The decision to halt the SER-155 program comes despite the company submitting a final Phase 2 protocol to the Food and Drug Administration. The candidate was intended to prevent life-threatening infections in patients undergoing stem-cell transplants for blood disorders. While the clinical protocol is finalized, Seres stated it will not invest further in the trial until it secures external funding.

Extending the Financial Runway

The latest layoffs follow a previous 25% staff cut in September, reflecting a deepening effort to stabilize the company's balance sheet. As of Sept. 30, Seres reported having $47.6 million in cash and equivalents. According to the company, these aggressive cost-cutting measures are designed to sustain operations until the end of the third quarter of 2025.

In the interim, the company is shifting its primary focus toward early-stage research. This includes:

• Advancing the SER-603 candidate for ulcerative colitis.
• Developing treatments for Crohn's disease.
• Targeting immune checkpoint-related enterocolitis.

Seres rose to prominence following the FDA approval of VOWST, a first-of-its-kind oral microbiome medication. However, the company now faces the challenge of maintaining its commercial momentum while scaling back its broader developmental ambitions to survive the current funding environment.