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In 1884, a patient’s luck seemed 
to go from bad to worse.

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This patient had a rapidly growing 
cancer in his neck,

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and then came down with an unrelated 
bacterial skin infection.

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But soon, something unexpected happened:

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as he recovered from the infection, 
the cancer also began to recede.

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When a physician named William Coley 
tracked the patient down 7 years later,

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no visible signs of the cancer remained.

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Coley believed something remarkable 
was happening:

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that the bacterial infection 
had stimulated the patient’s immune system

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to fight off the cancer.

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Coley’s fortunate discovery 
led him to pioneer

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the intentional injection of bacteria 
to successfully treat cancer.

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Over a century later, synthetic biologists
have found an even better way

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to use these once unlikely allies—

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by programming them to safely 
deliver drugs directly to tumors.

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Cancer occurs when normal functions 
of cells are altered,

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causing them to rapidly multiply 
and form growths called tumors.

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Treatments like radiation, chemotherapy, 
and immunotherapy

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attempt to kill malignant cells, 
but can affect the entire body

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and disrupt healthy tissues 
in the process.

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However, some bacteria like E. coli

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have the unique advantage of being able 
to selectively grow inside tumors.

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In fact, the core of a tumor forms 
an ideal environment

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where they can safely multiply, 
hidden from immune cells.

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Instead of causing infection,

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bacteria can be reprogrammed 
to carry cancer-fighting drugs,

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acting as Trojan Horses 
that target the tumor from within.

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This idea of programming bacteria 
to sense and respond in novel ways

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is a major focus of a field called 
Synthetic Biology.

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But how can bacteria be programmed?

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The key lies in manipulating their DNA.

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By inserting particular genetic sequences 
into bacteria,

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they can be instructed 
to synthesize different molecules,

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including those 
that disrupt cancer growth.

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They can also be made 
to behave in very specific ways

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with the help of biological circuits.

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These program different behaviors 
depending on the presence, absence,

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or combination of certain factors.

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For example, tumors have low oxygen 
and pH levels

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and over-produce specific molecules.

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Synthetic biologists can program bacteria 
to sense those conditions,

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and by doing so, respond to tumors 
while avoiding healthy tissue.

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One type of biological circuit,

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known as a synchronized lysis circuit, 
or SLC,

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allows bacteria 
to not only deliver medicine,

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but to do so on a set schedule.

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First, to avoid harming healthy tissue,

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production of anti-cancer drugs 
begins as bacteria grow,

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which only happens 
within the tumor itself.

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Next, after they’ve produced the drugs,

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a kill-switch causes 
the bacteria to burst

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when they reach a critical population 
threshold.

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This both releases the medicine 
and decreases the bacteria’s population.

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However, a certain percentage 
of the bacteria remain alive

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to replenish the colony.

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Eventually their numbers grow large enough
to trigger the kill switch again,

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and the cycle continues.

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This circuit can be fine-tuned 
to deliver drugs

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on whatever periodic schedule
is best to fight the cancer.

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This approach has proven promising 
in scientific trials using mice.

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Not only were scientists able 
to successfully eliminate lymphoma tumors

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injected with bacteria,

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but the injection also stimulated 
the immune system,

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priming immune cells 
to identify and attack untreated lymphomas

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elsewhere in the mouse.

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Unlike many other therapies,

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bacteria don’t target a specific type 
of cancer,

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but rather the general characteristics 
shared by all solid tumors.

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Nor are programmable bacteria 
limited to simply fighting cancer.

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Instead, they can serve 
as sophisticated sensors

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that monitor sites of future disease.

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Safe probiotic bacteria could perhaps 
lie dormant within our guts,

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where they’d detect, prevent, 
and treat disorders

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before they have the chance 
to cause symptoms.

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Advances in technology 
have created excitement around a future

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of personalized medicine 
driven by mechanical nanobots.

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But thanks to billions of years 
of evolution

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we may already have a starting point

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in the unexpectedly biological 
form of bacteria.

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Add synthetic biology to the mix,

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and who knows what might soon be possible.