Your microbiome and cancer

Lab studies indicate that the composition of your microbiome can help fight cancer. Your microbiome is the unique set of bacteria you carry around with you, or it might be more accurately said that they carry you around since they outnumber body cells ten to one.

Checkpoint inhibitors prevent T-cells from recognizing cancer as friend.

Checkpoint inhibitors prevent T-cells from recognizing cancer as friend.

Your microbiome can affect immune response, which in turn can fight cancer. Unfortunately, your immune system doesn’t always recognize cancer as a threat. Solid tumors are especially hard to target. Skin and lung cancers form solid masses that are hard to penetrate compared to liquid tumors in the blood.

Cancer cells hide by fooling immune cells into thinking they are not foreign at all. To determine friend or foe, immune cells check for a protein. If they find it on cancer cells, they appear as friends.

One innovative cancer treatment involves an immunotherapy drug called checkpoint inhibitors which do just what the name suggests –they block the checkpoint that looks for friend or foe. Seeing no friend because they are blocked, immune cells mount a defense.

This is where the microbiome comes in. Gut bacteria affect our immune system’s inflammatory response. Scientists at the University of Chicago found that mice responded to cancer invasion in varying degrees according to the type of bacteria in their guts (Scientific American, April, 2016).

Mice that were fed a particular strain of bacteria were able to fight skin cancer better than those who weren’t. When poop from the cancer-fighters was transferred to others, tumor growth slowed.

Remarkably, when checkpoint inhibitors were given to both the mice with the particular bacteria and those with the fecal transplant, tumors disappeared completely in the former and was reduced in the other. Then, when the mice with the fecal transplant were also given the bacteria, they were cured completely.

French scientists had similar results in which both the checkpoint inhibitor and a different bacteria were given. Next, the scientists gave antibiotics to the mice which killed bacteria, including the beneficial ones. The conclusion is obvious: doctors need to be cautious in prescribing antibiotics to cancer patients.

Not any bacteria will do. The Chicago team used either Bifidobacterium longum or Bifidobacterium breve. The French used Bacteroides. Yogurt contains Bifidobacterium lactis or Bifidobacterium bifidum remains untested.

Fine-tuning the immune system is a tricky business. The wrong kind of bacteria could cause the immune system to become too active and attack normal tissue. Autoimmune diseases include type-1 diabetes, inflammatory bowel disease, psoriasis, and rheumatoid arthritis. The effect of general bacteria on fine-tuning the immune system still needs to be investigated.

“Obviously we need to categorize the bacteria in the human microbiome and their potential antitumor effects more completely before we can recommend any treatments in people,” cautions the Chicago team.

The promise and peril of CRISPR gene technology

So far, the promise of genetic engineering to cure disease has been a bit of a dud. Up until now scientists could only read our genomes – now they can write. A gene-editing tool found in bacteria, called CRISPR, is poised to achieve that goal.

CRISPR

As well as read, the old technology allowed the ability to add says Dr. Elizabeth Simpson at the University of British Columbia on CBC Radio’s Quirks and Quarks. She’s begun to use CRISPR in her work on aniridia, a genetic eye disease.

“In the older technology we would add the missing gene, not insert it into the genome to make the eye function properly. We had a lot of trouble making the addition produce the right amount of protein at the right time. With CRISPR, all the natural regulation is still there and can be used by the eye to heal itself. We don’t have to be as clever and it’s a faster way to go.”

CRISPR (Clustered regularly-interspaced short palindromic repeats) is part of a natural bacterial defense. Scientists have known about these sections in bacterial DNA for years but they didn’t know what they were for or how they got there.

Then they discovered that these repeated clusters were sections of DNA gathered from attacking viruses: the bacteria had literally incorporated the enemy’s DNA into theirs. Still, their function remained a mystery.

Dr. Sylvain Moineau, Professor at the University of Laval, was one of the researchers to find out. He discovered that some yogurt bacteria weren’t susceptible to viral attack and some were. The ones that weren’t used the embedded viral DNA, described above, as a natural defense. These successful bacteria compared the embedded viral DNA with sections in the attacking viruses, and then cut that section out. As you can image, viruses don’t work well with gaping holes in their midsections: a pretty good defense.

While cut up viruses don’t work well, human DNA has the ability can stitch itself back up. That allows CRISPR technology to remove parts of our DNA that cause disease and replace it with functioning parts.

That’s the wonder of CRISPR. It cuts out the bad parts and inserts the good parts. Think of it as the search and replace function in word processors says Dr. Feng Zhang at the Massachusetts Institute of Technology who was key in transforming the natural CRISPR system into a gene editing tool. For example, if I’ve misspelled CRISPR throughout this whole article, I can use the search and replace function in Word to replace all incorrect instances of CRISTR with CRISPR.

Powerful tools in the hands of the wrong people can be disastrous. It would be wonderful to cure muscular dystrophy and Huntington’s disease. And since permanent genetic changes can be passed on through generations, malaria could be wiped out forever by making mosquitoes resistant to the parasite.

But In the hands of bio-hackers and unethical corporations, CRISPR could wreak havoc in areas of agriculture, biology, pharmaceuticals, ecology and wildlife preservation.

Ethical debates must take place before the technology becomes widespread. It’s another reason that we need strong government regulation.