Indoleamine-2,3-dioxygenase enzyme expression and activity in polarized dendritic cells

Background aimsPolarized mature dendritic cells (DC) can activate cytolytic T-lymphocyte (CTL) responses and may be a more effective clinical strategy in DC-based cancer vaccines. A subset of mature DC can down-regulate the T-cell immune response through expression of indoleamine-2,3-dioxygenase (IDO). We determined whether polarizing DC ex vivo increased IDO expression and activity.MethodsPeripheral blood monocytes from healthy volunteers were cultured ex vivo in polarizing and non-polarizing culture conditions. DC IDO expression was detected by Western blot. IDO enzyme activity was determined by high-performance liquid chromatography (HPLC) measurement of kynurenine (K) and tryptophan (T) concentrations in culture supernatants.ResultsIDO protein was markedly increased in DC after polarization (median 1222.4%, range 331.5–2113.3%) versus non-polarized DC (median 28.3%, range 3.7–119.8%; P = 0.04). The median K/T ratio was significantly higher in polarized DC versus non-polarized DC (6.34, range 6.02–6.65, versus 0.047, range 0.004–0.541; P = 0.04). IDO protein expression correlated with enzyme activity (r = 0.80, P = 0.002).ConclusionsDC polarizing culture conditions increased expression of IDO protein and IDO enzyme activity. DC culture and maturation methodologies may impact the effectiveness of adoptive DC therapy.