Seres Therapeutics (MCRB) shares fell 22% in early trade on Monday as positive topline results from a phase 1b study of SER-287 for patients with mild-to-moderate ulcerative colitis were overshadowed by clinical response data.

The company said it intends to “rapidly advance” SER-287 to further development for ulcerative colitis after the study results.

The study demonstrated that SER-287 resulted in a benefit in clinical remission rates, and also an improvement in mucosal appearance by endoscopy. The SER-287 safety and tolerability profile demonstrated no clinically significant safety findings. Microbiome study results, a co-primary endpoint, are expected in the coming months.

“The clinical data demonstrate the potential for microbiome therapeutics to provide an effective and safer alternative treatment modality for patients suffering from Ulcerative Colitis,” said CEO Roger Pomerantz. “Based on the strength of these data, Seres intends to work expeditiously to advance SER-287 into more advanced development studies.”

The company also said it will evaluate SER-287 in mild, moderate and severe forms of ulcerative colitis, in maintenance after induction therapy, and in Crohn’s disease, and pediatric forms of inflammatory bowel disease.

“We expect to discuss these data with the FDA as soon as possible, to determine the most accelerated path to advance SER-287 development,” said Pomerantz.

Seres Therapeutics later Monday issued a correction to its initial release with an amendment to the clinical response data, showing that an equal percentage of patients responded as compared to placebo while on a weekly basis, the clinical response was -17.1% compared to placebo.

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