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Go to Brilliant.org/SciShow to learn  how you can take your STEM skills to the next level! [♪ INTRO] Our immune system generally does  a good job at keeping us alive by fighting off foreign invaders  like bacteria and viruses. But sometimes, it's your own body that’s  an invader in the form of cancer cells, which are experts at evading the immune system.

According to a study published this week  in the journal Nature, there may be a way to “train” the immune system outside  the body to keep leukemia patients in remission for up to a decade. One of the many kinds of cells that  make up our immune system are T cells. Each T cell specializes in identifying  and / or attacking just one kind of invader.

To do their job efficiently, T cells are  covered in special proteins, called receptors, designed to match up with antigens, proteins at the surface of  invaders like bacteria and viruses. So, a T cells receptors are kind of like  chemical keys on the hunt for their lock. But some diseases, like cancer, are  experts at dodging T cells’ keys.

One way they can do this is by not  having enough detectable antigens dotting their cellular surfaces. The good news is that scientists have  figured out a way to take some T cells out of a patient’s body and train them  to better recognize cancer cell antigens, and then put them back into the  patient to fight the cancer. It’s called chimeric antigen  receptor, or CAR, T cell therapy.

The T cell training regimen is  actually a form of genetic engineering. Through a rather long and complicated  process, a snippet of DNA is eventually added to the T cell’s genetic  code, giving them instructions to make a tailored receptor  for the cancer cell antigen. So when the new tailored  receptor latches onto its target, the T cell calls for backup by releasing  a flood of molecules called cytokines.

Together, the cytokine molecules  and the army of T cells cause inflammation that,  ideally, kills their target. While CAR T cell therapy has been  approved for a few types of cancer, there hasn’t been a lot of research  looking at long-term effects. Like, how long will a single  infusion of T cells last in the body and keep the patient in remission?

So back in 2010, Two patients  with chronic lymphocytic leukemia received a single dose of CAR T cells. Within the year, it worked so  well they both entered remission. And here’s the kicker, they’ve stayed that  way, without any additional treatment.

The latest blood work was  collected a couple of years back. And the team found both patients still had some of the CAR T cells in their bloodstreams. Just trucking along after all that time.

While these are some great results, it doesn’t mean that every leukemia  patient is going to hop onto this therapy. When the study first happened,  there was a cohort of 14, but only two of those patients were  included in this ten-year follow-up. Also, this treatment is known for  having some pretty nasty side effects, like trouble breathing and even seizures.

Still, further studies may  improve CAR T-cell side effects making it a great option to keep cancer at bay. Speaking of body hacks… Last week in the Journal Science  Advances, a study announced it’s possible to help African Clawed Frogs regrow  the upper part of their amputated leg. We humans may be able to  stitch cuts back together, or even regrow a decent chunk of our liver.

But in general, we aren’t known for  having regeneration superpowers. We’re not like lizards or crabs, which can regrow way more complex  body parts, like entire limbs. The way it works in these critters is that  their brain recognizes they’ve lost a chunk of their body, and unspecialized  cells, called stem cells, suddenly flow to the stump and start getting jobs.

So they go from unspecialized  cells to bone cells, muscle cells, nerve cells, and so on. Their body already went through the  process of making that limb once, so the instructions are still  there to make another one. And humans have stem cells, too.

But when we lose a limb,  instead of sending STEM cells, our body sends instructions to  cover it over with scar tissue ASAP, so we don’t bleed out or catch an infection. The team of scientists wanted to know  if they could find a way to trigger limb growth in humans, so they turned  to 115 female African clawed frogs. As adults, that species  lacks regenerative abilities.

If they lose a limb, it's gone for good. To test their hypothesis, scientists  cut off part of one back leg. The frogs were either left to heal  on their own as a control group, or got their wound covered  with a small silicone cap filled with silk proteins and a 5-drug cocktail.

Each of the drugs had its own  job to do, prevent inflammation and the formation of scar tissue,  and stimulate regular tissue growth. During a previous study, the  team had just used one drug, which did grow something back, but  it was more of a spike than a leg, so it looked like a fleshy growth with  the first stage of bone regrowth showing. In this new study, the caps, called  BioDomes, were kept on for 24 hours, and then the team observed what ended up  growing over the next year and a half.

Just a few days in, the team observed  that, for the frogs that got the drugs, the molecular instructions their bodies  had used as embryos had reactivated. And over those 18 months, they  ended up regrowing a kind of leg. While none would be mistaken for a copy  of the frog's other leg, two-thirds of the frogs given the drugs had regrown way  more complex tissues and leg shape.

They even managed to regrow what researchers  are calling toes, but no toe bones. The legs could even respond to touch, and  the frogs could use them for swimming. And all that with just a day of treatment!

Of course, this research is on amphibians. Human trials are a long way away. A lot more work is needed to figure  out what the perfect drug cocktail needs to be to regrow the best limb possible.

So maybe decades in the future, people  could choose if they want to regrow a missing arm or have the  benefits of a robotic one instead. But while we wait for those superpowers arrive, you can hone your brains’ power,  problem-solving, with today’s sponsor, Brilliant. They’re an online learning platform  with courses about science, engineering, computer science, and math.

And they have a recently updated  course on Scientific Thinking with hands-on experiments that let  you discover the world in a new way. With this course, you can learn as you play  by solving different scientific puzzles. So if you’d like to see the world with new eyes, visit brilliant.org/scishow or click  on the link in the description.

The first 200 people will get 20% off  Brilliant's annual premium subscription, and checking them out also helps us, so thanks! [♪ OUTRO]