Will There Ever be a Cure for the Common Cold?


[ intro ] Medicine has made some pretty big leaps forward
in the last century. But one disease still outwits even the best
medical minds: the common cold. Part of the problem is that it’s caused
by a suite of pathogens, not just one. And those pathogens happen to be viruses that
mutate fast and hide inside their hosts’ cells. That said, we might be closer to getting rid
of it than you think—and knocking out a slew of other viral diseases at the same time. One of the reasons the common cold is so difficult
to attack is that it’s not a single target. The main culprits behind the common cold are
rhinovirus, but there are hundreds of variants of them
and they aren’t the only viruses to blame. All that diversity has kept us from making
any kind of ‘cold vaccine’ or targeted drug. It’s also why our best chance to defeat
the common cold once and for all is to develop a broad spectrum antiviral: a medication that can wipe out many different
viruses at once. Since we’ve already done this with antibiotics,
you might think it would be easy to apply the same strategy to viruses. But there’s a pretty big catch. Most broad spectrum antibiotics work by inhibiting
key proteins the bacteria need to reproduce or make their protective cell walls. These are usually things that are structurally
unique to bacteria as opposed to multi-celled organisms like us, so for the most part, the drugs don’t harm
human cells. Viruses hijack their host’s cells to reproduce,
using our cell’s machinery for their own ends. So fighting these viral invaders while leaving
our cells intact is a lot trickier. Not that we haven’t tried. The first attempts at a universal antiviral
tried boosting our body’s natural immune system. When our cells detect a virus, they start
making interferons: chemical messengers that signal the viruses’
presence to the rest of the body. So some of the first antivirals either were
interferons themselves, or boosted their effectiveness. And these drugs can work pretty well if taken
before the virus gets out of control. One kind of interferon, interferon a, is still
routinely used to treat hepatitis B and C, for example. But these drugs tend to come with the mess
of side effects that happen when you somewhat indiscriminately ramp up
your immune system. And what most antiviral researchers really
want to find is something that targets viruses more directly … kind of like the antivirals used against
HIV. These medications take advantage of the way
HIV inserts its genes into a person’s DNA by targeting the viral proteins which allow
it to do that. But the meds are designed to inhibit things
specific to HIV, so they don’t work against other viruses. And finding a single achilles heel common
to many different viruses has proven difficult. Still, back in 2011, a team from M.I.T. may
have found one. They developed a protein that detects double
stranded RNA, a type of genetic code that is made by a lot
of the most common viruses while they’re replicating. These molecules aren’t completely unique
to viruses, but the ones made by viruses are much longer
than the ones that happen naturally in human cells. In fact, their presence is one of the ways
your own immune system figures out that you’re infected. So the researchers took a protein that can
detect these molecules, and they attached it to another protein which
triggers cell suicide when more than one of the drug molecules binds
to the same chunk of double-stranded RNA. And in a 2011 PLoS ONE study, they showed
that this combined construct works against more than a dozen different viruses without
harming several types of human cells. Killing infected cells might sound extreme, but the viruses kill your cells anyway when
they’ve made enough copies, so the drug simply speeds things up and limits
the number of viruses made. Unfortunately, the project has been in a constant
battle for funding, so they haven’t gotten far enough along
in the research for human trials. Luckily, there are other promising antivirals
in the works. A team of researchers in San Francisco is
developing drugs that stop viruses from making the protein shells or capsids
they need to move about within and between hosts. Traditional studies have looked at capsid
formation as a thing that just sort of happens on its own, but these developers tested the idea that
the host cell unwittingly helps the virus with construction. And they found what appear to be traitorous
proteins scientists had no clue were aiding the viruses— any of which could be a target for a broad-spectrum
antiviral. Using this framework, the team has found inhibitors
that work in animals against rabies, influenza, and Ebola viruses. But, they still have a lot of testing to do
before anything would be ready for human trials. And there’s another potential broad-spectrum
antiviral hoping to beat them to those. This one takes advantage of natural hiccups
in viral replication—because, just like us, viruses aren’t perfect. Sometimes during the gene-copying process
they end up deleting big chunks of their genes. These defective viruses are unable to make
some really important proteins, so they can’t infect healthy cells, but
they can still create copies of themselves. And those copies, though harmless to your
cells, get in the way of other viruses— so scientists have taken to calling them defective
interfering viruses. Researchers are hoping to capitalize on these
helpful defects by creating clones or synthetic versions. And so far, they’ve successfully treated
multiple strains of influenza in mice with this approach. Of course, mice aren’t people, so like the
other universal antivirals in development, there’s a lot more work to be done. Still, the fact that there are so many potential
broad-spectrum antivirals already in development is a good sign. While scientists have yet to come up with
the silver bullet, we live in exciting times. And it might not be too long before we actually
get to say “I remember catching the cold.” Thanks for watching this episode of SciShow! If you liked learning about the latest cold-fighting
advances, you might like our episode on how cold medicines
actually treat those awful symptoms. [ outro ]

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