To create their tumor-killing program, the researchers designed a logic circuit — a system that makes a decision based on multiple inputs. In this case, the circuit is made of genes that detect molecules specific to a type of cervical cancer cell. If the right molecules are present, the genes initiate production of a protein that stimulates apoptosis, or programmed cell death. If not, nothing happens.

Because the genes used to create the circuits can be easily swapped in and out, this approach could also yield new treatments or diagnostics for many other diseases, according to Ron Weiss, an MIT associate professor of biological engineering and one of the leaders of the research team. “This is a general technology for disease-state detection,” he says.
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the researchers created a synthetic gene for a protein, called hBax, that promotes cell death. They designed the gene with two separate safeguards against the killing of healthy, non-HeLa cells: It can be turned off by high levels of microRNAs that are ordinarily low in HeLa, and can also be deactivated by low levels of microRNAs that are normally plentiful in HeLa. A single discrepancy from the target microRNA profile is enough to shut off production of the cell-death protein.

If all microRNA levels match up with the HeLa profile, the protein is produced and the cell dies. In any other cell, the protein never gets made, and the synthetic genes eventually break down.