Phase 2 MO-03 live biotherapeutic (microbiome modulator) plus pembrolizumab PD-1 blockade in early TNBC

This single-group, open-label Phase 2 study tests whether adding MO-03—a live biotherapeutic product intended to modulate the gut microbiome—can improve outcomes when layered onto standard neoadjuvant pembrolizumab (Merck’s PD-1–directed monoclonal antibody) plus chemotherapy in high-risk, early-stage triple-negative breast cancer. Fifty participants receive oral MO-03 (4 × 10^9 CFU per capsule, 1 capsule twice daily) concurrently with pembrolizumab 200 mg every 3 weeks and platinum/taxane-based chemotherapy (carboplatin, a DNA-damaging platinum; paclitaxel or docetaxel, microtubule inhibitors), followed by anthracycline/cyclophosphamide per the protocol regimen, then definitive surgery; MO-03 stops the day before surgery. The primary endpoint is pathologic complete response at surgery, with longer-term event-free survival and other time-to-event outcomes followed for up to 5 years. The sponsor lists Osel, Inc. and Miyarisan Pharmaceuticals as collaborators, framing a microbiome-oncology “add-on” strategy aimed at deepening checkpoint inhibitor benefit. Today’s care for high-risk early TNBC commonly uses neoadjuvant pembrolizumab plus multi-agent chemotherapy followed by surgery, with adjuvant pembrolizumab continuation and risk-adapted escalation (for residual disease) depending on pathology.