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Towards the Development of Xenogeneic Organs with Donor-derived Endothelium

Review of “Generation of human endothelium in pig embryos deficient in ETV2” from Nature Biotechnology by Stuart P. Atkinson

While the injection of human pluripotent stem cells (hPSCs) into blastocysts lacking a developmental regulatory gene for an organ of interest can allow for the generation of xenogeneic organs [1], any organs produced retain host-derived endothelium that can elicit rejection [2, 3]. Researchers led by Mary G. Garry and Daniel J. Garry (University of Minnesota, Minneapolis, MN, USA) previously established ETS Variant Transcription Factor 2 (ETV2) as a master regulator of hematoendothelial lineages [4-6], and in their most recent study, the team sought to explore the potential of embryo complementation with human PSCs to rescue ETV2-mutant embryos and generate donor-cell derived hematoendothelial cells [7].

Das et al. first evaluated ETV2-null pig embryos to confirm that they lack hematoendothelial lineages and phenocopy Etv2-null mice and then assessed the consequences of human induced pluripotent stem cell (hiPSC) injection into pig parthenogenetic embryos, which are developmentally incompetent embryos generated by the activation of a mature oocyte. Encouragingly, injected hiPSCs successfully integrated, survived, and proliferated in the porcine environment, thereby providing support for the subsequent embryo complementation studies.

The authors assessed ETV2-null pig embryo complementation at embryonic day 17 and 18 following the injection of hiPSCs and embryo transfer to surrogates. Interestingly, analyses found evidence for the responsiveness of injected hiPSCs to developmental cues and differentiation into the endothelial lineage; however, injected hiPSCs tended to undergo programmed cell death leading to the low-efficiency formation of human-porcine chimeras. To counteract this problem, the authors engineered hiPSCs that overexpressed the BCL2 anti-apoptotic factor and employed these cells for complementation using the ETV2-null porcine blastocysts. This approach provided for a greater-than fivefold increase in human-pig chimera formation efficiency and evidence of endothelial lineage differentiation of BCL2-overexpressing hiPSCs.

Overall, the authors provide evidence for the feasibility of human-pig chimeric embryo formation; however, they do underscore the need to increase efficiency, ensure the lineage-specific contribution of hiPSCs, and study immunogenicity in depth. 

For more on the future generation of xenogeneic organs with donor-derived endothelium, stay tuned to the Stem Cells Portal!

References

  1. Wu J, Platero-Luengo A, Sakurai M, et al., Interspecies Chimerism with Mammalian Pluripotent Stem Cells. Cell 2017;168:473-486.e15.
  2. Kobayashi T, Yamaguchi T, Hamanaka S, et al., Generation of Rat Pancreas in Mouse by Interspecific Blastocyst Injection of Pluripotent Stem Cells. Cell 2010;142:787-799.
  3. Usui J-i, Kobayashi T, Yamaguchi T, et al., Generation of Kidney from Pluripotent Stem Cells via Blastocyst Complementation. The American Journal of Pathology 2012;180:2417-2426.
  4. Ferdous A, Caprioli A, Iacovino M, et al., Nkx2–5 Transactivates the Ets-related protein 71 Gene and Specifies an Endothelial/endocardial Fate in the Developing Embryo. Proceedings of the National Academy of Sciences 2009;106:814.
  5. Rasmussen TL, Kweon J, Diekmann MA, et al., ER71 Directs Mesodermal Fate Decisions During Embryogenesis. Development 2011;138:4801.
  6. Koyano-Nakagawa N, Kweon J, Iacovino M, et al., Etv2 Is Expressed in the Yolk Sac Hematopoietic and Endothelial Progenitors and Regulates Lmo2 Gene Expression. STEM CELLS 2012;30:1611-1623.
  7. Das S, Koyano-Nakagawa N, Gafni O, et al., Generation of Human Endothelium in Pig Embryos Deficient in ETV2. Nature Biotechnology 2020;38:297-302.