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The McGRAW Trial

The Microbiome and Cancer: Can Gut Bacteria Help Immunotherapy Destroy Tumors?

Why This Trial

In the war on cancer, we have made serious progress. However some of our best weapons, called checkpoint inhibitors, still only work for 20% to 30% of patients.

In examining this problem, PICI investigator Jennifer Wargo, MD, discovered something interesting. Patients with certain types of gut bacteria and a more diverse gut microbiome overall respond better to checkpoint inhibitors, a type of immunotherapy treatment.

That begged the question: could the right gut bacteria be immunotherapy’s best new ally?

This study, one of the first of its kind, is designed to answer that question.

We are testing whether altering the gut microbiome of cancer patients can change – or even enhance – their ability to respond to checkpoint inhibitors.

About the Study

In this phase 1b, randomized, blinded clinical trial, all patients will first be treated with an antibiotic and then nivolumab, an FDA-approved checkpoint inhibitor that targets the PD-1 protein.

Patients will then take either a placebo or SER-401, a pill that contains a mix of select bacteria found to be associated with better checkpoint inhibitor response.

Researchers will sequence the gut of all patients before, during and after treatment with checkpoint inhibitors to record the types and amounts of microbes present.

We will also take tissue and blood samples to perform additional lab and imaging tests in order to track changes in a patient’s immune system over time.

Who’s Eligible

  • Patients with metastatic or unresectable melanoma (up to 30)

Treatments Tested

  • Nivolumab
  • SER-401 or a placebo

Where We’re At Now

The trial opened in January 2019 and is currently enrolling patients at multiple sites.




Principal Investigators

  • Genevieve Boland, MD, PhD | Massachusetts General Hospital
  • Isabella Glitza, MD, PhD | The University of Texas MD Anderson Cancer Center
  • Kenneth Grossman, MD, PhD | Huntsman Cancer Institute
  • Omid Hamid, MD | The Angeles Clinic
  • Janice Mehnert, MD | Rutgers Cancer Institute
  • Patrick Ott, MD | Dana-Farber Cancer Center
  • Alex Shoushtari, MD | Memorial Sloan Kettering Cancer Center
  • Hussein Tawbi, MD, PhD | The University of Texas MD Anderson Cancer Center


For more information on this trial (NCT03817125), visit