The new generation of blood components

Advances in the understanding of hematopoiesis and hematopoietic growth factors along with developments in cell culture, cell separation, and related technology have made it possible to produce new kinds of blood components. These new components are used in several different experimental therapies including hematopoietic cell transplantation, adoptive immunotherapy, gene therapy, and production of blood cells ex vivo for transfusion therapy. Hematopoietic cell transplants now involve a wide variety of transplant "products". This is due to differences in the relationship of the patient and donor, the source of cells (bone marrow, peripheral blood, cord blood), processing procedures (plasma removal, red cell depletion, preparation of mononuclear cells, purging of malignant cells or T-lymphocytes, positive selection of primitive progenitors such as CD34+ cells, prolonged culture to select a nonmalignant clone, or gene manipulation). Several of these processes can be done in a variety of ways, thus further increasing the variety of these novel blood components. Cytokines and cell culture techniques are being used to attempt increase the number of hematopoietic progenitors ex vivo so that small volumes of marrow, peripheral blood, or umbilical cord blood could be used as starting material and the number of stem cells needed for transplant produced in the laboratory. Adoptive immunotherapy is effective in several situations. Transfusion of donor mononuclear cells following hematopoietic cell transplantation reduces the recurrence of leukemia. Donor mononuclear cells cytotoxic for CMV or EBV can be selected and cultured ex vivo to restore immunity to these viruses and reduce post transplant infection or to treat posttransplant lymphoproliferative syndrome. Cells to serve as starting material for these new blood components can be obtained by stimulation of normal donors to generate peripheral blood stem cells (G-CSF), granulocytes (G-CSF), and platelets (TPO). Gene therapy has not been successful yet but the potential for treatment of inherited and malignant diseases is dramatic. Insertion of genes into autologous or allogeneic cells creates another new kind of blood component that may provide novel therapy in the future.