Improved Methods of Cell Selection for Bone Marrow Transplant Alternatives

Bone marrow transplants (BMT) are one form of treatment for disorders of the blood, including leukemia. However, because the procedure is often associated with potentially life-threatening reactions, it is usually reserved for patients with serious illnesses under the age of 60 years old. One serious reaction complicating bone marrow transplants is referred to as graft-versus-host disease (GVHD). GVHD is a potentially fatal incompatibility reaction. The reaction is caused by antigens found on the cells of the patient that are not present on the cells of the donor. The antigens are recognized by transplanted white blood cells (lymphocytes). These lymphocytes begin attacking the recipient s cells and tissues and may lead to death. In order to avoid GVHD, researchers have developed a technique using peripheral blood instead of bone marrow that allows transplantation of stem cells and removal of lymphocytes. Stem cells are the cells responsible for returning blood cell production to normal. Lymphocytes are the white blood cells that can cause GVHD. The technique requires two steps. In the first step blood cells are collected from donors who have received doses of a growth factor. The growth factor (granulocyte colony stimulating factor) is designed to increase the production of donor stem cells. In the second step white blood cell lymphocytes are removed from the collected blood, leaving only the stem cells. The main goal of this study is to develop and improve the method of processing cells that are collected after stimulation with growth factor (G-CSF), by removing the white blood cell lymphocytes which can cause graft-versus-host disease (GVHD) while keeping the stem cells necessary for healthy blood cell building. In addition, researchers are interested in studying whether giving G-CSF has an effect on lymphocyte function, which may influence the immune reactions occurring in bone marrow transplantation.

The NHLBI Stem Cell Transplantation program is exploring ways to make allogeneic transplantation safer and more widely applicable. Prior NHLBI transplant protocols have evaluated the strategy of using T cell depleted marrow transplants followed by delayed lymphocyte add-back to control or prevent GVHD while conserving useful donor immune function against residual leukemia and infectious agents. Over the past ten years, a number of increasingly efficient methods have been used to deplete T cells but retain stem cells, and we have shown the safety and utility of the delayed T cell add-back approach. We have also found a positive relationship between the administration of higher CD34+ cell doses and outcome. Investigation of highly purified grafts with the add-back of specific T cell populations is ongoing, and the ability to test new purification approaches and devices on clinical-scale PBSC products is critical to the continued development of new transplantation approaches in our program. This requires testing the approaches on G-CSF mobilized PBSCs collected by apheresis from healthy donors since this is the cell source that will be used in all clinical allogeneic transplantation protocols in our program. Therefore, the primary intent of this protocol is to provide a mechanism for mobilizing, collecting, storing, and analyzing G-CSF mobilized apheresis samples from healthy volunteers. Cells will be used to develop a method of processing the cells that are collected after stimulation with G-CSF, by removing the lymphocytes, which can mediate GVHD while retaining the stem cells which are necessary for hematopoietic reconstitution. At the same time, we will study whether G-CSF administration has an effect on lymphocyte, function which may influence the immune reactions occurring in allogeneic bone marrow transplantation. Furthermore, the CD34+ cells collected will be a valuable resource for experimental studies of lymphocyte-stem cell interactions in our laboratory.