INDIVIDUAL 鈥減iggy banks鈥� of immune cells might one day be used to boost our own immune systems or to fight HIV and cancer. The immune cells would be grown in piglets from each patient鈥檚 own cells.
Our immune system鈥檚 T-cells, which play a key role in fighting off diseases, are 鈥減rimed鈥� in childhood to fight particular pathogens. This plasticity diminishes after puberty, but at the University of Michigan, Ann Arbor, has come up with a way to revive it. He reckons that if a human鈥檚 immune cells are transferred into a young pig, they could become primed like a child鈥檚, then implanted back into the person they came from.
To see if growing a human immune system inside pigs is possible, Platt and his colleagues extracted stem cells from human umbilical cord blood and bone marrow, and injected them into developing pig fetuses. Lacking a mature immune system, the fetuses accepted the foreign tissue as their own, and when the piglets were born Platt found that the injected cells had multiplied and matured into a diverse range of human T-cells, alongside the pig鈥檚 own immune cells.
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The researchers separated out the human T-cells from the pig鈥檚 blood and mixed some of them with ordinary cells from the person whose cells had been injected into the fetus. The extracted T-cells did not mount an immune attack, indicating that it should be possible to implant them back into the donor, but they did attack cells from other people, showing they were functional (Tissue Engineering A, ).
The piglets could also be used to make human cells that fight specific diseases. When Platt vaccinated some of them against the pig pathogens parvovirus and Mycoplasma hyopneumoniae, human T-cells extracted from these animals mounted an immune response to the pathogens. As these are human cells, this immunity must have developed inside the pig.
鈥淚f I had HIV, I could put my stem cells in pigs and immunise them with an HIV vaccine,鈥� says Platt. This might work better than giving the vaccine to the person directly, as an adult鈥檚 immune system is often too mature to react. 鈥淵ou would get immunity in the pig that you would never get in my body,鈥� he says. The same could also be done to encourage cells to attack cancer.
鈥淚f I had HIV, I could put my stem cells in pigs and immunise them with an HIV vaccine鈥�
鈥淢ini pigs鈥� (like those pictured) 鈥� which are much smaller than farmyard pigs and therefore more efficient to rear 鈥� could be used for this. Platt says that the necessary technology is available now, if regulatory authorities can be convinced that the procedure can be safely tested in humans. The fear is that dormant pig viruses buried in their DNA could be spread to humans, but Platt says that this has never been shown to happen except in highly artificial laboratory conditions.
Another potential danger is that human-derived cells might pick up surface molecules from the pig. 鈥淭his could make the transferred cells themselves targets for immune destruction,鈥� says Charles Nicolette of , a company developing immunotherapies in Durham, North Carolina.
The pigs might also produce too few human cells to fight disease, Platt says.
Stem Cells 鈥� Learn more about the promise and the controversy in our cutting edge special report .
