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Human-Animal Hybrids from Stem Cells: What are They?

The formation of human-pig or human-cow embryos is among the latest scientific “advances” being questioned by ethicists.

Such chimeras are formed by combining [1] genetically-distinct cells, in this case human cells and animal cells.

The process, as outlined by Cell Journal, involves the in vitro grafting of human pluripotent stem cells [2] (hPSC)—obtained by undifferentiating human skin cells back to embryonic-like stem cells—into cattle or pig blastocysts.

More specifically, the process involves the following steps:

  1. Pig embryos are produced in vitro and cultured until they reach the blastocyst stage.
  2. hPSC are obtained from human skin cells by undifferentiating them, i.e. returning the cells to their original state, the state they occupied before they became skin cells.
  3. The hPSC are then injected into the pig blastocyst, using a laser to perforate the blastocyst cavity. This method results in nearly 100% injection effectiveness and 90% embryo survival.
  4. After injection, these blastocysts are cultured for an additional two days before analysis.
  5. Embryos that, upon analysis, remain healthy, are transferred to surrogate pigs, resulting in some pregnancies.

Post-implantation analysis indicates that these embryos have both pig and human cells in their bodies, i.e chimeras have been formed.

It is worth noting that the levels of chimerism from the transfer of human cells into pig embryos were much lower than the levels observed with rat-mouse chimeras.

Taking into consideration all published studies that have used the mouse as the host species, it is probably appropriate to conclude that interspecies chimera formation involving hPSC is inefficient. This apparent inefficiency results from species-specific differences between human and mouse embryogenesis.

Other studies respecting hPSC and embryos reflect the same inefficiencies.

While these processes have produced various levels of “success” to date, it is likely that alternative CRISPR/Cas9 (gene editing [3]) delivery methods, and improved culture conditions for manipulated embryos will further improve and optimize the process.

The Purported Goals Of The Research

The development of chimeras, it is argued, might allow human organ generation in animals whose organ size, anatomy and physiology are closer to humans.  Furthermore, the process may enable science to gain insights into species evolution, embryogenesis and human disease.

The Ethical Analysis

In obtaining hPSC though undifferentiating human skin cells, we create embryonic-like stems cells without harvesting actual embryonic stem cells—which necessitate the killing of human embryos.  This sounds wonderful, yet the process leaves room for questioning:

If there is no apparent biological difference between hPSC and actual embryonic stem cells—the hPSC even pass through a totipotent stage, a key attribute of early stages of embryo development—could what is called an embryoid body, a stage in the production of hPSC, actually be a human embryo?

The potential of interspecies blastocyst complementation could lead to the humanizing of a pig embryo and combining or substituting a pig/human identity.  Therefore, it cannot be definitively concluded that the resulting embryo is not a human embryo

Of course after the grafting, the new embryo is treated as a thing, subject to in vitro culture, high mortality, malformations, killing and development in an animal womb.  All of these actions violate the intrinsic value (dignity) of all human beings regardless of how they start their lives or their current stage of development.

Respecting organ generation, other, less troubling methods are available.  An approach that raises no ethical dilemmas and is meeting with good results is the use of adult stem cells (postnatal) to either repair damaged organs in situ (in place) or to create organs in the laboratory.  Regarding efficacy, xenografts—the transplanting of an organ that comes from an animal—and xeno-generating transplantable human tissues and organs, both result in higher risks of rejection.

Finally, as we have noted before, it is not clear if hPSC cause cancer, as has been seen in other studies.

Science must respect the value of every human being and can never use a person as an object.  To use and kill one human being to cure another is a clear violation of the therapeutic principle [4].  Adult stem cell research and therapies are the ethically-superior path to follow as they respect ethical principles and are yielding results.