Retroviral Mediated Transfer of the Human Multidrug Resistance Gene (MDR-1) into Hematopoietic Stem Cells During Autologous Transplantation after Intensive Chemotherapy for Metastatic Breast Cancer. National Institutes of Health,Bethesda,Maryland

Abstract

Retroviral Mediated Transfer of the Human Multidrug Resistance Gene (MDR-1) into Hematopoietic Stem Cells during Autologous Transplantation after Intensive Chemotherapy for Breast Cancer

Patients with metastatic breast cancer will receive 4–5 cycles of induction chemotherapy on one of the ongoing Medicine Branch protocols. Patients achieving at least a partial response, and who do not have evidence of bone marrow involvement and who do not have metastatic bone disease, will undergo PBSC and bone marrow harvest when hematologic recovery has occurred. Patients who have not achieved a PR, but who are responding to therapy, may be treated with additional cycles of therapy in an attempt to achieve a PR. Such patients will be eligible for transplant if a PR is obtained. 70% of the bone marrow and PBSC will be cryopreserved. The CD34⁺ subpopulation from the remaining 30% of the bone marrow and PBSC harvest will be obtained using an anti-CD34⁺ antibody and immunoabsorption column. The bone marrow and peripheral blood CD34 cells will be transduced with a retroviral vector expressing the human MDR-1 cDNA. Patients with positive bone scans or histologic evidence of bone marrow involvement will be excluded from the gene transfer component of the protocol. The MDR-1 transduced CD34 cells will be reinfused along with the non-transduced bone marrow and PBSC into patients following high dose ICE chemotherapy. Serial peripheral blood and bone marrow samples will be obtained to study hematopoietic reconstitution with MDR-1 transduced cells. Patients with residual or progressive disease after ABMT will be treated with taxol or vinblastine. In these relapsed patients, peripheral blood and bone marrow samples will be obtained to study whether chemotherapy amplifies the proportion of hematopoietic cells containing the MDR-1 provirus. We will monitor the nadir blood counts of each patient receiving salvage chemotherapy for evidence of myeloprotection and correlate this data with changes in the mean proviral copy number. Sites of relapsed tumor will be biopsied to test for the presence of the MDR-1 provirus.

NON-TECHNICAL ABSTRACT

Autologous Bone Marrow Transplantation (ABMT) is a method of treating breast cancer by giving patients very high doses of chemotherapy and then rescuing them with their bone marrow cells that have been removed and frozen. In this study, patients will be treated initially with standard doses of chemotherapy to cause a remission of their breast cancer. Then, blood cells which are capable of rebuilding patients' bone marrows will be removed from the patients' bloodstream and bone marrow. Seventy percent of these blood cells will be frozen directly and 30% will be used to separate the “stem” cells, those cells thought to be the forebearers of all other blood cells. These stem cells will be cultured with a disabled virus which carries genetic material referred to as the multidrug resistance gene (MDR-1). The virus transfers the MDR-1 gene into a portion of the patients' stem cells. The purpose of putting the MDR-1 gene into the patients' stem cells is to try to make these blood cells and their offspring resistant to the toxic effects of chemotherapy. The MDR-1 protein (PgP) that is made from the MDR-1 gene makes cells resistant to chemotherapy by pumping the drug out of cells before the drug is able to kill the cell.

Patients are then treated with very high doses of ICE (ifosfamide, carboplatin, and etoposide) chemotherapy and then the frozen blood cells as well as the MDR-1 blood cells are given back to the patient through a catheter in a vein. It is hoped that the MDR-1 stem cells will contribute to the rebuilding of patients' bone marrows following the high-dose chemotherapy. Samples of patients' bone marrows and peripheral blood cells will be obtained at several points after the bone marrow recovers to follow the course and life span of the cells containing the MDR-1 virus. Patients who still have evidence of breast cancer or whose breast cancer returns after ABMT will be treated with taxol, a chemotherapy drug that is pumped out of cells by the MDR-1 protein. We will again follow patients' blood counts closely to determine whether the number of blood cells that contain the MDR-1 gene increases in response to the chemotherapy. Patients will be treated with taxol for as long as there is evidence of a beneficial effect against their tumor.