production of animal proteins by cell systems - New Harvest

limited number of cell types. This is a serious drawback if stem cells are to be used for
biomedical purposes, but for the generation of cultured meat this would hardly be a
disadvantage since cells do not need to differentiate to other cells than myoblasts. For
cultured meat, it is however important that the cells have a minimal self-renewal
capacity since most adult stem cell types cannot be cultured in vitro indefinitely.
iPS cells. Differentiated cells can also be reprogrammed into an embryonic-like state by
introducing four (or less) genetic factors 29 . These cells, called induced pluripotent stem
(iPS) cells, behave exactly like embryonic stem cells in that they self-renew with
conservation of their truly pluripotent character if cultured under the right conditions.
With this technique both mouse and human cells have been reprogrammed 30, 31 . This
new technology has sparked the attention of many biomedical researchers, most
importantly because it opens up a possibility of creating human, even patient-derived,
pluripotent cells without the ethical difficulties that accompany pluripotent cells derived
from human embryos.
For the production of cultured meat, bovine or porcine iPS cells could be useful cells, as
these cells can also differentiate into muscle tissue. There are, however, some difficulties
in this approach. For the first iPS cells that were derived, the DNA that codes for four
transcription factors was delivered to the cells by retroviral infection. As a result, the viral
DNA integrated into the genome of the targeted cells at (multiple) random locations may
lead to uncontrolled behavior of the cells, and makes them non-suitable for large scale
production of food. For the production of an edible product, cells that have been infected
with a retrovirus also cannot be used, because of potential safety hazards. Very recently
however, human iPS cells have been generated that were made free of vector and
transgene sequences and it is anticipated that this technology will advance rapidly 32 .
The iPS technology proceeds rapidly and many labs are working on these cells, and
indeed the first iPS cells from farm animal species have recently been described. In 2009
two articles were published that describe the generation of porcine iPS cells 33 34 .
Although the use of these cells for the generation of an edible product is debatable, it is
clear that these results are very promising.
Bioengineering and bioreactors for tissue cultures
Adult skeletal muscle tissue is characterized by elongated, multinucleated cells with a
highly organized network of cytoskeletal proteins. Skeletal muscle cells can reach
considerable lengths and adult cells have a large myonuclear domain. Culturing skeletal
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