Non-human primate chimeras make a move

Imagine harvesting individualized human organs for transplantation from animal donors. Recent experimental progress on interspecies chimera has elevated this vision onto a more realistic level Pioneering work by Kobayashi et al. used rat pluripotent stem cells (PSC) to complement pancreas-deficient mouse blastocysts for the generation of chimeric interspecies mice with a rat pancreas, and Matsunari et al. generated pigs carrying a stem cell derived chimeric pancreas (1,2). However, the interspecies blastocyst complementation method to generate chimera for example from human PSC in a non-human host faces numerous prohibitive hurdles: Besides anatomical differences stands its inefficiency since chimerism across many tissues is highly toxic, and the problem increases with evolutionary distance. Even the evolutionary close rat-mouse chimeras produced by injection of mouse embryonic stem cells (ESC) into rat blastocysts can only accommodate a low degree of chimerism, yet already show morphological abnormalities (3). This observation seems to justify pessimism as to whether animal-human chimerism can be achieved by standard blastocyst complementation. The use of human PSC for the generation of interspecies chimera appeared even more challenging as it was not possible until now to even generate chimeric non-human primates using same species monkey PSC. This challenge has now been tackled in an elegant study by Chen et al. (4).