However, moDC may not be the optimal source of DCs for DC vaccination studies, due to extensive culture periods and compounds required to obtain mature moDC. Two principal subsets of human blood DC, called plasmacytoid DC (pDC) and myeloid DC (mDC), are possibly a better alternative since they do not require extensive culture periods and are directly isolable from the peripheral-blood. Based on promising immunological and clinical outcome with pDC and mDC vaccinations in metastatic melanoma patients, further testing of these blood DC subsets is warranted. Based on these observations investigators are convinced that pDC and mDC employ different, and probably more optimal mechanisms to combat cancer. In addition, based on in vitro data and preclinical studies that suggest that natural DC act synergistically, investigators hypothesize that the combination of pDC and mDC may induce stronger anti-tumor immune responses as compared to pDC or mDC alone.