Tumor specific cytotoxicity and telomerase down-regulation in prostate cancer by autologous dendritic cells loaded with whole tumor cell antigens.

OBJECTIVES

We investigated the efficacy of cytotoxic activity of whole tumor cell-antigen loaded dendritic cells in the treatment of hormone refractory prostate cancer.

MATERIALS AND METHODS

From 10 patients with HRPC, peripheral blood samples were obtained and cultured with GM-CSF and IL-4 to provide differentiation of peripheral blood mononuclear cells (PBMs) into dendritic cells (DCs). DC phenotype was confirmed by flow cytometry (MHC class II HLA-DR, CD80, CD86, CD83, CD14 expression analysis). Subsequently, whole tumor cell lysates of LNCaP, DU-145, and PC-3 lines were incubated with DCs. Direct antitumoral activity of induced DCs and activation of PBM cells by these DCs was assessed by lactate dehydrogenase (LDH) cytotoxicity assay. Post-treatment changes in the telomerase gene expression of tumor cells were investigated by real time RT-PCR analysis.

RESULTS

LDH activity was highest in the PC-3 cell line (9.5%) and lowest in the DU-145 line (3.2%). Co-incubation of PBMs with activated DCs resulted in a significant increase at the levels of cytotoxicity in all cell lines. Likewise, incubation of tumor cells with activated DCs caused significant down-regulation of telomerase gene expression in all cell lines. Most pronounced suppression was in the LNCaP cell line (decrease by 97.1%). The decrease in the level of telomerase gene expression in DU-145 and PC-3 cell lines was 80% and 70%, respectively.

CONCLUSIONS

Cytotoxic immune response to prostate cancer-associated antigens can be elicited in vitro in patients with HRPC using an allogeneic tumor cell-based strategy. DC-based active immunotherapy appears as an effective treatment method in the pre-clinical setting and further phase I/II trials are warranted.