Dendritic Cell-Based Treatment Plus Immunotherapy for the Treatment of Metastatic or Unresectable Triple Negative Breast Cancer

PRIMARY OBJECTIVE: I. To determine the clinical efficacy and safety and tolerability of a combination of intratumorally injected autologous dendritic cells (DCs) and pembrolizumab in PD-L1 negative treatment-naive and refractory metastatic triple negative breast cancer patients. SECONDARY OBJECTIVES: I. To assess progression-free survival and overall survival in metastatic triple negative breast cancer patients that received the combination of intratumorally injected autologous DCs and pembrolizumab. II. To assess the clinical efficacy in the non-injected target lesion (optional biopsies for this lesion). OUTLINE: Patients undergo leukapheresis over 90 minutes. Patients then receive ST-alpha-DC1 intratumorally (IT) on days 1, 8, and 50 in the absence of disease progression or unacceptable toxicity. Patients also receive pembrolizumab intravenously (IV) on days 8, 29, 50, and 71 in the absence of disease progression or unacceptable toxicity. Patients who are receiving clinical benefit from treatment at the end of day 85, may continue to receive pembrolizumab IV every 3 weeks beyond the 4 study doses. Patients also undergo tumor biopsies on days 1, 8, and 50 and computed tomography (CT) scans at baseline and days 50 and 85. After completion of study treatment, patients are followed up at 30 and 90 days after the last dose of study drug, and then every 3 months for up to 2 years.