Effect of alphavirus vaccine encoding HER2 during concurrent anti-HER2 therapies on induction of oligoclonal T cell and antibody responses against HER2.

3081 Background: Advanced HER2-overexpressing breast cancer eventually develops resistance to standard therapies; however, the HER2 receptor persists and may serve as a target for immunotherapy. We tested an immunization strategy with a novel alphaviral based vaccine encoding the extracellular and transmembrane domains of HER2 (VRP-HER2), alone and in conjunction with standard anti-HER2 agents, in patients with predominantly metastatic treatment refractory HER2-overexpressing breast cancer to determine safety, immunogenicity, and clinical activity. Methods: Cohort 1 (n = 4) enrolled patients not receiving any other anticancer therapy. Cohort 2 (n = 10) enrolled patients receiving either concurrent trastuzumab +/- pertuzumab, TDM-1, or Lapatinib. VRP-HER2 was given at 4 x 108 IU intramuscularly, every 2 weeks for three doses. Immune response specific for HER2 was determined by ELISPOT and ELISA. Progression-free survival (PFS) was defined as time to disease progression or death. Median length of follow-up ...