Phase 2 STEMVAC DNA vaccine targets CDH3/CD105/YB-1/MDM2/SOX2 in residual TNBC.

University of Washington is running a randomized Phase 2 adjuvant study testing STEMVAC, a multiantigen plasmid DNA cancer vaccine designed to induce T-cell responses against five “aggressiveness/stemness”-associated tumor proteins (CDH3, CD105/ENG, YB-1, MDM2, and SOX2). Patients with stage I–III triple-negative breast cancer and moderate/extensive residual cancer burden after standard neoadjuvant chemotherapy and definitive surgery (RCB 2–3) are assigned to STEMVAC plus sargramostim (GM-CSF) vs GM-CSF alone, with serial blood collection to study immune/ctDNA dynamics alongside outcomes. Mechanistically, STEMVAC provides DNA encoding antigen epitopes to prime/expand antigen-specific immunity, while GM-CSF (partnered here as an immune adjuvant) recruits/activates antigen-presenting cells to strengthen vaccine priming. The key commercial/scientific angle is a post-neoadjuvant, MRD-risk–enriched setting where relapse rates remain high and immunologic consolidation could be impactful. Today’s care for RCB 2–3 TNBC typically continues adjuvant systemic therapy tailored to prior treatment and biomarkers (often capecitabine for residual disease, pembrolizumab continuation if started pre-op, and olaparib for germline BRCA carriers) plus radiation when indicated—this trial asks whether multiantigen vaccination can further reduce recurrence beyond those standards.