BATs in Patients With Breast Cancer and Leptomeningeal Metastases

Once subjects are determined eligible, white blood cells (lymphocytes) are collected via leukapheresis procedure approximately 3 to 4 weeks prior to the first BATs infusion. The white blood cells, specifically T cells, are then mixed with two proteins in order to activate the cells to multiply. After approximately 14 days in culture, the activated T cells are coated with OKT3 and trastuzumab/Herceptin (HER2Bi), and washed to remove excess Herceptin in order to produce bispecific antibody armed T cells (BATs). Cells are then frozen and stored until scheduled to be infused. Up to 2 weeks following leukapheresis, participants will undergo surgery to place the catheter/reservoir into the lateral ventricle of the brain to allow intraventricular administration of HER2 BATs and a chemotherapy agent methotrexate. A few weeks later, participants will receive the intraventricular methotrexate in order to control disease while the BATs product is being manufactured. About 4-5 weeks following the leukapheresis and at least 7 days after receiving methotrexate, study treatment will begin with a test dose of HER2 BATs. If this dose is well tolerated by the participant, she will then receive 8 weekly doses of HER2 BATs at the assigned dose level.