Reduction of rigidity in human activated natural killer cells by thioglycollate treatment

Successful delivery of effector cells to tumor vasculature and the expression of cellular activities, such as extravasation and tumor infiltration are important aspects of the immune intervention of neoplastic disease. The structural rigidity of the effector cell, an indication of its cytoskeletal characteristics, plays an important role in influencing cellular functions and hemodynamic behavior as well as systemic distribution. The present study was designed to identify an agent which can modify the viscoelastic properties of human natural killer cells. A reducing compound, thioglycollate (TGA), was found to be an effective agent. Changes in cellular rigidity with respect to dose and duration of treatment with TGA were quantified. Micropipet aspiration was used to measure the resistance of NK cells to an imposed external deformation. Cultures of adherent human NK cells were expanded in interleukin 2 (IL-2) for 14 days, removed from culture and resuspended in medium with IL-2 and selected concentrations of TGA ranging from 0.032 mg/ml to 0.250 mg/ml. At 24 h intervals, the cell samples were removed and tested for their viscoelastic properties. Following 24 h of incubation, only TGA at 0.032 mg/ml produced a significant increase in cellular deformability. At 48 h of incubation, NK cell deformability was twice that obtained at 24 h. Higher concentrations of TGA also produced increased deformability after 48 h of incubation. Following 72 h of incubation, all concentrations of TGA tested produced increased deformability; however, the 0.032 mg/ml concentration produced the highest level of deformability combined with high viability (> 95%) as well as activated cell morphology. This treatment did not significantly alter the cytotoxic activity of these cells against a sensitive tumor target cell. These findings indicate that short term culture with TGA may be used to significantly reduce NK cell rigidity without decreasing cell viability or function. Thus, TGA may be a useful compound for altering the rheological properties of activated lymphocytes prior to adoptive transfer.