Immunocytochemistry Based on a Cell-Type-Specific Aptamer for Rapid Immunostaining of Adenocarcinoma Cells in Clinical Serosal Fluids.

All too often, conventional immunocytochemistry (ICC) via an antibody on cytological samples is limited to a few smears due to scant cellularity. To circumvent these limitations, this study employed a cell-type-specific aptamer as the core tool in ICC protocols for a timely and highly specific ICC diagnosis. S6, an aptamer against A549 lung carcinoma cells, was adopted instead of antibodies in this study for differentiating cancer cells in serosal fluids. Here, we developed three different strategies for discriminating the adenocarcinoma cells in effusion cytology specimens using the S6 aptamer in ICC. These strategies included a biotin-labeled S6 aptamer, an FAM-labeled S6 aptamer, and an activatable S6 aptamer. A total of 112 serosal fluid specimens with known diagnoses were evaluated by all three modes of use of the S6 aptamer. ICC procedures based on biotin-labeled or FAM-labeled S6 aptamers required time-consuming washing to avoid interference from nonspecific adsorption. ICC procedures based on an activatable S6 aptamer probe showed a weak fluorescence signal in the absence of target cells, but the procedures showed a strong fluorescence signal due to alteration of the conformation without any complicated washing steps, in the presence of targets. The specificity and sensitivity are higher in all three different ICC protocols based on the S6 aptamer than those for antibody protocols for differentiating adenocarcinoma cells in clinical effusion cytology. ICC based on cell-type-specific aptamers, instead of on a panel of a set of antibodies, is promising as an auxiliary method for the diagnosis of cancer.