Immune disguise for nanoparticles

21 February 2013
Posted by Chris Smith.

A means of masking nanoparticles from the immune system so that they can operate in the body for longer has been revealed by scientists in Polymorph CellAmerica.

They body's tissues are constantly patrolled by hoards of hungry cells called phagocytes that are programmed to gobble up foreign material. This process leads to the rapid removal of bacterial, viral and fungal pathogens, dead cells and foreign bodies.

But therein lies the problem, because under certain circumstances those foreign bodies might be there for a reason.

Take drugs, for example. Increasingly, scientists are exploring ways to combat cancer using injectible nanoparticles that preferentially accumulate inside cancers, delivering a toxic cargo, or concentrating radiation within a tumour to minimise damage to healthy tissue.

Attempts to develop just such a "magic bullet", however, are often thwarted because the body rapidly identifies the foreign material and sweeps it up for safe disposal.

Now University of Pennsylvania researcher Dennis Discher and his colleagues have found a way to sneak such materials under the immune radar, by disguising them chemically as part of the body itself.

The approach taken by the team, described this week in Science, hinges on a molecule called CD47.

Carried by every normal cell in the body, this behaves rather like a uniform worn on the battlefield, earmarking friends from foes and preventing phagocytes from attacking.

By endowing nanoparticles with a key part of the CD47 molecule, effectively disguising them as the body's own cells, the team were able to confer on their nanoparticles the same immunity from attack that healthy tissues enjoy.

And loading anti-cancer drugs or dyes onto the protected particles showed far greater accumulation of the agents in tumours in experimental animals.

Dubbing the approach "active stealth", the researchers speculate that their trick could be used therapeutically to improve drug delivery, or the targeting of imaging contrast agents, to certain tissues...

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