Patients with HER2-positive (HER2+) metastatic breast cancer will be treated with 6 weekly injections of dendritic cell (DC1) vaccines in combination with trastuzumab and pepinemab.~Investigators hypothesize these therapies will elicit CD4+ HER2 specific T cell responses. HER2 specific T cells will be expanded ex vivo which will be infused to patients subsequently following lymphodepletion therapy with cyclophosphamide. Trastuzumab and pepinemab will be given as maintenance in addition to booster DC1 vaccines.
The purpose of this study is to test the safety of Adoptive T-Cell therapy following the Dendritic Cell (DC1) study vaccine given in combination with pepinemab added to standard of care therapy, trastuzumab to help people with HER2 positive breast cancer.