As regards the therapeutic possibilities, the passage emphasizes the advantages of ----.

Stem cells, unlike all other cells in the body, can copy
themselves indefinitely. So-called adult stem cells are
found in many parts of the body, constantly
rejuvenating the brain, remodelling arteries so blood
can bypass clogs, and growing new skin to heal
wounds. However, adult stem cells have more limited
power than embryonic stem cells, which can turn into
any type of cell in the body. Indeed, scientists are
hoping that embryonic stem cells could be turned into
neurons to fix damaged brains, cardiac cells to repair
damaged hearts, or pancreatic cells to create insulin
for people with diabetes. Maybe they could even be
used to regenerate whole organs. To date, scientists
worldwide have made more than 100 different human
embryonic cell lines. Still, the existing lines have
serious limitations. Most have been grown on a
lattice of mouse embryonic skin cells for support.
Consequently, the human embryonic cells are
contaminated by mouse cells, and though they're still
useful for research, they cannot at present be used
to develop therapies for humans.