The Ethics of Human-Animal Chimeras

Chimeras  are organisms  composed  of cells or tissues from more than  one individual.  Chimeras  have been produced   for  research   for  many  years,  but  when human  and animal  cells are mixed in the laboratory, there is a clear need for heightened  ethical considera- tion.  Cells from different organisms can be combined either in the early developmental stages (for example, introducing human  cells into  a mouse  blastocyst  to observe  certain  developmental processes)  or after  an individual  is fully developed (for example, implanting human stem cell-derived pancreatic  cells into a mouse to  test  their  ability  to  function   in  a living  body). Chimeras are considered  essential for advancing  stem cell research to viable therapies,  since no therapy  can be tested in humans  without research in animals first.



Some people  believe that  the  creation  of chimeras involving human  cells for medical research is moral- ly acceptable  as long as the chimera  has no level of human  consciousness.   Therefore,  research in which it is possible for human  stem cells to produce  part of an  animal’s  brain  should  be conducted with  great care.  The  National Academies’  guidelines  prohibit the introduction of human  cells into  the blastocyst of a nonhuman primate,  or the introduction of any animal or human  cells into a human  blastocyst.  The guidelines also prohibit the breeding  of human-ani- mal chimeras  in the unlikely  event that  any human genetic material  would  be contained in their  reproductive cells.