While the primary purpose of radiotherapy (RT) is the
elimination of cancer cells by inducing DNA-damage, considerable evidence emerges
that anti-neoplastic effects extend beyond mere tumor cell killing. These
secondary effects are based on activation of dendritic cells (DCs) via induction
of antitumoral immune reactions. However, there is an ongoing debate whether or
not irradiation of the DCs themselves may negatively affect their maturation and
functionality. Human monocytes were irradiated with different
absorbed doses (1 15 Gy relative biological effectiveness (RBE), 5
2 Gy (RBE), 1 0.5 Gy (RBE)) with photons, protons and
carbon ions. Differentiation and maturation of DCs were assessed by staining of
corresponding cell surface molecules and functional analysis of irradiated DCs
was based on in vitro analysis of phagocytosis, migration and IL-12
secretion. Irradiation of CD14-positive DCs did not alter
surface phenotypes of immature DCs and mature DCs. Not only differentiation, but
also functionality of immature DCs regarding phagocytosis, migration and IL-12
secretion capacity was not negatively influenced through RT with photons, protons
or carbon ions as well as with different dose levels. After proton irradiation
migratory capacity of immature DCs was increased. Our
experiments reveal that phenotypic maturation of DCs remains unchanged after RT
with different fractionations and after irradiation with particle therapy.
Unaffected functionality (phagocytosis, migration and cytokine secretion) after
RT of DCs indicated possible persistent potential for inducing adaptive immune
response. Additional effects on the immunogenic potential of DCs will be
investigated by further functional assays.