Colorectal, pancreatic, esophageal and stomach cancers — some of the deadliest kinds of cancer — have high recurrence rates where the cancer comes back even after successful surgery or radiation treatment.

To combat these treatment-resistant cancers, Thomas University Jefferson researchers led by Adam Snook, PhD, an associate professor of pharmacology and experimental therapeutics, instead use what are, in essence, vaccines to train patients’ immune systems to keep the cancer from coming back. Typically, the vaccines use either modified viruses or modified bacteria.

Now new research from Dr. Snook’s lab shows in an animal model that using viral and bacterial vaccine approaches together is safe and far more effective at fighting the cancer than either approach by itself.

“The vaccine platforms are not unique,” says Dr. Snook who is also a researcher at the Sidney Kimmel Cancer Center — Jefferson Health. “But nobody’s put them together into a combination vaccine, yet that’s when we saw the immune response really take off.”

In previous work, Dr. Snook and his team used a modified form of a common virus known as adenovirus as the backbone of a cancer vaccine that trains patients’ immune systems to identify and attack a unique colorectal cancer molecule called GUCY2C (pronounced goosey-toosey). This vaccine treatment, dubbed Ad5.F35-GUCY2C, is currently in Phase II clinical trials.

Although the adenovirus-based vaccine approach stimulates a highly effective immune response in patients, the effect doesn’t last. To create the best possible immune response, vaccines often require additional doses. However, once introduced, the body becomes familiar with the adenovirus and as a result does not produce the same kind of immune response with additional doses. To keep the primed immune system pumping out cancer-fighting immunity, the body needed a different kind of booster.

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