and rat-human hybrids to term following a
change in Japanese regulation in March 2019.
Pending approval of the Japanese government,
the embryos no longer have to be destroyed after
14 days of development. Nakauchi’s hybrids will
be brought nearly to term in surrogate animals,
with mouse embryos developing for 14.5 days and
rats for 15.5; full-term is around 19 to 21 days for
mice, and 21 to 26 days for rats.
Similarly, the Spanish newspaper El País
reported in July that a team from the Salk
Institute in California had created human-
monkey hybrid embryos. The team, led by Prof
Juan Carlos Izpisúa Belmonte, carried out the
experiments in China, most likely since the
National Institute of Health in the USA has
placed a moratorium on funding human-animal
hybrid research. The research hasn’t yet been
published, so there are few details about the
work, but the embryos were most likely
SALK INSTITUTE terminated within 14 days.
ANALYSIS REALITY CHECKWhat is the goal of the experiments, and why
create hybrids in the first place?
Last year, more than 400 people in the UK died
waiting for an organ transplant, and over 6,000
are still waiting. Rather than relying on donated
organs, there are several projects working on
manufacturing replacements, from 3D-printed
hearts made of collagen (see p15) to bionic
pancreases. Human-animal hybrid experiments
are working towards the same goal: using animals
to grow tailored organs ready for transplant, with
a low risk of rejection. Nakauchi plans to grow a
pancreas made of human cells. In previous 2“Human-animal hybrid experiments
are working towards the same goal:
using animals to grow tailored
organs ready for transplant, with
a low risk of rejection”
LEFT: Cells derived from rat stem cells
developing in the heart of a mouse embryo
BELOW: Prof Juan Carlos Izpisúa
Belmonte has been carrying out chimera
experiments in China