A live biotherapeutic product for adult allogeneic hematopoietic cell transplantation recipients: a partially randomized, placebo-controlled phase 1b trial.

SER-155 was well tolerated in adult allogeneic hematopoietic cell transplant recipients and is linked to a lower bloodstream infection rate versus placebo (10.0% vs 43%).

• Why it matters: GI microbiome disruption and weakened GI barrier integrity raise bloodstream infection risk after transplant, leaving a need for safer microbiome-targeted interventions.
• What they did: In a phase 1b trial with two cohorts (open-label n=15; partially randomized placebo-controlled n=45), participants received SER-155 or placebo, then underwent transplant; safety, pharmacokinetics, and BSI incidence were assessed.
• The result: No treatment-related serious adverse events occurred and no infections with SER-155 species were seen; engraftment occurred for 16/16 strains (median 11.5 after the first course), and BSI incidence was lower with SER-155 (OR 0.15; 95% CI 0.01–1.13; P=0.0423).

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