Human dendritic cell precursors are commonly divided into two distinct subsets: myeloid DC and Plasmacytoid DC (pDC). The pDC, which show plasma cell like morphology, have been defined as the population that produce a large amount of type I interferon in response to viruses. The surface phenotypes of human pDCs are defined as CD4 + , DC11c − , CD45RA + , IL3Rα (CD123) + , CD1c (BDCA-1) − , CD303 ((BDCA-2) + and lineage negative. On the other hand, leukemia/lymphoma cells in CD4 + CD56 + leukemia/lymphoma have been proposed to be of pDC lineage. CD4 + CD56 + pDC leukemia/lymphoma are a rare hematological malignancy, totally only about 100 cases in the world by the literatures. We established a pDC like leukemia cell line (PMDC05) from leukemia cells of a patient with CD4 + CD56 + acute leukemia. PMDC05 showed a complex hypoploid chromosomal abnormalities (44, XY) including add(5)(q22), add(15)(q26) and del(15)(q11q15), which is identical to original leukemia cells. Abnormalities including 5q and 15q are reported as the frequent aberrations in CD4 + CD56 + pDC leukemia/lymphoma. PMDC05, which morphology was similar to plasma cells, was positive for CD4, CD56, CD123, CD33, CD86, HLA-ABC, HLA-DR, CD1a, CD40, and CD83 but negative for linage markers. Cytokine receptors for GM-CSF, IL3Rα and IL-6Rα were positive on PMDC05. The expression of Trail and Flt-3L was positive. By the culture with IL-3, CPG-A/B, GM-CSF, molecules associated with antigen presentation such as CD1a and CD40 were up-regulated. Besides, the addition of LPS increased the expression of CD40, CD80 and CD83 on PMDC05. PMDC05 by itself possessed a potent antigen presenting ability to naive T cells and the treatment of PMDC05 with IL-3, CPG-A/B, or GM-CSF enhanced the antigen presenting ability to naive T cells. TLR7, TLR 8 and TLR 9 as well as TLR1, TLR2, TLR4 were demonstrated to be expressed on PMDC05 by RT-PCR and RQ-PCR showed that the expression of TLR7 and TLR9 was most characteristic. λ-like 14.1 and preTα was also demonstrated to be expressed on PMDC05 by RT/RQ-PCR. PMDC05 possessed an ability to uptake the antigens like FITC-dextran and lucifer yellow. Although IFN-α was not identified to be secreted from PMDC05 by the stimulation of influenza virus, IFN-γ and TNF-α was demonstrated to be secreted to the similar level in pDC, which was examined simultaneously with PMDC05 by CBA assay. These data demonstrated that newly established leukemia cell line PMDC05 is involved in pDC lineage and PMDC05 provides invaluable tools not only for the elucidation of pathophysiology of CD4 + CD56 + leukemia/lymphoma but also for the investigation of differntiation and regulation of pDC. In addition, PMDC05 could be applied for generating tumor-specific CTL clone, which may be used for anti-tumor cellular immunotherapy.