Concise Review: Human-Animal Neurological Chimeras: Humanized Animals or Human Cells in an Animal?

Andrew T. Crane, Joseph P. Voth, Francis X. Shen, Walter C. Low

Research output: Contribution to journalReview articlepeer-review

18 Scopus citations


Blastocyst complementation is an emerging methodology in which human stem cells are transferred into genetically engineered preimplantation animal embryos eventually giving rise to fully developed human tissues and organs within the animal host for use in regenerative medicine. The ethical issues surrounding this method have caused the National Institutes of Health to issue a moratorium on funding for blastocyst complementation citing the potential for human cells to substantially contribute to the brain of the chimeric animal. To address this concern, we performed an in-depth review of the neural transplantation literature to determine how the integration of human cells into the nonhuman neural circuitry has altered the behavior of the host. Despite reports of widespread integration of human cell transplants, our review of 150 transplantation studies found no evidence suggestive of humanization of the animal host, and we thus conclude that, at present, concerns over humanization should not prevent research on blastocyst complementation to continue. We suggest proceeding in a controlled and transparent manner, however, and include recommendations for future research with careful consideration for how human cells may contribute to the animal host nervous system. Stem Cells 2019;37:444–452.

Original languageEnglish (US)
Pages (from-to)444-452
Number of pages9
Issue number4
StatePublished - Apr 2019

Bibliographical note

Funding Information:
We acknowledge Vibha Savanur, Antony Crane, and Georgette Danczyk for compiling and organizing background literature for this review and to Marra Evans who contributed illustrations for the figure and graphical abstract.

Publisher Copyright:
© AlphaMed Press 2019


  • Behavior
  • Blastocyst complementation
  • Cell transplantation
  • Chimera
  • Cognition
  • Stem cells


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