripotency levels of rodent PSCs are the highest known, as they are genuine naïve cells, and they can produce live offspring by tetraploid complementation, which is the most stringent test of pluripotency.

cmESCs (chimeric stem cells mixed into different species) explore the possibility of interspecies chimerism in the development of late embryonic stage pigs. By optimizing the medium in which the cmESCs and injected blastocysts were cultured, we observed an increase in the anti-apoptotic ability of cmESCs and in the extent of chimeric embryo development, resulting in the successful incorporation of xenogenous cmESC grafts into multiple tissues of the neonatal pigs. This work will enable developments in xenogeneic organogenesis towards producing tissue-specific functional cells and organs in large animal models via interspecies blastocyst complementation.

Blastocyst complementation by pluripotent stem cell (PSC) injection is believed to be the most promising method to generate xenogeneic organs. However, ethical issues prevent the study of human chimeras in the late embryonic stage of development. Primate embryonic stem cells (ESCs), which have similar pluripotency to human ESCs, are a good model for studying interspecies chimerism and organ generation. However, whether primate ESCs can be used in xenogenous grafts remains unclear. In this study, we evaluated the chimeric ability of cynomolgus monkey (Macaca fascicularis) ESCs (cmESCs) in pigs, which are excellent hosts because of their many similarities to humans. We report an optimized culture medium that enhanced the anti-apoptotic ability of cmESCs and improved the development of chimeric embryos, in which domesticated cmESCs (D-ESCs) injected into pig blastocysts differentiated into cells of all three germ layers. In addition, we obtained two neonatal interspecies chimeras, in which we observed tissue-specific D-ESC differentiation. Taken together, the results demonstrate the capability of D-ESCs to integrate and differentiate into functional cells in a porcine model, with a chimeric ratio of 0.001–0.0001 in different neonate tissues. We believe this work will facilitate future developments in xenogeneic organogenesis, bringing us one step closer to producing tissue-specific functional cells and organs in a large animal model through interspecies blastocyst complementation.