Aim: To investigate the effects of adenoviral gene transfer of IкBα mutant (IкBαM), a novel inhibitor of nuclear factor кB (NF- кB), on apoptosis, phenotype and function of human monocyte-derived dendritic cells (DC). Methods: Monocytes, cocultured with granulocyte/macrophage colony-stimulating factor (GM-CSF; 900 ng/mL) and interleukin (IL)-4 (300 ng/mL) for 5 d, followed by stimulation with lipopolysaccharide (LPS; 100 ng/mL) for 2 d differentiated into mature DC. Monocytes were either left untransfected or were transfected with Ad IкBαM or AdLacZ. The transcription and expression of the IкBαM gene, and the inhibitory effect of IкBαM on tumor necrosis factor (TNF)-α-induced NF-кB activation in mature DC were detected by polymerase chain reaction (PCR), reverse transcription-polymerase chain reaction (RT-PCR), Weste blot analysis, and electrophoretic mobility shift assays, respectively. The phenotype, apoptosis, IL-12 secretion level of DC, and ability to stimulate the proliferation of T cells were determined by flow cytometry, enzyme-linked immunosorbent assay and mixed leukocyte reaction. Results: PCR and RT-PCR were used to detect a unique 801 bp band in Ad IкBαM-transfected mature DC, and also a dose- and time-dependent expression of the IкBαM gene, which peaked at a multiplicity of infection of 100 pfu/cell and at 48 h. Furthermore, Ad IкBαM significantly suppressed the TNF-α-induced NF- кB activation, augmented apoptosis, downregulated CD80, CD83, and CD86 surface molecules, IL-12 secretion levels and the ability to stimulate the proliferation of T cells in mature DC. Conclusion: Ad IкBαM effectively transfected and potently inhibited NF-кB activation in monocyte-derived mature DC. Overexpression of the IкBαM gene in mature DC may contribute to T-cell immunosuppression through induction of DC apoptosis and downregulation of B7 molecules, providing a potential strategy for future DC-based immunotherapy of asthma.