Background: Immunotherapy with bacillus Calmette-Guérin (BCG) for bladder cancer is successful, although the precise mechanism is unclear. Natural killer (NK) cells are a candidate for BCG-activated killer cells, but the roles of other T lymphocytes, such as NKT cells and γδT cells, are not fully understood. Mycobacterium tuberculosis is a potent activator of both NKT cells and γδT cells. However, it is known that the patient's prognosis is good if there are increased numbers of dendritic cells (DCs) in the urine after BCG therapy. Therefore, we investigated whether DCs are matured by BCG and whether BCG-pulsed DCs stimulate NKT cells and γδT cells.
Methods: Naïve Pan T cells were isolated form peripheral blood mononuclear cells (PBMCs) and DCs were obtained by culturing CD14+ monocytes with granulocyte–macrophage colony-stimulating factor and interleukin-4. The DCs were pulsed with BCG and their maturation was measured by fluorescence-activated cell sorter analysis using the CD86 antibody. Naïve T lymphocytes were stimulated by coculture with BCG-pulsed DCs in vitro, followed by FACS analysis to estimate the ratio and activation of NKT cells and the ratio of γδT cells. The 51Cr (chromium) release assay was used to estimate the cytotoxic activity of the stimulated T cells. Cytolytic proteins in the patient's PBMCs were measured during BCG therapy using semiquantitative reverse transcriptase-polymerase chain reaction.
Results: The DCs were matured by BCG stimulation and the number of NKT cells and γδT cells increased after culturing with BCG-pulsed DCs. The BCG-pulsed DCs also activated the NKT cells and γδT cells. Also, the lymphocytes that were cocultured with the BCG-pulsed DCs showed unspecific cytotoxic activity against a bladder cancer cell line.
Conclusion: Sensitization of NKT cells and γδT cells by BCG-pulsed DCs might be one of the mechanisms of BCG immunotherapy.