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The success of autologous peripheral blood progenitor cell (PBPC) transplantation is challenged by relapse of malignant disease which might — at least in part — be mediated by graft contaminating tumor cells. Although the clinical role of tumor cell depletion still remains to be demonstrated in prospective, randomized trials, multiple purging strategies are currently pursued in the context of autologous stem cell transplantation. This report is discussing ex vivo manipulations of PBPC transplants with respect to purging of tumor cells, including the positive selection of CD34+ cells with or without negative depletion as well as ex vivo expansion techniques. In addition, adoptive immunotherapy strategies using ex vivo generated autologous dendritic cells for the treatment of minimal residual disease after stem cell transplantation will be discussed.

Die Fortschritte der vergangenen Jahre haben weitreichende Einblicke in die phanotypischen Eigenschaften, die Biologie und Regulationsprozesse hamatopoetischer Stamm- und Progenitorzellen gestattet. Diese Erkenntnisse forderten die rasche klinische Verbreitung innovativer Transplantationskonzepte und ermoglichten eine kontinuierliche Fortentwicklung der Hochdosischemotherapie und Stammzelltransplantation (Abb. 2.2.1).

Clinical trials to evaluate the potential of adoptive immunotherapy in cancer patients have been restricted to the use of lymphoid effector cells [1,2]. Of the other probably even more important host defense system against tumor growth, the mononuclear phagocyte system [3], only monocytes (mo) have been reinfused [4] which, however, represent immature precursor cells and acquire full functional competence only upon further maturation. This might at least in part be due to the many technical problems associated with the generation of human mature macrophages (MO).

Cells of the mononuclear phagocyte system (MPS) are involved in the immune surveillance against microbial pathogens and malignant cells but are also important regulator cells in hematopoiesis [1, 2]. They are able to secrete a variety of factors that suppress or sitmulate the proliferation and differentiation of hematopoietic progenitor cells. Of these, macrophage colony-stimulating factor (M-CSF) and granulocyte-CSF have been shown to be released from monocytes [3], whereas the synthesis of GM-CSF is disputed [3, 4]. However, monocytes have to undergo maturation into macrophages to acquire the functional competence which is significant in vivo [5–7].