For years, scientists have known that drug-carrying nanoparticles could provide new, potent treatments for diseases like cancer by sending them to targeted parts of the body. But there was one big problem: Before the particles could make it to their intended location, the patients’ immune systems would kill them off. Now a team of California-based researchers has figured out a way to disguise the particles to look like parts of blood cells, according to an article published today in Nature.

Typically, nanoparticles are made of metal or plastic—materials that the body immediately recognizes as invaders. To avoid that, the researchers coated antibiotic-containing plastic nanoparticles with cell membranes removed from human platelets, which are disk-shaped cell fragments found in the blood. The membranes of these platelets contain a number of proteins that shield the cells from immune attack, including one previously used to coat nanoparticles that tells the immune system, “don’t eat me” nanoengineer Dennis Discher told Nature News.

In this study, the researchers injected the membrane-coated antibiotic particles into mice infected with MRSA, which is notoriously resistant to antibiotic treatment. The mice treated with nanoparticles saw a 1,000-fold reduction in the number of bacteria living in their spleens and livers compared to the mice that received conventional antibiotics, and at one-sixth of the dose. The researchers also found ways to exploit the particles’ other natural tendencies. Since the particles tend to congregate around damaged blood vessels, the researchers found that effective delivery of the chemotherapy drug docetaxel could prevent artery walls from growing back too thick after surgery.

This isn’t the first attempt to coat nanoparticles with disguising proteins. Another paper published recently showed that Singaporean researchers were also able to do so. And while a number of nanoparticle experts were impressed with this new research, according to the Nature News article and an opinion piece published alongside the paper, others were less impressed. Because most of the particles ended up in the liver and the spleen—and not necessarily concentrated at sites of disease—some researchers aren’t sure that they actually are sneaking past the immune system undetected. The researchers plan to continue testing their nanoparticles on larger mammals before beginning clinical trials in humans.